Assessment of coma

CT is usually more readily available and faster than MRI, but it may provide less detail. Unenhanced scans are performed first, then contrast is added if needed to clarify nature of mass (e.g., differentiation from tumour or brain abscess). [Figure caption and citation for the preceding image starts]: Brainstem haemorrhage in the midbrain that extended from a hypertensive haemorrhage in the ponsFrom the personal collection of G. Bryan Young, MD; used with permission [Citation ends].

Post-MI cardiac emboli may cause ischaemic stroke.

AF may produce cardiac emboli that may cause ischaemic stroke. Patients with AF may be taking warfarin, which increases the risk of haemorrhagic stroke.

Usually performed later. MRI can provide more detail than CT. Can be helpful in showing the vascular supply to a vascular malformation that has bled.

With infective endocarditis, systemic embolisation may occur and cause ischaemic stroke.

Cardioversion with electrical shocks may be indicated. Intravenous adrenaline (epinephrine) is required for asystole. [Figure caption and citation for the preceding image starts]: Monomorphic ventricular tachycardiaFrom the collection of Amar Krishnaswamy; used with permission [Citation ends].[Figure caption and citation for the preceding image starts]: Torsades de pointesFrom the collection of Amar Krishnaswamy; used with permission [Citation ends].

This is performed between 1 and 3 days post-arrest or later. Bilateral absent cerebral cortical response (N20) indicates very poor prognosis (almost always in vegetative state [unresponsive wakefulness syndrome] or severe disability). The false-positive rate is very close to zero.

Serum test done at 1 to 3 days post-arrest. Values >33 micrograms/L are associated with poor prognosis. Test availability may vary by region.

Caused by acute/subacute elevations of blood pressure to levels that overcome cerebral autoregulation.

An apparent diffusion coefficient (ADC) map should be done to exclude infarction.

Performed if CT negative and condition not improving.

Often caused by accelerated hypertension. Performed secondary to imaging, but still important.

Often caused by accelerated hypertension. Performed secondary to imaging, but still important.

Often caused by accelerated hypertension. Performed secondary to imaging, but still important.

Occlusion is seen either in the proximal portion (feature of basilar syndrome, usually with midbrain and thalamic damage) or more extensively.

CT is more easily obtained and gives better detail than MRI.

Occlusion is seen either in the proximal portion (feature of basilar syndrome, usually with midbrain and thalamic damage) or more extensively.

MRI can be helpful in showing the vascular supply to a vascular malformation that has bled.

An accurate diagnosis, shown by CT or magnetic resonance venography is needed promptly. MRI can provide more detail than CT. Can be helpful in showing the vascular supply to a vascular malformation that has bled.

More than one third of cases are due to a coagulation disorder. This is done secondary to acute neuroimaging and anticoagulation. However, it is important to allow prophylaxis against further episodes/relapses.

Rarely comprehensive but can be specified to include alcohol, benzodiazepines, barbiturates, opioids, cocaine, amfetamines, tricyclic antidepressants, salicylates, paracetamol, and other agents. Some drugs, such as antihistamines, may not have an available assay and assessment must be based on clinical suspicion.

Respiratory alkalosis may be present with acute salicylate intoxication. Metabolic acidosis may be present with salicylate, methanol, ethylene glycol ingestion.

Smokers may have slightly elevated carbon monoxide (<15%).

Performed for prognostic purposes.

If shock is present, urgent simultaneous treatment is required. WBC count may be normal in early stages of infection or in older patients.

May be possible to measure lactate in the arterial blood gas sample.

Findings are not specific and can be found in other metabolic encephalopathies; the severity of the EEG abnormality reflects the severity of sepsis.

Often negative if patient has received earlier antibiotics. [Figure caption and citation for the preceding image starts]: Photomicrograph of Gram-stained Streptococcus species bacteriaFrom the CDC Public Health Image Library [Citation ends].

Blood cultures and initiation of treatment with empirical antibiotics is important while requesting neuroimaging.

Neuroimaging must be negative for mass effect.

It may be necessary to monitor patients for ≥24 hours to detect intermittent arrhythmias. There may be evidence of heart block of various degrees, which can be a clue for intermittent complete heart block causing syncope.

This can be helpful in cases of frequent syncope. It is fairly reliable if positive.

Seizures are usually generalised if the patient is comatose, but these are infrequently present; in most cases an EEG is needed for confirmation. Have a low threshold for ordering EEGs when the cause is not apparent. Risk factors include a preceding convulsive seizure followed by coma, past history of epilepsy, or a structural brain lesion.

Can be useful in determining the cause of unexplained seizures. Extreme hypoglycaemia or hyperglycaemia can cause provoked generalised or partial seizures.

Uraemia can cause provoked generalised or partial seizures.

