Anaesthesia in a patient with porphyria

A patient with known variegate porphyria presents with suspected acute appendicitis

and requires a laparoscopy. The patient is fasted, in pain and extremely anxious. Which

one of the following options describes the BEST peri-operative management?

a) Fluid: Hartmanns + 10% glucose; Premedication: Midazolam; Induction agent:

Propofol; Maintenance anaesthetic agent: Isoflurane

b) Fluid: Hartmanns; Premedication: none; Induction agent: Thiopentone;

Maintenance anaesthetic agent: Propofol

c) Fluid: Hartmanns + 10% glucose; Premedication: none; Induction agent: Propofol;

Maintenance anaesthetic agent: Sevoflurane

d) Fluid: 5% dextrose; Premedication: none; Induction agent: Propofol; Maintenance

anaesthetic agent: Isoflurane

e) Fluid: Hartmanns + 10% glucose; Premedication: none; Induction agent:

Thiopentone; Maintenance anaesthetic agent: Isoflurane

Answer: a

Explanation

The porphyrias are due to deficiencies in activity of one or more of the enzymes

required for normal haem synthesis, which results in an overproduction of porphyrins

and porphyrin precursors. Most types of porphyria are inherited, although the

most common type, porphyria cutanea tarda, is usually an acquired disorder associated

with liver disease and iron overload. Porphyrias can be classified in a number

of ways but from an anaesthetic point of view classification by whether or not they

cause acute symptoms is of most use as those that do are the only ones of major

anaesthetic relevance. The porphyrias causing acute symptoms are acute intermittent

porphyria, variegate porphyria, hereditary coproporphyria and plumboporphyria.

Symptoms of an acute attack vary but include abdominal pain, autonomic disturbance,

electrolyte abnormalities, neuropsychiatric manifestations and neuromuscular

weakness. A number of factors precipitate or exacerbate attacks, including starvation,

poor intake of carbohydrates, drugs, alcohol, smoking, infections and other forms of

stress. Although the pathogenesis is not completely understood, it appears likely that

many aspects of such an attack are due to adverse effects of excess 5-aminolevulinic

acid (ALA), which is structurally similar to γ-aminobutyric acid, the major inhibitory

neurotransmitter. Diagnosis is made by the measurement of ALA and porphobilinogen

in urine or serum. A variety of drugs are known to precipitate attacks and an

up-to-date list may be found via the website listed below. For the purposes of

answering this question the patient should have a source of carbohydrate perioperatively,

hence Option (b) is false. Thiopentone is on the list of drugs that carry

a risk of precipitating a porphyric crisis, so ruling out Option (e). Hyponatraemia is

known to precipitate a crisis, so fluid therapy consisting of solely 5% dextrose would

be unwise, thus ruling out Option (d). Option (c) is incorrect as Sevoflurane may

carry some risk (see website) and the lack of a premedication will increase the risk of

anxiety precipitating a crisis.

References

James MF, Hift RJ. Porphyrias. Brit J Anaes 2000; 85(1): 143–53.

University of Queensland Department of Medicine website. Online at www.uq.edu.

au/porphyria (Accessed 30 November 2009)