An unusual site of leak in anaesthesia circuit.

Sir,

The leakage in the anaesthesia circuit may result in hypoventilation, hypoxia, awareness, pollution of the operating theatre and ventillatory failure even leading to death.[1] Various causes of leaks in the breathing system have been reported in the literature that include failure of an adjustable pressure limiting (APL) valve to close,[2] mis-installation of a canister,[3] weak connections in between different parts of the breathing circuit, etc. However, most of the breathing system leaks can be prevented by performing the recommended preanesthetic check. We report an incident of an unusual site of air leak from the breathing circuit that escaped all the conventional tests used to detect leaks in the anaesthesia circuit.

A 46-year-old male patient with carcinoma pancreas was scheduled for Whipple's procedure. He had a previous history of smoking but no other co-morbidities and his body mass index was in the normal range. He was posted as the first case for the day. The routine anaesthetic machine and ventilator check (Datex Ohmeda –Avance S5) was performed using the electronic self-check, which showed a leak less than 250 mL. Later a manual positive pressure leak test[4] was done which also showed a minimal leak in the external tubing circuit.

The inhalational anesthesia technique was chosen using oxygen, nitrous oxide, and isoflurane. After inducing anesthesia using propofol, fentanyl, and vecuronium and adequate bag and mask ventilation trachea was intubated with the 8.5 mm (ID) PVC tube. The patient was put on volume control ventilation with a set volume of 450 mL, which showed a peak pressure of 16 cm of water. A few minutes later the ventilator bellows were seen to collapse at a fresh gas flow of 1 L/min. All connections in the external circuit were checked and no lose connection or any leak could be found. Connection to sampling line was replaced and inspected that also showed no leak. On close observation, we found a hissing sound with each delivered breath. Leak around the endotracheal tube cuff was also ruled out by inspecting the taught pilot balloon. Bains circuit was connected using the auxilary oxygen supply port keeping the possibility of damage to the external circuit. However, the hissing noise continued and it intensified on giving more positive pressure. Finding no possible cause for leak and noise, we replaced the endotracheal tube with an identical PVC tube. The noise and leak both resolved.

On close inspection of the previous endotracheal tube, we noticed that the site where the inflation line from the pilot balloon entered the shaft of the tube, the hole was much larger than that required for the inflation line and was the source of leak [Figure 1]. To confirm the leak site the endotracheal tube was filled with water, held vertically with lower end being the universal connector side (occluded), water leak was seen around the entry hole of inflation line.

Figure 1

Large point of entry of inflation line of pilot balloon into the shaft of the endotracheal tube

All the anesthesiologists should be aware of such a rare cause of leak in the breathing system. This problem highlights the need for close inspection of the endotracheal tubes prior to use that could have avoided the confusion and reintubation as in our case.