Respiration and Ventilation. Control of the Airways.

Securing the airway / Breathing / Ventilation

Securing the airway / Breathing / Ventilation

Posted by Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Secure (free) airway is fundamental in all emergency medical activities in the care of severely ill patients. Oxygen deficiency due to obstructed airway is the single most important anesthetic-related cause of severe injury or perioperative death. It usually occurs in a patient who is not breathing and is unable to ventilate. This is a situation that anyone working with emergency care can get into. A pre-devised action plan and access to relevant emergency equipment and intubation equipment is necessary to avoid serious incidents of insufficient airway control on an anesthetized or unconscious patient. Intubating the patient is about creating and securing the free airway.

The easiest way to create a free airway on an unconscious person is primarily to place the patient in the forward position with the upper arm’s hand under the chin. This mode is often used on patients after anesthesia during a wake-up phase or after termination of ventilator treatment, e.g. after extubation after cardiac arrest. When initiating an anesthesia, the patient is usually placed in the usual flat back position (supine) in order to best manage the airway and to be able to intubate in the easiest way. If the airway is obstructed by the back of the tongue, an oropharyngeal airway (OPA) or nasopharyngeal airway (NPA) may establish a free airway. Manually, the airway may be cleared by a chin lift, a head tilt backwards and by a solid jaw thrust. Manual ventilation with bag and mask is the basis for all airway management of unconscious or anesthetized patient.

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There are a number of different models of these aids as shown below in slide shows. However, a nasopharyngeal airway (NPA) may irritate the posterior pharynx and provoke nausea, vomiting and laryngospasm if it is deprived of an overly awake or insufficiently anesthetized patient. When properly placed on a sufficiently anesthetized patient, it can be a good help for establishing a free airway. Free airway tubes should therefore only be deployed when the patient is sufficiently anesthetized or relatively deeply unconscious. A nasopharyngeal airway (NPA) is usually tolerated at a higher degree of alertness but may also irritate the posterior pharynx, insertion of the NPA must always be preceded by proper gel instillation in the nasopharynx to avoid nasal bleeding. Blood and mucus in the nasopharynx should always be avoided and disposed of when handling and establishing the airway.

In order for an intubation attempt to be optimal, reasonable experience with the procedure, a well-functioning laryngoscope, best choice of laryngoscope blade, type and size and conductor, optimal patient placement, adequate muscle relaxation and optimal positioning of the larynx is required. Under good conditions, an intubation is usually not difficult, but nevertheless, a difficult intubation may appear unexpectedly. With the patient in the supine position, height of the headend, well-trained patient, well-oxygenated and fully muscle relaxant, the best conditions for a successful intubation are achieved.

Breathing bag and respiratory masks

Bag and mask ventilation is a crucial airway management skill and one of the most difficult to perform correctly.

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Oropharyngeal airways (OPAs) and nasopharyngeal airways (NPA) in various models

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Laryngeal mask airway (LMA) in various models

Laryngeal masks are one kind of supraglottic airway (SGA) device placed deep in the throat behind the tongue and thereby creating free airway. A laryngeal mask can be used under general anesthesia, both with spontaneous breathing and controlled pressure relief. The laryngeal mask can be deployed using a conductor or manually using the fingers. There are laryngeal masks both with and without a cuff.

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Laryngoscope in various models

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Endotracheal tubes in various models

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Endotracheal tube stylets and conductors

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Videolaryngoscope of various models

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Intubation

Posted by Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


An intubation is done to ensure the airway and to be able to ventilate the patient in a controlled manner and thereby ensure adequate oxygenation of the blood and adequate elimination of carbon dioxide. Ventilation passes from the patient’s own spontaneous respiration to a controlled pressure ventilation, either manually or mechanically. The patient can be ventilated using a breathing balloon (“Ruben balloon / hand bag of silicone) and breathing mask or via an endotracheal tube or laryngeal mask. Usually the mask and balloon are started to ventilate during the induction of an anesthesia, then the patient can be intubated.

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To be able to pressure the endotracheal tube is provided with an inflatable cuff that occludes the tube against the trachea on the outside and allows free air passage through the tube. The cuff is usually inflated with 5-10 ml of air. On small children, uncut tubes can be used as it is so narrow in the trachea that you can over-ventilate in any case. Normally, one hand valve to an overpressure of about 20 mm Hg in each breath. The respirator can ventilate the patient with lower pressure if the lungs are healthy, about 8-14 mm Hg in each breath.

In order for an intubation attempt to be optimal, reasonable experience with the intubator, well-functioning laryngoscope, best choice of laryngoscope blade, type and size and conductor, optimal patient placement, adequate muscle relaxation and optimal positioning of the larynx is required. The patient should normally be well anesthetized and muscle relaxed when intubating the trachea. Normally, the patient is intubated orally through the mouth and the tube is fixed using tape to the cheek. In emergency situations such as acute cardiac arrest, one may need to intubate without having given muscle relaxant or sedative drugs, but this may be technically more difficult than with the well-sedated and relaxed patient. You may also need to intubate in some circumstances without being able to anesthetize the patient deeply as with severe airway while maintaining spontaneous breathing. Then one often chooses to intubate nasally instead of orally during adequate sedation and local anesthesia (surface anesthesia). However, most “common” intubations are done orally with well-anesthetized and muscle-relaxed patient.

Intubation – Practical advice

The patient is most easily intubated in a supine position with a slight height head end (30 degrees) with back tilt. After preoxygenation via mask over mouth and nose, the patient is anesthetized and muscle relaxed. Breathing is controlled first via mask ventilation and free airway is created by a steady lifting of the lower jaw until a substantial underbite. If the tongue still obstructs the airway, you can put down a cooling tube or a nose tube (“chanterelle”) to be able to optimize the free airway and ventilation conditions. When the patient is well-groomed and muscle-relaxed, a laryngoscope is inserted through the mouth from the right mungipa towards the center where the laryngoscope blade brings the tongue. One can use a traditional battery-powered laryngoscope in metal or plastic (metal is standard) with fiber optics or a video laryngoscope, see below. Video laryngoscope has either a small screen connected directly to the laryngoscope or a standalone screen beside it. In traditional laryngoscopy, direct insight into the larynx is used, while video technology uses indirect transparency via a screen.

It is important that the laryngoscope blade is inserted deep into the throat. Then, firmly raise the tongue and lower jaw forwards upwards in the direction of the shaft with a slight bend backwards of the laryngoscope (not too strong bend) while checking that one does not strike the front teeth in the upper jaw. With this powerful lift you can inspect the larynx and find the vocal cords and the entrance to the trachea. Then you can bring down the tube. The tip of the laryngoscopic leaf is inserted above the epiglottis (in vallecula) whereby the epiglottis follows forward upward in the lifting one performs. One should not normally bring epiglottis with the laryngoscope blade without epiglottis being lifted in any case. When you see the vocal cords, one can usually simply insert a tube between the vocal cords into the trachea. It is essential to be able to see and identify the vocal cord opening during the intubation.

To be able to insert the tube, it may be necessary to slightly twist the tube clockwise (clockwise) when passing the vocal cord opening. The tube is brought down approximately 8-10 cm below the vocal cords of an adult. An ideal position of the tube is that the distal end of the tube is approximately 4 cm above the carina. At 8-10 cm from the end, on most tubes, there are 1-2 marking lines, the distal black line is below the vocal cords and the proximal line immediately above the vocal cords. In adults, the tube is fixed with a marking of 21-24 cm in the mouth pan in the normal case, here the tape is attached around the tube. In order to get more control in the tube during the intubation, a flexible conductor can be used in the tube which is removed as soon as the tube has passed the vocal cords.

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When the tube is in place you inflate the cuff and check that the tube is correct by checking and verifying:

  1. Fog in the tube back and forth during breathing (can also be heard and felt).
  2. Listen with stethoscope and hear breathing sounds from both lungs during manual ventilation. Listen in at least 4 positions.
  3. Verify with capnometry that respiration works through a normal carbon dioxide elimination curve that the tube is correctly positioned.

In doubtful cases, the position of the tube can be verified by bronchoscopy or X-ray. However, you do not have too much time to verify the tube position of the anesthetized patient. Capnometry and bronchoscopy are safest.

When the location is verified, the tube is secured by:

  • Taping with some form of healthcare tape.
  • Cotton band tied around the tube.
  • In rare cases, the tube can be fixed by suturing (eg in craniofacial surgery) but it is usually tracheal cannulae which are fixed by suturing

In the event of an emergency, the surgeon is notified when the tube is fixed and the airway is secured.


