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Estimation of the minimum effective volume of 0.5% bupivacaine for ultrasound-guided axillary brachial plexus block

Brenner, Dávid G.; Marjanek, Zsuzsanna; Iohom, Gabriella

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European Journal of Anaesthesiology: June 2016 - Volume 33 - Issue 6 - p 463-464
doi: 10.1097/EJA.0000000000000410
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Given the dose-limiting potential of ultrasound-guided regional anaesthesia techniques,1,2 our aim was to estimate the minimum effective volume of 0.5% bupivacaine for axillary brachial plexus blocks (ABPBs) in patients undergoing upper extremity surgery for/with extensive tissue damage (in which prolonged postoperative analgesia would be beneficial). Dose reduction in itself has the advantage of limiting block-related adverse effects.

The study was performed at Jávorszky Hospital, Vác, Hungary, approved by the Hospital Ethics Committee (Chairperson Zsuzsanna Kiss, MD) on 23 May 2013. Thirteen American Society of Anesthesiologists (ASA) physical status I to II patients enrolled in the study gave written informed consent to participate. All blocks were performed by the same investigator experienced in the field of ultrasound-guided ABPB. The identification of the target nerve was guided by ultrasound morphology and confirmed by the response to nerve stimulation. The volume to be injected around each nerve was determined using the nonprobability sequential step-up/step-down method.3,4 An arbitrary initial volume of 5 ml bupivacaine 0.5% per nerve was chosen based on our clinical experience and review of literature. Thereafter, the volume to be given depended on whether the volume used for the previous patient, for the same nerve, was sufficient or not. In case of a successful block, the target volume for the next patient's same nerve was 1 ml less, and after an unsuccessful block, 1 ml more than the volume applied in the previous patient. An evaluation was taken every 5 min from removal of the block needle until either surgical anaesthesia or the 45th post-block minute was reached. Sensory block evaluation was performed by assessment of cold sensation (0 – lack of cold sensation, 1 – decreased cold sensation, 2 – maintained cold sensation). Motor block was scored using the Bromage scale5 (0 – no movement, 1 – flicker of movement, 2 – able to move against gravity but not against resistance, 3 – decreased power, but able to move against resistance, 4 – full power), adapted for each nerve territory. Surgical anaesthesia was defined as total loss of cold sensation (score of 0) with a motor score of 2 or less in the relevant nerve territory. Motor block duration was defined as the time elapsed from removing the block needle till the Bromage score became at least 3 in all nerve territories. All adverse events, including those related to inadequate anaesthesia such as discomfort, pain, analgesic requirement intraoperatively, were recorded. In the postoperative period, analgesic medication was commenced at the patient's request (intravenous diclofenac/acetaminophen/tramadol pro re nata). Patients were trained to fill in a diary. They got both written and verbal guidance about the block evaluation protocol. The diary was divided into 2-h brackets for evaluation of motor function (elbow flexion, wrist extension, fist making), pain scores and analgesic requirements. Scoring scales [modified Bromage scale and 10-cm visual analogue scale (VAS) line] were attached.

Having started with depositing 5 ml of bupivacaine 0.5% around each nerve, the 1 ml per nerve volume was reached by the fifth recruited patient. Successful surgical anaesthesia was accomplished in the next eight consecutive patients with the same volume. No immediate adverse event related to the nerve blocks, that is vascular injury or signs of local anaesthetic toxicity, was noted. Sensory block onset times (median value and interquartile range) for musculocutaneous, median, ulnar and radial nerves were 10 (5–10), 10 (5–20), 10 (5–15) and 10 (5–20) min, whereas motor block onset times were 10 (5–10), 15 (10–15), 10 (10–15) and 10 (5–15) min, respectively. All but one nerve of the entire study group were fully anaesthetised within 45 min of completion of the ABPB block. The outlier was the motor block in the median innervation territory of one patient (who got 1 ml of bupivacaine 0.5%) with an onset time of 55 min. At that point, however, the patient had surgical anaesthesia of the entire forearm and the operation was uneventful under regional anaesthesia alone. The prolonged onset time could have been the consequence of an anatomical variation as branches have been described far away from the most visible main tract.6 Uneven local anaesthetic distribution could also delay the development of the block. All patients had adequate surgical anaesthesia without any discomfort in the surgical field. No patient requested intraoperative sedation. One patient (1 ml per nerve bupivacaine 0.5% used) experienced slight tourniquet pain 60 min after cuff inflation, which was successfully treated with 100 mcg of intravenous fentanyl. Tourniquet pain is not uncommon with higher doses of local anaesthetic; therefore it is unlikely to be a direct consequence of the low dose of local anaesthetic used.

The (mean +/− SD) resolution of motor blockade required 13.84 ± 3.96 h. Two patients noted mild paraesthesia in the postoperative period, from the sixth and 20th hour post-block (they got 5 and 4 ml per nerve local anaesthetic, respectively), which resolved completely in both the cases within 2 days (confirmed by telephone interview). VAS scores 4 or less were observed for 12 h (interquartile range 9 to 14.5 h) in the absence of any medication. Two patients had diabetes. Although neither of them had obvious preoperative sensory dysfunction on the affected arm, the prolonged block duration could have been the consequence of an underlying subclinical neuropathy in the territory of the blocked nerves. The time elapsed from removal of block needle to first analgesic requirement, VAS score at that time and the analgesic administered are shown in Table 1.

Table 1
Table 1:
Block characteristics: applied volume, surgical block onset time and first analgesic requirement

In conclusion, we can ascertain that the use of 1 ml per nerve bupivacaine 0.5% for ultrasound-guided ABPB is a feasible method, which results in acceptable block onset times, adequate surgical anaesthesia and excellent postoperative analgesia in patients undergoing surgical procedures with extended tissue damage.

Acknowledgements related to this article

Assistance with the study: none.

Financial support and sponsorship: none.

Conflicts of interest: none.


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