Haemodialysis (CRRT)

Dialysis – General Principles

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


Dialysis treatment is given in case of acute or chronic renal failure with uremia. There are many ways to measure renal function, usually the determination of S-Creatinine, Urea and Formula Calculation of GFR (eGFR). For more accurate determination, iohexolclearance or chromium EDTA clearance is usually used. For estimation of renal impairment, formula clearance is quite reliable. Renal function significantly decreases with age while P-Creatinine rises less.

There are several types of dialysis used in special dialysis departments or in an intensive care unit. The most common forms are hemodialysis (HD), continuous venous venous dialysis (CVVHF), plasmapheresis, peritoneal dialysis (PD) or molecular reabsorbent recirculation system (MARS) treatment. The most common form of dialysis in an intensive care unit today is venovenous continuous dialysis made by a single dialysis catheter, usually a variant of CVC with two or three lumen called central dialysis catheters (CDK). Peritoneal dialysis is rarely or never given to an intensive care unit and MARS treatment is given at regional centers for the treatment of acute fulminant hepatic failure, usually as a bridge for liver transplantation.

Dialysis works by perfusion of the blood through a filter whereby the blood is purified by osmosis and filtration of molecules such as urea and potassium. Dialysis uses two main principles for the purification of blood, diffusion and convection. With diffusion, the concentration gradient is used over a semipermeable membrane so that molecules are transported over the filter, much like tea diffusing out of a tea bag in hot water. Diffusion is effective to eliminate small molecules without volume loss. Clearance expresses the secreted amount of a substance through the kidneys due to urine concentration and urinary volume. Renal clearance expresses the association between the excretion of one substance per unit of time and its concentration in plasma, Cx = Ux x V/Px ml/min. With clearance, you can compare the ability of the kidney or dialysis machine to secrete different substances. Clearance depends on the blood flow through the filter and the amount of dialysis fluid per minute. The diffusion principle is used in hemodialysis, CVVHD and CVVHDF.

Convection cleans the blood through a pressure gradient that causes molecules to squeeze through a membrane along with fluid much like when brewing coffee. With convection, larger molecules can also be filtered depending on the size of the membrane and the size of the pores, compared to a large or small coffee filter. Since the number of pores for large molecules is less than for smaller molecules, the filtration rate is measured faster for larger particles than for small ones. Convection also causes a loss of fluid which can be replaced in the dialysis with replacement solutions, whereby the fluid balance can be controlled. Clearance varies with the volume of liquid removal per unit time and the volume of the replacement fluid. The principle of convection is used in the dialysis forms SCUF, CVVH and CVVHDF. The general indications for treatment with dialysis are urea urea > 40 mmol/l (relative indication at urea 30-40 mmol/l), therapy-resistant hypercalcaemia, pulmonary oedema with FiO2 >0.8 and concomitant fluid overload and resistance to diuretics. In acute life-threatening pulmonary oedema with chronic or acute renal failure, SCUF is the method that can best improve the condition as well as treatment with PEEP in ventilator or CPAP. Usually, treatment with CVVH, CVVHD and CVVHDF is controlled by an intensivist or anesthesiologist while treatment with plasma fever, MARS, hemodialysis or PD is controlled by a renal medication. It is therefore necessary for an anaesthesiologist to be well acquainted with the continuous dialysis form provided via CDK.

At the start of CRRT with continuous dialysis on IVA, basic settings are usually prescribed in the dialysis machine. These settings vary with the type of dialysis machine but usually a first-rate dose and a liquid distribution are usually prescribed. The effluent dose usually starts at 30 ml/kg/h, which is the same as the effluent dose. The effluent dose is the sum of dialysate, replacement fluid pre- and post filters and liquid removal. In sepsis, grave liver failure, burn or other catabolic condition, one may consider starting higher with a total effluent of 35-40-60 ml/kg/h.

The distribution between replacement fluid and dialysis fluid depends on the size of the particles that you want to eliminate in the first place. Elimination of large particles requires more replacement fluid while smaller molecules require more dialysate fluid. The settings also depend on which dialysis machine is being used. Prismaflex requires at least 500 ml post filter. With increased amount of fluid after filter, you get more efficient dialysis but greater risk of filter arrest. Predilution reduces the risk of filter arrest but gives a greater dilution effect of the blood to be dialyzed. The effect of dialysis is monitored by daily measurement of urea and creatinine as well as weighting of the patient and calculation of fluid balance.

