Urinary osmolal changes in renal dysfunction following open-heart operations

Detection of evolving acute tubular necrosis with renal 23Na MRI: studies in rats

The clinical detection of evolving acute tubular necrosis (ATN) and differentiating it from other causes of renal failure are currently limited. The maintenance of the corticomedullary sodium gradient, an indicator of normal kidney function, is presumably lost early in the course of ATN. Herein, sodium magnetic resonance imaging (23Na MRI) was applied to study the early alteration in renal sodium distribution in rat kidneys 6 h after the induction of ATN. Three-dimensional gradient echo sodium images were recorded at 4.7 T with high spatial resolution. ATN was produced by the administration of radiologic contrast medium, combined with inhibition of nitric oxide and prostaglandin synthesis. The sodium images revealed that the sham-controlled kidney exhibited a linear increase in sodium concentration along the corticomedullary axis of 30+/-2 mmol/l/mm, resulting in an inner medulla to cortex sodium ratio of 4.3+/-0.3 (n=5). In the ATN kidney, however, the cortico-outer medullary sodium gradient was reduced by 21% (P<0.01, n=7) and the inner medulla to cortex sodium ratio was decreased by 40% (P<0.001, n=7). Small, though significant, increments in plasma creatinine at this time inversely correlated with the decline in the corticomedullary sodium gradient. Histological findings demonstrated outer medullary ATN involving 4% of medullary thick ascending limbs. Hence, 23Na MRI non-invasively quantified changes in the corticomedullary sodium gradient in the ATN kidney when morphologic tubular injury was still focal and very limited. MRI detection of corticomedullary sodium gradient abnormalities may serve to identify evolving ATN at its early phases.

Renal function changes after elective cardiac surgery with cardiopulmonary bypass

Cardiac surgery can either induce acute renal failure or improve GFR by improving the cardiac performance. In order to study renal function changes after elective cardiac surgery (CS) with cardiopulmonary bypass (CPBP), 21 patients undergoing valvular CS (VCS) or coronary artery bypass (CAB) were prospectively evaluated in three time periods: before, 24 hours after surgery and 48 hours after surgery. Patients were divided in 2 groups according to the GFR percent change in comparison to the baseline value found 24 hours after CS (deltaGFR24): Group 1, deltaGFR24 decrease higher than 20% (n = 11) and Group 2, deltaGFR24 decrease < or = 20% or deltaGFR24 increase (n = 10). In Group 1, 73% of the patients underwent VCS (p = 0.05 vs. Group 2) and all of them had previous VCS in sharp contrast with Group 2, where none of the patients had previous CS (p = 0.006). Patients in Group I required more volume replacement than Group 2 during the first 24 hours after CS: 2,699+/-704 mL versus 217+/-603 mL respectively, p = 0.019. Despite similar baseline GFR, Group 1 presented lower GFR 24 hours after CS when compared to Group 2 (39+/-5 versus 75+/-8 mL/(min x 1.73m2), p = 0.001) and a significantly different deltaGFR 48 hours after CS as compared to Group 2 (-21+/-11 versus +88+/-36%, p<0.01). Baseline sodium fractional excretion (FENa) in Group 1 was lower than in Group 2 (0.27+/-0.04 versus 0.70+/-0.12%, p = 0.01). No changes were observed after CS in urinary osmolality (Uosm) and urinary pH (UpH) in both groups. The deltaGFR24 showed positive correlation with baseline FENa (r = 0.44 p = 0.04) and negative correlation with volume balance during the first 24h after CS (r = -0.63, p = 0.007). More patients in Group 1 required nitroprusside than in Group 2 (66% vs. 14%, p = 0.04). Anesthesia time was shorter in Group 1 as compared to Group 2: 323+/-21 vs. 395+/-26 min, p = 0.04. No significant hemolysis occurred during CS in either group. There were no differences in age, gender, CPBP time, need for dopamine and/or dobutamine between the two groups. In conclusion, patients who presented GFR decrease after CS underwent VCS more frequently, had more prevalence of previous CS, presented lower baseline FENa, required more volume infusion and more nitroprusside use. On the other hand, no tubular dysfunction was detected in the early follow-up of CS. These results suggest that the observed renal function changes should be the result of an appropriated renal response to a low effective blood volume. In fact, a low baseline FENa anticipated a GFR decrease in these patients. Consistently, CAB patients that usually improve their cardiac output after surgery showed a clear GFR improvement.

