Evaluation of noninvasive mechanical ventilation with positive pressure in the management of patients with difficult weaning from invasive mechanical ventilation
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KeywordsAcute Respiratory Failure Spontaneous Ventilation Invasive Mechanical Ventilation Spontaneous Breathing Trial 30th Minute
NPPV has been intensely investigated and used in patients with acute respiratory failure of several etiologies. However, recent studies have left several open questions with respect to the benefits of its use in invasive mechanical ventilation (IMV) weaning. A randomized controlled study has shown that NPPV has reduced the IMV use time in patients with persistent failure in weaning. However, some studies did not confirm these results.
To evaluate the application of NPPV, using the Bilevel mode, in patients with IMV weaning difficulties, characterized by spontaneous ventilation failure during a spontaneous breathing trial (SBT).
All patients under IMV for more than 48 hours from June 2003 to July 2004 were submitted to a SBT. Those that failed during the first 30 min of the T-piece trial, and without contraindications to NPPV, were randomized to be back to IMV (conventional treatment) or to be changed to NPPV. Contra-indications to NPPV included patients with facial trauma or cranial surgery, recent gastric or esophagic surgery, tracheostomy, respiratory secretion excess, agitation and noncooperative behaviour, and were excluded from the experiment. Inclusion in the experiment has been authorized by signed informed consent. Prior to subjecting the patient to the SBT we collected a sample of arterial blood gases and a measure of maximal inspiratory pressure (PImax) was taken. During spontaneous ventilation in the T-piece trial, in the first and 30th minutes measurements of tidal volume (VT), minute ventilation (Ve), respiratory rate (f), rapid shallow breathing index (f/VT), heart rate and peripheral oxygen saturation were taken. After randomizing to IMV or NPPV, patients were followed clinically and evaluated concerning time of ventilation, complications and mortality rate.
A total of 158 patients were submitted to a SBT. Among patients that failed in the T-piece trial 43 patients were eligible for this study, 21 being studied in NPPV and 22 in IMV. The mean age of the NPPV group was 68 ± 15 years, and of the IMV group was 59 ± 17 years. The average of mechanical ventilation previous to exposition to SBT was 7 days for the NPPV group and 8 days for the IMV group. The values of Ve, VT, and PImax were similar in both groups, in the first and 30th minute of ventilation in the T-piece. The average ventilation support use time, after failure in the T-piece, was 2 days for the NPPV group and 9 days for the IMV group, with statistical significance (P < 0.05). Total mortality was 26% (four patients in IMV and seven patients in NPPV). Considering the total number of complications, NPPV had a protective effect (RR 0.205).
From these preliminary data, we believe that NPPV could be an effective treatment for patients presenting difficulties in weaning from mechanical ventilation.