Fistula dysfunction: effect on rapid hemodialysis.

Rapid hemodialysis (Qb 400 to 500 ml/min) places considerable demands on hemodialysis vascular access. This six-month prospective study enrolled 52 patients and evaluated urea recirculation as a means of detecting fistula dysfunction. It evaluated the effects of fistula location and dialysis blood flow on urea recirculation during rapid hemodialysis and assessed the effect of rapid dialysis on fistula thrombosis. Urea recirculation increased as Qb increased from 300 to 400 ml/min (8 +/- 3% to 16 +/- 3%, P less than 0.05). The extent of urea recirculation was also fistula site dependent (radial fistulas 18 +/- 4%, upper arm fistulas 11 +/- 3%, Qb 400 ml/min, P less than 0.05). Site and blood flow dependent urea recirculations were an indicator of venous stenoses. When venous stenoses were corrected, urea recirculation rates improved (36 +/- 3% to 21 +/- 3%, P less than 0.05). There were no differences between methods of determining urea recirculation early in dialysis (contralateral arm venepuncture vs. stop flow technique; 30 to 60 min). However, at 120 minutes urea recirculation was significantly greater with the contralateral arm venepuncture technique. Venous dialysis pressure at Qb 400 ml/min had limited use as a predictor of venous stenoses unlike its value at lower Qb. Fistula thrombosis (0.26/patient year of dialysis) and fistula replacement (0.09/patient year of dialysis) were similar to our observations in a conventional hemodialysis facility where prospective correction of fistula dysfunction was also used.     

Increasing blood flow increases kt/V(urea) and potassium removal but fails to improve phosphate removal

BACKGROUND: Hyperphosphatemia and hyperkalemia are major determinants of morbidity and mortality in hemodialysis patients. Half of the dialysis population suffers from hyperphosphatemia which is now recognized as an important cardiovascular disease risk factor. It is, therefore, necessary to improve the removal of these molecules. In this study, we investigated the effect of enhancing blood flow on Kt/V for urea (Kt/Vu), potassium and phosphate removal. METHODS: Thirteen patients were investigated in a randomized, cross-over, prospective study using 3 blood flows (Qb) of 200,250 and 300 ml/min which gave 39 standardized high-flux hemodialysis treatments. Effective blood flows were measured by ultrasonic flow meter. Quantification of delivered dialysis dose was performed by partial dialysate and ultrafiltrate collection for the determination of potassium and phosphate removal and by blood urea concentrations for determination of Kt/Vu. RESULTS: Kt/Vu rose significantly from 1.10 +/- 0.14 to 1.22 +/- 0.14 and finally to 1.39 +/- 0.16 (p = 0.0001) with increasing Qb similar to the increase in potassium removal from 53.0 +/- 2.4 to 63.4 +/- 2.6 and to 74.2 +/- 3.8 mMol (p = 0.01). Phosphate removal only improved from 28.1 +/- 1.3 to 31.4 +/- 1.5 (p = 0.050) when Qb was increased from 200 to 250 ml/min but remained unchanged at 31.2 +/- 1.5 mMol (NS compared to phosphate removal at Qb = 250 ml/min) when Qb was increased to 300 ml/min. CONCLUSIONS: Increasing delivered Kt/Vu and potassium removal with higher Qb fails to produce the same desired effect with phosphate removal during high-flux hemodialysis.     

All currently used measurements of recirculation in blood access by chemical methods are flawed due to intradialytic disequilibrium or recirculation at low flow

