[Changes in inspiratory capacity during acute respiratory failure in COPD patients]

Inspiratory Capacity (IC), which reflects dynamic pulmonary hyperinflation, correlates with outcome in moderate exacerbation of COPD. Whether this is also true in COPD with acute respiratory failure (ARF) has not been studied.

A prospective multicenter assessment of IC measurement feasibility, reliability, time-course and relationship to outcome in COPD with ARF was conducted. Dyspnea (visual analogue scale) and IC were repeatedly measured. Outcome was classified as not favourable (death or intubation or non invasive ventilation increased or patient referred to ICU from respiratory ward) or favourable (none of the above criteria).

Fifty patients were included and 48 analysed. IC measurement was possible in all but one patient and its coefficient of variation was 9+/-8%. Between inclusion into the study and discharge, IC increased from 39.9+/-15.5 to 50.2+/-14.5% pred (p<0.001) and dyspnea declined from 48+/-23 to 33+/-22 mm (p<0.001). Inclusion IC was not different on average between patients with or without favourable outcome.

In COPD patients with ARF, IC measurement at bedside was feasible and reproducible. IC was low at entry and increased over time from inclusion to discharge tending to correlate with patient outcome.