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.     

Effects of oxygen breathing and erythropoietin on hypoxic vasodilation in uremic anemia.

Loss of hypoxic vasodilation has been proposed as a causative factor in the development of hypertension in dialysis patients treated with recombinant human erythropoietin (rHuEPO). Venous occlusion plethysmography was therefore performed on 22 dialysis patients (aged 23 to 71 years, dialysis duration 6 to 260 months, 8 males) before and after correction of anemia with rHuEPO, 50 U/kg 3x/week (Hb: 7.4 +/- 0.3 vs. 10.8 +2- 0.3 g/dl, P less than 0.0001). Hypertension (greater than 15 mm Hg rise in mean BP) occurred in 11 patients. The study was performed while breathing room air and repeated after breathing 60% O2 for 10 to 12 minutes. Before rHuEPO therapy, total blood O2 content increased from 10.01 +/- 0.39 to 10.32 +/- 0.29 ml O2/100 ml blood with breathing 60% O2 (P less than 0.01). After correction of anemia it was 14.65 +/- 0.40 ml O2/100 ml blood on room air (P less than 0.001). There was a significant decrease in forearm blood flow (7.9 +/- 0.5 vs. 6.5 +/- 0.6 ml/min/100 ml tissue, P less than 0.05) and increase in forearm vascular resistance (12.8 +/- 0.1 vs. 16.8 +/- 0.2 mm Hg/ml/min/100 ml tissue, P less than 0.05) with O2 breathing prior to rHuEPO therapy in the blood pressure responders, but no change in these parameters in the group in which blood pressure remained unchanged. When all patients were studied on room air, forearm vascular resistance rose significantly after correction of anemia (13.0 +/- 0.8 vs. 16.3 +/- 0.8 mm Hg/ml/min/100 ml tissue, P less than 0.05), compared with that prior to rHuEPO therapy.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Mechanisms of improvement of water and sodium excretion by immersion in decompensated cirrhotic patients

Eight patients with alcoholic liver disease, ascites, and edema were found to have impaired water (36 +/- 6% in 5 hr) and sodium (3.9 +/- 1.1 mEq/5 hr) excretion during a 20 ml/kg water load. These patients were submitted to a 5-hr head-out water immersion (HWI) with hemodynamic monitoring (Swan-Ganz). HWI increased cardiac index (3.3 to 4.2 liters/min/m2), right atrial pressure (RAP, 3.9 to 9.0 mm Hg), and wedge capillary pulmonary pressure (9.8 to 15.4 mm Hg) (all P less than 0.01). HWI decreased plasma renin activity (6.4 to 4.5 ng/ml/hr, P less than 0.001), aldosterone (73 to 43 ng/dl, P less than 0.001), arginine vasopressin (AVP, 1.03 +/- 0.15 to 0.76 +/- 0.08 pg/ml, P less than 0.005), norepinephrine (NE, 584 to 435 pg/ml, P less than 0.001) and increased the percentage of water load excreted (36 to 63%, P less than 0.005) and urinary sodium excretion (3.9 to 9.7 mEq/5 hr, P less than 0.05). The percentage of water load excreted was inversely correlated to AVP levels (r = 0.52, P less than 0.05) and directly correlated to RAP (r = 0.74, P less than 0.05). A significant positive correlation was also found between the increase in fractional excretion of sodium (delta FENa) and the increase in RAP (r = 0.77, P less than 0.001). FENa also correlated inversely with NE levels (r = 0.56, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The determination of hemodialysis blood recirculation using blood urea nitrogen measurements.

