Abstract

RUIZ-FERRON, Francisco et al. Respiratory work and pattern with different proportional assist ventilation levels. Med. Intensiva [online]. 2009, vol.33, n.6, pp.267-268. ISSN 0210-5691.

Objective: To study the minimum assistance level during proportional assist ventilation (PAV) to decrease the work of breathing to physiological limits (0.6 j/l) and the relationship between breathing pattern changes and respiratory effort at different PAV levels. Design: Prospective cohort study. Setting: Polyvalent intensive care unit of a teaching hospital of Jaen, Spain. Patients and methods: Twelve long-term mechanical ventilated patients who met criteria to initiate weaning from the ventilator. Interventions: We used the Puritan-Bennett 840 ventilator in proportional assist ventilation. The percentage of support was randomly modified between 5% and 80%, in intervals of 10%. Prior to the change in the PAV level, the patients were ventilated in assist-volume control followed by pressure support ventilation. Main variables of interest: Before PAV, we measured the respiratory mechanics and the breathing pattern and work of breathing during this mode. Results: The decrease in respiratory assist in PAV was related to significantly higher work of breathing, this going from 0.2 ± 0,07 (0.1-0.3) j/l with PAV80 to 0.9 ± 0.2 (0.4-1.5) j/l with PAV5 (p = 0.002). The coefficient correlation between PAV level and work of breathing (measured as j/l and j/min) was r = -0.8 and -0.6, respectively. Minimum PAV level related with physiological work of breathing was 30% (0.63 ± 0.13 j/l). Except for the tidal volume that increased significantly (PAV80 vs PAV5 = 0.4 ± 0.1 vs 0.3 ± 0.1; p = 0.02), the remaining variables defining the breathing pattern did not changed with the increase in PAV. Conclusions: In the group of patients studied, the increase in the PAV levels decreases work of breathing, without significantly changing the breathing pattern. Levels lower than 30% of PAV are associated to excessive work of breathing.

Keywords : Mechanical ventilation; Patient-ventilator interactions; Proportional assist ventilation; Work of breathing.

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