Use of Intranasal Dexmedetomidine as a Solo Sedative for MRI of Infants

In our outpatient sedation suite, we use 4 μg/kg per dose of IN dexmedetomidine with an atomizer device for infants presenting for noncontrast MRI, with an anticipated study duration of <1 hour. If patients fail sedation with IN dexmedetomidine, then either an additional 2 μg/kg dose of IN dexmedetomidine is given or an IV line is placed and followed with propofol administration per the physician’s discretion.

In this retrospective study, patients between 1 and 12 months of age presenting for sedation between June 2014 and October 2016 for noncontrast MRI studies with an anticipated study duration of <1 hour were included. Patients receiving initial sedatives other than IN dexmedetomidine alone and patients on assisted ventilation were excluded from the analysis.

We collected data on the following: patient age, sex, weight, and type and length of the procedure; the dexmedetomidine initial dose; and the number and amount of any additional doses. Adverse events were defined as the following: a >20% change in baseline heart rate or blood pressure, an apnea lasting more than 20 seconds, oxygen desaturations to <90%, and any seizures. MRI reports were examined for language that would suggest lack of quality or motion artifact.

Our aim with this study was to determine the rate of successful completion of the sedation procedure with IN dexmedetomidine alone. Failure of IN dexmedetomidine was defined as requiring propofol to complete the sedated MRI.

Statistical analyses were performed by using SPSS software version 15 (SPSS Inc, Chicago, IL). The variables were investigated by using visual (histograms and probability plots) and analytical methods (Kolmogorov-Smirnov or Shapiro-Wilk tests) to determine if they were normally distributed. Descriptive variables were presented by using medians and interquartile ranges (IQRs) for nonnormally distributed variables and frequencies and proportions for ordinal variables. The institutional review board approved the study and the need for informed consent was waived.

We identified 79 subjects between 1 and 12 months of age who presented for outpatient, noncontrast MRI. Twenty-seven patients were on assisted ventilation (including patients with tracheostomy and home ventilation, home bilevel positive airway pressure, and continuous positive airway pressure) and were excluded from the study. All 52 of the remaining subjects received IN dexmedetomidine (ie, no patients received an initial alternative regimen). Demographics of the 52 study subjects are presented in Table 1. The subjects were predominantly boys, with a median age of 7 months.

The success rate for an initial dose of 4 μg/kg of IN dexmedetomidine was 94.2% (95% confidence interval [CI], 84%–98.8%) and for IN dexmedetomidine alone was 96.2% (95% CI, 86.7%–99.5%). One patient received an additional 2 μg/kg dose of IN dexmedetomidine. Two patients (3.8%) could not be sedated with IN dexmedetomidine and required propofol. These patients were 4 and 6 months of age and were undergoing a brain MRI. Both patients awoke during the scan, and a second dose of IN dexmedetomidine was not given per physician discretion; the scans were completed with propofol. On the basis of the wording of the MRI reports, we found no evidence of motion artifact or poor image quality.

There were no documented episodes of oxygen desaturation or apnea. Sixteen patients had a documented >20% decrease from their baseline heart rate after receiving IN dexmedetomidine. Of these 16, the average decrease in heart rate was 25% (95% CI, 21%–32%). Two patients had a >20% decrease in mean arterial blood pressure. No patients received interventions for these vital sign changes.

In this retrospective investigation of infants undergoing sedated outpatient MRI, we demonstrate that a dose of 4 μg/kg of IN dexmedetomidine is highly effective and appears to be safe. Dexmedetomidine is commonly used as an IV sedative agent for imaging procedures, but the IN route is gaining popularity. Sulton et al¹⁶  demonstrated that a dose of 3 μg/kg of IN dexmedetomidine in combination with IN midazolam was effective for MRI of children. All 224 procedures were completed and there were no adverse effects. In contrast, Baier et al⁹  reported abandoning the combination of 3 μg/kg IN dexmedetomidine even when oral midazolam was added because of unacceptably low success rates. In a randomized study, Tug et al¹⁷  evaluated usage of IN dexmedetomidine for pediatric MRI and compared 4 μg/kg per dose to 3 μg/kg per dose. The authors concluded that subjects receiving the higher dose had better parental separation scores and more effective sedation. The need for rescue drug administration was 70% in the 3 μg/kg per dose group and 30% in the 4 μg/kg per dose group. In our study, we support the notion that the 4 μg/kg per dose is effective. The mean age in our study was lower than in the Tug et al¹⁷  study, which may indicate increased sedative effects of dexmedetomidine with younger age. Potts et al¹⁸  have shown decreased clearance of dexmedetomidine in neonates and infants compared with older children, which may translate into a longer duration of activity. In accordance with this, in a recent study it was demonstrated that the effective dose 50 of IN dexmedetomidine was higher in children with noncyanotic cardiac disease between 13 and 36 months of age compared with 1 to 6 and 7 to 12 months of age.¹⁹ 

There is increasing recognition that sedatives and anesthetics may cause neurotoxicity in the developing brain.¹¹  Even short-term use of sedatives like ketamine has been shown to have deleterious effects in some animal models.¹²  Dexmedetomidine emerges as a promising agent in the sedation of infants and neurologically injured children. Dexmedetomidine may ameliorate developmental neurotoxicity associated with other sedatives and has neuroprotective properties.^13,20 

IV access can be difficult to obtain in infants and requires skills and expertise. In contrast, IN medications are easy to administer and are associated with less pain and anxiety. These advantages make them very valuable in pediatric procedural sedation.

The safety of dexmedetomidine has been evaluated in children and infants with critical disease and congenital heart disease and has been found to be safe, with a minimal side effect profile,^21,22  although in general it has been associated with bradycardia and hypotension and can trigger seizures and arrhythmias.^23,24 

Our study has several limitations. First, our sample size is relatively small and originates from a single center, making generalizability difficult. Additionally, we did not have sufficient power to ensure that rare but serious safety events do not occur with this sedative regimen. The limited age range (1–12 months) precludes making a generalization about IN dexmedetomidine effectiveness beyond infancy. Additional studies are needed to clarify the dosage and safety profile in older populations.

In our study, we add support to recent findings that IN dexmedetomidine can be used successfully in procedural sedation for noncontrast MRI in infants.