• Increase
  • Increased central neurotransmitter levels (monoamine oxidase inhibitors, acute dextroamphetamine administration, cocaine, ephedrine, levodopa)
  • Hyperthermia
  • Chronic ethanol abuse
  • Hypernatremia
• Decrease
  • Increasing age
  • Metabolic acidosis
  • Hypoxia (PaO₂ 38 mm Hg)
  • Induced hypotension (MAP <50 mm Hg)
  • Decreased central neurotransmitter levels (α-methyldopa, reserpine)
  • α₂-Agonists
  • Hypothermia
  • Hyponatremia
  • Lithium
  • Hypo-osmolality
  • Pregnancy
  • Acute ethanol administration
  • Ketamine
  • Lidocaine
  • Opioids
  • Opioid agonist–antagonist analgesics
  • Barbiturates
  • Diazepam
  • Hydroxyzine
  • Delta-9-Tetrahydrocannabinol
  • Verapamil
  • Anemia (<4.3 mL oxygen/dL blood)

MAP = mean arterial pressure.