BACKGROUND: Despite a large number of studies on endotracheal suctioning, there is little data on the impact of clinically practical hyperoxygenation techniques on physiologic parameters in critically ill patients. OBJECTIVE: To compare the manual and mechanical delivery of hyperoxygenation before and after endotracheal suctioning using methods commonly employed in clinical practice. METHODS: A quasi-experimental design was used, with twenty-nine ventilated patients with a lung injury index of 1.54 (mild-moderate lung injury). Three breaths were given before and after each of two suction catheter passes using both the manual resuscitation bag and the ventilator. Arterial pressure, capillary oxygen saturation, heart rate, and cardiac rhythm were monitored for 1 minute prior to the intervention to obtain a baseline, continuously throughout the procedure, and for 3 minutes afterward. Arterial blood gases were collected immediately prior to the suctioning intervention, immediately after, and at 30, 60, 120, and 180 seconds after the intervention. Data were analyzed with repeated measures analysis of variance. RESULTS: Arterial oxygen partial pressures were significantly higher using the ventilator method. Peak inspiratory pressures during hyperoxygenation were significantly higher with the manual resuscitation bag method. Significant increases were observed in mean arterial pressure during and after suctioning, with both delivery methods, with no difference between methods. Maximal increases in arterial oxygen partial pressure and arterial oxygen saturation occurred 30 seconds after hyperoxygenation, falling to baseline values at 3 minutes for both methods. CONCLUSION: Using techniques currently employed in clinical practice, these findings support the use of the patient's ventilator for hyperoxygenation during suctioning.