Infraclavicular brachial plexus catheters provide intraoperative anaesthesia as well as control post-operative pain [1]. Anaesthesiologists use ultrasound (US) with or without peripheral nerve stimulation (PNS) for the placement of these blocks. When comparing the two modes of placement, most authors have looked at performance time and success in single injection blocks with small sample size [2-5]. We do not know if either technique alone improves success when used to place infraclavicular catheters.
We designed this study to test the primary hypothesis that placing infraclavicular catheter using US guidance alone improves block success when compared with PNS guidance. Secondary hypotheses included reduced procedure time and better patient satisfaction with US guided infraclavicular catheter placement. METHODS We performed this prospective, randomised, single blind study after gaining approval by University of Western Ontario research ethics committee and registration with clinicaltrials. gov (NCT01136447).
We approached adult patients of ASA physical status 1-3, aged between 18 and 80 years and scheduled to undergo elective elbow or forearm surgery under brachial plexus block. Exclusion criteria were coagulopathy, severe cardiopulmonary disease, local anaesthetic allergy, injection site infection, body mass index greater than 35 kgm-2, known neuropathy, uncontrolled diabetes mellitus, language barrier and chronic opioid use (more than six months). All patients gave written, informed consent for study participation.
Between September 2010 and February 2013, we randomly allocated 210 patients into two study groups according to a list of computergenerated numbers held in opaque envelopes until the procedure. Group allocations and randomisation codes were in a password-protected file with no access to the investigators. Senior attending anaesthetists (SD, KA, PA, SG) who had substantial expertise in both techniques placed all block catheters in a dedicated block room with full resuscitation facilities.
After intravenous access and routine monitoring (continuous electrocardiogram, oxygen saturation, non invasive blood pressure and oxygen via nasal prongs), patients received midazolam (1-3 mg) and fentanyl (25-100 ug) for anxiolysis, if necessary. The patients’ position was supine with adducted arm, flexed elbow, hand pronated and resting on the abdomen. For blinding, all patients had the coracoid process and block entry site marked. For both groups, we used 100 mm 18 g stimulating needle and catheter kit (Pajunk®, Geisingen, Germany). All patients received 40 ml of mepivacaine 1. % with 1:400,000 adrenaline.
An observer not involved in the study recorded procedure details. For needle and catheter insertion in group US, we used Sonosite S Nerve” (Sonosite, Bothell, WA) or GE Logiqi (General Electric Healthcare, Little Chalfont, UK), using the in-plane approach. Position of 25 mm (Sonosite) or 38mm (GE) high frequency linear array probe was medial to the coracoid process, in a parasagittal plane. We presumed the position of posterior cord to be inferior to the axillary artery (6’O clock position) and had the needle positioned near it.
One to two millilitres of 5% dextrose (D5W) confirmed needle tip position before introducing the block catheter. We advanced the catheter, 1-2 cm beyond the needle tip. The catheter tip location was again confirmed with 1-2 ml of hand-agitated D5W using colour doppler with appropriate gain and pulse repetition frequency (PRF). The authors have described this technique, elsewhere [6]. Delivery of the entire dose of mepivacaine was through the catheter in five ml aliquots, ensuring the spread around the artery with ultrasound imaging.
We secured the catheter with liquid adhesive (Dermabond AdvancedTM, Ethicon Inc, Somerville, NJ) and applied occlusive dressing (TegadermTM, 3M Canada, Canada). For needle and catheter insertion in group NS, we used coracoid approach, described earlier [7]. The point of needle entry was two cm medial and two cm inferior to the marked coracoid process. The direction of needle was perpendicular to the surface on the horizontal-supine patient.
We used a peripheral nerve stimulator (PNS) (Pajunk®Geisingen, Germany) with a 0. 6 mA current output and a progressive decrease and disappearance at 0. mA (pulse width 0. 1 ms, frequency 2Hz) to locate the brachial plexus. We aimed for motor responses in the posterior cord or combined posterior and lateral cord territory. Injection of 1-2 ml of D5W created a potential perineural space without abolishing neurostimulation. This technique has been described earlier [8]. Using PNS and maintaining the evoked motor responses, we advanced a stimulating catheter, 1-2 cm beyond the needle tip. If the responses disappeared, we removed the catheter, reconfirmed the motor response with the needle and then reintroduced the catheter.
