Year : 1994 | Volume
: 5 | Issue : 3 | Page : 379--383
Continuous arteriovenous and continuous venovenous haemodialysis
Faissal A.M Shaheen1, Iftikhar Ahmed Sheikh1, Mohammad Ziad Souqiyyeh2,
1 Jeddah Kidney Center, King Fahd Hospital, Jeddah, Saudi Arabia
2 Saudi Center for Organ Transplantation, Riyadh, Saudi Arabia
Faissal A.M Shaheen
Director, Jeddah Kidney Center, King Fahd Hospital, Jeddah
|How to cite this article:|
Shaheen FA, Sheikh IA, Souqiyyeh MZ. Continuous arteriovenous and continuous venovenous haemodialysis.Saudi J Kidney Dis Transpl 1994;5:379-383
|How to cite this URL:|
Shaheen FA, Sheikh IA, Souqiyyeh MZ. Continuous arteriovenous and continuous venovenous haemodialysis. Saudi J Kidney Dis Transpl [serial online] 1994 [cited 2020 Apr 6 ];5:379-383
Available from: http://www.sjkdt.org/text.asp?1994/5/3/379/41144
Extracorporeal dialysis therapy that can be used for an extended period of time offers specific clinical advantages in the management of the critically ill patients suffering from acute renal failure, fluid overload, electrolyte, and acid-base disturbances. The techniques most commonly used are continuous arteriovenous hemofiltration (CAVH) and continuous venovenous hemofiltration (CVVH). These techniques remove solutes and water over an extended period of time. Several investigators have tried to improve solute clearance in CAVH and CVVH  . These improvements include modifications of the above techniques called continuous arteriovenous haemodialysis (CAVHD) and continuous venovenous haemodialysis (CVVHD)  . In CAVHD and CVVHD, the same setting of CAVH or CVVH is used, but the need to replace a large volume of solution is obviated by running suitable fluid in the dialysate compartment of the filter. CVVHD offers the additional advantage of avoiding arterial puncture. All these techniques have advantages over standard dialysis procedures, especially in the hemodynamically unstable patients. Many investigators have performed this technique using various high-flux dialyzers with good outcome ,, .
CAVH has been covered in this Journal before . In this paper we will highlight the important points regarding indications, contraindications, clinical and practical applications of CAVHD and CVVHD.
The fragility of many a critically ill azotemic patient and the co-morbid conditions which affect the stability of this group of patients makes conventional intermittent haemodialysis difficult to perform in them. Such patients are often hypercatabolic and severely azotemic. Moreover, many of them often require removal of large amounts of excess fluid resulting from oliguria, anuria, accumulation of fluids infused and the administered parenteral alimentation. CAVHD and CVVHD are ideally suited in these patients. The main advantages of CAVHD and CVVHD are effective control of azotemia as well as satisfactory regulation of electrolyte and acid-base balance in hemodynamically compromised patients. Additional advantages include; highly effective fluid removal, better hemodynamic tolerance, easier administration of parenteral nutrition and intravenous medications, and the fact that it is a technically simple procedure. The patient groups, in whom CAVHD or CVVHD is a preferred mode of renal replacement therapy, are given in [Table 1].
There are no specific contraindications for CAVHD or CVVHD. Active bleeding should be considered a relative contraindication. However, if uremia is the cause of bleeding, it may be improved by this procedure.
In this procedure, blood is delivered via an arterial catheter through connecting tubings to a dialyzer, and is returned to the patient through a suitable large vein [Figure 1].
Patients' systemic blood pressure is used to propel the blood through the extracorporeal circuit. The rate of blood flow usually ranges from 100 to 150 ml/min according to the cardiac output of the patient.
Access to blood is usually obtained by percutaneous cannulations of femoral artery and vein, using commercially available kits. First, the femoral artery is entered by- a number '8' French catheter using a dilator and a guide wire. Then the femoral vein is cannulated in the same manner, on the ipsilateral or the contralateral side.
