Analgesia: Research Reports

The Addition of Lidocaine to Bupivacaine Does Not Shorten the Duration of Spinal Anesthesia

A Randomized, Double-Blinded Study of Patients Undergoing Knee Arthroscopy

Jacobsen, Jon MD^*; Husum, Bent MD, DMSc^†; von Staffeldt, Henrik MD^†; Qvist, Thorkild F. MD^†; Eske Jensen, Peer MD^*; Kledal, Susanne MD^*

Author Information

From the ^*Department of Anaesthesiology, Hilleroed Hospital, Hilleroed, Denmark; and ^†Department of Anaesthesiology, Section in Frederikssund, Hilleroed Hospital, Hilleroed, Denmark.

Funding: None.

The authors declare no conflict of interest.

Reprints will not be available from the authors.

Address correspondence to Jon Jacobsen, MD, Department of Anaesthesiology, Hilleroed Hospital, Dyrehavevej 29, DK-3400 Hilleroed, Denmark. Address e-mail to [email protected].

Accepted June 29, 2011

Published ahead of print September 14, 2011

Anesthesia & Analgesia: November 2011 - Volume 113 - Issue 5 - p 1272-1275

doi: 10.1213/ANE.0b013e31822d676f

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When using spinal anesthesia for ambulatory surgery, recovery of the sensory and motor functions should be fast and predictable after completion of the surgical procedure. Bupivacaine is widely accepted as a safe and reliable drug but may have a duration of action too long for short surgical procedures,¹ and inadequate spinal anesthesia may occur after bupivacaine in low doses.²

Recently, Lee et al. reported that the intrathecal addition of 0.6 mL of 1% lidocaine to 1.5 mL of 0.5% hyperbaric bupivacaine shortened the duration of bupivacaine spinal block, providing more rapid recovery in patients scheduled for transurethral resection of bladder tumor or prostate.³ They speculated that the additional lidocaine might induce vasodilation of spinal blood vessels, increasing the clearance of bupivacaine from the intrathecal space. Also, they suggested that the mixed-drug technique might have potential for improving the utility of spinal anesthesia in ambulatory patients.

This prospective, randomized, double-blind study sought to confirm the findings of Lee et al.³ in patients undergoing knee arthroscopy.

METHODS

The study was a randomized, controlled, double-blind clinical trial (ClinicalTrials.gov identifier: NCT01245868). Patients were included after written informed consent, and the study was approved by the Regional Ethics Committee, the Danish Data Protection Agency, and the Danish Medicines Agency. The study was monitored by the Good Clinical Practice unit at Copenhagen University Hospital.

Patients were recruited from the Sportsclinic at Frederikssund Hospital from March to October 2010. The inclusion criteria included (1) age between 18 and 65 years, (2) scheduled for elective unilateral arthroscopy of the knee, (3) ASA group 1 to 2, (4) height between 155 and 190 cm, and (5) body mass index <36. Exclusion criteria were known allergy to lidocaine or bupivacaine, neurological disorders, coagulation disorders, back surgery, and insulin-treated diabetes mellitus.

Study Groups

All patients received 2 mL 0.5% hypertonic bupivacaine (Marcain Spinal Tung®, AstraZeneca, Denmark) mixed with either 0.6 mL 1% lidocaine (lidocaine group) or 0.6 mL isotonic saline (control group). Thus all patients received the same dose of bupivacaine (10 mg) and the same volume (2.6 mL).

Paracetamol 1 g was given as premedication. Heart rate (electrocardiogram) and pulse oximetry were monitored continuously, and arterial blood pressure every 5 minutes. Oxygen of 2 L per minute was administered during the operation and in the postoperative care unit (PACU).

Spinal anesthesia was performed with a 27-G pencil point spinal needle using a midline approach at the L2 to 3 or the L3 to 4 intervertebral space with the patient in the lateral decubitus position, the dependent side the one to be operated on. Three minutes after the intrathecal injection of local anesthetic the patient was turned to the supine horizontal position. The patient was considered ready for surgery when the sensory block had reached L1, and the motor block graded on the Bromage scale was ≥2 on the leg that was to be operated on.

Clinically relevant hypotension, defined as a decrease in systolic arterial blood pressure exceeding 30% from baseline values, was treated with ephedrine 5 mg IV. Bradycardia, defined as heart rate ≤40 per minute without concomitant hypotension, was treated with atropine 0.5 mg IV.

Monitoring Effect of the Intervention

The sensory block was determined bilaterally by pinprick using an 18-G blunt needle (Becton, Dickinson & Co., Franklin Lakes, NJ), starting in the anesthetized area, every 5 minutes during the first 30 minutes and every 15 minutes thereafter. At the same times, the motor block was evaluated by the Bromage scale (0 = no motor block, 1 = hip blocked, 2 = hip and knee blocked, 3 = hip, knee, and ankle blocked). Evaluation of the block was performed by an anesthesiologist who was unaware of the patient's group allocation until the patient was ready for surgery and by specially trained nurse anesthetists thereafter. Time from intrathecal injection of local anesthetic to readiness for surgery, the maximum level of sensory block, time for complete regression of sensory and motor blocks, and to readiness for discharge from the PACU were recorded. Criteria for discharge were stable vital signs, ability to tolerate liquids by mouth, ability to walk with crutches, no pain or nausea, and ability to void or having <100 mL urine in the bladder confirmed by bladder scanning.⁴

Two days after the operation, the patients were interviewed by telephone about possible side effects or complaints (headache, nausea, difficulty voiding) and symptoms of transient neurological syndrome (pain or dysesthesia in the gluteal region radiating to the legs) using a standardized questionnaire.⁵ In case of any complaints the patient was contacted again 5 days later.

