A control device for controlling an infusion device for administering a drug to a patient, the control device being constituted to: (a) provide a model (p) to predict a time-dependent drug concentration (Clung, Cplasma, Cbrain) in multiple compartments (A1-A5) of a patient wherein the model (p) is a pharmacokinetic-pharmacodynamic model to predict a drug concentration (Clung, Cbrain, Cplasma) as a function of time (t) in multiple compartments (A1-A5) of a patient and wherein the multiple compartments (A1-A5) comprise a plasma compartment, a lung compartment, a brain compartment; (b) set a target concentration value (C T brain) to be achieved in at least one of the compartments (A1-A5) of the patient wherein the at least one of the compartments is the brain compartment; (c) determine a drug dosage to be administered to a first compartment of the multiple compartments (A1-A5) of the patient using the model (p) such that the difference between the target concentration value (C T brain) and a predicted steady-state drug concentration (Cplasma, Clung, Cbrain) in the at least one of the compartments (A1-A5) is smaller than a pre-defined threshold value (Δbrain) wherein the first compartment is the plasma compartment; (d) provide, as an output, a control signal indicative of the drug dosage to an infusion device for intravenously administering the drug dosage to the patient; (e) obtain, as an input, at least one measurement value (M1, M2) indicating a measured drug concentration in a least a second compartment (A2, A3) of the multiple compartments (A1-A5) at a measurement time (t1, t2) by measuring the drug concentration in an exhaled breath of the patient wherein the lung compartment is the second compartment, wherein a transfer function is used with the patient to convert signals measured in the breath of the patient into the drug concentration in the lung compartment wherein the transfer function is generated under steady-state conditions; (f) adjust the model (p) such that the model (p) is recalibrated to predict a drug concentration (Clung, Cbrain) in at least the second compartment (A2, A3) at the one or more measurement time (t1, t2) which at least approximately matches the measured drug concentration in at least the second compartment (A2, A3) wherein the model (p) is adjusted by using a least-squares fit such that the drug concentration predicted by the model (p) in the lung compartment at least approximately matches an actually measured drug concentration; and (g) determine a new drug dosage (D2, D3) to be administered into the first compartment of the patient using the recalibrated model (p) such that the difference between the target concentration value (C T brain) and a predicted steady-state drug concentration (Cplasma, Clung, Cbrain) in the at least one of the compartments (A1, A2, A3) is smaller than the pre-defined threshold value (a) provide a model (p) to predict a time-dependent drug concentration (Clung, Cplasma, Cbrain) in multiple compartments (A1-A5) of a patient wherein the model (p) is a pharmacokinetic-pharmacodynamic model to predict a drug concentration (Clung, Cbrain, Cplasma) as a function of time (t) in multiple compartments (A1-A5) of a patient and wherein the multiple compartments (A1-A5) comprise a plasma compartment, a lung compartment, a brain compartment; (b) set a target concentration value (C T brain) to be achieved in at least one of the compartments (A1-A5) of the patient wherein the at least one of the compartments is the brain compartment; (c) determine a drug dosage to be administered to a first compartment of the multiple compartments (A1-A5) of the patient using the model (p) such that the difference between the target concentration value (C T brain) and a predicted steady-state drug concentration (Cplasma, Clung, Cbrain) in the at least one of the compartments (A1-A5) is smaller than a pre-defined threshold value (Δbrain) wherein the first compartment is the plasma compartment; (d) provide, as an output, a control signal indicative of the drug dosage to an infusion device for intravenously administering the drug dosage to the patient; (e) obtain, as an input, at least one measurement value (M1, M2) indicating a measured drug concentration in a least a second compartment (A2, A3) of the multiple compartments (A1-A5) at a measurement time (t1, t2) by measuring the drug concentration in an exhaled breath of the patient wherein the lung compartment is the second compartment, wherein a transfer function is used with the patient to convert signals measured in the breath of the patient into the drug concentration in the lung compartment wherein the transfer function is generated under steady-state conditions; (f) adjust the model (p) such that the model (p) is recalibrated to predict a drug concentration (Clung, Cbrain) in at least the second compartment (A2, A3) at the one or more measurement time (t1, t2) which at least approximately matches the measured drug concentration in at least the second compartment (A2, A3) wherein the model (p) is adjusted by using a least-squares fit such that the drug concentration predicted by the model (p) in the lung compartment at least approximately matches an actually measured drug concentration; and (g) determine a new drug dosage (D2, D3) to be administered into the first compartment of the patient using the recalibrated model (p) such that the difference between the target concentration value (C T brain) and a predicted steady-state drug concentration (Cplasma, Clung, Cbrain) in the at least one of the compartments (A1, A2, A3) is smaller than the pre-defined threshold value