Patients undergoing renal surgeries often have impaired renal functions and require judicious use of systemic analgesics. In the post operative period, patients undergoing nephrectomy are often managed with either opioids or epidural analgesia. In such scenarios, multimodal analgesia is a better choice since it is associated with reduced opioid requirement and its adverse effects. 

The ultrasound guided Erector Spinae Plane Block is a newer regional anaesthesia technique being currently explored as a viable option for analgesia. it is performed by injecting local anaesthetic in the plane between the rector spinae muscle and transverse process. The transverse process is easily identifiable and at a relative distance from any major vascular or neural structures. The local anaesthetic diffuses into paravertebral spaces between adjacent vertebrae and blocks both the dorsal and ventral branches of thoracic spinal nerves thus providing extensive analgesia with a single puncture. 

Keeping in mind a multimodal approach to postoperative pain and the ease of adminstration of the Erector Spinae Plane Block, this study is being planned with the view that ultrasound guided erector spinae plane black and intravenous patient contolled analgesia have an additive effect on postoperative pain management and would enable enhanced recovery after surgery and decrease post operative analgesic consumption in patients undergoing open nephrectomy. 

 

The sample size was determined by using the NRS to compare the effectiveness by assuming a difference of 1 in NRS between the two groups (group1 and group 2 ) as clinically significant, thus sample size of 24 patients per group were considered necessary to detect statistical significance with an effect size of 1.0 at alpha 0.05 and power of 90%

 The formula for calculated sample size is given below

n = (σ1² + σ² ) . (Z α + Zβ) ²

 (M1 - M2) ²

 

 

 = (1² + 1²).(1.96+1.64)²

  (1) ²

 

 = (1+1)*12.96

1

  = 24

 

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 90%, β is 0.1 and its critical value is 1.282) and σ 1 and σ 2 are the Standard deviations of the two groups and M1 and M2 are the means of two groups.