Prediction of radiographic severity of renal osteodystrophy by serum values

Renal osteodystrophy, a frequent complication of chronic renal failure, is usually assessed by periodic X-rays of bone which are both poorly reproducible and expensive. Seeking a better screening test for osteodystrophy, we evaluated the usefulness of serum alkaline phosphatase as a predictor of bone disease and of hyperparathyroidism. Alkaline phosphatase, despite nonspecificity, correlates with the severity of osteodystrophy and with the increase in serum parathyroid hormone concentration. Serial measurements of alkaline phosphatase can predict changes in these parameters.

Augmentation of peritoneal mass transport by dopamine: comparison with norepinephrine and evaluation of pharmacologic mechanisms

The effect of catecholamines on transport during peritoneal dialysis was studied in unanesthetized rabbits. Intravenous I-norepinephrine consistently decreased peritoneal clearances of urea and creatinine to 84% of control values or less but did not affect osmotically induced water flux. Comparable pressor doses of dopamine increased clearances of urea and creatinine to 145% of control values, whereas osmotic fluid flux increased only slightly. Dopamine also increased urea transport when administered intraperitoneally. The augmentation of solute transport by dopamine was unaffected by simultaneous administration of propranalol, was decreased by phentolamine, and was abolished by haloperidol. Dopamine may be preferable toI-norepinephrine when vasopressor therapy is required during peritoneal dialysis. The augmented transport with dopamine appears to depend on the action of dopamine receptors causing mesenteric vasodilation and in part on alpha-adrenergic receptors simultaneously increasing blood pressure while mesenteric blood flow is maintained.

Acceleration of peritoneal mass transport by drugs and hormones

The major restrictions to the transport of solute and solvent across the peritoneum are the limited peritoneal blood flow, area and permeability. Recent investigations have demonstrated that several vasoactive drugs influence transport parameters. Isoproterenol, nitroprusside, dipyridamole and dopamine exemplify drugs that dilate the splanchnic vasculature, thereby augmenting transport, whereas vasoconstriction induced by l-norepinephrine decreases clearances. The tissue prostaglandins affect peritoneal mass transport in accord with their known vasoactive effects, suggesting a role in modulating peritoneal blood flow. The gastrointestinal hormones vasodilate the splanchnic circulation. Exposure of the endothelial surface to glucagon markedly increases peritoneal mass transport, while secretin increases the ultrafiltration rate significantly. These preliminary studies suggest the possible future clinical use of drugs and hormones to augment the efficiency of peritoneal dialysis.

Prediction of solute transport during peritoneal dialysis

Solute transport, predominantly diffusion, across the peritoneum correlates inversely with molecular weight. Provided that the solute is water soluble, not protein bound, not of unusual density, not ionized, does not have a large hydration shell, and is transported from plasma to dialysate, the peritoneal clearance is predictable over the molecular weight range from 60 to 11,000 daltons. Transport reates that deviate from the predicted can be explained by known physical properties of particular solutes.

Effects of gastrointestinal hormones on transport by peritoneal dialysis

Because the gastrointestinal hormones are known to dilate the splanchnic vasculature, their effects on transport of water and solutes during peritoneal dialysis were studied in an experimental model, the rabbit. In unanesthetized rabbits, dialysate volume was calculated by isotope dilution, and clearances were estimated by dialysate/plasma concentration ratio factored by minute volume. With isotonic dialysis solution, the mean increment in dialysate volume per minute of intraperitoneal dwell was 0.19 ml/kg/min, and mean clearances of creatinine and urea were 0.71 and 0.90 ml/kg/min, respectively. When administered intravenously, secretin significantly augmented osmotically induced water flux, but not when given intraperitoneally. Neither glucagon nor cholecystokinin affected dialysate volume. Intravenously, but not intraperitoneally, glucagon increased peritoneal clearances of creatinine and urea to more than 150% of control values. Neither cholecystokinin nor secretin augmented significantly peritoneal mass transport when given by either route. The data suggest that the site of acton is the endothelial surface of the membrane, that the mechanisms of augmenting transport involve increased permeability and/or surface area, and that agents which combine an increase in mass transport and capillary filtration coefficient may be clinically useful.