The patient should remain in bed during the procedure, and his movements should be restricted in the post-procedure period as well. It is mandatory to observe the cannulated leg(s) for signs of ischemia, bleeding from catheter site and other complications of arterial cannulation [Table 2].
The procedure is similar to CAVHD except that the blood is taken from a vein and is returned to the patient, preferably through the same vein [Figure 2]. A pump with an adjustable flow rate is used to propel the blood through the extracorporeal circuit. The vascular access is usually obtained using a number '8' French dual lumen catheter, inserted into internal jugular, subclavian, or femoral vein.
A variety of dialyzers can be used with comparable efficiency in CAVHD and CVVHD. Initially flat-plate dialyzers were the ones being widely used and are still in use in many places. However, at present, preference is shifting towards hollow fiber hemodialyzers. The membrane material can be cuprophan, polysulfone or polyacrylonitrile. The dialyzer allows diffusion of small and middle sized molecules into the dialysate. In both CAVHD and CVVHD, the dialyzer should be placed slightly below the patient's heart level.
Sterile dialysis fluid is pumped through the dialysate compartment of the dialyzer in a counter current fashion.
Usually, sterile, potassium-free peritoneal dialysis solution containing sodium (140 mmol/L), glucose (1.5%-4.25%), chloride (102 - 117 mmol/L), and lactate (30-35 mmol/L) is used in both CAVHD and CVVHD. According to the condition of the patient, the flow rate of the dialysis fluid is adjusted at a range between 10 to 40 liters per day. When the blood flow rate is between 100-150 ml/min, the dialysate becomes approximately 100% saturated with urea at a dialysate inflow rate of 40 liters per day  . Therefore, in those patients in whom there is no residual renal function or those who are in a hypercatabolic state, the rate of the dialysate flow has to be increased.
Prolonged anticoagulation is required in most of the patients. Heparin is the most common anticoagulant used, and is usually given at a rate of 500 IU per hour after 2000 IU of heparin is added to the rinsing solution during priming of the dialyzer. However, close monitoring of the coagulation profile is mandatory and the dose of heparin must be adjusted accordingly during the procedure.
There are many instances where we have to use heparin free CAVHD or CVVHD, especially in patients with active or recent bleeding, liver disease, heparin-induced thrombocytopenia, or in the post-operative period. Strict monitoring for clotting in the extracorporeal circuit is necessary. Regional anticoagulation using heparin and protamine can also be used in such patients to avoid bleeding.
For continuous dialysis therapy, generally replacement fluid is considered not necessary. However, in those cases where fluid loss is more, replacement can be done using solutions used for hemofiltration. Alternatively, saline, dextrose saline or ringer lactate solution also may be used as per the clinical assessment of treating physician.
The complications are mainly related to the vascular access namely, catheter related infection and thrombosis of the catheter as well as thrombosis of the tubing and dialyzer (extra-corporeal circuit), local or systemic bleeding in addition to the complications related to arterial cannulation [Table 2].
Management of the Complications
Catheter Related Complications (Infection, Thrombosis and/or Bleeding)
Removal of the catheter is advisable if evidence of infection is clear. Blood and catheter tip must be sent for culture and sensitivity. The patients should be covered with broad spectrum antibiotics, till the blood culture/catheter tip culture results are available after which appropriate antibiotics should be given.
Catheter related thrombosis of the vein or the artery should be treated by removal of the catheter and anticoagulation  . Catheter related bleeding is managed by local compression. If this does not control the bleeding it becomes necessary to remove the catheter.
Extracorporeal Circuit Thrombosis
Thrombosis is usually due to inadequate heparinization and/or systemic hypotension. It can be managed by increasing the heparin dose after changing the tubing and the dialyzer. Also, in patients with hypotension the level of the systemic blood pressure can be improved, by adjusting the fluid balance based on the central venous pressure, and/or by the usage of vasopressors like dopamine.
CAVHD and CVVHD are new modifications of continuous replacement therapy, most useful in patients who are hemodyna-mically compromised. They offer a smooth way of instituting dialysis treatment where conventional dialysis is difficult to perform.
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