Although previous surrogate outcomes have suggested that IV dexamethasone can prolong the duration of peripheral nerve blockade, new research indicates otherwise. When sensory blockade was measured by an objective pinprick assessment, neither a 4- nor 8-mg dose of systemic dexamethasone given at the time of peripheral nerve blockade had an effect on block duration.
“Based on these results, systemic dexamethasone should not be expected to prolong a psoas compartment block,” said James Turner, MD, a regional anesthesia and acute pain medicine fellow at Wake Forest Baptist Medical Center, in Winston-Salem, N.C. “Whether it prolongs other peripheral nerve blocks remains to be determined, but we think these conclusions could be extended to other peripheral nerve blocks. That being said, it is helpful in multimodal analgesic regimens in a dose greater than 0.1 mg/kg, as shown in prior literature.”
Although dexamethasone, commonly used as prophylaxis for postoperative nausea and vomiting, has been linked to improved overall quality of analgesia as well as decreased opioid consumption when given intravenously, prolongation of nerve blockade with systemic administration has not been consistently demonstrated.
“We felt that the literature, though full of information on dexamethasone, didn’t actually answer the question of how long a block lasts after dexamethasone is used intravenously or perineurally,” Dr. Turner said. “A surrogate outcome like block duration, as determined by the patient or time to first analgesic request, is typically used.”
To determine whether IV dexamethasone actually prolongs peripheral nerve blockade, Dr. Turner and his colleagues measured neurologic serial checks. Following institutional review board approval, 115 participants undergoing total hip arthroplasty received a psoas compartment block, or lumbar plexus block, with 25 cm3 of 0.25% bupivacaine with 1:200,000 epinephrine. Patients were then randomly assigned to one of three arms. In the first arm, 15 patients received IV placebo (normal saline). In the second arm, 50 patients received 4 mg of IV dexamethasone, and in the third arm, 50 patients received 8 mg of IV dexamethasone. The syringes for each arm were labeled “study drug,” and each contained 2 mL in volume.
“Our hypothesis was that IV dexamethasone at 4 mg and 8 mg would provide a significant prolongation of sensory block when compared to placebo, which is why only 15 patients received placebo,” Dr. Turner said. “We also thought that 4 mg and 8 mg of IV dexamethasone would have the same effect.”
Investigators assessed patients every two hours via pinprick (with a 25-gauge Whitacre needle) in order to determine the time of sensory recovery on the anterior thigh (L3-L4 region) at a midpoint between the patella and inguinal crease. Secondary outcomes included total opioid consumption, periodic pain scores and time to first analgesic.
As Dr. Turner reported at the 2017 annual Spring meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 3391), both the 4- and 8-mg IV dexamethasone groups were found to have an equivalent duration of sensory blockade. However, neither prolonged the duration of sensory blockade when compared with placebo. Average durations of sensory blockade in the placebo group, 4-mg group and 8-mg group were 19.6 hours (SD, ±7.0), 19.7 hours (SD, ±6.7) and 19.0 (SD, ±6.2) hours, respectively (Table).
| Table. Primary Outcomes | |
| Group | Block Duration (Mean hours ± SD) |
| Placebo | 19.6±7.0 |
| 4 mg | 19.7±6.7 |
| 8 mg | 19.0±6.2 |
“All blocks lasted approximately 19 hours, suggesting that statistically and clinically they are the same,” Dr. Turner said. “Our study would argue that when given systemically, dexamethasone did not prolong the block at all.”
Despite these findings, however, the investigators corroborated surrogate outcomes used in previous studies. In the 8-mg group (but not the 4-mg group), opioid consumption was reduced and time to first analgesic was prolonged when compared with placebo.
“This suggests there’s a dose-dependent effect on analgesia with systemic dexamethasone, as we’re all well aware,” said Dr. Turner, who underscored the importance of including a placebo in randomized controlled trials and supplanting surrogate outcomes with more objective end points.
“Lots of people argue that the literature is so replete with this information and that dexamethasone is so convincing that you don’t need placebos anymore,” said Dr. Turner, “but clearly, that’s not true.
“Moreover, we haven’t necessarily found the answer when using surrogate outcomes,” he added. “Surrogate outcomes as end points are often not helpful because they don’t actually define or answer the question we’re looking for.”
Finally, according to Dr. Turner, studies of perineural dexamethasone also need to be done separately because systemic absorption may account for previous results.
“We’re about 75% finished with those studies at Wake Forest,” he reported.
Results Called ‘Curious’
Daniel Sessler, MD, the Michael Cudahy Professor and chair of the Department of Outcomes Research at the Cleveland Clinic, in Ohio, called the result “curious” given several previous studies showing that perineural dexamethasone prolongs blocks.
“You may dismiss these studies because they just looked at time to first analgesic request, but that’s certainly a clinically relevant outcome, and there have been good randomized controlled trials comparing perineural and systemic dexamethasone that also show that perineural is superior,” Dr. Sessler said. “Why do you think your results differ?”
“Time to first analgesic, total opioid consumption and periodic pain scores are clinically relevant outcomes, which is why they were secondary outcomes in our study,” Dr. Turner replied.
“We thought they were important to know, and our study showed the same exact thing—that opioid consumption decreased and time to first analgesic request was prolonged, which is usually measured for duration of block.
“The reason that our study is different, though, is that we actually serially neurologically checked a sensory test for these blocks until they wore off as opposed to relying on a surrogate for block durations,” Dr. Turner continued.
“We measured block duration directly, which is why our results differ despite similar findings in secondary outcomes.”