Management of difficult airways

Posted by Per Nellgård, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Creating and maintaining an open and safe airway is always the primary aim in all anesthesia practice and intensive care. Failure to secure the free airway is both dangerous to the patient and may cause anxiety for the anesthetist. The situation “cannot intubate and cannot ventilate” is luckily very unusual (about 1/10 000 intubations). Often the airway accounts for about 30% of the very serious incidents associated with anesthesia (death and serious brain injury). What is dangerous is hypoxia not “lack of tube”. Failure of intubation constitutes approximately 10% of all intubations, and is between 0.13-0.3% of all intubations. In the Fourth National Audit Project (NAP 4 – UK) 184 cases of major adverse airway events were recorded among 2.9 million anesthesia. In order to avoid these situations it is important to make a careful preoperative assessment of cases of difficult airways and to prepare for the right equipment and sufficient expertise for anesthesia.

Feel free to learn SFAI’s airway algorithm, at www.sfai.se or below on the Anesthesia Guide (aka Narkosguiden.se). Learn where the airway car is located in the operating department and what it contains and how to use different airway aids.

All operating departments should have access to some type of video laryngoscopes. Video laryngoscopes have meant that many difficult airways can now be better managed and intubated with reasonable risks. In most cases, video laryngoscopes can reduce Cormac & Lehane’s rating by up to 2 grades, such as from C & L grade 4 to grade 2. However, video laryngoscopes do not solve all problems, and in the really difficult cases, flexible bronchoscopes are still needed and the ability to use them. Feel free to introduce an “airway hall” one day a week on a regular basis where you can train with varied airway equipment so that everyone gets good skills. Work in team and apply current airway algorithm.

In order for an intubation trial to be optimal, reasonable experience of the intubator, well-functioning laryngoscope, best choice of laryngoscope leaflets, type and size and conductor, optimal patient setup, adequate muscle relaxation and optimal positioning of larynx are required. Under good conditions, an intubation is usually not difficult, yet a difficult intubation may appear unexpectedly. With the patient positioned on their back, upheld head end, well- anesthetized patient, well oxygenated and fully muscle relaxed are the best conditions for successful intubation. Severe laryngoscopy occurs when no part of the laryngeal entrance can be visualized in optimal laryngoscopy (Cormack Lehane Grade III-IV). Severe intubation is also present when correct tubing has not been achieved despite three optimal intubation tests or within 10 minutes of intubation. Strong man with short, stiff throat and bullet nose is a typical hard-intubated patient. In case of sudden unexpectedly severe intubation, it may be best to awake the patient and reboot from the beginning, for example, through vigorous fiber intubation. Always avoid excessive mucus or bleeding in the nose and throat.

Tests for evaluation of difficult intubation

  • Mallampati test
  • Thyreomental distance
  • Ability to open mouth
  • Neck movement

Risk factors for difficult intubation

  • Small mouth
  • Short neck, “Bull’s neck”
  • Large or loose teeth
  • Bleeding or vomiting in the pharynx
  • Inability to open mouth or gape
  • Anatomical anomalies in the oral cavity or pharynx
  • Swelling in the oral cavity, tongue, throat or throat
  • Male gender
  • Mallampati level III or IV
  • Sleep apnea syndrome
  • Beard
  • Age> 55 years
  • Adipositas, BMI> 26
  • Tumors, infections, bleeding in the oral cavity or in the pharynx
  • Earlier radiation to the head and neck region
  • Stridor
  • Foreign body in the pharynx or in the upper respiratory tract
  • Large trauma in the head or neck region
  • Subcutaneous emphysema on the throat
  • Horseshoe-shape of the maxilla

Difficult airways can be categorized as

  1. Difficult mask ventilation (about 5%)
  2. Difficult ventilation with laryngeal mask (LMA / SGAD)
  3. Difficult laryngoscopy
  4. Difficult intubation (2-5-10%, in the ICU up to 20%)
  5. Difficult airways for surgical intervention

Assessment of the airways

Different airway tests are used to find those with difficult airways. A high sensitivity test means that most people are identified with “difficult” airways. A high specificity test means that most people with an “easy” airway can be ruled out.

Some of the most common assessment methods of the airway are as follows:

  • Modified Mallampati (Class 0-4)
  • Thyromental distance (<6 cm, 6-7 cm & > 7 cm) (TM)
  • Sternomental distance (<11 cm, 11-12.5 cm> 12.5 cm) (SM)
  • Wilson sum test
  • LEMON-law
  • Upper lip bite test (ULBT)
  • Gap capacity (<2 cm, 2-4 cm> 4 cm)

No test alone is good enough, but the combination of Mallampati and thyromental distance seems best, even better when combined with long experience and good judgement. Patients with Mallampati Class 0 (when looking at the upper edge of epiglottis) are almost always easily intubated, if there is no other larynx or tracheal pathology.

Risk patients for pronounced hypoxia

  • Unstable angina pectoris
  • Severe CNS pathology incl. severe carotid stenosis
  • Severe lung disease (COPD, fibrosis, etc.)
  • High BMI (lower oxygen reserves in the lungs)
  • High metabolism: sepsis / pregnant
  • Lowered alertness, unconscious patient
  • Aspiration of gastric contents
  • Acute fall with injury or swelling of the airways

On these patients, the airway must be secured in a “good” way with maintained oxygenation throughout the intubation. This means that you are more liberal in maintaining spontaneous breathing, avoiding apnea and choosing a “safer” method, such as tracheostomy in local anesthesia, intubation with flexible bronchoscope or intubation with video laryngoscopes in local anesthesia and possibly light sedation.

Predictors for difficult mask ventilation

  • High BMI or high body weight.
  • High age
  • Male sex
  • Limited subluxability of the lower jaw.
  • Short thyromental distance.
  • Modified Mallampati Class 3-4.
  • Beard (can be removed!)
  • Toothlessness
  • Snorers or OSAS
  • Previous radiation to the throat.

Predictors for difficult laryngeal mask use

  • Limited gap capability
  • Supra- or extraglottic pathology (radiation, large tonsils)
  • Glottic or subglottic pathology (larynx stenosis, etc.)
  • Limited flexion of the throat
  • Cricoid pressure
  • Male sex
  • Increased BMI (> 35)
  • “Bad teeth”
  • Position changes during operation.
  • Low lung compliance may require higher inspirational pressure with a risk of air leakage.
  • Patients with Mallampati grade 1-2 appears to be more difficult to get a good fit on LMA without leakage compared to Mallampati grade 3-4.

Predictors for difficult laryngoscopy

  • Limited gap capability (<4 cm).
  • Limited subluxability of the mandible (ULBT 2-3).
  • Narrow, often high, hard palate.
  • Short thyromental (<6-7 cm) and sternomental distance (<12 cm).
  • Modified Mallampati Class 3-4.
  • Indurations of buccal cavity.
  • Limited extension of the head and upper throat.
  • Increased circumference of the neck = High power measure (> 45 cm).

Predictors for difficult video laryngoscopy

  • Cormac-Lahane grade 3-4 in direct laryngoscopy.
  • Abnormal throat anatomy: radiation damage, scars inside the throat, thick throat and pathology in the throat.
  • Limited subluxability of the mandible.
  • Short distance between sternum and thyroid gland (larynx)

Predictors for difficult cricothyrotomy

  • Difficulties to identify the cricothyroid membranes
  • Female sex
  • Children before puberty (<8-12 years).
  • Thick or fat throat.
  • Local pathology (inflammation, radiation, tumor, etc.)
  • Difficulties to access the trachea through the front of the throat
  • Fixed neck back with motion limitation
  • Cervical spine fracture

How to handle difficult intubations

A successful intubation is based on the following factors:

  • Oxygenation, is it satisfactory?
  • The ventilation (via mask or LMA) is it functioning properly?
  • Is there any risk of regurgitation or aspiration?
  • Is there any other help available nearby, and how fast may you be assisted?
  • Is there any other (known) airway equipment nearby? Respiratory utilities!
  • Application of airway guidelines for difficult intubation. Predicting difficulties – and be prepared!
  • “Never fail to prepare for failure”
  • Tell us about your “Back-up plan” – so your employees know and understand.
  • Do not use technology or equipment that you are not used to.
  • “Learn to swim by swimming” – but train in the shallow part of the pool. Intubation should be good for the patient – not your “ego”
  • The patient does not die of failed intubation without oxygen deficiency!
  • It is important to know your own limitations.
  • One has to know when to end further intubation attempts – and how to handle the continuation.

