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

BACKGROUND

Ventilatory efficiency (V˙e/V˙co slope [minute ventilation to carbon dioxide output slope]) has been shown to predict morbidity and mortality in lung resection candidates. Patients with increased V˙e/V˙co during exercise also exhibit an increased V˙e/V˙co ratio and a decreased end-tidal CO at rest. This study hypothesized that ventilatory values at rest predict respiratory complications and death in patients undergoing thoracic 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. Postoperatively, 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 CO (28.1 ± 4.3vs 31.5 ± 4.2 mm Hg; p < 0.01), higher resting V˙e/V˙co ratio (45.1 ± 7.1 vs 41.0 ± 6.4; p = 0.02), and higher V˙e/V˙co slope (34.9 ± 6.4 vs 31.2 ± 4.3; p = 0.01). Logistic regression (age and sex adjusted) showed resting end-tidal CO 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 CO may identify patients at increased risk for postoperative respiratory complications of thoracic surgical procedures.