Is Dexmedetomidine Effective at Reducing Pain Scores and Opioid Consumption in Coronary Artery Bypass Grafting (CABG) Patients

Coronary artery bypass grafting (CABG) involves a median sternotomy and subsequent surrounding surgical dissection. Resulting tissue damage can lead to neurogenic inflammation and release of inflammatory mediators that promote acute postoperative pain . Given the location of the incision, uncontrolled acute postoperative pain after CABG can be associated with significant pulmonary complications . Additionally, acute pain activates the sympathetic nervous system which can have deleterious effects on multiple organ systems including the cardiovascular, gastrointestinal, and endocrine systems .

Dexmedetomidine is a sympatholytic agent acting on the alpha2 adrenergic receptor. It was originally used as an anxiolytic and sedative agent perioperatively and in the intensive care unit (ICU) by decreasing adrenergic response in the locus coeruleus and, thus, indirectly increasing gamma-aminobutyric acid (GABA) neurons downstream .

The use of perioperative dexmedetomidine has expanded; it has been studied as part of multimodal analgesic regimens as well as an adjuvant analgesic agent. It can directly work on the peripheral nervous system and inhibit C fibers and Aδ fibers to attenuate peripheral transmission of nociception . Within the central nervous system, dexmedetomidine inhibits adrenergic nociception transmission from the locus coeruleus through the spinal cord, which in turn prevent the release of nociceptive neurotransmitters and biochemicals at the presynaptic membrane . Also, alpha receptor agonism at the presynaptic membrane inhibits the release of norepinephrine and prevents nociceptive signals to the brain . Given its action at multiple sites within the nociceptive pathway, dexmedetomidine can be administered via various modalities including intravenous, intramuscular, neuraxial, peripheral nerve block, and topical.

Given its sympatholytic effect, reported side effects of dexmedetomidine are hypotension and bradycardia. In a meta-analysis of the safety of dexmedetomidine in cardiac surgery patients done by Wang et al., there was 3.4 times increased incidence of bradycardia with patients on dexmedetomidine compared to the control; however, there was no statistically significant difference in hypotension . Bradycardia occurs more often when dexmedetomidine is infused at 0.75-1 mcg/kg/hr than at 0.5mcg/kg/hr . The meta-analysis included publications that incorporated a loading dose prior to an infusion at a set dose; high plasma level of dexmedetomidine has been associated with cross reactivity with alpha1 stimulation and subsequent vasoconstriction resulting in hypertension and reflex bradycardia. However, elimination of the loading dose has been shown to eliminate the hemodynamic effect . Any intraoperative bradycardia or hypotension can be treated with anticholinergics and vasoactive agents, respectively, without postoperative bradycardia, hypotension, or related complications .

Compared to conventional opioid analgesia for acute postoperative pain, dexmedetomidine analgesia has limited adverse impact on the cardiovascular, pulmonary, and gastrointestinal systems . Perioperative dexmedetomidine has consistently demonstrated improved acute postoperative pain and reduced narcotic requirement in noncardiac surgeries including open and laparoscopic abdominal, open and laparoscopic gynecological, and neuro surgeries compared to traditional opioid therapy .