The ultrasound-guided posterior approach to the axillary brachial plexus block for postoperative analgesia of fractures in the forearm: a case report

¹Department of Anaesthesia, Charlotte Maxeke Johannesburg Academic Hospital, University of the Witwatersrand, Johannesburg, South Africa, ²Department of Anaesthesia, Faculty of Health Sciences, School of Clinical Medicine, University of the Witwatersrand, Johannesburg, South Africa

^&Corresponding author
Okitolela Scotty Tambwe, Department of Anaesthesia, Charlotte Maxeke Johannesburg Academic Hospital, University of the Witwatersrand, Johannesburg, South Africa

Introduction    

The axillary brachial plexus block is a technique where local anaesthetic is deposited within the axillary fossa to provide a regional block to the areas of the upper limb, including the elbow down to the hand, innervated by the radial, median, ulnar, and musculocutaneous nerves. In 1981, Abramowitz and Cohen made a significant advancement in ultrasound-guided regional anaesthesia (UGRA) by introducing the use of Doppler during difficult axillary blocks to make easy the localisation of the axillary artery when performing the block [1,2]. Christophe et al. [3] reported numerous topographic variations of the brachial plexus branches that need to be considered when planning to perform an axillary brachial plexus block. Of those variants, one was found to be the most predominant and was encountered in 64.7% of the studied population, showing the radial nerve located posterior and medial to the artery. Wingate et al. [4] described the radial nerve as the most difficult to identify and to reach compared to the ulnar, median, and musculocutaneous nerves because of its location deep and medial to the axillary artery (AA). The following is the approximate topographic representation of nerves in the predominant variant: i) radial nerve at around 5 to 6 O'clock; ii) ulnar nerve at around 2 O'clock; iii) median nerve at around 11 O'clock.

In this variant, the Musculocutaneous nerve is usually noted at around 9 o'clock, a bit eccentric from the axillary sheath towards a plane between the biceps and the coracobrachialis muscle. The Ultrasound-guided posterior approach to the axillary brachial plexus block (UGPAX) shows a mirror sonographic anatomy of the predominant variant as described in the classic approach, where the 4 nerves were visualised at approximately the following reciprocal positions (Figure 1): i) radial around 7-8 O'clock; ii) ulnar nerve around 11 O'clock; iii) median nerve around 12-1 o'clock; iv) musculocutaneous nerve around 4 o'clock, still eccentric to the rest of the neurovascular bundle and posterior to the artery and oriented within the coracobrachialis and biceps muscles. The primary aim of this case report was to evaluate the intra- and postoperative efficacy and effectiveness of the UGPAX for procedures of the elbow, forearm, and the hand and explore possible topographic and anatomical variations that could be encountered during the performance of this approach (Figure 2).

Patient and observation     

Patient information: a 13-year-old male weighing 34.1 kg, ASA 1, presented with an open fracture of his right arm requiring surgery.

Symptoms and concerns: patient displayed an anxious demeanour and was accompanied by his mother. Overall, the patient was clinically stable. He came in with his right arm immobilised in a back slab. He reported mild to moderate pain in the arm, and no neurological deficit was noted. Although it was reported that the child was starved, our main concern remained a potential aspiration risk due to anxiety and pain, which could have decreased his gastric emptying.

Medical history: the patient was healthy with unremarkable past medical and surgical history.

Clinical findings and assessment: his clinical examination yielded no abnormal findings. His initial vitals were as follows: i) BP: 115/74 mmHg ii) pulse rate: 81 beats per minute iii) saturation: 96%.

Timeline: patient had fresh fractures of the forearm sustained a day before surgical and anaesthetic interventions.

Diagnostic and assessment: in keeping with the radiographic findings and the urgency to reduce the fractures, the patient was booked for debridement, washout, and open reduction and internal fixation (ORIF) of radius - ulna fractures. During the preoperative assessment, there were no contraindications for an upper limb regional block. He was deemed a good candidate for an ultrasound-guided axillary brachial plexus block, and consent was obtained to perform the block.