Outcome Measures

The primary effect variable was the time from the intrathecal injection of local anesthetic to total regression of sensory and motor blocks. Secondary effect variables were the time from injection of local anesthetic to fulfillment of criteria for discharge from the PACU, and the highest dermatome blocked.

Randomization and Blinding

Randomization of patients was based on computer-generated random numbers sealed in consecutively numbered envelopes. Allocation of the individual patient by breaking the next unopened envelope, and preparation of the corresponding mixture of local anesthetic were performed by one of the authors in a separate room. He or she did not at any time participate in patient care. The spinal puncture and injection of the test solution were done by another of the authors who was unaware of the content of the solution. The patient was not informed of which of the 2 treatments he or she actually received.

Calculation of Sample Size

In a pilot study of 26 patients who had spinal anesthesia with hyperbaric bupivacaine 0.5% 2.0 to 2.2 mL, the SD of the time from injection of local anesthetic to discharge from the PACU was 40 minutes. Assuming the same SD—and accepting a risk of type 1 error of 5%, a risk of type 2 error of 10%, and a minimal relevant difference between groups of 45 minutes—17 patients would have to be included in each group. To compensate for possible dropouts, we included 50 patients.

Statistical Methods

Normal distribution of continuous variables was analyzed using the Kolmogorov–Smirnov test, and continuous variables were compared with the t test for independent samples using the SPSW 18 statistical package (SPSS, Chicago, IL). Ninety-five percent confidence intervals (CI) of mean differences were calculated. Categorical variables were compared using contingency table analysis. Mann–Whitney U test was used for comparison of maximal sensory blockade. A P value <0.05 was considered statistically significant.

RESULTS

Fifty-two patients who preferred spinal anesthesia for their arthroscopy were asked to participate in the study. Two women declined because they felt uneasy about research projects; both had an uneventful spinal anesthesia. The other 50 patients entered the study and were allocated to the lidocaine group (n = 25) or the control group. Four patients were excluded after being allocated but before the injection of local anesthetic; 1 changed his mind and requested general anesthesia, and 3 were excluded because of technical difficulties. One patient in the control group complained of severe pain at the start of surgery and underwent general anesthesia, thus leaving 24 patients in the lidocaine group and 21 patients in the control group for analysis (Fig. 1). There was no difference between the groups regarding age, gender, height, weight, ASA group, or duration of surgery (Table 1).

F1-48 — Figure 1:
Consort diagram showing the flow of participants through the randomized trial.

The mean duration of the sensory blockade in the lidocaine group was 185 ± 43 minutes versus 197 ± 40 minutes in the control group (P = 0.36, 95% CI of the difference −37 to 14 minutes), and the mean times to discharge from PACU were 195 ± 45 minutes versus 209 ± 49 minutes, respectively (P = 0.33). There was no statistically significant difference between the groups regarding time to readiness for surgery or maximum level of sensory block on the operated side (Table 2).

T2-48 — Table 2:
Profiles of Sensory and Motor Blocks

One patient in the lidocaine group was treated with ephedrine for hypotension, and 1 patient in the control group with atropine for bradycardia. Analgesia was sufficient for the operation in all patients, i.e., none of the patients needed supplemental analgesics.

After the operation, 2 patients in the control group and 1 patient in the lidocaine group described symptoms compatible with transient neurological syndrome. In the control group, 1 patient had perineal numbness and difficulty voiding until the day after the operation and another patient described numbness of the front of the thighs until the next day. In the lidocaine group, 1 patient had pain radiating from the gluteal region to both thighs for the first 12 hours. In the lidocaine group, 1 patient found it difficult to initiate voiding for 3 days but had no pain or dysesthesia. None of the patients had spinal headache or backache.

DISCUSSION

The long duration of spinal bupivacaine may be unsuitable for short ambulatory procedures such as knee arthroscopy. Attempts to use small doses of bupivacaine may increase onset time and may increase the failure rate of spinal anesthesia.¹^,² Therefore, Lee et al.'s report³ was interesting both from a pharmacological point of view and in a clinical perspective. However, we could not confirm that the addition of a small amount of lidocaine to intrathecal hyperbaric bupivacaine shortened the duration of the sensory blockade or the period of stay in the PACU.

In the present study we did not duplicate the experimental setup used by Lee et al.³; our choices of specific anesthetic solution and of spinal technique were chosen because they more closely approximate our routine clinical practice. Similarly to the procedure of Lee et al., we added 0.6 mL of either isotonic saline or 1% lidocaine to intrathecal hyperbaric bupivacaine. However, on the basis of our practice we used a dosage of 2 mL 0.5% hyperbaric bupivacaine (10 mg), whereas Lee et al.³ used only 1.5 mL (7.5 mg). Likewise, in our study the patients stayed in the lateral decubitus position for 3 minutes after the intrathecal injection, whereas in Lee et al.'s study the patients were turned to the supine horizontal position immediately after the injection. Furthermore, Lee et al. measured time to regression to L1 and S2 levels from peak sensory levels of blockade, whereas our primary effect variable was the time from the intrathecal injection of local anesthetic to total regression of sensory and motor blocks. Despite these differences in study design we believe that we have not overlooked any clinically relevant potential benefit of the mixed-drug technique proposed by Lee et al. When calculating the sample size, we applied a minimum relevant difference of 45 minutes between the groups, because in light of the very large interpatient variation in duration of bupivacaine blockade, only a substantial effect of mixing bupivacaine with a small dose of lidocaine would be useful in daily clinical practice.

In conclusion, in the present randomized, double-blind study of patients undergoing knee arthroscopy, the addition 0.6 mL of lidocaine 1% to 2.0 mL of intrathecal hyperbaric bupivacaine 0.5% did not shorten the duration of sensory or motoric blockade or the time to discharge of the patient from the postoperative care unit.