Impact of varying degrees of peripheral nerve blockade on experimental pressure and ischemic pain: adductor canal and sciatic nerve blocks in a human model of compartment syndrome pain

Abstract

IntroductionEarly diagnosis of acute extremity compartment syndrome is crucial to timely surgical management. Pain is commonly used as an early diagnostic sign for acute extremity compartment syndrome, making regional anesthesia after lower extremity surgery controversial. This randomized study tested whether different concentrations of local anesthetics, or combinations of nerve blocks, would differentially impact the perception of acute extremity compartment syndrome-like pressure and ischemic pain.MethodsHealthy volunteers underwent quantitative sensory testing, including determination of pressure pain thresholds and prolonged pressure/ischemic pain in the leg using a variable cuff inflation system. Subjects were randomized to receive (1) adductor canal block alone (ACB), (2) ACB with low-concentration sciatic nerve block (ACB +LC SNB), or (3) ACB with high-concentration SNB (ACB +HC SNB). For the primary outcome, we assessed block-induced increases in pressure threshold to reach 6/10 pain, and compared the degree of increase between the three groups. The main secondary outcome was a comparison of average pain score during a 5 min hold at the 6/10 pressure pain threshold between the three groups.ResultsAll blocks raised pressure pain threshold and decreased ischemic pain, but to variable extents. Specifically, the amount the block increased pressure pain threshold was significantly different among ACB, ACB+LC SNB, and ACB+HC SNB groups (mean±SD: 24±32 mm Hg, 120±103 mm Hg, 159±93 mm Hg; p=0.002), with post hoc testing revealing ACB as less than the other two groups. Similarly, average pain scores during a prolonged/ischemic cuff hold differed among the groups (4.2±1.4, 1.4±1.7, 0.4±0.7; p<0.001), with post hoc testing revealing ACB as significantly higher.DiscussionThis study suggests the possible utility of titrating regional anesthesia, to provide some analgesia while still allowing acute extremity compartment syndrome detection.Trial registration numberNCT04113954.

Pain Control with Regional Anesthesia in Patients at Risk of Acute Compartment Syndrome: Review of the Literature and Editorial View

“…There is a paucity of randomized controlled trials on the effect of regional anesthesia on compartment syndrome, but one study by Chen et al took healthy volunteers randomized to receive adductor canal block alone or in conjunction with either low or high concentration sciatic nerve block to see if the blocks affected the patients’ ability to sense 6/10 pain induced by prolonged pressure. 20 This study showed that all blocks increased the pressure-pain threshold to varying extents. Further study through randomized controlled trials is necessary.…”

Pro-Con Debate: Peripheral Nerve Blockade Should Be Provided Routinely in Extremity Trauma, Including in Patients At Risk for Acute Compartment Syndrome

“…Dilute local anesthetics, continuous nerve block infusions that can be paused, and direct targeting of sensory nerves often provide sufficient steady-state analgesia without impairing mental status or adequate nerve function. 5,7,28 Hence, a developing ACS with breakthrough pain might be more easily detected, as reported in several instances. 5,8,11…”

“…Dilute local anesthetics, continuous nerve block infusions that can be paused, and direct targeting of sensory nerves often provide sufficient steadystate analgesia without impairing mental status or adequate nerve function. 5,7,28 Hence, a developing ACS with breakthrough pain might be more easily detected, as reported in several instances. 5,8,11 Similar unfair generalization occurs when certain injuries are labeled substantial risk for ACS regardless of patient demographics or mechanism of injury, which vary quite significantly.…”