Blood flows and recirculations with standard and reversed direction of lines were measured by chemical (urea and creatinine) and ultrasound dilution (saline) methods in 47 chronic hemodialysis patients. Thirty-seven patients had 47 dual-lumen, central vein (CV) catheters: 32 were PermCath (Quinton Instruments Company, Seattle, WA), 6 were Access Cath (MEDCOMP, Harleysville, PA), 3 were Soft Cell PC (Vas Cath, Mississauga, Ontario, Canada) and 6 were SNIJ (experimental catheters). Three of these last catheters had the tip staggered 7 mm, and three had flush tips; PermCath, Access Cath, and Soft Cell PC catheters have the tips staggered 23 to 25 mm. Forty-six catheters were implanted into the superior vena cava/right atrium, and one catheter was implanted through the left saphenous vein into the left iliac vein. The catheters were studied 1 to 31 months after implantation (median, 3.0 months). Ten patients with arteriovenous (AV) graft access were also studied. The stop-flow method was used in catheter dialysis, and the slow-flow method was used to calculate recirculations in AV access dialysis with samples for systemic blood concentrations taken from arterial line both before and after samples from the arterial and venous lines. At 500 mL/min pump speed, actual blood flow was 436+/-18 mL/min (mean+/-SD; range, 407 to 464 mL/min) with standard direction of catheter lines. At 500 mL/min pump speed, the arterial chamber pressure was -330+/-48 mm Hg (mean+/-SD; range, -380 to -225 mm Hg, and the venous chamber pressure was 259+/-48 mm Hg (mean+/-SD; range, 140 to 310 mm Hg). Arterial chamber pressure was less negative, and venous chamber pressure was less positive with SNIJ catheters, which had larger internal diameter (2.1 mm) compared with the other catheters (2.0 mm). Recirculation varied with the catheter design and the location of the catheter tip. In the catheters with tip staggered more than 20 mm and with standard line connection at pump speeds of 50 mL/min and 500 mL/min, recirculations were approximately 1 % and 5%, respectively, when measured by the chemical method. In the same catheters with reversed lines, the recirculations were approximately 5% and 27%, respectively. Inflow failure catheters with reversed lines had similar recirculation values to those of well-functioning catheters with reversed lines. In catheters with tips staggered 7 mm, and with standard connection of lines, recirculations were approximately 3% and 8%, respectively, at pump speeds of 50 and 500 mL/min. With reversed lines, at the same pump speeds, the values were 7% and 12%, respectively. In flush-tip catheters, the recirculation was higher at a 50 mL/min pump speed (approximately 17%) than at a pump speed of 500 mL/min (approximately 13%). The ultrasound dilution method usually gave lower values than the chemical methods, most likely because of overestimation of recirculation by chemical methods. At least triplicate measurements are needed because single measurements by the ultrasound dilution method are associated with substantial variation. We conclude that both currently used methods (stop flow and slow flow) of taking systemic samples for measurements of recirculation by chemical methods are flawed because of disequilibrium and recirculation at low flow.     

Serial determinations of absolute plasma volume with indocyanine green during hemodialysis

Hemodynamic stability during hemodialysis depends largely on plasma volume (PV) preservation during ultrafiltration (UF). Current estimates of blood volume (BV) are indirect or involve the use of radioactive tracers, which does not allow repeated measurements during hemodialysis. Indocyanine green was used to measure PV during hemodialysis. After an initial pilot phase (phase I), PV values were determined before dialysis, repeatedly during isovolemic hemodialysis (phase II), and during stepwise UF (phase III). Absolute BV values were calculated from PV and hematocrit values. Patients were monitored for extracellular fluid volume (bioimpedance monitoring) and relative BV changes (ultrasonic monitoring). Phase I demonstrated dye stability in plasma, peak absorbance at 805 nm, and a short half-life (4.53 +/- 1.5 min). Ten milligrams of dye (2.5 mg/ml) were injected for each PV measurement. Eight plasma samples were obtained beginning 3 min after injection, at 1-min intervals, for assessment of decay characteristics. The isovolemic hemodialysis PV measurements demonstrated excellent reproducibility (r(2) = 0.98; method SD, 356 ml; mean coefficient of variation, 4.07%) and a difference of only 149 +/- 341 ml (mean +/- SD), compared with predialysis PV values (Bland-Altman method). PV values at the beginning of dialysis were significantly correlated with body surface area (r(2) = 0.82, P < 0.001) and extracellular fluid estimates (r(2) = 0.73, P < 0.001). BV prediction formulae significantly underestimated absolute BV at the start of dialysis (P < 0.0001). The findings demonstrate that this method can be used for repeated PV determinations during hemodialysis, with excellent reproducibility. It is a potential tool for further research on hemodynamic stability during UF.     

Randomized comparison of split tip versus step tip high-flow hemodialysis catheters

