Supplemental peripheral nerve blocks are not commonly performed in adults because of concerns of cumulative exposure of the nerve to the local anesthetic as well as increased ischemia from epinephrine. The purpose of this study was to compare the incidence of postoperative neurologic symptoms after a failed subgluteal sciatic nerve block and a supplemental popliteal sciatic nerve block.
Five hundred twelve adult patients undergoing ambulatory surgery were prospectively studied (1 yr). Sciatic nerve blocks were performed using levobupivacaine 0.625% with epinephrine 1:200,000 (0.5 ml/kg). Patients who failed to achieve sensory and motor anesthesia at 30-60 min were given a popliteal sciatic nerve block (lidocaine 2% 10 ml + levobupivacaine 0.5% 10 ml). Subjects were contacted at 24 h to 48 h, 2 weeks, and 1 month. Symptomatic patients were contacted biweekly and reevaluated during follow-up surgeon visits until symptom resolution.
Four hundred thirty-nine subjects were analyzed. Fifty-six received a popliteal sciatic nerve block. Four subjects (0.9%) had self-reported neurologic symptoms in the distribution of the sciatic nerve. Investigator-initiated follow-up revealed 33 subjects (8.7%) who received a single subgluteal sciatic block and 4 subjects (7.1%) after a supplemental sciatic nerve block with neurologic symptoms (P = 0.80). The median duration of symptoms was 4 weeks (95% CI 3-5) in the subgluteal and 4 weeks (95% CI 3-5) weeks in the popliteal group (P = 0.98). All symptoms resolved by 14 weeks postprocedure.
Blocking the sciatic nerve at a more distal site after a failed subgluteal sciatic nerve block does not appear to influence the incidence or duration of neurologic sequelae.
What We Already Know about This Topic
Supplementation of incomplete peripheral nerve block with additional injection of local anesthetic at another site could theoretically increase the risk of neural toxicity
What This Article Tells Us That Is New
In more than 400 subjects receiving sciatic nerve block, there was no difference in the incidence of neurologic symptoms in those who did or did not receive supplemental popliteal block for incomplete anesthesia
NERVE injury is an infrequent but serious complication of peripheral nerve blocks. Although severe deficits persisting longer than 4 weeks have been reported to occur at a rate of 0.4%, transient postoperative neurologic symptoms have been reported to occur at rates from 0 to 15%.1The actual rate of transient neurologic symptoms may be an underestimation because patients are not routinely evaluated for symptoms.1,–,3
Failed or incomplete sciatic nerve blockade has been reported to occur at a frequency of approximately 7%.4Routine use of supplemental peripheral nerve blocks is uncommon in adults because of concerns of cumulative exposure of the nerve to the local anesthetic as well as increased ischemia from epinephrine.5In addition to the effects of the anesthetics and adjuncts, additional procedures in a patient with proximal injury may increase the potential for transient or permanent nerve injury at a distal site.6The increased susceptibility for nerve injury at the distal site may be the result of previous disruption of axonal flow proximally. Conversely, conversion of the proposed anesthesia plan may decrease the benefits of a regional anesthetic as well as patient satisfaction.
The purpose of this study was to compare the incidence of postoperative symptoms of neurologic injury after a failed subgluteal sciatic nerve block and a supplemental popliteal sciatic nerve block. We hypothesized that the incidence of postoperative neurologic symptoms at 1 month would not be different in patients who received a supplemental popliteal sciatic nerve block compared with a single subgluteal sciatic nerve block.
Materials and Methods
The study was approved by the Northwestern University Institutional Review Board, Chicago, Illinois. Five hundred twelve adult patients undergoing foot and ankle surgery provided written informed consent and were prospectively studied over a 1-yr period. Patients were excluded if they had a history of hemostatic abnormalities, chronic pain syndrome, a foot deformity restricting normal foot movement, severe liver or renal disease, or a preexisting neurologic disorder.
