Pharmacology  ·  General Anesthesia

Central Nervous System and Cardiovascular Effects

Cerebral blood flow, intracranial pressure, seizure risk, and cardiovascular profiles of inhalational agents

• The organs these drugs are aimed at are the same organs that limit their dose. Every effect below is an extension of the mechanism that produces unconsciousness, which is why none of it can be engineered away by choosing a different agent — only traded between agents.
• Read the first two columns of the table as a single unresolved conflict: volatile agents lower cerebral metabolic rate, which protects the brain, while simultaneously dilating cerebral vessels, which raises intracranial blood volume. Both are true of every agent, and managing the collision between them is the whole of neuroanesthesia.
• Across most of that table the agents differ in degree rather than direction — the arrows point the same way and only the magnitude changes. The seizure column is the exception, and it is categorical: enflurane alone is disqualified outright.
• The cardiovascular cards are grouped by the mechanism of blood pressure reduction rather than by chemical family. Halothane sits alone because it depresses the myocardium directly; the ethers lower pressure by vasodilating with cardiac output preserved. That distinction, not the size of the pressure drop, predicts which patient tolerates which agent.
• Propofol appears in both rule boxes despite not being an inhalational agent at all. It is there as the exit route — the drug you switch to when a volatile agent's cerebral or pulmonary liability is the thing you cannot accept in a particular case.