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The arteria dorsalis pedis, when clearly palpable, is a suitable artery for direct arterial blood pressure monitoring. The systolic pressure and the pulse pressure are likely higher in the dorsalis pedis artery when compared to the radial artery but there is no clinically significant difference in mean pressures. In plethysmographic studies it was found that in 16 per cent of the patients examined the pulse in the second toe disappeared after occlusion of the dorsalis pedis artery indicating that it carried the main blood supply to the toes. Although no complications have resulted from cannulation of the dorsalis pedis artery in our practise, some caution is in order and preliminary testing may be advisable even if the posterior tibial artery is distinctly palpable.

A MAJOR PROBLEM affecting the surgical treatment of intracranial aneurysms is the rupture of the aneurysm prior to clipping. To prevent this occurrence the pressure within the aneurysm must be kept low. This was done in the past either by compressing the vessels supplying the aneurysm, in which case hypothermia was required, or by controlled hypotension. Until 1962 in the Neurosurgical Unit of the Victoria Hospital in London, Ontario, operation was done early after the bleeding and mainly under moderate hypothermia with controlled ventilation. Many anaesthetic agents were used and controlled hypotension was added in some eases. Although the surgical conditions were generally adequate, postoperative arterial spasm was a major factor in the prognosis. 1 The anaesthetic management and the time interval between the haemorrhage and operation seemed to affect the incidence of postoperative spasm z ( Table I ).When the operation was done early, the use of hypothermia seemed to predispose to postoperative arterial spasm, particularly when it was associated with artificial ventilation (Table II). As a consequence of this study, early operation was abandoned except when a significant clot was present or when there was repeated bleeding, and an attempt was made to utilize an anaesthetic technique that would give the surgeon optimal conditions without using hypothermia and controlled ventilation.A fairly standard anaesthetic technique is used by three anaesthetists involved in these eases which are operated upon usually six or more days after a haemorrhage. This technique includes light halothane anaesthesia with spontaneous ventilation throughout and controlled hypotension.Spontaneous respiration was felt to be advantageous because mild hyperearbia was produced which, when added to the effect of halothane, tended to increase cerebral blood flow. Although this would tend to raise intraeranial pressure prior to craniotomy and to increase brain size when the dura was open, so making surgery difflcult~ it could be compensated for by drainage of cerebro-spinal fluid (CSF). After the dura was opened, CSF was removed through a catheter placed in the subarachnoid space at the level of L3-4 or L4-5. 3 No problems arose, provided that drainage was stopped if the blood pressure rose or the heart rate decreased. Mannitol was sometimes used as well, although improper timing of its use may lead to hypervolaemia and later diffleulty with the management of the hypotension. The level of hypotension aimed for was about 40 mm Hg mean.

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