Dialysis Line Research Articles

Percutaneous fibrin sleeve stripping of failing haemodialysis catheters.

One of the most frequent reasons for failure of haemodialysis lines is catheter blockage caused by fibrin sheath formation. We report our experience of percutaneous fibrin sheath stripping in treating this problem. A consecutive series of failing haemodialysis catheters underwent percutaneous fibrin sheath stripping in an attempt to retrieve and prolong the life of the catheter. Immediate technical success, clinical success, and primary and secondary patency were measured based on clinical follow-up. Sixteen non-functional permanent haemodialysis lines in 15 patients underwent percutaneous fibrin sheath stripping on 21 occasions. Technical success rate was 100%. Catheter flow rates sufficient for initial dialysis were achieved in 12 (75%) lines. Successful percutaneous fibrin sheath stripping produced a mean catheter patency of 126 days (range 6-299 days). Percutaneous fibrin sheath stripping is a simple, repeatable procedure that can usefully extend the life of a failing dialysis line. However, a randomized trial will be needed to evaluate its role compared with catheter replacement.

Reinfusion and concentration of ascitic fluid during hemodialysis in a cirrhotic uremic patient

Management of tense ascites in cirrhotic patients on chronic hemodialysis is still a matter of speculation. A considerable problem with these patients is the frequent occurrence of hypotension during ultrafiltration. We describe a patient in whom ascitic fluid was reinfused on the arterial line and ultrafiltrated during standard treatment by using a single dialysis monitor, standard dialysis (SD) lines, and a standard hollow-fiber dialyzer. After 30 to 60 minutes of dialysis, with the patient lying on his left side, a gauge #16 IV catheter was introduced into the left lower abdomen and connected to the reinfusion line. The ascitic fluid was pumped from the abdomen to the arterious inlet of the coil at 500 to 2,000 mL/hr and ultrafiltered. In an individual patient, 13 sessions of ascites reinfusion-ultrafiltration dialysis (ARD) were performed over 3 months and compared with 18 SD sessions performed during the same period. In all procedures, the same SD equipment was used. During ARD, the average weight loss was 2.9 (SD 1.0) kg compared with a weight loss of 0.3 (0.04) kg during SD (P < 0.01). Baseline mean blood pressure was similar in both procedures; after starting dialysis, mean arterial pressure (MAP) dropped by an average of 15 mm Hg at 30 and 60 minutes. Subsequently, during ARD, MAP increased progressively by an average of 20 mm Hg at 180 minutes, whereas MAP did not change significantly during SD. Comparison between procedures by nonparametric one-way analysis of variance showed that body weight became significantly different at 120, 150, and 180 minutes (P < 0.01) and MAP at 150 and 180 minutes (P < 0.02 and P < 0.01, respectively). No major complications occurred. During ARD, on average urea reduction rate was 67%. ARD may represent an effective and safe combination between hemodialysis and the palliative treatment of tense ascites in cirrhotic uremic patients. (Am J Kidney Dis 1998 Jul;32(1):164-7)

Accuracy of dilution techniques for access flow measurement during hemodialysis

Access flow is now widely measured by creating artificial recirculation with the dialysis lines reversed and using dilution methods that sense either ultrasound velocity, electrical impedance, optical, or thermal changes. This study identifies and quantifies factors that influence the accuracy of access flow measurements and recommends ways to reduce these errors. Two major sources of access flow measurement error are identified, arising firstly from the second pass of the indicator by recirculation through the cardiopulmonary system (cardiopulmonary recirculation, CPR), and secondly from changes in venous line blood flow (Qb) and vascular access flow induced by the pressure of venous bolus injections. These errors are considered from theory, by direct measurement of access flow in a sheep model, and by analysis of clinical data. Two extremes for the venous introduction of indicator can be considered in access flow measurements, a slow infusion, which perturbs neither the venous line flow nor access flow but increases the error attributable to the second pass of the indicator by recirculation through cardiopulmonary system, or rapid injection, which eases separation of the second pass of the indicator signal but generates changes in the venous flow and access flow. If CPR is not eliminated, the area added to that of the first pass of indicator ranges up to 40%. Good time resolution could permit the separation of the areas generated by the first and second passage of the indicator. In sheep experiments, injections of 5 or 10 mL into a venous port close to the vascular access caused Qb to change by 20% to 40%. Both the animal experiments and analysis of raw data collected during routine clinical dialysis showed that moving the injection site sufficiently far from the patient, before or into the venous bubble trap, reduced the increase in Qb to only approximately 5% during the critical time when the concentration curve is changing for most tubing brands (Baxter, Belco, Gambro, Hospal, Medisystem, and National Medical Care). Because of the smaller volume of the venous bubble chamber in Cobe tubing (Cobe, Centrysystem 3), this brand showed approximately a 20% increase in Qb. Moving the site of bolus injections to before the bubble trap in the sheep experiments also eliminated the influence of changes in access flow. An additional error in access flow measurement of 20% or more arises from the use of flow reading taken from pump setting rather than a measured flow. The discrepancy between the real flow and pump setting is attributable to needle size, vascular access conditions, or pump calibration. The results show that problems can be minimized by using a dual sensor system that retains the precise timing necessary for separation of access recirculation from CPR; by accurate measurement of dialyzer blood flow; by moving the site of injection to before the venous bubble trap, sufficiently far from the patient, and correcting for any remaining deviations in flow in the venous line concurrent with the dilution curve. (Am J Kidney Dis 1998 Mar;31(3):502-8)

