Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Appendix
This additional burden is not negligible: Katz and coworkers have shown that the respirator (Puritan Benett 7200) induces an additional inspiratory work ranging from 10 to 40 percent. Fiastro and coworkers predicted that a 1-mm decrease in the tube diameter results in a 67 to 100 percent increase in this work. Nevertheless, low PSV level (6 cm H2O or 8 cm H2O) did not-significantly decrease the OCB of our patients.
The only objective benefit of PSV appeared when considering Vc^resp/sVE which represents the oxygen cost per liter of spontaneous ventilation and expresses the efficiency of the ventilation. The Vo2resp/ sVe significantly decreased across the weaning period in group 1 whereas it significantly increased in group 2 (Table 3 and Fig 4). Buy claritin online in detail Pressure support ventilation could improve the efficiency of the ventilation when added to SIMV. As PSV had allowed patients to breathe with larger sVt and lower Sf, the longer expiratory time might have contributed to reduce intrinsic PEEP and accelerated the recovery in lung mechanics. This could explain why sVt remained constant throughout the weaning period despite the degressive PSV levels and the decrease in Vc^resp/sVE. Nevertheless, these suggestions remain speculative as we did not measure the lung mechanics. The interpretation of our results depends to a large extent on the matching of the two groups of patients.
It should be noted that the two groups were not only similar in terms of clinical, functional, and blood gas data before the acute exacerbation, but that the deterioration in blood gas values induced by the acute episode was also similar (Tables 1 and 2). Therefore, we believe the two groups were strictly comparable. However, group 2 had been receiving mechanical ventilation longer, but not significantly so, than group 1 before reaching the weaning criteria. This could suggest that their acute disease was somewhat more severe than that of group 1. If this is so, the tendency to an advantage for SIMV/PSV over SIMV in terms of weaning duration could be even less than suggested by our figures.
In summary, this study compared SIMV/PSV with SIMV alone in 19 patients with COPD during the weaning period. First, we found the conventional weaning criteria to be inaccurate in patients with COPD receiving prolonged MV. Second, SIMV appeared very useful clinically, providing a weaning period of 5.3 ±1.0 days. Third, adding PSV to SIMV marginally reduced the weaning period, without any improvement in the success rate. Finally, no difference in the OCB was found with or without PSV, at any PSV levels.