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Interscalene brachial plexus anaesthesia with small volumes of ropivacaine 0.75%: effects of the injection technique on the onset time of nerve blockade

Fanelli, G.; Casati, A.; Beccaria, P.; Cappelleri, G.; Albertin, A.; Torri, G.

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European Journal of Anaesthesiology: January 2001 - Volume 18 - Issue 1 - p 54-58

Abstract

Introduction

The onset time and success rate of a peripheral nerve block are widely used as ‘efficacy’ parameters when comparing different anaesthetic solutions, but various factors can influence the onset time and success rate of peripheral nerve blockade. Physicians usually increase the volume and dose of the local anaesthetic solution to shorten the latency of nerve blockade [1,2]; however, the use of nerve stimulators and a multiple injection technique have been demonstrated to improve the onset time and quality of nerve block [3–5], providing effective nerve blocks with volumes of local anaesthetic solution markedly lower than those usually reported [6,7]. The ability to block major nerves with smaller volumes of local anaesthetic also has the theoretical potential for adding to the safety of peripheral nerve blocks by minimizing the risk for systemic toxicity [8]. For this reason, at our institution, peripheral nerve blocks are routinely performed by using a multiple injection technique with relatively small volumes of local anaesthetic solutions.

The aim of this prospective, randomized, single-blinded study was to evaluate the effect of the single or multiple injection techniques on the onset time and efficacy of interscalene brachial plexus anaesthesia performed with 20 mL of 0.75% ropivacaine, according to our clinical practice [9].

Methods

With Ethical Committee approval and written informed consent, we studied 30 inpatients, of ASA physical status I and II, aged 19–70 years, scheduled to have interscalene brachial plexus anaesthesia for elective shoulder capsuloplastic or acromioplastic surgical procedures. Patients with contraindications to regional anaesthesia, as well as those with respiratory or cardiac disease, diabetes, peripheral neuropathy, and those receiving chronic analgesic therapy were excluded. Based on our clinical experience [9], the sample size of the study population was calculated to detect a 5-min difference in the time required to achieve adequate surgical anaesthesia between the two injection techniques, accepting a one-tailed α error of 5%, and a β error of 10% [10].

After an 18-gauge intravenous (i.v.) cannula had been placed in a forearm vein, all patients received standard i.v. premedication with 0.05 mg kg−1 midazolam 10 min before placing the block. Nerve blocks were placed using a nerve stimulator (Plexival, Medival, Italy) and a short bevelled, Teflon coated stimulating needle (Locoplex, Vygon, France) (needle length/diameter were 3.5 cm/25 gauge). The stimulation frequency was set at 2 Hz, while the intensity of stimulating current was initially set to deliver 1 mA and then gradually decreased to ≤ 0.5 mA after each muscular twitch was observed.

Using a computer-generated random sequence, patients were randomly allocated to receive a single injection (Single group, n = 15) or a multiple injection (Multiple group, n = 15) technique. The needle was introduced caudal to a line through the cricoid cartilage according to the landmark described by Winnie [11]. After the skin of the region involved in block placement had been disinfected, the stopwatch was started. Paresthesiae were never sought. In the Single group, as soon as the first muscular twitch was observed, 20 mL of 0.75% ropivacaine were slowly injected with multiple aspirations to exclude intravascular injection. In the Multiple group, the stimulating needle was inserted and redirected, eliciting each of the following muscular twitches: shoulder abduction (contraction of the supraspinatus muscle – 8 mL were injected), flexion of the arm (contraction of biceps muscle – 6 mL were injected), and extension of the arm (contraction of the triceps muscle – 6 mL were injected). If the injection of 1 mL of the study solution immediately stopped the muscular twitch elicited at ≤ 0.5 mA, the needle location was considered adequate and the remaining volume of local anaesthetic solution was injected [6,7]. At the end of the local anaesthetic injection, the stopwatch was stopped, and block performance time recorded. The anaesthesiologist placing the block then reset the stopwatch and left the room. All blocks where performed by two anaesthesiologists with substantial expertise in regional anaesthesia, and were assessed by an independent, blinded observer.