Inconsistency in radiographic evaluation of progressive renal osteodystrophy

Five radiologists graded 49 series of bone X-rays of 20 patients with chronic renal failure treated by hemodialysis. There was a high incidence of osteodystrophy which progressed identifiably over intervals exceeding 12 months. The severity grade of osteodystrophy was poorly reproducible among patients, among radiologists, and even between interpretations by the same radiologist after an interval of 10 months. Although the severity of osteodystrophy correlated with serum alkaline phosphatase values, the latter was not an accurate predictor of the severity of the bone lesions. Radiographic reassessment at intervals of one year or less in the asymptomatic patient has less reproducibility than the anticipated changes. More sensitive and reliable techniques are recommended.

Divergent effects of catecholamines on peritoneal mass transport

In rabbits, intravenous vasopressor doses of dopamine augmented peritoneal clearances of creatinine and urea, suggesting increased mesenteric blood flow and possibly augmented permeability. Intraperitoneal dopamine also accelerated peritoneal transport of urea. Solute transport across the peritoneum was decreased by intravenous infusion of 1-norepinephrine. Intraperitoneal administration of the alpha-adrenergic antagonist phentolamine partially abolished the augmentation of peritoneal clearances induced by intravenous dopamine. The results suggest that in patients undergoing peritoneal dialysis who require vasopressor therapy, dopamine should be preferred to norepinephrine.

Therapy of iron deficiency anemia in patients on maintenance dialysis

A controlled, prospective study compared the effectiveness of oral ferrous sulfate to intravenous iron dextran, each with and without concurrent intramuscular androgen for therapy of iron deficiency anemia in patients with chronic renal failure treated with maintenance hemodialysis. During the 12-week period of therapy, the patients who received oral ferrous sulfate and androgens showed an increment in their mean hematocrit of 16.3% and those who received oral ferrous sulfate alone had an increase of 8.3%. Patients treated with intravenous iron dextran androgens showed an increment in their mean hematocrit of 9.4% and those given iron dextran alone showed an increase of 3.5%. Serum ferritin levels increased with iron repletion but correlated inversely with the erythropoietic response. The serum ferritin assay provides a simple and reliable method to demonstrate iron repletion, and oral ferrous sulfate is the preferred method of iron repletion in compliant patients.

Augmented peritoneal mass transport with intraperitoneal nitroprusside

Lightly restrained, alert New Zealand white rabbits underwent peritoneal dialysis by percutaneous instillation of standard dialysis solution with or without intraperitoneal nitroprusside. Corrected to a mean intraperitoneal dwell time of 36 minutes, mean clearances of creatinine and urea were 0.74 and 0.90 ml/kg/min in six rabbits. With intraperitoneal nitroprusside, 1.13 mg/kg clearances increased to 1.13 and 1.30 ml/kg/min (p less than 0.01) respectively. The 53% increment in creatinine clearance maintained the ratio clearance larger/smaller solute suggesting increased peritoneal permeability and/or area. Lower nitroprusside doses were less effective and not significantly above control. Nitroprusside also increased clearances during hypertonic peritoneal dialysis, but had no effect on osmotically induced water flux. Lavage studies demonstrated a persistent effect of nitroprusside after a single exposure and a sustained effect with repeated use.

Peritoneal dialysis in rabbits. A study of transperitoneal theophylline flux and peritoneal permeability

Since vasodilators can restore toward normal the decreased peritoneal clearances associated with vascular disease, the influence of aminophylline on peritoneal solute transport was studied in unanesthetized rabbits. Mean control creatinine clearance was 0.56 ml/kg/min and urea clearance 0.80 ml/kg/min. Neither intraperitoneal nor intravenous aminophylline increased peritoneal clearances, nor did the ratio creatinine clearance/urea clearance change from the control value, 0.70. Bidirectional flux of theophylline occurred at clearances of 0.70 ml/kg/min efflux and 0.64 ml/min influx. The removal rate of theophylline was 0.05% min, allowing therapeutic removal of excess aminophylline and warranting supplemental therapy during dialysis if therapeutic theophylline concentrations are required. As the intraperitoneal aminophylline was well tolerated, this route can be considered for therapeutic administration.

