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Imposed work of breathing during high-frequency oscillatory ventilation: a bench study
Marc van Heerde1, Huib R van Genderingen, Tom Leenhoven
1Department of Pediatric Intensive Care, VU University Medical Center, Amsterdam, The Netherlands. m.vanheerde@vumc.nl
Critical Care (London, England)
|February 14, 2006
Summary
High fresh gas flow during high-frequency oscillatory ventilation (HFOV) reduces work of breathing (WOB) in adult and pediatric patients. Lower WOB in infants suggests better tolerance for spontaneous breathing during HFOV.
Area of Science:
- Mechanical Ventilation
- Respiratory Mechanics
- Critical Care Medicine
Background:
- Spontaneously breathing mechanically ventilated patients experience increased work of breathing (WOB) due to the endotracheal tube and ventilator.
- Total WOB comprises elastic and resistive components.
Purpose of the Study:
- To assess the imposed WOB in spontaneously breathing patients during high-frequency oscillatory ventilation (HFOV).
- To evaluate the impact of fresh gas flow rate on imposed WOB.
Main Methods:
- A computer-controlled test lung simulated spontaneous breathing across a range of patient sizes (newborn to adult).
- The system was connected to an HFOV ventilator via an endotracheal tube.
- Airway pressures and flows were measured, and WOB was calculated using the Campbell diagram.
Main Results:
- Imposed WOB was significantly higher in pediatric and adult simulations compared to newborns and infants.
- Low fresh gas flow rates and high peak inspiratory flow rates significantly increased imposed WOB.
- Mean airway pressure decreased during spontaneous breathing, particularly at low fresh gas flow rates, leading to potential ventilator shut-off.
Conclusions:
- Spontaneous breathing during HFOV imposes considerable WOB in pediatric and adult patients, correlating with reported discomfort.
- Lower imposed WOB in neonates and infants explains their better tolerance of spontaneous breathing during HFOV.
- A high fresh gas flow rate reduces imposed WOB, suggesting the need for demand-flow systems to optimize spontaneous breathing during HFOV.
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