Assessment of access recirculation during haemodialysis.

With dialysis lines in the correct alignment, access recirculation only occurs when the access blood flow rate is exceeded by the extracorporeal blood flow rate. The degree of access recirculation is accurately measured by non-urea-based methods using indicator dilution or differential conductivity methods. The classical urea-based methods have inherent inaccuracies. Access flow rate can be calculated from an accurate measurement of the access recirculation induced by dialysis line reversal. Access flow rate monitoring can detect early access dysfunction; the existence of access recirculation indicates severe access dysfunction.

Measurement of Hydrostatic Intraperitoneal Pressure: A Necessary Routine Test in Peritoneal Dialysis

This paper summarizes our clinical studies on hydrostatic intraperitoneal pressure (IPP), showing the interest of this measurement in routine clinical practice. IPP can easily be measured routinely be a simple and safe method: the measure of the column of dialysate in the peritoneal dialysis (PD) line before drainage, with point 0 located on the midaxillary line. The normal value is 12 +/- 2 cm of water (cm H2O) with an intraperitoneal volume (IPV) of 2 L, with linear increases of 2.2 cm H2O for each additional liter. IPP must be measured to estimate the tolerance of IPV: the maximal permissible IPV is reached for an IPP of 18 cm H2O, squaring with a decrease of 20% in vital capacity and sometimes arising before clinical symptomatology. However, IPP measured at rest could not predict PD mechanical complications (hernias, dialysis leakages, hemorrhoids, etc.), which are more dependent on parietal previous history or predisposition. IPP is significantly higher during the first three days after peritoneal catheter implantation (17 +/- 3 cm H2O) than during the 12 following days (10 +/- 4 cm H2O). It is recommended to postpone the start of PD until after catheter implantation, and patients should remain supine for the first three days. On the other hand, IPP strongly reduces the overall ultrafiltration (UF) volume: an increase of 1 cm H2O in IPP caused a decrease of 70 mL in global UF after two hours. Therefore, IPP should be measured in diagnosis of losses of UF. However, UF loss during peritonitis is not due to an increase of IPP.

Novel method to measure access flow during hemodialysis by ultrasound velocity dilution technique.

This article presents the theory and bench validation of access flow measurement by ultrasound velocity dilution. Reversal of dialysis lines creates a zone of mixing in the vascular access, allowing the use of dilution technique for access flow measurement. The method of sound velocity dilution sensor calibration was analyzed. A single sensor system was investigated for blood circulation and isothermal injections. A dual sensor system was investigated with heated hypertonic saline circulation for both body temperature (isothermal) and room temperature (cold) injections. The accuracy of in vitro access flow measurement was studied on a two pump bench model, dialysis line flow was varied from 200 to 400 ml/min, access flow was varied from 300 to 2500 ml/min. For the dual sensor system, dilution access measurements tracked a gravimetrically calibrated in-line flow sensor within 3.25 +/- 0.34% for isothermal injections, and within 5.81 +/- 0.43% for cold injections. Measurements were repeatable within 3% independent of the temperature of the injected saline. For the single sensor system, results tracked the in-line flow sensor within 3.83 +/- 0.79%. These data show that access flow can be accurately measured by sound velocity dilution technique.

Theory and validation of access flow measurement by dilution technique during hemodialysis

The theory shows that access flow can be measured by the dilution technique by reversal of the blood dialysis lines with the venous outlet facing the access stream: (1.) with one dilution sensor in arterial line and two injections Equation (6); (2.) with two matched dilution sensors on the venous line and on the arterial line and one injection Equation (8); (3.) with blood sampling as for recirculation measurement using BUN or other methods in Equation (12). In all cases, accurate measurement of hemodialysis blood flow is required. The results of this bench validation demonstrate that dialysis blood flows, in the clinical range of 200 to 350 ml/min or more, create good mixing conditions in a vascular access model. Accurate measurements are provided for all clinically significant ranges of access flows, needle positions, and vascular access inner diameters. This simple, non-invasive, and inexpensive technique shows great promise for routine diagnosis of vascular access failure in hemodialysis patients.

