Porphyrias are a set of autosomally inherited metabolic disorders that are the result various defects in heme synthesis. Broadly, they can be classified into inducible, and non-inducible forms.
Inducible porphyrias (i.e. Acute Intermittent Porphyria) can present with acute neurological and/or GI symptoms. Patients may have anxiety, confusion, autonomic instability (manifested as hypertension or tachycardia), emesis, and severe abdominal pain. Acute attacks can be precipitated by stress, fasting, dehydration, sepsis, and certain medications, including some meds commonly used in the perioperative period.
- Triggering agents include: barbiturates, diazepam, ketorolac, phenytoin, birth control pills and sulfonamides.
- Drugs that are safe to use in the perioperative period include succinylcholine, atropine, neostigmine, pancuronium, nitrous oxide, procaine, meperidine, fentanyl and morphine.
- Local anesthetics are believed to be safe, but some practitioners avoid regional anesthesia in these patients, as it may be difficult to distinguish neurological complications of a regional procedure from sequelae of an acute attack.
- Although ketamine and etomidate have been used safely in patients with AIP, they have been found to be porphyrogenic in rats. Some practitioners avoid ketamine use altogether in these patients, as it can be difficult to distinguish psychoses associated with an inducible porphyria from those associated with ketamine use in some patients.
Noninducible porphyrias (i.e. Porphyria Cutanea Tarda) are not affected by drugs. They usually appear as photosensitivity reactions in males >35 years of age. These patients often have friable skin, so it becomes important to pay close attention to pressure points in the operating room environment. Practitioners should avoid excess pressure/irritation to exposed areas (i.e. with mask ventilation or securing ETT and protecting eyes with tape, etc.). Of note, non-inducible porphyrias do not cause neurologic sequelae.
Defined by: Andrew R. Crichlow, MD