Avoiding Topical Anesthesia-Induced Methemoglobinemia

Abstract

We read the interesting case reports by Carrodeguas et al1 and Srikanth et al2, regarding topical anesthesia-induced methemoglobinemia after using 20% benzocaine spray. Quickly recognizing and treating topical anesthesia-induced methemoglobinemia is laudable, but perhaps a better clinical strategy would be to avoid local anesthetic toxicity in the first place, by limiting how much local anesthetic is given. Estimating how much local anesthetic has been administered by a commercial anesthetic spray can be difficult; i.e. the recommended dose for 20% benzocaine spray is two sprays lasting a total of 1 sec, and the duration of the sprays (and thus the dose given) can be difficult to estimate. We suggest using an alternate topical anesthetic technique, a nebulizer facemask, to quantify and limit how much local anesthetic is used, and avoid topical anesthesia-induced methemoglobinemia. A nebulizer facemask can be assembled with a disposable hand-held nebulizer (e.g. Micro Mist Nebulizer, Hudson RCI, Temecula, CA) and a disposable aerosol mask (e.g. Elongated SEE-THRU Aerosol Mask, Hudson RCI, Temecula, CA). The nebulizer, typically used for aerosolizing medications for pulmonary patients, is filled with 4% lidocaine (5 ml). If nasal intubation is anticipated, phenylephrine 100 mcg in 1 ml can be added. The total potential lidocaine dose in the nebulizer (e.g. 200 mg) is easily calculated, and is low enough, in adults, to allow additional supplementation while remaining below a potentially toxic total dose (5 mg/kg lidocaine). The nebulizer is connected to oxygen supply tubing and the disposable aerosol mask. The nebulizer facemask requires less patient cooperation than a handheld nebulizer with a mouthpiece. The patient, in an upright position, is asked to breathe the nebulized local anesthetic solution for at least 10 minutes before intubation or endoscopy. This technique could also be used to blunt the gag reflex for esophagogastroscopy. The facemask nebulizer technique has other advantages: the equipment needed is readily available in most hospitals, and the nasopharynx, oropharynx, and trachea may all become anesthetized. In spontaneously breathing patients, when the intubation technique involves slowly advancing the endotracheal tube through the patient's airway as tolerated (e.g. blind nasal intubation or some fiberoptic intubation techniques), the nebulizer face mask can be placed over the end of the endotracheal tube outside the patient, delivering nebulized local anesthetic directly to the end of the endotracheal tube inside the patient, right where local anesthesia is most desired.