Hemodynamic Monitoring

Hemodynamic Monitoring

Standard monitoring of the hemodynamics in anesthesia is noninvasive measured blood pressure, pulse, ECG and oxygen saturation. In case of unstable patient or major surgery, invasive blood pressure is measured via an arterial catheter and possibly central venous pressure (CVP) via a central venous catheter (CVC). For more advanced surgery or very unstable patients, an extensive monitoring of central hemodynamics is often required. The goal is to maintain a stable circulation per- and postoperatively with a fluid treatment that provides good tissue perfusion and sufficient oxygen delivery to vital organs without overloading the heart.

Targeted fluid therapy is based on the so-called Frank-Starling mechanism. This means that the heart gets greater contraction force if it grows with a volume load. Thus, as blood volume increases by infusion of fluids, cardiac output increases. However, the increase stops at a plateau, after which the cardiac output decreases if even more volume is given.

The expanded and improved monitoring allows for goal-directed fluid treatment with optimization of circulation and fluid balance. Previously, the anaesthesiological standard has been a Swan-Ganz Catheter (Pulmonary Artery Catheter/PA Catheter) with thermodilution technology that provides continuous measurement of cardiac output (CO), central venous pressure (CVP), pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR). The PA catheter is relatively complicated to insert and use why in recent years it has been replaced by less invasive techniques that have been somewhat easier to use. Several different less invasive techniques are available for monitoring central hemodynamics, for example. PiCCO, NiCO, LiDCO, Cardio-Q and Vigileo. A number of clinical trials have shown better results when optimizing the circulation of large intestinal surgery using expanded central hemodynamics. Several of the new monitoring techniques are easier to apply compared to classic PA catheterization, but also include some approximations calculated on algorithms that cause some sources of error and some uncertainty in reliability. PA catheter is used primarily in right ventricular failure or pronounced pulmonary hypertension.

However, it should be noticed that the patients studied by Shoemaker had a relatively low middle age, which means that the group differs from the often elderly people who undergoes surgery on a regular basis in Swedish hospitals. It is likely that elderly patients withstand fluid loads worse than younger and heart-healthy. It is reasonable to imagine that too much and too little fluid can adversely affect the circulation and tissue perfusion. Edema by fluid overload of intestinal anastomosis and internal organs of the abdomen and thorax like liver, pancreas and lungs can have adverse effects.

The goal is to optimize the heart rate and thus the cardiac output volume, instead of providing a certain amount of fluid per unit of time, thereby ensuring good oxygen delivery to the tissue without excessive fluid supply. It is known that high pulse and high blood pressure for a long time are not good for the circulation as well as low blood pressure or a tight circulation to vital organs or splanchnicus. It is also unfavorably with pronounced blood pressure drops (> 40% of systolic baseline) or tachycardia with cardiac ischemia. You always try to avoid hypoxia, drop in blood pressure, tachycardia and cardiac disease. Excessive inotropic treatment may endanger the heart with adverse effects in the long term, even if cardiac output can be sustained peroperatively. Instead, one tries to optimize the circulation with controlled fluid supply. The goal is to maintain normal central filling pressures as well as SaO2> 94%, SvO2> 70%, Hgb 8-10 g/dL, Temp 37o and MAP of 60-100 mmHg (> 65-75 mmHg). A cardiac index (CI) of over 3.0 l/min/m2, global enddiastolic volume (indexed) (GEDI) above 700 ml/m2, intrathoracic blood volume (ITBI) is sought between 850-1000 ml/m2 and global ejection fraction GEF) > 30%, extravascular lung water (ELWI) should be below 10 ml/kg and pulse pressure variations below 10% (SVV% and PPV%). Signs of good hemodynamics are a stable calm circulation with good peripheral circulation (fine capillary filling), good urinary production, normal, ST-T segment of ECG, fine blood gases including SvO2 and no lactate production. NT-ProBNP should be <450 ng/L.

Targeted fluid treatment requires that you measure the hemodynamic effects of the added volume of fluid, often given as a bolus fluid, for example 250 ml of saline over 5 minutes (or 200 ml of colloid). One can then get an idea of ​​whether the patient’s increased fill volume increases heart rate and improved fluid response. Usually, the effects on stroke volume, cardiac output and impact volume changes or pulse pressure variations are measured. Measuring central ventricular pressure and blood pressure alone has been shown to be insufficient in several studies. The degree of response to fluid bolus gives an idea of ​​where on the so-called Frank-Starling curve man is, ie what degree of optimal fill you have received. When preload is increased by intravenous fluid, the volume of stroke increases significantly more if the patient is inoculated and is located on the lower part of the Frank-Starling curve. Then the arterial pressure curve also varies considerably more with breathing. Thus, from an individual value of the stroke volume, it is not possible to say if the patient is fluid optimized. For optimal filling, repeated measurements and continuous measurement of cardiac output (CO) and central hemodynamics are required. Further information is obtained from measuring venous oxygen saturation SvO2 that should exceed 70% and systemic vascular resistance (SVR) as an expression of afterload.

