2004 OPEN FORUM Abstracts
rapid-shallow breathing in patients with acute lung injury (ali) and acute respiratory distress syndrome (Ards).
RH
Kallet MS RRT, JA Alonso RRT, AR Campbell MD, R Dicker MD, RC
Mackersie MD. Departments of Surgery and Anesthesia, University of
California, San Francisco at San Francisco General Hospital.
Background:
A rapid-shallow breathing pattern is predicted when the elastic
recoil properties of the chest are elevated (1). This often presages
weaning failure during a spontaneous breathing trial (2). As
ALI/ARDS patients typically have increased lung and chest wall
elastance, We determined if the frequency-to-tidal volume ratio
(f/VT) is associated with specific measures of chest
mechanics and breathing effort during a spontaneous breathing trial.
Methods: Data were collected from 31 ALI/ARDS patients who
underwent brief (1-2 min) trials on continuous positive airway
pressure (CPAP) with a mean pressure of 5.4 ± 3.9 cm H2O.
Measurements were made with a pulmonary mechanics monitor (BICORE
CP-100) incorporating Campbell Diagram software. An average of 10-15
breaths was used for analysis. Eight variables were grouped into 6
multivariate, logistical regression models to assess their
association with f/VT. The models were designed to
account for various combinations of 1.) maximal inspiratory pressure
(Pmax), 2.) respiratory system compliance (Crs), 3.) elastic and
resistive work of breathing (WOBe, WOBr), 4.) mechanical indices of
inspiratory muscle oxygen consumption [inspiratory muscle power
output (W), and pressure-time product (PTP)], 5.) indices of
inspiratory muscle fatigue [pressure-time index (PTI),and inspiratory
pressure/maximal inspiratory pressure (Pi/Pmax)], and 6.) Central
respiratory drive [inspiratory pressure in 0.1sec (P0.1), peak
inspiratory flow rate (PFR) and mean inspiratory flow rate (MFR)].
Results:
Models with predominantly pressure-related variables appear to have
a higher predictive value in assessing f/VT changes than
WOB and W measurements. Measures of central drive contribute
strongly to the predictive value of the models.
| Model | Variables grouped in the model | R2 | p |
| 1 | Pmax + Crs+ P0.1 †+ MFR +PTI +PTP +Pi/Pmax + WOBe | 0.74 | 0.001 |
| 2 | Pi/Pmax + PTI + W + PTP + P0.1 + MFR + WOBe | 0.74 | 0.003 |
| 3 | Pmax + Pi/Pmax + PTI + PTP + WOBe + P0.1 + MFR | 0.68 | 0.0011 |
| 4 | Pmax + Crs + Pi/Pmax + PTI + W + PTP + P0.1 + WOBe | 0.66 | 0.0065 |
| 5 | Pmax + Crs + P0.1+ PFR + W + PTI + Pi/Pmax + WOBr | 0.62 | 0.012 |
| 6 | Pmax + Crs + W + WOBe + WOBr + PTP + PFR + P0.1 | 0.51 | 0.08 |
†
BOLD
denotes p < 0.05 for individual variables.
Conclusion:
Changes in f/VT ratio during brief CPAP trials in
ALI/ARDS patients appear to be strongly influenced by changes in
central respiratory drive and mechanical indices of respiratory
muscle oxygen consumption and fatigue. Variables related to the
elastic work load (WOBe and Crs) appear to have less influence.
1.
Otis AB, Fenn WO, Rahn H. J Appl Physiol 1950; 2:592.
2.
Yang KL, Tobin MJ. N Engl J Med. 1991;324:1445