Principles of dialysis and dialysis of drugs

Consideration of the interactions of drugs and dialysis must include an understanding of the mechanisms of transport during dialysis, i.e., diffusion, ultrafiltration and membrane-protein binding effects. Clearance is a function of molecular size, blood and dialysate flow, membrane area and permeability, and dialyzer support geometry. Protein binding and hematocrit decrease the in vivo clearances in comparison to those measured in vitro with aqueous solutions. The effect on the serum half-life is also determined by the distribution space and clearance by other routes. Other factors such as metabolic alterations of dialysis can affect pharmacologic activity, and the clinical response is the end product of many determinants. Numerous drugs are effectively removed by hemodialysis or at a slower rate by peritoneal dialysis, which occasionally allows considerable influx. The influence of intestinal contents on elimination rates by peritoneal dialysis is unknown. Peritoneal dialysis can be influenced considerably by vasoactive drugs.

Effect of intraperitoneal diuretics on solute transport during hypertonic dialysis

Hypertonic periotoneal dialysis in New Zealand white rabbits results in increased dialyzate volume, but the sodium content of net ultrafiltrate is 109.5 MEq/l, less than extracellular fluid sodium concentration. With intraperitoneal furosemide, mean net ultrafilrate sodium concentration increased significantly to 121.2 mE1/l while ethacrynic acid had no such effect and both drugs affected dialyzate volume very slightly. Hypertonic peritoneal dialysis increased urea clearance significantly above isotonic dialysis and the addition of ethacrynic acid increased clearances further (P LESS THAN.02). Added furosemide decreased urea clearances suggesting that the effect on sodium transport is not an overall permeability change. During isotonic peritoneal dialysis, furosemide increased peritoneal permeability, i.e. urea and creatinine clearances, but a significantly higher urea clearance resulted from intraperitoneal ethacrynic acid. Furosemide influx clearance average 0.31 ml/kg/min, a mean of 27 percent of the urea clearance. The data suggest that furosemide may be useful to prevent the hypernatremia that may complicate hypertonic peritoneal dialysis, but is not as efficacious as other vasoactive drugs in enhancing peritoneal permeability.

Isoproterenol enhancement of peritoneal permeability

As peritoneal dialysis is inefficient enouth to be time-consuming and sometimes clinically ineffective, we have evaluated pharmacologic enhancement of peritoneal permeability. Peritoneal dialyses were performed in New Zealand white rabbits by instillation of 50 ml/Kg of isotonic dialysis solution of standard composition. Mean peritoneal clearance of creatinine was 0.60 ml/Kg/min and urea was 0.80 ml/Kg/min, each decreasing as intraperitoneal dwell was prolonged (by .011 ml/Kg/min or less). With 0.04 micrometer/Kg of isoproterenol administered intraperitoneally, clearances increased to 0.91 and 1.30 ml/Kg/min (p less than 0.01). When isoproterenol was added to the dialysis solution one hour or more before instillation, the increment in clearances was less. Instillation of dialysis solution 24 hours after addition of a higher dose of isoproterenol (0.2 micrometer/Kg) did not increase clearances above control. No effect of isoproterenol on bulk flow of water, associated with the osmotic effect of dextrose, was demonstrated. As peritoneal clearances increased, the ratio creatinine clearance: urea clearance did not decrease, consistent with increased peritoneal permeability as well as blood flow.

Detrimental effects of ultrafiltration on diffusion in coils

Previous studies in dialysis coils have suggested decreases in diffusive transport with ultrafiltration. The present studies were designed to test whether increasing blood channel width, alterations in concentration gradients, or molecular sieving at high ultrafiltration rates might explain the phenomenon. Increases in blood channel width and molecular sieving can account only in part for the decreases in diffusion observed. The results suggest that ultrafiltration causes alterations in transmembrane concentration gradients from blood to bath presumably associated with solute accumulation on the bath side of the membrane or may alter bath flow kinetics. Increases in total dialysance with ultrafiltration would be even greater if decreases in diffusive transport could be prevented.

When should maintenance dialysis be initiated?

The present trend towared the use of maintenance dialysis in earlier stages of chronic renal failure, and more frequently in association with other morbid illness, raises the question of how well we understand the natural history and prognosis of chronic renal failure prior to total loss of renal function. Survival after serum creatinine exceeds 10 mg/dl is not necessarily very brief and is influenced by many variables. Morbidity and rehabilitation are poorly defined terms that should be approached as objectively and quantitatively as possible if the benefits of dialysis are to be assessed meaningfully.