In case of failure, consider to:

  1. Wake up the patient
  2. Laryngeal mask
  3. Alternative techniques
  4. Emerged surgical airway (Knife, Leader & Tube)

Keep in mind that the first intubation attempt is your best attempt. Limit the number of intubation attempts to three or four.

Extubation

Consider the following:

  • A pilot must plan both start (Intubation) and landing (extubation).
  • Extubation is always elective (if not accidental).
  • NAP4 shows that 23% of severe airway-related events occur during extubation.
  • The most common complications of extubation are: hypertension, tachycardia, elevated intracranial and intraocular pressure, etc.
  • Common problems: Inadequate oxygenation and ventilation. Inability to protect the respiratory tract and to remove mucus out of the airways.
  • During extubation, plans must be made on before hand, preparing for a failing extubation scenario.
  • During extubation, one must assess whether reintubation can be easy or difficult.
  • Reintubation under optimum conditions differs greatly from acute reintubation with hypoxic patients.
  • Consider laryngeal mask as a possible “bridge” in extubation.
  • Consider the “Airway Exchange Catheter”.When giving patients anesthesia, one can often choose between general anesthesia or alternatively any type of regional block, central or peripheral in combination with sedation for the surgical procedure. It may seem tempting to choose regional anesthesia for patients with difficult airways, but then one has to choose a variant that “works safely”, for example spinal anesthesia. If a blockade discontinues during operation and you are urgently forced to anesthetize a patient with a difficult airway you can quickly get into serious problems.

Procedure for difficult airways (non-acute)

Planned anesthesias on patients with known difficult airways should not cause any major problems if you prepare well with equipment and competence. Tracheostomy in local anesthesia “is always right” in the case of very difficult airways. Alternatively number two, should use flexible bronchoscopes in local anesthesia with or without sedation. Suitable patients for “awake intubation” can be;

Patients with recognized severe/very difficult airways

  • Various syndromes like Pierre-Robin, Treacher-Collins, Crouzon, Goldenhaar, etc. (There are about 70 different rare syndromes with airway problems)
  • Different storage diseases such as Hunters and Hurler’s syndrome.
  • Reduced gap capabilities (definitively those below <2 cm gap and relatively those with 2-3.5 cm).
  • Upper respiratory tract infections such as epiglottitis, oral bone marrow, harder mononucleosis and necklaces, etc.
  • Tumors et al. In the tongue, hypopharynx and larynx. Radiation-treated patients in oropharynx.
  • Vallecula cyst
  • Foreign body
  • Larynx and tracheal stenosis
  • Others with known difficult airway
  • Patients with increased risk of vomiting and aspiration.
  • Patients recently eaten/patients with gastroparesis.
  • Patients with pronounced and severe reflux problems.
  • Patients with elevated intraabdominal pressure / volume, such as Ileus, later part of pregnancy, big tumors, etc.
  • Trauma and patients receiving large doses of opiates.
  • Patients with nausea.

Procedure for difficult airways (acute)

  • Should this be done on call? Is there time for the consultant on call, and possibly ENT doctors to join in and assist?
  • Make a plan for this patient and communicate the plan and gather enough skills.
  • Use a difficult airway trolley, but use the equipment and methods you are familiar with.
  • Preoxygenate properly. Continue with oxygen supply.
  • Optimal body position, preferably the “Sniffing position.”
  • Consider elevated Head End and Cricoid Pressure (Release this if it is difficult).
  • If there’s enough time and skills, consider intubation with flexible bronchoscopes.
  • Otherwise, plan for video laryngoscopy and guide wire.
  • If there’s little to no space, a long tube sized number five often works well.
  • Use a good laryngeal mask if it is not possible to intubate initially. A “good” laryngeal mask has: two lumens, one for V-probe / guide wire and high sealing pressure, can be intubated through flexible bronchoscopes.
  • Consider early surgical airway (cricothyrotomy, PCT or surgical tracheostomy).
  • Consider the possibility of transtracheal ventilation with Ventrain through a 2 mm needle / cannula. You can ventilate 5-7 l / min with I / E 1: 1. Ventrain is new, cheap and not to say the least a life saving device in the airway equipment arsenal!
  • There are methods that we do not recommend, but that can solve an acute situation such as Retrograde intubation, blind nasal intubation and digital intubation, i.e. You feel your fingers in your throat and guide the tube.
  • Afterwards, always document what has been difficult and how to best solve the situation.

Intubation utilities

Various laryngoscopes, in addition to standard sheets with fiber optics include; Macintosh-alike blades for example In C-Mac, McGrath S3, and Glidescope Titan.

Macintosh-alike bladesC-Mac, McGrath S3, och Glidescope Titan
Advantages: Easy to use
Easy to see
Easy to intubate
Easy to use a guidewire
Low pressure against teeth.
Disadvantages:Difficult insight at very anteriorly high-seated larynx.
Heavily curved bladeC-Mac D-blade, McGrath S5, Glidescope
Advantages: Good insight at very anteriorly high-seated larynx
May be more difficult to intubate, despite good insight
Disadvantages:Slightly difficult technique. You must have a leader with the same curvature as the blade
Blade with a channel for an endotracheal tubeAirtraq, Pentax AWS, Kings Vision
Advantages: The tube slides protected in a channel
Once placed correctly, it is easy to intubate
Airtraq can send the image via the Internet to a "consultant"
Disadvantages:They may feel a bit "plastic"
They have been coarser (from Pentax AWS and difficult to get through the oropharynx
You have to go around epiglottis, which is sometimes difficult

Video laryngoscopy

There are several types of video laryngoscopes and each group has its advantages and disadvantages, as seen in the picture down below. Video laryngoscopy is the method of the future, and within 10 years, these are probably standard equipment in each and every operating theater.

Categories of video laryngoscopes

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APRV – Airway Pressure Release Ventilation


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Spontaneous breathing at two different levels of pressure that are regulated independent of each other in self-controlled breathing. APRV improves alveolar ventilation and increases functional residual capacity (FRC) while keeping the airway open. APRV provides CPAP at two different levels at complete spontaneous breathing. APRV is used in the treatment of both moderate and severe pulmonary failure. APRV is available in Drägers ventilators.

APRV settings in the ventilator
TV:6-8 ml/kg
RR:10-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-10 cm H2O
FiO2:25-40%
CPAP5-15 cm H2O
ASB8-15 cm H2O


BiPaP – Biphasic Positive Airway Pressure

Pressure controlled ventilation with room for spontaneous breathing throughout the entire breathing cycle. Adjustable pressure support in two positions. You set the pressure level in both CPAP breathing and supported breathing (ASB). BiPaP improves alveolar ventilation and increases functional residual capacity (FRC) while keeping the airway open. BiPaP is used in the treatment of both mild, moderate and severe pulmonary failure.

BiPAP-Assist (with SB): Pressure Controlled Assisted Ventilation

BiPAPNormal settings in the ventilator
ASB:3-10 cm H2O
TV:6-8 ml/kg
RR:10-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-10 cm H2O
FiO2:25-40%
CPAP:3-7 cm H2O


IPPV – Intermittent Positive Pressure Ventilation

IPPV keeps the lungs expanded by constantly blowing a volume of air into them. Constant volume is given in both controlled mode and assisted. The positive pressure can be controlled by stimulation of the patient’s own spontaneous inspiration or through complete mechanical ventilation. Access to the patient’s lungs occurs either by intubation or breathing mask. IPPV includes CPV (Continuous Positive Pressure Ventilation), PLV (Pressure-Reduced Ventilation), Auto-flow (Automatic Control of Inspiration Flow) and IRV (inversed ratio ventilation). IPPV is used primarily in the treatment of mild or moderate pulmonary failure.

IPPVIntermittent Positive Pressure Ventilation
ASB:3-12 cm H2O
TV:6-8 ml/kg
RR:10-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-10 cm H2O
FiO2:25-40%
CPAP:3-15 cm H2O

MMV – Mandatory Minute Ventilation

MMV provides spontaneous breathing with automatic adjustment of the compulsory respiration to the patient’s need for volume. Access to the patient’s lungs is through intubation or breathing mask. Possibility of pressure-reduced ventilation and auto-flow (automatic control of inspiration flow). MMV is used primarily in the treatment of mild or moderate pulmonary failure.

MMV - Mandatory Minute Ventilation Normal settings
ASB:3-12 cm H2O
TV:6-8 ml/kg
RR:10-20 breaths/minute
TU:5-15 cm H2O
I:E1:2
PEEP:5-10 cm H2O
FiO2:25-40%
CPAP:3-15 cm H2O


NAVA – Neurally Adjusted Ventilatory Assist

NAVA controls ventilation by capturing the electrical impulses in the patient’s diaphragm via an esophageal catheter (Edi).