The determination of blood recirculation using blood urea nitrogen (BUN) measurements in hemodialysis patients is a standard technique. The accuracy and reproducibility of these calculations have never been determined. Two pairs of recirculation studies (study A and study B) were performed in 13 patients during a single dialysis treatment. Blood samples were analyzed for BUN and recirculation was calculated. The first recirculation study (study A) was performed within 1 hour of the initiation of dialysis, with a duplicate test of recirculation performed within 15 minutes. In study B, the dialyzer blood lines were reversed in an attempt to enhance blood recirculation. After 15 minutes, duplicate tests of recirculation were again performed. Calculated recirculations before the line reversal (study A) ranged from -3.3% to 11.9% in the first test and -2.9% to 12.2% in the second test. In study A, there was no correlation (P > 0.05, r = 0.09) between the first and second calculated recirculations. In study B, an increase in recirculation was observed. Calculated recirculations ranged from 16.3% to 53.5% for the first test and 5.4% to 58.1% for the second test. A significant relationship was observed in the calculated recirculation in study B (P < 0.05, r = 0.81). The results from the present study show that the use of BUN measurements may not provide a consistent indicator of access recirculation in a patient with a low recirculation. This lack of consistency should be considered when determining further clinical treatment.     

Severe dialyzer dysfunction undetectable by standard reprocessing validation tests

It is generally accepted that careful monitoring of total cell volume and ultrafiltration rates will ensure adequate function of reprocessed dialyzers. During routine urea kinetic measurements we noted that the percent of patients with clearances less than 200 ml/min increased from 5% to 48% despite adherence to these validation tests. As these patients did not have evidence of recirculation in the vascular access, possible causes of dialyzer dysfunction were investigated. Injection of methylene blue into the dialysate port revealed non-uniform flow of dialysate in dialyzers from patients with markedly reduced clearances. In vitro studies of dialyzers subjected to sequential daily reprocessing, without patient exposure, demonstrated that in vitro clearances declined in one lot but not another. The initial clearances of 218 +/- 4 ml/min fell progressively to 112 +/- 18 (P less than 0.001) after 15 reuses. No effects of reprocessing were found in a different lot (230 +/- 2 vs. 226 +/- 4 ml/min). Soaking the dialyzers from the affected lot in either the disinfectant or dialysate solution caused a decline in the clearances which was less than that of serial reuse. Although the magnitude of the problem of dialyzer malfunction with reuse is unknown, careful attention to dialyzer function is warranted in patients treated with reprocessed dialyzers.     

Blood flow limitation in vivo of small solute transfer during peritoneal dialysis in rats

The aim of this study was to determine whether or to what extent transperitoneal flux of small solutes is reduced at low blood flows during peritoneal dialysis (PD) in rats. Peritoneal blood flow reductions were achieved by bleeding anesthetized (300 g) rats by 25% of their blood volume. After bleeding, a 2 h PD dwell was started using standard PD fluid. The permeability-surface area product (PS) for (51)Cr-EDTA and glucose were assessed, as well as the transperitoneal clearance (Cl) of albumin. Control animals were not bled. After bleeding, peritoneal blood flow declined from 145 +/- 17 perfusion units (PU) to 59 +/- 12 PU (P = 0.001). Concomitant with this reduction, PS for (51)Cr-EDTA fell from 0.284 +/- 0.01 ml/min to 0.216 +/- 0.01 ml/min (P = 0.006) and PS for glucose from 0.338 +/- 0.02 ml/min to 0.294 +/- 0.01 ml/min (P = 0.046). Mean arterial BP (MAP) dropped from 133 +/- 4 mmHg to 61 +/- 5 mmHg (P = 0.008). Cl of albumin fell largely in proportion to the estimated capillary hydrostatic pressure drop, i.e., from 6.1 +/- 0.7 microl/min to 2.3 +/- 0.3 microl/min (P = 0.001). The results demonstrate that the transperitoneal clearances of small solutes are blood flow limited during PD, when peritoneal perfusion is markedly reduced. The level of flow limitation was, however, much lower than expected and observed in other tissues. Albumin transport, which is not blood flow limited, was reduced largely in proportion to the calculated capillary hydrostatic pressure decrease.     

