Peripheral Flow Index Is a Reliable and Early Indicator of Regional Block Success

Abstract

We investigated the usefulness of peripheral flow index (PFI) measurement using a standard pulse oximetry digit probe for early prediction of successful regional blocks. Sixty-six patients scheduled for limb surgery underwent either axillary or sciatic block using a nerve stimulator technique with mepivacaine 1.5%. PFI, which is the ratio of the pulsatile versus the nonpulsatile component of the pulse oximetry signal, was recorded from 10 min before block insertion until 30 min afterwards. PFI recordings of the unblocked limb were similarly recorded. Pinprick and cold sensation were assessed at 5-min intervals until 30 min after blockade. An increase in PFI by a factor of 1.55 at 10 min after axillary block placement (P = 0.006), and 12 min after sciatic block placement (P = 0.001) was required to predict a successful block. The sensitivity and specificity of PFI was 100% for predicting axillary block outcomes at this time. Positive predictive value was 95% and negative predictive value was 93%. For sciatic blocks, sensitivity and specificity were 90% and 100%, respectively. The calculated positive predictive value at time 12 min for sciatic blocks was 94% and negative predictive value was 92%. At 15 min after block placement, cold and pinprick sensations had the same calculated values for sensitivity and specificity at 71% and 100%, respectively, for axillary blocks. For sciatic blocks, cold sensation had a sensitivity of 77% and a specificity of 100%, whereas pinprick had a sensitivity of just 20% with a specificity of 100%. We conclude that PFI provides a simple, early, and objective assessment of the success and failure of nerve blocks.

Perfusion index and plethysmographic variability index in patients with interscalene nerve catheters

“…The laser Doppler peripheral flow index (PFI) is a reliable parameter to predict successful regional anesthesia after axillary or sciatic blocks. 4 An increase in PFI went along with an increase in local blood flow and local vasodilatation. The present data show that PI (like PFI) is a sensitive parameter to indicate loss of vasomotor tone induced by local anesthetics.…”

“…3 The perfusion index can accurately reflect functional sympathetic blockade after interscalene nerve block placement as regional anesthesia induces vasodilatation and increased blood flow. 4 The objective of the current study was to assess the influence of interscalene nerve blockade on the PI of the anesthetized arm in comparison with PI values of the contralateral arm, and evaluate its use as an indicator for successful block placement.…”

Lumbosacral epidural magnesium prolongs ketamine analgesia in conscious sheep

“…This stimulation of the sympathetic system increased the ST in the three treatments in this study. Epidural local anaesthetics induce a local vasodilatation and increase local blood by sympathetic block 28 with a consequent increase in ST in the blockade regions. Also MG decreases baseline tension in vascular smooth muscle and attenuates the vasoconstrictor response to vasopressor agents 29,30 .…”

Is the change of percutaneous oxygen pressure available to judge the effects of brachial plexus block?

“…However, the perfusion index displays quite large individual variations, while their results had a large standard deviation. The peripheral flow index, the ratio of the pulsatile to non-pulsatile component of the pulse oximetry plethysmograph and an accurate indication of changes in digital blood flow [11], increased significantly due to the axillary block [12]. Cross et al [13] reported that the supraclavicular block increased blood flow in the fingers on the blocked hand, as well as cardiac output and blood flow of the non-blocked arm, while the increases in the non-blocked arm returned during the postoperative period.…”