Benzocaine-induced methemoglobinemia during general anesthesia

Asymptomatic benzocaine spray-induced methaemoglobinaemia in preoperative sedation for oesophagogastroduodenoscopy

Methaemoglobinaemia is defined as elevated methaemoglobin in the blood which is characterised by conversion of some of the reduced ferrous iron elements [Fe2+] to the oxidised ferric [Fe3+] form which does not have capacity to bind and transport oxygen resulting in functional anaemia. Causes can be genetic mutations or acquired by medications such as dapsone, nitrates or benzocaine. Benzocaine is currently being used as a topical anaesthetic agent before certain procedures. We report a case of benzocaine spray-induced methaemoglobinaemia in a patient who underwent oesophagogastroduodenoscopy for evaluation of upper gastrointestinal bleeding.

Severe methemoglobinemia from topical anesthetic spray: case report, discussion and qualitative systematic review

Few health care professionals realize that topical anesthetic spray can cause methemoglobinemia. We describe a 56-year-old woman who was transferred to our emergency department when severe cyanosis and chest pain developed after administration of topical oropharyngeal benzocaine and lidocaine during outpatient endoscopy. Investigations revealed a methemoglobin level of 51%. Despite rapid diagnosis and treatment with methylene blue, pulmonary edema consistent with adult respiratory distress syndrome developed, endotracheal intubation was required, and the patient suffered a lengthy course in the intensive care unit. This article presents a detailed discussion of the pathophysiology, diagnosis and treatment of methemoglobinemia, as well as a qualitative systematic review of the English literature on methemoglobinemia induced by topical anesthetic. The implications of this condition for emergency physicians are also outlined.

An evaluation of 10 percent and 20 percent benzocaine gels in patients with acute toothaches: efficacy, tolerability and compliance with label dose administration directions

BACKGROUND

The authors evaluated the efficacy and tolerability of 10 percent and 20 percent benzocaine gels compared with those of a vehicle (placebo) gel for the temporary relief of toothache pain. They also assessed the compliance with the label dose administration directions on the part of participants with toothache pain.

METHODS

Under double-masked conditions, 576 participants self-applied study gel to an open tooth cavity and surrounding oral tissues. Participants evaluated their pain intensity and pain relief for 120 minutes. The authors determined the amount of gel the participants applied.

RESULTS

The responders' rates (the primary efficacy parameter), defined as the percentage of participants who had an improvement in pain intensity as exhibited by a pain score reduction of at least one unit on the dental pain scale from baseline for two consecutive assessments any time between the five- and 20-minute points, were 87.3 percent, 80.7 percent and 70.4 percent, respectively, for 20 percent benzocaine gel, 10 percent benzocaine gel and vehicle gel. Both benzocaine gels were significantly (P ≤ .05) better than vehicle gel; the 20 percent benzocaine gel also was significantly (P ≤ .05) better than the 10 percent benzocaine gel. The mean amount of gel applied was 235.6 milligrams, with 88.2 percent of participants applying 400 mg or less.

CONCLUSIONS

Both 10 percent and 20 percent benzocaine gels were more efficacious than the vehicle gel, and the 20 percent benzocaine gel was more efficacious than the 10 percent benzocaine gel. All treatments were well tolerated by participants. Practical Implications. Patients can use 10 percent and 20 percent benzocaine gels to temporarily treat toothache pain safely.

Evaluation and management of acquired methemoglobinemia associated with topical benzocaine use

Benzocaine is a widely used topical oropharyngeal anesthetic and has been reported to cause methemoglobinemia. We discuss benzocaine-induced methemoglobinemia and review the causes, presentation, and management of this serious complication. Treatment with methylene blue will result in reversal of methemoglobinemia and clinical recovery in most cases but needs to be used at appropriate doses in carefully selected individuals. Physicians who perform procedures involving the application of benzocaine for topical anesthesia need to rapidly identify and treat methemoglobinemia to avoid significant associated morbidity and mortality.

Benzocaine-induced Methemoglobinemia

A case is reported in which a patient developed methemoglobinemia-induced cyanosis while under general anesthesia during surgery for multiple fascial space infections. The cause of methemoglobinemia was 20% benzocaine spray used for local anesthesia before intubation. Acutely developing methemoglobinemia is infrequently encountered in clinical practice. When confronted with cyanosis in the absence of cardiac or pulmonary disease, one must seriously consider the diagnosis of methemoglobinemia. The etiology of methemoglobinemia, the causative agents, the diagnosis, and the emergency treatment required are discussed.

