MEASUREMENT OF LUNG-VOLUME AND DL(CO) IN ACUTE RESPIRATORY-FAILURE

We have undertaken rebreathing measurements of functional residual capacity (FRC), carbon monoxide diffusing capacity (DL(CO)), and diffusing coefficient (KCO) during positive pressure ventilation in 15 patients with adult respiratory distress syndrome (ARDS). Measurements of oxygenation (Pa-O2:FIO2 ratio) and lung injury score (LIS) were also recorded. Eight patients subsequently died (mortality of 53%). There was no significant difference in mean FRC, Pa-O2:FIO2, or LIS at presentation between survivors and nonsurvivors. However, both DL(CO) and KCO at presentation were significantly greater in survivors than nonsurvivors. In a separate study of nine patients with less Severe lung injury, pulmonary capillary blood volume, derived from values of DL(CO) measured at two different values of FIO2, correlated with invasive pulmonary vascular resistance (PVR) measurements (r = 0.84, p < 0.01). DL(CO) measurements can be successfully undertaken in patients being ventilated with acute lung injury and may be a useful, noninvasive method of assessing the pulmonary circulation. The lowest values of DL(CO) were recorded in patients who subsequently did not survive.