Stroke volume variations (SVV%) and pulse pressure variations (PPV%) can provide an understanding of the physiological response to fluid treatment or pharmacological intervention. Preload corresponds to the filling of the chamber of the heart immediately before contraction. Preload can be estimated with GEDV, global enddiastolic volume (indexed) (GEDI) or intrathoracic blood volume (ITBI). Stroke volume variations (SVV% – stroke volume variation) and pulse pressure variations (PPV% – pulse pressure variation) also provide information about changes in preload (% SVV = SVmax-SVmin/SVmean). SVR (Systemic Vascular Resistance) primarily provides information about changes in afterload.

The choice of minimally intensive technology varies between different clinics in every country and is largely controlled by local practices and national practices. However, much suggests that these techniques could be used significantly more often to optimize patients hemodynamically per- and postoperatively. Hemodynamic reference values ​​are found down below.


Hemodynamics Reference Values

AbbreviationPractical nomenclatureParameterReference ValuesUnit/Notice
COCardiac OutputCardiac Output4,0-8,0l/min
CICardiac IndexCardiac Output (index)3,0-5,0l/min/m2
ScVO2 Central Venous SaturationCentral Venous Oxygenation70-80%
DO2I Oxygen Delivery (Indexed)Oxygen Delivery Index400-650ml/min/m2
VO2I Oxygen Consumption (Indexed)Oxygen Consumption Index125-175ml/min/m2
GEDVGlobal Enddiastolic VolumeGlobal Enddiastolic Volume900-1280ml. A measure of cardiac filling and contractility. Preload.
GEDI Global Enddiastolic Volume (Indexed)Global Enddiastolic Volume Index680-800ml/m2 . GEDV/BSA.
GEFGlobal Ejection FractionGlobal Ejection Fraction25-35%. A measure of the emptying of the heart all four chambers. (4xVS/GEDV). Contractility.
ITBI Intrathoracic Blood Volume (Indexed)Intrathoracic Blood Volume Index850-1000ml/m2
SVStroke VolumeStroke Volume60-100ml/beat
SVIStroke Volume IndexStroke Volume33-47ml/beat/m2
SVV Stroke Volume VariationsStroke Volume Variations< 10% A measure of preload. High value with hypovolemia (>15%).

SVmax-SVmin/SVmean
PPV Pulse Pressure VariationsPulse Pressure Variation< 10%. A measure of preload. High value with hypovolemia
SVRSystemic Vascular ResistanceSystemic Vascular Resistance900-1400Dyn*s*cm-5*m2. Measures peripheral vascular tone, a measure of afterload. Low when the patient is vasodilated.
SVRI Systemic Vascular Resistance (Indexed)Systemic Vascular Resistance Index1700-2400Dyn*s*cm-5*m2
CFI Cardiac Function IndexedCardiac Function Index4,5-6,51/min
GEF Global Ejection FractionGlobal Ejection Fraction25-35%
dPmx Left Ventricular Contractility (Indexed)Index of Left Ventricular Contractility-/-mmHg/s
LVSWILeft Ventricular Stroke Work (Indexed).

 
Left Ventricular Stroke Work Index50-62gm/m2. A contractility measure. At low levels, it is likely that inotropic drugs are needed.
CPI Cardiac Power IndexCardiac Power Index0,5-0,7W/m2
ELWI IndexExtravascular Lung Water (Indexed)Extravascular Lung Water3,0-7,0ml/kg
PVPI Pulmonary Vascular Permeability (Indexed)Pulmonary Vascular Permeability Index1,0-3,0-/-

PA-catheter Swan-Ganz

For more advanced anesthesia or very unstable patients, an extensive monitoring of central hemodynamics is often required in addition to arterial pressure and CVP. The goal is to maintain a stable circulation per- and postoperatively with a fluid treatment that provides good tissue perfusion and sufficient oxygen delivery to vital organs without overloading the heart. PA catheters are commonly used in patients with impaired cardiac function, especially in right ventricular failure, pulmonary hypertension or pronounced global failure. Since the 1970s, the anaesthesiological standard has been a Swan-Ganz catheter (PA catheter/pulmonary artery catheter) with thermodilution technology that provides continuous measurement of cardiac output (CO), central venous pressure (CVP), wedge pressure (PCWP), pulmonary arterial pressure (PA pressure systolic/diastolic) and systemic vascular resistance (SVR). The PA catheter is a four-lumen catheter with a thermistor and an inflatable balloon at the distal end. The balloon allows the catheter to be captured by the bloodstream and expelled into the pulmonary artery. The thermistor is used to use thermodilution technology for measurement of central hemodynamics.

