Changes in Blood Volume and Colloid Osmotic Pressure during Fluid Absorption in Patients Undergoing Endoscopic Urosurgery: An Observational Study

Background and Objective: Anesthesiologists need to be familiar with perioperative changes in blood volume (BV); however, there is no standard method for repeated evaluation of BV over a short interval of time. We evaluated BV in the operation room using repeatable estimation methods. Method: Eighty-five ASA physical status I-II patients scheduled to undergo endoscopic urosurgery using irrigation fluid under general anesthesia at Nippon Medical School Hospital were included in this study. Irrigation with 3% sorbitol in water was commenced after establishment of general anesthesia and volumetric fluid balance, which was defined as control water balance (WB). Hematocrit (Hct), colloid osmotic pressure (COP), total protein (TP) and albumin (Alb) were repeatedly determined before and during anesthesia. BV was calculated using Allen’s formula and the changes in Hct, COP, TP and Alb. Main Outcome Measures: The main outcome was the accuracy of measuring changes in BV (∆BV) calculated using the four serum markers. WB and the estimated ∆BV calculated from Hct, COP, TP and Alb (∆BV-Hct, ∆BV-COP, ∆BV-TP, and ∆BV-Alb) were analysed using Pearson’s correlation coefficient test and Bland-Altman analysis. Results: Sixty-five patients were excluded. In the remaining 20 patients, there was a significant correlation between WB and ∆BV-COP (R = 0.72; P < 0.01), WB and ∆BV-TP (R = 0.59; P < 0.01) and WB and ∆BV-Alb (R = 0.57; P < 0.01), while there was no correlation between WB and ∆BV-Hct (R = 0.06). Conclusion: ∆BV-COP, ∆BV-TP and ∆BV-Alb had correlation with WB. However, since COP can be measured repeatedly with simplified instruments under selected clinical circumstances, while TP and Alb cannot. COP is the most useful marker to measure ∆BV during perioperative period. Hct does not allow precise estimation of ∆BV.