There are three main settings in NAVA; NAVA level, PEEP and O2 concentration all of which must be set before starting. What is needed besides the SERVO-in ventilator is the NAVA software, an Edi module and an Edi catheter. The Edi catheter is placed in the esophagus as a common ventricular probe. NAVA provides good synchronization between patient and ventilator and reduces the discomfort of the ventilator treatment. NAVA provides possibilities for lung protection treatment by avoiding giving too much or too little respiratory support. Optimal synchronization favors spontaneous breathing. The Edi signal can be used as a support in deciding whether to weigh the ventilation treatment. The Edi signal can be used as a surveillance parameter because it provides information which allows ventilation to be “ventilator controlled”, the desired volume of time, fan settings, and can provide information about sedation and exhaustion from the ventilator. The Edi catheter is available in sizes between 6 and 16 Fr. The catheter can also be used to give an esophagus discharge on ECG. The Edi signal is obtained as a peak value and a valley value. When the patient triggers a breath, gas flows with a variable pressure proportional to the patient’s Edi. The highest possible pressure is 5 cm H2O lower than the preset upper pressure limit. Edi trigger can be set between 0.1 – 2 μV. Set a lower trigger level if no breath is given while there is a sufficient Edi signal. Increase the Edi trigger level if there is a sufficient Edi signal. Increase Edi Trigger Level if too many breaths are caused due to noise in the signal. The trigger is displayed with a symbol and a color mark on the curve.

There are four basic settings in NAVA: NAVA level, PEEP, O2 konc. and Edi triggers. In the ventilator, set the NAVA level (cmH2O / μV), PEEP (cm H2O), oxygen concentration (%) and Trigger Edi (μV). The basic setting of Trigger Edi is 0.5 μV (0.1 – 2 μV). Pressure support sets the trigger sensitivity, inspirational cycle (off), and pressure support over PEEP.

NAVA Peak = NAVA level x (Edi peak – Edi min) + PEEP. Estimated NAVA peak appears in the ventilator display.

NAVA-modeNormal settings in NAVA-mode
NAVA level1,5-2,0 cm H2O/μV
Trigger Edi0.5 μV
PEEP:5-10 cm H2O
FiO2:25-40%

PCV – Pressure Controlled Ventilation

Controlled breathing, patients does not need to breathe by themselves. The ventilator provides breaths with a constant predetermined pressure with decelerating flow for a predetermined inspiration time and with preset secondary frequency. The ventilator always gives a decelerating flow in the breathing air. Provides lower peak pressure compared to volume controlled ventilation. Reduces the risk of pressure in the lung tissue and may be beneficial to ARDS. In pressure controlled ventilation the top pressure is equal to the plateau pressure. Pressure-oriented operating modes maintain a constant set of pressure under inspiration (pressure control, pressure support). PC is used primarily in the treatment of moderate or severe pulmonary failure.

PC - Pressure Controlled VentilationNormal settings
PS:5-15 cm H2O
TV:6-8 ml/kg
RR:12-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-15 cm H2O
FiO2:25-40%


PEEP – Positive End-Expiratory Pressure

Increased resistance in exhalation of intubated patient via a valve connected to the ventilator. PEEP provides recruitment of the lung tissue and increases oxygenation. Airway pressure is not allowed to fall back to atmospheric pressure at the end of exspiration. PEEP is usually used in combination with any of the aforementioned ventilation methods. Provides a basic setting in all ventilation modes of the ventilator. The PEEP valve controls the exhalation valve via power steering. Used primarily in lung edema or atelectases.

PEEP can lead to impaired venous reflux and impaired hemodynamics as a consequence of blood pressure drop. May also lead to increased brain swelling and should be limited when increased intracranial pressure. Best effect in extrapulmonary causes of breathing failure such as obesity or heart failure. Has the best effect early in the course of severe lung disease. Normal levels of PEEP are 5-10 cm H2O, at ARDS higher resistance may be required as 10-20 cm H2O. Has more effect on diffuse infiltrates than located. At high PEEP, the lung can be overdispersed and damaged, with the risk of pneumothorax in pronounced cases. At high PEEP that gives rise to PCO2, the lung is overexpressed by poorer gas yield

PEEP-level: 3-20 cm H2O.

Positive End-Expiratory Pressure (PEEP)

Ventilator settingsHealthy lungModerate pulmonary failureSevere pulmonary failure
Breathing modePS, VC, VCPC, BiPAPPS, VC, PC, VCPC, BiPAPPC, (PS, VCPC), BiPAP
Tidal volume ml/kg< 6-8< 6-8< 6-8
Respiratory rate15-2015-2015-30
I:E quote1:21:2-1:11:1 - (2:1)
PEEP cm H200-55-1010-20
Oxygen fraction %< 4040-6040-100
Lung recruitement (RM)-YesYes, at an early stage

PS – Pressure Supported Ventilation

Assumes spontaneous breathing and that the patient triggers every breath himself. The ventilator provides breath with a preset pressure that is constant throughout the inspiration time. All breaths are patient-triggered. Provides a decelerating flow in inspired air. Gives the top pressure you set. Reduces the risk of high pressure in the lung tissues and may be beneficial to ARDS. In pressurized ventilation the top pressure is equal to the plateau pressure. Used primarily during respiratory training and good spontaneous breathing. Pressure-oriented operating modes maintain a constant set pressure level during the inspiration (pressure control, pressure support). TU is used in the treatment of mild, moderate and severe pulmonary failure.

PS - Pressure Support Ventilation.Normala settings
PS:5-15 cm H2O
TV:6-8 ml/kg
RR:12-20 breaths/minute
TU:5-15 cm H2O
I:E1:2
PEEP:5-10 cm H2O
FiO2:25-40%

SIMV – Synchronized Intermittent Mandatory Ventilation

Partially controlled breathing where the patient does not need to breathe himself. SIMV is a mixture of controlling and assisting ventilation modes. SIMV provides a guaranteed amount of predetermined breaths per minute. It also allows spontaneous breathing in-between the breaths. Thus, under the application of SIMV, both the patient’s assisted spontaneous breathing and the ventilator’s mandatory controlled breath are permitted. The breaths that the patient draws themselves is given either with deaccelerating or constant flow, that is volume controlled or pressure controlled breaths. SIMV is used primarily during weaning from the ventilator and good spontaneous breathing, usually in a transitional phase for spontaneous breathing. It can also be used for patients who do not enjoy volume controlled or pressure controlled ventilation. These patients have access to pressure reduction, ventilation and auto-flow (automatic control of inspiration flow). SIMV is used in the treatment of both moderate and severe pulmonary failure. Used for irregular breathing, during weaning or when the patient is about to breath by themselves

SIMV ASB (Assisted Spontaneous Breathing)

SIMV - modeNormal settings
ASB:3-12 cm H2O
TV:6-8 ml/kg
RR:5-10 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-10 cm H2O
FiO2:25-40%
CPAP:3-7 cm H2O


VC – Volume Controlled Ventilation

Controlled predetermined respiration, patients does not need to breathe by themselves. The volume of each breath is predetermined. Always provides a constant flow in the breathing air. Provides higher peak pressure in the inhalation (final inspiratory) compared with pressure controlled ventilation. It reduces the risk of hypoventilation. In volume controlled ventilation, the peak pressure is higher than the plateau pressure. VC is used primarily in the treatment of mild or moderate pulmonary failure. In flow / volume-oriented breathing mode, a constant inspiration volume is maintained. In these breathing modes, additional flow can be triggered upon request under inspiration. Additional breaths can be triggered between the regular ones if the set trigger criterion is met.

VC - Volume Controlled VentilationNormal Settings
VC:5-15 cm H2O
TV:6-8 ml/kg
RR:12-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-15 cm H2O
FiO2:25-40%


VCPC – Volume Controlled Pressure Control

Controlled breathing, patients does not need to breathe by themselves. This mode provides a decelerating flow in the inspired air. Gives sometimes higher peak pressure compared to pressure controlled ventilation. It also reduces the risk of hypoventilation, as well as controlling the pressure level so that the tidal volume is constant. Adjust the pressure to give the lowest possible pressure. VCPC is used in the treatment of mild, moderate and severe pulmonary failure.

