The tooth of the matter: Diastema as the rare cause of pilot tube obstruction of Proseal LMA!

ProSeal laryngeal mask airway (LMA ProSeal™) is widely used during anaesthesia for various surgeries.[1,2] We report a patient in which we were unable to inflate the cuff of LMA ProSeal™ due to the pilot tube getting stuck in the patient's lower teeth diastema (gap between two teeth).

A 60-year-old male patient, American Society of Anesthesiologists (ASA) Grade II, weighing 60 kg was scheduled for bilateral ureter stent removal under general anaesthesia. His preoperative history, examination and investigations were within normal limits. Airway examination revealed modified Mallampati Grade 2 with mouth opening more than three fingers. Anaesthesia was induced with intravenous fentanyl 120 μg, propofol 150 mg, and vecuronium 6 mg followed by an insertion of LMA ProSeal™ size 4 by standard introducer technique. 20 mL air was injected with a syringe through the pilot balloon to inflate the cuff; however, increased resistance was felt after injecting only 5 mL with the pilot balloon noticed to have ballooned up. On ventilation via the anaesthesia machine, there was an audible leak with a minor discrepancy seen between the set and delivered tidal volume (set 425 mL, delivered 345 mL) with a normal capnograph [Figure 1]. A second attempt at inflating the cuff resulted in a similar situation. The circuit was checked for any kinking or obstruction, which was negative. In the best interest of the patient, it was decided to remove the LMA ProSeal™ and reinsert it. While attempting to remove the LMA ProSeal™, it was noticed that the pilot tube of LMA ProSeal™ had slipped into the diastema between the two lower central incisors, which had kinked the pilot tube and resulted in inability to inflate the pilot balloon [Figure 2]. The pilot tube was freed and was found to be intact and was easily inflated this time. Subsequent ventilation showed no air leak with set tidal volume delivered to the patient. Rest of the case proceeded uneventfully.

Figure 1.

Minor difference in set and delivered tidal volume with normal capnograph

Figure 2.

Pilot tube caught in lower diastema with ballooning of pilot balloon

To the best of our knowledge, there is no previous report of obstruction to the pilot tube of LMA ProSeal™. However, the obstruction of the long and separate pilot tube of classic LMA has previously been reported in few cases. In one reported case, pilot tube was damaged by getting caught between the lids of the metal box while storing.[3] In another patient at the end of surgery, there was an inability to deflate the LMA cuff found to be due to the pilot tube getting wedged into a gap between the right upper molar and premolar teeth. It was suggested that the pilot tube should either be incorporated into the airway tube or anchored to side of it.[4] In another patient, the coil of pilot tube gained access to the grille side of LMA, which on inflation kinked it preventing further inflation. The authors suggested the manufacturers to incorporate pilot tube within the wall of the airway tube of classic LMA to prevent this.[5] In response, the manufacturers (Intravent Ltd) reasoned that if the pilot tube is incorporated into the wall of airway tube, it could be severed by accidental biting during anaesthesia which could lead to complete loss of seal and inability to ventilate and thus to prevent the above; the pilot tube was deliberately kept separate from the airway tube.[5]

We argue that unlike the classic LMA, the LMA ProSeal™ already has an integrated bite block; thus, its pilot tube can easily be incorporated in the airway tube to protect against its kinking and damage. We therefore suggest the manufacturers to consider integration of pilot tube with the airway tube within the bite block in LMA ProSeal™.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.