BACKGROUND: Our purpose was to compare the function and complications of two high-flow polyurethane hemodialysis catheters. METHODS: This prospective, randomized trial compared the Ash-Split (MedComp) and Opti-Flow (Bard Access Systems) catheters. All patients referred for tunneled hemodialysis catheter placement were offered entry in the study, provided they met inclusion criteria. Catheters were placed by interventional radiologists using ultrasound and fluoroscopic guidance. Procedure time and initial complications were recorded. Effective (QbEff) catheter flow rates and recirculation were studied at baseline, one month, three and six months using ultrasonic dilution (Transonic) at various pump speeds (Qb). Episodes of catheter malfunction and infection were recorded. Catheter removal or six months was the study endpoint. RESULTS: A total of 132 patients were enrolled in the trial. The groups did not differ as to age, sex distribution, height or weight (P> 0.05). Initial complications included kinking resulting in catheter failure (Optiflow N = 3), and tunnel bleeding (Optiflow N = 1; Ash N = 3). Adjusted mean flow rates (QbEff) at Qb300 were 299 mL/min Ash and 305 mL/min Optiflow (P = 0.06), at Qb400 were 365 mL/min Ash and 382 mL/min Optiflow (P = 0.01), and at QbMax were 414 mL/min Ash and 433 mL/min Optiflow (P = 0.03). Recirculation was significantly higher with the Optiflow catheter at most measurement points. Total late complications were lower in the Ash group (P = 0.04), and catheter survival was significantly higher in the Ash group (P = 0.02). CONCLUSIONS: Both catheters can deliver flow rates well beyond those recommended by the Dialysis Outcomes Quality Initiative. While the Optiflow delivered higher flow rates at some measurement points, this was offset by higher recirculation. The Ash catheter showed a long-term survival advantage and fewer late complications.     

Transvascular protein movement in the intact ischemic hindlimb

Postischemic limb swelling following reperfusion may be related to microvascular changes associated with ischemia. We used lymph-to-plasma total protein concentration ratios (L/P) and lymph flow (QL) as an index of transvascular exchange in the intact dog hindlimb during steady state (C) (1 hr), ischemia (I) (6 hr), and reperfusion (R) (3 hr). Central pressures, femoral arterial and venous pressures (PA, PV) and QL were recorded every 15 min. Lymph was collected from a femoral lymphatic in the passively flexed leg (50 cycles/min). Three groups of animals were studied: GI, sham-operated (N = 5); GII, moderate ischemia (N = 7, PA = 30-45% C); and GIII, severe ischemia (N = 7, PA = 5-20% C). In GI, QL gradually increased over 10 hr without change in L/P. Moderate ischemia produced a decrease in QL, 3.55 +/- 2.02 mg/hr to 0.92 +/- 0.53 mg/hr (P less than 0.0001), and QL remained below baseline during R with no change in L/P over the 10 hr. Severe ischemia produced a similar decrease in QL, 1.91 +/- 2.05 mg/hr to 0.15 +/- 0.1 mg/hr (P less than 0.01); however, an increase to 2.56 +/- 2.14 mg/hr occurred during R. Severe ischemia increased L/P 0.42 +/- 0.08 to 0.64 +/- 0.23 (P less than 0.001) and remained elevated during R at 0.63 +/- 0.18 (P less than 0.001). An increase in the wet-to-dry weight ratio of ischemic to nonischemic muscle after reperfusion was noted only in GIII, 3.82 +/- 1.17 vs 2.60 +/- 0.45 (P less than 0.04). Severe ischemia produces changes in vascular integrity which augment protein flow. Prevention of these vascular changes may help to minimize the muscle swelling of reperfusion.     

Slow-flow venous pressure for detection of arteriovenous graft malfunction

BACKGROUND: Early detection with elective intervention of malfunctioning arteriovenous (AV) grafts improves access viability. Herein, we evaluated outlet venous pressure (OP), normalized by mean arterial blood pressure (MABP), at varying blood flow (Qb) rates in the detection of venous outlet stenosis. METHODS: This single-center, observational study included stable dialysis patients with polytetrafluoroethylene (PTFE) AV grafts. Phase I involved the determination of the optimal Qb (0, 50, 250, or 400 mL/min) and threshold OP/MABP. Sixty-one patients were followed up for 6 months. The primary end point was graft thrombosis. Phase II assessed serial slow-flow pressure (SFpr = OP/MABP at Qb of 50 mL/min) in a larger sample size (N = 152). The primary end point was graft thrombosis. Phase III implemented the use of SFpr monitoring in the detection and correction of outlet lesion(s). RESULTS: In phase I, 21 patients developed graft thrombosis. The most significant difference in pressure between the functioning and thrombosed grafts was at Qb of 0 mL/min and SFpr. The threshold of OP/MABP at Qb 0 (>0.53) and SFpr (>0.6) were predictive of graft thrombosis. In phase II, 37 of 42 patients with graft thrombosis had SFpr>0.6 (sensitivity 88.1%; specificity 97.2%; positive and negative predictive values were 90.2% and 95.5%, respectively). In phase III, 13 patients with SFpr>0.6 had outlet lesions on angiography. CONCLUSION: Serial SFpr used in conjunction with angiography and angioplasty provides a strategy for reducing the incidence of thrombosis. This technique has comparable sensitivity and specificity to other existing methods. This technique is both time-efficient and cost-effective.     

