Dear Editor, Inflation and deflation of the cuff of an endotracheal tube (ETT) is a routine part of airway management. Inflation of the cuff ensures a seal that enables intermittent positive pressure ventilation and provides safety from aspiration of gastric contents.[1] Like inflation, deflation of the ETT cuff carries its own importance prior to extubation and during nasotracheal intubation. Quantification of cuff inflation is translated as positive intracuff pressure, which is widely measured using a cuff manometer.[2] However, there is no provision to quantify the intracuff pressure of a deflated cuff. We report a case indicating negative intracuff pressure inside a deflated cuff. A 26-year-old gentleman who had a history of road traffic accident three days back, presented with restricted mouth opening. The patient was diagnosed with a fractured mandible and was scheduled for fixation under general anaesthesia. The pre-anaesthetic check-up was within normal limits. Airway examination revealed a mouth opening of around 3 cm and a Modified Mallampati score of 3. The airway management plan was nasotracheal intubation using McGrath video laryngoscope. On the day of the surgery and after the induction of general anaesthesia, an armoured ETT of 7.0 mm internal diameter was introduced through the right nostril after deflating the cuff. After inserting around 10 cm of the ETT, the McGrath video laryngoscope size 3 was introduced in the oral cavity. As it was further advanced looking at the video screen, a pool of blood was observed in the oropharynx along with the ETT. The oropharynx was suctioned and as the vocal cords became visible, the ETT was inserted through the larynx and into the trachea. As the pilot balloon was picked up to inflate the cuff, blood was noticed in the pilot balloon and the inflation line [Figure 1]. Furthermore, we failed to inflate the cuff. The cuff was considered ruptured and the ETT was replaced. The inference was that the simultaneous rupturing of the cuff and the negative pressure contained inside the deflated cuff caused in-drawing of the surrounding blood into the inflation line and the pilot balloon.Figure 1: Blood inside the inflation line and pilot balloon of the endotracheal tubeIn a model experiment, the deflated cuff was ruptured in a bowl of coloured dye, and there was immediate siphoning of dye in the inflation line and the pilot balloon. This case and the experimental model highlighted that an unquantified negative pressure is contained inside the deflated cuff, contrary to the expected zero or atmospheric pressure. Any breach in the integrity of the cuff system acquired during the procedure of endotracheal intubation is unidentified until the attempted inflation of the cuff. The unusual observation of blood in the inflation line in the reported case indicated the breach. The clinical utility of this unique observation requires further exploration and study. Identical to the negative pressure test of the low-pressure system of an anaesthesia machine, a negative pressure test can be designed to confirm the integrity of the ETT cuff system prior to tracheal intubation. A conventional test for the cuff system needs inflation of the cuff system, which mandates deflation of the cuff prior to intubation: this makes it a multi-step process.[3,4] A negative pressure test, however, consists of a single step of cuff deflation and the deflated cuff for a pre-defined time period confirms integrity of the cuff system. Furthermore, ETTs can be factory supplied with a specified negative intracuff pressure rather than zero pressure. This practice bypasses the testing of the cuff system and requires only a mere visual inspection of the collapsed cuff through the transparent packing. Unlike cuff inflation, deflation of the cuff has not been not standardised. It is by tactile perception that cuffs are deflated before each extubation or prior to nasotracheal intubation. A measuring device can be designed to estimate the negative pressure inside the cuff system with a fixed standard rather than just the binary of yes or no. To conclude, this novel entity can hold a prominent place in the practice of anaesthesiology and opens up an arena of further research activity. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patient understands that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
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May 11, 2023
Zeng Wang + 2
Open Access