With thermodilution technology, you use Stewart-Hamilton’s formula for calculating cardiac output according to CO = V (TB-TI) x K1 x K2 / ∫ ΔTB (t) dt. The denominator expresses the area under the thermal dilution curve. The technique can be used for intermittent calculations of cardiac output by the injection of cold fluids, usually cold sodium chloride. A certain amount of liquid (10-20 ml) is injected into the proximal CVP portion of the PA catheter. The temperature change is recorded at the catheter tip and the cardiac output is calculated with the thermal dilution curve, usually a mean of the area under the curve is required in three different measurements. For continuous calculation of CO, an automatic method based on a heat filament on the catheter located in the right atrium is used. Pulsed heating (0.050 C) in 15 second sequences creates a thermal dilution curve. Multiple cycles are required, usually over 3-6 minutes. The use of PA catheters is “golden standard” for the calculation of central hemodynamics and is the reference method for other less invasive methods.

Insertion

The catheter is usually inserted under sterile conditions in the right jugular vein through an insertion instrument that is inserted into the vein over a guidewire. Through the insertion instrument, a ballooned PA catheter is inserted and the distal balloon is blown up in the right atrium to be captured by the blood flow. The PA catheter is inserted through the right ventricle and into a lung of the pulmonary artery. The distal balloon is blown up when the catheter is inserted 15-20 cm in the right atrium with air. You use the preformed curvature of the catheter to get through the right ventricle and into the pulmonary artery. Upon insertion, the catheter should be attached to a pressure dome in order to follow the pressure curve change when the catheter is passed through the right atrium and right chamber and further into the pulmonary artery (pulmonary artery). In the right chamber you have usually reached 35-45 cm from the skin plane and you reach the right position in the pulmonary artery at 45-55 cm. Once you have arrived in the pulmonary artery you must continue to a wedge position. Then the systolic component disappears and the appearance of the curve resembles a CVP curve, then you release the balloon. The catheter position should be confirmed by X-rays. The occlusion pressure (wedge pressure/inlet pressure) is approximately the same as the left ventricular end-diastolic pressure (LVEDP), an expression of preload.

Indications of a PA-Catheter

  • Septic shock
  • Major trauma
  • Comprehensive multiple organ failure
  • Right ventricular failure
  • Pulmonary hypertension
  • Severe cardiac failure that does not respond to initial treatment
  • Liver transplantation
  • Heart transplantation
  • Other monitoring of central hemodynamics is considered insufficient
Table 1. Hemodynamic parameters measured by PA catheter. Indexed values are calculated per m2 body area.
AbbreviationPractical nomenclatureReference ValuesUnit/Notice
COCardiac Output4,0-8,0 l/minSV x HR/1000. A measure of flow.
CI Cardiac Index3,0-5,0 l/min/m2SV x HR/m2. A measure of flow. CI=CO/BSA
PA-pressurePA pressure15-30 mmHg

Syst: 20-30 mmHg

Diast: 8-12 mmHg
Systolic pressure is generated by the right chamber in systole. Blood pressure in the pulmonary circulation.
PA-pressure averageMean PA pressure10-20 mmHgPA-pressure in the pulmonary circulation mean.
PCWP/PAOPPulmonary Capillary Wedge Pressure Pulmonary Occlusion Pressure5-15 mmHgCorresponds to LVEDP, a measure for Preload.
SVStroke Volume50-110 ml/beatStroke Volume. CO/HR x 1000
LVSWILeft Ventricular Stroke Work Index50-62 gm/m2A contractility measure. At low levels, it is likely that inotropic drugs are needed. LVSWI=SVI(MPA-MRA) x 0,0136
PVRPulmonary Vascular Resistance150-250 Dyn*s*cm-5*m2Corresponds to resistance in the pulmonary circulation. PVR=(MPAP-PAWP)x80/CO
PVRIPulmonary Vascular Resistance Index240-400 Dyn*s*cm-5*m2Corresponds to resistance in the pulmonary circulation. (indexed).
SVRSystemic Vascular Resistance900-1400 Dyn*s*cm-5*m2Measures peripheral vascular tone, a measure of afterload. Low when the patient is vasodilated.
SVRISystemic Vascular Resistance Index1700-2400 Dyn*s*cm-5*m2Measures peripheral vascular tone, a measure of afterload. Low when the patient is vasodilated.
CaO2Arterial Oxygen Content18-20 ml/dlThe amount of oxygen bound to hemoglobin plus the unbound fraction
Mixed venous oxygen contentScVO270%

13-16 ml/dl
A measure of DO2-VO2. Reflects CO.
Arterio venous O2-differenceCaO2-CvO24-5,5 ml/dlReflects oxygen consumption. High at oxygen debt.
DO2Oxygen delivery800-1000 ml/minOxygen delivery
VO2Oxygen consumption150-300 ml/minOxygen consumption

PiCCO (Pulsion Medical Systems)

The Pulse Contour Continous Cardiac Output System (PiCCO).

