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 1000-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 × l. 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 × l 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.