Ann Thorac Surg 1999;67:1776-1778
© 1999 The Society of Thoracic Surgeons
Case Reports
An unusual case of hypoxia from benzocaine-induced methemoglobinemia
Mark S. Slaughter, MDa,
Paul J. Gordon, MDa,
Jack C. Roberts, MDa,
Patroklos S. Pappas, MDa
a Sections of Thoracic Surgery and Adult Cardiac Surgery, Christ Hospital and Medical Center, Oak Lawn, Illinois, USA
Accepted for publication November 4, 1998.
Address reprint requests to Dr Slaughter, 4400 W. 95th St, Ste 205, Oak Lawn, IL 60453
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Abstract
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Hypoxemia during bronchoscopy occurs frequently. It can usually be managed by supplemental oxygen and bronchodilators or, in some cases, occasionally stopping the procedure. Benzocaine spray is commonly used as a topical anesthetic agent during bronchoscopy. However, it has been associated with the development of methemoglobinemia. The following is a case report of hypoxia during bronchoscopy from benzocaine-induced methemoglobinemia and its management.
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Introduction
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Bronchoscopy has become a common procedure and is performed by multiple specialists including cardiothoracic surgeons. Frequently it is performed with the patient awake which requires topical anesthesia to prevent the patient from gagging or coughing. Benzocaine spray is very effective for this purpose and is easy to apply. However, it has been associated with the development of methemoglobinemia. We report a case of benzocaine spray induced methemoglobinemia and its treatment.
A 71-year-old man underwent a left upper lobectomy for stage I adenocarcinoma of the lung. Postoperatively, the patient was doing well and was extubated on postoperative day (POD) 1. On POD 3, the patient developed significant left lower lobe (LLL) atelectasis, and it was felt that bronchoscopy was needed to restore adequate ventilation to the LLL. Before starting the bronchoscopy, the patient was on a nasal cannula at 5 L/min of oxygen, and the oxygen saturation was >94% by pulse oximetry. Midazolam (Versed; Hoffmann-La Roche Inc, Nutley, NJ) 1 mg, was administered intravenously and 20% benzocaine (Hurricane Spray; Beutlich LP Pharmaceuticals, Waukegan, IL) topical spray was used to anesthetize the upper airway. A flexible bronchoscope was inserted orally and advanced into the trachea. The right main stem bronchus and segmental orifices were normal. Thick secretions and mucous were identified in the left main stem and lower lobe bronchus and successfully removed. The patient’s oxygen saturation had decreased to 90% despite the supplemental oxygen and removal of secretions, so the bronchoscope was removed and the procedure was terminated. The patient’s oxygen saturations continued to decrease to < 85%, despite being placed on a 100% nonrebreather mask. Clinically, the patient had good air movement bilaterally, no wheezing, and no evidence of a pneumothorax or heart failure on exam. The patient became tachycardic and tachypneic, requiring immediate intubation. Despite initiating mechanical ventilation with 100% inspired oxygen and positive end-expitatory pressure, the patient was cyanotic. An arterial blood gas (ABG) was drawn, which revealed very dark blood. Due to the abnormally low hemoglobin saturation in the presence of an appropriately high oxygen tension, a repeat ABG with methemoglogin level was obtained (Table 1). The methemoglobin level was 10 times normal at 19.4% (normal 0%–1.9%) and a diagnosis of benzocaine-induced methemoglobinemia was established. Methylene blue was administered intravenously with immediate improvement in the arterial saturation and resolution of the cyanosis. Twenty minutes after the patient received methylene blue, he was extubated with improved ABGs and a normal methemoglobin level. A repeat methemoglobin level was normal 4 h later. The remainder of the hospital course was uncomplicated and the patient was discharged on POD 7.
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Comment
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Methemoglobinemia associated with benzocaine exposure was first reported by Bernstein in 1950 [1]. Since that time, fewer than 50 cases have been reported in the English literature [2]. It occurs more commonly in infants and the elderly, and if not recognized and treated it can be fatal [2–4]. Methemoglobinemia results from oxidation of heme iron moieties of the hemoglobin tetramer. The heme molecules of methemoglobin contain ferric iron bound to a water molecule or to a hydroxyl ion, thus preventing the normal reversible binding of oxygen. Using the intrinsic reducing system and red cell turnover, methemoglobin concentrations are maintained < 2% under normal physiological conditions. The clinical diagnosis should be considered in patients with a low oxygen saturation that is unresponsive to supplemental oxygen administration. Frequently, the patient is cyanotic and the arterial blood gas will have a characteristic brown color. Confirmation of the clinical diagnosis consists of laboratory documentation of elevated methemoglobin levels by cooximetry analysis. Pulse oximetry, as demonstrated in our case, is inaccurate in the presence of methemoglobinemia. Oxygen saturation readings by pulse oximeters will frequently be 80% to 85%, despite a much lower functional saturation [5].
The treatment of methemoglobinemia using methylene blue was first described by Wendel in 1937 [6]. Methylene blue augments the intrinsic reducing potential of the NADPH methemoglobinemia reductase system by serving as a cofactor of an electron transfer to the ferric heme ion [7]. Initial therapy is methylene blue (2 mg/kg) given intravenously over 5–10 min. If the diagnosis is correct, the hypoxia and low oxygen saturation will rapidly resolve with a reduction in the methemoglobin concentration within 30–60 min. Rebound methemoglobinemia can occur several hours and up to 20 h after successful treatment [2], and may require repeat administration of methylene blue.
Clearly, avoiding this potentially fatal complication is the most desirable option. Using topical anesthetic agents with a lower concentration or avoiding sprays without metered dosing may be helpful. When performing bronchoscopy after the topical use of benzocaine spray and the patient develops hypoxia that is refractory to the administration of supplemental oxygen, methemoglobinemia should always be considered in the differential diagnosis. Successful treatment can be obtained with the rapid administration of intravenous methylene blue. Although methemoglobinemia from topical benzocaine is an uncommon complication, all physicians performing endoscopic procedures should be aware of its possible occurrence and the appropriate treatment of this potentially life-threatening condition.
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References
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Bernstein B.M. Cyanosis following use of anesthesin (ethylaminobenzoate). Rev Gastroenterol 1950;17:123-124.[Medline]
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Rodriquez L.F., Smolik L.M., Zbehlik A.J. Benzocaine-induced methemoglobinemia: report of a severe reaction and review of the literature. Ann Pharmacother 1994;28:643-649.[Abstract]
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Tush G.M., Kuhn R.J. Methemoglobinemia induced by an over-the-counter medication. Ann Pharmacother 1996;30:1251-1254.[Abstract]
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Lee E., Boorse R., Marcinczyk M. Methemoglobinemia secondary to benzocaine topical anesthetic. Surg Laparos Endosc 1996;6:492-493.
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Dorsch J.A. Pulse oximetry. In: Dorsch J.A., Dorsch S.E., eds. Understanding anesthesia equipment. Baltimore, Maryland: Williams & Wilkins, 1994:660-661.
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Wendel W.B. Use of methylene blue in methemoglobinemia from sulfanilamide poisoning. JAMA 1937;109:1216.
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Curry S. Methemoglobinemia. Ann Emer Med 1982;11:214-221.[Medline]
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Abstract
Introduction
