Respiratory Systems 13 - Hypoxia Flashcards
Define hypoxia
A specific environment with low O2
Define hypoxaemia
A description of the PaO2 in the bloodstream
Define ischaemia
Tissuesrecieving inadequate oxygen
Define the oxygen cascade
- The decreasing oxygen tension from inspired air to respiring cells
Summarise the oxygen cascade
- PO2 decreases as gas moves from the ambient air to alveoli to the arteries, tissues and veins
- The greatest differences in PO2 are between upper airway and alveoli, and between arteries and veins due to exchange at tissues
Why does the oxygen cascade occur? What affects it?
- Due to diffusion capacity of the tissue
- Affected by hyper- and hypoventillation
How does CO2 change throughout the oxygen cascade?
- There is little difference in PCO2 levels from upper airway to the arteries
- increase in tissues and in air
How does the oxygen cascade change in exercise?
The PO2 is lower in each location
List the challenges of high altitude.
- Hypoxia
- Thermal stress (wind chill factor)
- Solar radiation (reflection off snow and less atmospheric screening)
- Hydration (water is lost humidifying inspired air, with induced diuresis)
- Dangerous (windy, confusion due to hypoxia)
Describe the process of accommodation and acclimatisation at high altitude
- Low PAO2 and PaO2 activates peripheral chemoreceptors to increase sympathetic outflow (increased heart rate/blood flow leads to increased O2 loading)
- Also increased erythropoietin production and RBC production
- Increased ventillation, PaCO2 decreases. pH increases
- Alkalosis detected by carotid bodies, resulting in increased H+ in blood and increased HCO2- excretion
- ODC normalises
- High pH causes leftwards shift of ODC so haemoglobin holds on to O2
- As PaCO2 decreases, central drive to breathe decreases and there is less O2 loading
Define prophylaxis
Treatment given or action taken to prevent disease
Define acclimation
This is similar to acclimatisation but is stimulated by an artificial environment
What drugs can be used to treat altitude sickness?
Acetazolamide, a carbonic anhydrase inhibitor which accelerates slow renal compensation to hypoxia induced hyperventilation
What innate adaptations do native highlanders have?
- Barrel chest (larger TLC, more alveoli more capillaries)
- Increased haematocrit
- Larger heart
- Increased mitochondrial density (greater oxygen utilisation at cellular level)
- Not present in all high-altitude populations
What is chronic mountain sickness? Describe the pathophysiology and symptoms
- Where acclimatised individuals spontaneously acquire mountain sickness
- Due to secondary polycythaemia increasing blood viscosity which impedes O2 delivery
- Symptoms include cyanosis and fatigue
List the consequences of chronic mountain sickness.
Ischaemic tissue damage, heart failure, death
List the possible treatments for mountain sickness
No medical treatment - people must descend to lower altitudes
Describe the cause of acute mountain sickness
- Caused by maladaptation to the high-altitude environment, associated with recent ascent
- Occurs within 24 hours and can last over a week.
Describe the pathophysiology of acute mountain sickness
Associated with mild cerebral oedema
List the symptoms of acute mountain sickness
- Nausea
- Vomiting
- Irritability
- Dizziness
- Fatigue
- Dyspnoea
List the consequences of acute mountain sickness
Development into high altitude pulmonary oedema or high altitude cerebral oedema
List the treatments for acute mountain sickness
- Monitor symptoms
- Stop ascent
- Analgesia (medication to reduce pain)
- Azetazolamide or hyperbaric O2 therapy
List the causes of high altitude pulmonary oedema
Rapid ascent or inability to acclimatise
Describe the pathophysiology of high altitude pulmonary oedema
- Vasoconstriction of pulmonary vessels in response to hypoxia
- Increased pulmonary pressure, permiability and fluid leakage from capillaries
- Fluid accumulates when lymph production exceeds maximum rate of lymph drainage
List the symptoms of high altitude pulmonary oedema
- Dyspnoea
- Dry cough
- Bloody sputum
- Crackling chest sounds
List the consequences of high altitude pulmonary oedema
- Impaired gas exchange
- Impaired ventilatory mechanics
List the treatments for high altitude pulmonary oedema
- Descent
- Hyperbaric O2 therapy
- Nifedipine
- Salmeterol
- Sildenafil (viagra)
List the causes of high altitude cerebral oedema
Rapid ascent/inability to acclimatise
Describe the pathophysiology of high altitude cerebral oedema
- 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
List the symptoms of high altitude cerebral oedema
- Confusion
- Ataxia
- Behavioural change
- Hallucinations
- Disorientation
List the consequences of high altitude cerebral oedema
- Irrational behaviour
- Irreversible neurological damage
- Coma
- Death
List the treatments for high altitude cerebral oedema
- Immediate descent
- O2 therapy
- Hyperbaric O2 therapy
- Dexamethasone
Define respiratory failure
A failure of pulmonary gas exchange, generally a V/Q inequality
What is type 1 respiratory failure?
- Hypoxic respiratory failure
- PaO2 < 8kPa
- PaCO2 is low/normal
List the causes of type 1 respiratory failure
- Hypoventilation
- Diffusion abnormality
- Pulmonary oedema
- Pneumonia
- Atelactasis
- Mismatching V/Q
What is type 2 respiratory failure?
- Hypercapnic respiratory failure
- PaO2 < 8 kPa
- PaCO2 > 6.7 kPa
List the causes of type 2 respiratory failure.
- Increased CO2 production and decreased CO2 elimination
- Decreased CNS drive
- Increased work of breathing
- Pulmonary fibrosis
- Neuromuscular disease
- Increased physiological dead space
- Obesity
