Life-threatening toxic methemoglobinemia induced by prilocaine

2023 American Heart Association Focused Update on the Management of Patients With Cardiac Arrest or Life-Threatening Toxicity Due to Poisoning: An Update to the American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

In this focused update, the American Heart Association provides updated guidance for resuscitation of patients with cardiac arrest, respiratory arrest, and refractory shock due to poisoning. Based on structured evidence reviews, guidelines are provided for the treatment of critical poisoning from benzodiazepines, β-adrenergic receptor antagonists (also known as β-blockers), L-type calcium channel antagonists (commonly called calcium channel blockers), cocaine, cyanide, digoxin and related cardiac glycosides, local anesthetics, methemoglobinemia, opioids, organophosphates and carbamates, sodium channel antagonists (also called sodium channel blockers), and sympathomimetics. Recommendations are also provided for the use of venoarterial extracorporeal membrane oxygenation. These guidelines discuss the role of atropine, benzodiazepines, calcium, digoxin-specific immune antibody fragments, electrical pacing, flumazenil, glucagon, hemodialysis, hydroxocobalamin, hyperbaric oxygen, insulin, intravenous lipid emulsion, lidocaine, methylene blue, naloxone, pralidoxime, sodium bicarbonate, sodium nitrite, sodium thiosulfate, vasodilators, and vasopressors for the management of specific critical poisonings.

Updates on Topical and Local Anesthesia Agents

Use of topical and local anesthesia (LA) is the workhorse of all aspects of dentistry. There was a time in the past when dentistry was performed without any local pain control. Owing to this there are patients with dental anxiety and fear of a dental office. The media portraying dentistry as being painful, or showing a dentist with needles, enlists fear and distrust of dentists. In contrast, pain is what brings the patient to the dental office and with local pain control measures a dentist is able to alleviate the patient's cause of pain.

Local anesthesia in oral and maxillofacial surgery: A review of current opinion

Local anesthesia (LA) is the most important pain management process in oral and maxillofacial surgery. Safe and effective LA not only enable patients to obtain high-quality treatment, but also relieve the anxiety of patients when they come to the clinic. The choices of local anesthetic and injection methods determine the success of LA to a great extent. At present, in most countries or regions, common local anesthetics used in oral and maxillofacial surgery belong to amides and they are injected into patients' body mainly through block or infiltration anesthesia. In addition, the operators' technique level, patient's subjective psychology and anatomical variation of maxillofacial structure also have a strong influence on LA in dental clinic. Due to the existence of above factors, the worldwide success rates of LA in oral and maxillofacial surgery is very different. There are no specific LA methods that ensure 100% successful LA rates. Fortunately, the development of new local anesthetic and injection technology are providing us with new ideas to solve this problem. This review mainly report the new research progress on LA in oral and maxillofacial surgery in recent decades and help clinicians with dental LA operation.

Methemoglobinemia caused by a low dose of prilocaine during general anesthesia

Methemoglobinemia is a blood disorder in which an abnormal amount of methemoglobin is produced, and prilocaine is one of the drugs that can cause this disorder. The maximum recommended dose of prilocaine is 8 mg/kg. We report a case of methemoglobinemia caused by the administration of 4.2 mg/kg of prilocaine without other methemoglobinemia-inducing drugs during general anesthesia. A 17-year-old girl with hyperthyroidism and anemia was scheduled to undergo maxillary sinus floor elevation and tooth extraction. The patient's peripheral oxygen saturation (SpO₂) decreased from 100% at arrival to 95% after receiving prilocaine with felypressin following induction of general anesthesia. However, the fraction of inspired oxygen was 0.6. Blood gas analysis showed that the methemoglobin level was 3.8% (normal level, 1%–2%), fractional oxygen saturation was 93.9%, partial pressure of oxygen was 327 mmHg, and arterial oxygen saturation was 97.6%. After administration of 1 mg/kg of methylene blue, her SpO₂ improved gradually to 99%, and the methemoglobin value decreased to 1.2%. When using prilocaine as a local anesthetic, it is important to be aware that methemoglobinemia may occur even at doses much lower than the maximum recommended dose.

