The Science Journal of the American Association for Respiratory Care
A lack of coordination between termination of patients' inspiratory efforts and the ventilators' inspiratory phase during pressure support (PS) can increase expiratory effort and ventilatory drive. We evaluated the performance of two new generation mechanical ventilators, (Hamilton Galileo and Nellcor Puritan Bennett 840) in 3 different expiratory sensitivity (minimum, medium, maximum) settings during pressure support (PS). Using a spontaneous breathing lung model set as follows: compliance 50 ml/cmH2O, airway resistance 8.2 cmH2O/L/s, respiratory rate 12 breaths/min, inspiratory time 1.0 second, and peak inspiratory flow 60 L/min. Throughout the evaluation pressure support was set at 15 cmH2O with PEEP of 5 cmH2O. Expiratory variables are shown below as mean ± SD. Differences exist between ventilators for all expiratory variables evaluated and for the individual ventilator at the three trigger settings. The minimum trigger setting resulted in the best transition to exhalation.
|Area E||minimum*||11.98 ± 0.10bc||-5.13 ± 0.31bc|
|medium*||12.86 ± 0.09ac||6.48 ± 0.06a|
|maximum*||13.00 ± 0.05ab||6.41 ± 0.33a|
|P-E||minimum*||8.25 ± 0.09||0.00 ± 0.00bc|
|medium*||8.25 ± 0.19||3.22 ± 0.19a|
|maximum*||8.25 ± 0.09||3.44 ± 0.16a|
|D-E||minimum*||0.17 ± 0.00bc||0.00 ± 0.00bc|
|medium*||0.19 ± 0.01ac||0.07 ± 0.01a|
|maximum*||0.22 ± 0.01ab||0.07 ± 0.00a|
a = p<0.05 VS minimum for specific ventilator, b = p<0.05 VS medium for specific ventilator, c = p<0.05 VS maximum for specific ventilator, * = p<0.05 among ventilators. Area-E-the area of sustained airway pressure during expiration; P-E-the pressure increase above set inspiratory pressure during the onset of exhalation; D-E-the time delay in airway pressure falling below set inspiratory level at the onset of expiration.