Hypoxia

Question 1

Define hypoxia

Answer 1

Describes a specific environment (PO2)

Much less oxygen in the ambient air

Question 2

Define hypoxaemia

Answer 2

Describes blood environment (PaO2)

Question 3

What is ischaemia

Answer 3

Describes tissue receiving inadequate oxygen

Question 4

Which factors put the body under hypoxic stress

Answer 4

Altitude
Disease
Exercise

Question 5

What is the partial pressure of oxygen in the atmosphere compared to the tissues

Answer 5

21.3kPa vs 5.3kPa

Question 6

Describe age related decline in lung function

Answer 6

As you age your PaO2 decreases

Question 7

What is the oxygen cascade

Answer 7

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

Question 8

Describe oxygen and carbon dioxide dissociation graphically

Answer 8

Linear dissociation for CO2

Sigmoid dissociation for O2

Question 9

Which factors can affect the oxygen cascade

Answer 9

Alveolar ventilation
V/Q matching
Diffusion capacity
Cardiac output

Question 10

What is the effect of the following on the oxygen cascade: oxygen therapy, humid air, hyper/hypoventilation, diffusion defect

Answer 10

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

Question 11

What may effect ambient air PO2

Answer 11

Oxygen therapy

Humid air

Question 12

What may affect the alveolar air PO2

Answer 12

hyper ventilation

Hypoventilation

Question 13

What may affect post-alveolar capillary PO2

Answer 13

Diffusion defect

Question 14

What is the limit of humans altitude wise

Answer 14

Mount Everest summit (just under 10,000)

Question 15

What altitude pressure are airplanes pressurised to

Answer 15

2000m

Question 16

Why must ascent to high altitude be done slowly

Answer 16

Allows body to acclimatise

Immediate exposure = incapacitate in less than a minute, kill in 2

Question 17

What is acclimation

Answer 17

Stimulated by an artificial environment e.g. hypobaric chamber or breathing hypoxic gas

Question 18

What are the anatomical and physiological adaptations of native highlanders

Answer 18

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

Question 19

What is acetazolamide

Answer 19

Carbonic anhydrase inhibitor

Accelerates slow renal compensation to hypoxia-induced hyperventilation

Question 20

Describe the causes and pathophysiology of chronic mountain sickness

Answer 20

Unknown cause

Secondary polycythaemia increases the blood viscosity
Blood sludges through the capillary and impedes delivery

Question 21

Describe the symptoms, consequences and treatment for chronic mountain sickness

Answer 21

Cyanosis and fatigue

Ischaemic tissue damage
Heart failure
Eventual death

Return to lower altitudes

Question 22

Describe the causes and pathophysiology of acute mountain sickness

Answer 22

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

Question 23

Describe the symptoms and consequences for acute mountain sickness

Answer 23

Nausea, vomiting, irritability, dizziness, insomnia, fatigue, and dyspnoea

Development into HAPE or HACE

Question 24

What is the treatment for acute mountain sickness

Answer 24

Monitor symptoms
Stop ascent
Analgesia
Fluids
Medication (acetazolamide) Hyperbaric O2 therapy
Symptoms tend to subside after 48 hrs of increased renal compensation

Question 25

Describe the causes and pathophysiology of High altitude pulmonary oedema

Answer 25

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

Question 26

Describe the symptoms and consequences for high altitude pulmonary oedema

Answer 26

Dyspnoea, dry cough, bloody sputum, crackling chest sounds Impaired gas exchange, impaired ventilatory mechanics

Question 27

What is the treatment for high altitude pulmonary oedema

Answer 27

Descent Hyperbaric O2 therapy Nifedipine (CCB)Salmeterol (relaxant Sildenafil (viagra)

Question 28

Describe the causes and pathophysiology of High altitude cerebral oedema

Answer 28

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

Question 29

Describe the symptoms and consequences for high altitude cerebral oedema

Answer 29

Confusion, ataxia, behavioural change, hallucinations, disorientation Irrational behaviour, irreversible neurological damage, coma, death

Question 30

What is the treatment for high altitude cerebral oedema

Answer 30

Immediate descent O2 therapy Hyperbaric O2 therapy Dexamethasone

Question 31

What is respiratory failure

Answer 31

Failure of pulmonary gas exchange, generally V/Q inequality | CO2 can diffuse but oxygen cannot

Question 32

Describe type 1 respiratory failure

Answer 32

Hypoxic respiratory failure PaO2 < 8kPa PaCO2 = low/normal Hypoventilation V/Q mismatch Diffusion abnormality Pulmonary oedema Pneumonia Atelectasis

Question 33

Describe type 2 respiratory failure

Answer 33

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 ```