Pharmacology  ·  General Anesthesia

Principles of General Anesthesia

Inhalational pharmacokinetics, anesthetic potency, intravenous agents, and preanesthetic medications

• General anesthesia has four components — unconsciousness, analgesia, amnesia, and skeletal muscle relaxation — and no single drug produces all four at safe doses. Every agent below earns its place by contributing one or two of them, which is why the panels that follow are organized by role rather than by chemical class.
• For inhalational agents, one physical property governs almost everything clinically observable: how readily the drug dissolves in blood. The first table ranks the agents by that property, and the ordering it produces is also the ordering of induction speed and of emergence speed.
• Potency is measured separately from speed. Minimum alveolar concentration is the standard yardstick, and the two panels of modifiers matter because the shifts are large enough to cause overdose — age being the most clinically consequential of them.
• The intravenous agents are chosen far less for potency than for what they do to the circulation, the airway, and the brain. Read the four cards as a selection guide: each one leads with the feature that makes that drug the right or wrong choice for a particular patient.
• Premedication is deliberately multimodal, targeting several receptor systems at once because anxiety, nausea, secretions, and gastric acid are separate problems. The closing table pairs each drug with the specific goal it serves and the caution attached to it.