Methemoglobinemia due to local anesthesia: a rare cause of cyanosis and chest pain after placement of implantable cardioverter defibrillator

Although methemoglobinemia is rare in adulthood, it may have fatal consequences if unnoticed. We planned to implant an implantable cardioverter defibrillator ICD in a 50-year-old male patient for primary prevention. Following sterile draping, prilocaine 5 mg/kg (400 mg) was injected subcutaneously for local anesthesia. We injected an additional dose of 200 mg due to pain during subclavian vein puncture. A DDD-R ICD was placed successfully within approximately 40 minutes. The patient complained of sudden chest pain and dyspnea 15 minutes after bed rest and was transferred to the coronary care unit due to cyanosis and deterioration of general status. Physical examination revealed blood pressure of 110/80 mmHg, pulse rate of 110 bpm, and otherwise unremarkable signs. Peripheral oxygen saturation was determined as 83% by pulse oximeter. Possible pneumothorax and cardiac perforation were excluded by emergency chest radiograph and echocardiography. Blood gas analyses was performed to assess for methemoglobinemia, which revealed pH 7.41, pCO2 40 mmHg, oxygen saturation 98.2%, and methemoglobin 7.9% that peaked to 12.3%. Methylene blue (1%) was slowly injected over 10 minutes at a dose of 1 mg/kg. Cyanosis waned and methemoglobin values decreased to 4.1%, 2.1%, and 1.1% at 2, 8, and 16 hours following the administration, respectively. The patient was safely discharged 2 days after implantation of pacemaker. Methemoglobinemia should be considered in cases presenting with cyanosis, non-diagnostic ECG, and a discrepancy in oxygen saturation between pulse oximetry and blood gas analyses.

Cost of Beauty; Prilocaine Induced Methemoglobinemia

Prilocaine induced methemoglobinemia is a rare entity. In the present paper, the authors aim to draw attention to the importance of this rare condition by reporting this case. A 30-year-old female presented to Emergency Department with headache, dispnea and cyanosis. The patient has a history of 1000–1200 mg of prilocaine subcutaneous injection for hair removal at a beauty center, 5 hours ago. Tension arterial: 130/73 mmHg, pulse: 103/minute, body temperature: 37 °C and respiratory rate: 20/minute. The patient had acral and perioral cyanosis. Methemoglobin was measured 14.1% in venous blood gas test. The patient treated with 3 gr ascorbic acid intravenously. The patient was discharged free of symptoms after 48 hours of observation. Emergency physician should consider methemoglobinemia in presentation of dispnea and cyanosis after injection of prilocaine.

Comparison of hemodynamic effects of lidocaine, prilocaine and mepivacaine solutions without vasoconstrictor in hypertensive patients

Objective

Local anesthetic solutions with vasoconstrictors are not contraindicated in hypertensive patients, but due to their hemodynamic effects, local anesthetics without vasoconstrictors are mainly preferred by the clinicians. The aim of this study was to compare hemodynamic effects of three different local anesthetics without vasoconstrictors during tooth extraction in hypertensive patients.

Material and Methods

Sixty-five mandibular molars and premolars were extracted in 60 hypertensive patients (29 females and 31 males; mean age: 66.95 ± 10.87 years; range: 38 to 86 years old). Inferior alveolar and buccal nerve blocks were performed with 2% lidocaine hydrochloride (HCl), 2% prilocaine HCl or 3% mepivacaine HCl without vasoconstrictor. Hemodynamic parameters namely systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), heart rate (HR), saturation rate (SR), rate pressure product (RPP) and pressure rate quotient (PRQ) were investigated before and at different intervals after anesthetic injection.

Results

The hemodynamic effects of the three agents were similar to each other, although some significance was observed for DBP, MAP, RPP and PRQ values in the lidocaine, prilocaine and mepivacaine groups.

