Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Conclusion
Our study reassessed in patients with COPD the previously described effects of PSV on the breathing pattern. For PSV levels >12 cm H2O, group 1 patients exhibited significant lower sVe and Sf with higher sVt than did group 2 patients. However, despite this difference in sVe, there was no difference in blood gas values between the two groups. Moreover, OCB was similar at these steps between groups 1 and 2. If we considered that OCB is the consequence of the inspiratory work, these results are consistent with those of Fleury and coworkers who found a poor correlation of inspiratory work per liter with sVe. High levels of PSV (“PSV max”) have been defined as the pressure sufficient to provide a tidal volume of 10 to 12 ml/kg. At these levels (above 15 cm H2O), nearly all the respiratory work is performed by the respirator and “PSV max” could be compared with conventional assist mode ventilation with an additional pressure limit To wean patients from MV, the “best PSV” level must unload the respiratory muscles without inducing atrophy, and must facilitate reconditioning without inducing diaphragmatic fatigue.
Thus, “best PSV” is probably lower than “PSV max” but its exact level is actually not known Brochard and coworkers have defined it as that one that maintained maximal diaphragmatic electrical activity without fatigue (ie, a reduction of the H/L ratio below 80 percent of the initial value of the diaphragmatic surface electromyographic activity). This level was 0 cm H2O for one patient, 10 cm H2O for four patients, and 20 cm H2O for three patients in detail canadian pharmacy levitra. For all these reasons, we chose to begin with a PSV level of 15 cm H2O. Nevertheless, with mild levels (12 cm H2O or 15 cm H2O), we found no difference in the OCB between group 1 and group 2. These results are not surprising according to Brochard and coworkers’ study, as for the four COPD patients they studied, the optimal PSV level was estimated to be 20 cm H2O in three and 10 cm H2O for the last one. So, in COPD patients, the optimal PSV level could reach “PSV max” as electrical evidence of diaphragmatic fatigue arose for lower levels. This might explain why, in our study, adding mild PSV levels to SIMV did not result in any improvement in COPD patients’ OCB. However, low PSV levels (5 to 8 cm H2O) have been described to improve the OCB by offsetting the work imposed by the resistance of breathing circuits and smaller-than-optimal-size artificial airways.