Fluid distribution kinetics during cardiopulmonary bypass

Area of Science:

• Cardiovascular Surgery
• Anesthesiology
• Fluid Physiology

Background:

• Cardiopulmonary bypass (CPB) involves significant fluid shifts.
• Understanding crystalloid distribution kinetics is crucial for managing hemodynamics during CPB.
• Isovolumetric CPB aims to maintain constant blood volume, but fluid shifts still occur.

Purpose of the Study:

• To investigate the distribution kinetics of crystalloid fluid during isovolumetric cardiopulmonary bypass.
• To quantify the rate of fluid distribution and transcapillary escape rate.
• To assess changes in intravascular albumin and preoperative blood volume.

Main Methods:

• Prospective observational study of 10 patients undergoing coronary artery bypass grafting.
• Repeated measurements of hemoglobin, albumin, and sodium concentrations during CPB.
• Calculation of crystalloid fluid distribution rate based on hemoglobin changes and extrapolation of preoperative blood volume.

Main Results:

• The distribution half-time for Ringer's acetate was 8 minutes, with a transcapillary escape rate of 0.38 ml/kg/min.
• Intravascular albumin mass increased by 5.4%.
• Preoperative blood volume was underestimated by anthropometric methods, suggesting hypovolemia in most patients. Sodium balance indicated intracellular to extracellular fluid shift in 80% of patients.

Conclusions:

• Crystalloid fluid distribution during isovolumetric CPB is rapid (8-minute half-time), similar to healthy subjects.
• Intravascular albumin increased, and intracellular edema was not observed.
• A significant proportion of patients were hypovolemic before anesthesia induction.