Renal function changes after elective cardiac surgery with cardiopulmonarybypass

Cardiac surgery can either induce acute renal failure or improve GFR by imp roving the cardiac performance. In order to study renal function changes af ter elective cardiac surgery (CS) with cardiopulmonary bypass (CPBP), 21 pa tients undergoing valvular CS (VCS) or coronary artery bypass (CAB) were pr ospectively 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 (Delta GFR(24)): Group 1, Delta GFR(24) decrease higher than 20% ( n = 11) and Group 2, Delta GFR(24) decrease less than or equal to 20% or De lta GFR(24) increase (n = 10). In Group 1, 73% of the patients underwent VC S (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). Pati ents in Group 1 required more volume replacement than Group 2 during the fi rst 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 ho urs after CS when compared to Group 2 (39 +/- 5 versus 75 +/- 8 mL/(min x 1 .73m(2)), p = 0.001) and a significantly different Delta GFR 48 hours after CS as compared to Group 3 (-21 +/- 11 versus +88 +/- 36%, p < 0.01). Basel ine sodium fractional excretion (FEN,) 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 (U-osm) and urinary pH (U-pH) in both groups . The Delta GFR(24) showed positive correlation with baseline FEN, (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 nitropr usside 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 n o differences in age, gender, CPBP time, need for dopamine and/or dobutamin e between the two groups. In conclusion, patients who presented GFR decrease after CS underwent VCS m ore frequently, had more prevalence of previous CS, presented lower baselin e FENa, required more volume infusion and moro nitroprusside use. On the ot her hand, no tubular dysfunction was detected in the early follow-up of CS. These results suggest that the observed renal function changes should be t he 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 afte r surgery showed a clear GFR improvement.