Am. J. Respir. Crit. Care Med., Volume 162, Number 5, November 2000, 1633-1640

Contribution of Expiratory Muscle Pressure to Dynamic Intrinsic Positive End-Expiratory Pressure
Validation Using the Campbell Diagram

SPYROS G. ZAKYNTHINOS, THEODOROS VASSILAKOPOULOS, EPAMINONDAS ZAKYNTHINOS, ANTONIS MAVROMMATIS, and CHARIS ROUSSOS

Department of Critical Care and Pulmonary Services, Athens University Medical School, Evangelismos Hospital, Athens, Greece

In spontaneously breathing (SB) patients expiratory muscle contraction leads to an overestimation of dynamic intrinsic PEEP (PEEP_i,dyn). To quantify this overestimation, PEEP_i,dyn measured with the esophageal balloon technique was corrected for the increase in Pga over the course of expiration (Pga,exp rise), for the whole decay of Pga during inspiration (Pga,total decay) or for the part of Pga decay restricted between the onset of inspiratory effort and the point of zero flow (Pga,zf decay). Corrections were compared with the reference PEEP_i,dyn (PEEP_i,dyn ref ), calculated by using the Campbell diagram. In 15 ventilator-dependent, SB, and actively expiring patients, we found that the difference PEEP_i,dyn  Pga,total decay (mean ± SD, 5.7 ± 1.9 cm H₂O) was quite similar to PEEP_i,dyn ref (5.3 ± 1.9 cm H₂O). Their mean difference was 0.37 cm H₂O with limits of agreement 0.09 to 0.83 cm H₂O, indicating strong agreement between these methods. PEEP_i,dyn  Pga,exp rise (6.0 ± 2.1 cm H₂O) was also similar to PEEP_i,dyn ref. Their mean difference was 0.72 cm H₂O with limits of agreement 1.69 to 3.13 cm H₂O, indicating good agreement. In contrast, mean difference of PEEP_i,dyn  Pga,zf decay and PEEP_i,dyn ref was 3.14 cm H₂O with limits of agreement 0.46 to 6.74 cm H₂O, indicating lack of agreement. The error in measurement due to the subtraction of Pga,zf decay from PEEP_i,dyn (i.e., [PEEP_i,dyn  Pga,zf decay]  PEEP_i,dyn ref ) was proportional to the intensity of expiratory muscle contraction, as expressed by the Pga,exp rise (r = 0.903, p < 0.001). We conclude that in actively expiring patients an adequate correction of PEEP_i,dyn for the overestimation caused by expiratory muscle contraction can be made by subtracting either Pga,total decay or Pga,exp rise from PEEP_i,dyn, the former achieving the best performance.

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