Chest
Clinical InvestigationsRespiratory Function during Pressure Support Ventilation
Section snippets
Clinical studies
Fifteen stable patients requiring mechanical ventilatory support in our medical intensive care unit were selected for study. Criteria for selection were as follows: (a) a spontaneous ventilatory rate greater than 10 when removed from mechanical ventilatory support; (b) a stable or improving intrapulmonary disease process as evidenced by stable chest roentgenograms, an arterial Pco2 less than 50 mm Hg and less than a 10 percent change in the alveolar-arterial oxygen difference P(A-a)O2 over the
Clinical Results
Characteristics of the 15 study patients along with the baseline mechanical ventilation parameters, arterial blood gases, respiratory system compliance, and ventilatory pattern during a brief period of unassisted ventilation are summarized in Table 1. All patients demonstrated tachypnea (ie, f of 19 or greater) during unassisted ventilation and most relied on mechanical ventilation for the majority of their ventilatory requirement.
PSVmax in these patients ranged from 13 to 41 cm H2O. PSVmax was
Discussion
The results of this study demonstrated that, in these patients, inspiratory pressure assist with PSVmax resulted in mechanical ventilatory support comparable to SIMV but with a slower spontaneous ventilatory rate and more subjective comfort. Lower levels of inspiratory pressure resulted in less tidal volume augmentation and acceleration of the spontaneous ventilatory rate. A mechanical ventilatory system model patterned upon these patients’ characteristics also demonstrated that PSV not only
Conclusions
High levels of PSV (ie, inspiratory pressure assist levels providing Vt of 10 to 15 ml/kg) clearly can provide gas exchange comparable to volume assisted modes of ventilation (ie, SIMV) in stable patients with intact ventilatory drives. This high level of support is characterized by apparently improved patient comfort, slower ventilatory rate, reduced patient work, and slightly higher mean airway pressures than SIMV. PSV, however, is an assist mode, and thus, it probably should not be used
ACKNOWLEDGMENTS
The writer thanks Ray Nagy, C.R.T.T., and the entire Respiratory Care Services staff of the Duke University Medical Center for their technical expertise and Ms. Barbara Powell for her secretarial skills.
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Manuscript received September 3; revision accepted November 15.