Glomerulotubular function in patients undergoing moderate surgical stress

Glomerular function and renal tubular function assessed by measurements of creatinine clearance rates (CCR), lithium clearance rates (CLi, and N-acetyl-beta-D-glucosaminidase (NAG) enzymuria were measured immediately prior to and within 24 h of operation (average operative time 150 min) in 16 patients undergoing a moderate surgical stress. Although serum creatinine concentrations and CCR were similar pre- and postsurgery at 105 +/- 21 and 108 +/- 21 mumol/L and 108 +/- 67 and 110 +/- 59 mL/min/100 kg body weight (mean +/- SD), respectively, both CLi and NAG were significantly increased following the surgical insult. CLi was increased from 19.7 +/- 6.1 to 31.7 +/- 16.7 mL/min/100 kg (p less than 0.01) and NAG from 71 +/- 58 to 164 +/- 10 U/mmol urinary creatinine (p less than 0.001). In addition, the absolute distal tubular reabsorption of sodium and water increased from 18.3 +/- 5.9 and 15.8 +/- 9.7 to 30.6 +/- 16.4 and 27.6 +/- 12.2 mL/min/100 kg body weight (both p less than 0.05), respectively. These results indicate early postoperative renal tubular dysfunction following a moderate surgical stress, undetected by conventional screening.