Profil ventilatoire et pression d'occlusion des insuffisants respiratories chroniques lors du sevrage de la ventilation artificielle

Abstract

Mechanical ventilation weaning in patients with chronic respiratory insufficiency is a period whose outcome is difficult to predict. Ventilatory patterns and occlusion pressure evolution were studied in ten hypercapnic COPD patients in the course of 31 attempts at weaning. The following constants were measured : respiratory frequency (f), tidal volume (V t), minute ventilation (V̊ e), inspiratory and expiratory duration (t i, t e) mean inspiratory flow (V t/t i) and occlusion pressure during the first 0.1 second. These values were taken every 15 minutes for two hours, then every two hours for twelve hours, finally every twelve hours for three days. Three types of behaviour (A, B, C) were observed during weaning. Type A evolution (ten courses), was characterized by an exhaustion occurring in less than two hours with a drop in V̊ e (6.1 ± 0.8 l . min −1), V t (163 ± 9 ml), V t/t i (304 ± 25 ml . s −1), t i (0.56 ± 0.08 s), and P 0.1 (5 ± 3.2 cm H 2O). Type B evolution (eleven courses) was characterized by the same ultimate failure as in type A when reconnected to the respirator. However, at the second hour, these patients had satisfactory ventilatory values : V̊ e = 8.4 ± 0.7 l . min −1, V t = 428 ± 19 ml, V t/t i = 382 ± 27 ml . s −1, t i = 1.12 ± 0.06 s, P 0.1 = 8.9 ± 0.5 cm H 2O. Type C grouped the ten succesfull weanings characterized by a stabilization of the parameters : V̊ e = 8.5 ± 0.9 l . min −1, V t = 400 ± 17 ml, t i = 1.14 ± 0.04 s, V t/t i = 350 ± 30 ml . s −1, at two hours, thirty-six hours and three days. On the other hand, the P 0.1 rised initially up to 7.5 ± 0.7 cm H 2O, then stabilized after thirty-six hours (8.9 ± 0.9 cm H 2O) and finally decreased at the third day (7.1 ± 0.7 cm H 2O). The ventilatory failure at reconnection suggests a diaphragmatic fatigue which may be primitive or secondary to a disturbance of intrapulmonary air-flow distribution.