Effect of multimodal perioperative analgesia on stress response to surgery and on post-operative pain score

Introduction

Management of acute pain gained importance in the early 1930s. Even after eight decades, the incidence of postoperative pain is 75%. Pre-emptive multimodal analgesia (MMA) can be effective in preventing and treating acute pain. Pre-emptive analgesia is an evolving concept where analgesics are timed to prevent establishment of central sensitization. The concept of MMA was pioneered by Prof Henrik Kehlet in early 1990s.   In MMA all the four elements of the pain processing pathway (1.Transduction, 2.Transmission, 3.Modulation and 4.Perception) are targeted with drugs having different mechanism of actions for clinically measurable pain relief.

Aim of the study was to assess the effect of MMA on random serum cortisol, random blood sugar, propofol requirement for induction, and to compare post extubation sedation and visual analog scale score between the two groups.

Materials and methods

After obtaining Institutional Review Board approval and Informed written consent, a prospective, double blind, randomized clinical trial involving 42 patients belonging to the American Society of Anaesthesiologists Class I and II scheduled to undergo elective lumbar spine surgery were allocated into two groups of 21 each. Study group received injection diclofenac sodium, paracetamol, clonidine, and skin infiltration with bupivacaine adrenaline and Control group received paracetamol and skin infiltration with saline adrenaline. Analgesics were administered as per their onset of action, providing adequate time for their clinical effects. BIS guided induction was done with incremental doses of injection propofol. Two blood samples were drawn; one just before tracheal tube placement and another one 30 min following skin incision for random serum cortisol and random blood sugar. Post operative sedation and pain score were assessed at 5min and 30min post-extubation respectively. Patients with moderate pain received rescue analgesic pethidine 0.5-1mg/kg.

Statistical Methods:

Statistical significance of mean difference between the two groups was analyzed using Independent t-test and within group using paired t-test. Repeated Measure Analysis of Variance (RMANOVA) was used to compare the outcomes between the groups with change over time. All the categorical data between groups were compared using Chi square test. The data that was not normally distributed were compared between the groups using Mann-Whitney U test. p<0.05 was considered statistically significant.

Results

Random serum cortisol (Table-1), random blood sugar (Table-1) and postoperative sedation score between the groups were comparable. Induction dose of propofol was significantly low in MMA group (Table-2). In the MMA group 100% patients had mild pain whereas in the control group 85.7% of the patients had moderate pain (Table-3) where rescue analgesic was administered. No side effects were noted in the study group.

Conclusion

As a response to tissue injury, inflammatory mediators are released irrespective of analgesics administered, but the response to painful stimuli depends on the intensity of analgesia. With pre-emptive MMA nociceptors at all levels of pain processing are primed with analgesics, which inhibits nociception and ensures intense analgesia with narcosis and potentiates the clinical efficacy of induction drugs with minimal adverse effects.