Transient Radicular Irritation After Spinal Anesthesia with Hyperbaric 4% Mepivacaine

Transient radicular irritation (TRI), defined as pain in the buttocks, posterior thigh, or legs has been reported after spinal anesthesia with the use of hyperbaric 5% lidocaine [1-3] and, rarely, with bupivacaine [4] and tetracaine [5]. Hyperbaric 4% mepivacaine has been used for spinal anesthesia for many years [6], especially in Europe [7], and has so far not been implicated clinically in causing TRI. We present two cases of TRI symptoms after spinal anesthesia with 4% hyperbaric mepivacaine. Case Reports Case 1 A 28-yr-old, 65-kg woman was scheduled for cervical dilatation and curettage for fetal demise in the eighth week of pregnancy. After skin preparation with povidone iodine 10%, an atraumatic spinal anesthetic was performed with a 27-gauge Whitacre needle (midline approach, sitting, L3-4). After free flow of cerebrospinal fluid was observed, 70 mg of 4% mepivacaine in 9.5% glucose (Astra Chemicals, Wedel, Germany) was injected. No pain, paresthesia, or bleeding was noted. The patient was placed in the lithotomy position for the procedure, which was uneventful and lasted 15 min. Adequate anesthesia was achieved with an upper sensory level of T7. Three hours after the anesthetic, the patient complained of an aching pain radiating from the buttocks to the posterior thighs. The pain was described as moderately severe, persisted for 12 h, and required treatment with diclofenac. No other neurological symptoms or signs were noted. Case 2 A 51-yr-old, 61-kg woman was scheduled for cervical dilatation and diagnostic curettage for postmenopausal bleeding. Her medical history included a hiatal hernia and occasional palpitations. Spinal anesthesia was performed at the L3-4 interspace with 70 mg 4% mepivacaine in glucose 9.5% using a 27-gauge Whitacre needle. An upper sensory level of T9 was achieved, and the procedure proceeded uneventfully in the lithotomy position. Four hours postoperatively, the patient complained of severe aching pains in the lower back radiating along the posterior aspect of both thighs and calves. An anesthesiologist was summoned because the patient could not lie or sit comfortably. No neurological abnormalities were found on examination. The pain improved after medication with acetaminophen, and the patient was pain-free after 24 h. Discussion There are many reports in the literature of TRI occurring with 5% hyperbaric lidocaine [1-3,8], but this is the first report of TRI after spinal anesthesia with 4% hyperbaric mepivacaine. In animal experiments, a link has been postulated between local anesthetic-induced injury and increasing concentration and dose of lidocaine [9,10]. In the clinical setting, a reduction in lidocaine concentration from 5% to 2% did not prevent TRI [8]. Furthermore, high concentrations of local anesthetics, when injected slowly, were not distributed homogenously in a laboratory spinal model [3]. We assume that these complications, with their potential for neurotoxicity, are also true for mepivacaine, as its anesthetic profile resembles that of lidocaine [11]. The initial clinical course of our patients was similar to those in other reports after intrathecal (IT) administration of 5% lidocaine. Common features include moderate to severe pain in the lower back, buttocks, and posterior thigh, which appear 1-24 hours postinjection after complete recovery from spinal anesthesia, normal neurologic examination, and full resolution of symptoms within one week [5]. However, our patients showed a more rapid resolution of symptoms than those found in reports with lidocaine and tetracaine [1,2,4,5]. Many needle types and sizes have been implicated in causing TRI [12]; however, some authors consider the pencil-point needle design to be a risk factor for TRI [13]. Nonhomogenous IT anesthetic spread, facilitated by slow injection and possible directional spread, may indeed unmask the inherent neurotoxic potential of hyperbaric 5% lidocaine, especially when high concentrations occur in the caudal region [3]. Hyperosmolarity, on the one hand, and adding epinephrine, on the other, were not found to contribute to TRI after spinal anesthesia with hyperbaric 5% lidocaine [2,8]. The lithotomy position may contribute to TRI by stretching the cauda equina and sciatic nerve and by exposing the sacral fibers to the highest local anesthetic concentrations [1], a theory that has been supported in a recent clinical study by Pollock et al. [8]. Although there is renewed interest in the use of spinal mepivacaine as an alternative to bupivacaine and lidocaine [14], our observations suggest that a concentration of 4% hyperbaric mepivacaine, as supplied by manufacturers for IT administration, exceeds that required for adequate blockade [15] and may be associated with neural symptoms. As TRI has been described after spinal anesthesia with 2% isobaric lidocaine [8], this may also be a possibility with 2% isobaric mepivacaine, because of its similar pharmacological and chemical profile. Further study is required to define the optimal concentration and dose of mepivacaine, as well as the incidence of TRI, and to identify other potential risk factors for its use in spinal anesthesia.