We aimed to identify the effect of suction pressure and catheter size on change in lung volume during open and closed endotracheal suction. Anesthetized piglets (n=12) were intubated with a 4.0mm endotracheal tube. Lung injury was induced with saline lavage. Three suction methods (open, closed in-line and closed with a side-port adaptor) were performed in random order using 6, 7, and 8 French gauge (FG) catheters, at vacuum pressures of 80, 140 and 200 mmHg. Lung volume change was measured with respiratory inductive plethysmography. Overall, open suction resulted in greater lung volume loss during and at 60 seconds post-suction than either closed method (p<0.001). When open and closed methods were analysed separately, volume change was independent of catheter size and suction pressure with open suction.With closed suction, volume lossincreased with larger catheter sizes and higher suction pressures (p<0.001). With an 8 FG catheter and suction pressure of 140 or 200 mmHg volume, loss was equivalent with open and closed suction. Lung volume changes are influenced by catheter size and suction pressure, as well as suction method. With commonly used suction pressures and catheter sizes, closed suction has no advantage in preventing loss of volume in this animal model.