PiCCO measures central hemodynamics continuously through a pulse contour method or intermittently through a thermal dilution technique. PiCCO provides the ability to guide fluid balance and optimize circulation in critically ill or hemodynamically unstable patients, often referred to as targeted fluid treatment.

Pulse contour analysis is based on the fact that the higher the volume of the blood, the greater blood volume accumulates on the arterial side and the greater the variations in systole and diastole. The stroke volume is calculated from the systolic part of the pulmonary wave curve. Pulse pressure is proportional to stroke volume (SV) and inversely proportional to vessel size compliance. Pulse pressure variations change with changes in vessel tone and stroke volume. The vessel tone is difficult to measure and is calculated from algorithms based on age, gender, ethnicity and BMI. Based on these algorithms and pulse contour analysis, cardiac output and central hemodynamics are calculated. PiCCO measures cardiac output (CO), cardiac index (CI), global enddiastolic volume (GEDV), intrathoracic blood volume (ITBV), global ejection fraction (GEF), extravascular lung (ELW), stroke volume variations (SVV%) and pulse pressure variations (PPV% ). CO (cardiac output)/PCC (pulse continuous cardiac output), systemic vascular resistance (SVR) and SVV are calculated from pulse contour analysis. SVR is calculated from the formula (MAP-CVP)/CO.

Cardiac Output volume determination with thermodilution technology is done by injecting an indicator (cold fluid) into the arterial catheter where a thermistor detects temperature change along the bloodstream. The cold fluid is injected centrally on the left side and the temperature change is measured peripherally on the arterial side via the PiCCO catheter. CO is calculated using a Stewart-Hamilton modified algorithm. CO, GEDV, ITBV and EVLW are calculated by the module based on thermodilution determinations.

Table 1. Hemodynamic parameters measured with PiCCO. Normally, indexed values are used. Indexed values are calculated per m2 body area (BSA).
AbbreviationParameterReference ValuesUnit/Notice
COCardiac Output4,0-8,0 l/minSV x HR/1000. A measure of flow.
CICardiac Index3,0-5,0 l/min/m2SV x HR/m2. A measure of flow. CI=CO/BSA
GEDVGlobal Enddiastolic Volume900-1280 mlA measure of cardiac filling and contractility. Preload.
GEDIGlobal Enddiastolic Volume Index680-800 ml/m2A measure of cardiac filling and contractility. Preload. GEDV/BSA.
ITBIIntrathoracic Blood Volume Index850-1000 ml/m2A measure of cardiac filling in all chambers and in the pulmonary circuit. Higher at higher filling pressures. Preload.
GEFGlobal Ejection Fraction25-35 %A measure of emptying from all chambers. Contractility. (4xVS/GEDV).
ELWIExtravascular Lung Water (Index)3-7 ml/kgA measure of cardiac filling in the lungs. Higher at pulmonary edema.
SVVStroke Volume Variation< 10 %A measure of preload. Higher values at hypovolemi (>15%). SVmax-SVmin/SVmean
PPVPulse Pressure Variation< 10 %A measure of preload. Higher values with hypovolemia.
LVSWILeft Ventricular Stroke Work Index50-62 gm/m2A measure of contractility. At low values there is need for inotropic drugs.
SVRSystemic Vascular Resistance900-1400 Dyn*s*cm-5*m2Measures peripheral vascular tone, a measure of afterload. Low when the patient is vasodilated.
SVRISystemic Vascular Resistance Index1700-2400 Dyn*s*cm-5*m2Measures peripheral vascular tone, a measure of afterload. Low when the patient is vasodilated.

PiCCO is based on measurement values ​​from two catheters, partly a central venous catheter and an arterial catheter, usually placed in the femoral artery. In order for the system to be reliable, it is necessary to have a fine arterial pressure curve, which causes difficulties in pronounced hypovolemia, vascular constriction or vascular occlusion. To obtain reliable flow data, PiCCO must be calibrated using a thermal indicator via CVC (at least every 8 hours). The CVC should be a 3-lumen CVC. The arterial catheter is a special PiCCO catheter with a thermistor at the invasive end that is branched into an electronic leg and a fluid-filled leg that goes to a pressure dome. The electronic skull from the femoral catheter is connected to PiCCO’s split arterial pressure cable that is also connected to the CVC. Connect the termometer and the cord to the PiCCO module. The link connected to the CVC provides electronic measurements from injections that are centralized to thermal dilution. In adults, usually a cold injection for calibration of 5-20 ml of sodium chloride is given. The injection is injected for seven seconds on command from the PiCCO module.

