Altitude Flashcards
What is the cause of AMS and HACE?
Thought to be due to hypoxia related vasodilation leading to cerebral oedema
What is the cause of High Altitude Pulmonary oedema HAPE?
A rise in pulmonary pressures occurs with altitude, susceptible patients have a higher rise and develop APO
What medications are used to prevent HACE/AMS?
Acetazolamide
- 250mg BD PO prevention
- CAI, causes a metabolic acidosis and diuresis, increases the hypoxic resp drive and decreases CSF production
- Better at prophylaxis than treatment
- Doesn’t help as such with HACE
Dexamethasone
- Acute is 8mg bolus IV/IM then 4mg QID
- Prevention is 4mg PO BD for max 10 days
- Decrease cerebral pressures, short term use (<4 days)
- Improves symptoms but doesn’t help acclimatisation
- Does help with HACE, but only temporising
What medications are used to prevent HAPE?
Nifedipine
- The mainstay of pharmacological treatment/prophlyaxis
- 30mg SR PO BD
Others
- Anecdotal, not proven to work
- PDE5 inhibitors ie Sildenafil
- B2 agonists ie Salbutamol
- Unclear mechanism, may increase alveolar fluid clearance
What are the RF’s for AMS?
Climb
- High Altitude (rare below 2500m, usually above 3000m)
- Rapid Ascent (>625m/day)
- Strenuous activity
- Sleeping at altitude
Patient
- Younger Age
- Female gender
- Obesity
- Dehydration
- Alcohol/depressant drug use
What are the general treatment for AMS, HACE and HAPE?
- Rapid Descent! (>500m, usually 1000m if possible)
- Supplemental O2
- Portable hyperbaric chamber
- Meds (Nifedipine for HAPE, Dex for AMS/HACE)
- Keep warm
- CPAP/NIV if available
What are the signs/symptoms of AMS and HACE
N/V and headache initially with AMS
Progressed to altered LOC and truncal Ataxia with HACE
What are the risk factors for HAPE?
Male Gender
Rapid ascent
Vigorous exercise
colder temperatures
Pre-existing PHTN
Intercurrent respiratory infection
Known cardiac shunts such as ASD’s, VSD’s and particularly a PFO (PFO increases risk 4 fold)
How high does the altitude physiological efficient zone extend to? what are the normal atomospheric pressures?
Sea level to approx 3800m
In this zone humans can adapt without the need for supportive equipment, most helicopters fly in this zone
Pressure 760-520mmHg
What is the altitude of the physiological deficient zone? What are the pressures?
3800m to 15,000m
Humans require supplemental 02 to survive
Most commerical planes fly in this zone
Pressure 520 - 90mmHg
What is the “time of useful consciousness” in reference to altitude medicine?
The amount of time a young + healthy person can function rationally before becoming delerious due to hypoxia at a given altitude, in the absence of supplemental 02
Mainly an issue with sudden cabin decompression, will affect how long you have to fix the situation or gain access to supplemental 02
How does Boyle’s Law affect different compartments and pathologies during flight?
Expansion of gas with higher altitude
- Main physiological compartment are sinuses, ears, teeth and bowels (lungs not affected unless holding breath)
- Pathologies affected are bowel obstruction, post abdo surgery, penuothoraces, fascial compartments, pneumocephalus, penetrating eye trauma etc
How does Boyle’s Law affect different retrieval aviation platforms?
Rotary (helicopter etc)
- No ability to pressurise
- Usually only fly to max 3500m
Fixed Wing (plane)
- Up to 10,000m
- Often pressurise cabin to 2000m
- If need be can pressurise further to ground level
- In practice maximum altitude felt by patients is 10,000 feet/3-3,500m, which is about 45% gas expansion
- However depressurisation can cause serious sudden rises in volume
How does Henry’s Law relate to decompression sickness?
If pressure suddenly drops externally (ie sudden cabin decompression) then dissolved gas in blood will equilibrate and form bubbles
Cutaneous (the creeps)
Arthropathy (the bends)
Cardiopulmonary (the chokes)
Neurological (The staggers)
How long should someone not fly for after SCUBA diving?
> 24hrs to reduce the risk of getting decompression sickness