The onset of sensory and motor blocks was evaluated every two minutes for the first 10 min and then, every 5 min, until surgical block was achieved. The patient was judged ready for surgery when he/she showed complete loss of pinprick sensation in the skin dermatomes involved in the surgical field (from C4 to C7) with concomitant inability to elevate the operated limb from the operating table. The stopwatch was then stopped and the time from the completion of the injection to the achievement of surgical anaesthesia, as defined previously, was recorded and surgery started. The total time required from skin disinfection to surgical anaesthesia was also calculated by adding the performance time to the onset time.

The degree of pain at skin incision was also assessed with a 5-point verbal rating scale score (VRS: 0 = no pain, 1 = mild pain, 2 = moderate pain; 3 = severe pain; 4 = unbearable pain); if VRS ≥ 2 was reported by the patient, 0.1 mg supplemental fentanyl was given i.v. If this did not provide adequate analgesia a propofol bolus of 1 mg kg−1 i.v. was given followed by a continuous i.v. infusion (2–4 mg kg−1 h−1). The quality of the nerve block was evaluated, as follows, according to the need for supplementary i.v. analgesia: satisfactory nerve block = no analgesia required to complete surgery; unsatisfactory nerve block = fentanyl supplementation required to complete surgery; failed nerve block = fentanyl and propofol administration required to complete surgery.

At discharge from the orthopaedic ward and one week after hospital discharge (at first routine postoperative orthopaedic examination), patients were also evaluated for the occurrence of neurological complications.

Statistical analysis was performed using the program Systat 7.0 (SPSS Inc, Chicago, IL, USA). The Mann–Whitney U-test was used to compare demographic data, performance time, and time for readiness to surgery. Categorical variables were analysed using the contingency table analysis with Fisher's exact test. The time from skin disinfection to readiness for surgery was also compared by a log-rank test using the Kaplan–Meier's survival analysis. A value of P < 0.05 was considered significant. Results are presented as median (range), or as numbers (%).

Results

The two groups were similar with respect to age, weight, height, ASA physical status and male to female ratio (Table 1).

Table 1
Table 1:
Anthropometric data of studied patients

Performance time was 5 min (4–10 min) with the multiple injection technique and 3 min (1–8 min) in the Single group (P = 0.001). The time from the completion of anaesthetic injection to achieve readiness for surgery was shorter in the Multiple group (10 min; range 5–20 min) than in patients receiving the single injection (20 min; range 10–60 min) (P = 0.003). Figure 1 shows survival analysis of the total time required from skin disinfection until patients were judged ready for surgery with interscalene brachial plexus block performed by using either a single injection or the multiple twitch technique. Even though block placement took less time with the single injection technique, the total preoperative time was shorter in patients receiving multiple injection technique (15 min; range 10–28 min) than in those of the Single group (23 min; range 14–60 min), and the log-rank curves were significantly different (P = 0.025)

Figure 1.
Figure 1.:
Survival analysis of the total time required from skin disinfection to achievement of surgical block. Percentage of patients judged ready for surgery after 20 mL of 0.75% ropivacaine had been injected in the interscalene brachial plexus sheath using either a single twitch (Single group, n = 15) or multiple twitches (Multiple group, n = 15) techniques. Complete loss of pinprick sensation in the skin dermatomes involved in the surgical field (from C4 to C7) with the inability to elevate the operated limb from the bed constituted the endpoint of the study for the patient concerned. The log-rank curves representing the two groups studied are significantly different (P = 0.025).

Additional fentanyl supplementation during surgery was required in two patients of the Multiple group (13%) and eight patients of the Single group (53%) (P = 0.05). Only one single-group patient (7%) receiving IV fentanyl supplementation also required propofol infusion to complete surgery (P = not significant). No complications were observed at hospital discharge and during the first routine postoperative orthopaedic visit.