Comparison of glucose pump test and urea test in measuring blood access flow

BACKGROUND: The Glucose Pump Test (GPT) is a new method for measuring the access blood flow (Qa) based on a constant glucose infusion (Qi), with known glucose concentration (Ci), in the arterial needle and on glucose determination in two blood samples from the venous needle, the first (C1) in basal conditions, the second (C2) during the infusion. Qa depends on the difference in glucose between the two samples and is computed from the formula: QaGPT = Qi x (Ci-C2)/(C2-C1). METHODS: The new method, previously evaluated by ultrasound dilution and color-Doppler techniques, was compared with the Urea Test (UT) in 20 patients measuring recirculation (R) during reversal of the arterial and venous needles (QaUT = Qb x (1/R -1)). All Qa determinations were done twice by both methods. Glucose and urea were determined respectively two and three times. RESULTS: Mean QaGPT = 841, SD 347 ml/min, mean QaUT = 872, SD 417 ml/min (p = n.s.); mean percent difference QaGPT-QaUT= 16%, SD 14; mean coefficients of variation of paired determinations: 8.1% and 12.1% respectively; Pearson coefficient between the two methods: r= 0.91. CONCLUSIONS: The comparison showed a good correlation between the two methods and similar mean values. The coefficient of variation of the new method was acceptable and lower than with the UT. The GPT is a reliable technique for measuring blood flow in vascular accesses.     

Evaluation of renal Kt/V as a marker of renal function in predialysis patients

BACKGROUND: The use of renal Kt/V (r-Kt/V) as an indicator for the need of dialysis initiation has been recommended in the NKF-DOQI guidelines. In analogy to clinical practice in peritoneal dialysis, a fall of r-Kt/V below a threshold of 2.0 per week may indicate inadequate renal toxin elimination. However, there are no studies linking r-Kt/V with other parameters of glomerular filtration rate (GFR) in predialysis patients, and the validity of r-Kt/V as parameter for timing of dialysis initiation is unknown. METHODS: Renal function was assessed repeatedly in 125 patients (N = 465 measurements). In predialysis patients (r-Kt/V <2.5 per week) r-Kt/V was compared with creatinine [CCr], urea [CUr], averaged creatinine/urea clearance [CCr/Ur], Cockcroft-Gault formula [CCG], and MDRD prediction equation 6 (MDRD6-GFR). The diagnostic performance of r-Kt/V as a parameter for timing the initiation of dialysis was evaluated. RESULTS: Renal Kt/V <2.5 was prevalent in 24.9% of cases (N = 116, mean 1.92 +/- 0.34). In this group mean CCr was 13.8 +/- 4.9, mean CUr 6.7 +/- 1.3, and CCr/Ur 10.2 +/- 2.9 mL/min/1.73 m2. There was no correlation of r-Kt/V with serum creatinine and MDRD6-GFR, but a significantly positive correlation with CCr/Ur (r2 = 0.3382, P < 0.001). Sensitivity of r-Kt/V to detect CCr/Ur < 10.5 mL/min/1.73 m2, defined as the threshold for dialysis initiation, was 73.6% with a specificity of 91.9%. CONCLUSIONS: These results suggest that r-Kt/V is a parameter of acceptable specificity but poor sensitivity for the timing of dialysis initiation. Additional measures of renal function, such as the average of measured creatinine and urea clearance, also should be taken into consideration when deciding on the timing of dialysis initiation prior to the development of clinical signs of uremia and malnutrition.     

Optimization of high-efficiency hemodialysis by detection and correction of fistula dysfunction

Recirculation studies were performed in 103 patients treated with high-efficiency dialysis over a 14 month period. Fistulograms were performed on 22 out of 25 patients with greater than 0.15 fractional recirculation at a 400 ml/minute blood pump setting. Clinically significant abnormalities were found in 82% (N = 18) and treated in 17. Two patients had second episodes of elevated recirculations and were treated again within the period of follow-up. Treatment with angioplasty (N = 11) or surgical revision (N = 8) resulted in a fall in recirculation from 0.33 +/- 0.04 to 0.12 +/- 0.02 (P = 0.001). The fractional reduction of urea clearance due to recirculation fell from 0.20 +/- 0.03 to 0.08 +/- 0.02 (P = 0.001) and the effective urea clearance of the dialysis treatment rose by 16% from 193 +/- 7 ml/min to 224 +/- 6 ml/min (P = 0.001). Pre-dialysis BUN fell from 72 +/- 4 mg/100 ml to 62 +/- 3 mg/100 ml (P = 0.012). There was no correlation between venous pressure (VP) at 400 ml/min blood pump setting and recirculation (R2 = 0.04), although VP changed significantly comparing values before and after fistula repair (211 +/- 10 vs. 186 +/- 7 mm Hg, P = 0.012). Venous pressures in 20 of the patients in our dialysis unit with recirculations of less than 0.10 were 201 +/- 6 mm Hg (P = NS compared to patients with recirculation greater than or equal to 0.15 at 400 ml/min blood flow).(ABSTRACT TRUNCATED AT 250 WORDS)     