Blood flow in the CRRT dialysis machine usually varies between 100 and 250 ml/min, now it is more common to lie between 200-250 ml/min. The advantage of high blood flow is that the amount of diluted blood increases per unit of time, which makes dialysis more efficient, preventing blood from reaching the same concentration as the dialysate at the end of the filter. With increased blood flow, this tendency is counteracted and the effect of dialysis increases. High blood flow also reduces the risk of stopping the filter. With SCUF, CVVH and CVVHDF without predilution, hemoconcentration may develop that may reduce function of the filter. The filtration fraction (FF) is defined as the amount of liquid removed in relation to the amount of blood passing the filter. In dialysis treatment, anticoagulation is co-administered if the patient is not already easily bleeding, usually heparin is used. Anticoagulation is given in order to not coagulate the blood when it is in contact with synthetic catheters and dialysis filters. Coagulation activation is also reduced by diluting blood through predilution. Usually, heparin in low concentration is first given as a bolus dose, then in a continuous infusion. In bolus, 10 IU/kg is usually followed by 10 IU/kg/hr. If the dialysis filter is already coagulating within 24 hours, the dose of heparin can be increased to 15 IU/kg in bolus followed by 15 IU/kg/hr. The effect is checked against PK-INR and APTT.

Common Settings for Treatment with CVVHDF
 Usual SettingsPossible SettingsTreatment in Sepsis
Blood Flow250 ml/min10-450 ml/min250 ml/min or more
Effluent Dose30 ml/kg/hour0-8000 ml/hour35 ml/kg/hour or more
Substitution Fluid10 ml/kg/hour, always > 0,5 l after the filter50-8000 ml/hour20 ml/kg/hour, always > 0,5 l after the filter
Dialysate Fluid20 ml/kg/hour50-4000 ml/hour10 ml/kg/hour
Removal of Fluid0-2000 ml/hour0-2000 ml/hourCustomized by status
Bolus dose of Heparin0-10 IE/kg0-10 IE/kg0-10-20 IE/kg
Continous infusion of Heparin0-5-10-20 IE/kg/hour0-5-10-20 IE/kg/hour0-5-10-20 IE/kg/hour
Example of Normal Settings in CVVHDF
Blood Flow250 ml/min
Effluent Dose2100 ml/hour
Substitution Fluid700 ml of which 500 ml post filter
Dialysate Fluid1400 ml
Removal of Fluid125 ml/hour
Bolus Dose of Heparin700 IE
Continous Infusion of Heparin350-700 IE/hour
Reference values for GFR
20-50 years80-125 ml/min/1,73 m2
51-65 years60-110 ml/min/1,73 m2
66-80 years50-90 ml/min/1,73 m2
Different stages of CDK - Chronic Kidney Disease
CKD 1GFR > 90 ml/minNormal renal function
CKD 2GFR 60-90 ml/minImpaired renal function reserve. Asymptomatic
CKD 3GFR 30-60 ml/minAsymptomatic renal failure. Phosphate retention Reduced synthesis of 1.25 Vit-D3. Reduced synthesis of erythropoietin.
CKD 4GFR 15-30Symptomatic renal failure. Clinical symptoms, electrolyte disturbances, calcium phosphate disorders, anemia, metabolic acidosis, uremic symptoms.
CKD 5Advanced terminal renal failurePronounced uremic symptoms. Fluid retention.

Continuous Renal Replacement Therapy – CRRT

Posted by Johan Mårtensson and Claes-Roland Martling, Karolinska University Hospital. Stockholm.
Updated 2018-12-21


The goal of all renal replacement therapy is to remove one due to kidney disease caused excesses of slag products and water from the body. How effective a substance is removed is usually stated as clearance (K) of the substance in question. Impaired renal function manifests itself in a decrease in glomerulus filtration (GFR). The volume of urine depends in part on glomerulus filtration, but also on the ability to recycle water. If the GFR is zero then the urine volume will also be zero, ie. anuri exists. Of a normal GFR of about 150 ml/min (9 liters/hour), 99% and only 1% (about 90 m/h) are recovered as urine. GFR can thus be significantly reduced without urinary output being affected if more than 1% of GFR is excreted as urine.

