Auto-PEEP is Common in Mechanically Ventilated Patients: A Study of Incidence,Severity,and Detection

Abstract

Auto-PEEP is unintentional positive end-expiratory pressure (PEEP) that occurs at the alveolar level in mechanically ventilated patients when there is incomplete exhalation; this complication is not evident unless looked for. Auto-PEEP is a recognized hazard in patients with chronic obstructive pulmonary disease (COPD), but its prevalence in a broad spectrum of mechanically ventilated patients with high minute volume ( ${\stackrel{\cdot }{\text{V}}}_{\text{E}}$ ) requirements (> 10 L) has not previously been studied. We designed this study of the incidence, severity, and detection of auto-PEEP in a major medical center to aid the clinician in predicting when this complication might occur and to describe simple maneuvers to measure it in a reproducible manner. Method: We looked for auto-PEEP in patients on controlled ventilation only (not assisting or breathing spontaneously). We checked for auto-PEEP through three ventilators-the Siemens Servo 900B and 900C and the Bennett MA-1- in patients requiring VE above 10 L. Results: Of 164 mechanically ventilated patients admitted to our ICUs during the study period, 62 were on controlled ventilation, required ${\stackrel{\cdot }{\text{V}}}_{\text{E}}$ > 10 L, and entered the study. We recorded measurable auto-PEEP- ranging from 1 to 16 cm H2O upon initial measurement-in 24 (39%) of the patients. In subsequent measurements, auto-PEEP increased from as little as 1 to as much as 25 cm H₂O in 7 (29%) of the 24 patients despite efforts to minimize it. Only 5 (21%) of the 24 had a known history of COPD. The incidence of auto-PEEP in subjects with a ${\stackrel{\cdot }{\text{V}}}_{\text{E}}$ above 20 L was 100%. The incidence of auto-PEEP increased with patient age: of those less than 40 years of age, 16% had auto-PEEP; 33% of those between 40 and 60 years old had it; and 60% of those above 60 years of age had this complication. The VE requirement to experience auto-PEEP decreased with age. When patients were classified by diagnosis, we found that most had primarily respiratory or cardiopulmonary disorders. Conclusions: We conclude that regardless of COPD, auto-PEEP is common in patients on controlled ventilation with a ${\stackrel{\cdot }{\text{V}}}_{\text{E}}$ above 10 L and that clinicians should regularly screen for it. Those at high risk are over 60 years of age, have respiratory or cardiopulmonary disorders, and/or require ${\stackrel{\cdot }{\text{V}}}_{\text{E}}$ over 20 L. (Respir Care 1986;31:1069-1074.)