Development of atelectasis and arterial to end-tidal PCO 2-difference in a porcine model of pneumoperitoneum

Abstract

Background: Intraperitoneal insufflation of carbon dioxide (CO2) may promote collapse of dependent lung regions. The present study was undertaken to study the effects of CO2-pneumoperitoneum (CO 2-PP) on atelectasis formation, arterial oxygenation, and arterial to end-tidal Pco2-gradient (Pa-E′CO2). Methods: Fifteen anaesthetized pigs [mean body weight 28 (sd 2) kg] were studied. Spiral computed tomography (CT) scans were obtained for analysis of lung tissue density. In Group 1 (n=5) mechanical ventilation (VT=10 ml kg -1, Fio2=0.5) was applied, in Group 2 (n=5) Fi o2 was increased for 30 min to 1.0 and in Group 3 (n=5) negative airway pressure was applied for 20 s in order to enhance development of atelectasis. Cardiopulmonary and CT data were obtained before, 10, and 90 min after induction of CO2-PP at an abdominal pressure of 12 mmHg. Results: Before CO2-PP, in Group 1 non-aerated tissue on CT scans was 1 (1)%, in Group 2 3 (2)% (P<0.05, compared with Group 1), and in Group 3 7 (3)% (P<0.05, compared with Group 1 and Group 2). CO2-PP significantly increased atelectasis in all groups. Pao2/Fi o2 fell and venous admixture ('shunt') increased in proportion to atelectasis during anaesthesia but CO2-PP had a varying effect on Pao2/Fio2 and shunt. Thus, no correlation was seen between atelectasis and Pao2/Fio2 or shunt when all data before and during CO2-PP were pooled. Pa-E'CO2, on the other hand correlated strongly with the amount of atelectasis (r2=0.92). Conclusions: Development of atelectasis during anaesthesia and PP may be estimated by an increased Pa-E'CO2. © The Author [2009]. Published by Oxford University Press on behalf of The Board of Directors of the British Journal of Anaesthesia. All rights reserved.