Cuprophan reuse and intradialytic changes of lung diffusion capacity and blood gases

The changes in arterial blood gas, pulmonary function tests, leukocyte counts and complement activation were evaluated during first use and subsequent reuse of cuprophan dialyzers. The dialysate buffer was bicarbonate. Reuse of cuprophan dialyzers significantly attenuated the fall in leukocyte counts and the rise in C3a des Arg seen during first use dialysis. First use dialysis also caused a drop in arterial paO2 from 93.0 +/- 12.4 mm Hg to a nadir of 82.8 +/- 12.6 mm Hg at 60 minutes (P less than 0.01). PaO2 levels did not change when reused dialyzers were employed (93.7 +/- 12.2 before dialysis and 96.4 +/- 15.2 mm Hg at 60 minutes, P greater than 0.05). Intradialytic paO2 curves obtained during first use and reuse were significantly different by variance analysis (P less than 0.001). There was also a significant decline in lung diffusion capacity (DLCO, from 30.70 +/- 8.89 to 23.77 +/- 7.76 ml/min X mm Hg, P less than 0.01) and transfer factor (KCO, from 6.07 +/- 1.97 to 5.65 +/- 2.13 ml/min X mm Hg, P less than 0.01), during first use at one hour after initiation of dialysis. This decrease was entirely prevented during reuse, (P less than 0.001 vs. first use by variance analysis). Percentual changes in leukocyte counts and C3a des Arg concentration on one hand, and in paO2, DLCO and KCO on the other were significantly correlated to each other. Other factors with a possible influence on intradialytic pulmonary function such as ultrafiltration volume, dialysate buffer composition, evolution of intradialytic blood pH and cardiac output, were all identical under both experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Delayed hypotensive response to dialysis in hypertensive patients with end-stage renal disease

This study was designed to determine the ambulatory arterial blood pressure profile in hypertensive patients with end-stage renal disease during and following hemodialysis. Blood pressure was noninvasively monitored at 15-min intervals for 24 h using a fully automatic portable recorder, while the 10 patients studied followed their customary activities and were not receiving any antihypertensive medications. Prior to dialysis, the blood pressure was 179 +/- 7.0/101 +/- 3.7 mm Hg. After 4 h of dialysis, the systolic blood pressure did not change, while the diastolic blood pressure fell only slightly (178 +/- 4.2/94 +/- 2.4 mm Hg). After dialysis was completed, a progressive fall in both systolic and diastolic blood pressures was observed reaching the lowest value in the 5th h after dialysis (146 +/- 5.5/75 +/- 3.2 mm Hg). Thereafter, the fall in blood pressure was sustained during sleep (147 +/- 1.7/77 +/- 0.9 mm Hg) and during routine daily activities (147 +/- 2.0/78 +/- 1.0 mm Hg). The delayed fall in blood pressure was observed in patients in whom the plasma renin activity was elevated (8.4 +/- 2.4 ng/ml/h) and in patients in whom the plasma renin activity was low or normal (0.9 +/- 0.2 ng/ml/h). Our data suggest that during dialysis vasopressor mechanisms are activated to sustain blood pressure and that following dialysis such mechanisms are attenuated allowing the blood pressure to fall towards normal levels. The delayed fall in blood pressure documented by this study indicates that in many hypertensive patients with end-stage renal disease antihypertensive drug therapy is not required the day after dialysis.     

Renal handling of urea in subjects with persistent azotemia and normal renal function