Hemodialysis access recirculation measured by ultrasound dilution.

The most widely used clinical method for measuring recirculation in the access device is based on urea dilution. The three simultaneous blood samples required during hemodialysis interrupt the treatment, and results of chemical analysis are often delayed for several days. Alternatively, detecting recirculation by dilution of arterial blood caused by a bolus of normal saline injected into the venous blood line has several advantages. In this study, an ultrasound sensor clamped onto the arterial line entering the dialyzer was used to detect such dilution from a reduction in sound velocity observed in the saline diluted blood. Within the target range, the change in ultrasound velocity (ultrasound dilution) is linearly correlated with the dilution of whole blood by normal saline. The same sensor was also used to measure flow in the blood line using an established ultrasound transit-time method. During 34 hemodialyses in 28 patients, only 3 patients had detectable recirculation measured by ultrasound dilution. To further evaluate the sensitivity of the new method the dialysis lines were reversed during hemodialysis in the 25 patients with no recirculation. After this, all had detectable recirculation ranging from 10 to 60%. The mean error of duplicate measurements was 3.9 +/- 2.8%. Recirculation by ultrasound dilution correlated closely with recirculation measured by urea dilution (r = 0.9156, p < 001). The data suggest that the ultrasound dilution method is both sensitive and accurate. Ease of use and immediate availability of results added to the clinical usefulness of this method for evaluating the integrity of the hemodialysis access.

Azygos catheter placement as a cause of failure of dialysis

Common complications of venous dialysis catheters include sepsis and accidental removal. Angiographic demonstration of dialysis lines is only rarely requested usually to confirm the presence of clot or stenosis as a cause for poor dialysis flow. Poor flow can also be due to inadvertent placement of the catheter in the azygos system. The use of dialysis catheters with a long venous limb which extends beyond the arterial port may predispose to such placement as their lumen is lateral to the central axis of the catheter. In those patients with poor venous access catheter placement under angiographic control may be helpful.

Dialysis Line Connectors Leak

Dialysis Line Connectors Leak

Air in Dialysis Lines May Reach Patient

Air in Dialysis Lines May Reach Patient

Conversion of acetate to CO2, lipids, proteins, and lipoproteins during hemodialysis in humans.

Acetate-1-14C or acetate-2-14C was infused into the venous dialysis line in 17 chronic stable patients over a 4-hr period of standard hemodialysis. Radioactive CO2 in expired air was measured continuously during dialysis and for 20 hr postdialysis. Significantly more acetate-1-14C (56 +/- 2%) was recovered as 14CO2 in the expired air than was acetate-2-14C (49 +/- 3%). A total of 81% and 71% of the radioactivity was recovered from the expired air and expended dialysate from acetate-1-14C and acetate-2-14C, respectively. Of the remainder, a significant portion was incorporated into plasma lipids and proteins. Incorporation of radioactivity into phospholipids, cholesterol esters, and triglycerides increased during dialysis and continued to increase during the postdialysis period. Free fatty acid radioactivity increased during dialysis but declined afterwards. In the lipoprotein fractions radioactivities remained elevated at 24 hr in the LDL and HDL fractions, but declined in the VLDLs after this time interval.

Effect of mean circulatory filling pressure and other peripheral circulatory factors on cardiac output.

I P ONE studies curves which depict the relationship of cardiac output to mean right atria1 pressure (one of the forms of Starling’s curves), it is obvious that, within the normal range of function of the heart, cardiac output can change tremendously while the right atria1 pressure changes only slightly. This fact led to the early belief that it is not the function of the heart itself which controls cardiac output but instead that cardiac output is controlled by the various factors in the peripheral circulatory system which regulate the return of blood to the heart. Though it is not entirely true that cardiac output is independent of the function of the heart (I), nevertheless, it is hoped to emphasize in the present paper the special importance of the peripheral circulatory factors which affect venous return. In order to do this, a mathematical circuit analysis of the closed circuit circulatory system has been made. This circuit analysis has been specifically simplified so that the factors derived would be amenable to experimental test. Two of the factors which have proved to be of importance, as shown both by this circuit analysis and by experimental data, are a) ‘capacitance’ and b) ‘mean circulatory filling pressure.’ As used in these studies the term capacitance means dV/dP or, in other words, the change in volume of a particular part of the circulatory system with each unit change in pressure. This term has been used in the present paper because there is at present no term in common usage in hydrodynamics which means dV/dP. This is different from the term ‘distensibility’ which is commonly used to mean dV/dP + V. The term mean circulatory filling pressure (MCFP) has been defined previously (2), and it means ,__-