Therapeutic intervention: he was admitted to theatre for the procedure, and standard ASA monitors were placed. An intravenous line was sited, and a general anaesthetic was done with a rapid sequence induction due to the emergent nature of the case and potential aspiration risk. The airway was secured with a size 6.0 (ID) endotracheal tube, 18 centimetres at the teeth. The patient was ventilated using intermittent positive pressure ventilation (IPPV), specifically in pressure-controlled mode with the following settings: i) tidal volume: 320 mL; ii) PEEP: 5 cmH₂O; iii) FiO₂: 0.5; iv) I:E ratio: 1:2; v) respiratory rate: 12 to 18bpm; vi) fresh gas flow: 1l/min. Pressure points were checked and protected, and the patient was actively warmed with a forced air warming device. Shortly after the intubation, the patient's right hand, still supported by a backslab, was positioned beneath the occiput in a "stargazer position," with the arm abducted at an estimated angle between 90° and 105°.

A scan of the axillary area was done with the probe in the sagittal position and the indicator directed towards the anterior fold. The axillary artery was identified on its short axis at about 7mm from the skin and the conjoint tendon at 10mm from the skin, with the rest of the neurovascular structures within that interspace. The right axillary area was cleaned with chlorhexidine gluconate 0.5% and allowed to dry completely. A pre-calculated total volume of 14ml 0.2% bupivacaine with adrenaline (28mg) was drawn in a 20ml syringe. A 22G, 50mm Stimuplex®A insulated nerve block needle was mounted on the syringe and flushed in preparation for the block. After sterile gel application within the axillary fold, a linear array ultrasound probe with a frequency ranging between 3.4-12.6 MHz was placed initially as if performing the classic approach, then rotated 180° clockwise and oriented in the sagittal position towards the posterior axillary fold. Once the axillary artery was visualised and the radial, median, ulnar, and musculocutaneous nerves were all mapped around the artery at different positions, like around a clock, the insulated nerve block needle was inserted in-plane about 1cm posterior to the ultrasound probe and was advanced straight at an angle of approximately 10° towards the radial nerve located at about 7 o'clock, with the needle shaft and tip kept in view on the screen. Local anaesthetic was administered in a circumferential spread around the axillary artery. The needle tip was repositioned at an angle of less than 15° towards 11 and 12 o'clock, where another 5mls was injected at the vicinity of the ulnar and median nerves.

Thereafter, the ultrasound probe was slid anteriorly within the axillary fold and, after identifying the musculocutaneous nerve at around 4 o'clock, the block needle was inserted at an approximate angle of less than 20°, and the remainder 4mls of the local anaesthetic was injected. At each needle repositioning and before injecting local anaesthetic solution, an increase in resistance was assessed to prevent inadvertent intraneural injections, detect potential vascular injuries, and prevent the administration of local anaesthetic into the systemic circulation. The right upper limb was repositioned on an armrest in approximately 60° abduction. The backslab was removed, the right hand was aseptically cleaned, then draped, and the surgery commenced. No tourniquet was applied to the arm for the whole duration of the surgical procedure. The patient remained hemodynamically stable throughout the intraoperative period, and no significant fluctuations in blood pressure or heart rate were observed. The intraoperative multimodal analgesia regimen included: i) 60 mcg of fentanyl administered 3 minutes before induction of general anaesthesia. ii) 4 mg of dexamethasone given right after induction of general anaesthesia. iii) ∼15mg/kg of paracetamol (520mg) administered right after the regional block was done and before the surgery started. At the end of the surgery, a plaster of Paris (POP) cast was placed extending from his mid-arm to the hand. The surgery time was 54 minutes, and the total duration of anaesthesia was 108 minutes. The patient's neuromuscular blockade was reversed; he was extubated and transferred to the recovery room, where a pain assessment was done before the patient was discharged to the ward.

