Application of near-infrared spectroscopy during fetal cardiac surgery.

BACKGROUND: Near-infrared spectroscopy (NIRS) has been shown to provide reliable noninvasive monitoring of regional oxygenation in a variety of clinical settings. We set out to test its feasibility as a monitor of fetal and placental oxygenation during fetal cardiac surgery. MATERIALS AND METHODS: Six ovine fetuses from 98-110 ds gestation were placed on fetal bypass for 30 min and followed post-bypass for 2 h. A NIRS probe (MI INVOS 5100B; Somanetics, Troy, MI) was placed on the pregnant uterine horn during and after fetal surgery. NIRS values were compared with blood gas values obtained by direct sampling from umbilical circulation. RESULTS: NIRS values positively correlated with umbilical venous oxygen saturation (R(2)=0.891, P<0.01) and partial oxygen pressure values (R(2)=0.810, P<0.01). NIRS values also correlated to a lesser extent with umbilical venous pH and pCO(2), and fetal arterial pH, pO(2), and oxygen saturation. CONCLUSIONS: This is the first report of application of NIRS in the setting of fetal surgery. NIRS permits noninvasive assessment of placental oxygen saturation and pO(2). This technology is a simple and useful tool for real-time monitoring of oxygen delivery to the fetus during maternal-fetal cardiac interventions and of overall well-being of the fetal-placental unit.

A simple solution is "prime" for fetal cardiopulmonary bypass.

Worsening fetal gas exchange is the hallmark of frequently observed placental dysfunction after fetal bypass. Several factors influence this pathophysiology, but the optimal prime constituents for fetal bypass have yet to be defined. Calcium and sodium bicarbonate are frequently added to prime solutions for adjustments toward physiologic values. We examined whether similar manipulations are warranted with fetal bypass. Ovine fetuses (n = 10) at 104-110 days' gestation were placed on bypass for 30 minutes. Calcium chloride and sodium bicarbonate were added to adjust prime ionized calcium and pH. Fetal hemodynamics and arterial blood gases were collected immediately before, and 15 and 30 minutes on bypass. Statistical significance was determined by Student's t test and best fit correlations. Calcium addition negatively correlated with fetal pH (R >or= 0.63) and po2 (R >or= 0.41), and displayed a robust positive correlation with pco2 (R = 0.88) during bypass. Similarly, bicarbonate addition revealed correlations for pco2 (R >or= 0.70) and po2 (R >or= 0.57), with a strong negative correlation to umbilical blood flow (R >or= 0.75). Calcium addition to the prime adversely affects fetal gas exchange worsening acidosis during fetal bypass. Bicarbonate addition to the prime is also detrimental to the fetus resulting in greater CO2 production and impaired hemodynamics.