Diseases Affecting the Brain

Intracranial pathology and neurological disorders demand specialized anesthetic approaches that fundamentally differ from general surgical practice. Cerebral physiology establishes the foundation for understanding how the brain responds to anesthetic drugs and surgical manipulation. Cerebral blood flow remains tightly autoregulated across a range of mean arterial pressures, though this protective mechanism shifts rightward in chronically hypertensive patients. Carbon dioxide exerts profound effects on cerebral vasculature, with each millimeter of mercury increase in arterial CO2 producing substantial increases in blood flow. Volatile anesthetics function as cerebral vasodilators that increase intracranial volume and pressure, whereas intravenous agents like propofol and barbiturates reliably decrease both through vasoconstriction. The Monro-Kellie hypothesis governs intracranial pressure dynamics within the rigid skull, where brain tissue, blood, and cerebrospinal fluid exist in fixed volumetric relationships. Managing elevated intracranial pressure requires multimodal strategies including head elevation for venous drainage optimization, controlled hyperventilation targeting specific carbon dioxide ranges, osmotic therapy with mannitol or hypertonic saline, and selective corticosteroid use for vasogenic edema. Intracranial tumors, cerebrovascular diseases including aneurysms and arteriovenous malformations, and traumatic brain injury each present distinct anesthetic challenges centered on maintaining cerebral perfusion while preventing pressure surges. Subarachnoid hemorrhage introduces the complication of vasospasm with its characteristic delayed neurological deterioration. Resection of arteriovenous malformations carries particular risk for normal perfusion pressure breakthrough, a dangerous phenomenon where chronically underperfused tissue becomes hyperemic following surgical removal. Traumatic brain injury management prioritizes prevention of secondary insults through careful airway management, optimization of cerebral perfusion pressure between specific targets, and judicious use of hyperventilation only for acute intracranial pressure crises. Degenerative neurological conditions including Parkinson disease, multiple sclerosis, and seizure disorders require modified anesthetic techniques and perioperative drug management. Multiple sclerosis patients demonstrate extreme sensitivity to even minimal temperature elevations that can precipitate severe symptom exacerbation. Postoperative neurocognitive disorders represent significant morbidity following neurological procedures, with evidence suggesting that benzodiazepine limitation and appropriate depth of anesthesia monitoring may reduce incidence. Venous air embolism during sitting position procedures demands vigilant monitoring through esophageal echocardiography and Doppler techniques. Ischemic optic neuropathy emerges as a serious postoperative complication particularly associated with prolonged prone positioning during spinal procedures.