Conclusion

Lidocaine, prilocaine and mepivacaine solutions without vasoconstrictor can be safely used in hypertensive patients. It is advisable that dental practitioners select anesthetic solutions for hypertensive patients considering their cardiovascular effects in order to provide patient comfort and safety.

Risk factors for prilocaine-induced methaemoglobinaemia following peripheral regional anaesthesia

BACKGROUND

The local anaesthetic prilocaine has a low systemic toxicity mainly because of a high absorption in the lung and a large volume of distribution and thus is associated with a lower risk of neurological or cardiac side-effects. However, the major disadvantage is the formation of methaemoglobin by its metabolite o-toluidine. This prospective observational study was performed to identify factors that are associated with increased prilocaine-induced methaemoglobinaemia.

PATIENTS AND METHODS

One Hundred and sixty two patients undergoing major knee surgery under general anaesthesia combined with peripheral nerve blocks (femoral nerve block, combined femoral/sciatic nerve block or lumbar plexus block) received a single bolus injection of 300 or 400 mg prilocaine about 30 min before surgery via a catheter. The proper placement was verified using nerve stimulation via a stimulating catheter. Three hours after prilocaine injection, venous blood samples were drawn and methaemoglobin levels were measured by standard photometric technique. Data was subjected to a stepwise multiple regression analysis.

RESULTS

The mean methaemoglobin for all patients was 2.7% (range: 0.9-15.4%). A higher dose of prilocaine and younger age were the most important predictive factors for higher methaemoglobin formation. Female sex and to a lesser extent the use of high-concentration/low-volume prilocaine also increased methaemoglobin levels. These four factors of the model explain 36% of the total variance. Other investigated factors, including the patient's height, weight, body mass index, the site of catheter insertion, the anaesthetist's judgement concerning the difficulty of catheter placement, duration of catheter placement or an inadvertent puncture of a venous or arterial vessel, had no significant impact on the concentration of methaemoglobin.

CONCLUSION

The use of prilocaine for regional block is safe, since the older patients who might be more susceptible to suffer from clinical symptoms of methaemoglobinaemia usually form less methaemoglobin. However, since prediction of high methaemoglobin levels is difficult, anaesthesiologists performing regional blocks in patients who might be jeopardized by a decreased oxygen transport capacity should avoid high doses of prilocaine.

Methaemoglobinaemia after cardiac catheterisation: a rare cause of cyanosis

Two young women had unexpected cyanosis a few hours after cardiac catheterisation for electrophysiological investigation. The first patient had atrioventricular septal defect, had undergone repeated surgical interventions, and was referred because of atrial flutter. The second patient had ablation of an accessory pathway in Wolff-Parkinson-White syndrome. Local anaesthesia was performed with 40 ml prilocaine 2%. Cyanosis with oxygen saturation of 85% developed in both patients a few hours after the electrophysiological investigation. The patients were transferred to the intensive care unit and for the first patient a considerable diagnostic effort was made to rule out morphological complication. Finally methaemoglobinaemia of 16.7% and 33.4%, respectively, was found. Cyanosis resolved within 24 hours and did not reappear. Underlying glucose-6-phosphate dehydrogenase deficiency and erythrocyte-methaemoglobin reductase deficiency were ruled out. Physicians should be aware of this rare side effect of local anaesthetics in patients with unexpected cyanosis.

[Methemoglobinemia due to prilocaine after plexus anesthesia. Reduction by prophylactic administration of ascorbic acid?]

OBJECTIVE

This study investigated in vivo and in vitro kinetics of o-toluidine-induced methemoglobinemia and the influence of ascorbic acid on resulting methemoglobin concentrations. o-Toluidine is a metabolite of prilocaline and ascorbic acid is recommended for treatment of methemoglobinemia as an alternative to methylene blue.

