Dexmedetomidine (Dex) is a centrally acting α2-adrenergic agonist that provides sedation, anxiolysis, and analgesia with minimal respiratory depression. It is commonly used in the ICU setting for procedural sedation or as an adjunct to reduce opioid requirements, particularly in patients undergoing intracranial procedures, including awake craniotomy, where its arousable sedation is useful. Dexmedetomidine is known to reduce CBF, likely through direct vasoconstriction of cortical vasculature by activating postsynaptic α2-adrenergic receptors.
In addition to reducing CBF, Dex also lowers CMRO₂. Transcranial Doppler work in volunteers shows the fall in flow is roughly matched by the fall in metabolism, so the flow-metabolism ratio is preserved, and both autoregulation and CO₂ reactivity remain intact. In humans, the reduction in CBF induced by Dex does not significantly affect cerebral oxygenation, provided that the patient remains hemodynamically stable. However, in cases of hypoxia or systemic hypotension, Dex can impair cerebral oxygenation, which raises concerns about its use in patients with compromised perfusion or hemodynamic instability.
Despite these concerns, Dexmedetomidine has found utility as an opioid-sparing agent in intracranial procedures, and it continues to be studied for its role in cerebral protection. However, caution is warranted when using Dex in patients with unstable cerebral or systemic oxygenation to prevent possible cerebral hypoperfusion.
