Assessment of Factors Related to Auto-PEEP

Abstract

BACKGROUND:

Previous physiological studies have identified factors that are involved in auto-PEEP generation. In our study, we examined how much auto-PEEP is generated from factors that are involved in its development.

METHODS:

One hundred eighty-six subjects undergoing controlled mechanical ventilation with persistent expiratory flow at the beginning of each inspiration were enrolled in the study. Volume-controlled continuous mandatory ventilation with PEEP of 0 cm H₂O was applied while maintaining the ventilator setting as chosen by the attending physician. End-expiratory and end-inspiratory airway occlusion maneuvers were performed to calculate respiratory mechanics, and tidal flow limitation was assessed by a maneuver of manual compression of the abdomen.

RESULTS:

The variable with the strongest effect on auto-PEEP was flow limitation, which was associated with an increase of 2.4 cm H₂O in auto-PEEP values. Moreover, auto-PEEP values were directly related to resistance of the respiratory system and body mass index and inversely related to expiratory time/time constant. Variables that were associated with the breathing pattern (tidal volume, frequency minute ventilation, and expiratory time) did not show any relationship with auto-PEEP values. The risk of auto-PEEP ≥5 cm H₂O was increased by flow limitation (adjusted odds ratio 17; 95% CI: 6–56.2), expiratory time/time constant ratio <1.85 (12.6; 4.7–39.6), respiratory system resistance >15 cm H₂O/L s (3; 1.3–6.9), age >65 y (2.8; 1.2–6.5), and body mass index >26 kg/m² (2.6; 1.1–6.1).

CONCLUSIONS:

Flow limitation, expiratory time/time constant, resistance of the respiratory system, and obesity are the most important variables that affect auto-PEEP values. Frequency expiratory time, tidal volume, and minute ventilation were not independently associated with auto-PEEP. Therapeutic strategies aimed at reducing auto-PEEP and its adverse effects should be primarily oriented to the variables that mainly affect auto-PEEP values.

Keywords

respiration artificial positive-pressure respiration intrinsic respiratory function tests respiratory mechanics respiratory physiological phenomena respiratory insufficiency

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