Dexmedetomidine is a potent α-2 agonist with sedative and analgesic properties. Dexmedetomidine exhibits α-2:α-1 specificity that is eight times greater than clonidine. Its’ sedative and anxiolytic properties are a result of its α-2 receptor specificity in the spinal cord and central nervous system. Dexmedetomidine has a much shorter half life than clonidine (2-3 hours vs. 12-24 hours). This pharmacokinetic profile can facilitate brief periods of deep sedation often needed for imaging procedures in pediatric sedation.
Use in MRI
Evidence supports the use of dexmedetomidine for sedation in mechanically ventilated adult patients. There has been increasing interest in the clinical application of dexmedetomidine in the pediatric population. High dose dexmedetomidine (3mcg/kg IV load over 10 minutes with an infusion of 1 mcg/kg/hour) has been used successfully for sedation of children undergoing sedation for MRI. Using this dose, Mason et al noted bradycardia and a 20% drop in blood pressure with minimal change in respiratory parameters.
Buccal and Intranasal
Antilla et al documented the high bioavailability(73%-92%) when dexmedetomidine was given via the buccal route. Onset occurred in 10-15 minutes with a peak effect at 90 minutes. Yuen et al demonstrated the efficacy of intranasal dexmedetomidine when used in a dose of 2mcg/kg as a premedication. Others have found dexmedetomidine, when used in a dose of 2 mcg/kg intranasal, to be an equivalent premedication to 0.5 mg/kg of po midazolam.
On the basis of this information, we have used intranasal dexmedetomidine as a premedication in a number of patients. Since this drug has a neutral pH it is virtually painless when given intranasally. In addition, the use of the nasal MAD (mucosal atomization device) has allowed quick and even administration of the drug.
We reported the case of an uncooperative 10 year old autistic child that was scheduled for MRI under general anesthesia in which we gave a dose of dexmedetomidine (4 mcg/kg IN) as a premed to assist in further care. Given this dose, this child calmed and fell asleep in the stretcher within 20 minutes. Minimal change in heart rate and blood pressure were noted. The child in fact slept through the duration of the scan without additional medication or anesthesia. He was recovered in the PACU for an hour and was discharged.
Since then, we have used the dose of 4 mcg/kg IN for short scans (CT) with success. We have also used this for ABR’s and repeated half the dose IN if the patient aroused during the study. It should be noted that for intranasal administration we use the undiluted product which is 100 mcg/ml. This allows for administration of a small volume which is dispensed quickly.
All of this is anecdotal and should be studied further. However, it is my belief that IN dexmedetomidine given alone or in combination with another drug such as ketamine may have broad application for sedation in children. I suspect that this type of sedation would work well for dental procedures, EEG, EMG, PICC line placement, and imaging such as VCUG.
Joyce Phillips, MD, FAAP
Department of Anesthesiology
University of New Mexico
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