Occupational methaemoglobinaemia. Mechanisms of production, features, diagnosis and management including the use of methylene blue

Methaemoglobin is formed by oxidation of ferrous (FeII) haem to the ferric (FeIII) state and the mechanisms by which this occurs are complex. Most cases are due to one of three processes. Firstly, direct oxidation of ferrohaemoglobin, which involves the transfer of electrons from ferrous haem to the oxidising compound. This mechanism proceeds most readily in the absence of oxygen. Secondly, indirect oxidation, a process of co-oxidation which requires haemoglobin-bound oxygen and is involved, for example, in nitrite-induced methaemoglobinaemia. Thirdly, biotransformation of a chemical to an active intermediate that initiates methaemoglobin formation by a variety of mechanisms. This is the means by which most aromatic compounds, such as amino- and nitro-derivatives of benzene, produce methaemoglobin. Methaemoglobinaemia is an uncommon occupational occurrence. Aromatic compounds are responsible for most cases, their lipophilic nature and volatility facilitating absorption during dermal and inhalational exposure, the principal routes implicated in the workplace. Methaemoglobinaemia presents clinically with symptoms and signs of tissue hypoxia. Concentrations around 80% are life-threatening. Features of toxicity may develop over hours or even days when exposure, whether by inhalation or repeated skin contact, is to relatively low concentrations of inducing chemical(s). Not all features observed in patients with methaemoglobinaemia are due to methaemoglobin formation. For example, the intravascular haemolysis caused by oxidising chemicals such as chlorates poses more risk to life than the methaemoglobinaemia that such chemicals induce. If an occupational history is taken, the diagnosis of methaemoglobinaemia should be relatively straightforward. In addition, two clinical observations may help: firstly, the victim is often less unwell than one would expect from the severity of 'cyanosis' and, secondly, the 'cyanosis' is unresponsive to oxygen therapy. Pulse oximetry is unreliable in the presence of methaemoglobinaemia. Arterial blood gas analysis is mandatory in severe poisoning and reveals normal partial pressures of oxygen (pO2) and carbon dioxide (pCO2,), a normal 'calculated' haemoglobin oxygen saturation, an increased methaemoglobin concentration and possibly a metabolic acidosis. Following decontamination, high-flow oxygen should be given to maximise oxygen carriage by remaining ferrous haem. No controlled trial of the efficacy of methylene blue has been performed but clinical experience suggests that methylene blue can increase the rate of methaemoglobin conversion to haemoglobin some 6-fold. Patients with features and/or methaemoglobin concentrations of 30-50%, should be administered methylene blue 1-2 mg/kg/bodyweight intravenously (the dose depending on the severity of the features), whereas those with methaemoglobin concentrations exceeding 50% should be given methylene blue 2 mg/kg intravenously. Symptomatic improvement usually occurs within 30 minutes and a second dose of methylene blue will be required in only very severe cases or if there is evidence of ongoing methaemoglobin formation. Methylene blue is less effective or ineffective in the presence of glucose-6-phosphate dehydrogenase deficiency since its antidotal action is dependent on nicotinamide-adenine dinucleotide phosphate (NADP+). In addition, methylene blue is most effective in intact erythrocytes; efficacy is reduced in the presence of haemolysis. Moreover, in the presence of haemolysis, high dose methylene blue (20-30 mg/kg) can itself initiate methaemoglobin formation. Supplemental antioxidants such as ascorbic acid (vitamin C), N-acetylcysteine and tocopherol (vitamin E) have been used as adjuvants or alternatives to methylene blue with no confirmed benefit. Exchange transfusion may have a role in the management of severe haemolysis or in G-6-P-D deficiency associated with life-threatening methaemoglobinaemia where methylene blue is relatively contraindicated.

Benzocaine-induced methemoglobinemia during an outpatient procedure

Outpatient transesophageal echocardiography was performed in a 69-year-old man with a history of aortic valve repair. During the procedure the patient became markedly cyanotic and hypotensive. Oxygen saturation measured by pulse oximetry decreased from 97% to the mid-80s. The man's condition continued to deteriorate. On transfer to a critical care unit, blood analysis by co-oximetry showed methemoglobin saturation of 67.8%. The patient's condition improved significantly after intravenous administration of methylene blue 1 mg/kg. With increasing numbers of outpatient procedures performed under topical anesthesia, measures should be in place to deal with a potential life-threatening adverse event such as methemoglobinemia.

