Volatility

The number of halogen binding sites contributes to chemical stability, not speed of induction.

Inspired concentration

Pungency or tolerability can limit the inspired concentration of agent.

Alveolar minute ventilation

Factors which increase alveolar anaesthetic concentration speed onset; factors which decrease alveolar concentration slow onset.

Ether has a saturated vapour pressure of 425 mm Hg (56.6 k Pa); it can therefore be given in high inspired concentrations (faster induction). It stimulates respiration (faster induction).

Gas solubility in blood

A high blood:gas partition coefficient results in greater uptake of anaesthetic gas by blood. Greater blood uptake of agent keeps the alveolar agent concentration low, relative to the inspired concentration.

Because the anaesthetic partial pressures in all tissues will approach that in the alveoli, the high blood solubility will delay the onset of anaesthetic effect in the brain (slower induction and recovery). Ether is highly soluble in blood.

The speed of uptake of more soluble agents can be increased by delivering a higher concentration of inspired agent than is aimed for in the alveoli.

Cardiac output

Ether tends to maintain the cardiac output. Higher cardiac output tends to slow induction by decreasing anaesthetic partial pressure in the alveoli.

Potency of anaesthetic agents is compared using Minimum Alveolar Concentration (MAC).

MAC is the alveolar concentration at one atmosphere which abolishes motor response to a standardized incision in 50 % of patients.

MAC

The MAC of ether is 1.92 % which makes it of low potency (slower induction).