[Decreased pressure of endotracheal tube cuff in general anesthesia without nitrous oxide]

Nitrous oxide diffuses into endotracheal tube cuff and then overexpand the cuff. This causes upper airway obstruction and trauma in intubated patients during general anesthesia. On the other hand, pressure of endotracheal cuff is reported to decrease in time-related fashion under artificial ventilation with oxygen and air. We evaluated the changes in the pressure of endotracheal cuff in intubated patient who underwent general anesthesia without nitrous oxide. After the intubation, endotracheal tube cuff was inflated until no leak of oxygen and air was recognized under positive airway pressure ventilation. This pressure was defined as clinically sealing pressure. Beyond the sealing pressure, the cuff was further inflated by air to 19 mmHg. This is defined as initial pressure. Pressure of the inflated cuff was recorded at an interval of 30 min until the extubation. Clinically sealing pressure was 11.6 +/- 1.0 mmHg and necessary volume of air was 5.5 +/- 1.8 ml. The initial pressure of the inflated cuff gradually decreased to clinical sealing pressure during 130.9 +/- 30.5 min. In conclusion, when regurgitation should be prevented at the point of the clinically sealing pressure, pressure and volume of inflated cuff by air should be re-checked at an interval of about 2 hrs in intubated patients under general anesthesia without nitrous oxide.