Axillary brachial plexus block is commonly used for upper limb surgery. Neurostimulation remains the gold standard technique for axillary brachial plexus block (axillary block) placement in our country. However, as demonstrated by some authors, nerve stimulation-assisted regional anaesthesia (neurostimulation) is sometimes recognized as an uncomfortable technique to place the axillary block, with patients identifying electrical stimulation as the most unpleasant moment of the block performance.1–3 In 2009, ultrasound-guided regional anaesthesia (ultrasound) has become an increasingly popular technique among regional anaesthesiologists. Ultrasound, which does not require electrical stimulation, should theoretically improve comfort during axillary block placement. However, depending upon the approach used for ultrasound, that is, the out-of-plane (OOP) approach (OOP) or the in-plane (in-plane) approach, the subcutaneous or intramuscular needle course varies, which may affect patient's comfort. Although many authors have assessed local pain and discomfort during axillary block performance, comparative data concerning the comfort of the patient are scarce. We have hypothesized that patient's comfort during axillary block placement wound be influenced by the technique of regional anaesthesia. We compared the comfort of the patients during axillary block placement using neurostimulation and two ultrasound approaches: OOP and in-plane.
Patients and methods
After approval by the local ethics committee, 120 American Society of Anesthesiologists (ASA) status I–III informed patients undergoing elective surgery of the forearm, wrist, elbow or hand wrote their consent to participate in this prospective study. No premedication was given to the patients.
Pregnant women, patients younger than 18 years old and those with any contraindication to regional anaesthesia, such as known allergic reaction to local anaesthetics, local infection at the site of puncture and treatment or disease that severely affects coagulation, were excluded from the study.
Sealed envelopes opened upon arrival in the preoperative holding area were used to randomize the patients into three equal groups of 40 patients: neurostimulation, OOP and in-plane. After standard monitoring systems including noninvasive arterial blood pressure, heart rate and haemoglobin arterial oxygen saturation were attached, an intravenous catheter was secured in the opposite forearm. Four senior anaesthesiologists experienced in both neurostimulation and ultrasound techniques performed the blocks. During the procedure, patients were placed in the supine position with the arm abducted at 90°.
Procedure of axillary blocks placement
Participants were requested to place axillary block with only two cutaneous punctures, using no more than 40 ml of local anaesthetic solution containing 1.5% mepivacaine.
Neurostimulation-guided regional anaesthesia
After antiseptic preparation of the axillary fossa, a 22-gauge, 30° bevel, 50-mm insulated needle (Stimuplex; B Braun, Melsungen AG, Germany) was inserted. The nerves' location was performed using a nerve stimulator (Stimuplex HNS 12; B Braun), with a stimulating frequency of 1 Hz and a pulse duration of 100 μs. The intensity of the current was initially set at 1.5 mA to search for motor responses. The arterial pulse was palpated at the level of the major pectoral muscle crossing the axillary fossa, and the needle was inserted first superior to the artery to locate the median and the musculocutaneous nerves and then inferior to locate the radial nerve. The nerves were located according to specific motor-evoked muscular contractions as follows: arm flexion, musculocutaneous-type response; radial-type response, wrist and finger extension; median-type response, wrist, second and third finger flexion and pronation. For each of these responses maintained while lowering stimulating current intensity to 0.5 mA, 15 ml of the local anaesthetics solution was injected for the median and radial nerves, and 5 ml for the musculocutaneous nerve.
