Neurologic Monitoring / Nervous System / Critical Care Manual

Pre-hospital assessment

Knowledge of the patient’s pre-hospital state is important, as any signs of deterioration suggest an ongoing insult (such as a mass lesion) which may be amenable to surgical therapy.

Vital Signs[edit]

Temperature below 32.2C (90F) can significantly alter the neurologic exam. Alcohol, drug intoxication, post-operative state are the most common causes. Complications of hypothermia include dehydration, lactic acidosis, arrhythmias. Temperatures > 42C (108F) will cause a coma {Plum FA. The Diagnosis of Stupor and Coma}. Less-elevated hyperthermia can cause lethargy or delirium. The most common causes in the NICU are infection and hypothalamic dysfunction (“central fever”) – infectious fevers are often variable, whereas central fever tends to be stable and sustained (can be as high as 40C). Fever increases CBF and ICP, and must be controlled.

Hypertension (with bradycardia) is part of Cushing’s triad, however according to Andrews, these patients will often present with hypertension and no change in heart rate. SBP < 60 mm Hg renders the neurologic exam inaccurate {Andrews et al. In normal patients, the brain autoregulates down to SBPs as low as 60 mm Hg but in the injured brain this may not be the case.

The combination of bradycardia and hypotension point to the possibility of a spinal cord injury – in these cases, atropine and/or alpha–agonists are first line, NOT fluids.

Any alteration in respiratory pattern should be viewed with suspicion.

Neurologic Exam Miscellanei[edit]

Note that in 25% of patients with the tentorial herniation triad (depressed consciousness, unilateral papillary dilatation, hemiplegia) the hemiplegia will be ipsilateral (due to Kernohan’s notch {Kernohan JW, Woltman HW: Incisura of the crus due to contralateral brain tumor. Arch Neurol Psychiatry 21:274, 1929., not available on PubMed}). Also note that flexion injuries suggest diffuse cerebral injury with intact brainstem, whereas extension suggests an additional injury to the midbrain or upper pons (or even a severe metabolic disorder).

Oxygenation and Ventilation[edit]

PaO2 < 60 mm Hg or PaCO2 > 50 mm Hg unequivocally intensifies respiratory failure {Rowland 0683304747}. Most patients will respond to severe hypoxia by becoming hypotensive secondary to reflexive myocardial depression {reference from Porciuncula et al given in original text, does not specifically mention this}, however humans can generally tolerate extremely low PaO2 as long as blood pressure is maintained. When hypoxia is associated with hypercarbia, recovery is much less frequent.