The cardiac output volume is determined as CO, or continuously as PCCO or indexed values ​​such as CI or CCI. SVI is stroke volume index which is a measure of heart contractility. Intrathoracic blood volume (ITBV) is a measure of preload. Extravascular Lung Water (ELW and ELWI), is a measure of how filled the lungs are, rises in case of failure and pulmonary edema.

Enhanced hemodynamic monitoring provides better possibilities for goal-directed fluid treatment and balanced anesthetic techniques. It is a matter of debate how much fluid is best to give peroperatively, but it has already been shown in the 80’s that patients with supranormal oxygen supply values ​​had better outcomes after surgery, which could later be confirmed in meta-analyzes. Oxygen delivery depends on hemoglobin concentration, arterial oxygen saturation and cardiac output. Cardiac output is due to heart rate and stroke volume. Today, it is primarily the cardiac output volume that is optimized and not oxygen delivery. In order to get a better idea of ​​optimal oxygen delivery, metabolic parameters must also be measured such as central venous oxygen saturation (SvO2) and lactate.

Usually, a cardiac index (CI) of more than 3.0 l /min/m2, global enddiastolic volume (indexed) (GEDI) exceeds 700 ml/m2, intrathoracic blood volume (ITBI) between 850-1000 ml/m2 and global ejection fraction (GEF)> 30%. Extravascular Lung Water (ELWI) should be below 10 ml/kg and pulse pressure variations below 10% (SVV% and PPV%). Signs of good hemodynamics are a stable calm circulation with good peripheral circulation (fine capillary filling), good urinary production, normal ST-T segment of ECG, fine blood gases (normally BE) including SvO2 and no lactate production (<2 mmol/l).

Practical instruction

Thermodilution/calibration is most suitable with 20 ml of saline <8 ° C. Prior to calibration, a typical measurement of CVP is performed. There should be 100 ml NaCl in the refrigerator in the medicine room. Feel free to put it in an ice bath (ice bags in the department’s kitchen, the temperature should preferably be <8° C). Luer-lock syringes are preferred. Press the “Start” button on the PiCCO module or “Main menu preset” + “Cardiac Output”. Now a large menu will pop up on the screen. Make sure the amount of 20 ml is inscribed. Connect the syringe with cold NaCl to the CVC. Touch “Start CO measurement”. It should then be “Stable baseline, inject now”. The injection should start within 20 seconds, should be at a steady rate and should not take more than 8 seconds. Check that the measurement has got a green check “CAL” = ok. Press “Start CO measurement” for new measurement and repeat as above.

Three approved measurements are sought. If any value/curve differs heavily or is ignored by the machine, just press the green curve (it turns red) and then it will not be counted in the calibration. You have 15 minutes to do all their thermal dilutions. When you have three reliable measurements, it is time to press “Save CO & Calibrate CCO”. The green curves will then become gray-green and locked; the question mark will disappear from the monitor’s continuous values. Calculations are made by pressing the “hemodynamic calculations” button (at the bottom in the previous menu, otherwise you can access the menu). To get indexed values, body weight and length are entered. CVP is required for SVR (resistance) calculation and manually entered. Then press “perform calculations” and all numbers appear in the table. Recalibration should take place every 8 hours.


NiCO (Non Invasive Cardiac Output - Novametrics)

NiCO measures central hemodynamics non-invasively via the airways – Non Invasive Cardiac Output.

NiCO requires a closed respiratory system, which is why this method is usually used in septic or sedated patients who are treated on a ventilator. NiCO can measure cardiac output based on changes in CO2 concentration in the exhalation air caused by a controlled period of reoccurring in a closed hose system. NiCO uses a partial carbon dioxide rebreathing method and a modified Fick’s equation to calculate cardiac output and central hemodynamics via sampling of carbon dioxide in the exhaled air. The system includes a CO2 sensor (infrared light meter), an airflow meter (“differential pressure pneumotachymeter”), an extensible return hose and a pulse oximeter. For this system, therefore, no CVC is needed.

The cardiac output volume can be calculated according to Fick’s principle from the ratio of oxygen consumption (VO2) to the arteriovenous oxygen difference (AVDO2). Through mathematical calculations, Fick’s principle can also be applied to measurements of carbon dioxide production with and without reversal. Venous CO2 can be calculated from the difference in carbon dioxide concentration in inhalation and exhalation with and without regurgitation. The method is based on the principle of calculation of cardiac output according to the formula CO = VO2/CaO2-CvO2 that can be used for carbon dioxide production according to CO = VCO2/CvCO2-CaCO2 with (å) and without rebreathing (ia). By VCO2/CvCO2 – CaCO2 = VCO2å/CvCO2å-CaCO2 then the formula can be written as CO = VCO2-VCO2å/CaCO2å-CaCO2. VCO2-VCO2å = ΔVCO2.  CaCO2å-CaCO2= ΔetCO2. VCO2 is lower in rebreathing than in non-rebreathing. EtCO2 is higher in reversal than in non-return. This formula can then be rewritten to CO = ΔVCO2/ΔetCO2 x S. S is a coefficient for the slope of the carbon dioxide dissociation curve.