Sciatic nerve blocks were performed a minimum of 60 min before the start of surgery. Blocks were performed at the subgluteal level by resident trainees supervised by faculty using the infragluteal-parabiceps approach.7The block was performed using a 100-mm, 21-gauge insulated needle (Stimuplex®, B-Braun/McGaw Medical, Bethlehem, PA) connected to the negative lead of a constant current nerve stimulator (Stimuplex® HNS-11, B-Braun/McGaw Medical). Stimulation frequency was 2 Hz, pulse width was 100 ms, and the initial current was set to deliver 1.0 mA. The needle was advanced until an elicited motor response was obtained between 0.2–0.4 mA. Needle adjustment was made to elicit a motor response of plantar flexion or inversion. If an elicited motor response of plantar flexion or inversion could not be obtained, a dorsiflexion response was accepted. Levobupivacaine 0.625% (Chirocaine®, Purdue Pharma, Stamford, CT) with epinephrine 1:200,000 was then injected incrementally in 3-ml aliquots to a total volume of 0.4 ml/kg (minimum, 20 ml; maximum, 35 ml).
Sensory and motor assessments were initiated by an investigator not involved in the clinical care (MCK) of the patient every 2 min for 10 min, and at 5-min intervals until 30 min had elapsed. Complete sensory block was defined as anesthesia (i.e. , pin prick not felt) in the distribution of the sural, tibial, deep, and superficial peroneal nerves. A complete motor block was defined as an inability to move the ankle or toes. A partial sensory block was defined as analgesia (i.e. , pinprick felt dull). A successful block was defined as a complete sensory and motor block at 30 min in the distribution of the terminal components of the sciatic nerve after local anesthetic injection.
Patients who did not demonstrate onset of sensory block in the tibial or common peroneal nerve distributions at the 30-min assessment were given the option of receiving a supplemental popliteal sciatic nerve block or general anesthesia. Patients who demonstrated a partial sensory block were assessed for an additional 30 min. If a complete sensory block did not develop by this time, the aforementioned anesthetic management options were offered. The supplemental popliteal sciatic nerve block was performed by the attending anesthesiologist using an intertendinous approach with a 100-mm, 21-gauge insulated needle.8The supplemental block was limited to one needle entry. The nerve stimulator settings and the accepted elicited motor response were the same as the initial procedure. A mixture of lidocaine 2% 10 ml + levobupivacaine 0.5% 10 ml with epinephrine 1:200,000 was then injected incrementally in 3-ml aliquots. In addition to the sciatic nerve block, patients received a saphenous nerve block (5 ml levobupivacaine 0.5%), or femoral nerve block (10 ml levobupivacaine 0.5%) when indicated for surgical anesthesia.
Subjects were instructed to contact the surgeon or the anesthesiologist if they were experiencing problems with respect to the anesthesia or surgery. In addition, all patients were contacted by telephone at 24 h to 48 h, 2 weeks, and 1 month after surgery and asked to answer questions regarding symptoms of residual anesthesia, dysesthesias, paresthesia, or motor weakness in the operated limb (appendix 1). Subjects were also questioned regarding pain control, satisfaction with anesthesia care, analgesic use, and side effects. Patients were reevaluated as previously discussed at follow-up visits with their surgeon (usually at 3 weeks, 6 weeks, 3 months, 6 months, and 12 months postoperatively). Physical examination of the patients was done for motor and sensory deficits after the removal of the cast (1–8 weeks). Sensory evaluations were made using 5.07/10 g Semmes-Weinstein monofilament (Touch-Test Sensory Evaluators; North Coast Medical, Morgan Hill, CA).
