Resting End-Tidal Carbon Dioxide Predicts Respiratory Complications in Patients Undergoing Thoracic Surgical Procedures

Background. Ventilatory efficiency ((V) over dot(E)/(V) over dot(CO2) slope [minute ventilation to carbon dioxide output slope]) has been shown to predict morbidity and mortality in lung resection candidates. Patients with increased (V) over dot(E)/(V) over dot(CO2) during exercise also exhibit an increased (V) over dot(E)/(V) over dot(CO2) ratio and a decreased endtidal CO2 at rest. This study hypothesized that ventilatory values at rest predict respiratory complications and death in patients undergoing thorac ic surgical procedures. Methods. Inclusion criteria for this retrospective, multicenter study were thoracotomy and cardiopulmonary exercise testing as part of routine preoperative assessment. Respiratory complications were assessed from the medical records (from the hospital stay or from the first 30 postoperative days). For comparisons, Student's t test or the Mann-Whitney U test was used. Logistic regression and receiver operating characteristic analyses were performed for evaluation of measurements associated with respiratory complications. Data are summarized as mean +/- SD; p < 0.05 is considered significant. Results. Seventy-six subjects were studied. Post-operatively, respiratory complications developed in 56 (74%) patients. Patients with postoperative respiratory complications had significantly lower resting tidal volume (0.8 +/- 0.3 vs 0.9 +/- 0.3L; p = 0.03), lower rest end-tidal CO2 (28.1 +/- 4.3vs 31.5 +/- 4.2 mm Hg; p < 0.01), higher resting (V) over dot(E)/(V) over dot(CO2) ratio (45.1 +/- 7.1 vs 41.0 +/- 6.4; p = 0.02), and higher (V) over dot(E)/(V) over dot(CO2) slope (34.9 +/- 6.4 vs 31.2 +/- 4.3; p = 0.01). Logistic regression (age and sex adjusted) showed resting end-tidal CO2 to be the best predictor of respiratory complications (odds ratio: 1.21; 95% confidence interval: 1.06 to 1.39; area under the curve: 0.77; p = 0.01). Conclusions. Resting end-tidal CO2 may identify patients at increased risk for postoperative respiratory complications of thoracic surgical procedures. (C) 2016 by The Society of Thoracic Surgeons