To the patient’s closed respiratory system, the hose loop is connected with a carbon dioxide meter and a flowmeter. During a three-month return cycle, the difference in carbon dioxide content in the exhaled air is measured for carbon monoxide prior to and after the return cycle. A loop system for reversal allows induction of a rise in CO2 production followed by a fall in CO2 production. The difference is used to calculate cardiac output. Carbon dioxide production (VCO2, ml/min) is calculated from the difference in inhaled air and exhalation air, while the amount of carbon dioxide (CaCO2 ml / 100 ml blood) is estimated from etCO2 (mmHg). NiCO utilizes the difference in etCO2 and CO2 elimination to calculate cardiac output. Delta VCO2 (carbon dioxide production) is calculated by measuring in normal landing and after return (VCO2-VCO2å = ΔVCO2). Delta CaCO2 can be approximated by multiplying etCO2 by a factor (S) for the slope of the carbon dioxide dissociation curve which is linear between 15 and 70 mmHg in the partial pressure of the carbon dioxide (2-9.3 kPa). CO2 production is calculated from the product of CO2 concentration and airflow during a breathing cycle and CaCO2 is obtained from etCO2 and the carbon dioxide dissociation curve.

NiCO calculates blood flow (COeff) through perfused lung, ie. only those parts of the small cycle that are not shuntflow. The shunt flow (COshunt) must be added to display the full cardiac output volume (CO = COeff + COshunt). CO shunt is automatically calculated from isoshunt diagram. The cardiac minus volume is the sum of COeff and COshunt. In order to use NiCO, stable ratios of cardiac output, metabolism, minute ventilation, arterio-alveolar CO2 difference, no CO2 recirculation and a correct shunt estimate are expected. NiCO is unsuitable for superficial sedation, spontaneous breathing, high ICP (due to risk of carbon retention) and hypercapnia.

Table 1. Table 1. Hemodynamic parameters measured with NiCO. Indexed values are calculated per m2 body area (BSA).
AbbreviationParameterReference ValuesUnit/Notice
COCardiac Output4,0-8,0 l/minSV x HR/1000. A measure of flow.
CICardiac Index3,0-5,0 l/min/m2SV x HR/m2. A measure of flow. CI=CO/BSA
SVStroke Volume60-100 ml/beatml/beat The amount of blood ejected from the left ventricle in every heartbeat.
SVIStroke Volume Index33-47 ml/beat/m2ml/beat. The amount of blood ejected from the left ventricle in every heartbeat/BSA.
HRHeart Rate60-90 beats/min Pulse rate, beats/min
CdynDynamic Compliance0-500 ml/cm H2OThe volume that the lung expands for a given pressure.
ETCO2Endtidal Carbon Dioxide0-20 kPaMaximum CO2 plateau at the end of the breathing cycle, end tidal.
Insp CO2Inspired Carbon Dioxide0,4-6,7 kPa 
PCBFPulmonary Capillary Blood Flow0,5-20 l/minBlood flow through ventilated parts of the lung
VCO2Carbon Dioxide Elimination0-3000 ml/minExhausted amount of carbon dioxide per minute.
VteExpired Tidal Volume200-3000 mlExhausted amount of air per breath.
PiPPeak Inspiratory Pressure0-120 cm H2O Peak Pressure


LiDCO

LiDCO’s monitoring system (LiDCO rapid/LiDCO Plus) measures central hemodynamics via the arterial pressure curve and provides the possibility to control fluid balance and optimize circulation in critically ill or hemodynamically unstable patients. LiDCO uses lithium calibration in the LiDCO Plus system and without lithium calibration with direct analyzes of the arterial pressure curve in LiDCO rapid. One can achieve goal-directed fluid treatment either with LiDCO rapid which is primarily intended for temporary use in the operating room or LiDCO Plus, which is primarily intended for continuous use on ICU.

With LiDCO rapid, you can connect the system to the arterial pressure curve via an arterial catheter and get arterial pressure (SBP, DBP, MAP), heart rate, cardiac output (CCO), stroke volume (SV), stroke volume changes (SVV%) and pulse pressure changes (PPV%). Stroke volume variations (SVV% – stroke volume variations) and pulse pressure variations (PPV% – pulse pressure variation) mainly provide information about changes in preload (% SVV = SVmax-SVmin/SVmean.). LiDCO uses an algorithm to calculate central hemodynamics called the Pulse CO algorithm.

