High Altitude Disorders

High-Altitude Disorders

• High altitude (>2440 m or >8000 ft) is a hypoxic environment with decreased partial pressure of oxygen (PO2) due to lower barometric pressure.

Altitude Staging

• Intermediate altitude (1520-2440 m or 5000-8000 ft): decreased exercise performance and increased alveolar ventilation without major impairment in arterial oxygen transport, with risk of Acute Mountain Sickness (AMS).
• High altitude (2440-4270 m or 8000-14,000 ft): decreased arterial oxygen saturation (SaO2), marked hypoxemia during exercise and sleep.
• Very high altitude (4270-5490 m or 14,000-18,000 ft): abrupt ascent can be dangerous, requires acclimatization to prevent illness, with SaO2 of 86-84%.
• Extreme altitude (>5490 m or >18,000 ft): severe hypoxemia and hypocapnia, progressive physiologic deterioration, and impossible sustained human habitation.

Adaptation Mechanisms

• Hyperventilation: hypoxic ventilatory response increases ventilation to compensate for low oxygen levels.
• Blood: increased serum erythropoietin levels within 2 hours of ascent, leading to increased red cell mass over days to weeks.
• Fluid balance: peripheral venous constriction increases central blood volume, suppressing secretion of antidiuretic hormone and aldosterone, and inducing diuresis.

High-Altitude Syndromes

• Acute Mountain Sickness (AMS): headache, GI disturbance, dizziness, fatigue, or sleep disturbance due to hypobaric hypoxia.
• Treatment: acetazolamide, dexamethasone, and hyperbaric therapy.

Treatment Principles

• Do not ascend to a higher sleeping altitude with symptoms.
• Descend if symptoms do not abate or become worse despite treatment.
• Descend and treat immediately if there is a change in consciousness, ataxia, or pulmonary edema.

High-Altitude Cerebral Edema

• Defined as progressive neurologic deterioration in someone with AMS or high-altitude pulmonary edema.
• Characterized by altered mental status, ataxia, stupor, and progression to coma if untreated.
• Treatment: oxygen supplementation, descent, and steroid therapy.

High-Altitude Pulmonary Edema

• Most lethal of altitude illnesses.
• Risk factors: heavy exertion, rapid ascent, cold, excessive salt ingestion, respiratory depressant use, previous history of susceptibility, and pulmonary hypertension.
• Early diagnosis critical, with decreased exercise performance and dry cough as early signs.
• Immediate descent is the treatment of choice.

Ultraviolet Keratitis (Snow Blindness)

• Increased UV radiation at high altitude due to less cloud cover, water vapor, and particulate matter.
• Radiation increases by 5% for every 300 m gained.
• Self-limited condition that heals within 24 hours, but warrants analgesic administration and cold compress application.
• Prevention crucial, with sunglasses that transmit <10% of UV radiation recommended.

Seizure Management

• Avoid unnecessary sedation as it can complicate evaluation and lead to a prolonged decrease in level of consciousness.
• Obtain serum anticonvulsant levels before administering supplemental or loading doses to prevent drug toxicity.

Patients with a First Unprovoked Seizure

• Guidelines do not recommend hospital admission or initiation of anticonvulsant therapy if the patient has returned to neurologic baseline.
• Patients with a normal neurologic examination, no acute or chronic medical comorbidities, normal diagnostic testing, and normal mental status can safely be discharged from the ED.

Neurocysticercosis

• Caused by CNS infection with the larval stage of the tapeworm Taenia solium.
• Most common cause of provoked (secondary) seizures in the developing world.

Pregnancy

• Eclampsia is defined as seizures in the setting of hypertension, edema, and proteinuria beyond 20 weeks of gestation.
• Magnesium sulfate has been used to treat eclampsia with good results.

Alcohol Abuse

• Seizures and alcohol use are associated through missed doses of medication, sleep deprivation, increased propensity for head injury, toxic co-ingestions, electrolyte abnormalities, and withdrawal seizures.

Status Epilepticus (SE)

• Defined as a single seizure ≥5 minutes in length or two or more seizures without recovery of consciousness between seizures.
• Pathophysiology of SE involves compromised blood-brain barrier, increased CNS penetration of potassium and albumin, metabolic disturbances, and toxins/drugs.

Paroxysmal Disorders: Differential Diagnosis

• Seizures
• Syncope
• Pseudoseizures or psychogenic seizures
• Hyperventilation syndrome
• Migraine headache
• Movement disorders

Laboratory Testing

• In patients with a well-documented seizure disorder, only tests needed may be glucose level and pertinent anticonvulsant medication levels.

Imaging

• CT imaging is indicated if there is concern for an acute intracranial process, even if there is a coexistent metabolic process.

Lumbar Puncture

• Indicated if the patient is febrile or immunocompromised or if subarachnoid hemorrhage is suspected and the noncontrast head CT is normal.

Emergent EEG

• Can be considered in the evaluation of a patient with persistent, unexplained altered mental status to evaluate for non-convulsive status epilepticus, subtle status epilepticus, paroxysmal attack, or ongoing status epilepticus after chemical paralysis for intubation.

Treatment of Uncomplicated Seizures

• IV anticonvulsant medications are not necessary during the course of an uncomplicated seizure, as most seizures will self-resolve within 5 minutes.

Clinical Features

• Presence of a preceding aura
• Abrupt or gradual onset
• Progression of motor activity
• Loss of bowel or bladder control
• Presence of oral injury
• Localization or generalization and symmetry or unilaterality of activity

Common Precipitating Factors

• Missed doses of antiepileptic medications
• Recent alterations in medication
• Sleep deprivation
• Increased strenuous activity
• Infection
• Electrolyte disturbances
• Alcohol or substance use or withdrawal