1.Outpouring of catecholamines from the tumour due to preoperative anxiety, to anaesthesia or especially as a result of surgical handling of the tumour leading to severe hypertension or arrhythmias.

2.Profound hypotension as a result of sudden expansion of the vascular bed after clamping of the last venous drainage from the tumour.

Most phaeochromocytomas are predominantly noradrenaline secreting, but not only does the proportion of noradrenaline to adrenaline vary from case to case, but also the lability of the tumour, i.e. the readiness with which it secretes catecholamines. Because of this, some tumours appear docile even during handling at surgery, and case reports abound describing apparently successful regimens of preparation of the patient. However, phaeochromocytomas are unpredictable and it is better to use one basic, effective technique of preoperative preparation modified as appropriate to suit each case. This is best achieved by giving drugs which block the &agr;- and &bgr;-adrenergic effects of catecholamines independently. The most useful long-acting &agr;-blocking agent is phenoxybenzamine, which when given by mouth does not reach its peak effect for 12 to 24 h. Treatment with this drug should therefore be instituted at least 48 h before adding a &bgr;-blocking agent, as a surge of catecholamine output in the absence of &bgr;-adrenergic activity may result in a very high blood pressure due to lack of &bgr;-induced vasodilatation. There is a wider choice of &bgr;-blocking drugs, but one of the longer-acting, cardioselective agents such as atenolol or metoprolol may give smoother control. Labetalol, a mixed &agr;- and &bgr;-blocking agent, can be used, but has the disadvantage of providing the &agr;- and &bgr;-blockade in fixed proportions, with the latter predominating, the reverse of that required to treat the &agr;-effects arising from the noradrenaline secreted by most tumours.

Some idea of the adequacy of &agr;-blockade can be obtained by sequential haematocrit measurements, which fall as the blood volume expands. However, the most reliable method of assessing the adequacy of both &agr;- and &bgr;-blockade is simply by charting the patient's pulse and blood pressure two-hourly (except during sleep) for several days. The blood pressure should be recorded both lying and standing, and use of different colours aids graphic representation. In addition, the pulse and blood pressure should be recorded if the patient has any symptomatic episode. The aim with effective treatment is a chart showing a steady pulse rate in the 60 to 70 beats/min range with no episodes of tachycardia and a blood pressure also devoid of surges, with a small postural drop. Because of the slow onset of adequate &agr;-blockade and its associated increase in blood volume, at least a week is required for effective preoperative preparation. Changes in phenoxybenzamine should not be made more often than once daily. In a few cases, effective control of the blood pressure may be very resistant to adrenergic blocking drugs alone and other antihypertensive drugs, e.g. calcium channel blocking agents and ACE inhibitors may be added. &agr;-Methyltyrosine, which inhibits tyrosine hydroxylase, the enzyme involved in the conversion of tyrosine to dopa—an essential step in the synthesis of both adrenaline and noradrenaline—may help stabilize blood pressure in difficult cases.

Brown MJ. Phaeochromocytoma. In: Weatherall DJ, Ledingham JGG, Warrell DA, eds. Oxford Textbook of Medicine. 3rd Edn. Oxford: University Press, 1994, in press.

Hull CJ. Phaeochromocytoma. Diagnosis, preoperative preparation and anaesthetic management. Br J Anaesthesia, 1986; 58: 1453–68.

Sheps SS, Jiang N-S, Klee GG, Van Heerden JA. Recent developments in the diagnosis and treatment of pheochromocytoma. Mayo Clin Proc, 1990; 65: 88–95.