Topical anesthetic-induced methemoglobinemia in sheep: a comparison of benzocaine and lidocaine

Radiographic and histological evidence of metabolic bone disease in gliding leaf frogs (Agalychnis spurrelli)

Bone alterations due to metabolic bone disease in captive animal populations can have a negative impact on repopulation and research initiatives. This investigation has the purpose of describing the principal radiographic and anatomopathological findings present in nine gliding leaf frogs (Agalychnis spurrelli) kept in captivity with alterations in their spines and long bones. The observed histopathological findings were in the canalis vertebralis, paraspinal muscle and long bones, and included deformed bones with alteration of the adjacent tissues, alterations in the ossification process, bone degeneration and resorption, decreased number of osteocytes and deposition of osteoid and fibrous material in the compact bone tissue. Additionally, the spinal cord showed compressed white matter, chronic meningitis in the duramater, alteration in the number of glial cells and loss of delimitation between the gray and white matter. Radiographical changes were found mainly in the long bones and included moth-eaten osteolysis, solid periosteal reaction, bone deformities, cortical tunneling and inflammation of adjacent soft tissues. Also, pathological fractures of the femur and urostyle were observed together with spinal column deviations with increased bone density.

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.

Methemoglobinemia in bronchoscopy: a case series and a review of the literature

BACKGROUND

Methemoglobinemia results from oxidation of ferrous iron to ferric iron within the hemoglobin molecule. This molecule cannot bind oxygen and increases the affinity of normal hemoglobin for oxygen, which results in decreased oxygen offloading in peripheral tissues. At elevated levels, methemoglobinemia can cause dyspnea, cyanosis, and even death. Common local anesthesia agents have been correlated with methemoglobinemia. Bronchoscopy is a commonly performed clinical procedure which uses topical application of these anesthetics to provide patient comfort. Methylene blue is an agent thought to help reverse the effects of methemoglobinemia by facilitating the methemoglobin reductase system.

METHODS

Using multiple search engines including PubMed and the Cochrane Database, available data on cases of methemoglobinemia after bronchoscopy were pooled. Adult and pediatric cases were considered.

RESULTS

Eleven cases were identified. Cases occurred from 1977 until present. Data gathering was complicated by the fact that a consistent reporting system was not used across cases. Arterial blood gas data and CO-oximetry reported levels of methemoglobin were reported where available. No patients died from methemoglobinemia. The most common finding across all patients was decreased peripheral oxygen saturation. Cyanosis was also frequently reported. There was a disparity between the low peripheral oxygen saturation which was reported and the pO(2) on the arterial blood gas. Dose and type of anesthetic agent varied widely across studies.

CONCLUSIONS

Using topical anesthetic during bronchoscopy appears relatively safe. No fatalities from methemoglobinemia after bronchoscopy have been reported. A high suspicion for methemoglobinemia is required in patients who develop hypoxia or cyanosis postprocedurally. Access to CO-oximetry can confirm the diagnosis but the clinical picture is often sufficient to proceed with methylene blue treatment or observation, based on how severely the patient is affected. Patients who return to baseline can be considered for discharge home.

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.

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.

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

BACKGROUND

Methemoglobinemia is a recognized complication of topical anesthesia with benzocaine during transesophageal echocardiography (TEE). Though several risk factors have been described, the importance of individual factors is not known. We performed a retrospective study to identify determinants of the risk of methemoglobinemia.

MATERIALS AND METHODS

All patients who underwent TEE with benzocaine topical anesthesia between June 2005 and June 2007 were included in this retrospective study.

RESULTS

Of the 886 patients who were included in the study, 140 had active infection (15.8%). The incidence of methemoglobinemia in this group was 2.9% (vs. 0%, P < 0.001). Compared to those without infection, patients in the active infection group were more likely to have a lower hemoglobin (P < 0.001), serum albumin level (P < 0.001), glomerular filtration rate less than 60 ml/min per 1.73 m(2) (P < 0.001), higher rates of dialysis (P < 0.001), a higher incidence of malignancy (P = 0.01), and increased use of acetaminophen and sulfa drugs (P < 0.001). However, multivariate logistic regression analysis did not identify any statistically significant covariates.

CONCLUSION

In conclusion, patients with an active systemic infection who undergo TEE are at a higher risk of methemoglobinemia. However, none of the risk factors for methemoglobinemia including active infection reached statistical significance in the regression analysis which has to be interpreted with caution in view of the low event rate.

