The distribution of symptoms in patients receiving 5% lidocaine is shown in Figure 1; in 98% of the cases, the symptoms were bilateral. None of the patients had sensory-motor deficits, bowel or bladder dysfunction, or abnormal muscle-tendon reflexes. Only one patient receiving 0.5% bupivacaine had transient neurologic symptoms--hypesthesia of the lateral aspect of the right foot.
The relevant aspects of the surgical and anesthetic procedures are provided in Table 3 and Table 4. Mean duration of surgery was significantly shorter in patients receiving lidocaine (16 min) than in those receiving bupivacaine (53 min). All patients receiving lidocaine underwent surgery in the lithotomy position, whereas only 62% of patients receiving bupivacaine were placed in this position. There were no significant differences between groups in the incidence of technical problems during subarachnoid puncture Table 3. There were no differences between groups in terms of the type of needles used or the level or approach for spinal puncture Table 4. Similarly, extension of block and maximal perioperative decline in MAP did not differ between groups Table 3. In patients receiving lidocaine, characteristics of the surgical and anesthetic procedures did not differ between patients with or without neurologic symptoms Table 5.
Lidocaine has been used for more than 40 yr for spinal anesthesia and has a remarkable safety record [4-6]. Although there has been several recent reports of severe neurologic sequelae after the use of 5% lidocaine for continuous spinal anesthesia [7-9], all were associated with the administration of a dose greater than that normally used for single-injection spinal anesthesia. The results of the present study suggest that the administration of a single subarachnoid injection of 5% lidocaine may be associated with less severe, but far more common, neurologic complications.
In the present study, we found a 37% incidence of transient neurologic symptoms after a subarachnoid injection of 5% lidocaine, whereas only one patient receiving 0.5% bupivacaine had transient numbness and hypesthesia along the lateral aspect of the right foot without dysesthesias or motor dysfunction Table 2. In this patient, symptoms occurred after surgery for vaginal hysterectomy lasting more than 200 min during which the patient's legs were held in lithotomy position by ankle straps. The consultant neurologist thought that this complication likely resulted from patient positioning.
One explanation for the high incidence of neurologic symptoms being previously unrecognized may be the transient nature of this complication. In fact, we became aware of this problem only after instituting a departmental quality assurance program that includes patient followup by specialized nurses. Of note, in 1985, Flaatten and Raeder  reported a similar incidence of symptoms in patients undergoing vasectomy under spinal anesthesia: 15 of 51 patients (29.4%) complained of backache radiating to a lower extremity; in 48 of the 51 cases, 5% lidocaine was administered and, in the remaining three patients, tetracaine was used. Unfortunately, the authors do not indicate whether any of the 15 patients with radiating pain had received tetracaine.
In the present study, neurologic symptoms occurred only in patients who had received 5% lidocaine, except for one patient (described above) given bupivacaine. That this phenomenon was a specific effect is suggested by the similar incidence among groups in reported pain at the site of injection Table 2. The incidences of technical problems, bleeding, and paresthesia were similar in both anesthetic groups Table 3, suggesting that direct trauma to the spinal nerves cannot explain the difference in the incidence of symptoms. Furthermore, nerves of the cauda equina are free-lying and thus rarely damaged by needles. Although nerve roots may be damaged in the intervertebral foramens where they are relatively fixed , such injury would occur as a result of lateral placement of the needle and would not be expected to cause bilateral symptoms.
Spinal cord ischemia seems an unlikely etiology, since reductions in MAP were unremarkable and did not differ among groups Table 3. Duration of surgery or patient positioning also do not appear to explain the difference in incidence of neurologic symptoms because complications are more likely to occur with longer procedures, and similar complaints were not observed in bupivacaine-treated patients operated in lithotomy position. The equivalence of block extension in all groups suggests that anesthetic distribution was not an important factor Table 3. Other causes of neural injury, such as infection or subarachnoid or epidural hemorrhage, are extremely unlikely given the rarity of these serious complications, the absence of associated symptoms in the present study, and the benign clinical course.
Although our patients developed symptoms suggestive of radicular origin, the complete absence of sensory-motor deficits or muscle-tendon reflex abnormalities precludes the conclusion that symptoms are due to acute radicular irritation. Acute low back pain or pain radiating to the buttocks or legs may also be the consequence of acute or chronic disease affecting a motion segment of the lumbosacral spine (referred pain) . Injections of 11% saline into the intervertebral disks or the facet joints of the lumbosacral spine have been shown to produce not only local pain but, in some cases, pain radiating to the extremities similar to nerve root irritation. Yet, injections into other structures of the motion segment tended to produce only localized back pain . However, referred pain as a result of a facet syndrome or other conditions affecting the motion segments tend to be chronic or to recur . As patients with a history of backache were excluded from our study, chronic diseases of the lumbovertebral spine or systemic disorders causing radicular type symptoms seem unlikely to be etiologies or to have contributed to these symptoms [12,15].
Our study has several limitations. First, the study was not randomized and the anesthetic technique, surgical procedure, and intraoperative management varied. Therefore, methodologic bias cannot be ruled out. Second, the anesthesiologist in charge of the anesthetic procedure was not blinded. However, both the patient and the investigator were unaware of the details of the anesthetic procedure or the LA administered. Thus, although this is not a doubleblind study in the usual sense, an investigator's bias is unlikely to have affected our results. Third, we used only a single formulation of lidocaine, a 5% solution containing glucose, and administered a relatively uniform dose. Fourth, based on relative potency, lidocaine was administered at a higher dose than bupivacaine, and the glucose content and the tonicity of the LA solutions differed . Therefore, although we found a difference in the incidence of transient neurologic symptoms with the solutions of lidocaine and bupivacaine administered in the present study, the role of the anesthetic concentration and dose, the tonicity of the solution, the presence of glucose, and, finally, the anesthetic drug per se, remain to be defined. Available data from animal studies suggest that local anesthetic neurotoxicity is, at least in part, concentration-dependent [17-21] and that the neurotoxic potential of lidocaine might exceed that of bupivacaine [17,18,22]. In contrast, experimental data suggest that 7.5% glucose does not contribute to neurotoxicity of 5% lidocaine [18,23]. Randomized studies are warranted to further define the etiology of transient neurologic symptoms and the factors that affect its occurrence.
The authors thank Dr. Kenneth Drasner for many helpful discussions and Joan Etlinger for excellent editorial advice.
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© 1995 International Anesthesia Research Society
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