ANESTHESIA FOR MICROLARYNGEAL SURGERY - THE CASE FOR SUBGLOTTIC JET VENTILATION

Although the techniques for surgery on the endolarynx using suspension and the operating microscope have been fully developed,(1-4) the safe st, and least obtrusive anesthetic technique has yet to be manifested, as evidenced by more than 200 references to anesthesia for microlaryn goscopy in the world literature. This study reviews the physiology, ph ysics, and problems of each anesthetic technique. In light of this rev iew, animal and human studies are reported demonstrating the utility a nd safety of subglottic ventilation when provided with proper monitori ng using an automatic ventilator. A modified Pen-Jet tube is reported, (5) which has a 1-mm ID channel to monitor Pco(2) and tracheal pressur e. This self-centering 3.0-mm tube, which extends 6 to 8 cm below the glottis, is unobtrusive for the surgeon. The subglottic tube, which is much less likely to be malaligned, is much more acceptable to the ane sthesiologist. Anesthesia, by intravenous sedation, utilizes neuromusc ular blockade while ventilating through the jet tube powered by an aut omatic ventilator with an automatic shutdown feature attached to the m onitor tube to prevent inadvertent barotrauma. The third phase of this study compared fluoroplastic, used in a prototype jet ventilation tub e, with 6-mm Silastic(R), Red Rubber, and polyvinyl chloride (PVC) tub es when struck by maximum power of CO2, Nd-YAG, and K-532 lasers. The test was performed in a closed chamber in which concentrations of oxyg en and nitrogen were controlled. Although damaged by the CO2 laser bea m, the fluoroplastic tubes did not continue burning when the laser was turned off in 100% oxygen, even when coated by blood. The other three tubes continued to burn in 23% oxygen. Neither the RTP nor Nd-YAG las er damaged the Teflon tube, while they ignited a sustained flame in 30 % oxygen. This study supports the use of fluoroplastic for a laser saf e jet ventilation tube. It also demonstrates the danger of tube fires, even in low oxygen concentrations, when using Silastic, rubber, and P VC tubes in laser laryngeal surgery. There was no difference in the fl ammability of Silastic, rubber or PVC when struck by these lasers in t his study. For these reasons, subglottic ventilation using a fluoropla stic, monitored, self-centering, subglottic, jet ventilation tube driv en by an automatic ventilator with a shutdown feature, in the event of excessive pressure buildup, is proposed for anesthetizing healthy pat ients undergoing suspension microlaryngoscopy, and who have no airway obstructing lesion. A large tube with inflatable cuff is indicated whe n a supraglottic lesion may obstruct the airway.