Hypoxia Flashcards
Define hypoxia
Describes a specific environment (PO2)
Much less oxygen in the ambient air
Define hypoxaemia
Describes blood environment (PaO2)
What is ischaemia
Describes tissue receiving inadequate oxygen
Which factors put the body under hypoxic stress
Altitude
Disease
Exercise
What is the partial pressure of oxygen in the atmosphere compared to the tissues
21.3kPa vs 5.3kPa
Describe age related decline in lung function
As you age your PaO2 decreases
What is the oxygen cascade
Describes decreasing oxygen tension from inspired air to respiring cells
Pressure gradient can be affected by breathing hypoxic gas, affecting flow rate
Largest proportion of oxygen loss is in the mixing phase
Describe oxygen and carbon dioxide dissociation graphically
Linear dissociation for CO2
Sigmoid dissociation for O2
Which factors can affect the oxygen cascade
Alveolar ventilation
V/Q matching
Diffusion capacity
Cardiac output
What is the effect of the following on the oxygen cascade: oxygen therapy, humid air, hyper/hypoventilation, diffusion defect
oxygen therapy - increased ambient air PO2
humid air - decreased ambient air PO2
Hyperventilation - increased alveolar PO2
Hypoventilation - decreased alveolar PO2
Diffusion defect - Decreased post-alveolar capillaries PO2
What may effect ambient air PO2
Oxygen therapy
Humid air
What may affect the alveolar air PO2
hyper ventilation
Hypoventilation
What may affect post-alveolar capillary PO2
Diffusion defect
What is the limit of humans altitude wise
Mount Everest summit (just under 10,000)
What altitude pressure are airplanes pressurised to
2000m
Why must ascent to high altitude be done slowly
Allows body to acclimatise
Immediate exposure = incapacitate in less than a minute, kill in 2
What is acclimation
Stimulated by an artificial environment e.g. hypobaric chamber or breathing hypoxic gas
What are the anatomical and physiological adaptations of native highlanders
Barrel chest - larger TLC, more alveoli, greater capillarisation
Increased haematocrit - greater O2 carrying capacity of the blood
Larger heart- pumps through vasoconstricted pulmonary circulation(pulmonary perfusion)
Increase mitochondrial density - greater O2 utilisation at cellular level
What is acetazolamide
Carbonic anhydrase inhibitor
Accelerates slow renal compensation to hypoxia-induced hyperventilation
Describe the causes and pathophysiology of chronic mountain sickness
Unknown cause
Secondary polycythaemia increases the blood viscosity
Blood sludges through the capillary and impedes delivery
Describe the symptoms, consequences and treatment for chronic mountain sickness
Cyanosis and fatigue
Ischaemic tissue damage
Heart failure
Eventual death
Return to lower altitudes
Describe the causes and pathophysiology of acute mountain sickness
Maladaptation to the high-altitude environment.
Usually associated with recent ascent, onset within 24 hours and can last more than a week
Associated with mid-cerebral oedema
Describe the symptoms and consequences for acute mountain sickness
Nausea, vomiting, irritability, dizziness, insomnia, fatigue, and dyspnoea
Development into HAPE or HACE
What is the treatment for acute mountain sickness
Monitor symptoms
Stop ascent
Analgesia
Fluids
Medication (acetazolamide) Hyperbaric O2 therapy
Symptoms tend to subside after 48 hrs of increased renal compensation
Describe the causes and pathophysiology of High altitude pulmonary oedema
Rapid ascent or inability to acclimatise
Vasoconstriction of pulmonary vessels in response to hypoxia increased pulmonary pressure, permeability and fluid leakage from capillaries fluid accumulates once production exceeds the maximum rate of lymph drainage
Describe the symptoms and consequences for high altitude pulmonary oedema
Dyspnoea, dry cough, bloody sputum, crackling chest sounds
Impaired gas exchange, impaired ventilatory mechanics
What is the treatment for high altitude pulmonary oedema
Descent
Hyperbaric O2 therapy
Nifedipine (CCB)Salmeterol (relaxant
Sildenafil (viagra)
Describe the causes and pathophysiology of High altitude cerebral oedema
Rapid ascent or inability to acclimatise
vasodilation of vessels in response to hypoxaemia (to increase blood flow) more blood going into the capillaries increases fluid leakage cranium is a ‘sealed box’ – no room to expand so intracranial pressure increases
Describe the symptoms and consequences for high altitude cerebral oedema
Confusion, ataxia, behavioural change, hallucinations, disorientation
Irrational behaviour, irreversible neurological damage, coma, death
What is the treatment for high altitude cerebral oedema
Immediate descent
O2 therapy
Hyperbaric O2 therapy
Dexamethasone
What is respiratory failure
Failure of pulmonary gas exchange, generally V/Q inequality
CO2 can diffuse but oxygen cannot
Describe type 1 respiratory failure
Hypoxic respiratory failure
PaO2 < 8kPa
PaCO2 = low/normal
Hypoventilation
V/Q mismatch
Diffusion abnormality
Pulmonary oedema
Pneumonia
Atelectasis
Describe type 2 respiratory failure
Hypercapnic respiratory failure
PaO2 < 8 kPa
PaCO2 > 6.7 kPa
Increased CO2 production
Decreased CO2 elimination (unable to clear out of the lungs)
Decreased CNS drive Increased work of breathing Pulmonary fibrosis Neuromuscular disease Increased physiological dead space Obesity
