A better way to perform the interscalene block?

“O peaceful Sleep! until from pain released I breathe again uninterrupted breath!” – Henry Wadsworth Longfellow.

Extrafascial injection for interscalene brachial plexus block reduces respiratory complications compared with a conventional intrafascial injection: a randomized, controlled, double-blind trial. N. Palhais, R. Brull, C. Kern, A. Jacot-Guillarmod, A. Charmoy, A. Farron and E. Albrecht. British Journal of Anaesthesia, 116 (4): 531–7 (2016)

 

Background: While interscalene block (ISB) can provide excellent analgesia after shoulder surgery, local anaesthetic spreads along the anteromedial surface of anterior scalene muscle to the phrenic nerve in up to 100% of cases, causing diaphragmatic paralysis. This limits its use in patients with moderate or severe respiratory dysfunction. ISB is also associated with the highest rate of post-operative neurological deficits in routine regional anaesthesia practice.

Methods: A randomized controlled double-blind trial comparing the effects of an ISB injection lateral to the brachial plexus sheath (extrafascial) to conventional intrafascial injection on the rate of hemidiaphragmatic paresis. Forty ASA 1-3 patients undergoing elective shoulder and clavicle surgery were randomised. Patients with moderate to severe pulmonary disease were excluded. 20 ml bupivacaine 0.5% with adrenaline 1:200 000 was injected either between C5 and C6 within the interscalene groove (intrafascial), or 4 mm lateral to the brachial plexus sheath (extrafascial). The primary outcome was the incidence of hemidiaphragmatic paresis (diaphragmatic excursion reduction >75%), measured by M-mode ultrasonography, before and 30 min after the procedure. Secondary outcomes: forced vital capacity, forced expiratory volume in 1 s, peak expiratory flow before and 30 minutes after the procedure, time to first opioid request, pain scores at 24 h postoperatively.  Block related outcomes: onset times of action of sensory and motor blocks, rate of paraesthesia, rate of Horner’s syndrome, duration of sensory and motor block.

Results: The incidence of hemidiaphragmatic paresis in the extrafascial injection group was significantly lower that that in the conventional injection group: 90% (95% CI: 68–99%) vs 21% (95% CI: 6–46%), with a p value of <0.0001. Other respiratory outcomes were significantly better preserved in the extrafascial injection group, and the rate of paraesthesia was lower in this group. The mean time to first opioid request and pain scores were similar in both groups. The onset of sensory and motor blocks was significantly longer in the extrafascial injection group.

Conclusion: Ultrasound-guided interscalene brachial plexus block with an extrafascial injection reduces the incidence of hemidiaphragmatic paresis and impact on respiratory function while providing similar analgesia, when compared with a conventional injection. Although there is a prolonged onset time of action of sensory and motor block, this is not relevant for post-operative analgesia.

Limitations:

  • As the authors point out, the results cannot be used to predict which patients are at risk of developing hemidiaphragmatic paresis despite an extrafascial injection. The group plan to carry out further work in this area.
  • Hemidiaphragmatic excursion was measured only at 30 minutes after injection of local anaesthetic, and therefore any delayed-onset hemidiaphragmatic paresis may have been missed.
  • The duration of paresis was not determined.
  • The study did not assess any local muscular effects of IM injection into the middle scalene muscle.
  • Although hemidiaphragmatic paresis was reduced with an extrafascial injection, we do not know the clinical implications of this in a patient group without significant respiratory co-morbidities.

Overall thoughts

  • This study scores highly in terms of methodological quality e.g. randomisation, blinding, follow-up etc.
  • As the treatment effect was so large, only small numbers were needed to achieve a significant result.
  • These results appear to be valid and applicable to my clinical practice, and therefore I will be trying an extrafascial injection when I next do an interscalene block!

Summary by Dr Serena Sodha

 

 

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