P045: PRONE TO TROUBLE: METHEMOGLOBINEMIA IN THE CT SCANNER
Ryan Stalder, MD1; Kevin Bennett, MD1; Merlin Perez Navarro, BS2; Douglas Rausch, DO1
1Memorial Healthcare System; 2Florida International University College of Medicine
Introduction: Methemoglobinemia is a rare condition (0.035% of patients undergoing procedure1) in which hemoglobin’s heme iron is oxidized from its ferrous (Fe2+) to ferric (Fe3+) state. The etiology of methemoglobinemia includes both genetic and acquired causes. Common acquired causes include topical anesthetics (benzocaine, lidocaine, and prilocaine), dapsone, antimalarial agents (chloroquine and primaquine), inhaled nitrous oxide, rasburicase, and nitrates. Methemoglobinemia can be fatal if not treated promptly, with mortality rates reported as high as 10% in certain clinical contexts. Here we describe the diagnosis and management of benzocaine-induced methemoglobinemia during CT-guided abscess drainage in the prone position.
Case Report: A 52-year-old female was scheduled for CT-guided drainage of pelvic abscess under general anesthesia in the prone position. Past medical history was significant for subsegmental pulmonary embolism, anemia (Hgb 8.6), and anastomotic leak following robotic hysterectomy complicated by extensive adhesions and enterotomy requiring small bowel resection. Due to a non-reassuring airway (Mallampati III with short thyromental distance), a decision was made to proceed with awake flexible fiberoptic intubation. Following topicalization with 20% benzocaine spray, the airway was secured, and general anesthesia was induced. During the procedure, the patient became cyanotic and her pulse oximetry reading decreased from 100% to 86%. The patient was placed on 100% FiO2 and the case was quickly completed. Due to suspicion of methemoglobinemia an arterial blood gas sample (ABG) was drawn for co-oximetry. Arterial blood was chocolate brown in color and showed a MetHb level > 30%. Methylene blue (100 mg IV) was slowly administered and the oxygen saturation progressively increased to the mid-90s over the course of the next hour. The patient was admitted to the ICU for further monitoring where her condition continued to improve. She was eventually discharged home on post-op day 24.
Discussion: While commonly featured on exams, benzocaine-induced methemoglobinemia occurs in only 0.067% cases2. Studies show that patients who develop methemoglobinemia are more likely to be inpatient, anemic, and showing signs of active systemic infection2, similar to our patient. There is also an increased risk for methemoglobinemia following topicalization for bronchoscopy (0.160%), EGD (0.005%), and ERCP (0.030%)1.
This case occurred in a non-OR location with the patient in prone position with arms tucked, making it very difficult to obtain an ABG. Fortunately, the procedure was completed quickly and our team was able to rapidly obtain an ABG with co-oximetry to confirm diagnosis.
Sources:
- 1. Chowdhary S, Bukoye B, Bhansali AM, Carbo AR, Adra M, Barnett S, Aronson MD, Leffler DA. Risk of topical anesthetic-induced methemoglobinemia: a 10-year retrospective case-control study. JAMA Intern Med. 2013 May 13;173(9):771-6. doi:10.1001/jamainternmed.2013.75. PMID: 23546303.
- 2. Kane GC, Hoehn SM, Behrenbeck TR, Mulvagh SL. Benzocaine-induced methemoglobinemia based on the Mayo Clinic experience from 28 478 transesophageal echocardiograms: incidence, outcomes, and predisposing factors. Arch Intern Med. 2007 Oct 8;167(18):1977-82. doi: 10.1001/archinte.167.18.1977. PMID: 17923598.