OBJECTIVES: During surgery the volume of administered fluid is debated. Pro-atrial natriuretic peptide (proANP) is released by atrial distension, and we evaluated the relationship between changes in proANP associated with perioperative fluid balance.

DESIGN: Prospective observational study.

SETTING: One university/tertiary centre.

PARTICIPANTS: The study included patients who underwent radical cystectomy. Plasma for determination of proANP was obtained before surgery, after resection of the bladder, and at the end of surgery for 20 robotic-assisted radical cystectomy (RARC) and 20 open radical cystectomy (ORC) procedures.

RESULTS: The blood loss was 1871 (95% CI 1267 to 2475) vs 589 mL (378 to 801) in the ORC and RARC groups (p=0.001), respectively, and fluid balance was positive by 1518 mL (1215 to 1821) during ORC, and by 1858 mL (1461 to 2255) during RARC (p=0.163). Yet, at the end of ORC, plasma proANP was reduced by 23% (14% to 32%, p=0.001), while plasma proANP did not change significantly during RARC. Thus, plasma proANP was associated both with the perioperative blood loss (r= -0.475 (0.632 to -0.101), p=0.002), and with fluid balance (r=0.561 (0.302 to 0.740), p=0.001), indicating that a stable plasma proANP required a fluid surplus by 2.4 L (2.0 to 2.7).

CONCLUSIONS: There was a correlation between intraoperative haemorrhage and a decrease in plasma proANP and, taking plasma proANP to indicate filling of the heart, about 2.5 L surplus volume of lactated Ringer's solution appears to maintain cardiac preload during cystectomy.

TRIAL REGISTRATION NUMBER: EudraCT (2012-005040-20), Results.