GFR (the formation of primary urine) can not be measured but instead must be calculated based on the ability of the kidney to secrete a model substance, i.e. clearance (K) of the model substance in question. In order to provide a correct measure of GFR, such a model substance must be filtered freely with water and must not be recycled or excreted via tubules.

K is defined in this context as the volume of plasma water which is completely purified from a substance for a certain period of time and is usually expressed in ml/min. K can be calculated for any substance but it is only if it is freely filtered and not recycled or excreted via tubules that K represents GFR. Creatinine is the body-specific substance most commonly used to estimate GFR.

Two healthy kidneys produce a GFR of about 150 ml/min, which is comparable to the continuous renal replacement therapy (CRRT), which at best is only a third as effective.

CRRT can remove water-soluble substances via two different principles (Figure 1):

  • Convection (haemophiltration) – then water (via ultrafiltration) and dissolved substances are transported across the dialysis filter from the bloodstream. This accomplishes the CRRT machine by creating a pressure gradient (transmembrane pressure) across the filter. Clearance (K) is determined by the amount of ultrafiltration flow across the membrane achieved.
  • Diffusion (hemodialysis) – substances (but no water) diffuse passively over the dialysis filter from the bloodstream (high concentration of substance) to the dialysis fluid (low concentration of substance). Clearance is then determined by the rate of dialysis fluid.

Figure 1. CRRT principles for filtration and dialysis. PB hydrostatic pressure on the blood side. PUF hydrostatic pressure on the ultrafiltrate side. PD hydrostatic pressure on the dialysis side

CRRT circuit

Modern CRRT machines have, in addition to the blood pump, pumping the dialysis fluid, the replacement fluid (before and after the filter) and the ultrafiltrate. The flow in the blood pump, in the pump for the replacement fluid before the filter (predilution pump), in the replacement fluid after the filter (post-dilution pump) and the dialysis fluid pump can be controlled separately within fairly wide ranges. However, the flow of the effluent pump (which exits the ultrafiltrate) can not be manually adjusted but calculated by the machine so that a proper pressure difference (TMP) occurs over the filter membrane. The flow in the effluent pump is the sum of the flow in the predilution pump, the post dilution pump and the liquid removal desired every hour. All pumps are integrated and connected to alarm functions. If an alarm is triggered in a pump, all pumps (except the blood pump) will stop at the same time. This reduces the risk of problems occurring throughout the circuit.

By controlling the different pumps, the continuous renal replacement therapy can be given in the form of ultrafiltration (CVVH), dialysis (CVVHD) or a combination of both (CVVHDF). Below is a description of the CRRT circuit in the various modalities.

SCUF – Slow Continuous Ultrafiltration

In the simplest form of CRRT, the active flow circuit consists only of the blood pump and the drain pump (Figure 2). The blood is pumped from the patient using the blood pump into the filter. This causes a positive hydrostatic pressure on the blood side of the filter which slightly exceeds the pressure on the ultrafiltrate side. This differential pressure across the membrane is called transmembrane pressure (TMP). TMP causes a small amount of plasma water (the so-called ultrafiltrate) to be “pushed” from the blood side to the ultrafiltrate side. Using a further pump (effluent pump) actively “sucking” the ultrafiltrate from the filter produces a negative hydrostatic pressure on the ultrafiltrate side. Thus, the pressure difference (TMP) across the membrane increases significantly and the convective ultrafiltration increases. By reducing or increasing TMP, the amount of ultrafiltrate can be precisely regulated.

The set flow in the effluent pump thus corresponds to the volume of plasma water removed from the patient’s bloodstream per unit of time. This CRRT modality is commonly called SCUF (slow continuous ultrafiltration).

Figure 2. SCUF – Slow Continuous Ultrafiltration

The goal of SCUF treatment is only to remove the patient’s excess water. Remember that in the plasma water transported across the membrane there are also dissolved molecules, e.g. creatinine and urea. The creatinine or urea clearance that the machine achieves at this modality is thus completely determined by the flow in the effluent pump, i.e. fluid removal.

