Airway occlusion pressure to titrate positive end-expiratory pressure in patients with dynamic hyperinflation

Abstract

Background: Although the use of external positive end-expiratory pressure (PEEP) is recommended for patients with intrinsic PEEP, no simple method exists for bedside titration. We hypothesized that the occlusion pressure, measured from airway pressure during the phase of ventilator triggering (P(0.1t)), could help to indicate the effects of PEEP on the work of breathing (WOB). Methods: Twenty patients under assisted ventilation with chronic obstructive pulmonary disease were studied with 0, 5, and 10 cm H2O of PEEP while ventilated with a fixed level of pressure support. Results: PEEP 5 significantly reduced intrinsic PEEP (mean ± SD, 5.2 ± 2.4 cm H2O at PEEP 0 to 3.6 ± 1.9 at PEEP 5; P < 0.001), WOB per min (12.6 ± 6.7 J/min to 9.1 ± 5.9 J/min; P = 0.003), WOB per liter (1.2 ± 0.4 J/l to 0.8 ± 0.4 J/l; P < 0.001), pressure time product of the diaphragm (216 ± 86 cm H2O · s-1 · min-1 to 155 ± 179 cm H2O · s-1 · min-1; P = 0.001) and P(0.1t) (3.3 ± 1.5 cm H2O to 2.3 ± 1.4 cm H2O; P = 0.002). At PEEP 10, no further significant reduction in muscle effort nor in P(0.1t) (2.5 ± 2.1 cm H2O) occurred, and transpulmonary pressure indicated an increase in end- expiratory lung volume. Significant correlations were found between WOB per rain and P(0.1t) at the three levels of PEEP (P < 0.001), and between the changes in P(0.1t) versus the changes in WOB per min (P < 0.005), indicating that P(0.1t) and WOB changed in the same direction. A decrease in P0.1 with PEEP indicated a decrease in intrinsic PEEP with a specificity of 71% and a sensitivity of 88% and a decrease in WOB with a specificity of 86% and a sensitivity of 91%. Conclusion: These results show that P(0.1t) may help to assess the effects of PEEP in patients with intrinsic PEEP.