Summary

In study session I you have learnt

• Drug pharmacology is classically divided into two disciplines, pharmacodynamics and pharmacokinetics. Pharmacodynamics can be defined as what drugs do to the body. Pharmacokinetics can be defined as what the body does to drugs.
• Inhalation anesthetics are substances that are brought into the body via the lungs and are distributed with the blood into the different tissues.
• There are many steps between the administration of an anesthetic from a vaporizer and its deposition in the brain. By controlling the inspired partial pressure (PI) of an inhaled anesthetic, a gradient is created such that the anesthetic is delivered from the anesthetic machine to its site of action, the brain.
• The primary objective of inhalation anesthesia is to achieve a constant and optimal brain partial pressure (Pbr) of the anesthetic. The alveolar partial pressure and ultimately the Pbr of an inhaled anesthetic are determined by input (delivery) into the alveoli minus uptake (loss) of the drug from the alveoli into the pulmonary arterial blood.
• Input of the inhaled anesthetic depends on the inspired partial pressure (PI), alveolar ventilation (VA.), and characteristics of the anesthetic breathing system.
• Uptake of the inhaled anesthetic depends on the solubility, cardiac output (CO), and alveolar-to-venous partial pressure difference (PA _ Pv).
• After discontinuation of anesthetic administration, elimination of anesthetic occurs by ventilation of the lungs. As the alveolar partial pressure decreases, anesthetic is subsequently transferred from the tissues (including the brain) into the alveoli. Hypoventilation or use of low fresh gas flows that permit rebreathing of anesthetic will lead to transfer of anesthetic back into the tissues (including the brain), delaying patient recovery.
• The main physical properties of inhalational agents are the minimum alveolar concentration, volatility and blood gas solubility
• The minimum alveolar concentration (MAC) of an inhaled anesthetic is the alveolar concentration that prevents movement in 50% of patients in response to a standardized stimulus (e.g., surgical incision).
• Halothane is a colorless liquid with a relatively pleasant smell used as an induction agent and maintenance of anesthesia with oxygen, muscle relaxants, opioids or alone