Carbon dioxide production (VCO2) predicts after heart surgery better than end tidal CO2
Introduction: Measures of metabolic recovery as VCO2, oxygen consumption (VO2) and cardiac output (CO) may predict outcome after CPB1. The purpose of this study was to compare the effiacy of monitoring post-CPB VCO2 with that of end-tidal CO2 (etCO2) in measuring ventilatory and metabolic recovery after CPB. Methods: Following IRB approval, 28 patients undergoing elective cardiac procedures under hypothermic CPB were prospectively selected with EF ≥ 45% and no organ dysfunction. Anesthetic regimens were similar in all patients. Hypothermia was achieved at 28-32°C. Simultaneous arterial and venous blood gases and hemodynamic measures (HR, MAP, PA pressure, CO) were collected under constant mechanical ventilation. VCO2 was measured with the CO 2SMO Plus monitor (Novametrix Ine, Wallingford, CT). VCO2 was calculated using Pick's principle. Measurement times were pre-CPB, then at 1,2,4 and 6 hours post-CPB. Statistical analyses included paired t-test, correlation Z-test and linear regression (95% CI); p<0.05 accepted as significant. Outcome variable was intubation time (Inttime); ventilatory and metabolic indicators were predictive variables. Results: VCO2 and etCO2 demonstrated parallel recovery patterns after CPB, both exhibiting maximal rise between 2 and 4 post-CPB. The two variables strongly correlated to each other (r=0.73, p<0.0001, 95%CI: 0.49-0.87); however, only VCO2 was positively correlated to other metabolic indicators as VO2, CO and RQ (table 1). Compared to etCO2, VCO2 correlated more significantly with Int time and predicted changes in it better (R2=0.49 vs. 0.26) (fig 1,2). Conclusion: Continuous monitoring of VCO2 is readily measured in mechanically ventilated patients, and is a reliable indicator of metabolic recovery and short-term outcome after CPB. Ref: (1) Crit Care Med 1998;26:1007-10. Correlation Time r 5% Cl VCO2/VO2 1hrpost-cpb 0.51 (p=0.005) 0.17, 0.74 6 hrs post-cpb 0.52 (p=0.01) 0.13, 0.77 VCO2/CO 2 hrs post-cpb 0.42 (p=0.02) 0.05, 0.68 6 hrs post-cpb 0.54 (p=0.009) 0.15, 0.78 VCO2/RQ 4 hrs post-cpb 0.60 (p=0.01) 0.27, 0.81 Table 1. Correlation of VCO2 vs metabolic indicators after cpb.
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