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Regular endotracheal tube cuff monitoring may prevent silent aspiration.We hypothesised that active management of the cuff of the tracheal tube during deep hypothermic cardiac arrest would reduce silent subglottic aspiration. We also determined to study its effect on postoperative mechanical ventilation and the incidence of postoperative positive tracheal cultures.A randomised clinical trial.The study was conducted in a University Teaching Hospital from September 2008 to November 2009.Twenty-four patients undergoing elective pulmonary endarterectomy were included in the study.After induction of general anaesthesia and tracheal intubation, the cuff of the tracheal tube was inflated to 25 cmH2O. Following this, 1 ml of methylene blue dye diluted in 2 ml of physiological saline was injected into the hypopharynx. Patients were randomly assigned to active cuff management during cooling and warming (where cuff pressure was monitored and the cuff was reinflated if it dropped below 20 cmH2O, or deflated if pressure exceeded 30 cmH2O) or passive monitoring (where cuff pressure was monitored but volume was not altered). Before weaning from cardiopulmonary bypass, fibreoptic bronchoscopy was performed. Silent aspiration was then diagnosed if blue dye was seen in the trachea below the cuff of the tube.The primary aim of this study was to determine the incidence of silent aspiration. Secondary outcomes included duration of postoperative mechanical ventilation of the lungs and incidence of positive culture of tracheal aspirate.Active cuff management patients were younger than controls (51.2 ± 11.6 vs. 63.2 ± 9 years, P = 0.028), but otherwise the two groups were similar. The primary endpoint was reached because we showed that silent aspiration was significantly less frequent in the study group (0/12 vs. 8/12 patients, P = 0.001). Significantly lower intracuff pressures were measured in the control group patients at several timepoints during cooling, just before hypothermic arrest and at all timepoints during rewarming.We recommend that the cuff of the tracheal tube should be checked regularly during surgery under deep hypothermia, and the cuff pressure adjusted as required.