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FP-C Neuro Transport Review: ICP, TBI & Stroke
Neuro transport is the discipline of protecting a brain that has already been injured once from being injured again by physiology you control: hypoxia, hypotension, hyper- and hypocapnia, fever, hypoglycemia. The exams test CPP arithmetic (CPP = MAP − ICP), the secondary insult list, herniation recognition with the correctly-ordered response, and the logistics layer — EVDs, stroke windows, and positioning at altitude.
The two sentences that answer half the questions: a single episode of hypotension or hypoxia measurably worsens TBI outcomes, and hyperventilation is a briefed temporizing measure for active herniation, never routine ventilation.
Pressure physiology and the secondary-insult war
The math: CPP = MAP − ICP. Normal ICP runs under ~15 mmHg; injured brains need CPP maintained per receiving targets (commonly quoted 60–70 mmHg in adults). The Monro-Kellie doctrine explains why: skull volume is fixed — blood, brain, CSF — and an expanding mass/edema first displaces CSF and venous blood (compensation), then ICP climbs steeply (decompensation). Your transport job is both sides of the equation: keep MAP up (treat hypotension aggressively per protocol) and avoid raising ICP (positioning, sedation/analgesia, CO2 control, treating fever/seizures).
The secondary insults, each a tested item: hypoxia (SpO2 floor commonly cited at 90% — avoid absolutely); hypotension (even one episode worsens outcomes — fluids/pressors per protocol); hypocapnia (overbagging vasoconstricts cerebral vessels and starves the penumbra — target normocapnia ~35–45 mmHg via waveform capnography); hypercapnia (vasodilates, raises ICP); hyperthermia (raises metabolic demand — treat fever); hypoglycemia (the brain's fuel — check glucose on every altered patient); seizures (metabolic firestorm — treat per protocol and consider prophylaxis orders); pain/agitation (sympathetic surges spike ICP — sedate and analgese adequately, especially for transport stimulation: sirens, vibration, turbulence).
Herniation, EVDs, stroke logistics
Herniation recognition: a unilaterally blown pupil (uncal herniation compressing CN III), Cushing's triad (hypertension, bradycardia, irregular respirations), motor posturing (decorticate → decerebrate is worsening), rapid GCS decline. The ordered response: optimize the basics first (head midline and elevated ~30°, collars not strangling venous drainage, sedation adequate); osmotherapy per protocol (hypertonic saline or mannitol — know your service's agent and its cautions: mannitol diureses — watch the pressure; hypertonic needs line considerations); temporizing hyperventilation to the briefed target (commonly EtCO2 ~30–35 mmHg) only with active herniation signs; and speed to neurosurgical care — the definitive treatments (craniectomy, drains) live there.
EVDs in transport: an external ventricular drain measures ICP and drains CSF — leveled at the tragus (foramen of Monro), open/clamped per the sending plan, and re-leveled after every position change (a drain left open and mis-leveled can overdrain catastrophically or under-read). Document ICP trends and CSF output. Stroke: the transport job is timestamp custody (last known well), glucose, pressure management per the receiving plan (ischemic strokes tolerate higher pressures pre-thrombolysis; post-tPA patients have strict ceilings and bleeding vigilance), neuro checks on an interval, and destination logic — thrombolysis windows and thrombectomy capability drive routing; minutes of transport efficiency are brain. Position: head elevated for ICP concerns; flat-ish positioning historically argued for ischemic perfusion — follow the receiving plan; at altitude, remember Boyle's law and pneumocephalus (post-craniotomy/skull-fracture air expands — lowest safe altitude).
Practice questions with answers & rationales
Q1. MAP 80, ICP 25. Compute CPP, interpret it, and name your two levers.
Answer: CPP = 80 − 25 = 55 mmHg — below the commonly targeted 60–70 band: the injured brain is being underperfused. Levers: raise MAP (fluids/vasopressors per protocol) and lower ICP (head up 30° and midline, sedation/analgesia, normocapnia, osmotherapy per protocol/orders, treat fever and seizures). The exam wants both sides of the subtraction named — candidates who only push MAP miss half the physiology.
