Pericapsular Nerve Block Versus Intrathecal Morphine for Analgesia After Primary Hip Arthroplasty

The aim of this clinical trial is to compare the analgesic effect of pericapsular nerve block (PENG) with intrathecal morphine in patients scheduled for total hip replacement surgery. The main question to be answered is whether the PENG block is equivalent to intrathecal morphine in reducing postoperative pain.

Participants will be randomised into two groups. Patients assigned to the PENG group will receive spinal anaesthesia with local anaesthetic (isobaric bupivacaine) alone and a PENG block. Patients assigned to the intrathecal morphine (ITM) group will receive spinal anaesthesia with a mixture of local anaesthetic (isobaric bupivacaine) and morphine (100 mcg) and a sham PENG block to ensure patient blinding.

The aim of this double-blind, non-inferiority study is to compare the analgesic effect of a PENG block with intrathecal morphine in patients scheduled for total hip arthroplasty. Postoperative morphine consumption and pain scores, morphine-related adverse effects and functional parameters will be compared between two groups.

The investigators believe that PENG block provides postoperative analgesia equivalent to intrathecal morphine. The research team plans to enrol 80 patients and randomise them to two groups - pericapsular nerve block (PENG) or intrathecal morphine (ITM). After written informed consent, patients will be allocated to one of the two groups according to a computer-generated randomisation list. The PENG group will receive central spinal anaesthesia with 12.5 mg isobaric bupivacaine followed by a PENG block with 20 cc of 0.75% ropivacaine. ITM groups will receive central spinal anaesthesia with 12.5 mg isobaric bupivacaine and 100 mcg morphine followed by a sham PENG block.

During the surgery, 0.15 mg/kg of dexamethasone iv, 1g acetaminophen iv, 30mg ketorolac iv and 40mg/kg magnesium iv will be administered for post operative analgesia.

In the post-operative care unit, pain management will be provided with as needed with 2mg of IV morphine at ten minute intervals for pain scores \>3. Once spinal motor block has ceded, the patients will be transferred to the surgical ward with a morphine patient controlled analgesia (PCA) pump. The pump parameters will allow 2 mg boluses of morphine with a 10-minute lockout and a maximum dose of 40 mg in 4 hours. Basal analgesia will be provided with paracetamol (1g/6h) and ibuprofen (400mg/8h). Ondansetron (4mg IV) will be provided in case of nausea or vomiting. A research assistant will conduct post operative visits at 2h, 1 day and 2 days post-operatively to record research data. Functional testing will be performed at day 1 and 2 by physiotherapy personnel.

Eligibility Criteria:
Inclusion Criteria:

* Male and female patients
* ASA (American Society of Anaesthesiologists) I-III
* 18 years of age or older
* Patients scheduled for elective primary hip arthroplasty
* Able to give written conformed consent autonomously

Exclusion Criteria:

* Refusal or inability to give consent
* Allergy to any of: ropivacaine, paracetamol, ibuprofen, ketorolac, morphine, ondansetron or dexamethasone
* Bleeding diathesis
* Neurological deficit of the operative side
* Existing preoperative opioid use
* Renal insufficiency (GFR\<30ml/min according to the Cockroft-Gault formula)
* Hepatic insufficiency
* Pregnant or lactating women