Elevated levels can indicate the risk of myoglobinuria and renal damage.

This is done for patients with known seizure disorders on antiseizure medications. Serum levels are usually very low in these patients. In special circumstances it is best to 'load' the patient with their usual drug.

CT is usually more readily available and faster than MRI, but it may provide less detail. For mass lesions, unenhanced scans are performed first and then contrast is added if needed to clarify the nature of the mass.

Neuroradiological confirmation of DAI is more problematic, as the axons cannot be visualised.

Only performed if CT is not available.

Usually performed later. For mass lesions, MRI can provide more detail than CT. Neuroradiological confirmation of DAI is more problematic, as the axons cannot be visualised, although it is more sensitive for DAI than CT.

Useful prognostic technique; shows tract damage much better than conventional MRI. Availability may vary by region.[100]Ashwal S, Babikian T, Gardner-Nicols J, et al. Susceptibility-weighted imaging and proton magnetic resonance spectroscopy in assessment of outcome after pediatric traumatic brain injury. Arch Phys Med Rehabil. 2006 Dec;87(12 Suppl 2):S50-8. http://www.ncbi.nlm.nih.gov/pubmed/17140880?tool=bestpractice.com

Useful prognostic technique that uses a single sensory pathway. Usually shows a poor prognosis and dependency if the patient survives. Has shown to be sensitive and specific for severe DAI.

May be abnormal in severe cases and can be helpful prognostically.

May produce hyperosmolar state, with serum osmolality >320 mmol/L.

Bilirubin is usually elevated and aspartate aminotransferas is markedly elevated in hepatitis or acute liver failure. Plasma ammonia is usually elevated but is not helpful in its correlation with the degree of encephalopathy.

Elevated when synthetic function of the liver is compromised. INR is useful in following the trend of worsening or improving liver function.

May be depressed in advanced liver failure. It is an index of the severity of acute liver failure.

Elevated in severe, acute liver failure. An index of severity of acute liver failure.

Usually no clinical features unless serum sodium <125 mmol/L (125 mEq/L), especially for acute hyponatraemia. Chronic hyponatraemia is often well tolerated.

TSH is elevated with thyroid gland failure and is reduced in central nervous system (CNS; hypothalamic or pituitary) causes.

Mild respiratory failure.

Not specific but helpful feature.

Elevated with reduced pyruvate dehydrogenase. Reference range: 6 to 17 micromol/L (0.5 to 1.5 mg/dL).

Diagnosis is primarily clinical. MRI confirmation should not delay thiamine administration.

Reference range is wide; useful in good labs with tight controls; it is often impractical, as it is not readily available.

Specific but seldom available.

Serum concentrations may fall precipitously after re-feeding, as there is an increased shift of phosphate into cells.

CT is highly sensitive if done in the first day or 2, but lumbar puncture is needed if there still is a possibility of subarachnoid haemorrhage and the CT is negative.

Preferred diagnostic test. Probably better than magnetic resonance angiography for detection of aneurysms. May be substituted for or precede CSF analysis. Could be used as 2ⁿᵈ test if history and findings are strongly suggestive. Reveals the source of subarachnoid haemorrhage >95% of the time, allowing for planning to prevent repeated bleeding (e.g., clipping or coiling of the responsible aneurysm).

Can be useful in showing the first signs of vasospasm.

Given a compatible clinical picture, this is almost diagnostic of herpes simplex encephalitis. Consider limbic encephalitis (an autoimmune disorder that is often a paraneoplastic syndrome) if only medial temporal lobe structures are involved.

Prior neuroimaging is wise to exclude significant mass effect, which can make lumbar puncture hazardous. PCR is highly specific and sensitive and is positive in 90% of cases. Diagnosis can be confirmed by finding IgM antibodies for certain viruses (herpes simplex virus, rabies virus, arthropod-borne virus) in the CSF.

PLEDS can be seen in other acute/subacute structural lesions but, given context, are sensitive in >80% of cases of acute herpes simplex encephalitis; can be helpful in monitoring for seizures.

CT is usually more readily available and faster than MRI, but it may provide less detail. Unenhanced scans are performed first, and then contrast is added if needed to clarify nature of mass (e.g., differentiation of tumour from brain abscess).

Important to do, although results are often negative.

WBC count is not reliably elevated.

