unable to enroll enough patients

This study is designed to identify the plasma concentrations which are required to achieve adequate sedation, using a Ramsay Sedation Scale. As an alpha 2 agonist, dexmedetomidine can elicit hemodynamic changes, fluctuations in blood pressure and heart rate. This study will attempt to determine whether these changes can be predicted by plasma concentrations.

Dexmedetomidine, an alpha2 agonist is currently the standard of care for sedation for diagnostic (MRI, CT and Nuclear Medicine) radiological studies at Boston Children's Hospital. Although it is FDA approved for sedation, its pharmacokinetics in children has not been carefully studied with prospective studies. The plasma concentration of dexmedetomidine necessary to achieve and maintain adequate sedation for motionless conditions for a MRI study has not been determined which is the purpose of this study.

Inclusion Criteria:

• Age 3 - 11.9 years

  • 2 age groups: 3.0 - 5.9 years, 6.0 - 11.9 years

• Patients will be equally distributed within each age group

• Meets criteria to receive dexmedetomidine sedation for MRI:

  • Active, uncontrolled gastroesophageal reflux - an aspiration risk
  • Active, uncontrolled vomiting - an aspiration risk
  • Current (or within past 3 months) history of apnea requiring an apnea monitor
  • Active, current respiratory issues that are different from the baseline status (pneumonia,exacerbation of asthma, bronchiolitis, respiratory syncytial virus)
  • Unstable cardiac status (life threatening arrhythmias, abnormal cardiac anatomy,significant cardiac dysfunction)
  • Craniofacial anomaly, which could make it difficult to effectively establish a mask airway for positive pressure ventilation if needed
  • Current use of digoxin
  • Moya Moya Disease
  • New-onset stroke
  • Provide written consent to take part in the research study

Exclusion Criteria:

• Do not meet established sedation criteria
• History of allergy, intolerance, or reaction to dexmedetomidine or hypersensitivity
• Previous diagnosis of hepatic insufficiency/failure or a serum glutamate pyruvate transaminase level > 2 times the normal limit determined by Children's Hospital Boston (TCH)
• Current diagnosis of renal insufficiency/failure or a current serum creatinine level > 1.5 times the normal limit determined by TCH
• Have received digoxin in the past (no time limit)
• Received phenobarbital, clonidine or valproic acid within 30 days
• Current, repaired or risk of Moya-Moya disease
• Recent stroke (cerebrovascular accident) within past 6 months
• Uncontrolled hypertension
• Concomitant use of beta antagonist, or calcium channel blocker
• Participated in a clinical investigation within the past three months

Children requiring sedation for MRI scanning