Anesthesiology
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Changes in basal temperature of > or = 1 degree C (e.g., fever-induced hyperthermia or anesthesia-related hypothermia) are a common occurrence in neurologically impaired patients. The current study tested the hypothesis that temperature changes as small as 1 degree C or 2 degrees C would significantly alter post-ischemic functional neurologic outcome and cerebral histopathology. The hypothesis was tested in a canine model of transient, complete cerebral ischemia. ⋯ Small, clinically relevant changes in temperature (1 degree C or 2 degrees C) resulted in significant alterations in both postischemic neurologic function and cerebral histopathology. Assuming that our results are transferable to humans, the results suggest that, in patients at imminent risk for ischemic neurologic injury, body temperature should be closely monitored. Further, the clinician should aggressively treat all episodes of hyperthermia until the patient is no longer at risk for ischemic neurologic injury.
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Systemic vascular resistance (the ratio of mean aortic pressure [AP] and mean aortic blood flow [AQ]) does not completely describe left ventricular (LV) afterload because of the phasic nature of pressure and blood flow. Aortic input impedance (Zin) is an established experimental description of LV afterload that incorporates the frequency-dependent characteristics and viscoelastic properties of the arterial system. Zin is most often interpreted through an analytical model known as the three-element Windkessel. This investigation examined the effects of isoflurane, halothane, and sodium nitroprusside (SNP) on Zin. Changes in Zin were quantified using three variables derived from the Windkessel: characteristic aortic impedance (Zc), total arterial compliance (C), and total arterial resistance (R). ⋯ The major difference between the effects of isoflurane and halothane on LV afterload derived from the Windkessel model of Zin was related to R, a property of arteriolar resistance vessels, and not to Zc or C, the mechanical characteristics of the aorta. No changes in arterial wave reflection patterns determined from Zin spectra occurred with isoflurane and halothane. These results indicate that isoflurane and halothane have no effect on frequency-dependent arterial properties.