Impact of Dexamethasone on the Duration of Sensory and Motor Block Following Spinal Anesthesia

Spinal anesthesia is commonly used for lower body surgery. The injection of local anesthetics in the lumbar intrathecal space allows the desensitization of the lower body by blocking sensory and motor nerve roots. In return, spinal anesthesia causes a sympathetic block which is associated with deleterious hemodynamic effects such as hypotension.

Using intravenous or intrathecal adjuvants to local anesthetics may prolong the duration of sensory and motor blockade following spinal anesthesia. Various intrathecal additives have been studied such as opioids, adrenalin, clonidine, dexmedetomidine, midazolam, ketamine, magnesium, ketorolac and neostigmine. Most of them failed to prolong the duration of spinal anesthesia and side-effects have restricted their use.

Dexamethasone is a potent corticosteroid with a half-life of 36 to 72 hours and an onset of action of 1 to 2 hours. The safety of single doses of intravenous dexamethasone is well documented. Dexamethasone is widely used in anesthesia to prevent nausea and vomiting and treat post-extubation sore throat and postoperative shivering. It is also increasingly used in orthopaedic surgery to reduce opioid needs without increasing the risks of infection, wound dehiscence and osteonecrosis. The use of dexamethasone in the perioperative period reduces postoperative edema allowing early mobilization and improved functional recovery.

Recent studies have demonstrated that both perineural and intrathecal administration of dexamethasone can prolong the duration of peripheral and spinal anesthesia. However, dexamethasone has not been approved by health authorities for these indications and thus, the safety of this practice remains controversial. A recent study has compared peripheral to intravenous administration of dexamethasone for interscalene blocks. This study demonstrated the equivalency of these regimens in increasing the analgesic duration of a single-shot interscalene block.

The impact of intravenous dexamethasone on the duration of spinal anesthesia remains unknown. This study will investigate the effect of a single-dose of dexamethasone 8 mg on the duration of the sensory and motor block following spinal anesthesia.

Sixty patients scheduled for lower body surgery under spinal anesthesia will be considered for this study.

After placement of standard non-invasive monitoring, spinal anesthesia will be performed in the sitting position using a 25 gauge (GA) pencil point needle (Whitacre, Pencan). After aspiration of cerebrospinal fluid (CSF), a dose of isobaric 0.5% bupivacaine 12 mg will be injected. The aspiration of CSF will be repeated at the end of the injection. While performing spinal anesthesia, an intravenous infusion of dexamethasone 8 mg or placebo will be initiated according to randomization.

Subsequently, the patient will be placed in supine position. Sensory block will be measured by loss of sensation to pinprick at 5, 10, 20 and 30 minutes following spinal anesthesia and then every 15 minutes until confirmation of regression by two dermatomes. Loss of sensation will be assessed every 30 minutes thereafter. Motor block will be assessed using the Bromage scale at the same frequency until full recovery.

Sedation will be allowed during the performance of the spinal anesthesia technique and surgery. In case of unsatisfactory quality of spinal anesthesia, general anesthesia will be performed.

At the end of surgery, patients will be transferred to the recovery room. Multimodal analgesia including celecoxib and acetaminophen will be administered. Pain will be assessed using a verbal numeric pain scale (VNPS) of 0 to 10, where 0 means "No pain" and 10 means "Worst pain imaginable". Intravenous hydromorphone will be administered when VNPS is superior to 3. Postoperative nausea and vomiting will be managed with intravenous ondansetron, dimenhydrinate and haloperidol.

Opioid intake, presence of side-effects and quality of sleep will be assessed during the first 24 hours following surgery.

Inclusion criteria

• Patients undergoing lower body surgery under spinal anesthesia
• American Society of Anesthesiologists' physical status of 1 to 3

Exclusion criteria

• Contraindication to spinal anesthesia (coagulopathy, local infection at the site of injection)
• Pre-existing neuropathy or nerve block that could compromise study assessments
• Preoperative use of systemic corticosteroids
• Allergy or hypersensitivity to local anesthetics, dexamethasone or other drugs used in this study
• Patient refusal or inability to consent