Chloroprocaine is a short-acting local anesthetic that allows rapid recovery and early ambulation but is currently recommended for procedures lasting 40 minutes or less.

Dexamethasone is commonly used during anesthesia for the prevention of postoperative nausea and vomiting and has also been shown to prolong the duration of analgesia and sensory block after regional anesthesia.

Dexamethasone may therefore extend the duration of chloroprocaine spinal anesthesia, potentially allowing its use for longer surgical procedures while maintaining the benefits of rapid postoperative recovery.

This study aims to evaluate whether intravenous dexamethasone can prolong the effects of spinal anesthesia performed with chloroprocaine in adults undergoing knee arthroscopy.

This is a monocenter, prospective, randomized (1:1 ratio), controlled, parallel-group, double-blind, phase III superiority trial assessing the efficacy and the safety of IV dexamethasone for prolonging sensory block in patients undergoing knee arthroscopy under spinal anesthesia with chloroprocaine.

Participants will be randomly allocated into two groups:

• Group CHLORO (control group): Patients will receive spinal anesthesia with chloroprocaine 40mg (Clorotekal®10 mg/mL, solution for injection, 4 mL) combined with an IV infusion of 3 mL of normal saline solution diluted in 100 mL of 0.9% sodium chloride, administered over 20 minutes.
• Group CHLORODEX (experimental group): Patients will receive spinal anesthesia with chloroprocaine 40 mg (Clorotekal®10 mg/mL, solution for injection, 4 mL) combined with an IV infusion of dexamethasone at a dose of 0.15 mg/Kg (maximum 16 mg), diluted in 100 mL of 0.9% sodium chloride, administered over 20 minutes.

To ensure blinding, study infusions (saline or dexamethasone) will be prepared in identical 100 mL bags and labelled by a pharmacy staff member or an "outside protocol" healthcare professional (physician or nurse) not involved in patient care or assessment.

The infusion will start approximately 10-15 minutes before the spinal punction.

In the operating room, patients will receive standard perioperative care for spinal anesthesia, including placement of a peripheral intravenous line, supplemental low-flow oxygen therapy to maintain SpO₂ > 93%, continuous hemodynamic monitoring, and strict aseptic precautions. Analgesic premedication with paracetamol combined with either ketoprofen or celecoxib will be administered according to institutional practice.

Spinal anesthesia will be performed with the patient in a semi-sitting position via the L3-L4 or L4-L5 interspace using a 25G x 80mm Sprotte needle. After cerebrospinal fluid reflux, 40 mg of chloroprocaine without adjuvant will be injected intrathecally, and patients will then be positioned in the supine position for the procedure.

Knee arthroscopy will be performed according to standard surgical practice, without any modification of the surgical procedure for study purposes.

No additional sedation or analgesia will be administered during the procedure. In the event of failure of spinal anesthesia or early recovery of sensation, conversion to general anesthesia or deep sedation may be performed at the discretion of the anesthesiologist, depending on the clinical situation.

Postoperatively, multimodal analgesia will be initiated according to the institutional protocol, combining paracetamol, nefopam, and either ketoprofen or celecoxib, with morphine administered if necessary.

Sensory and motor blocks will be assessed every 5 minutes after spinal puncture until regression of two dermatomes and then every 10 minutes until recovery of four dermatomes and complete motor function (maximum until hospital discharge).

Motor block will be assessed using the Bromage score and sensory block will be assessed using the Pin Prick test and the cold test.

The primary objective of the study is to evaluate the efficacy of intravenous dexamethasone in prolonging sensory block following spinal anesthesia with chloroprocaine, as assessed by the time from intrathecal injection to regression of sensory block by two dermatomes from the highest level of sensory block achieved, as measured by the pin-prick test.

Inclusion Criteria:

• Undergoing knee arthroscopy lasting ≤ 40 minutes requiring spinal anesthesia (diagnostic arthroscopy or meniscal surgery),
• Signed written informed consent form,
• Affiliation to a social security system,
• Negative pregnancy test on the day of procedure for non-menopausal patients.

Exclusion Criteria:

• Contraindications to spinal anesthesia with intrathecal chloroprocaine
• History of diabetes,
• Pre-existing peripheral neuropathy,
• American Society of Anesthesiologists (ASA) physical status IV,
• Contraindication to dexamethasone,
• Hypersensitivity of any drug used in this study,
• Long-term oral corticosteroid therapy,
• Chronic opioid use,
• Chronic pain syndromes,
• Contraindications to Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) (Ketoprofen, Celecoxib)
• Need for a peripheral nerve block in addition to spinal anesthesia (e.g. knee ligamentoplasty),
• Mental or linguistic inability to understand the study,
• Patients under legal protection (guardianship, curatorship or safeguard of justice),
• Patients currently included or planning to be included in another interventional study,
• Pregnant or breastfeeding women,
• Women of childbearing potential not using effective contraception.