Ultrasound-guided regional anaesthesia
In the ultrasound-guided regional anaesthesia groups, the axillary fossa skin area was applied with a sterile gel (Sterile Aquasonic Ultrasound Gel; Parker Laboratories, Inc. Hellendoorn, The Netherlands) after antiseptic preparation of the skin. A linear 8–13 MHz ultrasound probe (LOGIQe; GE Healthcare, Piscataway, New Jersey, USA) was prepared in a sterile fashion covered with a gel mattress and a sterile cover (Transducer cover; Civco Medical Solutions, Kalona, USA) and was placed transversally against the upper, inner arm just bellow the axillary fossa. Before performing the block, the axillary fossa and the arm were scanned to identify the targeted axillary nervous structures and the axillary vessels. In the ultrasound groups, the physicians used the hydrolocalization principle to control the needle tip progression4,5 towards each identified axillary nerve. In the in-plane group, the needle was first inserted above the axillary artery and advanced through the biceps muscle along the ultrasound beam. In the OOP group, the needle was first inserted at the brachial canal above the axillary artery, and the needle was advanced perpendicularly to the ultrasound beam. The ulnar, radial, median and musculocutaneous nerves were blocked separately with 5–7 ml of local anaesthetic for each nerve. The proper spread of the local anaesthetic around the targeted nerves was continuously evaluated under sonographic vision, and the needle tip position was continuously adjusted with minimum movements during injection under sonographic vision to optimize the impregnation of nerve structures.
Recordings and measurements
Duration of axillary block placement was measured as the time elapsing between needle insertion and to last removal of the needle from the patient's arm. Maximal insertion depth of the needle was recorded.
An independent observer unaware of the technique used to locate and progress towards the axillary nerves tested the sensory block, recorded maximal pain intensity resulting from block placements, questioned the patients about possible unpleasant events linked to the technique of regional anaesthesia and assessed patient's satisfaction.
The sensory examination (pinprick and cold responses) performed 30–45 min after the last injection of mepivacaine was evaluated for the sensory blocks of the musculocutaneous, median, radial, ulnar and medial cutaneous of the forearm nerves. A successful block was defined by the presence of a complete sensory block (no sensation at all) of the five major nerves' distributions of the arm and forearm (ulnar, radial, median, musculocutaneous and medial cutaneous of the forearm). Failure of the block was considered if one (or more) of these distributions was not blocked. In case of failure of the block, selective supplementation was performed at the humeral canal or more distally depending on surgery location. If the patient complained of any pain during surgery, we planned inducing general anaesthesia. Just before the start of surgery, the observer asked each patient to rate maximal pain intensity resulting from both peripheral intravenous venous catheter and block placement using a 100-mm visual analogue scale (VAS: 0, no pain–100, maximum or worst imaginable).
Then the patients were asked: ‘have you experienced an unpleasant event during axillary block placement?’ In case they responded yes to the question, they were solicited to declare which (if any) of the following event list read to the patient – cutaneous punctures, needle passes through the subcutaneous tissues, local anaesthetic injections, electrical nerve stimulations, axillary fossa pressure and tourniquet-induced discomfort – was considered as an unpleasant event and to identify the most unpleasant event.
Immediately after the surgery completion, patient satisfaction was also assessed using a four-point scale: unsatisfied, acceptable, satisfied and very satisfied. The patients were also asked whether they would accept the same block for the same surgery of the contralateral limb.
An original score of comfort was built to evaluate for the most comfortable technique of axillary block placement. This score of comfort was based upon a survey that we had performed before the study was programmed. In this postal survey proposed during postoperative homecare, patients were asked to define the comfort of the locoregional technique that had been used for their surgery. The patients had to identify and rank the three main items of a comfort score among possible propositions. We have used the three items selected in the postoperative patient's survey in the present study. The score of comfort included three criteria: maximum pain intensity perceived during block placement, the occurrence of unpleasant events during the procedure and the satisfaction of the patient.
For each criterion, a value of 0 or 1 was attributed depending upon maximum pain intensity measurements (VAS ≤30, 1; VAS >30, 0), unpleasant events occurrence (no unpleasant event, 1; one or more unpleasant event, 0) and patient's satisfaction assessment (satisfied or very satisfied, 1; acceptable or unsatisfied, 0).
The individual score of comfort was calculated as the sum of the values attributed to each of the three criteria. Procedure of axillary block placement resulting in a comfort score of 3 and 2 was considered as very comfortable and comfortable, respectively.
Preoperative holding area, operating room and postanaesthesia care unit (PACU) complications (blood vessel puncture, intravascular injection and transient paresthesia) were noted by the anaesthesiologist who was in charge of the patient. The surgeon investigated late complications during the follow-up visits, including persistent local pain haematoma or infection and dysesthesia, defined as abnormal sensory or motor symptoms related to one of the nerve's distributions affected by the axillary block.
