Intrathecal Hyperbaric 0.5% Tetracaine as a Possible Cause of Transient Neurologic Toxicity

Recent reports of minor neurologic sequelae after spinal anesthesia have all been associated with the use of lidocaine [1-5]. Recently, we became aware of a case in which similar symptoms may have resulted from subarachnoid administration of 0.5% tetracaine in 7.5% glucose. The patient developed transient bilateral buttock and leg pain after uneventful spinal anesthesia. Case Report A 53-yr-old, 59-kg woman was scheduled for removal of a lipoma in the right thigh. Physical examination and laboratory studies were unremarkable. Her medical history included mild osteoarthrosis of the right knee. With the patient in the right lateral decubitus position, the lumbar area was cleansed with an iodine-containing solution and wiped dry; then, approximately 2 mL of a 1% lidocaine solution was infiltrated at the L2-3 level. Using sterile technique, a 25-gauge Quincke needle was introduced into the subarachnoid space at the first attempt without difficulty. After aspiration of approximately 0.2 mL of clear cerebrospinal fluid, 2 mL of 0.5% tetracaine in 7.5% glucose with 1 mg of phenylephrine was injected over approximately 30 s. No paresthesias were elicited during needle insertion or anesthetic administration. The patient was kept in the right lateral decubitus position for 10 min and then turned to the left lateral decubitus position for the duration of the case. Adequate anesthesia was obtained with an upper sensory level of T-8 bilaterally 20 min after the injection. The surgical procedure was uneventful and lasted 1 h and 20 min. Hemodynamic values remained stable throughout the intraoperative period. The immediate postoperative course was uneventful. Twenty hours postoperatively, after complete recovery from the anesthetic, a moderately dull pain developed in the buttocks radiating to the dorsolateral sides of both thighs and calves. Neurologic examination 4 h later revealed no sensory-motor or muscle-tendon reflex abnormalities. Lasegue's test, in which attempted passive flexion of the fully extended leg and thigh at the hip caused stretching of the sciatic nerve, was negative. There were no signs of bladder or bowel dysfunction. A diclofenac sodium suppository was administered 25 to 50 mg/d for the next 3 days. The painful sensations in the buttocks and legs resolved completely 3 and 7 days, respectively, after the operation. Discussion In the present case, transient pain in the buttocks and legs was experienced after spinal anesthesia with hyperbaric 0.5% tetracaine containing phenylephrine. The clinical course of the present case is remarkably similar to that of previous cases of transient radicular irritation (TRI) after intrathecal administration of lidocaine [1-5]. This is the first report of TRI after an intrathecal anesthetic other than lidocaine. Since Schneider et al. [1] reported four cases of TRI after intrathecal administration of 5% lidocaine in 7.5% dextrose, several subsequent reports [2-5] and the results from prospective studies [6-8] have provided evidence for an association between the administration of a single injection of lidocaine and transient neurologic dysfunction. One common feature of all these cases and the findings of the studies was moderate-to-severe pain in the buttock, lower back, and/or legs that appeared 1-24 h postoperatively after complete recovery from uneventful spinal anesthesia. The pain was often characterized as dull, aching, cramping, sharp, or radiating. Except for two patients who developed dysesthesia [1], neurological examinations were normal. In all cases, the symptoms resolved fully within one week. There are many potential causes of neurologic symptoms and/or pain after spinal anesthesia. However, the present case cannot be readily explained by trauma, spinal cord ischemia, infection, or chemical contamination. The similarity to the previous cases suggests that a direct neurotoxic effect of the anesthetic solution is more likely. Substantial evidence suggests that all local anesthetics are potentially neurotoxic. For example, in rats, intrathecal administration of lidocaine or bupivacaine may produce both sensory impairment and histological damage to the spinal nerve roots [9]. Extrafascicular administration of 1% tetracaine can produce severe injury to rat sciatic nerves [10]. Local anesthetic-induced injury has been shown to be, to some extent, concentration dependent [11,12]. Clinically, major or minor neurologic injury after intended epidural [13,14] or intrathecal 2% lidocaine [2], respectively, has been reported. In view of the potency ratio of tetracaine to lidocaine [approximately 4 to 1 [15]], it is likely that 0.5% tetracaine might have effects on neural structures similar to those of lidocaine. Indeed, one of the four cases of cauda equina syndrome after continuous spinal anesthesia followed the administration of a solution containing 0.5% tetracaine [16]. Most of the reported cases of TRI (including the present case) have been associated with the administration of an anesthetic solution with a relatively high concentration of glucose. Thus, it is possible that glucose might induce or contribute to the neurological symptoms. However, if minor neurologic symptoms and major neurologic injury [13,14,16] represent different points on a continuum of toxicity, glucose is unlikely to play a role--animal experiments demonstrate that adding 7.5% glucose does not alter sensory impairment induced by intrathecally administered 5% lidocaine [17]. Phenylephrine was used in the present case to reduce systemic uptake and thus extend the effective duration of anesthesia. Administration of an adjuvant vasopressor to local anesthetics is thought to decrease peripheral nerve blood flow significantly during regional anesthesia [18]. Selander et al. [19] have shown that the addition of epinephrine to local anesthetics increases nerve damage caused by direct intrafascicular injection of local anesthetics. Therefore, it is possible that phenylephrine increased the effect of 0.5% tetracaine solution and that an anesthetic solution without a vasopressor may not have caused symptoms. It is worthy to note that the present case was performed in the lateral position. There has been concern that surgical positioning might play an important role in the development of TRI, since most of the previously reported cases were performed in the lithotomy position. The results of a prospective study performed by Pollock et al. [8] showed that there was a significant difference in the incidence of TRI between patients having surgery in the lithotomy position and those having surgery in the supine position. It has been postulated that stretching of the cauda equina in the lithotomy position can increase the vulnerability of the nerve fibers within these roots to the effects of local anesthetics [1]. In contrast, it seems unlikely that the lateral position was a contributary factor in the symptoms. In summary, we describe a case of transient radicular pain after subarachnoid administration of hyperbaric 0.5% tetracaine with phenylephrine. The clinical course of our patient was similar to previously reported cases after administration of lidocaine and suggests that TRI is not restricted to the use of a single local anesthetic. The authors thank Dr. Kenneth Drasner for critical review of the manuscript.