Further care and follow-up: this pain assessment included the Numerical Rating Scale (NRS) and the Face Pain Scale-Revised (FPS-R), yielding the following findings 2 hours after the regional block: NRS: 0 and FPS-R: 0, with both sensory and motor blocks still present. The sensory function was assessed using light touch, and motor block by finger opposition and spreading. The patient was followed up in the ward using the same pain assessment tools at 5 hours and 10 hours post-administration of the block. The following were the findings: i) at 5 hours post-block, i.e., 3 hours post-recovery: NRS=0 and FPS-R=0 with complete sensory and motor blocks; ii) at 10 hours post-block, i.e., 8 hours post-recovery: NRS=0 and FPS-R=0 with complete sensory block and partial motor block. A telephonic follow-up was done 16 hours postoperatively, and the patient was reported to be comfortable and pain-free by the day nursing team present in the ward at the time. No motor block assessment was done. The patient received doses of paracetamol and ibuprofen at 7, 13 and 20 hours postoperatively as part of a multimodal analgesia regimen. No opioid drugs were ever required or administered in the ward. The patient was physically reviewed again on day 1 postoperatively, at almost 30 hours post regional block, and was still comfortable with full recovery of the right upper limb's motor and sensory functions. The NRS was rated as 0 and the FPS-R at 1.

Outcomes: during all our follow-ups, we've noted that the UGPAX has produced reliable and effective sensory blocks in the immediate and early post-operative periods in this case.

Patient's perspective: the patient stated the following in both the immediate and early postoperative periods: "I am comfortable. I do not feel my arm at all and do not have any pain".

Informed consent: this case report was prepared with the written consent of the patient's mother, which can be provided upon request.

Discussion     

There are technical and procedural differences between the classic and the UGPAX approaches to achieve the axillary brachial plexus block. Wingate et al. [4] described the classic ultrasound-guided axillary brachial plexus block as adequate and practical for beginners, using two possible approaches: the in-plane and the out-of-plane. The classic in-plane approach consists of placing and transversally directing the ultrasound probe within the axillary region with the marker orientated up compared to the plane of the body as the patient is lying supine. The ultrasound transducer is maintained at the intersection of the pectoralis muscles and the biceps brachii. The operator could sit on either side of the patient's abducted arm, i.e., at the head end or facing the patient, while the patient's arm and elbow are abducted and positioned at 90°. The block needle is inserted at the upper lateral border of the pectoralis major muscle. However, during the performance of the UGPAX, the patient's arm is abducted in a stargazer position, with the plaster of Paris still on the affected limb, to allow wider exposure and optimal working area within the axillary fold. This permits a displacement of the neurovascular bundle more superficially towards the skin as described by Yoshida et al. [5] when employing the proximal approach for ultrasound-guided infraclavicular brachial plexus block. The ultrasound probe is rotated 180° clockwise or anticlockwise within the axillary fold during the pre-scanning and maintained at that angulation during the procedure. A reverse sonoanatomy of the classic ultrasonographic view is noted where the axillary vein, in this case, is almost antero-laterally situated compared to the needle entry point and the rest of the neurovascular bundle.

Subsequently, the block needle is viewed and advanced within the latissimus dorsi and teres major muscles. The radial nerve is easily reachable and is not located deep to the artery as opposed to the dominant variant in the traditional approach. Also, this approach has the potential advantage of allowing easy deposition of local anaesthetic to produce an adequate circumferential spread within the axillary sheath and provide blocks to the radial, the ulnar and the median nerves, possibly with a single or eventually after multiple needle passes. An additional injection around the musculocutaneous nerve is required to complete the block by sliding the ultrasound probe anteriorly within the fold while the needle is inserted in-plane at a given angle, depending on the patient's body habitus, or by inserting the needle from the anterior fold in an in-plane technique through the pectoralis major muscle to easily reach the musculocutaneous nerve located between the coracobrachialis and biceps muscles. The transducer indicator is maintained and still oriented initially towards the posterior fold in this case. In this case, the needle was inserted at a shallow angle.

