The most desirable sedative-analgesic agent used in infants with HIE would 1) have an excellent safety profile, 2) provide adequate analgesia and sedation, 3) reduce shivering, 4) cause minimal respiratory depression, 5) preserve cerebrovascular autoregulation, and 6) confer neuroprotection. Several lines of evidence suggest alpha 2 adrenergic receptor agonist class of sedatives-analgesics may have all these properties. The investigators have recently developed a sensitive assay to measure clonidine levels which will allow us to perform population Pharmacokinetic (PK)/Pharmacodynamic (PD) analyses of clonidine in sick newborns. Thus, this phase I/II trial is designed to test the hypothesis clonidine , an alpha- 2 adrenergic receptor agonist, will reduce the incidence of shivering without adversely affecting heart rate (HR), blood pressure (BP), temperature regulation or cerebrovascular autoregulation.
Essentially all classes of sedative-analgesic agents affect mean arterial blood pressure (MAP) which can alter cerebral perfusion and affect cerebrovascular autoregulation. Cerebrovascular autoregulation is when blood flow to the brain is held relatively constant over a wide range of MAPs; it ensures a steady supply of oxygenated blood to the brain, and is only functional within a specific range of MAP's. When MAP deviates from this range and drops below the lower limit of autoregulation, blood flow becomes passive to MAP and the brain is placed at risk for ischemic injury. Brain injury alters cerebrovascular autoregulation in the region of injury, and together with sub-optimal MAP after hypoxic brain injury could cause more brain ischemia leading to poor outcomes, seizures, and permanent neurologic injuries. Little information is available on the effect of HIE alone or in combination with hypothermia on cerebrovascular autoregulation, and no information is published on the direct effect of sedative-analgesics on alterations in hemodynamic parameters and subsequent indirect or direct effects on cerebrovascular autoregulation in newborns with HIE. Thus, this study will establish the safety of clonidine, a commonly used sedative-analgesic in infants and children, in a population of infants with HIE undergoing therapeutic hypothermia. A secondary exploratory outcome is to determine the efficacy of clonidine in reducing shivering during the cooling phase of the therapeutic hypothermia protocol.
