Determining the best mechanical ventilation mode and pressure combinations which predict successful rapid shallow breathing index nearest to values calculated in spontaneous ventilation

Time spent in the weaning process represents 40-50 % of the total duration of mechanical ventilation (MV) (3, 21, 25). There are some methods for conducting this process which will require the cooperation of the patient during the phase of discontinuation. Rapid shallow breathing index (RSBI), was the best predictive parameter for the initial assessment of the readiness for discontinuation of MV support (37). In this study we aimed to determine the best MV mode and pressure combinations which predict successful RSBI nearest to values calculated in spontaneous ventilation and estimate the patients readiness to weaning.Twenty five mechanically ventilated patients were included in the study. Spontaneous breathing trial (SBT) was applied to the patients who meet the criteria of daily secreening (DS) after 24th hours of intubation. RSBI and other weaning parameters were calculated in different combinations before T tube trial in all patients. RSBI did not differ significantly between spontaneous mode and other combinations, but the best correlation was found in PS 5 PEEP 0 (p = 0.0001, r = 0.719) combination, the worst in PS 0 PEEP 5 combination compared with spontaneous mode. RSBI showed no predictive value for weaning success ineach combination. Systolic (SBP) and diastolic blood pressure (DBP) measurements were significantly different accross the SBT success and failure groups (p = 0.041, p = 0.046, respectively). Thereshold values for SBP and DBP were found to be 120 mmHg and 70 mmHg respectively. Respiratory rate (f) was higher in SBT success group than SBT failure group. When measuredat PS 0 PEEP 5 and PS 5 PEEP 0 combinations thereshold value of f was found to be 27 /min. The mean VD / VT (deadspace / tidal volume ratio) was 0.53 ± 9.7 in all patients, 0.47 ±0.1 in SBT success group, 0.56 ± 7.8 in SBT failure group, the difference between success and failure groups was significant (p = 0.032).Although there was a good correlation between RSBI measured in T tube and RSBI measured in different mode and pressure combinations, a thereshold value was not detected for RSBI to predict SBT success. In addition SBP, DBP, VE anf f parameters measured before weaning were found to be predictors of weaning success.