The primary outcome was the incidence of clinical symptoms describing sensory and motor sequelae in the distribution of the sciatic nerve innervating the surgical site at 2 weeks. Symptoms involving the saphenous nerve distribution were reported but were not considered as sciatic nerve-related postoperative neurologic symptoms. All patients with persistent postoperative neurologic symptoms that were not improving by the time follow-up phone calls or office visits were made were referred for a neurologic evaluation and diagnostic testing (e.g. , nerve conduction velocities, electromyography). Any patient who reported a postoperative neurologic symptom was contacted biweekly until resolution of symptoms. Secondary outcomes included the duration of postoperative neurologic symptoms between single-injection sciatic nerve block and supplemental sciatic nerve block groups, duration of sensory analgesia, distribution of the symptoms among the tibial, peroneal, and sural nerves, postoperative analgesic use, patient satisfaction, and side effects.
Prospective studies that have used investigator assessments at specific intervals have suggested an incidence rate of transient postoperative neurologic symptoms after peripheral nerve blocks between 10–15%.9,10Borgeat et al. found an incidence of postoperative neurologic symptoms of approximately 16% at 1 week after interscalene block.11However, the incidence of transient postoperative neurologic symptoms after a single-injection sciatic block has not been reported. We assumed that the incidence of transient postoperative neurologic symptoms after sciatic nerve block would be similar to that of other peripheral nerve techniques, and that the risk of postoperative neurologic symptoms with a supplemental popliteal sciatic nerve block would be doubled (increased by 15%). Assuming a 10% failure rate of sciatic nerve block for surgical anesthesia requiring supplementation, a sample size of 371 patients with single-injection sciatic nerve block and 41 with supplemental popliteal sciatic nerve block would be required to detect a difference of 16%versus 30% in the incidence of neurologic symptoms persistent at the median time using a two-sided log-rank test. This corresponds to a hazard ratio of 1.57 for the rescue popliteal block. Continuous data were analyzed using independent Student t test or Mann–Whitney U test and categoric data using the Fisher exact test. Estimates of exact P values were determined using a Monte Carlo method with 10,000 samples and confidence limits of 99%. Kaplan–Meier plots were constructed for duration of postoperative neurologic symptoms from the day of surgery until complete resolution. The log-rank test was used to compare duration of postoperative neurologic symptoms times between single-injection sciatic nerve block and supplemental popliteal sciatic nerve block groups. All reported P values are two-tailed. Statistical analysis was performed using PASS 2008 version 8.0.13, release date Jan 14, 2010 (PASS2008, NCSS, LLC; Kaysville, UT) and PASW Statistics 18.0.2, release date April 2, 2010 (SPSS Inc.; Chicago, IL).
Subject flow through the study is shown in figure 1. Five hundred twelve subjects consented for study participation. Forty-two subjects received peripheral nerve blocks at other sites (ankle block, initial popliteal block). Four hundred sixty-nine subjects received a single-injection subgluteal sciatic nerve block. Sixty-two subjects had partial sensory block, 5 received general anesthesia, and 57 received a supplemental popliteal sciatic nerve block. Thirty subjects were lost to follow-up: 27 single injection sciatic, 2 general anesthesia, and 1 supplemental popliteal sciatic nerve block. Four hundred thirty-nine subjects had complete follow-up and were included in the analysis.
There were no differences in patients' characteristics between single-injection subgluteal and supplemental popliteal sciatic nerve block groups (table 1). Block characteristics are shown in table 2. In addition to an increased volume of local anesthetic, subjects receiving a supplemental popliteal sciatic block had a greater total number of needle attempts and a shorter duration of nerve block analgesia.
Fourteen subjects (3%) had self-reported symptoms or concerns. Four subjects (0.9%) had self-reported symptoms that were consistent with a neurologic symptom in the distribution of the sciatic nerve. Two of the four subjects were from the single-injection group and two were from the supplemental sciatic nerve block group (P = 0.03). Follow-up evaluation identified postoperative neurologic symptoms in 37 subjects. There was no difference in the incidence after single-injection subgluteal sciatic (33, 8.7%) and supplemental popliteal sciatic nerve blocks (4, 7.1%), respectively (P = 0.80). Twenty-three subjects (21 after single-injection sciatic nerve blocks and 2 after a supplemental popliteal sciatic nerve block) reported postoperative neurologic symptoms at 2 weeks but not at the 48-h follow-up period. The median (95% CI) for the duration of symptoms was 4.0 weeks (range, 3.3–4.7 weeks) after single-injection sciatic nerve block compared with 4.0 weeks (range, 3.1–4.9 weeks) after supplemental sciatic nerve block group (P = 0.98) (fig. 2). No patient demonstrated persistent neurologic sequelae related to the initial complaint by 14 weeks after surgery.
