To the Editor:-A 57-yr-old woman presented to the emergency room with confusion, weakness and cyanosis. Her history included a muscle biopsy and contracture test consistent with malignant hyperthermia, confirmed hypertrophic obstructive cardiomyopathy, and an undiagnosed neurologic condition characterized by progressive, episodic confusion, somnolence, dysarthria, and headache. She had been started on amiodarone and sotalol by a cardiologist for paroxysmal atrial fibrillation.
Progressive somnolence and hypercapnic acidosis led to a decision to intubate. Airway evaluation revealed mild micrognathism but no other abnormalities. Monitoring consisted of continuous electrocardiography, oximetry, and invasive arterial blood pressure. Lidocaine spray was applied to the oropharynx and hypopharynx, but direct laryngoscopy was poorly tolerated. After preoxygenation, sleep was induced with propofol. Bag and mask ventilation was easily provided, and vecuronium was administered. With appropriate positioning, direct laryngoscopy using Macintosh and Miller blades permitted visualization of the epiglottis but not the vocal cords. Despite external laryngeal pressure and a stylet, the trachea could not be intubated. Oral intubation using a fiberoptic bronchoscope was unsuccessful due to an inability to pass posterior to the epiglottis. Finally, after neosynephrine drops were used to provide nasal vasoconstriction, a 7.5-mm outer diameter nasal tracheal tube was successfully introduced fiberoptically using a vigorous jaw thrust.
A decision was made to convert the nasal tube to an oral tube. A fiberoptic bronchoscope, LMA. and cricothyroidotomy kit were immediately available. After ventilation at a FiO21.0, unconsciousness and paralysis were maintained with supplemental propofol and vecuronium bromide. An endotracheal tube exchanger, (endotracheal ventilation catheter, ETVC[trademark symbol] CardioMed Supplies, Gormley, ON) was inserted through the nasal tube. The nasotracheal tube was then withdrawn, leaving the ETVC[trademark symbol] in situ. Direct pharyngoscopy was performed, and the ETVC[trademark symbol] was grasped and secured with Magill forceps. A second Magill forceps was used to pull the ETVC[trademark symbol] in through the nose and out the mouth. This was readily accomplished without significant change in arterial saturation. A 8.0 mm OD ETT was then loaded onto the ETVC[trademark symbol]. The ETVC[trademark symbol was connected to oxygen tubing and insufflation at 4 LPM was commenced. The endotracheal tube was easily threaded over the ETVC[trademark symbol] to a depth of 22 cm. Before withdrawing the ETVC[trademark symbol], it was threaded through a bronchoscopic adaptor and carbon dioxide was detected during positive pressure ventilation. The ETVC[trademark symbol] was withdrawn, and the position of the endotracheal tube was confirmed bronchoscopically. Arterial saturation remained in excess of 98% throughout the tube exchange.
Seven days later, she was extubated uneventfully, using the ETVC[trademark symbol] to maintain airway access. 
Novella has described the intraoperative conversion of a nasotracheal to orotracheal tube in a patient with Klippel-Feil syndrome, using a Sheridan tube exchanger. Although his conversion was achieved within 90 s, the patient desaturated from 100% to 85%. The provision of oxygen by insufflation, or jet ventilation if necessary provides an additional measure of safety should the conversion be prolonged or the patient unstable. It is equally important to be prepared for possible reintubation. In the present case, a tube exchanger was used to maintain airway access after extubation.
It is important to point out that commercial tube exchangers vary in their stiffness and diameters. Such physical properties may prevent this maneuver from being successful with a stiffer or larger caliber catheter.
Richard M. Cooper B.Sc., M.Sc., M.D., F.R.C.P.C.
University of Toronto; Department of Anaesthesia; The Toronto Hospital and Mount Sinai Hospital; 600 University Avenue; Toronto, Ontario M5G 1X5
(Accepted for publication June 16, 1997.)