Plateau Pressure and Peak Pressure in Mechanical Ventilation
Plateau pressure (Pplat) represents the static pressure in the airways during an inspiratory hold when there is no airflow, reflecting alveolar pressure and respiratory system compliance, while peak inspiratory pressure (PIP) is the maximum pressure reached during active gas delivery and includes both the elastic recoil pressure and the resistive pressure from airflow through the airways and endotracheal tube.
Key Physiological Distinctions
Plateau pressure is measured during a brief inspiratory pause (typically 0.5-1 second) when airflow has ceased, eliminating the resistive component of pressure. This makes Pplat the critical parameter for assessing:
- Alveolar distension and risk of ventilator-induced lung injury 1, 2
- Respiratory system compliance (static compliance = tidal volume / [Pplat - PEEP]) 3
- Driving pressure (DP = Pplat - PEEP), which is a strong predictor of outcomes in ARDS 1, 2
Peak inspiratory pressure reflects the total pressure required to overcome both elastic forces (lung and chest wall recoil) and resistive forces (airway resistance, endotracheal tube resistance, and gas flow). PIP is continuously displayed on ventilators but includes a resistive component that varies with flow rates and airway resistance 3, 4.
Clinical Significance of the Difference
The PIP-to-Pplat gradient (also called resistive pressure) represents the pressure dissipated by airflow resistance. This gradient is normally ≤5 cm H₂O but increases with:
- Higher airway resistance (bronchospasm, secretions, small endotracheal tubes) 3, 4
- Higher inspiratory flow rates 4, 5
- Shorter inspiratory times (less time for flow to decelerate toward zero) 4
- Decelerating flow waveforms (though these actually produce lower PIP than square waveforms) 5
Critical Clinical Pitfall: PIP Cannot Reliably Estimate Pplat
In patients with increased airway resistance, PIP substantially overestimates Pplat and should not be used as a surrogate for lung-protective ventilation targets 3. In infants with severe respiratory viral infections and high airway resistance (mean 136 cmH₂O/L/s), PIP overestimated Pplat by a mean of 7.3 ± 4 cmH₂O 3.
However, in pediatric ARDS patients without significant airway obstruction during decelerating-flow ventilation, PIP may approximate Pplat when inspiratory flow approaches zero (within 1.0 ± 0.6 cm H₂O in 96% of cases) 6. This approximation fails in patients with coexistent obstructive disease where flows do not reach zero 6.
Lung-Protective Ventilation Targets
Guidelines recommend maintaining Pplat <30 cm H₂O in ARDS patients 1. More recent evidence suggests that driving pressure (Pplat - PEEP) is a better predictor of outcome than either tidal volume or Pplat alone 1. The 2019 international consensus recommends:
- Initial tidal volume of 6-8 mL/kg predicted body weight 2
- PEEP ≥5 cm H₂O, individualized thereafter 2
- Monitoring driving pressure as a key determinant of lung injury 2
Practical Measurement Considerations
Ventilator waveform significantly impacts pressure measurements 5. Changing from decelerating to square-wave flow increases both Pplat (21.3 vs 24.8 cm H₂O) and the PIP-to-Pplat gradient (3.8 vs 8.3 cm H₂O) 5. This can prompt unnecessary interventions if clinicians expect a gradient of ≤4 cm H₂O on square-wave ventilation 5.
In spontaneously breathing patients, the direction and magnitude of Pplat-PIP change during inspiratory holds can identify respiratory effort 7. When Pplat exceeds PIP by ≥7 cm H₂O during an inspiratory hold, this indicates high inspiratory effort with maximum negative esophageal pressure >10 cm H₂O 7.
Bottom Line for Clinical Practice
- Always measure Pplat directly via inspiratory hold maneuvers rather than relying on PIP for lung-protective ventilation decisions 1, 3
- Target Pplat <30 cm H₂O in ARDS 1
- Monitor driving pressure (Pplat - PEEP) as the primary predictor of ventilator-induced lung injury 1, 2
- Recognize that PIP-to-Pplat gradients >5 cm H₂O indicate increased airway resistance requiring investigation for reversible causes 3, 4
- Be aware that ventilator mode and waveform affect pressure measurements and avoid unnecessary interventions based on expected "normal" gradients 5