Despite its widespread use during the perioperative period, there remain limited data regarding the use of dexmedetomidine in MH-susceptible patients. Given its mechanism of action and the pathophysiology of MH, dexmedetomidine would appear to be safe for use in MH-susceptible patients. There is also an increasing body of evidence regarding the possible advantages of dexmedetomidine during and after pediatric cardiac surgery. Mukhtar et al
. examined the effects of dexmedetomidine on the surgical stress response following cardiac surgery in infants and children.[5
] Patients who received dexmedetomidine had lower plasma concentrations of several stress hormones including cortisol, epinephrine, and norepinephrine as well as lower plasma glucose concentrations. The blunting of catecholamine levels may be beneficial in MH-susceptible patients as norepinephrine and epinephrine may trigger MH.[6
To date, there are only three previous reports regarding the use of dexmedetomidine in MH-susceptible patients.[7
] Unger used a dexmedetomidine infusion along with propofol, nitrous oxide, and fentanyl to provide anesthesia for a 59-year-old woman with MH diagnosed by muscle biopsy.[7
] Dexmedetomidine dosing included a loading dose of 1 μg/kg over 10 minutes followed by an infusion of 0.6 μg/kg/hr during the procedure and 0.4 μg/kg/hr for the initial 30 minutes in the PACU. Propofol was added to the dexmedetomidine infusion and titrated to maintain the BIS at 40–55. There were no adverse effects related to the anesthetic care and the patient had an uncomplicated perioperative course. Hudcova and Schumann reported the use of a dexmedetomidine infusion as part of the intraoperative anesthetic care of a 35-year-old woman with a positive family history of MH, during excision of two neuroendocrine tumors.[8
] The authors were concerned regarding the potential for the development of the propofol infusion syndrome due to the expected prolonged operative time and the elevated catecholamine levels from the tumor. Dexmedetomidine was used as part of the intraoperative anesthetic care to limit the propofol dose. Following anesthetic induction, a dexmedetomidine infusion was started at 0.7 μg/kg/hr. Following the prolonged surgical procedure (10 hrs and 49 minutes), the propofol and dexmedetomidine infusions were discontinued and the patient's trachea was extubated. The patient's postoperative course was uneventful. The final report described the use of dexmedetomidine in three MH-susceptible pediatric patients with associated allergies which precluded the use of propofol.[9
In our case, we used dexmedetomidine as the primary maintenance anesthetic, supplemented by caudal morphine and clonidine and intravenous midazolam and fentanyl (8–9 μg/kg). We noted no additive adverse hemodynamic or respiratory effects from the combined use of dexmedetomidine and caudal clonidine. The intraoperative benefit of this combination was illustrated by the minimal stress response during the surgical procedure and CPB with stable intraoperative plasma glucose and lactate concentrations. Additionally, the technique resulted in a reduction of the postoperative opioid requirements in our patient during the 48-hr postoperative CTICU admission.
When considering the options for TIVA in the pediatric cardiac surgical patient, there are several potential alternatives including propofol, ketamine, and dexmedetomidine. Given our experience with the agent and its potential advantages over propofol, we chose to use dexmedetomidine as the primary intravenous anesthetic agent in our patient. Advantages of dexmedetomidine over propofol include more effective blunting of the surgical stress response related to its sympatholytic properties and the potentiation of opioid analgesia thereby limiting postoperative opioid requirements.[5
] Like propofol, dexmedetomidine can have adverse hemodynamic effects including bradycardia and hypotension. However, these effects are less common in the pediatric population and generally respond to termination of the infusion, rarely requiring pharmacologic intervention.[4
] Given its limited use as a primary anesthetic agent, there are relatively few data documenting its amnestic properties. However, in a cohort of eight healthy adult volunteers, Hall et al
. demonstrated that dexmedetomidine at 0.6 μg/kg/hr resulted in an average BIS value of 66 with no recall as demonstrated by a comprehensive memory test using word recall.[11
Although anecdotal, our case provides further evidence for the role of dexmedetomidine in pediatric cardiac surgery and its role as the primary agent of a non-triggering anesthetic for patients with history of MH. We used dexmedetomidine in doses up to 2 μg/kg/hr supplemented with moderate doses of fentanyl (8–9 μg/kg) and midazolam (0.2 mg/kg) to provide intraoperative anesthesia during cardiac surgery and CPB. Several factors must be considered in our case report. Although there is ample experience with its use in the pediatric population, dexmedetomidine is currently not approved by the United State's FDA for use in the pediatric population. When used as an adjunct to general anesthesia, doses in the range of 0.4–0.7 μg/kg/hr have generally been reported. Given that dexmedetomidine was the primary agent in the anesthetic care of our patient, larger doses (up to 2 μg/kg/hr) were used to maintain hemodynamic stability and the BIS at 40–60. With such caveats in mind, we found that dexmedetomidine provided effective anesthesia and blunted the surgical stress response. In combination with caudal morphine and clonidine, these agents provided a stable postoperative course with a limited need for postoperative opioid administration. Future studies are needed to fully define the role of dexmedetomidine in pediatric cardiac surgery.