LiDCO Plus, with lithium calibration (lithium dilution technique), can measure continuous cardiac output (CCO) volumes, stroke volume (SV), impact volume changes (SVV%) and pulse pressure changes (PPV%). A lithium-sensitive electrode is connected to the arterial catheter during calibration. Cardiac Output is calculated by Q = Li x 60/A x (1-PCV *). Stroke volume variations (SVV%) and pulse pressure variations (PPV%) provide an idea of ​​the physiological response to fluid treatment or pharmacological intervention. Stroke volume variations are calculated from the volume of the arterial pressure curve (area) while pulse pressure variations are calculated from amplitude changes in the arterial pressure curve. SVR (Systemic Vascular Resistance) primarily provides information on changes in afterload. In lithium calibration, lithium is injected for external calibration of pulse contour analysis. Lithium is injected into a peripheral or central vein.

A graphical lithium analysis is made of the patient’s arterial blood that is withdrawn in a certain amount from an existing arterial catheter. This analysis calculates the rinsing curve of lithium over time. The curve is similar to a thermal dilution curve used with PA catheter and determines the cardiac output. Lithium dilution technology has good correlation with the thermodilution technology.

LiDCO provides continuous monitoring of central hemodynamics with minimal invasive equipment. LiDCO is validated against Swan-Ganz catheter-measured measurements of central hemodynamics. The LiDCO rapid monitor can also show continuous non-invasive blood pressure (“non invasive CNAP”) and measurement of consciousness with BIS. LiDCO rapid is connected via an electronic cable to the monitor or device that detects arterial blood pressure. Each patient registration requires login with a SmartCard in the LiDCO rapid monitor, which is patient-specific and fee-based.

The LiDCO monitor shows arterial blood pressure (SBP, DBP, MAP), heart rate, CO/CI, SV/SVI, SVV% and PPV% and, if necessary, BIS and BIS trends. The stroke volume is displayed as nSV in ml and intermittently recorded values, for example every two minutes. Changes in volume compensation are recorded as percentage change in the SV Event Response, which gives a perception of volume status and can be used to control fluid treatment against optimal oxygen delivery. A common procedure is to give a liquid solution of 250 ml of saline in less than 5 minutes and evaluate changes in impact volume. Positive response is interpreted as more than 10% increase in SV (fluid responsive). If positive response, renewed bolus is given about 250 ml of saline until the volume increase is saturated. If the stroke volume does not increase by more than 10%, the patient is “fluid non responsive” and is higher on the Starling curve with a higher pre-load. The stroke volume is checked every 15 minutes. The goal is to keep SaO2> 94%, Hb 80-100 g/L, Temp 37o and MAP around 60-100 mmHg.

LiDCO uses an algorithm to calculate cardiac output. In this algorithm, the pulse is multiplied by a value from the standard deviation of changes in the arterial pressure curve measured in mmHg. This standard deviation has been approximated as the stroke volume multiplied by the heart rate gives the cardiac output. This measure is also multiplied by a factor that compensates for changes in vascular tone measured in the arterial pressure curve.

Lithium calibration does not work for lithium treated patients. Lithium calibration should not be used on pregnant women in the first trimester. Certain muscle relaxants, vecuronium, pancuronium, atracurium may affect the measurement.

* PCV = packed cell volume. A = area below the lithium dilution curve.


Cardio-Q (Deltex Medical)

Cardio-Q measures central hemodynamics continuously by an esophageal doppler technology (tranesophageal Doppler) that measures blood flow rate in the aorta using an ultrasound probe inserted into the esophagus. The probe has a doppler transducer at the end directed towards the descending part of the thoracic aorta. The probe uses a 4 MHz wave for continuous doppler analysis or 5 MHz for a pulse wave analysis and utilizes the relationship to the cardiac output Q = v x A (v = Df x s / 2 x f x cosθ).

In the M mode, the ultrasound wave passes through the aorta while in Doppler mode it measures the size of aorta. By measuring the flow and area, the cardiac output can be calculated. The probe usually requires a sedated and mechanically ventilated patient lying still where the probe is brought into the esophagus through the mouth in the same way as a nasogastric tube. Optimal location is level with Th5-Th6. The probe must then be twisted so that an optimal signal from the aorta can be captured, so the probe can be relatively sensitive to rotations, slides and twists. The person who sets the probe must adjust the depth, position and rotation. The cardiac output is calculated from the aortic diameter, the distribution of cardiac output to the aorta and the measured blood flow signal. A suboptimal position tends to underestimate cardiac output. Cardio-Q has been able to achieve good correlation with PA catheters for cardiac output measurements, up to 86% correlation, in several studies. In particular, this technique has been able to function well when changes in hemodynamics occurs peroperatively and the probe was standing still. The advantage of the technology is that it is non-invasive and easy to apply. Changes in peroperative hemodynamics have higher reliability than absolute values ​​of central hemodynamics. A source of error is that the flow in the descending aorta only represents about 70% of cardiac output. Measurement errors can occur from measured area, average velocity and the angle to the aorta. Another drawback is that diathermy interferes with the measurement and that the probe may need to be adjusted during the current procedure. Cardio-Q provides the ability to control fluid balance and optimize circulation in critically ill or hemodynamically unstable patients, often referred to as targeted fluid treatment.

