Porphyria

OVERVIEW

• Porphyria = group of disorders where patients have a inability to synthesis Hb resulting in an accumulation of precursors oxidised to porphyrins
• hepatic and erythropoietic varieties
• 3 hepatic forms that effect are affected by anaesthesia

(1) AIP – acute intermittent porphyria (Sweden)
(2) VP – variegated porphyria (Afrikaners)
(3) HCP – hereditary coproporphyria (rare – dermal hypersensitivity)

HISTORY

• Female
• 30-40 yrs
• FHx
• May never have had symptoms
• Many precipitants — drugs, stress, infection, alcohol, menstruation, pregnancy, starvation, dehydration
• Abdo pain
• Vomiting
• Motor and sensory neuropathy
• Autonomic dysfunction
• Cranial nerve palsies
• Confusion
• Coma
• Seizures
• Fever

EXAMINATION

• as directed by history

INVESTIGATIONS

• urinary porphyrins & porphyrin precursors (ALA and PBG)
• serum porphyrins
• faecal porphyrins
• erythrocyte porphyrins
• DNA testing

MANAGEMENT

Prevention

• avoidance of precipitants
• premedication to decrease stress
• minimize preoperative fasting (IVF)

Anaesthetic precipitants

• Definite – barbiturates, phenytoin, sulphonamides, ropivacaine
• Possible – etomidate, lignocaine, chlordiazepoxide, diazepam, halothane, corticosteroids, ketamine, atracurium

Safe drugs

• Antacids – Na+ citrate
• Induction – propofol
• Inhalational agents – N2O, halothane, isoflurane (use with caution)
• NMBD – sux, pancuronium and vecuronium
• Reversal – atropine, glycopyrulate, neostigmine
• Analgesia – opioids
• LA – bupivacaine
• Sedatives – midazolam, temazepam, lorazepam
• Antiemetics – droperidol
• Cardiovascular drugs – adrenaline, phenylephrine, salbutamol, Mg2+, beta-blockers, phentolamine

MANAGEMENT OF PORPHYRIC CRISIS

Goals:

(1) stop precipitating agent
(2) reverse factors that increase haem production (ALA synthase activity)

Resuscitate

• Call for help
• Stop administering precipitent
• A – may need to be intubated if unresponsive or has uncontrolled agitation/pain
• B – ventilation may be indicated for progressive weakness -> respiratory failure
• C – often hypertensive and tachycardic -> beta-blockers (also decreases action of ALA), autonomic instability, invasive monitoring
• D – midazolam, MgSO4 or propofol for seizure control

Acid-base and Electrolyte abnormalities

• Hyponatraemia – fluid restriction, hypertonic saline with slow correction
• Give glucose (20g/hr)

Antidote

• Haem arginate 3mg/kg IV OD for 4/7
• Plasmapheresis
• Opioids for analgesia

Underlying Cause

Avoid precipitants