Thus, if the flow in the effluent pump is 200 ml/h, the convective ultrafiltration flow across the membrane will be 200 ml/h. Clearance (K) of the molecules that pass freely across the membrane (eg creatinine and urea) and thus dissolved in the ultrafiltrate will then be: K = Ultrafiltrate Flow = 200 ml/h, which can be rewritten as 3.3 ml/min. With this modality we can thus effectively remove the water surplus. However, SCUF is not an effective renal replacement therapy.

K (SCUF) = Ultrafiltrate flow

Can not we increase the fluid removal to increase the clearance of different molecules? Yes, the CRRT machine can handle this but the patient’s circulation is restrictive. An excessive fluid removal would either dehydrate the patient or require large volumes of fluid to be given intravenously.

How, then, can you remove an adequate amount of water while achieving a high clearance? Yes, by adding a pre-dilution fluid or after the post-dilution filter, we can increase the ultrafiltration flow across the membrane without the patient wiping out.

CVVH – Continuous Veno Venous Hemofiltration

For CVVH with post dilution, all replacement fluid is given after the filter. The post-dilution flow is driven by a separate pump (Figure 3).

Figure 3. CVVH with post-dilution

The purpose of the replacement fluid is thus to maintain an adequate fluid balance while a large volume of ultrafiltrate can be removed from the patient. If you do not want the patient to be drawn on liquid, then the ultrafiltrate flow rate (velocity of the drain pump) and replacement flow (the speed of the post dilution pump) should be the same. Instead, if you want a negative fluid balance, the ultrafiltrate flow must be greater than the replacement flow.

Ultrafiltrate flow = Replacement flow + Liquid removal

If we set the post dilution pump on eg. 3800 ml/h and at the same time setting a liquid removal of 200 ml liquid/h, the machine will automatically calculate the velocity of the effluent pump to 3800 ml/h + 200 ml/h = 4000 ml/h. What will then be the clearance (K) for e.g. creatinine and urea in this example?

Creatinine and urea are small molecules that pass freely across the membrane together with the water. K for these molecules therefore becomes the same as the ultrafiltrate flow, i.e. 4000 ml/h. This can be written as 67 ml/min.

K (CVVHpost dilution) = Ultrafiltrate flow = Replacement flow + Liquid absorbed

However, this type of treatment has its limitations. The high flow of plasma water across the membrane from the blood side to the ultrafiltrate side will significantly increase the blood side hematocrit (Hct) with the risk of the coagulation of the filter. Figure 4 illustrates how Hct is affected on the blood side of the filter at CVVH by post dilution and a 4 l/h ultrafiltrate flow if the blood flow is set at 200 ml/min (= 12000 ml/h) and the patient’s Hct = 0.3. Hct rises to 0.45 at the end of the filter and returns to 0.31 after the filter (where the replacement liquid is given).

Figure 4. Hematocrit in the filter at CVVH with post dilution.

One way to assess the risk that the filter should coagulate at CVVH with post dilution is to calculate the so-called filtration fraction (FF). FF indicates the proportion of plasma water removed from the blood upon hemophiltration and can easily be calculated according to: FF = ultrafiltrate flow/blood flow. Optimal FF in a patient with Hct = 0.3 is below 20-25%. At an FF above 30%, the risk of the coagulation of the filter increases significantly. Note that the calculation of FF does not take into account the patient’s Hct. It is therefore not certain that a high FF leads to coagulation in the filter if the patient’s Hct is very low when the blood reaches the filter. Conversely, a low FF can lead to coagulation in the filter if the patient’s Hct is high. However, the most common is that Hct’s intensive care patients are between 0.3 and 0.4. In this range, FF gives a sufficiently good idea of ​​the risk of coagulation.

FF = Ultrafiltrate Flow/Blood Flow

One way to get past the problem of high FF is to provide the replacement fluid before the filter – predilution.

CVVH with predilution

In CVVH with pre-dilution, all replacement fluid is given before the filter. Predilution flow is driven by a separate pump (Figure 5).

Figure 5. CVVH with predilution

The blood entering the filter will be diluted by the replacement fluid. Thus, the blood entering the filter will have a lower hematocrit compared to the patient’s true hematocrit.

Figure 6 illustrates how hematocrit is affected on the blood side of the filter at CVVH with predilution and an ultrafiltration flow of 4 l/h if the blood flow is set to 200 ml/min (= 12000 ml/h) and the patient’s Hct = 0.3. Hct increases as much in the filter as at CVVH with post dilution but because Hct is lower when the blood enters the filter, Hct will only reach up to 0.31 at the end of the filter.

