Effect of PEEP on work of breathing in mechanically ventilated COPD patients.

OBJECTIVE: To study the effects of PEEP on the inspiratory work done per breath on the respiratory system (W(I,rs)) in patients with chronic obstructive pulmonary disease (COPD).

DESIGN: Physiological study.

SETTING: Fourteen-bed Medical ICU of a 1,000-bed teaching tertiary hospital.

PATIENTS AND PARTICIPANTS: Ten patients with COPD intubated and mechanically ventilated for acute respiratory failure.

INTERVENTIONS: PEEP of 0 (ZEEP), 5, 10, and 15 cm H2O were applied randomly and measurements done at the end of a 15-20 min period.

MEASUREMENTS AND RESULTS: Using the rapid airway occlusion technique during constant flow inflation, we partitioned W(I,rs) into its static and dynamic components. On ZEEP, the mean +/- SD values of W(I,rs) amounted to 15.1 +/- 5.7 cm H2O x 1. With increasing PEEP, W(I,rs) was significantly reduced to 12.6 +/- 5.7, 11.1 +/- 4.1, and 10.4 +/- 2.8 cm H2O x 1 at PEEP of 5, 10, and 15 cm H2O, respectively (P < 0.05). This reduction was entirely due to the decline of the work due to intrinsic PEEP (PEEPi) and was abolished when the applied PEEP counterbalanced PEEPi. The other components of W(I,rs) were not affected by PEEP. By increasing PEEP up to the level of PEEPi on ZEEP, no further increase in end-expiratory lung volume was observed.

CONCLUSIONS: In COPD patients the application of PEEP levels close to PEEPi can substantially reduce W(I,rs) without promoting further dynamic pulmonary hyperinflation.