Factors Affecting Inspiratory Concentration

FACTORS AFFECTING INSPIRATORY CONCENTRATION F_I

The fresh gas leaving the anesthesia machine mixes with gases in the breathing circuit before being inspired by the patient. Therefore, the patient is not necessarily receiving the concentration set on the vaporizer. The actual composition of the inspired gas mixture depends mainly on the fresh gas flow rate, the volume of the breathing system, and any absorption by the machine or breathing circuit. The higher the fresh gas flow rate, the smaller the breath-ing system volume, and the lower the circuit absorp-tion, the closer the inspired gas concentration will be to the fresh gas concentration. Clinically, these attributes translate into faster induction and recov-ery times.