PEEP
Formal Definition
Positive end-expiratory pressure: a ventilator setting that maintains airway pressure above atmospheric at end expiration, preventing alveolar collapse (atelectasis) and improving oxygenation by keeping recruited lung units open throughout the respiratory cycle.
How It's Used on the Ward
"PEEP at 8" or "titrating PEEP" — a core ventilator dial adjusted to balance oxygenation improvement against hemodynamic compromise.
Example
""ARDS: FiO2 1.0 and SpO2 still 86%. PEEP incrementally increased from 8 to 14 cmH2O — SpO2 improved to 92%, but BP dropped from 110/70 to 88/58. Higher PEEP recruits alveoli but reduces venous return. Fluid bolus given, MAP recovered. PEEP 14 maintained.""
Clinical Context
PEEP works by preventing end-expiratory alveolar collapse — once an alveolus opens, PEEP keeps it open. The cost: increased intrathoracic pressure reduces venous return to the right heart, dropping cardiac output and BP. In ARDS, the ARDSnet protocol provides PEEP tables based on FiO2 to target adequate oxygenation (SpO2 88–95%). Intrinsic PEEP (auto-PEEP): occurs in obstructive disease (COPD, asthma) when expiration is incomplete — trapped air builds pressure, worsening hemodynamics. Detect by inspecting the expiratory flow waveform.
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