Cardio-Q measures cardiac output (CO), cardiac index (CI), stroke volume (SV), corrected flow rate (FTc), stroke volume spacing (SD), heart rate (HR), and peak aorta (PV) velocity.

Table 1 Hemodynamic parameters measured with Cardio-Q. Indexed values are calculated per m2 body area (BSA).
AbbreviationParameterReference ValuesUnit/Notice
COCardiac Output4,0-8,0 l/minSV x HR/1000. A measure of flow.
CI Cardiac Index3,0-5,0 l/min/m2SV x HR/m2. A measure of flow. CI=CO/BSA
SDStroke Distance4-7 cm (?)The distance each stroke volume is ejected into each heartbeat in aorta.
SVStroke Volume60-100 ml/beatThe volume of blood that is ejected into each heartbeat into aorta.
SVIStroke Volume Index33-47 ml/beat/m2The volume of blood that is ejected into each heartbeat into aorta./BSA.
FTcFlow Time Corrected330-360 msThe time of the flow during systole corrected for heart rate. A low value for hypovolemia. High value in vascular dilation.
PVPeak Velocity90-120 cm/s for a 20-year old. 70-100 cm/s for a 50-year old. 50-80 cm/s for a 70-year old.A measure of cardiac contractility.

 
HRHeart Rate60-90 beats/min Pulse rate, beats per minute.

HemoSphere Advanced Monitor

Edwards Life Sciences offers systems that can monitor central hemodynamics both through the arterial pressure curve (formerly: Vigileo) and via Swan-Ganz PA catheter as via Edward’s oximetric CVC. A new monitoring unit called HemoSphere Advanced Monitor provides a good visual overview of central hemodynamics with a clear color display that can show continuous measurement of central hemodynamics with, inter alia, SvO2, SV, CO and CI (see chapter on PA catheter). With connection to a Swan-Ganz PA catheter, you get a complete overview of central hemodynamics. Edward’s oximetric CVK allows for continuous measurement of mixed venous oxygen saturation (SvO2).

HemoSphere Advanced Monitor measures central hemodynamics via the arterial pressure curve and provides the ability to control fluid balance and to optimize circulation in critically ill or hemodynamically unstable patients. One can achieve goal-directed fluid treatment. With Vigileo you can choose whether you want to connect the device to the arterial pressure curve and view the cardiac output (CCO), stroke volume (SV) and stroke volume variations (SVV) or if you want to add a central venous catheter (FloTrac) and also get vascular resistance (SVR). Stroke volume variation (SVV – stroke volume variation) provides information about changes in preload (% SVV = SVmax-SVmin/SVmean). SVR provides information about changes in afterload.

HemoSphere Advanced Monitor provides continuous monitoring of central hemodynamics with minimal invasive equipment. The catheter-borne equipment used is called the FloTrac sensor and PreSep (or PediaSat) oximetry catheters that provide hemodynamic information on a single monitor. Together with the FloTrac sensor, continuous information on central hemodynamics with automatic cardiac output (CCO) calculations, stroke volume (SV), stroke volume variations (SVV) and system vascular resistance (SVR) is provided. SVR calculations require CVP from a central venous catheter. With PreSep or PediaSat oximetrics, you also receive continuous information about central venous oxygen saturation (ScvO2). These catheters are positioned in the same way as a central venous catheter. The FloTrac sensor uses the arterial pressure curve from an existing peripheral arterial catheter, usually from the radial artery. The sensor automatically performs self-calibration, taking into account vascular tone (compliance and resistance) and calculates current parameters every 20 seconds. Vigileo is validated against Swan-Ganz catheter-measured measurements of central hemodynamics.

HemoSphere Advanced Monitor monitor displays CO/CI, SV/SVI, SVV and SVR/SVRI.

The FloTrac sensor uses an algorithm to calculate the cardiac output. In this algorithm, the pulse is multiplied by a value from the standard deviation of changes of the arterial pressure curve measured in mm Hg. This standard deviation has been approximated as the stroke volume multiplied by the heart rate results in the cardiac output. This measure is also multiplied by a factor that compensates for changes in vascular tone measured in the arterial pressure curve.