Under physiologic conditions, the brain employs aerobic metabolism exclusively for energy production. Accordingly, the brain is critically dependent on the near continuous delivery of oxygen and glucose to sustain cellular energy production. Although the brain accounts for only 2% of total body weight, it requires 20% of the cardiac output, 20% of inspired molecular oxygen at rest and consumes the liver's entire production of glucose in the fasting state.
Depending on the measurement technique, resting CBF in the awake patient is approximately 50-55 ml/100 g brain tissue/min. As CBF decreases, neuronal dysfunction and injury occur. At levels of 16-18 ml/100 g/min, cortical electrical function fails, as evidenced by attenuation in electroencephalographic and somatosensory evoked potential recordings. At levels of 10-12 ml/100 g/min or less, rapid changes in intracellular and extracellular ion concentrations occur, along with the development of intracellular acidosis. Persistence of CBF at levels below this threshold of maintaining ionic balance will result in membrane disruption, irreversible neuronal injury and cell death.
Understanding cerebral blood flow physiology is of great importance to neurosurgeons engaged in the management of patients with cerebrovascular disease. Over the past 50 years, techniques to measure CBF and mathematical methods to calculate CBF have evolved substantially. Intraoperative measurement of cerebral blood flow, both qualitatively and quantitatively, has contributed to improved outcomes from cerebrovascular procedures. In patients undergoing carotid endarterectomy, the use of intraoperative CBF measurements has proven to be effective in reducing operative morbidity. Intraoperative CBF monitoring has
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The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.