METHODS

We measured the formation of methemoglobin in vitro in a whole blood culture system of 8 healthy individuals 30, 60, and 360 min after the addition of different concentrations of o-toluidine (0.5, 5, 50 micrograms/ml) with and without addition of ascorbic acid (0.5 and 5 mg/ml). In a prospective randomized clinical study, a total of 72 patients of ASA risk I-III were investigated. The 3 groups of 24 patients received either an axillary, an infraclavicular vertical brachial plexus, or a combined femoral and ischiadic blockade. In each plexus anesthesia group, 12 patients were given 2,000 mg ascorbic acid intravenously before applying the local anesthetics. For surgery of the upper limb the patients received 40 ml 1% prilocaine and 10 ml 0.5% bupivacaine, for surgery of the lower limb they received 60 ml 1% prilocaine and 0.25 mg adrenaline. Blood samples for measurement of methemoglobin concentrations were taken before and 30, 60, 120, 180 and 360 min after the injection of the regional anesthetic. A p < 0.05 was considered to be significant.

RESULTS

There was a dose-dependent increase of methemoglobin due to addition of o-toluidine after 360 min in vitro. The application of 0.5 mg/ml ascorbic acid to the whole blood samples with 0.5 and 5 micrograms/ml o-toluidine resulted in a further increase of methemoglobin formation whereas there was no difference in the samples with 50 micrograms/ml. The higher concentration of 5 mg/ml ascorbic acid attenuated the methemoglobin formation only with 50 micrograms/ml o-toluidine. No effect was observed with lower concentrations of o-toluidine. In the in vivo study plexus anesthesia with prilocaine resulted in an increase of the methemoglobin concentration with a maximum after 120-180 min. The highest measured methemoglobin concentration found was 11.3%. The methemoglobin concentration already showed a decrease 360 min after the application of the regional anesthetic 2,000 mg ascorbic acid given intravenously before plexus anesthesia was not able to influence the resulting methemoglobin concentrations.

CONCLUSIONS

In vitro high concentrations of ascorbic acid are able to reduce the resulting methemoglobin concentration 360 min after addition of 50 micrograms/ml o-toluidine. The application of 2,000 mg ascorbic acid i.v. before plexus anesthesia with prilocaine does not reduce the concentration of methemoglobin.

Topical use of local anesthetics in neonates

INTRODUCTION

Various local anesthetics as in lidocaine ointment, amethocaine cream and EMLA cream are used topically for minor invasive interventions, such as venipuncture, both in children and adults. Since neonates have a nervous system that, albeit immature, enables them to feel pain, analgesia for these procedures is also indicated. Several studies in neonates have been carried out to establish effectiveness and safety of topically applied local anesthetics. These studies are reviewed in order to assess effectiveness and safety.

METHODS

A Medline search was made in order to review all studies on effectiveness and safety of topical use of local anesthetics in neonates. Effectivity or safety studies using local anesthetics for circumcision were rejected.

RESULTS

Seven studies on effectiveness were found: Three studies examined lidocaine ointment and four examined EMLA cream. Effectiveness of lidocaine ointment was questionable in two studies and negative in one. Effectiveness of EMLA cream was positive in two studies and negative in the other two. Four studies were found on safety of EMLA cream. All studies indicated that use of EMLA cream was safe.

DISCUSSION

The poor effectiveness found in the reviewed studies is possibly due to too long an application time, a lipophilic carrier used and difficulties in assessing pain. The time of application is often based upon studies in children. Since the skin of neonates acts more as a mucosa than as mature skin the local anesthetics are able to cross this barrier more rapidly. Also a high bloodflow in the heel enhances the uptake of the drug. The application time in neonates should therefore be reduced compared to children. The use of a lipophilic carrier should be avoided since a lipophilic carrier impedes the local anesthetic to be absorbed, leading to reduced effect. Various methods of pain assessment were being used. Since not all methods used are validated it is difficult to obtain an objective end point.