Delivery of the entire dose of mepivacaine was through the catheter in five ml aliquots and dressing applied, as described above. We selected definitions, a priori. For group US, procedure time was the time US probe touched the skin to the end of local anaesthetic injection. For group NS, procedure time was the time from needle insertion to the end of local anaesthetic injection. This measurement did not include time required for fixing the catheter and application of dressing. Vascular puncture was presence of blood in the needle or aspiration of blood through the catheter.
Patients from group NS would be crossed over to group US if there were no motor responses for 15 minutes. The primary outcome was time to sensory block success. Secondary outcomes included procedure time, percentage of complete blocks at 30 minutes and postoperative patient satisfaction. A blinded researcher (AB, JM, JY), unaware to the group assignment and not present during the block placement did the motor and sensory block assessment every 5 min for 30 minutes.
Sensory block was ested in the skin areas supplied by the upper limb terminal nerves (median, ulnar, musculocutaneous and radial) using a 3point scale (O=normal sensation; 1=loss of some cold sensation; and 2=complete loss of sensation to ice). Motor block was tested at the same time as sensory block by thumb opposition (median nerve), finger adduction (ulnar nerve), elbow extension (radial nerve), and elbow flexion (musculocutaneous nerve) using a 3point scale (O=normal movement; 1= decreased movement and unable to perform against resistance; and 2=complete loss of motor power). All incomplete blocks at 30 min were treated as failures.
As all assessments were complete before the patient entered the operating room, intraoperative anaesthetic management was not standardised, but left to the operat ting room anaesthetist’s discretion. After surgery, patients recovered in the post anaesthesia care unit (PACU). Before removal, all block catheters received a bolus with local anaesthetic drug in the PACU and the spread noted by ultrasound assessment. Not being part of primary or secondary assessments, intraoperative conduct of anaesthesia, postoperative block evaluation and detailed PACU data is not presented.
The blinded researcher did follow-up telephone interviews at day 1, 7 and 14 after surgery and questioned patients about pain, satisfaction and any new onset and block related neurological impairment. For pain intensity measurement, we used a numeric rating scale of 0-10 (O=no pain, 10=worst pain possible). For satisfaction, we used a ten point Likert scale [9] of 0-10 (0=extremely dissatisfied, 10= very satisfied). If we could not contact any patient by phone on day 7 or 14 per protocol, a call was made everyday until they responded or attended the follow-up surgical clinic.
We based the power calculations on empirical clinical observations and previous study by the authors [10]. Assuming a mean (SD) block failure of 25% at 30 minutes in control group (standard PNS technique), we estimated that a sample size of 105 participants per group would be required (80% power to detect a 15% reduction in block failure at a two tailed significance of 0. 05 with 5-10% drop out). Data is presented as mean (SD), proportion or number. We used unpaired t-test to compare primary outcome measure (time to sensory block) and other categorical variables.
We used chi-square test and Fisher’s exact test to analyse nominal variables, where appropriate. For time to success, to include all subjects, we used a ‘time to event’ or ‘survival approach. For comparison of failure at 30 min, we used a log rank test. For satisfaction, we applied both parametric (unpaired t test) and non-parametric (Wilcoxon 2-sample) tests. An independent statistician not involved in the study performed all calculations using SAS version 9. 3 (SAS Software, Cary, NC). Analysis of any crossed over patients was with intention to treat.
RESULTS We screened 236 and recruited 210 patients (Figure 1: consort diagram). Two hundred and three patients completed study assessments and are included in the analysis. One patient had incorrect assignment to group US. Three patients from group NS crossed over to group US. Two patients had exclusion criteria (ASA 4) but included in analysis. Both groups had patients with similar characteristics (Table 1). Proportion of complete blocks in the 30 min period is in figure 2. Block performance time was significantly shorter in group US (7. 19 (2. 5) min vs. 9. 64 (3. 6) min).
All other times were similar (Table 2). At 30 min, a complete block was not established in 19 patients (group US) and 17 patients (group NS). We contacted patients on day 1, 7 and 14 after surgery (Table 3). We could not contact 11 patients on day 7 (8 in group US, 3 in group NS) and 149 patients on day 14 (75 in group US, 74 in group NS). We could contact all these patients, subsequently. Seven patients from group US and five patients from group NS reported new sensory/motor deficit on day 14. We followed them (outside observation period) and all deficits had resolved by 1 month.