Superior hypogastric plexus nerve block in minimally-invasive gynaecology: a double-blind randomised controlled trial

Published: 2 March 2021| Version 2 | DOI: 10.17632/j4ydkpct6b.2
Contributors:
Praveen De Silva,
Praveen De Silva

Description

Clinical trial to evaluate the efficacy of a superior hypogastric plexus nerve block with 10ml 0.75% ropivacaine in reducing opiate requirements in the first 24 hours after minimally invasive gynaecological surgery. This was a double-blind RCT at a single institution. Primary outcome was the total opiate use in first 24h after surgery (in morphine milliequivalents). Secondary outcome was patient pain measured on a visual analogue scale (1 to 10) at 1, 2, 6, 12 and 24-hours post-surgery. Patients were randomised over a 5-month period, March to July 2020. 27 patients were randomised to receive a nerve block and 23 to the control. There were no significant demographic or intraoperative differences between the two groups. 27 patients were randomized to receive a nerve block and 23 to the control. There was a difference of -21.8 MME in the block group compared to the no-block group (95% CI -38.2 – -5.5, p=0.008). This correlated to a 38% reduction in opioid use in the block group. The mean opioid use in block patients was 33.1 MME (95% CI, 24.2 – 41.9) and in the non-block group 54.9 MME (95% CI, 40.7 – 69.1). For the SHPB group opioid use ranged from 1.0-76.5 MME with an interquartile range (IQR) of 37 (14-51). For the control group the range was 7.5- 113.5 MME with a higher IQR of 60 (28-88). Pairwise comparisons of mean pain scores over the 24 hours showed a lower pain score with a nerve block of 1.8 (95% CI 1.5 – 2.1) compared to no-block of 2.6 (95% CI 2.3 – 2.9) No adverse effects of local anesthetic toxicity, nerve injury or bowel/vascular injury were noted in any patient.

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Recruitment included patients who were undergoing either laparoscopic hysterectomy, laparoscopic myomectomy, robotic-assisted hysterectomy or robotic-assisted myomectomy. These were the most common benign gynaecological surgeries being performed in our unit. Patients needed to be over the age of 18 years and able to give informed consent. Exclusion criteria were known malignancy, liver failure, long-term opiate medication use (to avoid opiate tolerance confounding), allergy to local anaesthetic and anaesthetic concerns on patient using patient-controlled analgesia (PCA) post-operatively. Total opiate used for the 24h was summarized in micrograms (mcg) of fentanyl. This was calculated by adding up the total volume of Fentanyl PCA used during the 24h period. If the PCA was able to be discontinued prior to 24h enteral opiate doses of tapentadol were included in our calculation of total use. We used Visual Analogue Scale (VAS) scores as a marker of a patient’s pain. This was a well-studied marker of pain scores in research (11). VAS scores were taken by nursing staff at intervals of 1h, 2h, 4h, 6h, 12h and 24h post operatively. A VAS form was attached to the notes of all patients participating in the trial with a pictorial Likert scale for patients to refer to. The SHPB consisted of 10ml 0.75% Ropivacaine injected to the retroperitoneal area where the SHP lies. The landmark to determine area of infiltration was the peritoneum overlying the sacral promontory at the level of L5/S1. Two laparoscopic/robotic instruments were used to grasp the peritoneum and tent it up. A third instrument inserted a fine needle (interject) in the sub-peritoneal space (see figure 1). Infiltration then took place ensuring a large bleb of fluid appeared under the peritoneum in the desired site. This block was performed under vision at the end of the operation prior to withdrawal of laparoscopic or robotic instruments. As the patient was anaesthetized and therefore not aware of receiving the block the control arm was no block rather than a placebo injection. Patients underwent stratified-randomisation taking into account what surgery they were having. This was done to ensure similar proportions of the different laparoscopic and robotic operations received the intervention or control. The four stratified groups were laparoscopic hysterectomy, laparoscopic myomectomy, robotic-assisted hysterectomy, robotic-assisted myomectomy.