Fourteen subjects with persistent azotemia and normal glomerular filtration rate were studied by renal clearances and hormonal determinations to establish the nephron site of altered urea transport and the mechanism(s) responsible for their azotemia. During constant alimentary protein, urea nitrogen appearance was normal and urea clearance was much lower than in 10 age-matched control subjects (23.3 +/- 2.1 ml/min and 49.6 +/- 2.6 ml/min per 1.73 m2, P less than 0.001). Inulin and para-aminohippurate clearances, blood volume and plasma concentration of antidiuretic hormone were within normal limits. During maximal antidiuresis, in spite of greater urea filtered load, the urinary excretion of urea was less, and both the maximum urinary osmolality and the free-water reabsorption relative to osmolar clearance per unit of GFR were greater than in control subjects. After sustained water diuresis, the plasma urea concentration markedly decreased to near normal levels in azotemic subjects. The basal urinary excretion of prostaglandins E2 was significantly reduced in azotemic subjects and was directly correlated with fractional urea clearance (r = 0.857, P less than 0.001). An additional group of control subjects (N = 8) showed a marked reduction of fractional clearance of urea after inhibition of prostaglandin synthesis (P less than 0.01). These data suggest that azotemia is due to increased tubular reabsorption of urea in the distal part of nephron, presumably because of increased back diffusion in the papillary collecting duct, accounting for the enhanced maximum urinary osmolality and free-water reabsorption. Renal prostaglandin E2 may participate in the pathogenesis of azotemia by altering recycling of urea in the medulla.     

Hypotension and hypertension as consequences of baroreceptor dysfunction following carotid endarterectomy.

Arterial pressure regulation is often labile following carotid endarterectomy. Hemodynamic data from 100 consecutive endarterectomies allowed definition of three distinct postoperative blood pressure responses. A hypotensive response (group I) affected 28 patients in whom mean arterial pressure decreased from 168 +/- 29/90 +/- 15 mm Hg before operation to 110 +/- 21/68 +/- 16 mm Hg after operation (P less than 0.001). Maximum hypotension occurred 5.3 hours after endarterectomy. The preoperative pulse, 80 +/- 9 beats/min, fell to a low of 64 +/- 12 beats/min after operation (P less than 0.001). A significant hypertensive response (group II) affected 19 patients in whom mean blood pressure rose from 160 +/- 29/87 +/- 15 to 223 +/- 32/110 +/- 22 mm Hg (P less than 0.001). Maximum hypertension was noted 2.3 hours after endarterectomy. This was unaccompanied by significant pulse changes. Fifty-three patients remained normotensive (group III). Their preoperative blood pressure (150 +/- 14 mmHg). Fluctuations in pressure did not correlate with age, indication for operation, or degree of ipsilateral and contralateral carotid arterial stenosis. Postendarterectomy hypotension and hypertension appear to represent transient baroreceptor dysfunctions.     

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.     

Relationship between urea clearance and ionic dialysance determined using a single-step conductivity profile

BACKGROUND: On-line determination of ionic dialysance (ID) has been used to measure the clearance of small solutes like urea. However, attempts to determine the in vivo relationship between ID and urea clearance have led to discordant findings. The aim of this study was to determine the relationship between the mean values of repeated instantaneous determinations of ID throughout a dialysis session ((m)ID), obtained using a single-step inlet dialysate conductivity profile, and the mean values of urea clearance corrected for access recirculation (K(eu1)), total recirculation (access plus cardiopulmonary recirculation, K(eu2)), and the entire postdialysis urea rebound (K(wb)). METHODS: Eighty-two anuric patients on chronic thrice-weekly hemodialysis were studied using an Integra machine equipped with the Diascan module for the automatic determination of ID. The mean values of repeated ID measurements made at 30-minute intervals were compared with K(eu1) (available for only 31 patients), K(eu2), and K(wb). RESULTS: The results in all 82 patients were: (m)ID = 176 +/- 23 mL/min; K(eu2) = 181 +/- 25 mL/min; K(wb) = 159 +/- 22 mL/min. The mean (m)ID/K(wb) and (m)ID/K(eu2) ratios were, respectively, 1.11 +/- 0.06 and 0.98 +/- 0.06. The results in the 31 patients for whom K(eu1) values were available were: (m)ID = 179 +/- 24 mL/min and K(eu1) = 200 +/- 27 mL/min; the mean (m)ID/K(eu1) ratio was 0.90 +/- 0.05. CONCLUSION: The mean value of repeated ID determinations obtained using a single-step conductivity profile underestimates urea clearance corrected for access recirculation, and may be considered an adequate estimate of urea clearance corrected for total recirculation.     