Determining factors for hemodiafiltration to equal or exceed the performance of expanded hemodialysis

The aim of the study was to compare expanded hemodialysis (HDx) with hemodiafiltration (HDF) at different infusion flows to identify the main determinants, namely blood flow (Qb), replacement volume, infusion flow (Qi), ultrafiltration flow (Q_uf), filtration fraction (FF), and the point at which the effectiveness of HDF equals or exceeds that of HDx. We conducted a prospective, single-center study in 12 patients. Each patient underwent 12 dialysis sessions: six sessions with Qb 350 and six with Qb 400 mL/min; with each Qb, one session was with HDx and five sessions were with FX80 (one in HD, and four with Qi 50, 75, 90/100 mL/min or autosubstitution in postdilution HDF). The reduction ratios (RR) of urea, creatinine, ß₂-microglobulin, myoglobin, prolactin, α₁-microglobulin, α₁-acid glycoprotein, and albumin were compared intraindividually and the global removal score (GRS) was calculated. The mean replacement volume with Qb 350 mL/min was 13.77 ± 0.92 L with Qi 50 mL/min, 20.75 ± 1.17 L with Qi 75, 23.83 ± 1.92 L with Qi 90, and 27.51 ± 2.77 L with autosubstitution. Similar results were obtained with Qb 400 mL/min, and the results were only slightly higher with Qi 100 mL/min or in autosubstitution. The GRS was positively correlated with replacement volume with Qb 350 (R² = 0.583) and with Qb 400 (R² = 0.584); with Q_uf with Qb 350 (R² = 0.556) and with Qb 400 (R² = 0.604); and also with FF with Qb 350 (R² = 0.556) and with Qb 400 mL/min (R² = 0.603). The minimum convective volume in HDF from which it is possible to overcome the efficacy of HDx was 19.2 L with Qb 350 and 17.6 L with Qb 400 mL/min. The cut-off point of Q_uf at which HDF exceeded the effectiveness of HDx was 80.6 mL/min with Qb 350 and 74.1 mL/min with Qb 400 mL/min. The cut-off point at which FF in HDF exceeded the effectiveness of the HDx was 23.0% with Qb 350 and 18.6% with Qb 400 mL/min. In conclusion, this study confirms the superiority of postdilution HDF over HDx when replacement volume, convective volume, Q_uf, or FF exceeds certain values. Increasing the Qb in postdilution HDF manages to increase the convective dose and more easily overcome the HDx.     

Peritoneal clearance of homocysteine with icodextrin or standard glucose solution exchange

BACKGROUND: The aim of the study was to assess plasma homocysteine concentration in peritoneal dialysis patients, and to compare the effect of different peritoneal solutions (glucose-based and icodextrin-based) on peritoneal clearance of homocysteine. METHODS: The study group comprised 10 chronic peritoneal dialysis patients; the control group comprised 15 healthy, age-matched non-obese subjects with normal renal function. Patients with vitamin B(12) or folate deficiency were excluded. In all subjects, plasma homocysteine and dialysis adequacy parameters were assessed at baseline. The clearance study was carried out with 2.27% glucose and 7.5% icodextrin solutions (12-h dwell time). RESULTS: Mean dialysate concentration of homocysteine was similar for both glucose and icodextrin solutions (8.3 +/- 3.2 and 8.4 +/- 1.9 micromol/L, respectively), but homocysteine clearance was significantly higher for icodextrin than glucose solution (1.82 +/- 0.57 vs 1.39 +/- 0.53 mL/min per 1.73 m(2)P = 0.01). Net ultrafiltration after icodextrin solution was also higher than after glucose solution (599 +/- 136 mL vs 134 +/- 337 mL, P < 0.01). A correlation between total plasma level of homocysteine and its peritoneal clearance was found (r = 0.69; P = 0.03). CONCLUSION: It appears that peritoneal elimination of homocysteine depends primarily on its plasma concentration. Icodextrin-based solution for peritoneal dialysis seems to be more efficient in homocysteine elimination than a standard glucose-based solution.     

