Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Comment
Respiratory acidosis alone, even without clinical signs of respiratory muscle fatigue, was enough to return to the previous step. With PSV, the average weaning time showed a tendency to be shorter, but the difference between the two groups did not reach the significance level, which is not surprising given the small number of patients studied. A few prospective studies have assessed the potential benefits of PSV in weaning patients from MV but none were performed exclusively in patients with COPD. The preliminary results of the European multicenter trial have shown in difficult-to-wean patients that duration of successful weaning attempts was shorter with pressure support alone than with SIMV (PSV: 6±4 days in 36 patients vs SIMV; 10±7 days in 42 patients, p<0.05. With SIMV, the weaning duration appeared shorter in our study than in the European multicenter trial (5.3 ±1.0 days vs 10 ±7 days), and furthermore, our SIMV/PSV procedure seemed to provide shorter weaning periods than PSV alone (SIMV/PSV: 4.2±0.8 days vs 6±4 days with PSV for the European multicenter trial). It must be noticed that populations and procedures may be different, explaining perhaps these differences. Canadian health care mall in detail Nevertheless, SIMV provided satisfying weaning durations in our patients with COPD, with a little, but not significant, advantage arising for the SIMV/PSV modality. Our results on the success rate are in agreement with those of Chinski and coworkers who have compared IMV with and without PSV (10 cm H2O throughout the weaning process) in stable patients who fulfilled weaning criteria and have concluded that weaning success was not different between the two groups.
Because the patient’s work of breathing is difficult to measure directly and depends on numerous factors, we chose to evaluate it indirectly through the oxygen cost of spontaneous breathing. This is usually less than 5 percent of the Vo2tot in normal subjects breathing quietly, but increases in patients with COPD and in patients undergoing artificial ventilation. Indeed, we found high values of OCB in COPD patients when breathing spontaneously via the respirator circuitry. The Vo2resp ranged from 50 to 108 ml/min (or from 17.2 to 40 percent of the Vo2tot), with Vo2resp/sVE ranging from 5.5 ml/L to 10.3 ml/L. Although these results agree with those of previous studies performed on patients with COPD, the OCB could have been underestimated as some respiratory muscle activity might have persisted on assisted controlled ventilation, even in the absence of any triggering. Indeed, we did not directly assess the absence of respiratory muscle activity with possible overestimation of the Vo2nonresp.