The Effect of Laparoscopic Cholecystectomy on Cardiovascular Function and Pulmonary Gas Exchange

Abstract

In Response: We are well aware of the importance of the two points raised by Dr. Fletcher as far as the conclusions of our recent paper [1] are concerned. Referring to Dr. Fletcher's first point, we obviously agree that the PETCO2 method tends to overestimate the alveolar dead space (VD A) whenever Phase III of the CO (2) expirogram is not horizontal. This is the case, for instance, of patients with VA/Q maldistribution [2]. However, as mentioned in the Methods section of our article, our patients did not suffer from any detectable cardiopulmonary disease (ASA physical status I). Indeed, throughout the data collection, the alveolar plateaux were always horizontal, or very nearly so. Therefore, the error introduced in VD A estimation is negligible for clinical proposes. Concerning Dr. Fletcher's second observation, the physiological dead space to tidal volume ratio (VD [centered dot] VT-1) was obtained from the classical Equation 1 of Bohr: Equation 1 where PaCO2 and PeCO2 are the arterial and the mean expired CO2 partial pressures, respectively. The latter was obtained from expired gas analysis performed using the metabolic unit (Deltatrac; Datex, Helsinki, Finland), using a mixing box. Since both gas flows and compositions were measured at an overall gas pressure equal to atmospheric, to our knowledge, no correction for compressed gases are needed. Finally, we think that the observed relatively high VD [centered dot] VT-1 values cannot be attributed to the respiratory pattern [3] because VT and respiratory rate ranged from 500 to 770 mL and from 11 to 13 breaths/min-1, respectively. M. Girardis, MD U. Da Broi, MD G. Antonutto, MD A. Pasetto, MD Cattedra di Anestesiologia e Rianimazione; Dipartimento di Scienze e Tecnologie Biomediche; Universita degli Studi di Udine; Italy