How to improve dialysis adequacy in patients with vascular access problems

Blood flow rate is a critical factor in the achievement of an adequate dialysis dose. The aim of this review is to evaluate the possibility of optimizing dialysis dose in terms of Kt/V in patients with reduced vascular access (VA) flow rate, considering effective blood flow (Qb eff), recirculation, access flow and hemodialyzer. In patients where the achievement of adequate blood flow rates are difficult to obtain and no surgical revision is necessary, to avoid under dialysis the increase in the treatment time should be the first choice solution. If such a solution is difficult for various reasons, a forced partial blood flow recirculation, especially in central venous catheters (CVCs) with reversed lines can be useful, on condition that the dialysis session is prolonged. The possibility of increasing the efficiency of dialysis through an increase in filter clearance has to be considered. Monitoring arterial pre-pump pressure (P asp) and optimizing ratio P asp/Qb eff during hemodialysis (HD) is one possible solution to improve blood flow rates, but it is necessary to educate and involve the staff. Recent developments in a new class of highly effective hemodialyzer due to dialysate distribution, has opened up interesting opportunities in terms of dialysis adequacy in patients with reduced VA flow rate.     

Factors influencing permanent catheter performance

Permanent dual lumen catheters (PDLC) provide an alternative vascular access in patients considered unsuitable for arteriovenous fistula, graft or peritoneal dialysis. However, the use of PDLC is often complicated by inadequate blood flow. The aim of this study was to identify catheter dysfunctions. We studied prospec-tively 57 chronic hemodialyzed patients, 73+/-11 years of age, with PDLC for 18+/-14 (1-48) months. Catheters were tunneled in silicone (MedComp Tesio n= 40) or in polyurethane (Permcath Quinton n = 11, GamCath Gambro n = 6) in left or right internal jugular (n = 49), in left or right subclavian (n = 3) and in right femoral vein (n = 5). We studied the blood viscosity indices (hematocrit, total protein, cholesterol and triglycerides), catheter intra-dialytic parameters (pre-pump and venous pressure), localization of the catheter tip (superior vena cava = SVC, right atrium = RA, inferior vena cava = IVC), blood pressure before and after hemodialysis during the 3 last dialyses, use of anticoagulant (ACT) or antiaggregant therapy (AAT) and previous infectious episodes. The mean blood flow was 269+/-37 ml/min (median 280 ml/min). The patients were divided according to the median value into groups I (Qb < 280, n = 28) and group II (Qb > 280, n =29). Results: Blood viscosity, patients' mean arterial pressure and venous catheter line pressure did not differ between the two groups. Pre-pump pressure, at the start and at the end of treatment, was higher in group I. ACT, AAT and previous infectious episodes could not explain the low-performance. Blood flows of catheters localized in RA, SVC, and in IVC were respectively 287+/-20, 268+/-39, 244+/-27 ml/min. In the first case the Qb was significantly higher than IVC (p = 0.03) and SVC (p = 0.04). In conclusion, the most important factor influencing blood flow rates seems to be the position of the catheter tip in the venous system. The best blood flows were found in catheters with the tip localized in the right cardiac cavities, while PLDC placed in inferior vena cava showed lower blood flow.     

Ultrafiltration method for measuring vascular access flow rates during hemodialysis.

BACKGROUND: The vascular access blood flow rate (QA) has been shown to be an important predictor of vascular access failure; therefore, the routine measurement of QA may prove to be a useful clinical method of vascular access assessment. METHODS: We have developed a new ultrafiltration (UF) method for determining QA during HD from changes in arterial hematocrit (H) after abrupt changes in the UF rate with the dialysis blood lines in the normal (DeltaHn) and reverse (DeltaHr) configurations. This method accounts for cardiopulmonary recirculation and requires neither intravenous saline injections nor accurate knowledge of the dialyzer blood flow rate. Clinical studies were conducted in 65 chronic HD patients from three different dialysis programs to compare QA determined by the UF method with that determined by saline dilution using an ultrasound flow sensor. RESULTS: Arterial H increased (P<0.0001) after abrupt increases in the UF rate when the lines were in the normal and reverse configurations. An increase in the UF rate from the minimum setting to 1.8 liter/hr resulted in a DeltaHn of 0.3+/-0.2 (mean +/- SD) H units and a DeltaHr of 1.6+/-1.0 H units. Q(A) values determined by the UF method (1050+/-460 ml/min) were 16+/-25% higher (P<0.001) than those determined by saline dilution (950+/-440 ml/min); the calculated QA values by the UF and saline dilution methods correlated highly with each other (R = 0.92, P<0.0001). The average coefficient of variation for duplicate measurements of QA determined by the UF method in a subset of these patients (N = 21) was approximately 10% when assessed in either the same dialysis session or consecutive sessions. CONCLUSIONS: The results from this study show that changes in arterial H after abrupt changes in the UF rate can be used to assess Q(A).     

