Effects of endotracheal suctioning on mixed venous oxygen saturation and heart rate in critically ill adults. The purpose of this multisite study was to determine the effects of endotracheal suctioning on mixed venous oxygen saturation (SvO2) and heart rate in 189 critically ill adults. One-pass, intermittent suction was applied for 10 or fewer seconds, with three prehyperoxygenation and three posthyperoxygenation breaths of 100% oxygen. Subjects at three hospitals (n = 127) underwent suctioning using hyperoxygenation with anesthesia bags and traditional suction catheters (open suction method). Subjects at one hospital (n = 62) underwent suctioning with hyperoxygenation by ventilator and in-line suction catheters (closed suction method). For subjects from all hospital sites combined, the SvO2 decreased from 67% to 64% (p = 0.001), a 4% change from baseline, and returned to baseline within 2 minutes. However, in subjects receiving the open method of suction, SvO2 dropped from 66% to 62% immediately after suctioning and returned to baseline within 4 minutes. In contrast, when the closed suction method was used, SvO2 rose from 67.7% to 67.86% immediately after suctioning, drifting upward to 71% for the next 2 minutes before dropping toward the baseline after 4 minutes. Mean heart rate increased from a baseline of 99 beats/min to 104 beats/min immediately after suctioning (p = 0.001), a 5% change from baseline, and gradually returned to baseline over the next 4 minutes. No significant differences were seen in heart rate between subjects having the open versus closed suction method. In conclusion, the closed suction method showed a higher SvO2 after endotracheal suctioning compared with the open suction method (p = 0.0001). Some form of hyperoxygenation before and after endotracheal suctioning is recommended. 