Respiratory Depression and Difficult Ventilation After Inadvertent Epidural Administration of Remifentanil

Abstract

To the Editor: An otherwise healthy 60-year-old man weighing 61 kg was scheduled for elective cholecystectomy under epidural anesthesia. A T8–T9 epidural catheter was placed and 5 mL of a local anesthetic mixture was given via the catheter. The local anesthetic mixture (30 mL) was intended to contain 50 mg tetracaine (lyophilized powder), 1% lidocaine, and epinephrine 1:200,000. However, 1 mg remifentanil was mistakenly substituted for 50 mg tetracaine in the mixture. Two additional 6-mL doses of the mixture were given epidurally at 5-min interval. The patient reported slight light-headedness after the first dose. His hemoglobin oxygen saturation (SPo2) decreased to 36% and the patient became unconscious while developing rigidity of the chest and abdominal muscles after the third dose. Mask ventilation was initiated, but was difficult, and the SPo2 increased to 76%. The patient received IV propofol 100 mg and vecuronium 8 mg and the SPo2 increased to 100% with mask ventilation. The trachea was intubated and surgery was performed under general anesthesia. There were no neurological sequelae after the surgery. Our patient received 567 μg remifentanil epidurally via three injections over 10 min. The recommended IV bolus dose of remifentanil during general anesthesia is 1 μg/kg. (1) Although 167 μg remifentanil given in the first dose to this patient was much larger than the recommended IV dose of 61 μg, muscle rigidity, respiratory depression, and change of consciousness did not occur. The absence of these signs may have been due to a delay caused by diffusion of remifentanil from the epidural space into the systemic circulation, and its rapid metabolism by nonspecific esterases (1,2). The remifentanil formulation contains 15 mg glycine per 1 mg remifentanil powder and our patient received 8.5 mg glycine epidurally. Intrathecal administration of glycine in dogs caused hindlimb twitching, pain, and convulsions (1). Intrathecal infusion of glycine alone or as part of the remifentanil formulation resulted in dose-dependent, but reversible, motor impairment in rats (3). The ED50 for this effect was 6.5 μg glycine/min over 90 min (3). The lack of neurological deficits in our patient may have been due to the different routes (epidural versus intrathecal) of injection. Xuebing Xu, MD Shouzhang She, MD Departments of Anesthesiology the First People's Hospital of Guangzhou Guangzhou, China Shanglong Yao, MD Departments of Anesthesiology Union Hospital of Tongji Medical College Wuhan, China Martin Mok, MD Departments of Anesthesiology Taipei Medical University Taipei, Taiwan Zhiyi Zuo, MD, PhD Departments of Anesthesiology University of Virginia Charlottesville, VA [email protected]