Randomized, prospective trial of pressure-limited versus volume-controlled ventilation in severe respiratory failure.

OBJECTIVE: Volume-controlled ventilation is frequently chosen as the initial mode of ventilatory support in patients with hypoxic respiratory failure. Recent data, however, suggest that pressure-limited ventilation, using a rapidly decelerating flow delivery pattern, may produce a more desirable clinical effect through reduced peak airway pressures and increased static compliance, tissue oxygen delivery, and consumption. This study was performed to assess the feasibility and utility of early and sustained use of pressure-limited ventilation in patients with this clinical syndrome. DESIGN: Randomized, prospective trial. SETTING: Medical intensive care unit (ICU) of a university hospital. PATIENTS: The study encompassed all patients (n = 27) receiving care in a medical ICU for acute, severe hypoxic respiratory failure (PaO2/FIO2 ratio of < 150) during a 6-month period. INTERVENTIONS: Ventilatory support via either pressure-limited or volume-controlled ventilation, initiated within 24 hrs of endotracheal intubation. MEASUREMENTS: On-line monitoring of the following ten ventilatory variables at 1-min intervals for 72 hrs or until extubation or death (maximum of 43,200 data points per patient): peak airway pressure, mean airway pressure, end-tidal CO2 concentration, CO2 minute excretion, inspiratory tidal volume, expiratory tidal volume, pause pressure, end-expiratory pressure, static thoracic compliance, and inspiratory resistance. Additionally, PaO2/FIO2 values and Acute Physiology and Chronic Health Evaluation (APACHE) II scores were recorded on a daily basis, as were significant clinical events and changes in ventilator settings. RESULTS: Although the severity of illness at study entry as determined by APACHE II score and PaO2/FIO2 was similar in patients treated with pressure-limited or volume-controlled ventilation, peak airway pressure was consistently lower in patients randomized to pressure-limited ventilation (p = .05 at 12 hrs postintubation). The use of pressure-limited ventilation also was associated with a more rapid increase in static compliance (p = .05) than that found with volume-controlled ventilation. There was a trend toward more rapid normalization of CO2 minute excretion in patients treated with pressure-limited ventilation. Pressure-limited treated patients who survived their illness and were extubated, required fewer days of mechanical ventilation than did patients randomized to volume-controlled treated ventilation (p = .05). No pneumothoraces occurred in any study patients. One volume-controlled patient developed subcutaneous emphysema. Pressure-limited ventilation was well tolerated, and sedation requirements were equivalent in the two groups. CONCLUSIONS: Pressure-limited ventilation can be used safely and is well tolerated as an initial mode of ventilatory support in patients with acute hypoxic respiratory failure. Because the early initiation of pressure-limited ventilation is associated with lower peak airway pressure and more rapid improvement in static thoracic compliance than volume-controlled ventilation, pressure-limited ventilation may have a beneficial role when used as the primary ventilatory modality in patients with this clinical condition.

Cardiorespiratory effects of pressure controlled ventilation in severe respiratory failure.

Cardiorespiratory values were measured in ten patients with severe respiratory failure on volume controlled and pressure controlled ventilation. Tidal volume, respirator rate, PEEP, auto-PEEP, inspiratory:expiratory ratio (1:2) and FIo2 were maintained at the same value for both ventilatory modalities. Changing from VCV to PCV was associated with significant improvements in PaO2, oxygen delivery, and tissue oxygen consumption. Peak inspiratory pressure fell. There were no significant changes in other cardiorespiratory values, such as arterial blood pressure, nor in ventilatory measurements, such as mean airway pressure, associated with the use of PCV. These results suggest that PCV may be a beneficial ventilatory modality in the treatment of severe respiratory failure since it results in improvement in arterial oxygenation, tissue oxygen delivery and utilization without any concomitant adverse effects on other hemodynamic or ventilatory factors.

Cardiorespiratory effects of pressure controlled inverse ratio ventilation in severe respiratory failure.

Cardiorespiratory values were measured in nine patients with severe respiratory failure before and following initiation of pressure controlled inverse ratio ventilation (PC-IRV) at an inspiratory to expiratory ratio of 2:1. All patients showed increases in PaO2, with the mean PaO2 rising from 63 +/- 4 (mean +/- SEM) to 76 +/- 8 mm Hg. Peak inspiratory pressure fell from 44 +/- 4 to 39 +/- 2 cm H2O. There were no significant changes in any hemodynamic or oxygen metabolism variable associated with the institution of PC-IRV. In particular, no significant alteration in cardiac index, pulmonary artery pressures, oxygen delivery, oxygen consumption, or oxygen extraction ratio occurred with the use of PC-IRV. These results suggest that PC-IRV may be a useful ventilatory modality in the treatment of severe respiratory failure since it results in improvement in arterial oxygenation without any deterioration in hemodynamic or tissue oxygen metabolism parameters.