Two cases of methemoglobinemia following zopiclone ingestion

INTRODUCTION

Most cases of methemoglobinemia result from exposure to certain medications and chemicals such as nitrates, nitrites, aniline, dapsone, phenazopyridine, benzocaine, and chlorates which oxidize the iron from the ferrous state. Intoxication with zopiclone is expected to produce drowsiness, confusion and coma but not methemoglobinemia. We report two cases of zopiclone overdose with methemoglobinemia.

CASE REPORTS

Case one: A 43-year-old woman presented to the emergency department two hours after ingesting 100 tablets of 7.5 mg zopiclone. Her initial vital signs, physical examination, chest x-ray, and electrocardiogram were normal. Two hours post-ingestion her methemoglobin level was 9.8%; 14 hours post-arrival she showed cyanosis of the lips and extremities and dyspnea after walking. The blood sample 16 hours post-ingestion was dark brown in color and the methemoglobin was 23.8%. Shortly after the second of two doses of methylene blue (1 mg/kg each) her methemoglobin was 3.6%. Case two: A 30-year-old woman came to the emergency department 50 hours after ingesting 150 to 200 tablets of 7.5 mg zopiclone. Her vital signs and physical examination were normal. Her methemoglobin level was 5.2% at 52 hours post-ingestion and it peaked at 10.4% one hour later. She recovered following symptomatic care.

DISCUSSION AND CONCLUSIONS

Methemoglobinemia has not previously been reported following acute zopiclone overdose. In our patients, there were no identifiable alternative causes explaining the methemoglobinemia and zopiclone was confirmed in both patients by laboratory analysis. These two cases suggest that zopiclone overdose is capable of producing delayed methemoglobinemia, which may be related to formation of a sufficient quantity of the N-oxide metabolite.

Benzocaine and lidocaine induced methemoglobinemia after bronchoscopy: a case report

Introduction

Methemoglobinemia is a rare cause of hypoxemia, characterized by abnormal levels of oxidized hemoglobin that cannot bind to and transport oxygen.

Case presentation

A 62-year-old male underwent bronchoscopy where lidocaine oral solution and Hurricaine spray (20% benzocaine) were used. He developed central cyanosis and his oxygen saturation was 85% via pulse oximetry. An arterial blood gas revealed pH 7.45, P_CO2 42, P_O2 282, oxygen saturation 85%. Co-oximetry performed revealed a methemoglobin level of 17.5% (normal 0.6–2.5%). The patient was continued on 15 L/minute nonrebreathing face mask and subsequent oxygen saturation improved to 92% within two hours. With hemodynamic stability and improved SpO₂, treatment with methylene blue was withheld.

Conclusion

Methemoglobinemia is a potentially lethal condition after exposure to routinely used drugs. Physicians should be aware of this complication for early diagnosis and treatment.

Methemoglobinemia After Fiberoptic Intubation in a Patient With an Unstable Cervical Fracture

Methemoglobinemia, a condition associated with cyanosis and diminished pulse oximetry values, has been reported after use of local anesthetics to facilitate fiberoptic intubation. The majority of reports in the literature detail this development during diagnostic procedures such as endoscopy and bronchoscopy. A case of methemoglobinemia in a multiple-injury patient with an unstable compressive-flexion injury of the cervical spine undergoing fiberoptic intubation is presented. A literature review of this entity is also presented. The patient underwent fiberoptic intubation using topical pharyngeal anesthetics before planned cervical corpectomy, strut grafting and instrumentation. He became acutely cyanotic with abruptly diminished pulse oximetry readings. Subsequent blood gas analysis demonstrated methemoglobinemia. Intravenous methylene blue administration led to an uncomplicated resolution of the condition. Surgeons and anesthesiologists who manage such patients should be aware of methemoglobinemia, a rare but potentially fatal complication related to topical airway anesthetics.

The need for caution with topical anesthesia during endoscopic procedures, as liberal use may result in methemoglobinemia

During upper gastrointestinal endoscopy, topical oropharyngeal anesthesia with lidocaine and/or benzocaine is used routinely by many endodscopists. Although such a practice is usually safe, there have been a number of reports of methemoglobinemia induced by topical anesthesia. Early treatment is extremely important as the development of methemoglobinemia is potentially fatal. Methemoglobinemia should be considered when oxygen desaturation occurs without another explanation. In this case series, we report 4 cases of methemoglobinemia that followed the liberal application of Cetacaine for ERCP. All patients recovered after appropriate treatment but these cases serve to highlight the potential problem, the importance of early recognition and treatment, and the most appropriate treatment options.

