The effect of perineural dexamethasone on duration of sciatic nerve blockade: a randomized, double-blind study.

BACKGROUND: Major hindfoot and ankle surgery is associated with severe postoperative pain, which is effectively alleviated by combined sciatic and saphenous nerve blockade. Local anaesthetics with added dexamethasone consistently prolongs the duration of pain relief compared to local anaesthetics alone. However, whether the extended duration of pain relief is due to an effect on duration of sensorimotor block per se vs. systemic absorption of the dexamethasone is still not fully elucidated. We aimed to investigate the postoperative duration of sensorimotor blockade with either dexamethasone or saline added to bupivacaine-epinephrine. METHODS: Fifty six patients scheduled for surgery were randomly assigned to a popliteal sciatic nerve block of 18 ml 0.5% bupivacaine-epinephrine with either 2 ml of 0.4% dexamethasone or 2 ml 0.9% normal saline added. Sensory and motor functions were tested every 30 min until normalized nerve functions. Primary outcome was time until complete return of sensorimotor functions. RESULTS: Mean (SD) time until return of normal sensory and motor functions was 26 (6) vs. 16 (4) hours, P < 0.001, postponing block remission by 10 (95% CI: 8-13) hours. Mean (SD) time until first opioid request was 34 (11) vs. 15 (7) hours, P < 0.001, extending first opioid request by 19 (95% CI: 13-25) hours. Total oral morphine equivalents administered 0-48 h differed significantly between the two groups by 39 (95% CI: 23-55) mg. CONCLUSIONS: Addition of 8 mg dexamethasone to 0.5% bupivacaine-epinephrine significantly prolongs the duration of sensorimotor popliteal sciatic nerve blockade, and reduces pain and opioid consumption in patients after major hind foot and ankle surgery.

Displacement of popliteal sciatic nerve catheters after major foot and ankle surgery: a randomized controlled double-blinded magnetic resonance imaging study.

BACKGROUND: Popliteal sciatic nerve catheters (PSNCs) are associated with a high frequency of displacement. We aimed to estimate the frequency of catheter displacement after 48 h with magnetic resonance imaging (MRI) in patients with PSNCs after major foot and ankle surgery randomized to catheter insertion either with a short-axis in-plane (SAX-IP) approach perpendicular to the nerve or with a short-axis out-of-plane (SAX-OOP) approach parallel to the nerve. METHODS: Forty patients were randomly allocated to SAX-IP or SAX-OOP PSNC. Ropivacaine 0.75% 20 ml was injected via the catheter followed by ropivacaine 0.2% 10 ml h(-)1 infusion. Correct primary catheter placement was ensured after initial injection of local anaesthetic via the catheter. Forty-eight hours after insertion, MRI was performed after injection of saline with added contrast (Dotarem) via the catheter. The primary outcome was catheter displacement estimated as the frequency of spread of contrast exclusively outside the paraneurium. RESULTS: All patients had correct primary catheter placement. The frequency of displacement 48 h after insertion of the PSNC was 40% when inserted perpendicular to the nerve vs 10% parallel to the nerve (difference was 30 percentage points, 95% CI: 3-53 percentage points). The relative risk of displacement was four times larger (95% CI: 0.8-10, P<0.028) in the SAX-IP vs the SAX-OOP group. The morphine consumption was 150% greater in the SAX-IP compared with the SAX-OOP group. CONCLUSION: Popliteal sciatic nerve catheters for major foot and ankle surgery inserted with ultrasound guidance parallel to the sciatic nerve have a significantly lower frequency of displacement compared with those inserted perpendicular to the nerve. CLINICAL TRIAL REGISTRATION: NCT02200016.