Elevated flow rate during cardiopulmonary bypass is associated with fluid accumulation

Objective

High flow rates during cardiopulmonary bypass are assumed to increase fluid accumulation. This study aimed to determine whether two different flow rates during cardiopulmonary bypass alter the intraoperative fluid balance and extravasation rate.

Methods

Sixteen pigs underwent 60 minutes of normothermic bypass, followed by 90 minutes of hypothermic bypass. A high-flow group (HF group, n = 8) had a cardiopulmonary bypass flow rate of 110 mL · kg⁻¹ · min⁻¹ and a low-flow group (LF group, n = 8) had a rate of 80 mL · kg⁻¹ · min⁻¹. Blood chemistry, hemodynamic parameters, plasma and interstitial colloid osmotic pressure, net fluid balance, plasma volume, fluid extravasation rate, and total tissue water content were measured or calculated. Results are presented as mean (standard deviation).

Results

The average net fluid balance during cardiopulmonary bypass was 1.02 (0.25) and 0.73 (0.23) mL · kg⁻¹ · min⁻¹ in the HF group and LF group, respectively (P < .05). The average fluid extravasation rate was 0.98 (0.22) and 0.77 (0.22) mL · kg⁻¹ · min⁻¹ in the HF group and the LF group (P = .07). Total water content was higher in the kidneys (P < .05) and tended to be higher in the lungs (P = .05), liver (P = .07), and brain (P = .07) of the HF group than in those of the LF group. The between-group differences in net fluid balance and fluid extravasation rate were present during the first 30 minutes of normothermic cardiopulmonary bypass. Thereafter, the values stabilized and remained similar in the two groups. Plasma volume and systemic vascular resistance differed between the groups.

Conclusion

Cardiopulmonary bypass flow rate of 110 mL · kg⁻¹ · min⁻¹ was associated with higher positive net fluid balance and fluid extravasation rate than 80 mL · kg⁻¹ · min⁻¹. The effect was mainly observed in the initial phase of cardiopulmonary bypass.

CTSNet classification: 17, 25

Abbreviations and Acronyms: COP, colloid osmotic pressure, COPi, colloid osmotic pressure in interstitial fluid, COPp, colloid osmotic pressure in plasma, CPB, cardiopulmonary bypass, CVP, central venous pressure, HF, high flow, LF, low flow, MAP, mean arterial pressure, PV, plasma volume