Anesthetic considerations in porphyrias.

Four hereditary types of porphyria are now classified as acute porphyrias. Enzymatic defects result in accumulation of porphyrin precursors (usually ALA and PGB). The quantity of these precursors may be normal or slightly increased in latent periods but increase to toxic levels during a porphyric crisis. Iatrogenic induction of ALA synthetase by administration of certain triggers (classically barbiturates) is only one of several factors which contribute to porphyric crisis. Signs and symptoms of acute porphyric attack consist primarily of neurologic dysfunction, which occurs secondary to neurotoxicity of ALA or diminished intraneuronal heme levels. Appropriate anesthetic management of porphyria requires knowledge of the type of porphyria (acute vs non-acute), assessment of latent versus active (crisis) phase, awareness of clinical features of porphyric attack, and knowledge of safe pharmacologic intervention.