PCA Ketamine-Morphine Versus PCA Morphine as Post-Operative Analgesia in Colorectal Surgery

INTRODUCTION

Patient-controlled analgesia (PCA) is an established, efficient and safe technique for providing postoperative analgesia and has been associated with better pain relief and patient satisfaction with less postoperative complications and side effects [1]. Despite years of advances in pain management, opioids have been the mainstay for treatment of postoperative pain particularly in moderate to severe pain. Of all opioids, morphine is the most studied drug and remains the drug of choice for PCA, especially in Malaysian hospitals. However, morphine usage is also associated with known side effects such as sedation, nausea and vomiting, pruritus, urinary retention and respiratory depression [2]. A review of 32 studies involving opioids-based PCA-22 of which were PCA morphine-reported an incidence of 19% nausea, 18.1% vomiting, 30.9 % of nausea and/or vomiting, 25.7% sedation, 17.9% urinary retention, 17.9% pruritus and 15.2% hypoxia and 1.6% respiratory depression that may be life-threatening associated with PCA opioids use [3, 4]. The concept of multimodal analgesia hence was introduced to reduce opioid-related side effects. Adjuvants such as acetaminophen and non-steroidal anti-inflammatory drugs are commonly used nowadays in combination with opioids as opioid-sparing agents to reduce opioid usage [5].

Ketamine, an N-methyl-D-aspartate (NMDA) antagonist, has undergone a recent resurgence of interest among acute care providers as an adjunct in acute pain management [6, 7]. Ketamine at a sub-anesthetic dose (0.2-0.5 mg kg-1) produces intense analgesia [5, 8]. Since its development in 1962, various studies have been conducted to prove the efficacy of ketamine as post-operative analgesia and as an opioid-sparing agent [8-10]. A review by Laskowski and colleagues described that IV ketamine improved the quality of pain control, in addition to decreased opioid consumption with the particular benefit being observed in painful procedures, such as upper abdominal, thoracic, and major orthopedic surgeries [11]. While Carstensen and co-workers in a qualitative review comparing PCA ketamine-morphine with PCA morphine alone also described the superior efficacy of ketamine-morphine in providing pain control with a significantly higher incidence of opioid-related side effects in the morphine group [12]. In comparison to opioids, ketamine's lack of respiratory depressant effects also favors its use as an opioid adjunct in patients with airway and respiratory compromise, especially in morbid obesity and post-thoracotomy patients [13, 14].

Despite the potential efficacy with published evidence of PCA ketamine-morphine in postoperative pain management, its use is not well established in most Malaysian hospitals including the current study site. Hence, the aim of this study was to evaluate the effectiveness of PCA ketamine-morphine in comparison to conventional PCA morphine alone as postoperative analgesia in colorectal surgery patients in the current study site.

METHODS