Definition
For a volatile anesthetic agent, the time constant (τ) is volume divided by flow. From the standpoint of the anesthesia circuit, the time constant is the volume of the circuit divided by the fresh gas flow rate (units of L divided by L/min results in min). From the standpoint of the lungs, the time constant is the volume of the lungs (FRC) divided by the minute ventilation. It takes three time constants for 95% of a concentration change to be achieved.
Time Constant (τ)
 Definition (circuit): volume of the circuit divided by the fresh gas flow rate
 Definition (lungs): volume of the lungs (FRC) divided by minute ventilation
 Meaning: it takes three time constants for 95% of a concentration change to be achieved
Subspecialty
Related Media
Keyword history
13%/2009
See Also:
Sources

Barash, PG. Clinical Anesthesia, 6th ed. (Philadelphia), p. 417, 2009
http://en.wikipedia.org/wiki/Time_constant

Time Constant, Wikipedia.org