Journal of neurosurgical anesthesiology
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J Neurosurg Anesthesiol · Jul 1994
Ketamine directly dilates bovine cerebral arteries by acting as a calcium entry blocker.
This in vitro study was performed to determine the role of calcium in ketamine-induced cerebral vasodilation. Isolated bovine middle cerebral arteries were cut into rings to measure isometric tension development or into strips to measure radioactive 45Calcium (45Ca) uptake. Ketamine produced direct relaxation of arterial rings; the relaxation was attenuated in Ca(2+)-deficient media. ⋯ In Ca(2+)-deficient media containing potassium or the stable thromboxane A2 analogue, ketamine produced competitive inhibition of subsequent Ca(2+)-induced constriction. Ketamine blocked potassium- and thromboxane A2-stimulated 45Ca uptake in a dose-dependent manner, but had no effect on basal 45Ca uptake, the externally bound 45Ca content, or the volume of the 3H-sorbitol space. These results indicate that ketamine can directly dilate cerebral arteries by acting as a calcium channel antagonist; ketamine inhibits 45Ca uptake through both potential-operated (potassium) and receptor-operated (thromboxane A2) channels in cerebrovascular smooth muscle.
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J Neurosurg Anesthesiol · Jul 1994
Effects of THAM and sodium bicarbonate on intracranial pressure and mean arterial pressure in an animal model of focal cerebral injury.
Episodes of arterial hypotension are associated with an increased mortality in head injury patients. Rapid infusion of sodium bicarbonate in such patients may cause hypotension and elevate intracranial pressure. Therefore, we examined the effects of tromethamine (THAM) versus bicarbonate on intracranial pressure and blood pressure in a model of focal cerebral injury. ⋯ THAM infusion was associated with a significantly lower intracranial pressure and blood pressure than bicarbonate. The fall in blood pressure was great enough that cerebral perfusion pressure after THAM infusion was significantly lower than after bicarbonate infusion. In this model of cerebral injury, rapid infusion of THAM offered no therapeutic advantage over bicarbonate.
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J Neurosurg Anesthesiol · Apr 1994
Soluble fibrin and D-dimer as detectors of hypercoagulability in patients with isolated brain trauma.
To test the hypothesis that hypercoagulability after brain trauma was related to the severity of injury and also to outcome, new coagulation markers were used in 20 patients with isolated brain trauma. In addition to routine coagulation tests, soluble fibrin (SF), D-dimer, and antithrombin (AT) levels were assessed. Thirteen of 20 patients had a Glasgow coma score (GCS) of < or = 7 on admission and severe disability (SD) or worse on the Glasgow outcome scale (GOS). ⋯ Six of 13 patients with a significant drop in AT levels had a bad outcome (D or V) whereas only two of seven patients without AT consumption did poorly. Routine coagulation studies were often pathologic, i.e., reduced platelet count, but there was no relation to outcome. Increased SF and D-dimer levels at admission followed by a secondary decrease in AT concentration and platelets seem to be good markers of the posttraumatic hypercoagulation often seen after brain injury.(ABSTRACT TRUNCATED AT 250 WORDS)
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J Neurosurg Anesthesiol · Apr 1994
Sitting position for neurosurgery: experience with preoperative contrast echocardiography in 301 patients.
A persisting foramen ovale (PFO) is the most common cause of paradoxical air embolism. To detect right-to-left shunting, transthoracic contrast echocardiography was performed preoperatively in 301 patients scheduled for neurosurgical procedures in the sitting position. Echocardiography yielded evaluable results in 285 patients (94.7%). ⋯ If echo signals appeared in the left heart after more than 5 heart cycles, an intrapulmonary right-to-left shunt was considered (11 patients, 3.9%). Venous air embolism (VAE) occurred in 27.4% of 226 patients operated on in the sitting position and in none of the 59 patients operated on in a nonsitting position. We conclude that the sitting position during neurosurgery should be avoided in patients with preoperative evidence of a right-to-left shunt at contrast echocardiography to reduce the risk of paradoxical air embolism (PAE).