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Basics ⬇

Basics

Overview

  • Stupor-unconscious but arousable with noxious stimuli.
  • Coma-unconscious, not arousable with noxious stimuli.

Pathophysiology

Ascending reticular activating system-network of neurons situated in the core of the brainstem; arousal system for the cerebral cortex; any severe pathologic change (anatomic or metabolic) that causes interruption can lead to depression, stupor, or coma.

Systems Affected

  • Nervous
  • Cardiovascular
  • Neuromuscular
  • Ophthalmic
  • Respiratory

Signalment

  • Dog and cat
  • No breed, age, or sex predilection

Signs

Historical Findings

  • Possibility of trauma or unsupervised roaming.
  • Past medical problems of significance-diabetes mellitus and insulin therapy; hypoglycemia; cardiovascular problems; hypoxic episodes; renal failure; liver failure; neoplasia.
  • Patient's environment-possible heatstroke; hypothermia; drowning; exposure to drugs, including owner's medications narcotics, and toxins (e.g., ethylene glycol, lead, anticoagulants).
  • Onset may be acute or slowly progressive, depending on underlying cause.

Physical Examination Findings

  • Look for evidence of external or internal trauma.
  • Severe hypothermia or hyperthermia.
  • Evidence of hypoxia or cyanosis, ecchymosis or petechiation, or cardiac or respiratory insufficiency-warrants investigation for metabolic causes.
  • Palpate for evidence of neoplasia.
  • Retinal hemorrhages or distended vessels-hypertension.
  • Papilledema-cerebral edema.
  • Retinal detachment-infectious, neoplastic, or hypertensive causes.
  • Chorioretinitis-infectious causes (distemper, FeLV-related diseases, toxoplasmosis, cryptococcosis, or coronavirus).
  • Sustained bradycardia (with normal serum potassium)-midbrain, pontine, or medullary lesion.

Neurologic Examination Findings

  • Differentiate cerebrum-diencephalon lesion from brainstem lesion (better vs. worse prognosis).
  • Determine level of consciousness and if patient arousable.
  • Pupillary light reflexes-small responsive pupils: cerebral or diencephalic lesion; dilated unresponsive pupils (unilateral or bilateral) or fixed in midposition: midbrain or severe medullary lesions.
  • Oculocephalic reflex (when cervical manipulation possible)-loss of physiologic vestibular nystagmus: brainstem involvement.
  • Respiratory patterns-Cheyne-Stokes respiration: severe, diffuse cerebral or diencephalic lesion; hyperventilation: midbrain lesion; ataxic or apneustic breathing: pons or medulla lesion.
  • Cranial nerves-no deficits with lesion of cerebrum-diencephalon; deficits of cranial nerve III: midbrain lesion; deficits of cranial nerves V–XII: pons and medulla lesions.
  • Postural changes-decerebrate rigidity: midbrain lesion.

Causes

  • Drugs-narcotics; anesthetics; depressants; ivermectin
  • Anatomic-hydrocephalus.
  • Metabolic-severe hypoglycemia; hyperglycemia; hyperosmolar syndromes; hypernatremia; hyponatremia; hepatic encephalopathy; hypoxemia; hypercarbia; hypothermia; hyperthermia; hypotension; coagulopathies; renal failure; lysosomal storage disease, severe hypothyroidism
  • Nutritional-hypoglycemia; thiamin deficiency
  • Neoplastic (primary)-meningioma; astrocytoma; gliomas; choroid plexus papilloma; pituitary adenoma; others
  • Metastatic-hemangiosarcoma; lymphoma; mammary carcinoma; others
  • Inflammatory non-infectious-granulomatous meningoencephalomyelitis
  • Infectious-bacterial; viral (distemper, FCoV); parasitic (aberrant larva migrants); protozoal (neosporosis, toxoplasmosis); fungal (cryptococcosis, blastomycosis, histoplasmosis, coccidioidomycosis, actinomycosis); tick-borne diseases
  • Idiopathic-epilepsy (post–status epilepticus)
  • Immune-mediated-vasculitis and thrombocytopenia leading to hemorrhage
  • Traumatic
  • Toxins-ethylene glycol; lead; rodenticide anticoagulants; others
  • Vascular-hemorrhage (bleeding disorders, hypertension); infarction (feline ischemic encephalopathy, microfilaria, or migrating adult heartworm)

Risk Factors

  • Diabetes mellitus-insulin therapy
  • Hepatic failure
  • Insulinoma
  • Severe heat or cold exposure without protection
  • Free-roaming animals-trauma
  • Young and unvaccinated animals
  • Hypertension

