Physiological effects of constant versus decelerating inflation flow in patients with chronic obstructive pulmonary disease under controlled mechanical ventilation.

OBJECTIVE

To study the cardiorespiratory effects of inspiratory flow rate and waveform in COPD patients.

DESIGN

Prospective physiological investigation with randomized allocations of experimental conditions.

SETTING

A 14-bed medical ICU in a 1000-bed university hospital.

PATIENTS AND

PARTICIPANTS

Ten COPD intubated, sedated and paralyzed patients with chronic obstructive pulmonary disease (COPD), mechanically ventilated for acute respiratory failure.

INTERVENTIONS: In volume-controlled mode, three inflation flow rates of 0.40, 0.70, and 1.10 l/s for 20 min with a constant (CF) or a decelerating (DF) inflation flow profile. Each patient received all six experimental conditions in a random order. Tidal volume and respiratory frequency were similar during the experimental conditions.

MEASUREMENTS AND

RESULTS

Arterial blood gases, hemodynamics ( n=8), and respiratory mechanics were measured with zero end expiratory pressure. Between flow rates the median (25th-75th percentiles) values of PaO(2)/FIO(2) were 232 (132-289), 253 (161-338), 231 (163-352) for CF and 253 (143-331), 249 (164-360), 231 mmHg (187-351), for DF, respectively; the maximal airway pressures were 25.6, 28.3, 34.6 cmH(2)O for CF and 21.7, 29.6, 34.8 cmH(2)O for DF, respectively, the mean airway pressures were 8.9, 6.1, 5.4 cmH(2)O for CF and 9.1, 7, 6.5 cmH(2)O for DF, respectively.

CONCLUSIONS

Changing the ventilator in volume-controlled mode with a DF or CF profile has no significant cardiorespiratory effect in intubated COPD patients mechanically ventilated for acute respiratory failure.