Single Shot Lumbar Erector Spinae Plane (ESP) Block in Total Hip Replacement (THR)

After a pilot study regarding opioid use for patient after THR, the sample size for either treatment or control arm is calculated to be 35 patients per group to achieve adequate power to detect such a difference.

Sealed opaque envelopes with allocation inside is prepared forehand and is subsequently drawn on the day of surgery. The attending anaesthetist receives the envelope right before induction, and opens the envelope after the patient is put under general anaesthesia (GA). If the operation is cancelled or the patient cannot use PCA post-operatively (e.g. post-operative mechanical ventilation) or post-operative delirium), the envelope is put back into the pool.

After the patient is put under GA and turned lateral, the envelope is opened. For the treatment arm, lumbar ESP block is performed while for control arm no regional anaesthesia is performed nor saline is injected into the ESP. Before proceeding to ESP block, the back is cleaned with aseptic technique and draped. 40 mL of 0.25% levobupivacaine (or maximum of 2mg/kg body weight made up to same volume) is injected into the ESP.

After the injection, the surgeon is told not to infiltrate any local anaesthetics into the incision site or the wound. Intra-operatively, intravenous fentanyl is given as the only analgesic by the attending anaesthetist. Post-operatively, the patient is given fentanyl PCA of standard setting anaesthetist). The patient is also given all the pre-operative regular oral analgesic agents post-operatively, including paracetamol, NSAID, gabapentinoid and/or weak opioid (DF118 or tramadol).

The patient is assessed by an independent assessor from the acute pain service team 24 hours after the operation, who is blinded from the allocation result. Primary outcomes, that are post-operative 12 and 24 hour PCA fentanyl use and pain score in numeric rating scale (NRS) from 0 to 10 at rest and upon mobilisation are assessed and documented in the electronic system and also the patient chart. Secondary outcomes like presence/absence of PONV and knee flexion power in MRC scale are also noted.

The data are collected by the investigator and input to Excel 2003. 2-sided student's t test is used to compare the primary outcomes and also knee flexion power between treatment group and control group, while the rate of PONV between two groups is compared by Chi-square test. Multi-variate regression is done to control for the effect of oral analgesics on study outcomes.

Inclusion criteria

• Adult patients (age >=18)
• American Society of Anesthesiologists (ASA) class 1-3
• primary elective unilateral THR
• understand and accept the risk for general anaesthesia and ESP block
• counselled of post-operative patient controlled analgesia (PCA) and deemed fit for its use.

Exclusion criteria

• emergency THR
• bilateral THR
• revision THR
• THR done under neuraxial technique (e.g. spinal anaesthesia, combined spinal epidural anaesthesia)
• Patient with contraindication for ESP block (i.e. patient refusal, injection site infection or spine pathology/surgery, coagulopathy with international normalised ratio (INR) > 1.4 and thrombocytopenia < 75 x 10^9/L)
• patient who are mentally incompetent
• severe obesity (Body Mass Index >= 35)
• severe obstructive sleep apnea syndrome (Apnoea hypopnoea index >= 30, no matter on treatment or not)
• patient on regular strong opioid (e.g. morphine, oxycodone, methadone, buprenorphine, fentanyl)
• patient who have undergone hip neurolysis