Page 26 - CASA Bulletin of Anesthesiologisy 2022 9(6)-1 (3)

CASA Bulletin of Anesthesiology

Acetaminophen continues to be a crucial part of the perioperative multimodal analgesic
regimen for its analgesic and opioid-sparing properties, which has been an important
consideration in the setting of rising challenges with perioperative use of opioids (such as
adverse events, misuse and abuse). However, the optimal dose and route of administration of
acetaminophen for preemptive analgesia remains to unclear .
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Ketamine

Although primarily known as an anesthetic, ketamine has also been successfully used as an
adjunct for perioperative pain management due to its safety profile & profound analgesic
properties. Ketamine is a non-competitive NMDA antagonist derived from phencyclidine. At
subanesthetic doses, ketamine can prevent central sensitization and subsequently reduce the risk
of developing opioid induced hyperalgesia and opioid tolerance . This can be particularly
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helpful in spine surgery patients, many of whom are already opioid dependent and struggle with
chronic pain which confer high risk for postoperative pain.

In the setting of acute postsurgical pain, ketamine infusions have recently been gaining favor
as part of a multimodal opioid sparing analgesia regimen and is the standard of care in some
institutions for the management of postoperative pain in opioid tolerant patients. In patients
undergoing major lumbar spine surgery, intraoperative high-dose ketamine was shown to have
morphine-sparing effects and decreased pain scores postoperatively . Similarly in patients
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undergoing scoliosis surgery, Hadi et al. reported that in combination with remifentanil, the use
of ketamine resulted in lower pain scores, reduced morphine consumption, and prolonged time to
first analgesic rescue .
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In another study, perioperative ketamine with clonidine premedication has shown to
potentiate the analgesic effects of opioids and reduce the consumption of morphine through
patient controlled analgesia (PCA) following spine surgery . In chronic pain patients, a study by
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Nielson et al., demonstrated that postoperative morphine consumption and sedation 24 hours
following spinal fusion surgery was significantly reduced in patients who received ketamine
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infusions compared to placebo . Ketamine has been associated with nausea, headaches and
disturbing psychomimetic effects (ie hallucinations, emergence phenomenon, sedation,
disorientation). However, these are transient occurrences that last less than 60 minutes following
administration. For these reasons, ketamine is considered to be a safe and relatively well
tolerated medication . The recommended dose of ketamine infusions for pain management
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consists of a 0.1-1mg/kg bolus upon induction followed by an infusion ranging between 0.1-0.25
mg/kg/hr. Ketamine also has promising prospects for chronic pain patients with concurrent
depression. The closely intertwined relationship between chronic pain and depression is well
known and commonly seen occurring together because they are mediated by the same
modulatory neural system. Central nervous system nociceptive pathways (descending, ascending
pain pathways in the midbrain, brainstem – periaqueductal gray matter, nucleus raphe, locus
ceruleus) and brain regions involved in mood management are both mediated by
neurotransmitters such as serotonin, glutamate and norepinephrine. There are a wide variety of
antidepressants that are used to treat depression with associated pain such as SNRIs, SSRIs,
TCAs and although they are effective in treating neuropathic pain, it has not always been
effective in treating musculoskeletal pain. Chronic pain patients with clinical depression have
worse physical, mental and social functioning compared to those without depression and

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