[Variations in the internal pressure of the pneumatic cuffs of endotracheal tubes according to their contents and the anesthetic mixtures used. Experimental study].

With the purpose of measuring pressure changes in the pneumatic cuffs of endotracheal tubes when the composition of the mixture of gases used for ventilation had to change for the same content, we designed a model of artificial respiration that consisted of a tube with a low pressure pneumatic cuff measuring 8.5 mm in inner diameter introduced in a replica of a human trachea, adjusted to two anesthetic bags. The cuff valve was connected to a pressure transducer by a three-ended stopcock and, after aspiration of its content, it was inflated with air, saline or nitrous oxide and oxygen at 60% up to a basal pressure of 20 mmHg. The tube was connected to a respirator adjusted to inflate 10 l/min at a rate of 15 insufflations/min of: oxygen 100% for 5 minutes, then nitrous oxide and oxygen at 60% for 30 minutes and oxygen 100% again for 15 minutes. When inflating the pneumatic cuff with air and ventilating with nitrous oxide and oxygen at 60%, its pressure reached a maximum mean value of 58 mmHg (190% with respect to base values). When insufflating with saline and ventilating in the same conditions, pressure reached a maximum mean value of 33 mmHg (65% with respect to base values). When the pneumatic cuff was inflated with nitrous oxide and oxygen at 60%, important changes in pressure were observed when the characteristics of the inspired gases were modified. We conclude that some method for monitoring pneumatic cuff pressure should be systematized.