Infection and the risk of topical anesthetic induced clinically significant methemoglobinemia after transesophageal echocardiography

Identification of N-Hydroxy-para-aminobenzoic acid in a cyanotic child after benzocaine exposure

CONTEXT

Methemoglobinemia (MetHb) after exposure to benzocaine (BZC) has been reported for more than 50 years, however the pathophysiologic mechanism has not been previously established. Direct administration of BZC to blood does not produce MetHb. After topical use, due to the lipophilicity and rapid acetylation in the tissue, little BZC reaches the liver for hepatic biotransformation. However, isolated human livers have been shown to produce MetHb forming N-hydroxyl metabolites from BZC. We report a case of BZC-induced MetHb with the first identification and quantification of the reactive metabolite responsible for the oxidative stress: N-Hydroxy-Para-amino benzoic acid (N-OH-PABA).

CASE DETAILS

An 8 year old male was admitted to a hospital for an appendectomy. Several applications of BZC spray were used during multiple attempts at nasogastric tube placement. In various attempts to achieve local anesthesia, benzocaine spray was used in both nares and through the mouth aimed at the posterior oropharynx. The patient subsequently became cyanotic with an initial MetHb level of 32.9 %. Methylene blue was administered and the patient promptly responded with resolution of cyanosis. Blood taken within 20 min of the initial symptoms contained benzocaine (5.2ug/mL), bupivacaine (740ng/mL), lidocaine (530ng/mL), acetaminophen (12ug/mL), midazolam (60ng/mL), PABA and N-OH-PABA (35ng/mL). Serum was analyzed using Liquid Chromatography- Quadrupole Time-of-Flight Mass Spectrometry. Mass spectrometry was done using an electrospray ionization source run in negative and positive polarities. A reference standard for N-OH-PABA was synthesized for confirmation and quantification.

DISCUSSION

The rare and idiopathic nature of methemoglobinemia after benzocaine use has made study of the pathophysiologic mechanism in humans difficult. Lack of understanding has brought calls for restriction of use of the widely used medication that may not be based on evidence. Our case presents several unique features: 1) benzocaine absorption after topical administration was documented with serum concentrations 2) confirmation of an in vivo formation of MetHb-forming n-hydroxyl-metabolite after benzocaine use and 3) the documentation of N-OH-PABA in humans within 20 min of MetHb post-benzocaine administration.

Benzocaine-induced methaemoglobinaemia: a life-threatening complication after a transoesophageal echocardiogram (TEE)

Acquired methaemoglobinaemia is a potentially fatal impairment in oxygen delivery if not recognised early and treated appropriately. Benzocaine used as an anaesthetic for endoscopic procedures is an uncommon but clinically important precipitant of acquired methaemoglobinaemia. We present a case of an elderly woman who developed perioral cyanosis and desaturation 20 min after a transoesophageal echocardiogram. Further evaluation led to the diagnosis of benzocaine-induced methaemoglobinaemia and timely treatment with intravenous methylene blue was initiated.

Risk of acquired methemoglobinemia with different topical anesthetics during endoscopic procedures

INTRODUCTION

Methemoglobinemia is a recognized complication of the use of topical anesthetic sprays. The true scope of the problem or the risk with different topical anesthetic sprays and endoscopic procedures is unknown.

METHODS

We retrospectively identified all cases of methemoglobinemia that occurred in a university affiliated community hospital from 2001 to 2007.

RESULTS

Eleven cases of methemoglobinemia were identified over the 6-year period. Nine (82%) occurred with use of benzocaine spray during transesophageal echocardiography (TEE). Patients who developed methemoglobinemia secondary to the topical anesthetic spray compared to other causes were more likely to be older, have lower mean hemoglobin levels (10.5 ± 0.5 g/dL vs 11.3 ± 0.0 g/dL), and a higher mean methemoglobin concentration at diagnosis (40.8% ± 5.2% vs 24% ± 10%). However, only age reached statistical significance (P = 0.004).

CONCLUSION

In a university-affiliated community hospital, topical anesthetic sprays account for most of the burden of methemoglobinemia. Benzocaine use in the context of TEE caused more methemoglobinemia compared to lidocaine and other endoscopic procedures. This observation supports previous data and findings deserve further study.

Unusual cause of severe toxic methemoglobinemia in an infant: a case report

Toxic methemoglobinemia is an uncommon blood disorder induced by exposure to certain oxidizing agents and drugs. In severe cases, this condition may rapidly lead to major cardiopulmonary compromise and constitutes an emergency requiring prompt recognition and early management. We report an unusual case of severe toxic methemoglobinemia following wide cutaneous application of a pomade containing benzocaine, resorcin, and oxyquinoline (Nestosyl®) in an infant.

Methemoglobinemia due to topical pharyngeal anesthesia during endoscopic procedures

Acquired methemoglobinemia is a known complication of topical anesthesia during endoscopic procedures. Benzocaine has been implicated in a majority of cases and has been removed from some hospital formularies. However, a lot of uncertainty exists about the risk factors for this uncommon complication. This review attempts to summarize the current knowledge of this condition and describe known risk factors. Anesthetic and patient-specific risk factors are described along with some hypothetical procedure-related factors. Clinicians should identify patients who are at high risk and apply appropriate postprocedure screening. Prospective studies are needed to further our knowledge and improve patient safety.