Abnormal sensory physical examination findings in subjects who reported persistent complaints beyond 2 weeks are shown in table 3. All 10 subjects with abnormal sensory findings reported symptoms during follow-up phone interviews. All subjects who had an abnormal physical examination reported symptoms during telephone follow-up. Nine of the 10 subjects with clinical findings on physical examination received a single-injection subgluteal sciatic nerve block.
The distribution and type of postoperative neurologic symptoms are shown in table 4. All reported symptoms were in the distribution of the tibial and superficial peroneal nerves. The most common symptom was paresthesia in the distribution of the tibial nerve. Eleven subjects reported symptoms in more than one nerve distribution or more than one symptom. No subject reported more than two symptoms. There was no difference in the duration of symptoms among the nerve distributions (P = 0.93). There was no association between subject or block characteristics and the occurrence of postoperative neurologic symptoms (table 5). Subjects who reported postoperative neurologic symptoms had greater median postoperative opioid requirements.
The important finding of this study was that a supplemental popliteal sciatic nerve block performed after a partial or failed sciatic nerve block did not cause a statistically significant increase in the incidence or prolong the duration of postoperative neurologic symptoms in patients undergoing foot and ankle surgery in comparison with a single-injection subgluteal sciatic nerve block. This is the first study to evaluate nerve injury symptoms after repeat blockade along the same nerve compared with those reported with an initial successful nerve block. Despite the additional procedure, patient satisfaction with surgical anesthesia and postoperative pain control was similar to that of subjects who received a single-injection subgluteal sciatic nerve block. The number of patients with continuing symptoms decreased by approximately 50% every 2 weeks postoperatively. We found that a substantial number of the postoperative neurologic symptoms were not reported by the patient during the 48-h follow-up phone call. This may reflect delayed onset of symptoms, but more likely suggests that awareness of postoperative neurologic symptoms may be masked by confounding factors such as postoperative pain, analgesic use, immobility, casts, dressing, and bandaging in the early postoperative period.
Most of the available data on neurologic injury and postoperative neurologic symptoms occurring after peripheral nerve blocks are from studies of upper extremity rather than lower extremity procedures, and there are no reports on the incidence of postoperative neurologic symptoms after supplemental nerve blocks. Our data suggest that after a supplemental popliteal sciatic block, the incidence of postoperative neurologic symptoms is not substantially increased in accordance with other studies reporting on postoperative neurologic symptoms. In our series, all postoperative neurologic symptoms resolved with a median duration of 4 weeks, a finding similar to that of other studies on the duration of postoperative neurologic symptoms.
There are a limited number of prospective studies in the literature examining the risk of neurologic injury and symptoms after sciatic nerve blocks.12Auroy et al. reported the incidence of serious sciatic nerve injury to occur in approximately 5 in 10,000 cases using an anesthesiologist hotline call-in method.5Barrington et al. reported neurologic complication in five subjects after a sciatic nerve block using direct contact by phone at a single time point.13Twelve hundred eighty-five subjects received sciatic blocks, but the overall follow-up rate for all the study subjects at 6 weeks was only 34%. Assuming the follow-up rate was similar for the sciatic blocks as for the other peripheral blocks studied, the incidence of persistent injury at 6 weeks after sciatic block was 1.1%. In the current study, the incidence of reported postoperative neurologic symptoms by telephone interview was 8.4%, with persistence of symptoms at 6 weeks in 2.9% of subjects and 2.2% of subjects demonstrating abnormal sensory findings at physical examination. Taken together, these data suggest that there is significant underestimation of the initial rate of transient symptoms when subject-initiated reporting is used as the primary method of evaluation.
