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Respiratory system > Hypoxia > Flashcards

Hypoxia Flashcards

1
Q

What is hypoxia?

A

adjective to describe a low-oxygen environment

Specifically low PO2

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2
Q

What is hypoxaemia?

A

specifically low blood oxygen tension (e.g. low PaO2)

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3
Q

What is iscahaemia?

A

Tissue receiving inadequate oxygen

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4
Q

What factors can cause hypoxic stress?

A

Altitute
Exercise
Disease

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5
Q

What is the oxygen cascade?

A

partial pressure of oxygen decreases from atmospheric air to respiring tissues.
Ficks law: flow rate proportional to pressure gradient
Most oxygen lost during mixing phase
Another big drop in tissues

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6
Q

What determines the effectiveness of the oxygen cascade?

A
  1. Alveolar ventilation
  2. Ventilation-perfusion matching
  3. Diffusion capacity
  4. Cardiac output
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7
Q

What is the effect of exercise on the oxygen cascade?

A
  1. increased rate of cellular metabolism, CO2, dec pH
  2. mild acidosis and hypercapnia shift the ODC to the right to improve oxygen unloading at the tissues
  3. increased PCO2is detected by central chemoreceptors in the medulla that increase the ventilation rate to maintain oxygen delivery to tissues
  4. If oxygen supply is inadequate (e.g. PaO2< 4.5 kPa) then anaerobic metabolism takes over
  • Unsustainable as lactate and H+ cause acidosis
  • Reduces enzyme effectiness
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8
Q

What determines the total capacity to deliver oxygen?

A

VO2 max

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9
Q

What happens at high altitude?

A

barometric pressure reduces
Content of atmospheric gases reduced
reduced PIO2causes a reduced PaO2
reduce the concentration gradient and slow the rate of O2diffusion

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10
Q

What are the initial physiological responses to hypoxia?

A
  1. Renal compensation – bicarbonate excretion; this helps pH to return to normal and shifts the ODC into its normal position
  2. Increased production of 2,3-DPG to improve oxygen unloading at the tissues.
  3. Hypobaric hypoxia: Low PaO2stimulates ventilation, causing dec PaCO2
    • Inc. pH shifts ODC to left
    • Increased affinity of Hb for O2
    • Reduced O2 unloading
  4. Increased HR and CO
  5. Increased O2 utilisation
    • Oxidative enzymes increase
    • Increase rate of aerobic respiration
    • Increased mitochondria
    • Small increase in DPG in RBC
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11
Q

What are the consequences of increased oxygen unloading in tissues?

A
  1. Low CO2 causes decreased central drive to breathe
  2. Decreased ventilation
  3. Decreased O2 loading
  4. Increased pH
  5. Shifts ODC to the left
  6. Decreased O2 unloading
  7. Alkalosis detected by carotid bodies
  8. Increased bicarb excretion causing inc H+
  9. ODC normalizes

see notes

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12
Q

What is a long term adaptation to hypoxia?

A

Secondary erythrocytosis

  1. Chronic hypoxia detected in kidney
  2. Release EPO
  3. Stimulate erythropoiesis in bone marrow increased RBC concentration
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13
Q

What is the ventilatory response to hypoxia?

A

restore the PaO2to sealevel values

Become hypoxaemic

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14
Q

What are initial symptoms of hypoxia?

A 
Feel unwell 
Poor physical and mental function 
Headache
Nausea
Vomiting 
Photophobia 
Poor sleep

Usually mild but if become more severe cause acute mountain sickness (AMS)

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15
Q

What is acclimation?

A

Adapation stimulated by artificial environment

E.g carbonic anhydrase inhibitor accelerates slow renal compensation to hypoxia induced hyperventilation

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16
Q

What is the pathphysiology, symptoms and consequences of chronic mountain sickness?

A

Causes: unknown
Pathophysiology: secondary polycythaemia increases blood viscosity, which sludges through systemic capillary beds impeding O2 delivery (despite more than adequate oxygenation)
Symptoms: cyanosis, fatigue
Consequences: ischaemic tissue damage, heart failure, eventual death
Treatment: no interventional medical treatment – sufferers are exiled to lower altitudes

17
Q

How long acclimitisation take?

A

2-10 days
Steady resolution of symtpoms
Improved performance

18
Q

What happens during acclimitisation?

A

Ventilation and PaO2increase with a fall in PaCO2
Renal compensation for the respiratory alkalaemia
Slow increasing ventilatory sensitivity to hypoxia

19
Q

How do you avoid adverse effects of moving to high altitudes?

A

Slow descent for 2 days

20
Q

What are consequences mild AMS?

A

pulmonary oedema (HAPE), cerebral oedema (HACE) or both

21
Q

What are the signs and symptoms of HAPE?

A

usual symptoms and signs of AMS
severe breathlessness
chest pain
dry cough
Haemoptysis
Bloody sputum
Crackling chest sounds
chest X-ray would show patchy pulmonary oedema
vasoconstriction of pulmonary vessels in response to hypoxia increased pulmonary pressure
permeability and fluid leakage from capillaries fluid accumulates

22
Q

What are the signs and symptoms of HACE?

A 
Increased intracranial pressure 
Impairs neurological function (occulomotor palsies, ataxia, extensor plantar response)
Severe headache
Impaired cognitive and physical function 
Clouding consciousness 
Coma 
Hallucinations 
disorientation
23
Q

What is the first line of treatment for mild AMS?

A

Rapid descent
Hyperbaric O2 therapy
Sleeping in hyperbaric tent

HAPE:

- nifedipine: in HAP decreases pulmonary arterial pressure so dec pulmonary cappilary leakage and right ventricular workload 
- aildenafil

HACE:
- dexamethasome

24
Q

What are the types and symptoms of respiratory failure?

A 
Type 1: 
Hypoxic 
PaO2 < 8 kPa
PaCO2 = low/normal
	- Hypoventilation
	- V/Q mismatch
	- Diffusion abnormality
	- Pulmonary oedema
	- Pneumonia
	- Atelectasis
Type 2: 
Hypercapnic
PaO2 < 8 kPa
PaCO2 > 6.7 kPa
	- Increased CO2 production
	- Decreased CO2 elimination
	- Decreased CNS drive
	- Increased work of breathing
	- Pulmonary fibrosis
	- Neuromuscular disease
	- Increased physiological dead space
	- Obesity
25
Q

How high is high altitude?

A

2400m

Respiratory system (20 decks)

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