Stacked breaths - complication of low tidal volume? - itself causing high tidal volume?
Very interesting study, published last month to determine frequency, risk factors, and volume of stacked breaths during low tidal volume ventilation for acute lung injury.
Rationale: Low tidal volume ventilation strategies for patients with respiratory failure from acute lung injury may lead to breath stacking and higher volumes than intended.
Design, Setting, and Patients: Prospective cohort study of mechanically ventilated patients with acute lung injury in a medical intensive care unit at an academic tertiary care hospital. Patients were ventilated with low tidal volumes using the ARDS Network protocol.
Continuous flow-time and pressure-time waveforms were recorded. The frequency, risk factors, and volume of stacked breaths were determined. Sedation depth was monitored using Richmond agitation sedation scale.
Results: 20 patients were enrolled and studied for a mean 3.3 +/- 1.7 days. The median (interquartile range) Richmond agitation sedation scale was -4 (-5, -3).
- Stacked breaths occurred at a mean 2.3 +/- 3.5 per minute and resulted in median volumes of 10.1 mL/kg predicted body weight, which was 1.62 times the set tidal volume
- Stacked breaths were significantly less common with higher set tidal volumes (relative risk 0.4 for 1 mL/kg predicted body weight increase in tidal volume)
Conclusion: Stacked breaths occur frequently in low tidal volume ventilation despite deep sedation and result in volumes substantially above the set tidal volume. Set tidal volume has a strong influence on frequency of stacked breaths.
Reference: click to get abstract
Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury - Critical Care Medicine. 36(11):3019-3023, November 2008.
