Abstract
Background
Previously published reports imply that the beneficial effects of pressure-control ventilation (PCV) depend on the use of inverse inspiratory-to-expiratory-time ratios (I:E) greater than those used during conventional ventilation (CMV, volume-cycled assist-control or intermittent mandatory ventilation).
Research Questions
Can PCV provide PaO2 and PaCO2 comparable to CMV at lower peak inflating pressure (Paw-peak), positive end-expiratory pressure (PEEP), fractional concentration of inspired oxygen (FIO2), and minute ventilation (VE)? Is an inverse I:E necessary to obtain the comparable PaO2 and PaCO2?
Subjects & Method
We ventilated 14 patients on PCV (via Puritan-Bennett 7200a) who had required FIO2 ≥ 0.40 and Paw-peak ≥ 40 cm H2O on CMV for ≥ 24 hours and whose clinical condition had failed to improve as re-flected by unchanged or deteriorating compliance, chest radiograph, PaO2, and PaCO2, and by stable or rising Paw-peak, FIO2, VE, and PEEP. After the initial tran-sition from CMV to PCV at comparable settings, we increased inspiratory time (ti) in 0.1-s increments until VT decreased, at which point ti was decreased by 0.1 s and maintained. Other changes in ventilator variables were guided by blood-gas values and results of hemodynamic and noninvasive monitoring.
Results
Twenty-four hours after initiating PCV, statistically significant dif-ferences were seen (level of significance ≥ 0.0042 with Bonferroni's adjustment for multiple t tests) in Paw-peak (decreased, p = 0.002), dynamic compliance (in-creased, p = 0.004), VE (decreased, p = < 0.001), FIO2 (decreased, p = 0.002), al-veolar-arterial partial pressure difference for oxygen [P(A-a)O2] (decreased, p = 0.002). The increase in PaO2 (p = 0.046) and PaO2/FIO2 (p = 0.006) and the de-crease in ventilatory rate (p = 0.005) failed to reach significance. Eight patients were ventilated at ti ≥ 50%, 2 patients at 51-60%, and 4 patients at 70-78%.
Conclusions
(1) PCV can adequately ventilate and oxygenate patients in se-vere respiratory failure and (2) inversing I:E is not universally necessary during PCV.
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