On the basis of the postal comfort survey that we conducted, 98 patients considered that maximal pain intensity perceived during the regional anaesthesia procedure was the main criterion of their own comfort. This study was powered to demonstrate 30% difference in maximal pain VAS [mean (SD): 36 (19), 95% confidence interval (CI) 35–43; α = 0.05 and β = 0.2] between neurostimulation and the two ultrasound groups. A sample size of 40 patients randomized in each group was requested to demonstrate the hypothesis. The study was continued until at least 40 patients were included in each group. Statistical analysis was performed by using the StatView software (V5; SAS Institute, Inc., Cary, North Carolina, USA). Values are expressed as means ± SD, medians (range) or percentages (number) unless specified. Characteristics of patients were compared with an analysis of variance. A Dunnet correction test for multiple group comparison was applied using neurostimulation as a control group. Chi-square and Fisher exact tests were used to compare percentages. P values of less than 0.05 were considered statistically significant.
The study was completed 4 months after the first patient was included. Demographics and surgical data of the patients are presented in Table 1. The success rate of axillary block was 100% in each group. No patients requested general anaesthesia. Patient's perception and comfort evaluation data are presented in Table 2. Comfort of the patient significantly differed between the groups. In the OOP group, 55% (22/40) and 25% (10/40) of the procedures were very comfortable and comfortable, respectively, as compared with 32% (13/40) and 20% (8/40) in the in-plane group and 25% (10/40) and 8% (3/40) in the neurostimulation group, respectively. All patients in the ultrasound groups and 39 patients of the neurostimulation group were very satisfied with the regional anaesthesia technique used and would accept the same block in case of opposite arm surgery. Peripheral catheter insertion resulted in similar low pain intensity in the three groups. Mean VAS resulting from axillary block placement significantly differed between the groups with significantly fewer patients demonstrating VAS of more than 30 mm in the OOP group as compared with the other two groups. Although the most unpleasant component of axillary block placement differed between the three groups, significantly more patients of the neurostimulation and in-plane groups perceived an unpleasant event as compared with the OOP group. Characteristics of axillary block placement are presented in Table 3. Duration of axillary block placement was significantly shorter in theOOP group as compared with that of in-plane and neurostimulation groups. The maximal insertion depth of the needle was significantly smaller in the OOP group as compared with that of the in-plane and neurostimulation groups.
We have prospectively compared ultrasound and neurostimulation techniques of regional anaesthesia with regard to patient's comfort during axillary block placement. We demonstrated that ultrasound approaches were less painful and were more comfortable than neurostimulation. Moreover, we showed that among ultrasound approaches, patients were more comfortable with the OOP than with the in-plane.
A block was arbitrary defined as comfortable if it was placed with low pain intensity, without perception of any unpleasant event, resulting in a patient either satisfied or very satisfied with the regional anaesthesia technique. Interestingly, almost all, but one, of all the enrolled patients were either satisfied or very satisfied with the regional technique that we employed to place axillary block and would accept the same technique in case they had to be operated for the contralateral limb. On the contrary, the incidence of patients free from unpleasant event during block placement seemed to be a determining factor influencing patient's comfort during regional anaesthesia techniques. Indeed, the incidence of patient who did not experience an unpleasant event was almost two-fold higher in the OOP group as compared with the neurostimulation group. Similarly, the main criteria that we selected as a primary endpoint to evaluate for the comfort, which was maximum pain intensity during axillary block placement, significantly differed between the groups. We demonstrated a pain intensity reduction of 45 and 28% with OOP and in-plane approaches, respectively, as compared with neurostimulation. Moreover, the incidence of patients demonstrating VAS of more than 30 was significantly increased with neurostimulation technique as compared with that of both ultrasound approaches. The reasons for increased pain intensity during neurostimulation are numerous. First, the depth of insertion of the needle is one of the parameters that has possibly affected pain intensity measurement.1,6 We have observed that ultrasound in-plane and neurostimulation techniques, requiring the highest needle insertion depth, were associated with increased pain intensity during block placement. Second, the duration of axillary block placement has also possibly affected pain perception,7 as confirmed by several studies8–10 showing significantly shorter axillary block placement duration with ultrasound as compared with other regional anaesthesia techniques including neurostimulation. Third, the occurrence of unpleasant events may have participated in higher VAS measurements in the neurostimulation group. Finally, it was suggested that ultrasound requested a lower number of needle passes than neurostimualtion.11 Although we did not measure the number of needle subcutaneous manipulations, we assume that lowering the number of needle passes during shorter ultrasound procedures might have promoted less painful axillary block placements.