Benzocaine-induced methemoglobinemia: experience from a high-volume transesophageal echocardiography laboratory

Benzocaine (ethyl aminobenzoate), a topical anesthetic widely used before transesophageal echocardiography, has been reported to cause acquired methemoglobinemia. The incidence of benzocaine-induced methemoglobinemia in clinical practice, however, has been difficult to estimate. After systematic review of our institutional experience for clinically recognized cases of benzocaine-induced methemoglobinemia in patients undergoing transesophageal echocardiography, we report an estimated incidence of 0.115% (95% confidence interval 0.037-0.269). This report also provides the largest analysis of the incidence of methemoglobinemia in readministration cases. Although controversy remains as to whether this is an idiosyncratic versus dose-related response, a description of purported patient risk factors is included.

Bioactivation of benzocaine to a methaemoglobin-forming metabolite by rat and human microsomes in vitro

Benzocaine-mediated methaemoglobin-generation was compared with that of dapsone in vitro. Direct incubation of benzocaine with washed human erythrocytes alone at up to 15 mM did not result in significant methaemoglobin formation (0.4 ± 0.1%). With rat microsomes, dapsone-dependent methaemoglobin formation was almost two-fold that of benzocaine at 30 min (56.5 ± 0.7% vs 31.6 ± 2.4% P < 0.005)). Benzocaine-mediated methaemoglobin formation was significantly reduced in the presence of DDC (diethyldithiocarbamate) at the 10 (P < 0.005) and 20 (P < 0.025) min time points. At 30 min, cimetidine reduced benzocaine-mediated methaemoglobin from 34.4 ± 8.7% to less than 3% (P < 0.005). The methaemoglobin forming capacity of dapsone was significantly inhibited at all three time points by both DDC (P < 0.005) and cimetidine (P < 0.005). Incubation of benzocaine with microsomes from five human livers showed that each liver produced methaemoglobin-forming metabolites. No inhibitory effect was seen with DDC, although cimetidine caused a significant reduction (32.8 ± 12.4% overall) in benzocaine-mediated methaemoglobin formation in the four livers tested.

Topical anesthetic-induced methemoglobinemia and sulfhemoglobinemia in macaques: a comparison of benzocaine and lidocaine

Benzocaine (BNZ) and lidocaine (LC) are commonly used topical (spray) anesthetics approved for use in humans. Benzocaine has structural similarities to methemoglobin (MHb)-forming drugs that are current candidates for cyanide prophylaxis, while LC has been reported to increase MHb in man. In this study, we compared MHb and sulfhemoglobin (SHb) production in three groups of Macaques (Chinese rhesus and Indian rhesus (Macaca mulatta) and pig-tailed macaques (Macaca nemestrina)) after exposure to BNZ and LC. Formation of SHb, unlike MHb, is not thought to be reversible and therefore is considered to be of greater toxic significance. Both MHb and SHb levels were measured periodically on a CO-Oximeter. All rhesus macaques (n = 8) were administered an intratracheal/intranasal) dose of 56 mg (low dose) or 280 mg (high dose) of BNZ or 40 mg of LC in a randomized cross-over design (all animals received all three treatments). Pig-tailed macaques (n = 6) were given an intranasal dose of 56 mg of BNZ and 40 mg of LC. As no differences in the peak MHb or time to peak (mean +/- SD) were observed among the three macaque subspecies, the data were pooled. Lidocaine did not cause MHb or SHb formation above baseline in any monkey. In contrast, all monkeys (n = 14) had a significant elevation in peak MHb formation after 56 mg of BNZ, which ranged from 4.0% to 19.4% with an average of 8.6 +/- 4.0% (mean +/- SD), with peak MHb levels reached at 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

A prospective evaluation of benzocaine-associated methemoglobinemia in human beings

STUDY OBJECTIVE

This study determined the frequency and severity of benzocaine-associated methemoglobinemia in routine clinical use.

DESIGN

Prospective, crossover, convenience study.

SETTING

Gastroenterology clinic at a US Army medical center functioning as a community hospital and tertiary referral center.

PARTICIPANTS

Healthy adult volunteers and patient volunteers undergoing an upper gastrointestinal endoscopic procedure.

INTERVENTIONS

Baseline methemoglobin levels were measured. Subjects then received a 2-second spray of benzocaine to the oropharynx. Venous blood for methemoglobin analysis was collected 20, 40, and 60 minutes after benzocaine dosing and analyzed using a co-oximeter.

RESULTS

A statistically significant (P < .05) increase in methemoglobin level between baseline (0.8 +/- 0.2%) and 20-, 40-, and 60-minute measurements (0.9 +/- 0.2%) was identified using one-way analysis of variance followed by Fisher's protected least-squares difference.

CONCLUSION

A 2-second spray of 20% benzocaine applied to the oropharynx of human beings induces a statistically significant, but clinically insignificant, increase in methemoglobin levels.