Vasoconstrictive Eicosanoid Responses to Extracorporeal Circulation with or without an Oxygenator in Fetal Lambs

Abstract

Introduction

This study measured levels of vasoconstrictive eicosanoids during ovine fetal cardiac bypass and compared the measurements between two groups: (1) a group in which the placenta functioned as the only source of oxygen supply during the bypass (the placenta group), and (2) a group in which an artificial oxygenator, instead of the placenta, was included in the bypass circuit (the oxygenator group).

Materials and Methods

A total of 16 fetal lambs were randomly assigned into either the oxygenator group or the placenta group. Following anesthesia, the fetal cardiac bypass procedure was performed. The placenta group used a centrifugal pump as the pumping device without an oxygenator during the bypass. The bypass circuit in the oxygenator group consisted of a roller pump and a membrane oxygenator. The fetal cardiac bypass procedure was performed for 30 minutes at normothermia in both groups. For the measurements of thromboxane B₂(TXB₂) and prostaglandin E₂ (PGE₂), blood sampels were taken before the bypass, at 5 minutes, 15 minutes, and 30 minutes after the start of cardiac bypass, and at 15 minutes after weaning from the bypass. TXB₂ and PGE₂ levels were determined by radioimmunoassay with PGE₂(¹²⁵I) and TXB₂(¹²⁵I) assay systems. Hemodynamic observations and arterial blood gas analyses were done every 10 minutes.

Results

The mean arterial pressure and heart rate ranged from 69.8 to 82.6 mmHg and 169 to 182/min during the bypass in the oxygenator group, and from 14.4 to 44.7 mmHg and 64.3 to 75/min in the placenta group. Arterial blood gas analysis showed severe hypercapnia and hypoxemia with acidosis during and after the bypass in the placenta group. Bypass flow rates were maintained at 140.3–164.0 ml/kg/min in the oxygenator group, while flow rates were suboptimal (74.3–97.0 ml/kg/min) in the placenta group. There were no statistically significant differences in PGE₂ concentrations before, during, or after bypass, although the placenta group displayed a tendency to higher measurements during bypass, compared to the oxygenator group. The placenta group also showed higher TXB₂ measurements than the oxygenator group during the bypass (p=0.0457).

Conclusions

We have demonstrated increase measurements of PGE₂ and TXB₂ in the placenta group when compared with the oxygenator group in an ovine fetal cardiac bypass model, although the PGE₂ difference failed to reach statistical significance.