Renal, metabolic and hormonal responses to ingestion of animal and vegetable proteins

Renal and hormonal responses were studied in a group of healthy individuals fed, in random order, for three weeks, a vegetable protein diet (N = 10), an animal protein diet (N = 10), or an animal protein diet supplemented with fiber (N = 7), all containing the same amount of total protein (chronic study). In seven additional subjects the acute renal, metabolic and hormonal response to ingestion of a meat or soya load of equivalent total protein content was investigated (acute study). In the chronic study GRF, RPF and fractional clearance of albumin and IgG were significantly higher on the animal than the vegetable protein diets (GFR: 121 +/- 4 vs. 111 +/- 4 ml/min/1.73 m2, P less than 0.001; RPF: 634 +/- 29 vs. 559 +/- 26 ml/min/1.73 m2, P less than 0.001; theta alb: 19.5 +/- 3.1 vs. 10.2 +/- 1.6 x 10(-7), P less than 0.01; theta IgG: 11.6 +/- 3.1 vs. 7.5 +/- 1.7 x 10(-7), P less than 0.05). Renal vascular resistance was lower on the animal than vegetable protein diet (82 +/- 5 vs. 97 +/- 5 mmHg/min/liter; P less than 0.001). Fiber supplementation to APD did not have any effect on the renal variables measured which were indistinguishable from APD. In the acute study, GFR and RPF both rose significantly by approximately 16% (P less than 0.005) and approximately 14% (P less than 0.05), respectively, after the meat load, while RVR fell by approximately 12% (P less than 0.05). There were no significant changes in these parameters following the soya load.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of low flow, low pressure pulsatile bypass

The effects of low flow low pressure pulsatile bypass were studied in 90 consecutive patients undergoing coronary artery surgery. Overall pump flow rate (OFR) was 19-49 (mean 31 +/- 7) ml/kg/min at all temperatures. Moderate (28 degrees C) hypothermia was used. When cross-clamped flow was 17-49 (mean 27 +/- 7) ml/kg/min and mean perfusion pressure 50-60 mmHg. Priming volume (PV) was reduced to 1.45 +/- 0.02 L (range 1.2-2.0 L) PV, cardioplegia and volume additions were considered as total bypass crystalloid (TBC) and this correlated positively with increased post-operative positive water balance (r = 0.58, P less than 0.001). Bypass urine output averaged 135 +/- 24 ml (range 0-1,000 ml) was unrelated to OFR and correlated only with TBC (r=0.47, P less than 0.001). In 86 a single cardioplegia dose of 0.7 L (range 0.4-0.8 L) sufficed for this ischaemic period (mean 46 +/- 16 min). Four required a further 0.2-0.3 L. Their ischemic times were 44-74 min (mean 59 +/- 13 PNS). Inotropes were used in only 3 patients. Post-operatively 7 required diuretics for low hourly urine flow. Of the 76 with normal pre-operative renal function urea rose transiently in 15. Three had raised urea for over 9 days. Creatinine rose transiently in 7 but persisted in only one. Plasma cortisol (n=78) rose in 67 and fell in 11, indicating, overall, an adequate metabolic response. Plasma free haemoglobin before and after bypass varied widely and did not correlate with flow rate or perfusion time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ionic dialysance vs urea clearance in the absence of cardiopulmonary recirculation.