Figure 6. Hematocrit in the CVVH filter with predilution

CVVH with predilution also has its limitations. The slag products that are present in the blood and which we want to remove using our renal replacement therapy will be diluted by the replacement fluid. The composition of the ultrafiltrate at CVVH with post dilution consists of the patient’s plasma water and dissolved molecules. In CVVH with predilution, the ultrafiltrate of the patient’s plasma water is mixed with replacement fluid and dissolved molecules. Since the dissolved molecules (e.g., slag products) then have a lower concentration, the clearance (K) of different slag products will be smaller with this modality compared with whether the replacement liquid is given after the filter.

Therefore, in order to calculate clearance at CVVH with predilution, one must take into account how much the blood has been diluted by the replacement fluid. This is most easily done by calculating the so-called dilution factor.

Dilution factor = Blood flow / (Blood flow + replacement flow before filter)

In the example illustrated in Figure 6 Hematocrit in the CVVH with predilution) dilution factor = 12000/(12000 + 3800) = 0.76. Clearance (K) then becomes the ultrafiltrate flow x dilution factor, ie. 4000 ml/h x 0.76 ≈ 3000 ml/h.

K (CVVHpredilution) = Ultrafiltrate Flow x Dilution Factor = (Replacement Flow + Liquid Removal) x Dilution Factor

Compare Figure 4 and Figure 6. Although the same flows have been used in both examples, clearance 1000 ml/h will be lower only by giving all replacement fluid before the filter instead of after the filter.

CVVHD – Continuous Veno Venous Hemodialysis

Vid ren CVVHD avlägsnas molekyler från blodsidan genom diffusion, dvs. molekyler men (i princip) inget vatten passerar över filtret från blodsidan till dialysatsidan. Dialysatvätskan drivs av en separat dialysatpump och det är dialysatvätskans flödeshastighet som avgör clearance (K), dvs hur effektivt blodsidan renas från olika molekyler. Det är förstås möjligt att avlägsna vatten (genom ultrafiltration) även vid denna modalitet men då måste avflödespumpen hålla en högre hastighet än dialysatpumpen. Detta görs genom att det önskade vätskeborttaget ställs in i maskinen (Figur 7).

Figur 7. CVVHD

  • K(CVVHD) = Dialysatflödet

CVVHDF – Continuous Veno Venous Hemodiafiltration

Vid CVVHDF kombineras dialys och filtration (Figur 8). Totalt clearance (K) beräknas enklast genom att först beräkna K för de enskilda modaliteterna och sedan addera dessa.

Figur 8. CVVHDF

Let’s illustrate this with three examples. In the first example (1) we calculate K at combined CVVHD and CVVH with mail dilution. In the second example (2) we calculate K at combined CVVHD and CVVH with predilution. Finally (3) we calculate K at combined CVVHD and CVVH with both pre and post dilution.

In all examples, we assume a blood flow of 200 ml/min (= 12000 ml/h) and a liquid removal of 100 ml/h.

(1) CVVHDF with dialysate flow = 1000 ml / h and a post dilution flow = 1000 ml/h.

K (CVVHD) = Dialysis flow = 1000 ml / h
K (CVVHpost dilution) = Ultrafiltrate flow = Replacement flow + Liquid removal = 1000 + 100 = 1100 ml/h

Now, we simply sum up the contribution from the different modalities:
K (CVVHDF) = K (CVVHD) + K (CVVHpost dilution) = 1000 + 1100 = 2100 ml/h, which is the same as 35 ml/min

(2) CVVHDF with dialysate flow = 1000 ml/h and a predilution flow = 1000 ml/h.

K (CVVHD) = Dialysis flow = 1000 ml/h

K (CVVHpredilution) = Ultrafiltrate Flow = Replacement Flow + Liquid Removal = 1000 + 100 = 1100 ml/h

We summarize the contribution from the different modalities and get:

K (CVVHDF) = K (CVVHD) + K (CVVHpredilution) + K (Liquid Removal) = 1000 + 1000 + 100 = 2100 ml/h

In this example, we need to take into account the dilution factor. Because the replacement fluid is given before the filter, all substances contained in the blood (including those we want to remove) will be diluted. This will reduce the K that is achieved both from the dialysis and the filtration.

