Neurotrauma and Critical Care
Core concepts
Traumatic brain injury (TBI) management rests on preventing secondary injury: hypotension and hypoxia are the two most modifiable insults. Know the Monro-Kellie doctrine and the volume-pressure curve - small added volume is tolerated until compensation is exhausted, then ICP rises steeply. Understand cerebral perfusion pressure (CPP = MAP − ICP), the rationale for head-of-bed elevation, sedation, osmotherapy (mannitol vs hypertonic saline), and short-term hyperventilation only as a bridge for herniation. Know the Glasgow Coma Scale components and that the motor score carries the most prognostic weight. Recognize the classic hematoma patterns: epidural (lens, middle meningeal artery, lucid interval), subdural (crescent, bridging veins), and traumatic subarachnoid hemorrhage. Understand when to reverse anticoagulation and when surgery is indicated (e.g., epidural hematoma with mass effect, depressed skull fracture).
Traps
Questions love the "lucid interval" and ask you to localize the bleeding source. Another trap: confusing CPP targets with blood pressure targets - raising MAP does not always lower ICP. Watch for the patient on hyperventilation whose PaCO2 is driven too low, causing ischemia. Also beware attributing a fixed, dilated pupil to a drug rather than uncal herniation.
Worked rule of thumb
CPP = MAP − ICP. If MAP is 80 and ICP is 25, CPP is 55 - below the usual 60–70 target, so the priority is lowering ICP (CSF drainage, osmotherapy, sedation) rather than simply pushing pressors.