VCPS - Volume Controlled Pressure SupportNormal Settings
PC:5-15 cm H2O
TV:6-8 ml/kg
RR:12-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-15 cm H2O
FiO2:25-40%


CPAP – Continuous Positive Airway Pressure


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Increased resistance to breath. Requires spontaneous breathing and that the patient triggers every breath. Can be done with the patient in the ventilator or with a closed breathing mask with a pressure valve. Can be combined with pressure-sustained breaths in a BiPAP system or CPAP with ASB. A pressure in addition to the atmospheric pressure is maintained throughout the breathing cycle (exspiration + inspiration + paustid). CPAP facilitates inhalation but exacerbates exhalation. The term CPAP is usually used for patients with spontaneous breathing.

The CPAP system provides high airflows (80-100 l/min) with constant pressure and flow through mask ventilation. The system can, to some extent, compensate for losses during malfunctioning mask ventilation. Provides recruitment of the lung tissue and increases oxygenation. Used primarily for sustained respiratory pressure in case of pulmonary edema or atelectasis. CPAP can be dangerous in case of insufficient breathing power. The advantage is that the airway is kept open and that the FRC increases, which facilitates breathing. CPAP is stressful for the patient in the long run and tires out the patient. In the case of pneumonia, it may lead to respiratory collapse. It is very effective against pulmonary edema.

Normala settings in CPAP
CPAP-level3-10 cm H2O
RR:Varying
FiO2:30-100%

Mechanical ventilation

Mechanical ventilation


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Patients, who cannot breathe satisfactorily due to lung disease or other lung damage, can be treated with a ventilator that ventilates the lungs mechanically. Normal breathing is done by establishing a negative pressure , air is sucked into the lungs using the breathing muscles meanwhile in controlled ventilation air is blown into the lungs by means of an positive pressure. The ventilator’s compressed air is normally located on the backside of the ventilatory system. A precision valve controls the flow of gas to the patient. The most common basic settings of the ventilator’s system are volume controlled ventilation (VC/VCV, 20-1500 ml/breath) or pressure controlled ventilation (PC/PCV, 5-60 cm H2O in inhalation pressure). Putting the patient on the ventilator relieves the breathing work, but unfortunately, it is possible to add additional injuries to already sick or injured lungs due to pressure injuries (so-called ventilator induced lung injury), atelectasis, pneumothorax or infections.

Mechanical ventilation in ARDS is almost always required, as people with acute respiratory distress syndrome are by definition severely hypoxemic. Minimizing any additional damage while maintaining adequate gas exchange (“compatible with life”) is the central goal of mechanical ventilation in ARDS and acute lung injury, its less-severe form.

Therefore, in order to minimize the risk of damage due to treatment on a ventilator, it is desirable to adjust the ventilator settings for each individual patient and to minimize the amount of burden to the lung tissue. Controlled ventilation means major changes in lung volume changes and airway pressure. The gas exchange in the lungs is affected by both ventilation and circulation. Common causes of breathing failure are pulmonary edema, pneumonia, sepsis, atelectases, severe COPD or asthma. Other causes may be severe trauma, lung contusions, skeletal trauma, stroke, drug overdose, poisoning, unclear unconsciousness, or conceited and exhausted patient. Mechanical ventilation is usually done with a ventilator. Either the patient is intubated endotracheally (invasive ventilation) or the ventilation is performed with the help of a tight facial mask, non-invasive ventilation (NIV). A tube or breathing mask is connected to the ventilator hose system and its ventilation gases.

Mechanical ventilation is usually instituted with volume controlled ventilation (VC/VCV) or pressure controlled ventilation (PC/PCV). Volume controlled ventilation means that the given volume in each breath is predetermined and pressure controlled ventilation means that the given pressure in each breath is predetermined. Volume controlled ventilation always provides a constant flow in the inspired air, while in pressure controlled ventilation, a decelerating flow is obtained. Pressure controlled ventilation favors gas distribution and produces lower peak pressure compared to volume controlled ventilation. Volume controlled ventilation provides a smaller risk of hypoventilation and may be beneficial to ARDS. You always want to minimize the ventilation treatment time.

Ventilator treatment

Ventilator settingsHealthy lungModerate pulmonary failureSevere pulmonary failure
Breathing modePS, VC, VCPC, BiPAPPS, VC, PC, VCPC, BiPAPPC, (PS, VCPC), BiPAP
Tidal volume ml/kg< 6 - 8< 6 - 8< 6 - 8
Respiratory rate15 - 2015 - 2015 - 30
I:E quote1:21:2 - 1:11:1 - (2:1)
PEEP cm H200 - 55 - 1010 - 20
Oxygen fraction %< 4040 - 6040 - 100
Lung recruitement-YesYes, at an early stage

Adjustments of the ventilatory settings


By Vitus Krumbholz, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


It is important to remember that normal breathing is a physiological masterpiece. A large diffusion surface in the lungs in a relatively small cavity interacts with an effective muscle engine and partly with the blood flow in the small circulation. The combination mainly regulates oxygenation as well as elimination of carbon dioxide. Breath is centrally controlled by efferent and afferent neurophysiological pathways that can react and adjust the respiratory momentarily as needed. Ventilation and perfusion are a finely tuned system that is the result of an evolution for millions of years. Ventilation in the ventilator, on the other hand, is not that but depends entirely on our settings in a mechanical ventilator under positive pressure ventilation.

Today’s mechanical ventilation is a rather clumsy imitation of natural breathing, even though it is the foundation of modern intensive care.

In the simplest case of volume controlled ventilation (VC), where the patient does not breathe by themselves, the ventilator ensures oxygenation and carbon dioxide elimination with sustained volume but with variable insufflation pressure. Respiratory treatment means high pressure ventilation of the lungs while normal breathing is a form of negative pressure ventilation. It is the positive pressure that in various ways damages the lungs during prolonged respiratory treatment. The goal of the modern ventilator treatment is therefore to limit the barotrauma. A limited barotrauma is only possible as long as we stay within safety margins regarding time volume, peak pressure and transpulmonary driving pressure

With assisted ventilation (ASB/PS/CPAP), the patients manages to breathe by themselves, which requires increased attention and adaptation of the ventilator settings to an individual and dynamic need. The most widely used form of assisted ventilation is likely to be pressure-assisted ventilation, so-called PS/CPAP. Other assisted ventilation modes such as NAVA, APRV, PAV are available but are used to a lesser extent. However, most of all ICU patients with a respiratory time over a day will spend some time with PS/CPAP.

Adjustable ventilatory settings in the PS/CPAP mode are:

  1. Trigger sensitivity
  2. PEEP
  3. Pressure support (= press PEEP)
  4. Inoperative rise (Inspiratory rise)
  5. Cycling off

 

Figure 1. Pressure-assisted ventilation (PA). The inspiratory rise time defines the time from when the breath is triggered to when maximum inhalation flow is achieved. Cycling-off airflow threshold describes the point where inhalation changes to exhalation as a percentage of maximum inhalation flow.

Trigger sensitivity

In pressure support ventilation/CPAP, the ventilator uses a pneumatic trigger that is either flow or pressure based. During flow-based triggering, the ventilator feels of an inhalation attempt through a measured reversal in the exhalation flow. In order to register and, above all, measure the reversal, the ventilator uses a so-called bias flow. This means that during expiration the ventilator exerts an airflow of 2 l / min that runs parallel to the expiratory flow. This is to obtain a constant “baseline” that is measurable and neither individual nor varied as a physiological exhalation. When the patient initiates a breath, this bias flow is reduced relative to the patient’s inspiration. The change in airflow that occurs triggers an assisted breath when it passes the predetermined trigger value. A similar default setting in PS / CPAP could be 1.4 l/min. A reduced value means increased sensitivity and a faster response time that can increase patient comfort, the patient can therefor be able to trigger each breath more easily. One should be aware of the risk of auto-triggering at very low trigger sensitivity, for example by movements or leaks in the breathing circle, which increases the more we lower the bar. This can create a dyssynchrony breathing pattern which in turn, in addition to stressing the patient, also increases the risk of ventilation-induced lung damage.

When a pressure-based trigger occurs it initiates a breath when the patient through a breathing attempt creates an under pressure under the preset PEEP. The principle is “simple” and works in most ventilators. The disadvantage is that it usually increases respiratory response time and can be stressful for the patient with increased respiratory effort, compared to flow-based triggering. The risk of self-triggering breathing appears to be less in pressure-based trigger setting even with low threshold. However, with a high trigger value, you can really challenge the patient or even prevent breathes from being triggered at all. Excessive triggering causes spontaneous breathing and can thus be perceived as unpleasant to the patient.