Methemoglobinemia from topically applied anesthetic spray

Topically applied anesthetic spray is commonly used as part of premedication for general anesthesia and for endoscopic procedures; it is rarely associated with side effects. In this report, we describe two cases of toxic methemoglobinemia that resulted from topically applied anesthetic spray used before endoscopy. In both cases, standard doses were used; however, methemoglobin levels of 45% and 38% developed within 1 hour of the procedure. Both patients had normal levels of erythrocyte methemoglobin reductase, an indication that this rare but potentially fatal side effect can occur in persons who have no predisposing factors. Because toxic methemoglobinemia is easily treated, our report emphasizes the need to recognize this problem when topically applied anesthetic sprays are used.

Methemoglobinemia in a patient undergoing gastrointestinal endoscopy

OBJECTIVE

To report a case of methemoglobinemia induced by benzocaine in a patient undergoing gastrointestinal endoscopy.

CASE SUMMARY

Before undergoing an upper gastrointestinal endoscopy, a 15-year-old girl received 20% benzocaine as a spray, to locally anesthetize the pharyngeal mucosa. Thirty minutes after the endoscopy, the patient suddenly became cyanotic, short of breath, and comatose. She was intubated and transferred to the intensive care unit. Her blood methemoglobin concentration was 54 percent. The patient was treated with intravenous methylene blue. Four hours later she was extubated. She was alert, awake, and asymptomatic.

DISCUSSION

This is the fourth reported case of methemoglobinemia induced by benzocaine spray in patients undergoing gastrointestinal endoscopy. Pathways for the formation of methemoglobin in the body are reviewed. Intravenous methylene blue is the drug of choice for this condition, and produces rapid and dramatic reversal of methemoglobinemia.

CONCLUSIONS

It is common to use benzocaine spray prior to upper gastrointestinal endoscopy. Benzocaine rarely induces methemoglobinemia in these patients. Prompt diagnosis and treatment with intravenous methylene blue is warranted in such cases.

Chemically induced methaemoglobinaemia in a neonate

A case of toxic methaemoglobinaemia is presented, which followed the use of a local anaesthetic containing prilocaine (Citanest, Astra Pharmaceuticals Ltd) which was used to provide analgesia prior to the suturing of a facial laceration. Although this complication is well documented, this case is unusual in that it involved a neonate and was not produced by an overdose of prilocaine (the recommendations of the British National Formulary and the product monograph were followed). Explanations for the increased susceptibility of neonates and young infants to methaemoglobinaemia are presented together with the salient clinicopathological features. The diagnostic dilemmas and investigative procedures related to the condition are considered together with the various treatments available.

Methemoglobinemia as a complication of 20% benzocaine spray for endoscopy

Topical 20% benzocaine (Hurricaine, Beutlich, Inc., Niles, Ill.) spray is frequently used for oral anesthesia before upper endoscopy. Side effects attributed to this agent are exceedingly rare. The author reports one of these rare complications, drug-induced methemoglobinemia, in a patient with methemoglobin reductase deficiency. The mechanisms for the development of methemoglobinemia and its treatment are reviewed.

Methemoglobin levels following intravenous lidocaine administration

Methemoglobin levels were obtained before and after administration of IV lidocaine in 40 cardiac patients. Patients were given a 1-mg/kg bolus of IV lidocaine hydrochloride, started on a maintenance infusion at 2.0 mg/min, and given a second bolus of lidocaine of 0.5 mg/kg 15 minutes after the initial bolus. The maintenance infusion was adjusted from 1 to 4 mg/min according to clinical needs. Methemoglobin levels were drawn at zero, one, and six hours, and lidocaine levels were drawn at one and six hours after the initial bolus. Elevation of methemoglobin levels after lidocaine administration was statistically significant (P less than .05), but not clinically significant. The highest methemoglobin level obtained was 1.2%. Only one other patient had a level above 1%. No patient developed either signs of lidocaine toxicity or toxic levels of methemoglobin. Routine determination of methemoglobin levels is not clinically indicated following routine lidocaine administration. It may have some as-yet-undetermined value in lidocaine-toxic patients.