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Acute onset-most commonly caused by toxins, drugs, trauma, or vascular accidents
  • Slow progression of neurologic signs without systemic abnormalities-suggests primary neurologic disorders of inflammatory, neoplastic, or anatomic causes
  • Bilateral diffuse cortical signs-metabolic diseases, toxins, systemic infection, drugs, and nutritional causes
  • Brainstem signs-trauma, inflammation, neoplasia, vascular accidents, or commonly from progression of cerebral disease causing tentorial herniation

CBC/Biochemistry/Urinalysis

CBC

  • Lead toxicity-may show nucleated red blood cells or basophilic stippling
  • Severe infection-inflammatory hemogram
  • Severe anemia-suggests hypoxemia

Biochemistry

May see hypoglycemia, hyperglycemia, hypernatremia, azotemia, hyperosmolarity, and other metabolic derangements

Urinalysis

  • Diabetes mellitus-glycosuria
  • Renal failure-isosthenuria, granular casts Immune-mediated disease or severe infection-proteinuria
  • Hepatic encephalopathy-ammonium biurate crystals
  • Ethylene glycol toxicity-calcium oxalate or hippurate crystals

Other Laboratory Tests

  • Serum ethylene glycol level and osmolar gap-acute onset.
  • Serum ammonia concentrations and preprandial and postprandial bile acids-high levels indicate hepatic encephalopathy.
  • Serum and CSF titers-suspected infectious disease.
  • Arterial blood gases-evidence of hypoxemia; severe pH changes; hypo- and hyper-carbia.
  • Coagulogram-including PT, PTT, fibrinogen, fibrin degradation product, d-dimer, platelet count, antithrombin, and buccal bleeding time; suspected intracranial bleeding or thrombosis.
  • Serologic testing-FeLV, FIV, FCoV, protozoal and heartworm disease.
  • Serum toxicity levels (e.g., lead, macrolide).
  • Thyroid panel.

Imaging

  • Survey radiographs (chest and abdomen)-evidence of heavy metal, organ enlargement, infiltration, or neoplasia.
  • Skull radiographs-fractures in trauma cases, masses.
  • CT-excellent for detecting acute hemorrhage within calvaria; depressed fractures; penetrating foreign bodies.
  • MRI with contrast-demonstrates cerebral edema, hemorrhage, mass, infiltrative diseases.

Diagnostic Procedures

  • CSF-cytology, protein and immunoglobulin concentrations, and titers for infectious diseases; perform only when no evidence of trauma, increased intracranial pressure, coagulopathies, or metabolic disease.
  • Brainstem auditory-evoked response-determine brainstem function.
  • ECG-determine cardiac dysfunction; abnormalities may contribute to stupor or coma or may be caused by brain disease.
  • EEG-detect nonclinical seizure activity that can prolong stupor and coma.

Pathologic Findings

Cerebral edema; hemorrhage; infarct; ischemia; inflammation; neoplasia; herniation; laceration; contusion; hematomas; skull fracture; necrosis and apoptosis.

Treatment ⬆ ⬇

Treatment

Poor Perfusion

  • Small volume fluid resuscitation technique; a combination of hydroxyethyl starch with balanced isotonic crystalloids.
  • Use peripheral veins, leaving the jugular vein blood flow unobstructed; shifting blood volume into the jugular veins is an important compensatory mechanism during high ICP.
  • Maintain systolic BP >90 mmHg; avoid hypertension.
  • Hydration-maintain with a balanced electrolyte crystalloid solution.
  • The head and neck should be leveled with the body or elevated to a 20° angle.
  • Oxygen supplementation-avoid a cough or sneeze reflex during intubation or nasal cannula placement; administer lidocaine (dogs, 1–2 mg/kg IV) before intubation to blunt the gag and cough reflex.
  • PaO2 must be >50 mmHg to maintain cerebral blood flow auto-regulation in normal tissue.

VENTILATION

  • PaCO2-maintain between 35–45 mmHg.