BACKGROUND: Several studies have shown a slight discrepancy between ionic dialysance (D) and dialyser urea clearance (UK), even in the absence of access recirculation. As it has been suggested that this discrepancy could be due to the cardiopulmonary recirculation, we studied the relationship between these two parameters in a particular dialysis setting without cardiopulmonary recirculation. METHODS: Paired measurement of urea clearance and ionic dialysance were performed in five patients without arterio-venous access who were dialysed via an internal jugular vein twin catheter. Fifty paired measurements were used for statistical analysis. Vascular access recirculation was assessed by an ultrasound dilution technique. The measured value of ionic dialysance was corrected (D(0)) for the effect of vascular access recirculation and was compared with instant urea clearance calculated from the dialysate side. RESULTS: The difference between the paired measurements of D(0) and UK (n=50) was equal to 0.6+/-16.9 ml/min (NS). With a statistical power of 90% and taking into account this standard deviation, this study might have shown a difference of at least 10.9 ml/min. The correlation was highly significant (P<0.0001). The discrepancy of the two parameters varied with dialysis efficiency, with a decreasing D(0):UK ratio for the higher dialysis efficiency. CONCLUSIONS: Compared with our previous results obtained in patients dialysed on arterio-venous access and performed with similar methods, the relationship between D(0) and UK is modified. This difference between D(0) and UK gets lower in patients dialysed on central catheters and this variance is in accordance with that expected when the influence of the cardiopulmonary recirculation on the measurement of ionic dialysance is taken into account. The limits of agreement (+/-2 SD) between D(0) and UK (+/-34 ml/min, Bland-Altman analysis) were higher than expected and raised questions about the accuracy of the measurement of each parameter via a central venous catheter.     

Recirculation Measures with Urea and Mannitol During Hemodialysis

Abstract: A simple, accurate, and reproducible method of measuring recirculation in grafts during hemodialysis is essential for improving the efficiency of dialysis. In our studies, plasma samples for plasma urea nitrogen (PUN) were taken from the arterial line of the dialyzer at blood flows (A) of 200, 300, and 400 ml/min, preceded by a 5–min period of equilibration, and at 15 s and 2 min after turning the flow down to 100 ml/min (S), the latter serving as systemic samples. Recirculation was calculated as (S – A)/(S – V). Total blood flow (Q_b) through the grafts was measured by color Doppler ultrasound. We found a significant, inverse relationship between recirculation and total flow through the graft at dialyzer Q_b of 400 but not 300 or 200 ml/min. The magnitude and prevalence of recirculation was always greater when the 2 min sample was used as S compared to the 15 s sample and as dialyzer Q_b increased. As a qualitative, urea–independent measure of recirculation, we assayed the appearance of mannitol in the arterial line in blood drawn 15 s after initiating a mannitol push into the venous line. Blood obtained just prior to the mannitol push was used as the zero blank. Thirteen of 18 patients had a measurable, but low, level of mannitol, 5 did not, and 2 had inconsistent results in studies done on separate days. We conclude that the majority of patients receiving chronic hemodialysis have a low degree of recirculation and that methods relying on urea must be suspected of exaggerating the true degree of recirculation.     

Progression of chronic renal failure on substituting a ketoacid supplement for an amino acid supplement.

Twelve patients with severe chronic renal failure (average initial GFR, 13 mL/min) were monitored for 4 to 23 months while receiving an essential amino acid supplement and were then switched to a ketoacid supplement for 6 to 40 months, while continuously receiving a very low-protein (0.3 g/kg), low-phosphorus (7 to 9 mg/kg) diet. Urinary urea N excretion indicated that actual dietary protein intake averaged 0.46 g/kg. Progression, estimated as the linear regression slope of radioisotopically determined GFR on time, slowed from -0.46 +/- 0.31 (SD) to -0.24 +/- 0.15 mL/min/month (P = 0.029). Serum urea N, creatinine, phosphate, and uric acid rose significantly as GFR fell; blood pressure, plasma lipids, and urinary urea excretion were unchanged. Urinary 17-hydroxy-corticosteroid excretion decreased 18%, but this change was only marginally significant (P = 0.087). There was no change in plasma or urinary cortisol or urinary aldosterone. Viewed in light of previous evidence that progression seldom slows when treatment remains constant, the results suggest that this ketoacid supplement slows progression by approximately half, compared with an essential amino acid supplement, with no change in diet.