Additionally, the UGPAX offers convenient access to the intercostobrachial and medial brachial cutaneous nerves due to their subcutaneous locations and not part of the brachial plexus. This approach allows extra coverage of the upper medial and posterior regions of the arm, which can be particularly beneficial when tourniquet application is required. Chang et al. [6] reported that, when utilizing ultrasonography guidance to examine the scanning techniques of upper and lower extremity cutaneous nerves, the intercostobrachial and medial brachial cutaneous nerves can be efficiently accessed by positioning the ultrasound probe directly above the latissimus dorsi and teres major muscles due to their subcutaneous locations. We also postulate that the ultrasound-guided posterior approach (UGPAX) could also be indicated when there is noticeable tissue damage affecting the ipsilateral neck and anterolateral chest regions, specifically at the needle entry point through the pectoralis major border of the affected limb, or when there are conditions affecting the anterior border of the axillary fold, i.e., the apex of the axilla, such as burns or wounds.

When considering anatomical variations within the axillary fossa, tributary veins may be visualized during this approach, and the axillary vein is observed lateral and anterior to the remainder of the axillary neurovascular bundle. Satapathy et al. [2] recommend that exercise caution when performing the ultrasound-guided axillary brachial plexus block, ensuring minimal pressure is applied with the ultrasound probe so that the patency and position of the axillary vein are consistently preserved. We believe that this precaution allows real-time visualization of venous structures, enables efficient needle redirection around them, and facilitates precise targeting of a specific brachial plexus branch located medial to the axillary vein, thereby minimizing accidental vascular puncture and unintended systemic administration of local anaesthetic.

Finally, and as outlined above, the routine postoperative opioid-free analgesia regimen with a combination of simple analgesics and non-steroidal anti-inflammatory drugs (NSAIDS) was commenced 9 hours after the performance of the UGPAX, i.e. an hour before our third physical block assessment and follow-up in the ward. The sensory block was still effective as the NRS and FPS-R scores remained 0 at 10 hours post regional block and the patient was still comfortable up to 16 hours at the time of our telephonic follow-up. The additional analgesia could have acted as a potential confounder but would not have impacted the effectiveness of the sensory block induced after the performance of the UGPAX.

Conclusion     

The UGPAX represents a potentially innovative approach that requires further training and studies to establish its efficacy compared to the described traditional approach. While the UGPAX has shown its effectiveness to be used as a potential alternative approach, the recognition of topographic and anatomical variations of the neurovascular bundles within the axillary region remains crucial. This will direct the operator in maximising block coverage during the performance of this procedure and avoid the advent of complications such as nerve injuries or vascular punctures.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Okitolela Scotty Tambwe: regional block procedure and performance, data collection, manuscript and case report writing. Nana Yaa Fening: supervision and manuscript review. All authors have read and approved the final version of this manuscript.

Acknowledgements     

This case report was published with the written consent of the patient's mother, and we would like to express our sincere gratitude both to her and the patient.

Figures     

Figure 1: A, B) illustrating different positions of the brachial plexus branches around the axillary artery as around a clock seen in the dominant variant (64.7%), with image displaying the mirror image of A (classic); AA: axillary artery; M: median nerve; MCN: musculocutaneous nerve; R: radial nerve; U: ulnar nerve

Figure 2: mirror image of the classic sonoanatomy of the dominant variant of the axillary neurovascular bundle showing: AA: axillary artery, AV: axillary vein, V: vein, RN: radial nerve, UN: ulnar nerve, MN: median nerve, MCN: musculo cutaneous nerve, CT: conjoint tendon, BM: biceps muscle, CBM: coraco brachialis muscle, LDM: latissimus dorsi muscle; orange arrow showing block needle's different entry points and sides

References