The effect of prostaglandin E1 during cardiopulmonary bypass on renal function after cardiac surgery

We have evaluated the effect of prostaglandin E1 (PGE1) on renal function after cardiac surgery with cardiopulmonary bypass in 20 patients, ten of whom received 0.02 microgram.kg-1.min-1 of PGE1 by infusion into the oxygenator during bypass; ten patients served as controls. Serum beta 2-microglobulin fell significantly and urine beta 2-microglobulin increased significantly after surgery in both groups. Urine N-acetyl-beta-D-glucosaminidase was high after surgery in both groups, but it was significantly lower in the PGE1 group. Free water clearance fell significantly on the 1st, 3rd, and 5th postoperative days compared with preoperative values in the control but not in the PGE1 group. These results suggest that PGE1 may prevent renal dysfunction after cardiopulmonary bypass.

The effect of prostaglandin E1 on renal function after cardiac surgery involving cardiopulmonary bypass

This study was performed to evaluate the effect of prostaglandin E1 (PGE1) on renal function after cardiac surgery in patients undergoing cardiopulmonary bypass (CPB). Haemodynamic and renal functional response to low dose PGE1 (0.02 microgram kg-1 min-1) (group A) or saline (group B) infusion via peripheral vein during CPB was evaluated in 20 patients who underwent cardiac surgery. The perfusion pressure was maintained at about 60 mmHg during CPB in both groups. Urine beta 2-microglobulin (UBMG) (P < 0.01), and urine N-acetyl-beta-D-glucosaminidase (NAG) (P < 0.05) demonstrated significantly high values after CPB in both groups compared with the presurgical value. Free water clearance (CH2O) decreased significantly at the first postoperative day compared with the pre-surgical value in both groups (P < 0.01). Statistical analysis of NAG, UBMG and CH2O demonstrated significant differences between both groups, in CH2O values at the third (P < 0.05) and fifth days (P < 0.05) after surgery, in NAG values at the fifty (P < 0.01) and seventh days (P < 0.01), and in UBMG values at the first (P < 0.05) and third (P < 0.05) postoperative day, respectively. Cardiac output (co) did not change in either group throughout this study. Pulmonary capillary wedge pressure (PCWP) in group A decreased significantly at 30 and 60 min after CPB, but in group B did not change throughout the study. Cardiac index (CI) decreased significantly at 60 min after CPB in group A (P < 0.05) and at 30 min in group B (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Osmolal excretion after open heart surgery

Water and osmolal balance was investigated during the peri-operative period in twenty unselected adult patients presenting for open heart surgery. On the day before surgery the mean urine output was 1.13 litres/sq m/24 hours and osmolal output 430 mOs/sq m/24 hours. Using a haemodilution cardiopulmonary bypass technique, patients received 2.62 litres/sq m and 792 mOs/sq m in the operating room. The pattern of excretion of this water and solute load was identified. Patients were still in positive balance on the day following surgery despite a considerable diuresis, with solute retention exceeding water retention.

