High altitude syndrome

High altitude medical problem

ดอยลั�งกาหลัวง 2,031m

ภู�สอยดาว 2,102 m

ดอยหลัวงเชี�ยงดาว2,195 m

ดอยผ้�าห�มปก 2,285 m

Altitude Height Effect

Intermediate altitude

1520 - 2440 m (5000 - 8000 ft)

exercise performance alveolar ventilation↔arterial oxygen transport

High altitude >2440 m (>8000 ft) AMS

Very high altitude

4270 - 5490 m (14,000 - 18,000 ft)

AMS

PATHOPHYSIOLOGY

ventilation

• PaO2 carotid body& respiratory center

ventilation PaCO2

Performance

Chronic hypoxiaSedative agentDuring sleep

ventilatory acclimatization

ventilation

pH (respi alkalosis)

HCO3 excrete via kidney

pH return to normal

Acetazolamide

Blood

• EPO w/in 2 hr • Rbc mass w/in

days to wks• if excessive

chronic polycythemia

Fluid Balance

• Reset Osm stat: plasma volume and hyperosmolality (s osm290 - 300)

• diuresis and hemoconcentration :healthy response• Antidiuresis is a hallmark of AMS

Peripheral venous constriction

in central blood

volume

ADH &aldosterone

diuresis

Cardiovascular System

CO = SV HR

Pulm.vasoconstriction pulm.pressure

Cerebral blood volume O2 to brain ICP

Exercise capacity

• measured by VO2max, drops dramatically on ascent to altitude

• During acclimatization, submaximal endurance after 10 days

Sleep at High Altitude

• Sleep stages III and IV ↓ stage I frequent arousals (improve with time at altitude)

• Cheyne-Stokes respiration in those sleeping at >2700 m (>8860 ft)

• the frequent awakenings & periodic breathing not related to AMS

• mechanism of the lighter sleep →cerebral hypoxia. • Quality of sleep and arterial oxygenation during

sleep improve with acclimatization and with acetazolamide

HIGH-ALTITUDE SYNDROMES

High altitude syndrome

• Acute hypoxia• Acute mountain sickness• High-Altitude cerebral edema• High-Altitude pulmonary edema• Peripheral edema• High-altitude retinopathy• High-altitude pharyngitis and bronchitis• Chronic mountain polycythemia• UV keratoconjunctivitis

Acute hypoxia

• occurs in the setting of sudden and severe• Unacclimatized persons become unconscious

at SaO2 50 - 60%, PaO2 < 30 mm Hg, or a jugular venous PO2 of <15 mm Hg

• immediate administration of oxygen, rapid descent

Acute Mountain Sickness

• setting of more gradual and less severe hypoxic

• characterized by headache, GI disturbances, dizziness or light-headedness, and sleep disturbance

What’re factors determine individual susceptibility to AMS ?

• Age • Sex • Body weight • physical fitness

Pathophysiology

• renin-angiotensin aldosterone ADH

The cerebral edema, interstitial pulmonary edema, peripheral edema, and antidiuresis

Clinical feature

• mild : alcohol hangover• Headaches : bifrontal and worsen with

bending over or performing a Valsalva maneuver

• GI symptoms : anorexia, N/V• irritable & wants to be left alone• Sleepiness • deep inner chill also are common

Clinical feature

• rapid ascent of an unacclimatized person to ≥2000 m

• Symptoms develop between 1 -6 hours later, but sometimes are delayed for 1 - 2 days

Severe headache vomiting oliguria Ataxia

and AOC HACE

Physical examination

• percent SaO2 overall correlates poorly with the diagnosis of AMS

• postural hypotension may be present• Localized rales ≥ 20%• Funduscopy :tortuosity and dilatation, and

retinal hemorrhages (at altitudes >5000 m)• facial and peripheral edema is a hallmark

The goals of treatment are to

prevent progression

abort the illness

improve acclimatization

3 principles of Rx

(1) do not proceed to a higher sleeping altitude in the presence of symptoms

(2) descend if symptoms do not abate or become worse despite treatment

(3) descend and treat immediately in the presence of a change in consciousness, ataxia, or pulmonary edema

Treatment

• Oxygen effectively relieves symptoms, but it is generally unavailable in the field or reserved for those with moderate to severe AMS

Medication

Indications for acetazolamide (1) a history of altitude illness(2) abrupt ascent to >3000 m (>9840 ft)(3) AMS requiring treatment(4) bothersome periodic breathing during sleep

Symptomatic treatment of AMS

• Headache :aspirin, acetaminophen or ibuprofen

• N/V: ondansetron• f/q wakening: zolpidem,diphenhydramine

Prevention

• Graded ascent with adequate time for acclimatization is the best prevention

• Prophylactic acetazolamide – started 24 hr before the ascent – continued for the first 2 days at altitude– restarted if illness develops

HACE

• HACE : progressive neurologic deterioration in someone with AMS or HAPE

• altered mental status, ataxia, stupor, and progression to coma if untreated

• severe, diffuse cerebral edema with multiple small hemorrhages and sometimes thrombosis

Treatment of HACE

• oxygen supplementation• descent(the highest priority)• steroid therapy• acetazolamide may be used as an adjunct

MRI findings reversible white matter edema evidenced byT2 signal, esp.in the splenium

of the corpus callosum

HAPE

• most lethal of the altitude illnesses• easily reversible with descent and oxygen

administration• Risk factors:heavy exertion, rapid ascent, cold,

excessive salt ingestion, use of a sleeping medication

Pathophysiology

• HAPE is a noncardiogenic, hydrostatic edema• The culprit in HAPE is high microvascular

pressure Pulmonary hypertension

Clinical

• Early diagnosis is critical, exercise performance & dry cough are enough to raise the suspicion of early HAPE

• The condition typically worsens at night • Low-grade fever is common, and tachycardia

and tachypnea• SO2 low for altitude

Chest radiographic

progress from interstitial localized alveolar generalized alveolar infiltrates

Treatment

• The key to successful Rx : early recognition, early stage is easily reversible

• Immediate descent is the Rx of choice, but this is not always possible

• The optimal therapy depends on – the environmental setting, – evacuation options– availability of oxygen or hyperbaric units– ease of descent

Portable hyperbaric bag

medication

• Because oxygen and descent are so effective, experience with drugs has been limited

• nifedipine, phosphodiesterase 5 inhibitors:sildenafil and tadalafil

Other high altitude medical problem

• Peripheral edema• High-altitude retinopathy• High-altitude pharyngitis and bronchitis• UV keratoconjunctivitis

Special population

• Patients who have hypoxic cardiovascular and pulmonary diseases such as COPD or CHF , CAD, pregnant