An Unusual Presentation of Metallic Taste after Lidocaine Injections (1999)

Regional anesthesia may have advantages for surgery when the surgical field is small and the innervation of the area is readily accessible. One complication, however, is intravascular injection of local anesthetic. Thus, when regional anesthesia is performed, the practitioner often asks the patient about any symptoms that might identify the early accidental injection of intravascular local anesthetic. Common, but nonspecific symptoms are vertigo, light-headedness, circumoral numbness, or a metallic taste. We report here an unusual presentation of metallic taste after local anesthetic injection. Case History The patient was a 73-yr-old, 101-kg-female, who presented for left cataract extraction and intraoccular lens implantation. She had a medical history of coronary artery disease, peripheral vascular disease, hypertension, and type 2 diabetes mellitus. Medications at the time of surgery were glyburide, clonidine, and lovastatin. Her electrocardiogram showed nonspecific changes and an old inferior infarction. Serum electrolytes were within normal limits, and her fasting blood glucose concentration was 180 mg/dL. After informed consent, routine monitors were applied, as was a nasal canula supplying oxygen at 4 L/min. The patient was sedated with 100 μg of fentanyl and 50 mg of propofol. After sedation, the patient was unconscious, but breathing spontaneously with an oxygen saturation greater than 95%. A Nadbath Rehman block was then performed behind the insertion of the left pinna (1). A 1.5-cm, 25-gauge needle was placed in the space between the mastoid bone and the condyle of the mandible. The length of the needle was advanced in the direction of the pititary gland and 3 mL of local anesthetic (2% lidocaine, .375% bupivacaine) was injected. This was followed by a left retrobulbar block. In this procedure, a 23-gauge, 4-cm needle was inserted at the inferolateral border of the orbit. The needle was advanced parallel to the floor of the orbit, past the equator of the globe, and then directed behind the globe into the space surrounding the optic nerve. Five millileters of local anesthetic (2% lidocaine, 0.375% bupivaccine) was injected. The heart rate and arterial blood pressure were within normal limits and unchanged throughout the procedure. Her respiratory rate decreased from 18 to 12 breaths/min during the period that she was unconscious. Several minutes after the block was performed, the patient was awake and alert. Examination at that time showed a motor block of the left seventh nerve as well as block of cranial nerves II, III, and VI. The patient complained of an unusual taste in her mouth. On further questioning, she said it felt like she had bitten or chewed a piece of tin foil. She denied vertigo, light-headedness, or circumoral numbness. The patient was monitored an additional 10 min. As there was no change in her status, surgery commenced. At the end of surgery, 11/2 h later, the patient still complained of a metallic taste. Examination showed that cranial nerves II, III, VI, and the motor branch of VII were still anesthetized. At that time, it occurred to the author that the patient might have anesthesia of the sensory branch of cranial nerve VII (the corda tympani). The patient was tested with salt and sugar solutions on the anterior surface of the left side of her tongue. She was unable to identify either of these substances; however, she could identify both salt and sugar solutions on the anterior surface of her right tongue. The patient was discharged to home 1 h later. On follow-up the next day, her taste had returned to normal. Discussion Dysgeusia is a distortion in taste perception. Patients who complain of dysgeusia usually report a salty, bitter, rancid, or occasionally metallic taste. Frequent causes of dysgeusia are pharmaceutical agents, damage to the taste or olfactory pathways, dehydration, or intracranial lesions. The afferent taste pathway travels through several cranial nerves. The soft palate supplies taste via the superficial petrosal nerve (cranial VII). Innervation of the anterior two-thirds of the tongue travels first through the lingual nerve, then the chorda tympani, and then joins the seventh nerve. The posterior two-thirds of the tongue is via cranial nerve IX, and then to the pharynx, epiglottis, and upper esophagous are via cranial nerve X (2). In this case, the patient had a Nadbath block behind the left pinna. Normally, this anesthetizes the motor branches of cranial nerve VII where they exit the stylomastoid foramen. Taste to the anterior part of the tongue begins in the lingual nerve. It then joins the chorda tympani medial to the condyle of the mandible and then joins the seventh nerve in the mastoid bone proximal to the stylomastoid foramen (Figure 1). It is possible that the Nadbath injection dissected proximally along the path of the motor seventh nerve and anesthetized the chorda tympani at the level of the middle ear. Another possibility is that the Nadbath block was performed more distally so that the chorda tympani was anesthetized in the soft tissue before it joined the lingual nerve. In either case, the Nadbath block resulted in a sensory block of the anterior left tongue. The patient perceived this as a metallic taste until the block wore off. This case illustrates an unusual presentation of metallic taste after local anesthetic injection.Figure 1: Skull with chorda tympani nerve.