ObjectiveTo study comparatively the effects of volume-controlled vs. biphasic positive airway pressure mechanical ventilation on respiratory mechanics and oxygenation in leukopenic patients with severe respiratory failure.DesignProspective, comparative study.SettingMedical intensive care unit of a university hospital.PatientsLeukopenic (less than 1000 leukocytes/micro Liter) patients (n equals 20) after cytoreductive chemotherapy requiring mechanical ventilation for severe respiratory failure (Murray score of more than 2.5).InterventionPatients were assigned in a consecutive, alternating manner to receive either volume-controlled or biphasic positive airway pressure mechanical ventilation, starting within 12 to 24 hrs after endotracheal intubation.Measurements and Main ResultsTidal volume, inspiratory flow, peak inspiratory and positive end-expiratory pressures, FIO2, and arterial blood gas analyses were recorded hourly for a study period of 48 hrs. Biphasic positive airway pressure ventilation was associated with a significant reduction in peak inspiratory pressure (mean differences at 24, 36, and 48 hrs: 4.4, 3.4, and 4.2 cm H2O; p equals .024,.019, and .013, respectively) and positive end-expiratory pressures (mean differences at 24, 36, and 48 hrs: 1.6, 1.4, and 1.5 cm H2O; p equals .023,.024, and .023, respectively) at significantly lower FIO2(mean differences at 12, 24, 36, and 48 hrs; p equals .007,.015,.016, and .011, respectively). PaO2/FIO2ratios and CO2removal were similar under ventilatory conditions.ConclusionsBiphasic positive airway pressure ventilation offers the advantage of significantly reduced peak inspiratory and positive end-expiratory pressures at a lower FIO2and with at least similar oxygenation and CO2removal as achieved by volume-controlled mechanical ventilation. Our results are in line with previous reports on nonleukopenic patients and suggest that the positive effects of pressure-limited mechanical ventilation are independent of circulating white blood cells. Further studies are mandatory to demonstrate clinical benefit in this critically ill patient population.(Crit Care Med 1996; 24:780-784)