1. INSPIRED ANESTHETIC CONCENTRATION: Dalton's Law; high partial pressure of the gas in the lungs results in more rapid achievement of anesthetic levels in the blood
2. ALVEOLAR VENTILATION: the greater the ventilation,the more rapid is the rise in the alveolar and blood partial pressure of the agent and the onset of anesthesia.
3. BLOOD/GAS SOLUBILITY (λ b/g): the more rapidly a drug equilibrates with the blood, the more quickly the drug passes into the brain to produce anesthetic effects. Drugs with a low b:g partition coefficient equilibrates more rapidly than those with a higher blood solubility.
4. PULMONARY PERFUSION (CARDIAC OUTPUT): at high pulmonary blood flows, the gas partial pressure rises at a slower rate → speed of onset of anesthesia reduced. At low flow rates, onset is faster.