Sensorimotor Block Dynamics and Hemidiaphragmatic Palsy: Selective Trunk Block vs Supraclavicular Brachial Plexus Block

Ultrasound guided supraclavicular brachial plexus block (BPB) has been extensively studied and recommended as a sole anesthetic for upper extremity surgeries. The supraclavicular BPB is often touted to be the 'spinal of the upper extremity' as it produces anesthesia of the entire upper extremity except for the T2 dermatome.

However, based on clinical experience, such a claim is grossly unsubstantiated. This is evident from the finding that supraclavicular BPB is associated with 2-36% inferior trunk or ulnar nerve sparing. In addition, since the suprascapular nerve takes off more proximally from the superior trunk and the supraclavicular BPB is performed distally at the supraclavicular fossa, the effect of supraclavicular BPB on the suprascapular nerve, which predominantly supply the shoulder and proximal humerus, is not known and has not been objectively documented.

Nonetheless, supraclavicular BPB has been successfully used for shoulder surgery albeit with a large local anesthetic (LA) volume (50-60 ml) or combined with interscalene BPB, a hybrid BPB technique using 30-50 ml LA volume, for proximal humerus fracture surgeries. But such high LA volume is invariably associated with potential complications in the high risk population and therefore not used in contemporary clinical practice.

Since all major nerves supplying the upper extremity, including suprascapular nerve, passes through the trunks of the brachial plexus, we proposed that by selectively identifying and blocking the three trunks of the brachial plexus with small doses of LA-selective trunk block (SeTB), it is feasible to produce anesthesia of the entire upper extremity, i.e., from shoulder to hand. This is further confirmed from the results of our research evaluating the efficacy of ultrasound-guided (USG) SeTB for surgical anesthesia of the entire upper extremity and cadaver anatomic study evaluating the spread of the injectate after a simulated SeTB. Although these are encouraging results, there is a paucity of data on the sensorimotor blockade and incidence of hemidiaphragmatic palsy comparing SeTB and supraclavicular BPB techniques which this study aims to evaluate. We hypothesize that USG SeTB is superior to supraclavicular BPB in anesthetizing the entire upper extremity from shoulder to hand.

Inclusion criteria

• ASA 1-3 patients
• Undergoing elective or emergency upper extremity surgery involving anywhere from the proximal humerus to distal hand or surgery involving any combination of these regions

Exclusion criteria

• Patient refusal
• Pregnancy
• Skin infection at the site of block placement
• History of allergy to local anaesthetic (LA) drugs
• Bleeding tendency or with evidence of coagulopathy
• Pre-existing respiratory disease
• Neurological deficit or neuromuscular disease.