The relationship between systemic and whole-body hematocrit is not constant during ultrafiltration on hemodialysis

The measurement of relative blood volume (RBV) changes during ultrafiltration assume a constant mass and distribution of circulating blood components such as hematocrit. The authors examine the validity of this assumption in 10 subjects undergoing repeated direct measurements of systemic hematocrit and plasma volume (PV(icg)) using indocyanine green dilution at four stages of dialysis with intermittent ultrafiltration. Ultrasonic RBV changes were monitored. Absolute blood volumes (ABV) were initially derived for each PV(icg) estimate, and corresponding measured systemic hematocrit was adjusted by a factor of 0.86 to correct for the difference between the systemic and whole-body hematocrit (constant Fcell ratio). PV(icg) and ABV changes correlated closely (R = 0.98; P <0.001). ABV changes overestimated reduction in PV(icg) during ultrafiltration (mean difference, -140 +/- 202 ml). The calculated red cell mass however was variable (P <0.01). Fcell ratio was then adjusted at each blood volume measurement (Fcell(1), 0.87 +/- 0.02; Fcell(2), 0.89 +/- 0.03; Fcell(3), 0.94 +/- 0.06; Fcell(4), 0.94 +/- 0.04; P <0.01) to maintain a constant red cell mass (2146 +/- 460 ml). When ABV was recalculated using PV(icg), systemic hematocrit and variable Fcell (ABV(Fvariable)), the mean difference between PV(icg) changes and ABV(Fvariable) changes, was negligible (-0.2 +/- 35 ml). During intermittent ultrafiltration, RBV changes systematically underestimated the percentage reduction in ABV (mean difference, 7.7 +/- 10.6%). When corrected for variations in Fcell, ABV(Fvariable) and RBV differences were negligible (mean difference 1.2 +/- 2.6%). Varying Fcell ratio probably reflects microvascular volume change with net fluid shift from the microcirculation to macrocirculation (intravascular refill). This may result in underestimation of changes in systemic hematocrit and RBV during dialysis such that they were less than those predicted by directly measured changes in plasma volume.     

Correlates of habitual physical activity in chronic haemodialysis patients.

BACKGROUND: Results of physical performance tests may not reflect the level of habitual physical activity and health status of the dialysis patients. The aim of our study was to assess interdialytic spontaneous physical activity in chronic haemodialysis (HD) patients in relation to their nutritional status, severity of anaemia, inflammation and dialysis adequacy. METHODS: Sixty HD patients [27 female, 33 male; mean age 60+/-13 years, time on dialysis 46.2+/-62.1 months and body mass index (BMI) 25.1+/-4.7 kg/m2] without physical and neurological disabilities and 16 healthy individuals (10 female, six male, mean age 56+/-6 years, BMI 26.6+/-4.9 kg/m2) were enrolled into the study. In all patients, spontaneous daily physical activity was measured during 48 h between mid-week dialysis sessions by pedometers. Nutritional status was estimated by anthropometric methods (BMI and mid-arm muscle circumference) and serum albumin concentration. Additionally, body composition was estimated using a multifrequency phase-sensitive bioimpedance analysis (BIA). Severity of anaemia was determined by blood haemoglobin level and haematocrit value, and the presence of inflammatory state was determined by high sensitivity plasma C-reactive (CRP) protein measurements. RESULTS: The total number of steps during daily activities in dialysis patients and in healthy individuals was 6896+/-2357 vs 14 181+/-5383 per 48 h, respectively (P<0.001). Dialysis patients showed typical signs of malnutrition in the BIA, i.e. high extracellular mass/body cell mass index (1.17+/-0.28 in dialysis patients vs 0.97+/-0.1 in controls; P<0.001), low percentage cell mass (46.7+/-5.6 and 51.0+/-3.6, respectively; P = 0.002) and low phase angle (5.1+/-0.9 and 5.8+/-0.7, respectively; P = 0.006). Dialysis patients also showed lower serum albumin and blood haemoglobin and higher serum CRP levels than healthy controls. In dialysis patients, the number of steps taken positively correlated with body water (R = 0.28, P = 0.03), fat mass (r = 0.29, P = 0.04), BMI (R = 0.25, P = 0.04), lean body mass (R = 0.26, P = 0.04), intracellular water (r = 0.30, P<0.01), phase angle (R = 0.40, P = 0.002), serum albumin (R = 0.32, P = 0.01), haematocrit (R = 0.46, P = 0.001) and haemoglobin (R = 0.44, P = 0.001). Furthermore, the number of steps taken correlated significantly with mid-arm muscle circumference (r = 0.35, P = 0.006). A negative correlation was found between the number of steps and extracellular mass/body cell mass index (R = -0.37; P = 0.004). No significant relationships were found between the measures of physical activity and high sensitivity CRP or adequacy of dialysis. Multiple regression analysis revealed the independent associations between the number of steps taken by the patients and haemoglobin concentration, age, total body water, extracellular mass/body cell mass index and phase angle. CONCLUSIONS: Low habitual physical activity assessed in HD patients with simple portable pedometers is strongly related to several factors of major clinical importance in this population.     

