|Ahead of print
Epidural or TAP block to curtail insulin resistance in colorectal cancer surgeries: The jury is out!
Anju Gupta1, Nishkarsh Gupta2
1 Department of Anesthesiology, Pain Medicine and critical care, All India Institute of Medical Science, Delhi, India
2 Department of Onco-Anesthesiology and Palliative Medicine, All India Institute of Medical Science, Delhi, India
|Date of Submission||12-May-2020|
|Date of Decision||20-May-2020|
|Date of Acceptance||10-Jan-2021|
|Date of Web Publication||02-Jul-2021|
Department of Onco-Anesthesiology and Palliative Medicine, All India Institute of Medical Science, Delhi
Source of Support: None, Conflict of Interest: None
Surgical incision and related trauma stimulate the endocrine and inflammatory response and result in metabolic stress. This occurs due to an increase in release of pituitary hormones and sympathetic nervous system activation, which in turn increases plasma catabolic hormones (e.g., cortisol and glucagon concentration) and decreases anabolic hormone levels (e.g., insulin)., Overall, this tilts the balance in favor of catabolism and leads to increased consumption of all substrates (carbohydrate, fat, or protein) by the body. The net effect of reduced insulin secretion due to sympathetic stimulation, reduced peripheral action, or increased levels of counter regulatory hormones may lead to insulin resistance (IR). This IR may persist for days or weeks in the postoperative period and lead to postoperative complications. In addition, this becomes more relevant in cancer surgeries because of the possible cause–effect relationship between IR and cancer recurrence. The most important factor to reduce this surgical stress response and subsequent IR is an effective analgesia. The presence of acute pain after surgery is known to stimulate surgical stress response and cause IR. Traditionally opioid-based analgesia has been used but their usefulness is limited by related side effects like postoperative nausea and vomiting, respiratory depression, ileus, and may result in prolonged hospital stay. Epidural analgesia before incision has been shown to provide effective analgesia and reduce the stress response and IR. A study by Zhang et al. in this issue of the journal has compared the effect of the two analgesic techniques, i.e., continuous epidural with single-shot bilateral transversus abdominis plane (TAP) block on postoperative pain and IR after radical colon surgery. They have reported that thoracic epidural effectively blunted the nociceptive stimulus and lead to reduced IR as assessed by change in fasting plasma glucose, fasting insulin, and hemostasis model from baseline. The epidural analgesia effectively obtunds the sympathetic nerve supply of liver, which reduces its glucose output and the delivery of gluconeogenic substrates. It also reduces the release of cortisol and catecholamine from adrenals in response to surgical stress. So, overall, there is decrease in substrate availability and decrease in counterregulatory catabolic hormones that results in decreased IR. In addition to effect on IR, the activation of surgical stress response also leads to an increase in inflammatory mediators. Zhang et al. have also recorded IL-6 as a marker of inflammatory response and reported an increase in IL-6 levels after surgery in all patients. However, this increase was much less with epidural as compared to TAP block.
TAP block delivers local anesthetic between internal oblique and transverse abdominis muscle to block the thoracolumbar nerves that supply the abdominal wall. It is a superficial block and is preferred over epidural in patients with coagulation abnormalities or those who are difficult to position. The analgesic efficacy of TAP block for colorectal surgery has been previously reported. Felling et al., have compared TAP with liposomal bupivacaine provided equivalent analgesia and reduced the need of postoperative opioid and overall cost in patients undergoing minimally invasive colon surgery. Zhang et al. have also showed that though TAP block provided comparable analgesia to epidural block as assessed by visual analogue scale (VAS) scores but could not demonstrate similar favorable effect as that of epidural block on IR. This may be because TAP only provides somatic analgesia for pain due to abdominal incision but not to other visceral sources of pain following colorectal surgery unlike epidural. Moreover, bilateral TAP was given as a single injection, while epidural was continued in the postoperative period through a patient-controlled epidural analgesia pump. This may have led to more sustained analgesia and blunting of the surgical stress response and subsequent reduced IR in the epidural group. It is well understood that a single-shot interfacial plane block although effective as an analgesic cannot reduce IR unless it is also continuous using catheters like epidural analgesia. We believe that the effects would have been different if the TAP block was continued postoperatively using bilateral catheters.
Nowadays, the enhanced recovery after surgery (ERAS) protocols have been suggested to reduce surgical stress response and improve overall outcomes of the patients. ERAS protocols encompass all the measures in the preoperative, intraoperative, and postoperative period that may help to reduce the surgical stress and associated catabolic responses. In ERAS, a comprehensive approach, including maltodextrin-based liquid in the preoperative period to reduce preoperative fasting, a good epidural-based perioperative analgesia, and early postoperative feeding has been suggested to reduce the IR. The practice of extended preoperative fasting may exaggerate IR and may lead to postoperative morbidity. Hence, limiting the duration of preoperative fasting to minimum recommended, continuing clear liquids till then, and preoperative carbohydrate loading would tend to reduce IR in the perioperative period.
In conclusion, surgical stress response and resulting IR is an important modifiable factor that needs to be identified especially in major surgery like colonic resection surgeries. Strategies for good perioperative analgesia using continuous thoracic epidural block have shown promise in mitigating IR, but the role of interfacial plane blocks like TAP is yet to be substantiated. We need further adequately powered multicentric studies to compare continuous epidural with continuous TAP to further validate the role of TAP for colonic surgeries.
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