Abstract
BACKGROUND: The spontaneous breathing pattern and its relationship to compliance, resistance, and work of breathing (WOB) has not been examined in patients with acute respiratory distress syndrome (ARDS) or acute lung injury (ALI). Clinically, the ratio of respiratory frequency to tidal volume (f/VT) during spontaneous breathing may reflect adaptation to altered compliance, resistance, and increased WOB. We examined the relationship between f/VT, WOB, and respiratory system mechanics in patients with ARDS/ALI.
METHODS: Data from spontaneous breathing trials were collected from 33 patients (20 with ARDS, 13 with ALI) at various points in their disease course. WOB and respiratory system mechanics were measured with a pulmonary mechanics monitor that incorporates Campbell diagram software. Differences between the patients with ARDS and ALI were assessed with 2-sided unpaired t tests. Multivariate linear regression models were constructed to assess the relationship between f/VT and other pulmonary-related variables.
RESULTS: Patients with ARDS had significantly lower compliance than those with ALI (24 ± 6 mL/cm H2O vs 40 ± 13 mL/cm H2O, respectively, p < 0.001), but this did not translate into significant differences in either WOB (1.70 ± 0.59 J/L vs 1.43 ± 0.90 J/L, respectively, p = 0.30) or f/VT (137 ± 82 vs 107 ± 49, respectively, p = 0.23). Multivariate linear regression modeling revealed that peak negative esophageal pressure, central respiratory drive, duration of ARDS/ALI, minute ventilation deficit between mechanical ventilation and spontaneous breathing, and female gender were the strongest predictors of f/VT.
CONCLUSION: The characteristic rapid shallow breathing pattern in patients with ARDS/ALI occurs in the context of markedly diminished compliance, elevated respiratory drive, and increased WOB. That f/VT had a strong, inverse relationship to peak negative esophageal pressure also may reflect the influence of muscle weakness.
- acute lung injury
- acute respiratory distress syndrome
- breathing pattern
- frequency-to-tidal volume ratio
- lung compliance
- minute ventilation
- rapid shallow breathing index
- work of breathing
- inspiratory time
Footnotes
- Correspondence: Richard H Kallet MSc RRT FAARC, Respiratory Care Services, San Francisco General Hospital, NH: GA-2, 1001 Potrero Avenue, San Francisco CA 94110. E-mail: rkallet{at}sfghsom.ucsf.edu.
Richard H Kallet MSc RRT FAARC presented a version of this paper at the 34th Critical Care Congress of the Society of Critical Care Medicine, held January 15–19, 2005, in Phoenix, Arizona.
The authors report no conflicts of interest related to the content of this paper.
- Copyright © 2007 by Daedalus Enterprises Inc.