Usually performed later. MRI can provide more detail than CT.[99]Goldstein LB, Adams R, Alberts MJ, et al; American Heart Association; American Stroke Association Stroke Council. Primary prevention of ischemic stroke: a guideline from the American Heart Association/American Stroke Association Stroke Council: cosponsored by the Atherosclerotic Peripheral Vascular Disease Interdisciplinary Working Group; Cardiovascular Nursing Council; Clinical Cardiology Council; Nutrition, Physical Activity, and Metabolism Council; and the Quality of Care and Outcomes Research Interdisciplinary Working Group. Circulation. 2006 Jun 20;113(24):e873-923. https://www.ahajournals.org/doi/full/10.1161/01.STR.0000223048.70103.F1?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed http://www.ncbi.nlm.nih.gov/pubmed/16785347?tool=bestpractice.com

CT is usually more readily available and faster than MRI, but it may provide less detail. Unenhanced scans are performed first and then contrast is added if needed to clarify nature of mass (e.g., differentiation of tumour from brain abscess). [Figure caption and citation for the preceding image starts]: Meningioma: coronal contrast-enhanced image demonstrates meningioma in cavernous sinus on left sideFrom the personal collection of William T. Couldwell; used with permission [Citation ends].[Figure caption and citation for the preceding image starts]: Craniopharyngioma: coronal post-contrast MRIFrom the personal collection of Marc C. Chamberlain; used with permission [Citation ends].

Usually performed later. MRI can provide more detail than CT. Can be helpful in showing multiple lesions: for example, metastases. [Figure caption and citation for the preceding image starts]: Medulloblastoma: sagittal view MRI showing an avidly enhancing solid and cystic lesion filling the fourth ventricle; obstructive hydrocephalus presentFrom the collection of Peter B. Storm; used with permission [Citation ends].[Figure caption and citation for the preceding image starts]: Acoustic neuroma: coronal post-contrast MRIFrom the collection of Ryojo Akagami; used with permission [Citation ends].

Patients are usually asymptomatic until serum sodium is >160 mmol/L (160 mEq/L).

Caused by diarrhoea/vomiting.

Severe CNS dysfunction occurs at >4 mmol/L (>16 mg/dL).

Performed shortly after establishing hypercalcaemia. The diagnosis of primary hyperparathyroidism is based on substantial elevation of PTH despite hypercalcaemia. The normal range is up to 65 nanograms/L (65 picograms/mL). Multiple myeloma or leukemia may cause slightly low PTH.

Performed shortly after establishing hypercalcaemia. Elevated >400 mg/24 hour with primary hyperparathyroidism.

Performed shortly after establishing hypercalcaemia. If positive, may indicate multiple myeloma, leukaemia, or bone secondaries.

It is most helpful to measure serum ionized calcium (usually <0.5 mmol/L [2.0 mg/dL]) or total serum calcium (<1.75 mmol/L [<7.0 mg/dL]). If measuring total serum concentrations, consider serum albumin, as calcium is albumin-bound (corrected [Ca] = measured [Ca] + [40- {albumin} x 0.02 for g or mg/L]).

Clinical are features usually only present when serum Mg is >2.5 to 4 mmol/L (5 to 8 mg/dL).

Hypercapnia, indicating respiratory failure, is one of the main life-threatening complications of hypermagnesaemia. Patients may require intubation and assisted ventilation in the intensive care unit (ICU).

Elevated concentrations are usually marked during attacks. The presence of PBG can be confirmed in a single-void urine specimen using a PBG test kit.

Caused by lactic acidosis.

Performed after preliminary investigations to define the clinical syndrome.

Often helpful but may not be sufficiently specific. Can show discrete metabolic strokes that often do not respect arterial territories.

Score is based on the severity of thermoregulatory dysfunction, GI-hepatic dysfunction, cardiovascular dysfunction, heart failure, CNS effects, and the presence or absence of known triggers.[101]Burch HB, Wartofsky L. Life-threatening thyrotoxicosis: thyroid storm. Endocrinol Metab Clin North Am. 1993 Jun;22(2):263-77. http://www.ncbi.nlm.nih.gov/pubmed/8325286?tool=bestpractice.com

Only useful if the patient is not already known to have hyperthyroidism.

Only useful if the patient is not already known to have hyperthyroidism.

EEGs show a graded pattern of severity. Mortality is 70% with the burst suppression patterns, but patients die of multi-organ failure rather than nervous system complications.

Hyperthermia often causes seizures.

WBC count can be elevated in cases of sepsis (sometimes associated with low body temperature in older or disabled people).

Worth doing to help rule out infection, especially in older people.

Hypothyroidism may cause hypothermia.

At core temperatures <28°C, there is a risk of ventricular fibrillation and cardiac arrest.

These changes are thought to reflect a progressive failure of synaptic transmission in the brain.

No seizure activity during the ictus. This test is often not necessary if the episode is captured on video or witnessed, but does add conclusive evidence.

Readily available and of some confirmatory value. Convulsive seizure shows a profound, mixed metabolic-respiratory acidosis.

The 'train of 4' in the ICU transcutaneous nerve stimulation (usually of the median nerve) looks for muscle response. Neuromuscular blockade demonstrated in AIDP and Guillain-Barre syndrome.