Dilution factor = Blood flow/(Blood flow + Replacement flow before filter) = 12000/(12000 + 1000) = 0.92

The dilution factor tells us that, by giving the replacement fluid before the filter, we will only achieve 92% of the K that we would otherwise achieve if all replacement liquid was given after the filter.

K (CVVHDF) = 2100 x 0.92 = 1932 ml/h or 32 ml/min

(3) CVVHDF with dialysate flow = 1000 ml/h, predilution flow = 1000 ml/h and post dilution flow = 1000 ml/h
K (CVVHD) = Dialysis flow = 1000 ml/h
K (CVVHpredilution) = Ultrafiltrate Flow = Replacement Flow Before Filter = 1000 ml/h
K (CVVHpost dilution) = Ultrafiltrate flow = Replacement flow after filter + Liquid removal = 1000 + 100 = 1100 ml/h

Note that the liquid removal should be counted only once. In this example, we have chosen to add it to the replacement flow after the filter, but it would have been possible to add it to the replacement flow before the filter – the result will be the same. Now let’s add the contribution from the different modalities:

K (CVVHDF) = K (CVVHD) + K (CVVHpredilution) + K (CVVHpost dilution) = 1000 + 1000 + 1100 = 3100 ml/h

Here too we have to take into account the dilution factor. It is still only the replacement fluid that is given before the filter (predilution) that can dilute the blood, so the dilution factor will be the same as in example (2), namely 0.92.

K (CVVHDF) = 3100 x 0.92 = 2852 ml/h or 48 ml/min

  • K (CVVHDF) = (K (CVVHD) + K (CVVHpredilution) + K (CVVHpost dilution)) x dilution factor

Hemodialysis (HD)

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


Hemodialysis provides a purification of the blood through osmosis and the extraction of molecules (urea, potassium) and liquid over a semipermeable membrane extracorporeally (outside the body as opposed to PD).

Indications

  • Acute or chronic renal failure with uremia.
  • Fluid overload. Over transfusion.
  • Certain poisonings such as methanol, ethylene glycol, lithium and some other poisons (methformin).

Procedure

Hemodialysis is usually done by filtration of the blood through a dialysis filter with a surface area of ​​2 m2 extracorporeal where the blood is withdrawn from the body, purified and given back. The blood is withdrawn through coarse vascular catheters, fistula or shunt. A common blood flow (Qb) in the dialysis filter is around 150 ml/min and a normal dialysis flow (Qd) around 500 ml/min. Normal fluid removal is 2-4 liters per dialysis treatment depending on the patient’s hemodynamics, uremic status and current fluid balance status. The treatment is conducted via cannulation of a surgical AV fistula on the upper or lower arm. An AV fistula takes 4-8 weeks to mature. Graft is used if thin, fragile vessels are present in the patient (increased risk of thrombosis and infection). Central dialysis catheters (CDK) with double lumen can be used acute if vascular access is lacking alternatively via two vascular catheters, an arterial catheter and a venous catheter, usually in a femoral artery and in a femoral vein or with two venous catheters. Treatment is given intermittently 3-4 days a week, for 2-4 hours per treatment. Careful weight control and control of urea and potassium is important. Usually anticoagulation therapy is given during the treatment.

Ultrafiltration

(UF) is another possibility. UF removes fluids effectively from the bloodstream. UF provides fastest effect in the treatment of pulmonary edema.

Complications related to a hemodialysis are possible drops in blood pressure, cramps, nausea, vomiting, access problems, amyloidosis, bleeding complications.


MARS

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


This is a dialysis form that removes whole blood and returns all blood components except plasma. MARS does not remove any fluid normally. The procedure is replacing the plasma with albumin solution. It filters the blood through a carbon filter and an ion exchanger. Antibodies, immune complexes and pathological proteins are removed. MARS may be used in acute liver failure with encephalopathy and acute paracetamol poisoning with hepatic failure. Central dialysis catheters (CDK) with double lumen can be used acutely if vascular access is lacking, alternatively, an arterial catheter, usually placed in the femoral artery together with a catheter in the femoral vein. The treatment is performed in 2-3 consecutive days, during 4-8 hours each time with careful control of uremic and liver function tests. There is a risk of bleeding complications. The MARS procedure is very resource-demanding, usually carried out in an intensive care department.


