Dynamic Fluid Shifts Induced by Fetal Cardiopulmonary Bypass
Pirooz Eghtesady1, Scott Baker2, Christopher Lam1, Hilshorst Jerri1, Ferguson Robert1, Lombardi John1; 1Cardiothoracic Surgery, Cincinnati Children's Hospital, Cincinnati, OH; 2University of Cincinnati, Cincinati, OH
Comment on this Abstract
Objective: Significant fluid shifts have been reported with fetal bypass. The degree or mechanisms behind these volume changes have not been defined. Therefore, we characterized changes in fetal plasma volume and third space fluid losses with fetal bypass, and correlated the findings to fetal plasma vasopressin concentrations, the critical peptide of osmoregulation.
Methods: Eight ovine fetuses at 105-111 days gestation underwent 30 minutes of bypass using maternal blood prime (placenta as oxygenator) and were followed for up to 2 hours post-bypass. Fetal hemodynamics were measured continuously and volume infusions required to maintain normal physiologic parameters noted. Blood samples were collected before, during and after bypass to assess gas exchange and vasopressin levels and plasma volume was calculated. All blood sampling was accounted for and no transfusions were given. Statistical analysis was performed using 2-tailed Students t-test with significance at p<0.05, and best-fit correlations.
Results: Fetal plasma volume declined from 177 ± 50 to 164 ± 51 (mean ± SD) by 30 min post bypass, p=0.02, averaging 0.1 ml/kg/min over that one hour period. Fetal hematocrits did not differ at baseline. Hematocrit declined by 30 minutes of bypass to 27 ± 4% from 30 ± 6, p=0.02, then elevated to 32 ± 5 by 30 minutes post-bypass, p=0.04. All bypass animals required crystalloid volume addition during and after bypass to maintain normal fetal hemodynamics. Vasopressin levels increased dramatically by 30 min of bypass, going from 39 pg/ml to 51.5 pg/ml. Increasing vasopressin levels strongly correlated with declining fetal plasma volumes, R2 = 0.91.
Conclusion: Bypass leads to significant fluid shifts (third space fluid losses) and hemoconcentration which strongly correlates with rising vasopressin levels. This is consistent with osmoregulation mediated by vasopressin. Rehydration of the fetus is necessary post bypass for adequate fluid regulation, especially in setting of associated placental dysfunction.
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