There are theoretic disadvantages to performing a supplemental nerve block at a second site along a peripheral nerve. A partial nerve block may result in a subclinical nerve injury and when the supplemental block is performed, a second insult may occur, producing a double-crush syndrome with clinical symptomatology.2,14In addition, partial sensory blockade may reduce patient report of sensation on needle localization or injection, although this finding has not been shown to be associated with an increased incidence of postoperative neurologic symptoms. Despite these theoretic disadvantages, a supplemental sciatic nerve block in the popliteal fossa was not associated with a significant increase in postoperative neurologic symptoms within the framework of our study.
There are limitations to our study. We used an unvalidated survey tool modeled after the McGill Pain Questionnaire and the self-report version of the Leeds Assessment of Neuropathic Symptoms and Signs Pain Scale, accepted any symptom as an outcome, and did not attempt to validate the symptoms as arising from neuropathic origin. A physical assessment was performed only at a follow-up surgeon visit and not at each follow-up interval. Our study was underpowered to detect a difference in the observed rates of neurologic symptoms. Even assuming the original hypothesis of a 50% increase in symptoms after a supplemental popliteal sciatic block based on our observed incidence of neurologic symptoms (8.7–17.4%), a sample of 1,500 in the single injection block and 151 in the supplemental block would be required to detect a difference. Nonetheless, based on the observed incidence of symptoms in the single block group 8.7% (95% CI 6.2–12.3) and in the supplemental group 7.1% (95% CI 1.9–17.3), the binominal probability of observing only 4 events in the supplemental sample (n = 56) was P = 0.017 if the actual incidence of symptoms was 17.4%. It is highly unlikely we would have observed this low of a number of events if the supplemental block had increased the incidence of transient nerve injury.
Other limitations to our study include our decision to inform the subjects to contact the surgeon or anesthesiologist at any time; because the subjects were aware that they would be contacted by the investigators, we may have reduced the rate of self-reported symptoms. We did not specify the minimal current threshold before injection, which varied from 0.05 to 0.55 mA. Although the possibility of subepineural injection in the lower range of thresholds obtained in this series is possible, the study was not powered to detect a difference in the incidence of postoperative neurologic symptoms at different current threshold intervals. We accepted all reported symptoms consistent with neurologic pain and did not attempt to evaluate compounding factors or other etiologies for postoperative neurologic symptoms after foot and ankle surgery such as patient position, compression due to cast presence, selection of arthroscopy ports, and incision site.11,15
In conclusion, we observed that a supplemental popliteal sciatic block does not appear to increase the incidence or duration of postoperative neurologic symptoms after failed sciatic block. We did not observe significant differences in patient satisfaction, block duration, or pain control after the rescue block. Future studies are warranted to evaluate the increase in risk of subclinical nerve injury after repeat block of the sciatic nerve.
Appendix 1 Phone Call Questionnaire
What time did you notice the numbness in your leg wearing off after surgery?
Do you have any pain at any site where you received a shot?
Did you have to contact the doctor? Reason__________
Did you return to the hospital?_______
Are you taking any of the pain medication you were given by the doctor?
About how many pills have you taken per day?
Did you take any other medications for pain?
On a scale of 0–10, please rate your satisfaction with your anesthesia care. (first call only)
On a scale of 0–10, please rate your satisfaction with the pain control (first call only)
Would you elect or recommend to a family relative a nerve block anesthesia in the future? Yes No Undecided. (first call only)
Have you experienced any of the following?
Pin and needle sensation or tingling
Pain that is burning, shooting, stabbing, sharp, hot-burning
Loss of feeling or numbness
Pain in any other area of your body
If you are experiencing any of these feelings, please tell us the location on your body and when the sensation started.
If you were experiencing any of these symptoms when I last contacted you have they changed in any way since then? Have they gotten worse, stayed the same, or gone away?
Please rate the pain you are experiencing now on a 0–10 scale.