Peritoneal Dialysis (PD)

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


The dialysis procedure is usually performed via a Tenchoff catheter through the abdominal wall (PD catheter). It provides an osmosis and removal of slag products and fluid across the peritoneum. The peritoneum acts as dialysis filter. PD is frequently used in the treatment of chronic renal failure, but usually not more than 4 years of treatment. It is good in heart failure (even blood volume) and for diabetics (continuous insulin delivery). An inflammatory bowel disease is a contraindication. PD can be carried out at home or at day care centers. Peritonitis and amyloidosis (b2-μglobulin) are known complications. The treatment is usually performed intermittently 3-4 days a week, at 2-4 hours each time. Normal fluid removal is 2-4 liters depending on whether the patient is hemodynamically stable with a balanced fluid status. A careful weight control and control of uremia and potassium problems are important. Complications of peritoneal dialysis are primarily infectious problems, peritonitis with or without general impact.


Plasmapheresis

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


This procedure removes venous whole blood and returns everything except plasma. It does not remove any fluid normally. Plasmapheresis replaces the patient’s plasma with donor plasma or albumin solution, usually albumin solution. Antibodies, immune complexes and pathological proteins are removed. PP is used in TTP/HUS, SLE, Wegener’s syndrome, Goodpasture’s syndrome, Guillain-Barré syndrome, Myastenia gravis. Central dialysis catheters (CDC) with a double lumen can be used acutely if vascular access is lacking, alternatively, an arterial catheter, usually in the femoral artery tohether with a catheter in the femoral vein. The treatment is performed intermittently 3 days a week, for 2-4 hours per time. Careful weight control and control of uremia and potassium problems are important.


Continuous Veno-Venous Dialysis (CVVHF)

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


Continuous venovenous hemofiltration, CVVHD or CVVHD-F, often called Prismadialysis. Prismadialysis provides continuous ultrafiltration of the blood with or without concomittant dialysis. The method removes slag products and fluid from the bloodstream. Water molecules are pressed through a semi-permeable membrane by a hydrostatic force with lower pressure on the dialysis side.

Indications

Acute or chronic renal failure with uremia. Hyperhydration (fluid overload) at sepsis and other major surgery. Poisoning with lithium and some other poisons.

Complications

Blood pressure drops, hypovolemia, muscle cramps, nausea, bleeding, vomiting, headache, infection, hypersensitivity, hypoxemia, amyloidosis.

Technique

Central dialysis catheters (CDC) with double lumens are usually inserted as a CVC in a central vein, usually in the right jugular internal vein or the subclavian vein. It is important with a X-ray check of the catheter position before usage. The treatment is given continuously around the clock for 2-3 weeks. Normal fluid removal is 0.5-2 liter per day depending on the patient’s fluid balance status. Normal blood flow is 150-250 ml/min and the dialysis flow is 500-1500 ml/h. Careful weight control, control of uremia and potassium problems is important. Ultrafiltration is possible with Prismadialysis. Removal of only fluid by Ultrafiltration has the fastest effect on pulmonary edema.

Recommended Prismaflex Dialysis Settings:
Blood flow is usually set at:250-300 ml.
Dialysate flow:500-1500 ml/h.
Actual fluid removal:100-300 ml/h.
Outlet Pressure:-50-75 mm Hg.
Reflux Pressure:50-100 mm Hg.
Anticoagulation: Heparin is given in a continuous infusion 500 units/ml 0,5-2 ml/h (1 ml/h).
Recommended Flow Settings for Continuous Venovenous Dialysis
Weight50 kg60 kg70 kg80 kg90 kg100 kg
Pre Blood Pump ml/hour375 ml/hour550 ml/hour725 ml/hour900 ml/hour1075 ml/hour1250 ml/hour
Substitution Fluid ml/hour500 ml/hour500 ml/hour500 ml/hour500 ml/hour500 ml/hour500 ml/hour
Dialysate Fluid Flow ml/hour625 ml/hour625 ml/hour875 ml/hour1000 ml/hour1125 ml/hour1250 ml/hour
Blood Flow250 ml/hour250 ml/hour250 ml/hour250 ml/hour250 ml/hour250 ml/hour