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ANALGESIA

The Effects of Arm Position on Onset and Duration of Axillary Brachial Plexus Block

From the SICU and Emergency Medicine, Centre Hospitalier Universitaire (CHU) de Rabat, Université Mohamed V, Rabat, Morocco.

Address correspondence and reprint requests to Prof. Adil Ababou, Service d'anesthésie réanimation Hôpital Cheikh Zaid, Avenue allal el fassi, Madinat al irfane, Hay riad 10000, Rabat, Morocco. Address e-mail to a.ababou{at}yahoo.fr.

Abstract

BACKGROUND: We assessed the effects of arm position after block performance on success rate, onset time, and duration of axillary block (AXB).

METHODS: After performing AXB, patients were randomized into two groups: group adduction in which the arm was immediately placed in adduction along the body and group abduction in which the arm remained in abduction. These positions were maintained until the block was achieved.

RESULTS: The sensory and motor blocks onset time were significantly shorter in the abduction group compared with that in the adduction group and their duration was significantly prolonged (P < 0.001).

CONCLUSION: Maintaining the arm in abduction after performing AXB allows a shorter onset time and a prolongation of the sensory and motor blocks.

During the last decade, axillary brachial plexus block (AXB) studies focused on the improvement of the technique by modifying the number of stimulation (1,2) and the minimal intensity in the nerves' approach (3).

AXB is performed with the upper extremity adducted at 90° and bent at the elbow with the forearm supinated. The aim of this study was to compare the effect of arm position on the quality of the AXB by nerve stimulation.

METHODS

This prospective, randomized, double-blind study was approved by the institutional ethics committee. Informed consent was obtained from patients scheduled for an upper limb trauma surgery. Patients with a history of allergic reaction to local anesthetics and coagulation abnormality were excluded.

The patients were placed with the arm abducted at 90°, with external rotation and the elbow flexed to 90° with the forearm supinated. All AXB were performed by two senior anesthesiologists. Nerves were localized with a 22-gauge 50-mm-long needle (Locoplex® Vygon) connected to a nerve stimulator (Plexival® Vygon) adjusted at 2 Hz with a current duration of 50 µs. The needle position was deemed appropriate when a motor response was obtained with a threshold stimulation of 0.5 mA. A triple injection method was chosen in which the ulnar nerve was not purposely located. Using a single needle entry point, the median nerve was localized first followed by the radial nerve and then the musculocutaneous nerve. Ten milliliters of a mixture of equal parts 2% lidocaine and 0.5% bupivacaine was injected on each nerve. Subcutaneous infiltration through the skin puncture by 5 mL of the mixture was performed. Immediately after, patients were assigned by prerandomized sealed envelopes into two groups:

Group adduction ADD: in which the arm was immediately placed in adduction along the body.

Group abduction ABD: in which the arm was maintained in abduction.

These positions were assessed by two other anesthesiologists every minute and maintained until the sensory and motor blockade were achieved. Sensory block was confirmed by the loss of temperature sense assessed by using an ether-soaked compress. Motor block was confirmed by an absence of muscular contraction.

The anesthesia was qualified a "success" if the sensory and motor block were obtained for all the nerves of the axillary plexus; and a "failure" if sensory and/or motor block in at least one nerve distribution was not achieved.

Calculation of the required sample size was based on the assumption that the arm abduction would reduce the global motor block onset time to 8 min with standard deviation estimated at 16 min. For an level of 0.05 and power of 80%, the analysis required 32 patients per group. Data were expressed as means ± sd with confidence intervals of 95%. Parametric variables were compared with the Mann–Whitney test. The qualitative variables were analyzed with Fisher's exact test. Probability values below 0.05 were considered significant.

RESULTS

Sixty-four patients were included in the study, 32 in each group. The demographic data and the time needed to perform the AXB were similar between groups (Table 1).

The success rate of AXB was 100% in group ABD versus 90.6% in group ADD (P = 0.078).

In group ABD, the sensory and motor onset time of each nerve was significantly shorter (P < 0.001) (Fig. 1) and their duration (P < 0.001) (Fig. 2) were significantly prolonged compared with group ADD.

View larger version (13K): [in this window] [in a new window]   Figure 1. The onset time for sensory block of each nerve. Mean ± sd. *P < 0.001. CM: medial cutaneous nerves of the arm and forearm; MC: musculocutaneous nerve.

View larger version (18K): [in this window] [in a new window]   Figure 2. Sensory block duration of each nerve. Mean ± sd. *P < 0.001. CM: medial cutaneous nerves of the arm and forearm; MC: musculocutaneous nerve.

The overall sensory and motor onset time were significantly shortened in group ABD: 12 ± 3 vs 17 ± 7 min (P < 0.001) and 17 ± 5 vs 22 ± 10 min (P < 0.05).

The duration of these blocks was significantly longer in group ABD: 325 ± 53 vs 189 ± 67 min (P < 0.001) and 349 ± 55 vs 208 ± 89 min (P < 0.001).

DISCUSSION

The axillary neurovascular sheath was supposed to improve local anesthetic drug spread around all the nerves after a single injection on the median nerve (4).

In addition, to improve the central spread of the local anesthetic solution, several techniques were described including manual compression below the axillary injection and putting the arm back in adduction (5).

Previous publications suggested that arm abduction at 90° would decrease central spreading through pressure on the sheath from the abducted humeral head. This maneuver would impair free circumferential spread by stretching the neurovascular bundle in close contact with the narrow lateral wall of the axilla (6). However, all these maneuvers have been determined to be inefficient (7–9).

We hypothesized that placing the arm in adduction along the body immediately after the selective injection would modify pressure applied on the neurovascular bundle and could disperse local anesthetics, and thus modify the onset time and quality of AXB. The results of this study sustain this hypothesis. This technique also avoids pain caused by mobilization of the traumatic upper limb. Reducing onset time may also improve the turnover of operating rooms. Keeping the arm abducted allowed a gain of 6 min in onset time and prolonged analgesia 135 min.

We conclude that maintaining the arm at an abduction of 90° after achieving the AXB by nerve stimulation allows a shorter onset time and prolongation of sensory and motor blocks.

Footnotes

Accepted for publication December 12, 2006.

REFERENCES

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Ababou, A. Articles by Sbihi, A. Search for Related Content PubMed PubMed Citation Articles by Ababou, A. Articles by Sbihi, A. Related Collections Regional Anesthesia