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Helge Nornes

✓ Intracranial epidural pressure (EDP) was recorded in 29 patients admitted with ruptured saccular aneurysms, but unfit for immediate surgery. In 10 patients a total of 13 recurrent hemorrhages were recorded; the average time before rerupture was 7.7 days after the last hemorrhage. Ten of the rebleedings started from intracranial pressure levels at or below 400 mm H2O whereas three started from higher prerupture levels. The observations indicate an increasing risk of rebleeding as the epidural pressure decreases toward normal pressure. Most repeat hemorrhages are arrested at EDP levels about that of the diastolic blood pressure. The resulting reduced pressure gradient across the aneurysm wall is important in the arrest of hemorrhage and the maintenance of hemostasis. Measurement of internal carotid artery blood flow during the acute stage of recurrent hemorrhage shows marked changes in blood flow pattern. Arrest of blood flow occurred only at the end of diastole; forward flow occurred only during systole. The effect of intracranial-pressure-buffering mechanisms on the increased EDP after rupture is discussed. Activation of these mechanisms may reduce the EDP to acceptable pressure levels within minutes and should be awaited before decompressive management is considered. Continuous recording of the EDP in patients unfit for immediate aneurysm surgery is important in the selection of the optimal time for operation.

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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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Helge Nornes and Arne Grip

✓ Local hemodynamics were studied in 16 patients undergoing total extirpation of cerebral arteriovenous malformation (AVM). Directional Doppler technique was used for the registration of blood velocities in vessels feeding and draining the AVM. Calculated flow in single feeding arteries ranged from 3 to 550 ml/min (average, 180 ml/min). An estimation of total AVM flow was possible in nine patients, and ranged from 150 to more than 900 ml/min (average, 490 ml/min). Pressure recordings were made from feeding arteries at their entrance to the AVM. This pressure was well below the systemic arterial blood pressure in all cases, and ranged from 40 to 77 mm Hg (average, 56 mm Hg). On temporary occlusion, this stump pressure instantly rose to from 55 to 95 mm Hg (average, 76 mm Hg). Draining vein pressure before occlusion ranged from 8 to 23 mm Hg (average, 15 mm Hg), and fell to zero in all patients when the AVM was occluded. These data and other clinical observations are discussed with regard to adjacent brain-tissue perfusion, and with special emphasis on the circulatory breakthrough that can follow the occlusion of these high-capacity shunts.

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Helge Nornes and Björn Magnæes

✓ Intracranial pressure was recorded in 21 patients with subarachnoid hemorrhage due to rupture of a saccular aneurysm. Two different pressure patterns were found in nine patients who had verified recurrent hemorrhages while awaiting clinical improvement. One was associated with massive hematoma while the other occurred with edema but only minimal hematoma; the terms “hemorrhagic-compressive lesion” and “ischemic-edematous lesion” have been used for these two conditions. Four patients showed transient deterioration concomitant with marked pressure peaks in the continuous record. Although there was no evidence of fresh hemorrhage, three of these episodes were followed by a verified hemorrhage within 24 hours. Since no such “warning episode” was seen after the aneurysm had been clipped, the authors consider this pressure peak and concomitant clinical deterioration to be related to the mechanism of aneurysm rupture and possibly a forerunner of a life-threatening hemorrhage. These three pressure patterns showed the whole range from full spatial compensation to total decompensation. The determining factors are considered to be the volume of extravasated blood, the vasomoter reaction, and the intracranial spatial buffering capacity.

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Helge Nornes and Björn Magnæs

✓ Supratentorial epidural pressure (EDP) was recorded during posterior fossa surgery in 14 patients. It was found that the operative position had great influence on the supratentorial EDP and that a correct position, especially of the head, was important in the control of the intracranial pressure. Rapid and extensive ventricular drainage may set up a secondary rise in pressure and must be avoided. Craniectomy alone did not have any definite decompressive effect as judged from the EDP. Splitting of the dura or resection of a tumor usually resulted in a fall in the EDP in patients with previously increased pressure. Inadequate ventilation as well as hyperventilation was rapidly manifested through variations in the EDP. EDP monitoring combined with single determinations of PaCO2 was a valuable guide in securing adequate ventilation.

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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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Rune Aaslid and Helge Nornes

✓ A transcranial ultrasonic method for the recording of murmurs from cerebral vessels is described. Using the new approach the authors have observed musical murmurs of pure tone quality in 15 patients with increased flow velocities in the cerebral arteries after spontaneous subarachnoid hemorrhage (SAH). The frequency range of the pure tones was from 140 to 820 Hz, corresponding to flow velocities between 73 and 215 cm/sec. The musical murmurs occurred as a transitional state between silent flow and the well known phenomenon of bruit. They were observed between the 4th and the 20th day after SAH. The most likely cause of the musical murmur is a periodic shedding of vortices in the cerebral arteries, commonly referred to as “a von Kármán vortex street.” Clinically the presence of musical murmurs indicated that pathologically increased blood velocities were present in the artery under investigation. This probably reflected the degree of spasm.

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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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Rune Aaslid, Thomas-Marc Markwalder and Helge Nornes

✓ In this report the authors describe a noninvasive transcranial method of determining the flow velocities in the basal cerebral arteries. Placement of the probe of a range-gated ultrasound Doppler instrument in the temporal area just above the zygomatic arch allowed the velocities in the middle cerebral artery (MCA) to be determined from the Doppler signals. The flow velocities in the proximal anterior (ACA) and posterior (PCA) cerebral arteries were also recorded at steady state and during test compression of the common carotid arteries. An investigation of 50 healthy subjects by this transcranial Doppler method revealed that the velocity in the MCA, ACA, and PCA was 62 ± 12, 51 ± 12, and 44 ± 11 cm/sec, respectively. This method is of particular value for the detection of vasospasm following subarachnoid hemorrhage and for evaluating the cerebral circulation in occlusive disease of the carotid and vertebral arteries.

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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.