Ultrasound guidance has been integrated into regional anesthesia clinical practice. When comparing ultrasound to nerve stimulator techniques, higher success rates1–3 and shorter onset times3–5 have been reported. Visualization of needle, nerve, and injectate permits effective peripheral nerve blockade using low local anesthetic doses.6–9 Our group reported successful ultrasound-guided axillary block with low-dose local anesthetic in upper limb trauma surgery.10 In addition, we demonstrated successful ultrasound-guided axillary block with 1 mL per nerve of 2% lidocaine with 1:200,000 epinephrine (2% LidoEpi).11 The use of a very low dose of local anesthetic in peripheral nerve block has been reported by other authors.12,13
Our initial low-dose study11 failed to accurately measure block duration. We designed a prospective observational study to measure the duration of ultrasound-guided axillary brachial plexus block using 1 mL per nerve 2% LidoEpi in patients undergoing upper limb surgery.
The Cork Teaching Hospitals Research Ethics Committee granted approval for this study. After written informed consent, patients aged 18 to 80 years, ASA grade I to III, undergoing unilateral upper limb surgery with an expected duration of <90 minutes were enrolled in the study.
Intravenous access was established and standard monitoring was attached (noninvasive arterial blood pressure, electrocardiography, and pulse oximetry). The operative arm was abducted and externally rotated. The elbow was flexed to 90°. Ultrasound examination of the axilla was performed using a SonoSite Titan unit (SonoSite®, Bothell, WA) with a 38-mm high-frequency (7–10 MHz) linear array transducer (L38). The ultrasound-guided axillary brachial plexus block was performed as previously described10 by a single anesthesiologist (BOD) without the supplemental use of nerve stimulation. Once appropriate perineural needle placement was visualized, 1 mL of 2% LidoEpi was injected in 0.2- to 0.3-mL aliquots using a 2.5-mL syringe. Dynamic needle manipulation during injection facilitated circumferential perineural injectate placement. Intraneural injection (evidenced by increase in cross-sectional nerve diameter) and paraesthesia were avoided at all times during the block procedure. The median, ulnar, radial, and musculocutaneous nerves were individually sought and blocked in this order. The block performance time was defined as the interval from needle insertion to final perineural injection.
An independent assessor evaluated the presence and degree of motor and sensory blockade in each nerve territory (Table 1). Sensory and motor functions were simultaneously compared in the contralateral limb. Block assessment was performed at 5-minute intervals beginning at completion of the final perineural injection. Block assessment was halted when either surgical anesthesia was achieved or 30 minutes had elapsed. Surgical anesthesia was defined as a motor score of ≤2, with absent appreciation of cold and pinprick sensation. Each nerve was assessed individually. The block onset time was defined as the interval from final perineural injection to attainment of surgical anesthesia.
Block failure was defined as absence of surgical anesthesia at 30 minutes in ≥1 of the 4 nerve territories. Block failure was to be managed by either the performance of a “rescue block” or conversion to general anesthesia.
The independent assessor reexamined the blocked limb every 15 minutes from completion of surgery to block regression. Because the operative limb was covered in surgical dressings, assessment of sensory function was limited to exposed portions of skin on dorsal and palmar aspects of the fingers. Regression of surgical anesthesia was deemed to have occurred once pinprick and cold sensation had returned and the motor power scored ≥3 in any nerve territory.
Sedation was provided upon patient request using either midazolam 2 mg or a propofol infusion, titrated to a Ramsay sedation score of 3 (responsiveness to voice command).14
All patients underwent surgery necessitating the placement of an arm tourniquet inflated to 250 mm Hg. The duration of surgery was defined as the time interval from tourniquet inflation to deflation.
All patients received 1 g IV acetaminophen and 75 mg diclofenac sodium during surgery. Postoperative analgesia consisted of oral acetaminophen 1 g 6 hourly and diclofenac sodium 75 mg twice daily for 72 hours after surgery. Oxycodone 5 mg was prescribed for rescue analgesia after block regression.
Summary data were calculated using EpiInfo™ 2002 (Centers for Disease Control and Prevention, Atlanta, GA) statistics software and presented as median (range) or mean (SD) as appropriate.
Seventeen consecutive patients completed the study protocol (Table 2). There were no block failures and no patients were excluded from the study.
The mean (SD) block duration was 160.8 (30.7) minutes, block onset time was 9.7 (3.7) minutes, and the block performance time was 271 (67.9) seconds (Table 3). Anxiolytic sedation was requested in 5 of 17 cases. No patients required either a “rescue block” or conversion to general anesthesia. The block durations for each individual nerve are displayed in Table 3 (Fig. 1).
The mean (SD) duration of surgery was 74.6 (33.3) minutes. Tourniquet discomfort was not reported, and rescue opiate analgesics were not required. There were no adverse incidents during the study period, and all patients were discharged within 24 hours of surgery. No patients required hospital readmission.
Ultrasound guidance has made the performance of low-dose peripheral nerve block possible. Our initial study of low-dose lidocaine axillary brachial plexus anesthesia10 failed to accurately measure block duration. In this observational study, we addressed this by measuring the duration of axillary block in adults undergoing upper limb surgery. The observed duration of block was comparable to previous reports of LidoEpi use15,16 and was sufficient for procedures performed during the study period. A short block duration can be beneficial in the ambulatory setting, particularly when there are concerns regarding home discharge with an insensate limb17 despite evidence to the contrary.18–20 Our patients did not experience significant pain requiring opiate analgesia before hospital discharge, and there were no unanticipated readmissions for pain relief.
We acknowledge that this study is limited by both its size and scope. However, the study addresses an important question as to whether the duration of brachial plexus anesthesia with 2% LidoEpi is sufficient for ambulatory upper limb surgery. The small number of patients included (n = 17) and the superficial nature of the surgical procedures performed may further limit the external validity of the data.
In summary, the duration of anesthesia resulting from ultrasound-guided axillary brachial plexus block with 1 mL of 2% LidoEpi per nerve (4 mL total) was sufficient for our patient cohort undergoing soft tissue ambulatory hand surgery.
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