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Types of PEEP
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Now I have comprehensive information from multiple authoritative textbooks. Here is a full breakdown:
Types of PEEP
PEEP (Positive End-Expiratory Pressure) is the maintenance of positive airway pressure above atmospheric at the end of passive exhalation. The ventilator's PEEP valve allows expiratory flow only when airway pressure exceeds the set PEEP level.
1. Extrinsic PEEP (Applied PEEP / ePEEP)
This is PEEP deliberately set on the ventilator by the clinician. It is the intentional application of positive pressure at end-expiration.
Mechanism and effects:
- Increases functional residual capacity (FRC)
- Recruits (re-expands) collapsed alveoli, especially above the lower inflection point (LIP) of the pressure-volume curve
- Reduces intrapulmonary shunting - improves arterial oxygenation
- Reduces ventilation-perfusion (V/Q) mismatch
- Reduces ventilator-induced lung injury (VILI) by preventing repetitive alveolar collapse-reopening
- Most effective in diffuse parenchymal lung disease (e.g., ARDS)
Adverse effects:
- Elevated intrathoracic pressure - reduced venous return, decreased cardiac output
- Right ventricular dysfunction
- Barotrauma / pneumothorax
- Increased cerebral venous pressure (worst PEEP for cerebral venous drainage may be the "best" for oxygenation)
- In focal processes (e.g., lobar pneumonia), may overdistend well-aerated regions and worsen V/Q matching
"Applied PEEP must be specifically differentiated from intrinsic PEEP (iPEEP, or auto-PEEP)."
- Rosen's Emergency Medicine
2. Intrinsic PEEP (Auto-PEEP / iPEEP)
This is PEEP that develops unintentionally due to incomplete exhalation - air traps in the alveoli, generating positive alveolar pressure at end-expiration that is NOT set by the clinician.
Mechanism: Occurs when expiratory time is insufficient for full lung emptying. Alveolar pressure remains positive above set PEEP.
Major determinants:
- High minute ventilation (high respiratory rate)
- Increased expiratory airway resistance (asthma, COPD)
- Increased respiratory system compliance (emphysema)
- Shortened expiratory time (high I:E ratio)
- Expiratory flow limitation
Detection:
- Flow at end expiration remains detectable on the flow-time waveform
- End-expiratory occlusion maneuver: airway opening is occluded at end expiration and the equilibrated pressure is read on the manometer - the difference from set PEEP is the auto-PEEP
- Patients fail to trigger the ventilator (must overcome auto-PEEP before triggering)
- Failed inspiratory efforts ("ineffective efforts") occur in >10% of breaths in ~25% of PSV patients
Clinical significance:
- Can falsely lower measured respiratory system compliance
- Causes hemodynamic compromise (increased intrathoracic pressure)
- Auto-PEEP of 4-6 cmH2O is typical in COPD/lung cancer patients on one-lung ventilation (OLV)
- Is a primary reason to reduce tidal volume
Interaction with extrinsic PEEP:
- The effects are complex and depend on baseline auto-PEEP levels
- Patients with low auto-PEEP (<2 cmH2O) experience a greater rise in total PEEP from added extrinsic PEEP
- Patients with high auto-PEEP (>10 cmH2O) experience a smaller additional rise
- Total PEEP = set PEEP + auto-PEEP
- Goldman-Cecil Medicine & Miller's Anesthesia, 10e
3. Total PEEP
Total PEEP = Extrinsic PEEP + Auto-PEEP (Intrinsic PEEP)
This is the actual alveolar end-expiratory pressure. When interpreting respiratory mechanics, total PEEP must be accounted for - if auto-PEEP is missed, compliance measurements will be falsely low.
4. "Best PEEP" / Optimal PEEP
A strategy rather than a fixed type, "best PEEP" refers to the PEEP level that optimizes the balance between alveolar recruitment and overdistention/hemodynamic compromise for an individual patient.
Methods to determine best PEEP:
| Method | Principle |
|---|---|
| Incremental PEEP titration | Increase PEEP until PO2 no longer rises; monitor for CO2 rise or hemodynamic compromise |
| Pressure-volume (P-V) curve | Set PEEP at or slightly above the lower inflection point (LIP) of the compliance curve |
| Driving pressure minimization | Titrate PEEP to minimize driving pressure (plateau pressure - PEEP); considered optimal for OLV |
| Esophageal manometry | Use esophageal balloon to measure transpulmonary pressure; distinguish lung vs. chest wall compliance; guides individualized best PEEP |
| ARDSnet table-based approach | Use FiO2/PEEP combination tables; minimum PEEP of 5 cmH2O in ARDS |
Important caveat: Although optimal PEEP improves arterial oxygenation, achieving "best PEEP" has not been definitively shown to improve clinical outcomes and may cause barotrauma or hypotension from decreased right ventricular preload. - Harrison's Principles of Internal Medicine, 22e
5. CPAP vs PEEP (Related Concept)
| Feature | PEEP | CPAP |
|---|---|---|
| Breathing type | Ventilator-cycled (mandatory) breaths | Spontaneous breathing |
| Setting | Invasive mechanical ventilation (by convention) | Invasive or noninvasive |
| Mechanism | Pressure threshold at end-expiration | Continuous positive pressure through entire cycle |
| Airway | Artificial airway typically required | Can use tight-fitting mask (if CPAP <15 cmH2O) |
In practice, the distinction is often blurred because patients may receive a mix of mandatory and spontaneous breaths. BiPAP/BPAP uses IPAP (inspiratory) + EPAP (expiratory, equivalent to PEEP).
- Morgan & Mikhail's Clinical Anesthesiology, 7e
Summary Table
| Type | Source | Detectable at Airway Opening? | Clinical Intent |
|---|---|---|---|
| Extrinsic PEEP | Ventilator-set | Yes | Deliberate - oxygenation/recruitment |
| Intrinsic PEEP (Auto-PEEP) | Air trapping | No (occult) | Unintentional - must be recognized |
| Total PEEP | Sum of both | Via occlusion maneuver | Monitoring/mechanics |
| Best/Optimal PEEP | Titrated strategy | Via P-V curve / esophageal pressure | Individualized optimization |
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