Objective: To investigate the influence of intravenous (iv) fluid volumes on the secretion of N-terminal-pro-brain natriuretic peptide (NT-Pro-BNP) in colorectal surgical patients and its association with cardiopulmonary complications (CPC). In addition, to examine if preoperative NT-Pro-BNP can predict the risk for postoperative CPC.

Methods: Blood samples from patients enrolled in a previously published clinical randomized assessor-blinded multicenter trial were analyzed.(1) Included were adult patients undergoing elective colorectal surgery with the American-Society-of-Anesthesiologists-scores of 1-3. Samples from 135 patients were available for analysis. Patients were allocated to either a restrictive (R-group) or a standard (S-group) iv-fluid regimen, commencing preoperatively and continuing until discharge. Blood was sampled every morning until the fourth postoperative day. The primary outcome for this study was NT-Pro-BNP changes and its association with fluid therapy and CPC.

Results: The S-group received more iv-fluid than the R-group on the day-of-surgery [milliliter, median (range) 6485 (4401-10750) vs 3730 (2250-8510); P <0.001] and on the first postoperative day. NT-Pro-BNP was elevated in the S-group compared with the R-group on all postoperative days [area under the curve: median (interquartile range) pg/mL: 3285 (1697-6179) vs 1290 (758-3719); P <0.001 and in patients developing CPC vs no-CPC (area under the curve), median (interquartile range): 5196 (1823-9061) vs 1934 (831-5301); P = 0.005]. NT-pro-BNP increased with increasing fluid volumes all days (P <0.003). Preoperative NT-Pro-BNP predicted CPC [odds ratio (confidence interval): 1.573 (0.973-2.541), P = 0.032; positive predictive value = 0.257, negative predictive value = 0.929].

Conclusions: NT-pro-BNP increases with iv-fluid volumes given to colorectal surgical patients, and the level of NT-Pro-BNP is associated with CPC. Preoperative NT-Pro-BNP is predictive for CPC, but the diagnostic value is low.