• Altitude physiology
• At altitude, the FiO₂ is constant at 0.21 but the PB decreases non linearly
• Effects on equipment
• Vaporisers
• SVP is unaffected by altitude so the partial pressure is the same as sea level but higher concentrations are delivered so same settings are used
• Flow meters
• Lower density gases means they under read but are used as normal
• Risks at altitude
• Hypothermia
• Expansion of gas containing cavities
• Acute mountain sickness
• General symptoms
• Nausea, vomiting, fatigue, dizziness, sleep disturbances
• High-altitude pulmonary (o)edema (HAPE)
• Dry cough, fever, dyspnoea, pink sputum
• May be due to HPV leading to high PAP
• Idiopathic component with increased capillary permeability
• High-altitude cerebral (o)edema (HACE)
• Usually occurs after 1/52
• ? Due to local vasodilatation with increased CBF
• Causes convulsions, drowsiness, coma and death
• Compensation to high altitude
  >1500m
• The ODC ensures SpO₂ stay >90% up to
  10,000 ft
• Acute measures
• Aortic/carotid bodies detect low pO₂ and stimulate respiratory and CV systems leading to hyperventilation and low PCO₂
• Alkalaemia moves the ODC to the left and increases renal HCO₃⁻ loss
  Link:ODC
  
• CVS responds with sinus tachycardia with a low SV
• Diuresis occurs
• RBC metabolism increases and 2,3-DPG levels increase (ODC moves right)
  Link:ODC
  
• Chronic measures
• Polycythaemia due to increased erythropoietin
• Higher red cell mass
• Increased 2,3 DPG
• HPV leads to RVH
• Increased myoglobin concentration
• Increased aerobic enzyme capacity
• Increased mitochondrial size
• Chronic mountain sickness (Monge's disease)
• Hypoxaemia, fatigue, PAH, polycythaemia, CCF