The clinical spectrum of ascites associated with maintenance dialysis

Among 197 patients being treated with maintenance dialysis, six were found to have ascites. Unlike previous reported series, the cause of ascites and the clinical course were variable. Two patients responded to definitive therapy directed against the specific cause. No consistent association was found with the etiology of renal disease or therapy of uremia including the duration of hemodialysis or prior peritoneal dialysis. Nonspecific therapy attempting to alleviate ascites was unsatisfactory. Severe hypertension was not characteristic and bilateral nephrectomy did not influence the course. An extensive diagnostic evaluation is recommended along with skepticism before declaring that idiopathic, refractory ascites exists signaling progressive deterioration.

Dialysance and clearance measurements during clinical dialysis-a plea for standardization

Mass transfer and dialysance measurements were determined using (1) whole blood solute concentrations with blood flow rates, (2) plasma solute concentrations with plasma flow rates, and (3) plasma solute concentrations with whole blood flow rates by standard formulas during 30 clinical hemodialyses. Resulting values by these three methods were compared for potassium, urea, and creatinine. The three techniques yield significantly different values and, accordingly, the type of measurement must be specified before such clinical measurements of solute transport are interpretable. Multiple mechanisms to account for the differences are suggested and include minimal or no immediate effect of a single coil blood transit on intracellular solute concentrations for all solutes studied.

NaHCO3 and NaC1 tolerance in chronic renal failure

In patients with chronic renal failure, NaHCO3 therapy may correct or prevent acidemia. It has been proposed that the NaHCO3 required will not result in clinically significant Na retention comparable to that from similar increases in NaC1 intake. In each of ten patients with chronic renal failure, creatinine clearance (Ccr) range 2.5-16.8 ml/min, on an estimated 10-meq Na and C1 diet, electrolyte excretion was compared on NaHCO3 vs NaC1 supplements of 200 meq/day. Periods of NaHCO3 and NaC1 (in alternate order for successive patients) lasted 4 days, separated by reequilibration to base-line weight. Mean +/- SEM excretion (ex) of Na, C1, and HCO3 and deltaCcr and deltaweight (day 4-1) are compared below for the 4th day of NaC1 vs. NaHCO3 intake. Mean Ccr +/-SEM on day 4 of NaC1 and NaHCO3 were 10.8 +/-1.6 and 9.0 +/-1.4 ml/min, respectively (P less than 0.02). Mean systolic blood pressure (but not diastolic) increased significantly on NaC1 (P less than 0.05). No significant blood pressure changes were seen on NaHCO3. Net positive HCO3 balance occurred on NaHCO3 as indicated above and reflected a rise in mean serum HCO3 from 19 to 30 meq/liter (day 1 vs. 4) (P less than 0.01). Mechanisms for the greater excretion of Na on NaHCO3 may relate to C1 wasting as noted above on low C1 intake and limited HCO3 reabsorptive capacity. Thus, Na excretion by day 4 was greater on NaHCO3 than on NaHCO3 did Na excretion near intake (210 meq/day).

Effect of hemodialysis on factors influencing oxygen transport

Ten patients underwent 4 study hemodialyses, one with standard dialysis conditions, one with an isophosphate dialysate, one with simultaneous ammonium chloride loading, and other, after pretreatment, with sodium bicarbonate. Measurement of hemoglobin oxygen affinity (P-50), erythrocyte 2,3-DPG, blood-gasses, and serum chemistries revealed biochemically effective hemodialyses and slight changes in oxygen transport parameters. The P-50 (in vivo) values decreased slightly but significantly (p greater than 0.05) with dialysis. When corrected to pH 7.4, eliminating the Bohr effect, P-50 increased (p greater than 0.05). With unmodified dialysis elevated values of 2,3-DPG (in comparison to normal) decreased, a change that did not correlate with delta-p-50, delta-serum phosphate, or delta-serum creatinine. With standard and isophosphate dialyses Po-2 decreased significantly. The decrease correlated with delta-hydrogen ion concentration and did not occur with dialyses designed to maintain pH constant. Thus, hemodialysis influences many factors that affect oxygen transport in different and counterbalancing directions. These changes are not totally explained by alterations in 2,3-DPG, pH or serum phosphate. Maintenance of acidosis or hyperphosphatemia during dialysis is not recommended.