Systemic coagulation changes caused by pulmonary artery catheters: laboratory findings and clinical correlation

BACKGROUND: A higher rate of pulmonary embolism has been associated with pulmonary artery (PA) catheters; however, no mechanism has been described. Conventional tests of coagulation reveal no changes related to PA catheterization. The purpose of this study was to determine whether PA catheterization resulted in a hypercoagulable state detectable by thrombelastography (TEG). METHODS: Animal: Healthy, anesthetized, swine (n = 19) underwent PA catheterization. Samples were drawn from 7F femoral arterial catheters before and two hours after PA catheterization, at 5 mL/min, and analyzed (native whole blood, n = 15, kaolin activated blood, n = 4) by TEG (Hemoscope, Niles, IL) at precisely two minutes. Human: An IRB-approved prospective, observational trial was conducted in critically ill patients (n = 19). Samples were drawn from 22-gauge radial artery catheters, before and three hours after PA catheterization. Kaolin-activated TEG samples were analyzed at precisely five minutes. Data are mean +/- SE; Groups were compared with analysis of variance and significance was assessed at the 95% confidence interval. RESULTS: In both animals and patients, PA catheterization truncated R times (time to initial fibrin formation). In swine, the R times were 17.6 +/- 1.3 minutes (native) and 3.8 +/- 0.4 (kaolin) before PA catheterization, and decreased to 6.3 +/- 1.0 minutes (p = 0.002) and 1.9 +/- 0.5 minutes (p = 0.010) afterward. There were no changes in pH or temperature during the experiment. In patients, 4 of 19 were excluded for protocol violations. The R time was 6.3 +/- 1.0 minutes (kaolin) before and 3.0 +/- 0.3 minutes after catheterization (p = 0.003). No changes were observed in conventional coagulation parameters, temperature or pH. CONCLUSION: In healthy swine, and critically ill patients, PA catheters may enhance thrombin formation and fibrin polymerization, indicating a systemic hypercoagulable state. This may explain why PA catheters are associated with an increased risk of pulmonary emboli.     

Effect of cyclosporine on endothelial albumin leakage in rats.

Short-term treatment of rats with cyclosporine (cyclosporine A [CsA]; Sandimmune) results in a marked reduction in intravascular plasma volume, a factor that might contribute to the renal dysfunction associated with this potent immunosuppressant. To examine the role of plasma extravasation in CsA-induced hypovolemia, intravascular plasma volumes (PV), blood volumes, [125I]albumin disappearance, and changes in hematocrit (Hct) were measured in Inactin-anesthetized rats subjected to minimal surgery. The rats were treated for 3 wk with either 25 mg/kg/day of CsA s.c. or vehicle. Plasma creatinine and urea were significantly elevated, and magnesium was reduced in the CsA group (N = 6) as compared with controls (CON) (N = 6). CsA treatment had no effect on urinary protein and albumin excretion. Blood volume was significantly lower in CsA than in CON (8.4 +/- 0.5 versus 10.6 +/- 0.3 mL/100 g body wt) as was PV (4.3 +/- 0.2 versus 5.5 +/- 0.2 mL/100 g body wt). Two hours after injection, plasma [125I]albumin concentration had fallen by 41 +/- 4% in CsA versus 23 +/- 5% in CON. Because Hct, and, hence PV, was unchanged in both groups during these 2 h, these data indicate enhanced endothelial albumin leakage in the CsA group. In two additional groups of six rats each, acute volume expansion with fresh whole blood (2 mL/100 g body wt) resulted in extravasation of plasma. Hct rose by 8.0 +/- 0.2% in CsA versus 3.8 +/- 0.2% in CON after 150 min, corresponding to 27 +/- 3 and 15 +/- 2% decreases in total PV, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)