Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury.
BACKGROUND
Low tidal volume ventilation strategies for patients with respiratory failure from acute lung injury may lead to breath stacking and higher volumes than intended.


OBJECTIVE
To determine frequency, risk factors, and volume of stacked breaths during low tidal volume ventilation for acute lung injury.


METHODS
Prospective cohort study of mechanically ventilated patients with acute lung injury (enrolled from August 2006 through May 2007) treated with low tidal volume ventilation in a medical intensive care unit at an academic tertiary care hospital.


METHODS
Patients were ventilated with low tidal volumes using the Acute Respiratory Distress Syndrome Network protocol for acute lung injury. 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
Twenty 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). Inter-rater agreement for identifying stacked breaths was high (kappa 0.99, 95% confidence interval 0.98-0.99). Stacked breaths occurred at a mean 2.3 +/- 3.5 per minute and resulted in median volumes of 10.1 (8.8-10.7) mL/kg predicted body weight, which was 1.62 (1.44-1.82) 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, 95% confidence interval 0.23-0.90).


CONCLUSIONS
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.
Pohlman
Mark C
MC
Departments of Medicine, Section of Pulmonary and Critical Care Medicine, University of Chicago, Chicago, IL, USA.
McCallister
Kathryn E
KE
Schweickert
William D
WD
Pohlman
Anne S
AS
Nigos
Celerina P
CP
Krishnan
Jerry A
JA
Charbeneau
Jeff T
JT
Gehlbach
Brian K
BK
Kress
John P
JP
Hall
Jesse B
JB
D000328:Adult; D015331:Cohort Studies; D003422:Critical Care; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D012307:Risk Factors; D013990:Tidal Volume / Q000502:physiology*; D012122:Ventilators, Mechanical