Blood recirculation in malfunctioning catheters for haemodialysis

Effects of the tip structure of temporary indwelling catheters on blood recirculation at various blood flow rates and diameters of the mock blood vessel

AIMS

The aim of the present study was to determine the effects of the tip structure of the catheters used for hemodialysis on blood recirculation at varying blood flow rates and diameters of the mock blood vessel in a well-defined in vitro experimental system, focusing on reverse connection mode.

METHODS

A mock circulatory circuit was created with silicon tubing (15 or 20 mm), a circulatory pump, connected through the catheter to dialysis circuit and dialyzer attached to dialysis machine. The tip of the inserted catheter was fixed to the center of the silicone tube, and 3 L of pig blood was poured into the blood side of the dialyzer and the recirculation rates were measured at blood flow rates of 100, 150, and 200 mL/min. Five types of commercially available catheters were used: (A) Argyle™, (B) Gentle Cath™ (Hardness gradient type), (C) Gentle Cath™, (D) Niagara™, and (E) Power-Trialysis®.

RESULTS

In the case of reverse connection mode, (1) the recirculation rates were lower in the catheter with a relatively large side hole (catheter C, 17%), catheters with a greater distance between the end hole and side hole (catheters C and D, 25%), and catheter with a symmetrical tip structure (catheter E, 10%) as compared with those in catheters A and B (40% and 25%); (2) increase of the blood flow rate in the dialysis machine was associated with a reduced recirculation rate; and (3) a wider inner diameter of the mock blood vessel and faster flow rate in the vessel were associated with a reduced recirculation rate.

CONCLUSION

The lowest recirculation was observed with the catheter with symmetrical holes, which produces a helical blood flow line that does not intersect with the blood streamline flowing out to the blood supply hole.

Optimizing Dialysis Delivery in Tunneled Dialysis Catheters

Long-term dialysis is often delivered through tunneled central venous catheters (CVC) despite their associated morbidity and mortality rates. Because poor solute clearance might contribute to this risk, we examined the relation between blood pump speed (QB), access recirculation (AR), and dialysis delivery in patients with CVC. We conducted a prospective study on 102 patients receiving long-term hemodialysis with CVC. QB was systematically varied, and AR was measured by saline dilution with the blood supply lines in both the straight and the reversed positions during each of two dialysis sessions. During a third session, we measured ionic dialysance (EID) in patients with AR>0% and those in whom dialysis was usually delivered with catheters in the reversed position.Approximately one third (34.3%) of patients were usually run in the reversed position. Clinically significant AR (>10%) was infrequent (3%) in the straight position but common in the reversed position (86%). QB and EID were linearly correlated for both the straight and reversed positions. Approximately half (48.6%) of patients who were generally treated with their lines reversed were able to receive dialysis with the lines in the straight position within acceptable pressure limits when blood lines were switched part way through the run. In these patients, solute clearance was equivalent (EID straight 204 ml/min vs. reversed 196 ml/min, p=0.58) with lines in the straight configuration despite lower achieved QB (straight 354 ml/min vs. reversed 404 ml/min, p=0.04). Maximization of prescribed QB in CVC increased AR when blood line position was reversed but improved small solute clearance regardless of line position. This suggests that QB in CVC should be set as high as circuit pressure limits will allow, regardless of the potential for AR, and that reversal of line position confers no benefit with respect to solute clearance.

Urea Clearance in Dysfunctional Catheters Is Improved by Reversing the Line Position Despite Increased Access Recirculation

BACKGROUND

Problematic or dysfunctional hemodialysis (HD) catheters are routinely reversed to achieve adequate blood flow for dialysis delivery. The purpose of the study is to determine the effect of varying blood pump speed (Qb) on access recirculation (AR), and urea clearance (K) in dysfunctional catheters in the normal and reversed positions.

METHODS

Nineteen HD patients with tunneled cuffed catheters (5 functional and 14 dysfunctional catheters) were included; dysfunctional catheters are defined as the inability to attain a Qb of 300 mL/min or greater on 2 consecutive HD runs. AR and K measurements were obtained systematically for each catheter in the normal and reversed positions at increasing Qbs. K was measured using the ionic dialysance technique.

RESULTS

In functional catheters, AR in the normal position was 0% and increased to 15% +/- 13% when reversed. Dysfunctional catheters had a greater AR of 25% +/- 16% when reversed. In functional catheters, there was no evidence of an increase in AR with increasing Qb irrespective of position. Similarly, there was no relationship between increasing AR and greater Qbs (r 2 = 0.10) in dysfunctional catheters. In dysfunctional catheters, when reversed, mean K increased from 128 +/- 10 mL/min at a Qb of 200 mL/min to 157 +/- 38 mL/min at maximal Qb (P < 0.05).

CONCLUSION

We show that at increasing Qbs, K is improved in both functional and dysfunctional catheters. Data from the study are used to describe a nomogram to determine minimum Qb for a dysfunctional catheter in reversed position to maximize K.

Reverse transcriptase/polymerase chain reaction analyses of hemodialysis ultrafiltrates and sera of hepatitis C virus positive patients

The hepatitis C virus is a highly prevalent infection among chronic dialysis patients and represents one of the major problems of hemodialysis units. Hepatitis C virus transmission occurs either by blood transfusion or nosocomially. One of the proposed pathways of nosocomial transmission of the hepatitis C virus is cross-contamination through the dialysis procedure. In an effort to elucidate whether the hepatitis C virus may pass across the hemodialysis membrane, we have performed analyses of ultrafiltrates collected in different stages of hemodialysis treatments, using different types of hemodialysis membranes and different types of dialysis machines. Samples collected from the dialysis compartment during the rinsing of the blood compartment at the end of the hemodialysis treatment were also analyzed. The hepatitis C virus was found in 17 out of 58 ultrafiltrate samples taken at different times of the hemodialysis treatment. Moreover, the hepatitis C virus was present in 15 out of 17 samples collected from the dialysate compartment during the saline solution rinsing step of the blood compartment. The presence of the hepatitis C virus had no strict correlation with the type of dialysis membrane or with the type of dialysis machine. Although the results suggest that the passage of the hepatitis C virus during the hemodialysis treatment is multi-factorial and case- specific, the most critical point is when the blood is flushed out with physiological saline.