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  • Author or Editor: Helge Nornes x
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Helge Nornes and Per Wikeby

✓ This paper presents the results of a total of 468 aneurysm operations performed on a consecutive series of 463 patients in an 8-year period, using microsurgical techniques. About two-thirds of the patients were operated on within the first 2 weeks after hemorrhage. The postoperative mortality was 4.5%. A good result was obtained in 74.5% of cases, and a fair result in 11.8%, whereas 9.2% were permanently disabled. Hypothermia was used in 142 operations, and 326 were carried out under induced hypotension. Immediate and late results of surgery are discussed with reference to selection of patients, timing of surgery, and the anesthetic and operative procedures.

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Cerebral arterial blood flow and aneurysm surgery

Part 1: Local arterial flow dynamics

Helge Nornes and Per Wikeby

✓ Cerebral arterial blood flow was monitored in 22 patients undergoing surgery for intracranial saccular aneurysms. An electromagnetic flow probe was used to record the internal carotid artery (ICA) flow in the neck or intracranially in seven patients. The ICA flow ranged between 100 and 175 ml/min (average 144 ml/min). Intracranial flow measurements with specially designed probes were made in 17 patients. The middle cerebral artery (MCA) showed flow values between 75 and 120 ml/min (average 97 ml/min). Flow figures recorded from the proximal anterior cerebral artery (ACA) were lower (average 65 ml/min), and had a wider range from 30 to 110 ml/min.

Test occlusion of the terminal ICA showed a retrograde flow in the proximal ACA to the MCA ranging from 15 to 125 ml/min (average 78 ml/min). This test was used to investigate the collateral potential of the anterior portion of the circle of Willis, which is essential to the decision of whether to undertake trap ligation procedures in this location. Flow monitoring in the parent vessel was also of use in some patients to assess flow conditions after the clipping of the aneurysm neck.

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Helge Nornes, Arne Grip and Per Wikeby

✓ The use of a pulsed echo Doppler technique during procedures for occlusion of intracranial aneurysms is described. Saccular aneurysms can be located with reference to probe position and depth setting. Tracings of intra-aneurysmal flow are presented, and the characteristic flow pattern is discussed. Special emphasis has been placed on the parent artery flow, particularly the effect of lumen reduction on flow velocity. Results of flow velocity studies on the cognate (direct) and collateral flow in the middle cerebral artery and the proximal anterior cerebral artery are presented and discussed.

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Helge Nornes, Arne Grip and Per Wikeby

✓ The use of a pulsed echo Doppler technique during surgery for cerebral arteriovenous malformation is described. The equipment and the methods employed are presented. The main advantages are easy determination of flow direction and pattern of the vasculature involved, allowing a precise discrimination between inflow and outflow channels. Deep-seated malformations, not visible at the brain surface, can be located with the Doppler technique. The ultrasound probe was placed on the brain surface with a slight pressure on the intact pia mater. The precise direction and depth of the malformation could be determined in relation to the recording site. This facilitated the planning of cortical incisions, identification of vessels involved, and the vascular procedure to be employed.

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Cerebral arterial blood flow and aneurysm surgery

Part 2: Induced hypotension and autoregulatory capacity

Helge Nornes, Hanna Berit Knutzen and Per Wikeby

✓ A study of 21 patients was conducted to clarify the autoregulatory capacity in patients subjected to induced hypotension during intracranial surgery for saccular aneurysms. Trimethaphan camsylate (Arfonad) was used for induced hypotension and arterial blood flow was measured with an electromagnetic flow probe on the internal carotid artery or one of its main intracranial branches. In Grade I and II patients the control arterial blood pressure (ABP) ranged from a mean of 90 to 135 mm Hg (average 110 mm Hg), with a lower level of autoregulation (LLAR) from 35 to 85 mm Hg (average 62 mm Hg). Grade III patients had a control ABP of between 105 and 145 mm Hg (average 124 mm Hg) and the LLAR was found to be between 60 and 95 mm Hg (average 76 mm Hg). There was a significant difference between the two groups with regard to both the control ABP and the LLAR. A surprising result obtained from these data was that the average lower autoregulatory range (the difference between control ABP and LLAR) is practically the same in the two groups. A systematic investigation of the upper limit of autoregulation was not possible for ethical reasons. In those few patients in whom spontaneous increase in the ABP made such observations possible, upper limits up to 150 mm Hg with a total autoregulatory capacity of about 75 mm Hg were observed. In some patients, however, lower limits and corresponding “breakthroughs” of cerebral blood flow were seen, demonstrating that the upper limit of autoregulation is markedly influenced by several factors.