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Riddle of the persistent leak

The case below highlights an unusual cause of a significant leak from the patient breathing system intra-operatively. A 68-year-old man suffering from a squamous cell carcinoma of the supraglottic region was scheduled for total pharyngolaryngectomy, neck dissection and jejunal loop-free graft with microvascular anastomosis. Following induction of anaesthesia with thiopentone, ventilation of the lungs by mask proved easy and suxamethonium 100 mg was given to facilitiate tracheal intubation. At laryngoscopy only the epiglottis was visible, but a 6.5 mm disposable cuffed tracheal tube was successfully railroaded over a gum elastic bougie. Attempted wide bore nasogastric intubation using Magill intubating forceps proved more difficult due to tumour spread and oedema of the laryngopharynx. A decision not to persist was made and the nasogastric tube was left in the pharynx, with its tip thought to be at the laryngopharynx. The patient breathed spontaneously 66% nitrous oxide in oxygen and isoflurane 1.5% whilst invasive monitoring lines were inserted. After transfer into the operating theatre an atracurium infusion was established and controlled ventilation was commenced manually using a total fresh gas flow of 7.5 litres/minute. On connecting the patient to a circle breathing system driven by a Manley Servovent and reducing the fresh gas flow to 1.7 litres/minute, the expired tidal volume was noted to be approximately 250 ml lower than the preset tidal volume. In addition, the ventilator reservoir bag was collapsed, and it became evidence that there was a significant leak from the system. Although a ventilator alarm was connected and set to alarm at 5 cmH,O above or below the peak inspiratory pressure, it was not activated. All circuit connections were checked and found to be secure. An occasional leak was audible at the mouth and some extra air was added to the cuff of the tracheal tube as the pilot balloon did not seem well inflated. The audible leak became more pronounced and the patient's trachea was re-intubated after passing a bougie down the existing tracheal tube. However, the problem persisted and it became apparent that the source of the leak was the unspigotted nasogastric tube, whose tip was lying in the trachea. Repositioning of the nasogastric tube resolved the situation. It is well known that fine bore feeding catheters may enter the lungs, but it is salutary to remember that even wide bore nasogastric tubes may be passed beyond the cuff of a tracheal tube. This case illustrates how such a misplaced nasogastric tube may interfere with lung ventilation. It is especially useful to remember this complication when a nasogastric tube cannot be placed under direct vision. In addition, leaks between the breathing system and the patient are much more reliably detached by expired volume monitoring than by a ventilator alarm.'