Hemodynamic and oxygen transport responses to four preoxygenation techniques prior to endotracheal suctioning (ETS) were evaluated in 24 critically ill trauma patients with no preexisting lung disease. A within-subjects, repeated measures design was used. All patients had functional arterial and pulmonary artery catheters and were ventilated with a Puritan-Bennett 7200 which could immediately deliver a fraction of inspired oxygen (FIO2) of 1.0. Six breaths of maintenance FIO2 and hyperinflation without hyperoxygenation caused a fall in tissue oxygen delivery as measured by continuous transcutaneous oximetry (PtcO2). The largest increases in PtcO2 and arterial oxygen tension were seen with hyperoxygenation alone and a combination of hyperoxygenation and hyperinflation. No significant changes were found in hemodynamic (cardiac index, mean arterial pressure, mean pulmonary artery pressure, pulmonary capillary wedge pressure, systemic vascular resistance, pulmonary vascular resistance) or oxygen transport variables (oxygen delivery, oxygen extraction, oxygen consumption) 5 minutes postsuctioning. During both hyperinflation protocols, patients experienced dyspnea. It was concluded that three hyperoxygenation breaths before ETS, using a clinically feasible protocol, are adequate in preventing postsuction hypoxemia in young, hemodynamically stable trauma patients. Large volumes of hyperinflation, although found to increase PtcO2, are not advocated because of demonstrated patient discomfort and the possibility of barotrauma.