Determination of Dead-Space Ventilation and CO 2 Production in the Presence of Gas Leak from Bronchopleural Fistula Complicating ARDS

Abstract

Determining dead-space ventilation (VD/VT) and CO₂ production ( $\dot{V}C{O}_2$ ) is helpful in the management of patients with the adult respiratory distress syndrome (ARDS) who require mechanical ventilation. Bronchopleural gas leak resulting from bronchopleural fistula (BPF) is a severe and not uncommon complication seen in ARDS patients. We studied the effect of a BPF gas leak on the calculation of VD/VT and $\dot{V}C{O}_2$ . Methods: We collected and analyzed leaked and exhaled gas from six patients who had severe ARDS in order to compare 'apparent' VD/VT and $\dot{V}C{O}_2$ (calculated from exhaled gas only) with actual VD/VT and $\dot{V}C{O}_2$ (calculated from both exhaled and leaked gas). Results: Apparent VD/VT% (78 ± 11.8%) correlated well with actual VD/VT% (79 ± 9.5%) (r = 0.99, P < 0.001). However, apparent $\dot{V}C{O}_2$ (187 ± 83 ml/min) did not correlate with actual $\dot{V}C{O}_2$ (266 ± 32 ml/min) (r = 0.57, P = 0.17). Conclusions: These data suggest that both leaked and exhaled gas must be collected and analyzed for the accurate calculation of $\dot{V}C{O}_2$ in ARDS patients with BPF but that analysis of exhaled gas alone is sufficient for the calculation of VD/VT in these patients.