2000 OPEN FORUM Abstracts
Robert S. Campbell, RRT FAARC University of Cincinnati Medical Center, Cincinnati, Ohio
Pepe and Marini coined the term "Auto-PEEP" in 1982 and defined it as the end-expiratory intrapulmonary pressure that develops as a result of dynamic airflow resistance during mechanical ventilation in patients with COPD. The reported incidence of Auto-PEEP during mechanical ventilation is as high as 40%. It has been suggested that the measurement of Auto-PEEP be incorporated into the routine patient-ventilator system check. Optimal management of Auto-PEEP requires clinicians be aware of risk factors, provide accurate measurement using the appropriate measurement technique, and employ the most appropriate treatment strategy.
Risk factors may be intrinsic (excessive secretions, acute or chronic airflow limitation) or extrinsic (high minute ventilation, small ET tube, etc) in nature. Identifying the presence of Auto-PEEP may be easily and reliably carried out using the expiratory flow graphics available on most ICU ventilators. Measurement of Auto-PEEP is more difficult and may require advanced patient manipulation/instrumentation. In passive patients, an expiratory hold may be administered for measurement of end-expiratory (alveolar) pressure. Most common ICU ventilators provide for automation of the expiratory hold to eliminate timing and measurement errors. In active patients, placement of an esophageal balloon may be required to accurately measure auto-PEEP. Recently, some ventilators are measuring auto-PEEP breath-by-breath using advanced measurements and mathematical software.
The presence of auto-PEEP may cause significant increases in patient work of breathing, especially triggering work. Other clinical effects of auto-PEEP, such as hemodynamic embarrassment, mimic those of machine-set PEEP.
Treatment of auto-PEEP may be as simple as shortening the inspiratory time or administering inhaled bronchodilators. More advanced manipulation of the mechanical ventilator is often required. Application of external PEEP may be necessary and helpful in the treatment of auto-PEEP resulting from dynamic airway closure during expiration.
Successful management of mechanically ventilated patients requires clinician awareness, knowledge, and skill regarding the recognition, measurement and treatment of auto-PEEP.