Q2. Why is a single episode of hypotension so heavily penalized in TBI care?
Answer: Autoregulation is damaged in the injured brain — cerebral blood flow becomes passively pressure-dependent, so a systolic dip that a healthy brain would autoregulate through becomes frank ischemia in penumbral tissue. Outcome studies associate even one documented hypotensive episode with significantly worse mortality/disability, which is why transport protocols treat pressure floors as hard limits with pressors ready, not as values to observe.
Q3. Your TBI patient's left pupil suddenly dilates and the heart rate falls to 48 with rising BP. Order your actions.
Answer: Active herniation (uncal, with Cushing's response). Order: confirm and optimize basics — airway/oxygenation, head midline and elevated, collar loosened if compressing, sedation adequate; osmotherapy per protocol (hypertonic saline or mannitol); institute temporizing hyperventilation to the briefed EtCO2 target (~30–35) now that herniation is active; notify the receiving neurosurgical center and fly fast. The trap answers: hyperventilating prophylactically before herniation, or skipping the venous-drainage basics that cost nothing.
Q4. What's wrong with 'bagging a head injury fast to keep the pressure down'?
Answer: Hyperventilation lowers ICP by vasoconstriction — it shrinks cerebral blood volume by reducing cerebral blood flow, which strangles marginal tissue. Routine hyperventilation trades a number (ICP) for ischemia and worsens outcomes; guidelines reserve it as a short-acting temporizer for active herniation, at a defined EtCO2 target, while definitive therapies are mobilized. The transport standard: continuous waveform capnography with normocapnia (~35–45) unless herniation forces the briefed exception.
Q5. You're transporting a patient with an EVD set open to drain at 10 cm above the tragus. The crew repositions the litter 15° head-up for loading. What must happen and why?
Answer: Re-level the transducer/drip chamber to the tragus (external auditory meatus — the foramen-of-Monro reference) immediately after any position change, and verify the prescribed drain height and clamp status per the sending orders. An open drain that's now too low overdrains CSF (risking collapse/hemorrhage); too high under-drains and under-treats ICP. Also record ICP and CSF output trends. EVD questions are leveling-and-logistics questions — the physics is the test.
Q6. Why does 'last known well' outrank 'symptom discovery time' in stroke transport, and what else rides on your documentation?
Answer: Thrombolysis and thrombectomy eligibility windows count from the last moment the patient was verifiably normal — a wake-up stroke's clock starts at bedtime, not at waking. Your timestamp custody (witness names, phone numbers, exact times), glucose result, anticoagulant history and neuro-exam baseline ride directly into the receiving team's treatment decision. Sloppy time documentation can disqualify a treatable patient; precise documentation is, literally, therapy access.
Q7. A post-craniotomy patient with documented pneumocephalus needs fixed-wing transfer. What's the flight-physiology concern and the mitigation?
Answer: Boyle's law: intracranial air expands as cabin pressure falls with altitude — tension pneumocephalus can raise ICP acutely. Mitigations: confer with the sending/receiving physicians, request the lowest safe cabin altitude (or sea-level cabin where the airframe allows), maximize ICP-protective basics, monitor neuro status closely during climbs, and brief the crew on descent options if deterioration occurs. Linking gas laws to neuro patients is exactly the crossover question the FP-C favors.
Common mistakes to avoid
- Routine hyperventilation of head injuries — it's a herniation-only temporizer with a briefed target.
- Tolerating 'brief' hypotension or desaturation; the secondary-insult list is a zero-tolerance list.
- Forgetting venous-side basics: head midline, 30° elevation, collars and tube ties not strangling drainage.
- Leaving an EVD open and unleveled through position changes — or clamping/opening against the sending plan.
- Accepting vague stroke timelines; last-known-well custody is part of the transport's clinical value.
- Ignoring sedation/analgesia for the stimulating transport environment — every siren and jolt is an ICP spike.