Difference in the value of arterial and end-tidal carbon dioxide tension according to different surgical positions: Does it reliably reflect ventilation-perfusion mismatch? / 대한마취과학회지

ABSTRACT

BACKGROUND: Body posture, as a gravitational factor, has a clear impact on pulmonary ventilation and perfusion. In lung units with mismatched ventilation and perfusion, gas exchange and/or elimination of carbon dioxide can be impaired. In this situation, differences in the value of arterial and end-tidal carbon dioxide tension [Delta(PaCO2 - PETCO2)] are expected to increase. This study was conducted to observe how Delta(PaCO2 - PETCO2) changed according to the 3 different surgical positions, and to determine whether Delta(PaCO2 - PETCO2) is a reliable predictor of ventilation/perfusion mismatch when a patient is in different postural positions. METHODS: Fifty-nine patients were divided into either the chronic obstructive pulmonary disease (COPD) group (n = 29) or the non-COPD group (n = 30). PaCO2 and PETCO2 were measured during surgery in the supine, prone, and lateral decubitus positions after a 10 minute stabilization period. The Delta(PaCO2 - PETCO2) were calculated and compared among positions. RESULTS: The Delta(PaCO2 - PETCO2) decreased slightly in the prone position and increased significantly in the lateral decubitus position compared with the supine position in both groups. These patterns almost corresponded with the degree of ventilation/perfusion mismatch from the results of the radiological studies. The Delta(PaCO2 - PETCO2) in the COPD group was significantly greater than that in the non-COPD group at all surgical positions. CONCLUSIONS: Lateral decubitus position is associated with marked increase in Delta(PaCO2 - PETCO2), especially in patients with COPD. The Delta(PaCO2 - PETCO2) is a simple and reliable indicator to predict ventilation/perfusion mismatch at different surgical positions in patients with or without COPD.