Physiologic determinants of ventilator dependence in long-term mechanically ventilated patients

Citation
A. Purro et al., Physiologic determinants of ventilator dependence in long-term mechanically ventilated patients, AM J R CRIT, 161(4), 2000, pp. 1115-1123
Citations number
34
Categorie Soggetti
Cardiovascular & Respiratory Systems","da verificare
Journal title
AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE
ISSN journal
1073449X → ACNP
Volume
161
Issue
4
Year of publication
2000
Pages
1115 - 1123
Database
ISI
SICI code
1073-449X(200004)161:4<1115:PDOVDI>2.0.ZU;2-3
Abstract
To investigate the pathophysiologic mechanisms of ventilator dependence, we took physiologic measurements in 28 patients with COPD and 11 postcardiac surgery (PCS) patients receiving longterm mechanical ventilation during a s pontaneous breathing trial, and in 20 stable, spontaneously breathing patie nts matched for age and disease. After 40 +/- 14 min of spontaneous breathi ng, 20 of 28 patients with COPD and all 11 PCS patients were judged ventila tor-dependent (VD) We found that in the 31 VD patients tidal volume was low (VT: 0.36 +/- 0.12 and 0.31 +/- 0.08 L for COPD and PCS, respectively), ne uromuscular drive was high (P-0.1: 5.6 +/- 1.6 and 3.9 +/- 1.9 cm H2O), ins piratory muscle strength was reduced (Pdi(max): 42 +/- 12 and 28 +/- 15 cm H2O), and lung mechanics were abnormal, particularly PEEPi (5.9 +/- 3.0 cm H2O) and lung resistance (22.2 +/- 9.2 cm H2O/L/s) in COPD. The load/capaci ty balance was altered (Pdi /Pdi(max) and Ppl /Ppl(max) > 0.4) and the effe ctive inspiratory impedance was high (P-0.1/VT/TI greater than or equal to 10 cm H2O/L/s). Failure to wean occurred in patients with f/VT > 105 breath s/min/L and 56% of patients with COPD with f/VT < 80 breaths/min/L. Those w ho failed despite a low f/VT ( < 80 breaths/min/L) either showed ineffectiv e inspiratory efforts, which artificially lowered f/ VT (n = 8), or did not increase breathing frequency (n = 5), but P-0.1 and P-0.1/VT/TI were as hi gh as in other VD patients. In the 31 VD patients, Pa-CO2 increased during the weaning trial (+12.3 +/- 8.0 mm Hg). We conclude that in the presence o f a high drive to breathe, the imbalance between increased work load and re duced inspiratory muscle strength causes respiratory distress and CO2 reten tion. Noninvasive measurements (breathing pattern, P-0.1, P-0.1/ VT/TI) may give better insight into weaning failure useful in clinical decision-makin g, particularly in patients with COPD not showing rapid shallow breathing ( 56% in this study).