To the Editor:—
Burkle et al. 1perpetuate the belief held by younger practitioners of the specialty that Robert Macintosh added the curve to his laryngoscope blade to “lessen the chance of damage to the patient's upper teeth.” Although Sir Robert indicated that exposing the larynx with a long straight blade “occasionally jeopardizes the patient's upper teeth or takes a minor divot out of the posterior pharyngeal wall,”2his primary purpose was to facilitate exposure of the vocal cords. Avoidance of damage to the teeth or soft tissue was not his primary purpose. Having observed a pediatric anesthetist use a straight blade in much the same manner as we now use the Macintosh blade, he modified the blade to allow the tip to “fit into the angle made by the epiglottis and the base of the tongue.” Elevation of the laryngoscope pushes the base of the tongue upward whereas the epiglottis, because of its attachment to the tongue, is drawn upward, providing a clear view of the larynx.
Of greatest import, however, was Macintosh's observation, confirmed 2 months later by Rowbotham,3that it was possible to easily expose the larynx at a lighter plane of anesthesia than with any of the standard blades. Before the ubiquitous use of neuromuscular blocking agents to facilitate intubation and of intravenous agents and halogenated hydrocarbons to induce and maintain anesthesia, relatively deep anesthesia was required to avoid laryngospasm when the epiglottis was elevated because the glottis and the inferior surface of the epiglottis are innervated by the vagus nerve. When the use of cyclopropane became commonplace, bradycardia and hypotension, attributed to a vagal-vagal reflex when the epiglottis was lifted with a straight blade, was said to occur with alarming frequency. This untoward event, too, could be avoided with the use of Macintosh's blade because the superior surface of the epiglottis and the vallecula are innervated by the glossopharyngeal nerve.
Over the years, there have been a number of modifications of the Macintosh blade4that purportedly reduced the danger of damage to the upper incisors and facilitated exposure of the larynx. None have met with even a modicum of success. Although Sir Robert's blade is still one of the most popular, contemporary anesthetic techniques have eliminated its original purpose—intubation of the trachea under light anesthesia.
Professor Emeritus, State University of New York, Upstate Medical University, Syracuse, New York. firstname.lastname@example.org