[The effects of position and ventilation during thoracotomy on oxygen uptake and carbon dioxide elimination in...

The effects of position and ventilation were investigated in ten adult patients undergoing scheduled thoracotomy. Oxygen uptake (VO2) and carbon dioxide elimination (VCO2) in gas phase were measured continuously, while gas exchange ratio (R) and dead space ventilation ratio (VD/VT) were calculated with these results. VO2 and VCO2 during general anesthesia decreased about 60% from the normal values due to reduction of metabolism. Position and ventilation had no obvious effect on VO2 during surgery. VCO2 decreased slightly during bilateral ventilation with lateral decubitus position, because of mismatch of ventilation-perfusion distributions, and/or reduction of metabolism without surgical stress. The results suggest that carbohydrate calories are mainly metabolized under surgical stress, resulting in an R equal to 1.0. Continuous non-invasive monitoring of VO2 and VCO2 is one of the most effective parameters to evaluate the oxygen balance and systemic metabolism.