Discussion

This prospective, randomized, single-blinded study demonstrated that, when performing interscalene brachial plexus block with relatively small volumes of 0.75% ropivacaine, the use of a multiple injection technique provided a significant reduction in the time required to achieve readiness for surgery compared with the single injection technique, and provided a clinically relevant improvement in the efficacy of nerve block itself.

The onset time we observed with multiple injections is similar to that reported in previous investigations [9,12], while the onset time observed with the single injection technique is slightly longer than that reported by other authors using a larger volume of 0.75% ropivacaine with epinephrine [13]. In fact, when a single injection technique is used, larger volumes of local anaesthetic solution are usually injected to improve the local anaesthetic spread along the neurovascular sheath [1,2,11]. This could be responsible for the unacceptably high number of patients requiring fentanyl supplementation in the Single group. However, Urmey and his colleagues [14], evaluating pulmonary function changes during interscalene brachial plexus block with either 40 mL or 20 mL of anaesthetic solution, demonstrated that a 20-mL injection volume is enough for shoulder surgery, even if only partial C3 and absent C2 dermatomal sensory anaesthesia is observed [14,15]. In agreement with our findings, other authors [3,4,16,17] have reported clinically relevant improvement in the onset time and quality of nerve block when using multiple injections; and similar results have been demonstrated also with lower limb peripheral nerve blocks [18]. The advantages of providing adequate nerve block with a small volume/dose of local anaesthetic solution should be carefully considered by physicians when choosing for the injection technique during block placement; overall considering that the main morbidity risk associated with peripheral nerve blocks is systemic toxicity [8].

Eliciting multiple muscular twitches requires that the stimulating needle is inserted and redirected, leading to a prolongation of the performance time compared with the single injection technique. However, this extra time was compensated for by the shorter onset time of nerve block with better spread of analgesia compared with the single injection, leading to a nearly 35% reduction in total preoperative time. Similar results have been reported by other authors [3–5,16], who demonstrated longer performance time, but shorter preoperative time in patients receiving the multiple injections compared with those receiving a single injection technique for axillary brachial plexus anaesthesia.

Achievement of surgical block after local anaesthetic solution has been injected depends on the concentration gradient between the injection site and the nerve, the distance between the two, and the rate of absorption from the injection site. Because volume, dose and site of injection of 0.75% ropivacaine were the same in the two groups, only the shorter distance for diffusion of local anaesthetic molecules to the nerve involved in surgical procedure can explain our findings.

In spite of clinical advantages of the multiple injection technique for peripheral nerve blocks, physicians are often concerned about using it for two reasons: first, the patient acceptability of an awake multiple injection technique; and secondly, the theoretically increased risk for needle trauma or intraneural injection by moving the stimulating needle toward a partially anaesthetized nerve. Multiple nerve stimulation blocks are painful and may affect patient acceptance [7]. The present investigation was not designed to provide an adequate power for evaluating patient acceptance; however, it has been demonstrated that light sedation before placing a multiple nerve block improves patient acceptance without altering consciousness [19]. Considering the nerve injury concern, only properly designed and sufficiently powered, randomized studies can solve this philosophical problem. However, no evidence of an increased risk for postoperative neurologic dysfunction has been reported in the literature with the multiple injection technique [7], while the incidence of nerve injury after peripheral nerve blocks ranges between 0.5/10 000 and 4.8/10 000 [8].

In conclusion, this prospective, randomized, single-blinded study demonstrated that searching for multiple muscular twitches when performing interscalene brachial plexus anaesthesia with small volumes of 0.75% ropivacaine shortened the total preoperative time and improved the quality of nerve blockade. This effect was related only to the injection technique, and must be carefully considered when different clinical studies evaluating the use of new local anaesthetic solutions for peripheral nerve blocks are compared.

References

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Keywords:

ANAESTHETICS; LOCAL; ropivacaine; ANAESTHESIA; CONDUCTION; nerve block; brachial plexus.

© 2001 European Academy of Anaesthesiology