Reduce Increase In Icp

  • Prevent thrashing, seizures, or any other form of uncontrolled motor activity that can elevate ICP; diazepam infusion (0.5–1 mg/kg/h), midazolam (0.2–0.4 mg/kg), or propofol (3–6 mg/kg IV titrated to effect; then 0.1–0.6 mg/kg/min CRI); levetiracetam 20 mg/kg IV/IM/rectal q8h if seizure activity.
  • Ensure systolic BP >90 mmHg.
  • 7% hypertonic saline (2–4 mL/kg IV); can reduce fluid volume needed to reach resuscitation endpoints; combine with colloid.
  • Furosemide 0.75 mg/kg IV; may decrease CSF production; used in patients with congestive heart failure, volume overload, hyperosmolar diseases, or anuric renal failure; use before mannitol.
  • Mannitol 0.1–0.5 g/kg IV bolus repeated at 2-hour intervals 3 or 4 times in dogs, and 2 or 3 times in cats; repeated doses must be given on time; improves brain blood flow and lowers ICP.
  • Hyperventilation (PaCO2 32–35 mmHg) for 48 hours using mechanical ventilation; requires intensive monitoring.
  • Ventriculostomy for drainage of CSF if critical elevation of ICP nonresponsive to medical treatment.
  • Consider surgical decompression and exploration-if cerebral dysfunction is progressing to midbrain signs with a history of trauma or bleeding (tentorial herniation); high ICP not responsive to medical therapy (if monitoring instrumentation available); depressed skull fracture fragments; penetrating foreign body; requires intensive monitoring.

Nursing Care

  • Prevent secondary complications of recumbency-eye lubrication; aseptic technique with catheters; turning.
  • Prevent urine/fecal scalding.
  • Careful nasogastric tube feeding for early trickle flow feeding; cisapride (0.5 mg/kg PO q8–12h) and metoclopramide (1–2 mg/kg/day) may promote GI motility.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Underlying Disease

  • Glucocorticosteroids-inflammatory, immune-mediated and space-occupying intracranial abnormalities.
  • Lactulose enemas, flumazenil (0.02 mg/kg IV) and fluid support-hepatic encephalopathy.
  • Fluid diuresis, dialysis-renal failure.
  • Rehydration and insulin-diabetes mellitus with hyperosmolality; lower glucose slowly.
  • Glucose supplementation-hypoglycemia.
  • Support intravascular volume; cool-hyperthermia.
  • Support intravascular volume; warm to 98°F-hypothermia.
  • Gastric lavage and instillation of activated charcoal with a cathartic-toxin ingestion.
  • Specific toxins may require specific therapeutics (e.g. ethylene glycol treated with ethanol and peritoneal/hemo dialysis).
  • Antibiotics-use agents that cross the blood-brain barrier for suspected bacterial infections (e.g., trimethoprim-sulfa, clindamycin, doxycycline, and metronidazole).
  • Adjust crystalloid fluid selection to correct electrolyte disorders.
  • Thiamin (cat, 5–50 mg; dog, 1–20 mg IV)-possible thiamin deficiency.

Contraindications

N/A

Precautions

  • Avoid hypo- and hypertension, hypo- and hyperglycemia.
  • Avoid intravascular volume overload.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Serial neurologic examinations-detect deterioration that warrants aggressive therapeutic intervention.
  • BP-keep fluid therapy adequate for perfusion while avoiding hypertension.
  • Blood gases-assess need for oxygen supplementation or ventilation; monitor PCO2 when hyperventilating.
  • Blood glucose-ensure adequate level to maintain brain functions while avoiding hyperosmolality.
  • ECG-detect arrhythmias that may affect perfusion, oxygenation, and cerebral blood flow.
  • ICP-detect marked elevations; track success of therapeutics.
  • Electrolytes-detect hypernatremia and hypokalemia.

Prevention/Avoidance

  • Keep pets confined or leashed.
  • Prevent exposure to toxins or in-home medications.
  • Routine healthcare program to minimize infectious and metabolic disease complications.

Possible Complications

  • Residual neurologic deficits and seizures.
  • Complications consistent with underlying disease.

Expected Course and Prognosis

  • Pathology of brainstem worse than pathology of cerebral cortex.
  • Glasgow Coma Score can provide prognostic information.

Miscellaneous ⬆

Miscellaneous

Abbreviations

  • BP = blood pressure
  • CSF = cerebrospinal fluid
  • CT = computed tomography
  • ECG = electrocardiogram
  • EEG = electroencephalogram
  • FeLV = feline leukemia virus
  • FCoV = feline coronavirus
  • FIV = feline immunodeficiency virus
  • ICP = intracranial pressure
  • MRI = magnetic resonance imaging
  • PaCO2 = partial pressure of carbon dioxide in arterial blood
  • PaO2 = partial pressure of arterial oxygen
  • PT = prothrombin time
  • PTT = partial thromboplastin time

See Also

Brain Injury

Suggested Reading

Chrisman CL, Mariani C, Platt S. Dementia, stupor and coma. In: Neurology for the Small Animal Practitioner. Jackson, WY: Teton NewMedia , 2003, pp. 41–84.

Dewey CW. A Practical Guide to Canine and Feline Neurology, 2nd ed. Ames, IA: Wiley-Blackwell, 2008.

Authors Rebecca Kirby and Elke Rudloff

Consulting Editor Joane M. Parent

Client Education Handout Available Online