There are very few scientific studies of different trigger settings valued against clinical outcomes. Flow-based triggering seems to be a more modern and smarter variant. The recommendation could thus be to not change the predetermined flow trigger if there is no obvious clinical triggering problem.

PEEP

The basic idea for the setting of PEEP is simple, to always maintain an intra-alveolar pressure above zero cm H2O to prevent end-expiratory collapse of the lung tissue. The goal is, hypothetically, a global (= the entire lung), constant (= throughout the breathing cycle) and persistent (throughout the treatment period) ventilation/perfusion ratio (V/Q) as close as possible. It is therefore about finding the right PEEP level that is neither too low nor too high, a so-called optimal PEEP. Too low PEEP can increase the risk of shunt development, dynamic recruitment/derecruitment that leads to “shearing stress” and atelectic trauma, which in turn increases the risk of lung damage and ARDS development. Excessive PEEP may increase the risk of end-time over-distension of the lungs with increased dead-space, which in turn may create a need for increased driving pressure (> 15-20 cm H2O). The best method for finding the right PEEP level under controlled ventilation is debatable, no conclusive data yet. In addition, several methods are relatively difficult in practice.

A fundamental problem with all PEEP methodologies is that an instantaneous improvement in lung mechanics or gas exchange does not necessarily mean an improvement over time. Existing ventilator-induced pulmonary damage and ARDS, the benefit or damage of a given change may sometimes be assessed only after several days of treatment. It should also be borne in mind that all pressure measured in respiratory treatment is measured as global measurements. The patient’s lung, on the other hand, is exposed to different pressures in different parts, while elasticity, resilience and atelectic tendency also vary in different parts of the lung.

What happens under assisted ventilation is that the inspirational pressure that the lung is actually exposed to, the transpulmonary pressure can not yet be measured easily, but method development is ongoing. In addition, the supported ventilation is patient controlled and therefore varied in both volume and dynamics. This makes it more difficult or even impossible to draw conclusions of most measurement methods that have been used for bedside purposes. In other words, in terms of PEEP and PA/CPAP, we have relatively little benefit from measuring:

  • Static compliance
  • Lowest infliction point
  • Lowest shunt
  • Lowest dead space fraction

Although oesophageal balloon manometry appears to be a good method of measuring transpulmonary pressure with high clinical potential to control respiratory treatment, it does not seem to have become enough of a regular procedure for finding the right PEEP level under assisted ventilation.

Electrical Impendance Tomography (EIT) appears as a practical, more promising and useful method of PEEP adjustment, both in controlled and assisted ventilation. But despite the fact that the technology itself is not new and that it has been used successfully in several clinical studies, it is far from a routine use.

In summary, regarding PEEP, there is not much substantial evidence that could help us find the right level. Usually, in clinical practice one can study the ventilator trend image with changes in dynamic compliance over the past 24 hours. For example, recurring impairments may be related to repositioning of an otherwise painless and stressed patient may result in increased atelectic tendency. The patient’s condition would most likely improve with increased PEEP. At low dynamic compliance with high pressure requirements for adequate tidal volumes, as well as a patient who needs to use accessory breathing muscles, possibly lowering of PEEP may lead to immediate improvement. Regardless of the way in which we adjust PEEP, we should follow and evaluate changes in dynamic breathing measurements over time along with the clinical picture.

Pressure Support

When switching from pressure controlled ventilation (alternatively VCPS) to pressure-assisted ventilation, the support level (PS over PEEP, “driving pressure”) can usually be reduced. This occurs when the patient in question begins to contribute to the breathing through a diaphragm contraction. In pressure-assisted ventilation, the pressure during the inspiration phase is constant while the flow decreases. As long as PS is set to a value where the patient is not dependent of pressure support, the patient can determine their own tidal volume (TV). On the other hand, if we underestimate the value to a level where the patient can no longer compensate by their own effort, TV will decrease in relation to the pressure support. As a general goal for adjustment of PS, ​​one should aim for a breathing rate below 30/min and a tidal volume below 6 ml/kg (IBW). Furthermore, one should seek breathing without auxiliary breathing muscles with a “calm” and relaxed patient. The assessment of the last point is obviously difficult, as there is usually a lot more in addition to the respiratory treatment that may stress the patient.


Lung recruitement (RM)


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


These maneuvers (RM) are rarely effective later than 48 hours after the onset of ARDS and can also cause serious damage. In all pulmonary recruitment, circulation and pulse oximetric saturation should be carefully monitored. Lung recruitment has the best effect early in the course of respiratory collapse and development of acute pulmonary failure.

Method 1

Insufflate an air oxygen mixture in the lung to an airway pressure of 40-50 cm H2O for 20-30 seconds. Continue to ventilate in the usual way, but initially keep a PEEP of 15-20 cm H2O. The manoeuvre can be repeated again after a few minutes if the oxygenation does not improve. During and after insufflation, use as low oxygen content in the respiratory gas as possible to minimize the development of absorption electrolysis. The PEEP level can then be slowly reduced if the arterial saturation is maintained. The above can either be achieved by allowing the ventilator to prolong the lung long-lasting by placing the ventilator on CPAP respiration (continuous positive airway pressure) at a total pressure of 40-50 cm H2O or by prolonging the inspiration time under pressure controlled ventilation and adjusting the ventilator to total peak pressure becomes 40-50 cm H2O. You can also manually perform the same maneuver using a breathing balloon with a plugged-in manometer. It is extremely important that the airway pressure is maintained at least at the PEEP level after maneuvering and not allowed to fall to zero or to be negative. Therefore, avoid if possible airway suction at this stage.

Method 2

The lungs insufflates frequently with an airway pressure of 40-50 cm H2O over a period of 5-10 minutes. This is accomplished by setting the ventilator at a low respiratory rate (10 / min), a long inspiration time (50 percent), a 20cm H2O PEEP and a total peak pressure (including PEEP) of 40-50 cm H2O and ventilating with these settings For 5-10 minutes. Thereafter, the ventilator is set to the settings indicated under Method 1.


Weaning from mechanical ventilation


By Vitus Krumbholz, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


As with PC, it is essential to keep the inflation pressure under 20 cm H2O. Regarding the support level (where we achieve adequate tidal volumes), it is not necessarily the level the patient may be in need of. The goal during weaning may be the maximum practice effect with minimal effort. A protocol-controlled weaning with structured escalation of support and ultimately extubation has been shown to provide more respiratory-free days. Because respiratory treatment and weaning is usually controlled by doctors on the basis of individual decisions, standardized weaning protocols are lacking at most clinics. A pragmatic advice is to regularly evaluate and possibly lower PS until the patient needs to increase the breathing work. Signs of increased breathing work may be an increased respiratory rate or visible efforts of auxiliary respiratory muscles, most often in m. sternocleidomastoideus. Another possibility is, of course, to talk to the patient, who is usually communicable during the weaning phase, and ask the patient when breathing efforts starts to feel exhausting. The level of support we choose is just over the effort threshold. However, the patient should never “wear out” in the ventilator at risk of becoming fatigue. Extubation of an exhausted patient is contraindicated. Acceptance of 5 over 5 in negative pressure/PEEP with FiO2 under 0.3 is considered a safe level to extubate. Even at higher pressure levels the patient can be extubated in some cases. It is always a clear advantage if the patient is communicable and calm during extubation. One should always avoid “crash extubation”.

Rising time

The pressure set or airflow that assists the patient during inhalation (pressure over PEEP in PS/CPAP mode) is not at the peak of the beginning but gradually increases after the breath has been triggered. Increase speed is set with inspiratory rise time.

Figure 2. Pressure support ventilation (PS).

A shortening of the inspirational rise time (A + B) leads to a reduced inspiration time without a major change in tidal volume (VT) by a left shift of the inspiration curve. An increased inspiration termination (C + D) reduces both breathing time and VT through previous cycling-off.

The default setting of the rise time in PS/CPAP is 0.15 sec. A decrease in inspiratory rise time affects, at least in theory, not the tidal volume. This is only theoretical speaking because an inadequate shortening of the rise time can cause premature interruption of the occurrence of occasional double breath (double triggering). This is due to too high resistance in the breathing circle caused by secretion or the patient’s “flow in excess” (see curve A below). Double breaths do not necessarily imply a requirement for increased inspirational rise time, but must always be related to the clinical situation. An extension of inspirational rise time may be beneficial in an ARDS-diseased patient with the atelectic tendency, as it creates time for an adequate redistribution of tidal volume between alveoli with different time constants. However, too long rise time can lead to a sense of breathlessness and increased breathing work. This can be seen by a concave deflection of the inspiratory pressure curve (curve C below).