Renal function in children undergoing cardiac operations

Because we sometimes observed large amounts of uric acid crystals in the urine of infants and children after open-heart operations and since renal insufficiency from any cause can be a serious complication of cardiac procedures, 8 acyanotic and 5 cyanotic children were studied prospectively by comparing several preoperative and postoperative measures of renal function. There were no significant differences between the acyanotic and cyanotic groups in terms of age, time on cardiopulmonary bypass, or other preoperative variables. Postoperatively, children in both groups had a wide range of free water clearances (CH2O), with some values in the range reported to be diagnostic of renal insufficiency in adults. Since none of these children had renal insufficiency by other criteria, CH2O may not be as reliable an indicator of renal insufficiency in children. The major difference between the cyanotic and acyanotic groups was seen in postoperative serum uric acid levels (SUA); the mean SUA levels in the acyanotic and cyanotic groups were 5.3 +/- 0.5 mg/dl (+/- standard error of the mean) and 10.4 +/- 1.7 mg/dl (range, 8.0 to 15.5 mg/dl), respectively. Since the hyperuricemia in the cyanotic children could not be related to increased exogenous administration or decreased renal excretion, it is probably caused by increased endogenous production and may be related to the resolution of the cyanotic state.

Dynamics of glomerular ultrafiltration following open-heart surgery

To elucidate how individual determinants might lower the rate of glomerular ultrafiltration (GFR) in some patients following cardiac surgery, we performed hemodynamic measurements and clearance of inulin (as a measure of GFR), PAH (as a measure of effective renal plasma flow [ERPF]), and dextran-40. Two groups of 17 patients each were distinguished by the presence or absence of prerenal azotemia. Glomerular hypofiltration (GFR = 21 +/- 2 vs. 76 +/- 6 ml/min/1.73 m2, P less than 0.001) in the former was accompanied by depressed left ventricular function, arterial pressure, and ERPF (152 +/- 26 vs. 317 +/- 32 ml/min/1.73 m2, P less than 0.001). To determine if factors beside ERPF play a role in lowering GFR, we calculated the efferent oncotic pressure (pie). Failure of GFR to change over a 24-hour period despite increases in ERPF suggested that both patient groups were at filtration pressure disequilibrium (FPD). This condition permits calculation of a unique glomerular ultrafiltration coefficient (Kf). Over a range of pressures for transcapillary hydraulic pressure (deltaP), such that 3 less than or equal to (deltaP - pie) less than or equal to 10 mm Hg (to simulate FPD), Kf was less than 0.08 ml . sec-1 . mm Hg-1 . 1.73 m-2 in azotemic, but exceeded this value in nonazotemic patients. Although a selective reduction of Kf is predicted to lower the fractional clearance of dextrans, these were significant elevated in azotemic relative to nonazotemic patients (molecular radii 30 - 40 A). A theoretical analysis of the latter data suggests that over the foregoing range of FPD, a 15 to 30% decline in deltaP combined with a 30 to 0% reduction in Kf from values in nonazotemic patients best explains the experimental findings in azotemic patients.

Effects of hypothermia, hemodilution, and pump oxygenation on organ water content, blood flow and oxygen delivery, and renal function

Hypothermia, hemodilution, and the pump-oxygenator each contribute important effects during cardiopulmonary bypass. We studied their separate effects with a 2(3) factorial, completely fixed experimental design in 16 adult male mongrel dogs. Animals undergoing hypothermia were cooled to 25 degrees +/- 1 degree C. In dogs having hemodilution, hematocrit was adjusted to 25 +/- 2%. An analysis of variance was used to determine the effects of hypothermia, hemodilution, and pump oxygenation. The experiments show that hemodilution produces increased water content in tissue and that edema is greatest in heart and gastrointestinal organs. The pump-oxygenator decreased flow to the subendocardium, whereas hemodilution increased subendocardial flow. Both hypothermia and pump oxygenation diminished flow to the outer kidney cortex, and hemodilution augmented flow to this region. Hypothermia and pump oxygenation decreased and hemodilution raised renal free-water clearance. Although none affected glomerular filtration rate, hypothermia increased filtration fraction while hemodilution diminished it. Hypothermia lessened cerebral cortical flow, an effect opposite that of hemodilution. Thus, hemodilution opposes the adverse effect of hypothermia or pump oxygenation on blood flow, oxygen delivery, or renal function. Increased water content in gastrointestinal organs and myocardium accompanies the beneficial vascular and renal effects of hemodilution.