A system for monitoring a concentration of an anesthetic drug using a patients breath is provided. The system comprises a sampling subsystem for processing the patients breath to form a breath sample, one or more sensors to measure drug concentration in the breath sample, one or more sensors to measure a concentration of gases in the breath sample and one or more microprocessors for determining a concentration of the drug in a plasma of the patient using a transfer function and the concentration of the drug in the breath sample. A system for monitoring propofol concentration in patients breath sample is also provided.