Figure 3. Pressure-assisted ventilation (PA) is an example of dyssynchronism due to inadequate inspirational rise time. (A)The figure shows short inspirational rise time (0.0 sec) with early pressure peak during the inspiration phase as signs of “flow in excess of demand” or obstruction in the airways or in the tube. (B) Shows normal breathing curve. (C) Shows a long inspirational rise time (0.5 sec) with concave deformation of the curve during flow increase as a sign of “demand in excess of flow” with consistently increased breathing work.

Generally speaking, a brief inspirational rise time (shortened inhalation in relation to exhalation time) benefits primarily the obstructive patient (asthma, COPD), and that an extension may sometimes be used for patients with atelectric tendency at slow respiratory rate.

Inspiration finish

The airflow during inhalation begins to decrease as soon as the predetermined pressure level is reached. When the flow is below a certain level, expressed as a percentage of the max flow, the inspiration merges intto expiration. The predetermined value is 30%. If we increase the value by changing the inspiration end, thus shortening the patient’s breath and vice versa.

Figure 4. Pressure-assisted ventilation (PA) increased inspiration termination to 50% (C) with consecutive reduced tidal volume (VT). Image (D) shows attempts to VT compensation by reducing inspiration termination to 30% as well as shortened inspiratory rise time to 0.0 sec.

The purpose is obvious to affect the I:E relationship. To give the obstructive patient more time to breathe out and reduce the risk of auto-PEEP (increased inspiration termination, preferably in combination with shortened inspiratory rise time) or increase the inspiration time for the low-compliance atelectic-restricted restrictive patient with a low compliance (reduced inspiration termination with possible prolongation of inspirational rise time ). Double breath can express the need for further lowering of inspiration termination.

In summary: 

Fine adjustments in the ventilatory settings allow us to optimize the respiratory treatment for the individual patient. Although there are alternatives to PA/CPAP, this breathing mode can generally be considered the most effective weaning pattern. Default settings in PA/CPAP should be the basis of the respiratory setting, but adjustments may be required in consideration of the specific lung pathology and change during different phases of the weaning procedure. In order to achieve effective respiratory treatment, active attendance with relevant adjustments of respiratory settings and some acceptance of the “trial and error”-principle requires consideration of lung physiological principles and continuous monitoring of respiration and patient’s overall clinical picture. Several different measurement methods exist to find optimal ventilatory settings, but basic clinical examination supplemented with ultrasound examination, frequent blood gas analyzes, and common chest x-rays are usually sufficient to optimize ventilation. Computer tomography scanning or magnetic camera pictures will increase the understanding of the patient’s lung disease and should be performed relatively liberally in intensive care patients.


Extubation

By Per Nellgård, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.

and Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.

Updated 2018-12-21


Extubation of an exhausted patient is contraindicated. Acceptance of 5 over 5 in pressure support/PEEP with FiO2 under 0.3 is considered a safe level to extubate from. Even higher pressure levels can be extubated in some cases. It is always a clear advantage if the patient is communicable and calm during extubation. One should avoid “crash extubation”.

Evaluate the patient’s ability to spontaneously breathe before extubation

  • Can the patient have supported ventilation in the ventilator?
  • Are there acceptable values for TU, PEEP 10, FiO2 <40%?
  • Are blood gases acceptable with SaO2> 95%, PaO2> 10 kPa, PaCO2 <6 kPa?
  • Reduce to extubation settings with PEEP 5-7 and TU 5-7

Extubation criteria

  • Alertness RLS <3?
  • Swallowing ability, coughing ability?
  • Manages PEEP 5-7 and PS 5-7 or spontaneous breathing through the tube >30 min?

Evaluation after extubation

  • Free airway, as expected after extubation?
  • Pulse, blood pressure, respiratory rate, blood gases?

Consider the following:

  • A pilot must plan both start (Intubation) and landing (extubation).
  • Extubation is always elective (if not accidental).
  • NAP4 shows that 23% of severe airway-related events occur during extubation.
  • The most common complications of extubation are: hypertension, tachycardia, elevated intracranial and intraocular pressure, etc.
  • Common problems: Inadequate oxygenation and ventilation. Inability to protect the respiratory tract and to get mucus out of the airways.
  • During extubation, plans must be made on before hand, preparing for a failing extubation scenario.
  • During extubation, one must assess whether reintubation can be easy or difficult.
  • Reintubation under optimum conditions differs greatly from acute reintubation with hypoxic patients.
  • Consider laryngeal mask as a possible “bridge” in extubation.
  • Consider the “Airway Exchange Catheter”.

When giving patients anesthesia, one can often choose between general anesthesia or alternatively any type of regional block, central or peripheral in combination with sedation for the surgical procedure. It may seem tempting to choose regional anesthesia for patients with difficult airways, but then one has to choose a method that “works safely”, for example spinal anesthesia. If a blockade discontinues during operation and you are urgently forced to anesthetize a patient with a difficult airway you can quickly get into serious problems.


Optiflow


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Optiflow is a type of respiratory support for patients with spontaneous breathing that allows airway breathing with resistance breathing without tight closing mask. Optiflow, therefore, provides many times better comfort and less effort for the patient than CPAP in tight-closing mask. Optiflow uses oxygen in a very high air flow, 20-60 L / min with active NHF nasal high flow. The system can be connected either by nasal grid or tracheal coupling. It enables comfortable and efficient delivery of up to 100% inhaled oxygen.

Background

High oxygen demand almost always means dehydrated airways and poor secretion. Active oxygenation of oxygen can be used for spontaneous breathing when the oxygen demand is high but there is no need for positive pressure of CPAP or NIV. Active humidification thus allows high inhaled oxygen concentrations without dehydration of the respiratory tract. Gas flow rate greater than 20 liters / minute also creates a certain positive airway pressure (low), as well as a recovery of exhaled gas from the nose / throat which minimizes carbon dioxide recontamination. Preferred oxygen content is controlled by the gas blender.

Indications

This method can be used instead of oxygen mask when you want to avoid dehydration of the upper respiratory tract.  For instance, when switching between NIV and mask ventilation or for long-term oxygen demand. Gas flows up to 35 liters / minute can be tested without a physician’s recommendation. Higher flow rates are only used after approval by the responsible physician. Exercise from non-invasive respiratory treatment may be as good with Optiflow as close-fitting mask (NIV).

Contraindications:

• Unconsciousness• Carbon dioxide retention• Skull base fracture• Liqourrhoe, aka leakage of cerebrospinal fluid• Nose fracture• Nose blood in the family• Thrombocytopenia <85• Nasal strictures• Recently performed surgery in the nose region Practical instructions Material• Mixer / flowmeter• Humidifier Fisher & Paykel• Hose set with hose and humid chamber• Gas connection to the humid chamber• Sterile water• Optiflow nasal prong• Optiflow tracheal connection

1. Connect the mixer / flowmeter to air and oxygen outlet. 2. Bring out the hose and connect the humidity chamber to sterile water. 3. Place the blue breathing hose on one outlet of the humid chamber and the adapter on the other. Yellow-labeled cable now only warms the inspiration hose. Blue-labeled cable measures the temperature of the inspirational hose. 4. Turn on humidifier 5. The humidifier should be on invasive ventilation, it can not be adjusted to an exact degree since it automatically adjusts; container 35.5 – 42o, airway 35 – 40o. It warns of low temp, <35.5o, and high temp, respectively> 41o. 6. Set the desired oxygen value (FiO2) to the mixer. 7. The flow from the mixer should be at least 20 liters / minute to provide the correct oxygen concentration. The maximum flow that can be set is 60 l / min. The aim of the high flow is to exceed the patient’s inhalation flow and therefore create a minimal dilution with room air. In this way, the patient will get the predetermined oxygen amount. 8. Connect Optiflow nasal grid / Optiflow tracheal coupling to the blue humidifier hose and connect to patient. Increase gas flow gradually at start-up until humidifier has approached operating temperature.

Optiflow via nasal prongs

Optilfow bild

Optiflow via tracheal connection

Active humidification via high flow Optiflow tracheal connection is a good alternative to patients with tracheostomy who breathes spontaneously though periodically, for example in ventilator weaning.The blue cup is cup-shaped to capture the original secretion. May be removed and cleaned with sterile water. The system is connected in the same way as described above.