Our results also showed that electrical stimulation was qualitatively considered as the main unpleasant event during axillary block placement using neurostimulation. Several studies1–3,6,7,12,13 have already assessed global discomfort during axillary and humeral blocks using multiple nerves neurostimulation. Almost all of these trials identified electrical stimulations as the main cause of discomfort for the patients. This is certainly one of the reasons explaining why the comfort score that we calculated in the neurostimulation group was inferior to that of the ultrasound groups.
Our data also demonstrated significant difference in the score of comfort between the two ultrasound approaches. We showed that the OOP was more comfortable than the in-plane approach, mainly because the latter promoted higher pain intensity and resulted in higher unpleasant event report rate. We believe that as compared with the OOP approach, the higher pain intensity measured in patients and the increased number of unpleasant events reported are both closely associated with the length of subcutaneous needle course imposed by the in-plane approach. Indeed, we showed that axillary block placement using the in-plane approach requested a long needle progression through the biceps muscle. Interestingly, the humeral block, which requires a long progression of the needle in the biceps muscle, was also correlated with high pain scores.1,6 Detailed analysis of the causes of unpleasant event reports confirms this assertion. In the in-plane group, 77% (20/26) of unpleasant event reports are related to the needle progression in subcutaneous tissues as compared with 33% (6/18) in the OOP group. Then, our results suggest that long intramuscular needle course requested by the in-plane approach promoted more discomfort and possibly increased pain intensity for the patients.
Surprisingly, although the total volume of anaesthetic solution injected towards nervous structure was higher in the neurostimulation group, only one out of 40 (2%) patients reported local anaesthetic injection as an unpleasant event as compared with 61% (11/18) and 23% (6/26) of ultrasound patients using OOP and in-plane approaches, respectively. This observation suggest that the volume is certainly not the only variable affecting unpleasant sensation during injection of local anaesthetic solution towards nervous structure, but the site of injection is also of concern.14 Of interest, almost all unpleasant injections concerned an upper injection targeting the musculocutaneous nerve in the biceps muscle. Ultrasound techniques have promoted a new concept of selective injection using the ‘diffusion concept’, allowing reduction of the volume of local anaesthetics. However, blocking the musculocutaneous nerve requires injecting a high volume (5–7 ml) of solution in a low compliance tissue compartment. Thus, the resulting hydrodissection pressure may have unpleasant sensations during the diffusion of the anaesthetics solution towards the targeted nerve.
Our study has limitations. First, although we blinded the investigator evaluating the sensory quality of the blocks to the technique used to place the axillary block, the same participant questioned the patient for comfort assessment. By recording unpleasant events occurrence, the investigator might have been informed of the patient's group in case he responded ‘yes, electrical stimulations’ to the question that he was asked. This limit in the blinding process might have affected our results. Second, we have used an original comfort score, which has not been validated in the literature. However, this comfort score is based upon real-life patient's data exploitation. We had proposed that the patients build their own score in order to evaluate for our professional practice quality evolution. By using this score, we observed that benzodiazepine intravenous injections were not any more requested to obtain highly comfortable procedures by using the ultrasound techniques. Moreover, our comfort score is made of three criteria, which have already been investigated in most studies on this particular topic.
Our study in 120 unpremedicated patients demonstrated that ultrasound is less painful and more comfortable than neurostimulation to place the axillary block. Moreover, we showed that among ultrasound approaches, the OOP is more comfortable than the in-plane.
Support for this study was received from the Anesthesia and Intensive Care, Department of Jean Verdier University Hospital of Paris (APHP), Bondy, France.
This trial was funded by departmental sources.
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