Predicting Successful Supraclavicular Brachial Plexus Block Using Pulse Oximeter Perfusion Index.

Abdelnasser A, Abdelhamid B, Elsonbaty A et al.

British Journal of Anaesthesia 2017; 119 (2): 276-80

https://doi.org/10.1093/bja/aex166

Background

Ultrasound guided supraclavicular nerve block anaesthetic technique for patients undergoing upper limb surgery. Success is currently evaluated clinically by assessment of sensory & motor function, which is subjective, time consuming and dependent on patient co-operation. Perfusion Index is a numerical value for the ratio between pulsatile & non-pulsatile blood flow in a blood vessel measured by specialised pulse oximeter. It is a marker for vasodilation and therefore has could be used to predict successful brachial plexus blockade.

Methods

A prospective observational study conducted in the Orthopaedic Theatre Cairo University Hospital. Studies patients aged 18-60 undergoing supraclavicular block for elective upper limb surgery. Perfusion index measured using a specialised pulse oximeter (in both blocked & unblocked limb) at baseline, 10 minutes, 20 minutes and 30 minutes. Standard neurological assessment (sensory assessment every 3 minutes, motor assessment every 5 minutes) was also performed. The correlation between changes in perfusion index and successful brachial plexus blockade was analysed. A failed block was defined as need for general anaesthesia.

Results

77 patients received a supraclavicular block of which 70 where successful (failed block group n=7). Successful blocks were paralleled by an increase in perfusion index from baseline when compared to failed blocks. When individual patients where assessed Perfusion Indices where higher in blocked limbs compared to unblocked limbs (P<0.001). The perfusion index ratio (which is a ratio between the perfusion index at 10 minutes compared to baseline) was also higher in blocked limbs compared to unblocked limbs (P>0.001).

Conclusion

Perfusion Index can be used as a reliable predictor of supraclavicular block success. Perfusion index ratio is a more reliable indicator as it removes inter-patient variability in baseline perfusion index.

Group Discussions

• Providing a solution where there isn’t a clinical problem. This will never replace neurological assessment
• Failed block group is a small heterogenous group (i.e. includes total failure and missed segments) Too small to make results meaningful, and key to this is understanding if perfusion index changes occur where there are missed segments. Does this test have enough specificity?
• Changes in perfusion index occurred within first 10 mins, further work needed, possible role as an early indicator of block success?

Summary by Dr R Chapman. Journal Club 31 August 2017.