Inspiratory Hold: Clinical Purpose and Applications
The inspiratory hold (inspiratory pause) on a mechanical ventilator serves two primary clinical purposes: (1) measuring plateau pressure to assess lung mechanics and prevent ventilator-induced lung injury, and (2) improving CO2 elimination by enhancing gas distribution in the lung periphery.
Primary Clinical Uses
1. Measurement of Plateau Pressure and Respiratory Mechanics
The most critical use of inspiratory hold is to measure plateau pressure (Pplat), which is essential for lung-protective ventilation. During the pause, airflow stops and pressure equilibrates throughout the respiratory system, allowing accurate measurement of:
- Plateau pressure - Must be kept ≤30 cm H2O in ARDS patients 1
- Driving pressure (Pplat - PEEP) - A key predictor of outcomes
- Static compliance - Indicates lung recruitability and overdistension
The 2017 ATS/ERS/SCCM ARDS guidelines strongly recommend monitoring Pplat in all mechanically ventilated ARDS patients to ensure plateau pressures remain ≤30 cm H2O 1. Similarly, the 2019 lung-protective ventilation consensus recommends monitoring dynamic compliance, driving pressure, and Pplat on all controlled mechanically ventilated surgical patients 2.
2. Enhancement of Gas Exchange
Prolonging the inspiratory pause improves CO2 elimination through several mechanisms:
Dead Space Reduction: Extending inspiratory pause from 0.12 seconds to 0.7 seconds significantly decreased dead space-to-tidal volume ratio (Vd/Vt) from 0.70 to 0.64 and reduced PaCO2 from 54 to 50 mmHg in ARDS patients 3. This improvement occurs because the pause allows more time for fresh gas distribution to the lung periphery 4.
Mechanical Benefits: The prolonged pause enabled reduction of tidal volume from 6.3 to 5.6 mL/kg PBW while maintaining the same PaCO2, which decreased plateau pressure (24 to 22 cm H2O) and driving pressure (13.4 to 10.9 cm H2O), while increasing respiratory system compliance 3. This suggests less overdistension and reduced dynamic strain.
Magnitude of Effect: Studies show that increasing inspiratory pause from 0% to 30% of the breathing cycle can increase CO2 elimination per breath by 19%, while reducing it to 0% decreases elimination by 14% 4. The relationship between CO2 elimination and mean distribution time follows a logarithmic pattern 4.
Practical Implementation
Setting the Inspiratory Pause
When using inspiratory pause for improved gas exchange, titrate to achieve:
Ventilatory Effects
The inspiratory pause produces favorable changes in respiratory mechanics:
- Lower peak airway pressures
- Higher total compliance
- Better alveolar ventilation, particularly with bronchial obstruction 6
- Reduced physiological dead space 7
Important Caveats
Oxygenation: The inspiratory pause does not significantly improve oxygenation (PaO2) 3, 7. If oxygenation is the primary concern, adjust PEEP or FiO2 instead 2.
Hemodynamics: The pause can affect venous return and cardiac output. Ensure hemodynamic stability before implementing prolonged pauses 2.
Patient Population: Most evidence supports use in passively ventilated patients with ARDS or acute lung injury. Benefits may differ in spontaneously breathing patients or those with different underlying pathophysiology 3, 4.
Clinical Algorithm
For measuring plateau pressure: Apply a 0.5-second inspiratory hold at end-inspiration to obtain accurate Pplat measurement. Ensure patient is not actively breathing during measurement.
For improving CO2 elimination: Start with 0.5-second pause, monitor PaCO2 response, and titrate up to 0.7 seconds if needed, stopping if intrinsic PEEP develops or I:E ratio reaches 1:1. Once CO2 elimination improves, consider reducing tidal volume to achieve lower plateau and driving pressures while maintaining acceptable PaCO2 3.