GASTRIC TONOMETRY MONITORING DURING DEEP HYPOTHERMIC BYPASS FOR CARDIAC SURGERY IN NEONATES AND INFANTS

Abstract

Introduction. Infants with congenital heart defects (CHD) are at risk for splanchnic hypoperfusion. Multiple risk factors contribute to this circumstance including anatomic lesions characterized by reduced splanchnic flow or excessive systemic run-off, cardiopulmonary bypass and deep hypothermia (DH), reperfusion injury following hypothermic circulatory arrest (CA), increased levels of circulating vasoconstrictors or low cardiac output. This preliminary study evaluates gastric tonometry as a possible monitor of regional perfusion during infant cardiac surgery with DHCA. Methods: Following IRB approval, 15 neonates and infants undergoing complete repair under DH were studied. A 7 Fr tonometric catheter (TRIP sigmoid catheter, Tonometrics, MA) was placed oro-gastrically in each patient after induction of anesthesia. Measurements of gastric CO2 (PgCO2), arterial blood gas, perfusion pressure, hematocrit and lactate were made at 4 time intervals: T0 prebypass, T1 end of cooling, T2 end rewarming, and T3 post bypass. By application of the Henderson-Hasselbach equation, mucosal pH (pHi) was calculated. The difference between PgCO2 and PaCO2 (DCO2) was evaluated. Comparisons were made within groups by ANOVA and between variables using linear regression. Results. Median age was 6 days (range 2 to 320) and median weight 3.9kg (range 2.9 to 8.4). Mean total bypass time was 107 +/- 23 min, and CA time 12.4 +/- 9.0 min. Data for each time interval is shown in Table 1. There were no significant differences in pHi or DCO2 over time intervals. Lactate at T2, T3, T4 was significantly higher than at T0. (mean +/- SD, # p<0.001 T0 vs T2, T3, T4)Table 1Although DCO2 and lactate trended together, no significant correlation was found because of the wide SD. All patients weaned from CPB and survived to discharge. Discussion. While gastric tonometry may enable early detection and intervention of regional splanchnic hypoperfusion, thereby reducing perioperative morbidity in patients with CHD, no conclusive correlation with global indices of perfusion used during bypass could be made in this study. The wide variability of DCO2 at each time point was a limitation, but may reflect sampling and measurement errors inherent with saline CO2 tonometry. Technologic refinements including the development of pediatric catheters with suction lumens enabling automated, intermittent air tonometry, and better identification of the population at risk, will enhance the utility of tonometry in perioperative management.