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Combined metabolic parameters and gas exchange to predict morbidity after extracorporeal circulation


Under normal resting conditions, the oxygen delivery (DO2) matches the overall metabolic demands of the organs, the oxygen consumption (VO2) is about 25% of the DO2, and energy is produced basically through the aerobic mechanism. In cardiac surgery with extracorporeal circulation (ECC), several factors (for example, hemodilutional anemia, myocardial stunning resulting in a low cardiac output (CO)) can determine an imbalance between O2 demand and DO2 and may affect the outcome. Below the critical DO2 there is a linear decrease of both VO2 and CO2 production (VCO2), but due to the anaerobic VCO2 the respiratory quotient increases. This study is aimed to evaluate the role of O2 and CO2 derived parameters to predict postoperative morbidity in cardiac surgery.


Eight hundred and twenty-seven consecutive adult patients who underwent coronary surgery were studied. We selected 38 intraoperative and postoperative O2 and CO2 derived parameters, which could be associated with postoperative morbidity. Postoperative data were collected in the first 3 hours after admission to the ICU. The influence of each predictor on outcome was analyzed. Morbidity was defined as one or more of the following events: cardiovascular, respiratory, neurological, renal, infectious, and hemorrhagic complications. Univariate and multivariate analyses were performed. ROC curve analysis was also used to define the best predictive variables.


Intraoperative predictors of morbidity were ECC and aortic cross-clamp times, and lowest hematocrit during ECC. The area under the ROC curve (AUC) was 0.74 for the lowest hematocrit on ECC, and its cutoff value was 24%. Among the postoperative variables, DO2, oxygen extraction ratio (O2ER), DO2/VCO2 ratio, and VCO2/CO ratio were related to morbidity. The AUCs for oxygen and CO2 derived parameters were 0.80, 0.76, 0.75, and 0.70 (DO2, O2ER, DO2/VCO2 ratio, and VCO2/CO ratio, respectively). The best predictive cutoff values were 590 ml/minute, 38%, 3.9, and 40, for DO2, O2ER, DO2/VCO2 ratio, and VCO2/CO ratio, respectively.


Various predictors of hypoperfusion have been tested in critically ill patients and correlations have been found for O2 and CO2 derived parameters. Long ECC time plays a major role in the balance between VO2 and DO2; O2 and CO2 derived parameters could be useful markers to detect anaerobic metabolism in cardiac surgical patients.

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Scolletta, S., Maglioni, E., Franchi, F. et al. Combined metabolic parameters and gas exchange to predict morbidity after extracorporeal circulation. Crit Care 11 (Suppl 2), P253 (2007).

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