A prospective comparative study on USG guided erector spinae block versus local infiltration on port site for post-operative pain management of adult patient undergoing laparoscopic cholecystectomy.

Laparoscopic cholecystectomy has become the procedure of choice for routine gall bladder removal. It is currently the most commonly performed major abdominal procedure. One of the greatest advantages with laparoscopic procedures is that patients can be discharged on the same day (day care surgeries). The success of any day care procedure depends highly on the postoperative pain management of the patient.

Intraoperatively, in laparoscopic cholecystectomy access is provided with small ports created on the anterior abdominal wall. In spite of these small ports, laparoscopic cholecystectomy causes moderate to severe post-operative pain. This pain is partly due to segmental innervation of nociceptor afferent pathways along the trans abdominal fascial plane. The pain can be due to; incisional pain from the port site i.e. somatic pain, local visceral pain (deep abdominal pain), parietal pain and referred visceral pain. The visceral pain that occurs with tissue trauma during gall bladder resection is the most predominant component.

Currently several therapeutic options like non-steroidal anti-inflammatory drugs, opioids, dexamethasone, port site infiltration with local anaesthetic drugs, transversus abdominus block and oblique subcostal abdominis plane block have been used. .In spite of a great control of pain with opioid, perioperative physicians are still looking forward to newer techniques. One of the reasons being the side effects associated with opioids. Despite all the currently available multimodal analgesic regimes, laparoscopic cholecystectomy is still associated with moderate to severe post-operative pain.

Erector spinae block (ESP) is a new technique of regional anaesthesia. The technique was originally described by Forero et al in 2016, when it was used to treat thoracic neuropathic pain. The reason this block is gaining popularity is because it blocks both somatic and visceral pain and is thus suitable for laparoscopic upper abdominal surgery.

The erector spinae block is performed under ultrasonographic guidance by injecting local anesthetic solution between the erector spinae muscles and the transverse process. The local anaesthetic then spreads into the para vertebral space through diffusion between adjacent vertebrae. Thus, it acts on both dorsal and ventral branches of the spinal nerves.

The safety profile of ESP block is better than any other regional anesthesia. First, it is performed under ultrasound guidance so the anatomy is easily identifiable, second it acts on both somatic and visceral pain and third, this technique targets transverse process which is easily identifiable. Transverse process is distant from major vascular, neural structures and the pleura. It provides extensive analgesia with a single puncture.

The study is designed to compare and evaluate the effect of ultrasound guided erector spinae block and port site instillation on the duration and quality of postoperative analgesia, analgesic requirement and patient satisfaction in patients undergoing laparoscopic cholecystectomy.

Sample size:

With reference to previous study(3), the sample size was determined by using the VAS to compare the effectiveness by assuming a difference of 1 in VAS between any two groups as clinically significant, thus sample size of 35 patients per group were considered necessary to detect statistical significances with an effect size of 0.67 at alpha 0.05 and power of 80%.

  The formula for calculated sample size is given below

 n = (σ12 + σ22). [Z 1- α/2 + Z 1- β]2

(M1 - M2) 2

= (1.52 + 1.52).[1.96+0.842] 2

(1*1)

= (2.25+ 2.25)*7.85

1

= 35.325

where Zα/2 is the critical value of the Normal distribution at α/2 (e.g. for a confidence level of 95%, α is 0.05 and the critical value is 1.96), Zβ is the critical value of the Normal distribution at β (e.g. for a power of 80%, β is 0.2 and its critical value is 0.842) and σ 1 and σ 2 are the Standard deviations of the two groups and M1 and M2 are the means of two groups.