Does metabolic recovery predict time to extubation after cardiac surgery?

Introduction: Carbon dioxide production (VCO₂), and oxygen consumption (VO₂), measures of metabolic recovery, are significant determinants of outcome after CPB. The purpose of this study was to determine whether body temp (T_B) is a surrogate of metabolic recovery and time to extubation (Intub_T) after CPB. Methods: Following IRB approval, we enrolled 27 patients undergoing elective cardiac procedures under hypothermic CPB. Selection criteria included EF≥45% and absence of significant organ dysfunction. Moderate whole body hypothermia was achieved to a range of 28-32°C. T_B was recorded via PA cath, while VCO₂ was measured with the CO₂SMO Plus monitor (Novametrix Inc., Wallingford, CT). Simultaneous arterial and venous blood gases and hemodynamic measures were collected from anesthetized patients, under constant mechanical ventilation, and with the chest closed. VO₂ was calculated using Fick's principle. Measurement times were pre-CPB, then at 1, 2, 4 and 6 hours post-CPB. Statistical analyses included correlation Z-test (95% Cl; p<0.05 accepted as significant) and simple linear regression of Intub_T vs. T_B. (Figure Presented) Results: Longer Intub_T was associated with lower T_B (Fig 1). VCO₂ and T_B showed parallel increases with time after CPB (Fig 2). T_B was positively correlated to VCO₂ and VO₂. Age was negatively correlated to T_B, VO₂ and VCO₂. Of all CPB factors examined (duration, cardioplegia volume, and cooling temp), T_B correlated positively to cooling temp and BSA. (Figure Presented) Conclusion: T_B and associated VO₂ and VCO₂ changes may be predictive of postoperative intubation time following open heart surgery, and warrant further study of rewarming techniques especially with regard to metabolic recovery in the elderly.