T HE value of a chemical or pharmacological agent that temporarily would lower cerebrospinal-fluid pressure and decrease the mass of the brain is apparent to neurosurgeons. Since Weed and 1VfcKibben 4e,47 demonstrated that various hypertonic solutions could accomplish these effects, many agents have been tested. 6,14,17,22,29,45,49,55 Each of these substances has been found to have certain disadvantages or toxic effects. The use of hypertonic urea for these purposes originally was proposed by Fremont-Smith and Forbes, 15 and Wolff and Forbes, 64 and was restudied by Fremont-Smith eta/., ~3 Smythe et a/., 39 and Javid and Settlage. ~5 This material was difficult to prepare for sterile intravenous injection, but when lyophilized urea and invert sugar became available it found wide acceptance. ~4,42,44 While hypertonic urea frequently is effective in lowering cerebrospinal-fluid pressure and decreasing the mass of the brain, there are certain theoretical and practical objections to its use. Urea is distributed throughout total body water, n.4~ although it does equilibrate relatively slowly with brain water and cerebrospinal fluid, s.33 Thus, unless the urea administered were excreted fairly rapidly, one would expect dissipation of its osmotic gradient as equilibration of urea with brain water and cerebrospinal fluid
Forty-seven patients with middle cerebral artery (MCA) stenosis and 18 patients with MCA occlusion underwent extracranial-intracranial arterial bypass procedures. Patients presented with a history of transient ischemic attacks (TIA's), reversible ischemic neurological deficits, TIA's after initial stroke, stroke-in-evolution, or completed stroke. Angiography revealed that the MCA stenosis ranged from 70% to over 95%. Two patients (4.3%) in the stenosis group had a perioperative stroke (within 30 days of operation). There was no perioperative mortality. In the occlusion group, no patient had a perioperative stroke, and one patient (5.5%) died from a non-neurological disease. The TIA's resolved completely in 90% of the patients with stenosis and in 91.6% of those with occlusion. No patient with MCA stenosis had a late ipsilateral stroke, although five had a contralateral or vertebrobasilar stroke. One patient with MCA occlusion had a late ipsilateral stroke. The bypass patency rate at late follow-up review was 100%. The results of intracranial-extracranial arterial bypass procedures appear to be similar for patients with either stenosis or occlusion of the MCA. Symptomatic relief of TIA's was excellent and, in two patients with progressive stroke-in-evolution, the deficit was stabilized. The incidence of postoperative ipsilateral stroke was low in patients with TIA's alone or with TIA's after an initial stroke, but among patients with completed stroke, improvement was confined to slight reduction in the neurological deficit.
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