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.