Effect of TAP Block on Stress Hormones

Total abdominal hysterectomy (TAH) is a commonly performed major surgical procedure that results in substantial postoperative pain and discomfort. It has been shown that surgical pain and trauma can lead to a number of hormonal changes initiated by the neuronal activation of the hypothalamic pituitary-adrenal axis and the sympathetic nervous system, which can have a detrimental effect on the patient. Strenuous effort has been made to inhibit the stress response to surgery and evaluate its outcome.

It has been shown that this stress response is influenced by the mode of anesthesia and postoperative analgesia. A surgery induced stress response blunted by regional technique and the potential benefits of regional analgesia on surgical outcome are still under scrutiny. Among the postoperative analgesic technique, epidural analgesia has shown to significantly abolish the perioperative stress responses after number of surgeries including hysterectomy. In Pakistan only a small proportion of women wants to avail the epidural service due to fears and misconception.

Another modality of regional technique that has gained popularity as a part of multimodal analgesia is transversus abdominis plane (TAP) block. It is a newly developed block involving the nerves of the anterior abdominal wall. The abdominal wall sensory afferents course through the transversus abdominis plane superficial to the transversus abdominis muscle. An important component of the pain experienced by patients after abdominal surgery derives from the abdominal wall incision.

The efficacy of the TAP block in providing postoperative analgesia as a part of multimodal analgesia has been demonstrated in number of surgeries including colonic resection surgery, caesarean delivery, radical prostatectomy and also hysterectomy. In literature search investigators did not find any clinical study that has been carried out to see the effect of TAP block on stress response after hysterectomy. This study is designed to test the hypothesis that the TAP block, as part of a multimodal analgesic regimen, would attenuate stress response after TAH when compared with placebo. The investigators will also see any difference in postoperative pain and rescue analgesic demands and side effects among patients.

Rationale for the study

Background information:

Failure to adequately control postoperative acute pain can have a number of unwanted physiological and psychosocial consequences for the patient including dissatisfaction, myocardial problems, prolonged hospital stay and even the potential progression to chronic pain. Pain associated with abdominal surgery can be very severe and can lead to a number of hormonal changes initiated by the neuronal activation of the hypothalamic pituitary-adrenal axis and the sympathetic nervous system, which can have a detrimental effect on the patient.

Current postoperative analgesic regimens rely heavily on systemic opioid analgesics which are associated with a number of undesirable side effects including nausea, vomiting, constipation, respiratory depression, and many others. In addition developing countries like Pakistan have limited supply of good quality opioids ,thus safer alternatives need to be evaluated. As a result postoperative pain management in a developing country like Pakistan has been less than suboptimal and barriers include general lack of resources in terms of personnel, drug availability and basic equipment

It has been observed that in developing countries only 45% of anesthetist had ready access to morphine and pethidine. Currently, the cost of importing morphine to developing countries is disproportionately high. A survey of opioid costs in 2003 showed that opioid drugs were up to 10 times more expensive in the developing world than in the developed world, after adjustment for differences in gross domestic product. Therefore in order to find the alternatives; local anaesthetic techniques by means of regional analgesic technique can provide excellent postoperative pain relief and their use should be encouraged whenever possible. There is a need to find techniques to improve postoperative analgesia which will decrease the requirement for opioids, are safe, cost effective, easy to perform and acceptable to patients.

TAP block a form of regional analgesia has been investigated as a part of multimodal analgesia and has shown promising result in decreasing the pain scores and opioid consumption but its role in inhibiting the surgical stress response is still not known. TAP block has been practiced at Aga Khan University hospital (AKUH) since 2012 now, but no data regarding its effect on stress hormones has been collected.

Work has been done on epidural analgesia, which is also a type of regional technique and attenuation of stress hormones is seen by the investigators with this form of analgesia. Epidural analgesia is an invasive procedure, which is expensive and requires expertise and equipment. It is not routinely practiced in our part of the world due to the above mentioned reasons. Epidural analgesia is used at AKUH, but it often less acceptable to patients as it is performed near the spinal cord and also because of the cost related issue.

Therefore the rational of this study is to observe, if a less expensive, easy to perform and safer form of regional analgesia like TAP block has an inhibitory effect on the surgical response or not. If favorable results are seen with TAP block, it can be incorporated in the practice guidelines of pain management for abdominal hysterectomies and related surgeries.

Primary Objective

This study is designed to test the hypothesis that the TAP block, as part of a multimodal analgesic regimen, would attenuate stress response after TAH when compared with placebo. An ultrasound (US)-guided TAP block will be performed before surgical incision.

Venous blood samples (20 ml) for metabolic and stress hormones, including cortisol and norepinephrine will be collected before anesthesia (T1) at the time of cannulation, and 30 minutes after incision(T2) 6hrs (T3)and 24 h (T4) after the surgery.

Secondary Objectives The investigators will observe any difference in postoperative pain by numeric rating score (NRS) and rescue analgesic demands by the reading on patient controlled analgesia pump, total opioid consumption and side effects like nausea, vomiting, sedation by scoring them.

Patient satisfaction score by scoring system