Effect of carbon dioxide pneumoperitoneum on development of atelectasis during anesthesia, examined by spiral computed tomography.

BACKGROUND: Anesthesia per se results in atelectasis development in the dependent regions of the lungs. The effect of pneumoperitoneum on atelectasis formation is not known. The aim of the current study was to measure by spiral computed tomography the effect of carbon dioxide pneumoperitoneum for laparoscopic surgery on the development of atelectasis, overall lung volume, and regional tissue volumes of gas and tissue.
METHODS: Seven patients (American Society of Anesthesiologists physical status I), scheduled to undergo laparoscopic cholecystectomy, were observed. After induction of anesthesia, the patients were mechanically ventilated and positioned supine on the computed tomography table. Tomography of the lungs (10 mm spiral) was performed before and 10 min after induction of carbon dioxide pneumoperitoneum at an intraabdominal pressure of 11-13 mmHg. The Student t test was used for statistical analysis. A P value less than 0.05 was considered significant.
RESULTS: Induction of pneumoperitoneum increased the mean atelectasis volume in the dependent lung regions by 66% (range, 11-170%). The overall lung volume and gas as well as tissue volume significantly decreased. Relative to the total lung volume, lung tissue volume increased, while gas volume decreased significantly. Both upper and lower lobes reacted the same way. A cranial displacement of the diaphragm between 1 and 3 cm (mean, 1.9 cm) was registered.
CONCLUSION: Pneumoperitoneum at an intraabdominal pressure level of 11-13 mmHg increased the volume of atelectasis. Because lung tissue volume increased in the lung, there may have been an opening of previously closed vessels, which could explain previously seen increase in arterial oxygenation after induction of pneumoperitoneum.