CONCLUSION AND RECOMMENDATION

The articles reviewed are non conclusive in their results of effective analgesia. Due to a lipophilic base form and a hydrophilic matrix EMLA cream is most effective. An application time of 30 minutes is recommended. In spite of the present precautions due to fear of methemoglobinemia, use of EMLA cream proved to be safe when used once a day. Since the clinical situation often requires more than one application a day, more research is needed to establish a safe and effective local anesthetic which can be applied topically several times a day in the neonate.

When patients become cyanotic: acquired methemoglobinemia

BACKGROUND

The authors conducted literature review to create a heightened awareness of the potential for developing toxic methemoglobinemia from local anesthetics. Methemoglobin normally is present in the blood at levels less than 1 percent. Levels may become toxic as hemoglobin is oxidized to methemoglobin after local anesthetics such as benzocaine and prilocaine are administered.

TYPES OF STUDIES REVIEWED

The authors searched the medical and pharmaceutical industry literature. They found and reviewed case studies of incidences of methemoglobinemia that resulted from local anesthetic overdoses.

RESULTS

Cases of local anesthetic-induced methemoglobinemia in dental practice are under-recognized and rare. Reported cases of prilocaine-induced methemoglobinemia have resulted in recent changes in some prilocaine literature. These changes include maximum recommended doses for patients of various weights.

CLINICAL IMPLICATIONS

Dentists should identify patients who are at increased risk of developing methemoglobinemia before administering local anesthetics. They also should follow new recommended dosing guidelines for prilocaine and be aware of symptoms of this adverse reaction.

Demineralization of resected root-ends with methylene blue dye

OBJECTIVES

This study evaluated the ability of methylene blue solutions of different concentration, pH, and time exposure to remove the smear layer from resected root-ends.

STUDY DESIGN

Resected root-ends were treated with either 2% methylene blue dye for intervals of 5 to 11 minutes or 1% methylene blue for 7 to 9 minutes and examined with a scanning electron microscope for smear layer removal. Two minute applications of saline solution and 50% citric acid served as controls.

RESULTS

All methylene blue solutions were found to be ineffective in removing the smear layer at all time intervals tested. An experimental solution of 1% methylene blue in 50% citric acid was found to predictably remove the smear layer during a 2 minute application and retained all the favorable staining characteristics of the dye. Fifty percent citric acid solutions applied for 3 minutes appeared to overdemineralize the root-end and gave poorer results than 2 minute applications.

CONCLUSIONS

Smear layer removal was pH dependent. Methylene blue solutions are clinically unsuitable for smear layer removal.

Toxic methemoglobinemia caused by topical anesthetic given before transesophageal echocardiography

Transesophageal echocardiography was performed on a patient with critical aortic stenosis and severe three-vessel coronary artery disease. Immediately after the procedure the patient experienced marked cyanosis (oxygen saturation of 53%) secondary to methemoglobinemia (methemoglobin saturation of 45%). Toxic methemoglobinemia was thought to be caused by topical anesthetic. He responded dramatically to treatment with intravenous methylene blue. Toxic methemoglobinemia should be suspected in unexplained cyanosis occurring after transesophageal echocardiography and other endoscopic procedures during which potentially causative agents have been used.

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.

Methemoglobinemia

Oxygen transport, the major function of hemoglobin, is dependent upon reduced heme iron. In the red cell, the heme iron is maintained in the reduced form by the methemoglobin reduction system. When the balance between oxidation and reduction of heme iron is perturbed due to the presence of excessive oxidants, decreased reducing capacity or the presence of abnormal hemoglobin, methemoglobinemia ensues. In most cases methemoglobinemia is transitory and of no major clinical consequence. Occasionally, however, it can be life threatening and must be rapidly diagnosed and treated. When methemoglobinemia is of hereditary nature, either due to deficiency of red cell NADH-methemoglobin reductase or due to the presence of M hemoglobin, it is a lifelong problem. Since most of these patients do not have major disabling symptoms, the treatment is aimed at correction of cyanosis.