Tracheostomy

A patient who has a speaking valve has an extremely limited ability to moisten the respiratory tract. By switching on Optiflow nasal prongs during the time the valve is used, the patient can achieve a good humidification with the help from oxygen gas. You can thus refrain from connecting oxygen through the valve.Replacement / CleaningApply sterile water by 1 time a day. Hoses / grim / tracheal connection are for one patient at a time and are changed once a week. Clean the halter with sterile water if necessary.

Troubleshooting

If the humidifier does not reach the predetermined temperature, empty if possible the condensate water at temperature probe and check that the hoses are warm. Make sure that the temperature probe is installed from above and properly pressed!LEDs show what triggered possible alarms. Tip: Hold the humidifier’s “silent alarm” button to read the temp on multiple measurement points.


Mechanical ventilation with Maquet/Siemens (Getinge) ventilators


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Servo-I Maquet, Siemens Servo 300, Siemens Servo 900 C.

Siemens has been incorporated by other companies, the Getinge Group and Maquet. Servo-I is made by Maquet.

Maquets and Siemens Servoventilators use controlled and supported breathing patterns.

Volume controlled ventilation (VC), Pressure controlled ventilation (PC), Volume controlled pressure support (VCPS), Pressurized ventilation (PV) and SIMV (Synchronized intermittent mandatory ventilation). The servo ventilator has Automode, improved volume support, new SIMV combinations (synchronized intermittent compulsory ventilation) and Open Lung Tool. The Siemens Servo 900 C has Volume Control Ventilation (VC) and Pressure Controlled Ventilation (PC) as the base. Servo-I (Maquet) has volume control pressure support (VCPS) as basic but equally good possibilities for VC and PC and several other breathing patterns. The ventilator can be used for accurate measurements of controlled, assisted ventilation or spontaneous breathing/CPAP.

Maquet/Siemens (Getinge) VentilatorsNormal Settings
PS:5-15 cm H2O
TV:6-8 ml/kg
RR:5-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-15 cm H2O
FiO2:25-40%
ASB:3-12 cm H2O
CPAP:3-10 cm H2O
Maquet/Siemens (Getinge) ventilators,Display Settings
Pulmonary Airway Pressure (Paw): Peak Pressure,"Plateau Pressure ",Airway mean pressure ,PEEP
Minute volume (MV):"Inspiratory MV ", Expired MV, Spontaneous MV,
Tidal volume (VT): Inspired TV, Expired TV.
Respiratory Rate (RR):" RR ","Spontaneous RR "
Breathing Work (WOB):WOB in patient & ventilator, Shallow breathing index (SBI)
O2-concentration:Inhaled O2- Fraction (FiO2)
Time Measures:Inspiration-/Expiration (I:E), Inspiration-/tot. Respiratory time (TI/TTOT), Time constant (TC),
Lung mecanics: Respiratory restistance,"Compliance (C) static (in the respiratory system)", Dynamic elastanse (E),
Air temperature: 10-40 °C
Configuration of Curves:"Airway Pressures vs Time ",Flow vs time“ ,"Volume vs time ",CO2 vs Time
Capnography: End-tidal CO2-conc. (etCO2), Minute elimination of CO2, Tidal CO2 elimination (VTCO2),
Trends: "MV, TV, RR, PEEP, R, C, etCO2, Peak-, plateau & mean pressures"
Loops:Paw vs Vol,Flow vs Vol,,
Oxygen Saturation (SpO2):SpO2, Pulse,


Mechanical ventilation with Datex-Ohmeda (GE Healthcare) ventilators


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


ADU, Aisys Carestation

Aisys has a variety of breathing modes to choose from. Volume Controlled Ventilation (VCV), Pressure Controlled Ventilation (PCV), Pressure Supported Ventilation (PSVPro (Pro = Protection)), SIMV (Synchronized Intermittent Mandatory Ventilation, SIMV-VC, SIMV PC), PCV-VG: Pressure-Controlled Ventilation With Volume Assurance and CPAP / PSV. Aisys has improved volume support and various new SIMV combinations (synchronized intermittent compulsory ventilation). Aisys have volume controlled ventilation (VCV) as a base but equally good possibilities for PC (PCV-VG) and other selective breathing patterns. The ventilator can be used for accurate measurements of controlled, assisted ventilation or spontaneous breathing/CPAP-PSV. The ventilator’s compressed air is located on the back of the respiratory system. A precision valve controls the flow of gas to the patient. Under inspiration, this gas flow closes the exhalation valve and pushes down the bellows. During expiration, a small flow exhalation membrane presses to apply a PEEP pressure.

ADU Carestation VentilatorsNormal Settings
PS:5-15 cm H2O
TV:6-8 ml/kg
RR:5-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-15 cm H2O
FiO2:25-40%
ASB:3-12 cm H2O
CPAP:3-10 cm H2O
ADU Aisys Carestation ventilatorDisplay Settings
Pulmonary Airway Pressure (Paw): Peak Pressure,"Plateau Pressure ",Airway mean pressure ,PEEP
Minute volume (MV):"Inspiratory MV ", Expired MV, Spontaneous MV
Tidal volume (VT): Inspired TV, Expired TV
Respiratory Rate (RR):" RR ","Spontaneous RR ",,
Breathing Work (WOB):WOB in patient & ventilator,Shallow breathing index (SBI),,
O2-concentration:Inhaled O2- Fraction (FiO2),,,
Time Measures:Inspiration-/Expiration (I:E), Inspiration-/tot. Respiratory time (TI/TTOT), Time constant (TC)
Lung mecanics: Respiratory restistance,"Compliance (C) static (in the respiratory system)",Dynamic elastanse (E),
Apnéa Time
Air temperature: 10-40°C
Configuration of Curves:"Airway Pressures vs Time ",Flow vs time“ ,"Volume vs time ",CO2 vs Time
Capnography: End-tidal CO2-conc. (etCO2), Minute elimination of CO2, Tidal CO2 elimination (VTCO2),
Trends: MV, TV, RR, PEEP, R, C, etCO2, Peak-, plateau & mean pressures"
Loops: Paw vs Vol,Flow vs Vol,,
Oxygen Saturation (SpO2):SpO2, Pulse,
You choose standard settings or "Paw-Manom, Loops, Big curves or Local"


Mechanical ventilation with Dräger ventilators


By Kai Knudsen, Senior Physician in Anesthesia & Intensive Care. Sahlgrenska University Hospital.
Updated 2018-12-21


Evita XL, Evita 4, Pulmovista

Dräger ventilators use several breathing patterns (breathing mode) such as: IPPV, BiPaP, BiPaP Assist, CPAP + ASB, SIMV, APRV, MMV.

Respiratory mode provides different types of assisted or controlled ventilation via mask or endotracheal tube. The fans have advanced breathing modes such as the “open breathing system” in Auto-Flow, APRV, and graphical support tools integrated in the display as default. Typically, the airway pressure in CPAP breaths and in assisted breaths (ASB) is usually set at 5-12 cm H2O.

Dräger Evita VentilatorsNormal Settings
PS:5-15 cm H2O
TV:6-8 ml/kg
RR:5-20 breaths/minute
PS:5-15 cm H2O
I:E1:2
PEEP:5-15 cm H2O
FiO2:25-40%
ASB:3-12 cm H2O
CPAP:3-10 cm H2O
Dräger Evita VentilatorDisplay Settings
Pulmonary Airway Pressure (Paw):Peak Pressure, "Plateau Pressure ", Airway mean pressure , PEEP
Minute volume (MV):"Inspiratory MV ", Expired MV, Spontaneous MV, MV leakage
Tidal Volume (VT):Inspired TV,Expired TV, Assisted Spontaneuos TV (VTASB)
Respiratory Rate (RR):" RR ", "Spontaneous RR ", Obligatory RR,
Breathing Work (WOB):WOB in patient & ventilator, Shallow breathing index (SBI)
O2-concentration:Inspiratory O2- Fraction (FiO2)
Time Measures:Inspiration-/Expiration (I:E), Inspiration-/tot. Respiratory time (TI/TTOT), Time constant (TC)
Lung Mecanics:Respiratory restistance, "Compliance (C) static (in the respiratory system)", Dynamic elastanse (E)
Apnéa Time
Air temperature: 18-51°C
Configuration of Curves:"Airway Pressures vs Time ", Flow vs Time“ , "Volume vs Time ", CO2 vs Time
Capnography: End-tidal CO2-conc. (etCO2), Minute Elimination of CO2, Tidal CO2 Elimination (VTCO2)
Trends: "MV, TV, RR, PEEPi, R, C, etCO2, Peak-, plateau & mean pressures"
Loops:Paw vs Volume, Flow vs Volume
Oxygen Saturation (SpO2):SpO2, Pulse