Evaluation of Ultrasound-guided Erector Spinae Block for Postoperative Analgesia in Laprascopic Ventral Hernia Repair.

Hypothesis, aims and objectives

The postulated nullhypothesis and alternativ hypothesis is:

H0= there is no difference in opioid consumption postoperatively between multimodal analgesia and ESPB. HA= there is a reduction in opioid consumption postoperatively between standard multimodal analgesia and ESPB.

Sample size calculation

Sample size estimation was calculated from our series of 20 pilot-patients on ventral hernia surgery without block, who needed on average 24.6 mg oral morphine equivalents (OME) iv oxycodone rescue analgesia during the first hour, SD=17.35 mg. Assuming a one sided study and in order to show a 50% reduction in rescue opioid consumption after a successful block with 80% power and 0.05 as level of significance, at least 2 x 26 patients should be studied, total of 52 patients. In order to adjust for missing data and protocol violations we decided to include 2 x 30 patients in our study.

This is a study where all parties are blinded for the allocation. A study nurse draws up the allocated study medication in an unmarked syringe so that the anesthesiologist is blinded. The study nurse responsible for the medication is not the same nurse that does the postoperative scoring. The study nurse responsible for the medication puts masked containers of the allocated medication into opaque envelopes and delivers the envelope to the ward. The ward personnel will then be masked for the allocation. The study nurse responsible for the follow up calls are not the same study nurse responsible for the medications and as such is also blinded for the allocation.

The primary outcome measure is the opiate consumption measured in oral morphine equivalents after 1 hour.

Secondary outcome measures are;

• Opiate consummation after 4 hours, 24 hours, 48 hours and 7 days. As patients receive different types of opiates, opiate consumption will be measured as oral morphine equivalents for ease of comparison. Oksykodon iv is converted by a factor of 1:1,5 to oral morphine.
• Time to first mobilization
• Time to first analgesic requirement
• Pain measuring tool used in this project is the validated numerical rating scale (NRS), which is a 11- point scale from 0-10, where no pain is NRS=0, mild pain is NRS 1-3, moderate pain NRS 4-6 and severe pain 7-10. NRS will be measured at rest and with activity at the time points 1, 2 and 3 hours.
• Sedation is measured by the validated Pasero opioid-induced sedation scale (POSS). The POSS measures normal sleep as S and then the degree of sedation on a numerical scale from 1-4. Will be measured at 1, 2 and 3 hours.
• Nausea and vomiting is measured by the validated PONV impact scale. This is a tool that entails two questions about nausea and vomiting, and each question gets rated on a numeric scale from 0-4. Will be measured at 1, 2 and 3 hours.

After the operation the patients will be asked to answer the QoR-15, which consist of 15 questions distributed on two dimensions: "physical" and "mental" well-being, where the patients report their experiences on a scale from 0 (=not at all) to 10 (=all the time). As a complementing measure to the QoR-15 the patients will also be asked the EQ-5D questionnaire. The EQ-5D questionnaire is an outcome measure of patient health after operation. The EQ-5D-5L is comprised of two different measures; the EQ-5D descriptive system and the EQ visual analogue scale (EQ VAS). Both QoR-15 and EQ-5D will be measured at 48 hours and 7 days.

The objective is to gain knowledge to support anesthesiologists when deciding analgesic approach, as well as in shared decision-making with patients (including the patient perspective). All results are expected to be presented during the project period.

The inclusion criteria:

• Age >18
• BMI (body mass index) 18,5 - 40 and weight >65 kg
• ASA (American Association of Anesthesiologists Classification system for physical status) I-III .
• Scheduled for elective ventral hernia operation
• Planned hospital stay >24 hrs

The exclusion criteria;

• Allergy to latex, local anesthesia, Non-Steroidal Anti-Inflammatory Drugs or opioids
• Diabetes
• Chronic pain with daily opiate use
• Patients with severe renal and/or hepatic disease
• Local infection at the site of injection
• Systemic infection
• AV block 2-3
• Inability to understand written or spoken Norwegian
• Inability to cooperate
• Dementia
• Known abuse of alcohol or medication
• Pregnancy
• Weight under 65 kg