Evaluation of change in perfusion index as indication of effective supraclavicular blockade

The supraclavicular block (SCB) guided by ultrasound is a frequently used peripheral nerve block for anesthesia during upper extremity surgeries. Due to the close proximity of the plexus parts at this site, it has the greatest level of sensory blockade of all brachial plexus approaches and also a single penetration procedure.

Typically, sensory and motor function are used to determine the effectiveness of peripheral nerve blocks. However, this approach is subjective, time-consuming, and cannot be used on individuals who are sedated, unconscious, or otherwise unable to offer input. Numerous objective techniques have been developed, including thermographic temperature measurement, laser Doppler perfusion imaging, and skin electrical resistance. These techniques are based on the assessment of sympathetic block and the resulting physiological changes such as vasodilation, blood flow alterations, and skin temperature changes. However, the majority of these objective procedures need the use of complex and costly equipment.

The perfusion index (PI) is a non-invasive, straightforward approach for determining the efficacy of central neuraxial and peripheral nerve blocks. It is computed as a percentage or absolute number by dividing arterial blood flow (pulsatile) by venous, capillary, and tissue blood flow (non-pulsatile blood flow). It is used to examine the dynamics of peripheral perfusion in response to changes in peripheral vascular tone and involves the use of a specialized pulse oximeter. However, it is now accessible on a variety of different displays.

Due to the paucity of research examining PI as a surrogate for determining the effectiveness of peripheral nerve blocks, the current research was designed with the goal of evaluating PI as a predictor of success for US-guided SCB. The primary purpose was to analyze the changes in the PI value after SCB. Secondary goals included determining the cut-off value of PI for a successful SCB, comparing the change in PI value between successful and failed SCBs, grading sensory/motor block, and identifying any "complications." Secondary goals included determining the cut-off value of PI for a successful SCB, comparing the change in PI value between successful and failed SCBs, grading sensory/motor block, and identifying any "complications." Authors recruited 65 patients of either sex, aged 18–60 years, with American Society of Anesthesiologists physical status I or II who were scheduled for upper limb surgery using ultrasound-guided SCB. At baseline, PI was monitored every two minutes until ten minutes, and then every five minutes until 30 minutes after block.

The PI ratio was defined as the difference between the PI at 10 minutes and the baseline PI. Sensory and motor blocks were tested every five minutes for a total of thirty minutes. For quantitative data, mean and standard deviation were used; for categorical variables, frequency and percentage were used.

The mean PI climbed constantly from baseline to 10 minutes, then declined somewhat until 30 minutes, but values at later time intervals remained fairly high in comparison to baseline. In the event of successful blocks, the median PI climbed linearly over the next two minutes, but in the case of failure blocks, it increased just a little.

The authors conclude that PI is a simple, non-invasive monitor that may be used to evaluate the performance of USG-guided SCB more objectively than standard approaches. A cut-off value of 3.25 for PI and 3.03 for PI ratio at 10 min demonstrated a very excellent capacity to predict SCB effectiveness with high sensitivity and specificity. At ten minutes, the PI ratio was shown to be a more sensitive indicator than PI.

Reference -

Lal, Jatin; Bhardwaj, Mamta, Malik, Aanchal; Bansal, Teena A study to evaluate the change in perfusion index as an indicator of a successful ultrasound-guided supraclavicular block, Indian Journal of Anaesthesia: October 2021 - Volume 65 - Issue 10 - p 738-743

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