Chest
Volume 89, Issue 5, May 1986, Pages 677-683
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Clinical Investigations
Respiratory Function during Pressure Support Ventilation

https://doi.org/10.1378/chest.89.5.677Get rights and content

Pressure support ventilation (PSV) is a pressure assist form of mechanical ventilatory support that augments the patient's spontaneous inspiratory efforts with a clinician selected level of positive airway pressure. To understand the effects of PSV on respiratory function, experiments were performed on 15 stable patients requiring synchronized intermittent mandatory ventilation (SIMV), as well as on a mechanical model simulating these patients’ ventilatory systems. In the clinical study, gas exchange, airway pressures, blood pressure and heart rate were measured while SIMV was replaced by enough PSV to approximate the baseline SIMV tidal volume (Vt). Measurements were repeated while this PSV level was then reduced in three 5 cm H2O steps every 10 to 15 minutes. It was found that PSV was a reasonable form of mechanical ventilatory support in patients with spontaneous ventilatory drives. It improves patient comfort, reduces the patient's ventilatory work, and provides a more balanced pressure and volume change form of muscle work to the patient. The clinical significance of these properties during the weaning process remain to be determined.

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.

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