Response of ventilator-dependent patients to different levels of proportional assist

Abstract

Proportional-assist ventilation (PAV) is a form of ventilatory support in which airway pressure increases in proportion to patient effort. Because it effectively reduces the mechanical load to an adjustable extent, PAV permits the study of the pattern of breathing in patients with respiratory disease when unconstrained by abnormal respiratory mechanics. We studied 11 patients with assorted medical problems requiring ventilatory support. The patients were switched to PAV, and the level of support was varied from near-maximal levels to the lowest tolerable level. Each level was maintained for several minutes while ventilation (VE), tidal volume (VT), and respiratory rate (f) were monitored. The breathing pattern observed with the highest assist varied substantially among patients. The ranges (and means) of VE, VT, and f were 5.6-18.7 (12.8) l/min, 203-844 (517) ml, and 18-33 (25) breaths/min, respectively. The correlation between VT and VE at the highest assist was very high (r = 0.91), suggesting that ventilatory demand is the most important determinant of VT variability. There were no systematic changes in breathing pattern as the level of assist was altered; at the highest and lowest levels of support, VE, VT, and f were, respectively, 12.8 +/- 5.4 (SD) vs. 11.6 +/- 4.3 l/min, 517 +/- 217 vs. 459 +/- 175 ml, and 25.0 +/- 4.2 vs. 25.7 +/- 3.9 breaths/min. These results indicate that within each patient, in a given state, there exist unique values for a desired VE, VT, and f that are largely independent of the mechanical load; if assist is increased, patient effort is decreased to maintain the desired ventilatory targets.

Effect of Different Levels of Pressure Support and Proportional Assist Ventilation on Breathing Pattern, Work of Breathing and Gas Exchange in Mechanically Ventilated Hypercapnic COPD Patients with Acute Respiratory Failure

“…The advantage of PAV for a better patient-ventilator coupling has been discussed in previous studies [1, 4, 5]. Indeed, ME occurred in nearly all our patients with increasing level of PSV.…”

“…Several studies have been carried out to examine its effectiveness in patients with acute respiratory failure (ARF) of diverse etiology [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. These studies have shown advantages of PAV, in comparison to other modes of assisted ventilation, in terms of patient-ventilator synchrony and tolerance of mechanical ventilation.…”

Effects of proportional assist ventilation on exercise tolerance in COPD patients with chronic hypercapnia

“…Furthermore, the level of pressure delivered to the patient increases and decreases according to the patient's ventilatory demand. PAV has been used to unload the inspiratory muscles for the treatment of patients with acute respiratory failure [11,[13][14][15][16], as well as in a noninvasive manner [17].…”

Short-term effects of nasal proportional assist ventilation in patients with chronic hypercapnic respiratory insufficiency

“…A few short-term studies in acutely ill patients have shown that PAV applied noninvasively is able to im-prove arterial blood gases and to unload the inspiratory muscles [7][8][9][10][11][12][13][14]. By contrast, the effects of PAV in chronic respiratory insufficiency have not previously been reported, although it is potentially attractive to match ventilation with the spontaneously varying breathing pattern of patients in stable conditions.…”