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The Respiratory System > Oxygen > Flashcards

Oxygen Flashcards

1
Q

Why is more oxygen not dissolved in the blood instead of mostly being bound to haemoglobin?

A

The partial pressure of oxygen is not high enough

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2
Q

In which two ways can oxygen be carried in the blood?

A
  1. Directly dissolved
  2. Bound to haemoglobin
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3
Q

Each molecule of haemoglobin can bind how many molecules of oxygen?

A

4

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4
Q

What is the difference between SpO2 and SaO2?

A
  • SpO2 - saturation of blood with oxygen as measured by a pulse oximeter - non invasive
  • SaO2 - Oxygen saturation of arterial blood is measured by a blood test which analyses blood gases
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5
Q

How soes a pulse oximeter work?

A
  • The pulse oximeter emits both red light and IR radiation from an LED
  • Arterial blood is bright red so will absorb more of the IR wavelengths
  • Venous blood is dark red will absorb more red light and let more IR pass through
  • A photodiode will measure the received wavelengths and determine the level of oxygenation based on the ratios of light absorption
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6
Q

What is PaO2?

A

A measure of the actual oxygen concentration dissolved in arterial blood plasma - has units mmHg or KPa

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7
Q

How is PaO2 related to both SaO2 and SpO2?

A

A higher partial pressure of oxygen will result in a higher saturation of haemoglobin with oxygen

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8
Q

What is FiO2?

A

This is the amount of oxygen prescribed to a patient

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9
Q

Why can a fall in PaO2 be extremely dangerous when prescribing oxygen to a patient?

A

It depends on what the patient’s starting oxygen saturation is

Since the percentage saturation/oxygen partial pressure curve is sigmoidal, a fall in partial pressure when the starting saturation is near 100% may not affect the patient

However if the patient has a saturation of around 90% and then PaO2 falls, this can lead to a massive drop in saturation due to the PaO2 drop coinciding with the steepest part of the sigmoidal curve

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10
Q

What is type 2 respiratory failure?

A

An abnormally high amount of carbon dioxide is retained in the blood meaning blood pH stays low

This is due to poor alveolar ventilation

(Hypoxemia (PaO2 <8kPa) with hypercapnia (PaCO2 >6.0kPa))

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11
Q

Which conditions lead to type 2 respiratory failure?

A
  • Cystic fibrosis
  • Ptosis
  • Obesity
  • COPD
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12
Q

What is the normal range for blood pH?

A

7.35-7.45

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13
Q

How is normal blood pH levels mainatined?

A

Through action of buffer systems

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14
Q

What is the most important extracellular buffer system for maintaining blood pH?

A

CO2 + H2O ⇌ HCO3 + H+

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15
Q

How is accumulation of CO2 compensated for in metabolic acidosis?

A

Metabolic acidosis - an excess of H+ is produced due to disease e.g. renal failure, sepsis etc

CO2 + H2O ⇌ HCO3 + H+

The equilibrium shifts to the left because there is an increase in H+

This means tachypnoea will occur to blow off excess CO2

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16
Q

What is respiratory acidosis?

A

A respiratory problem causes CO2 to build up in the blood

17
Q

How is respiratory acidosis counteracted?

A

Kidneys retain HCO3 - this is a slow process as bicarbonate levels take a while to rise

This happens because bicarnonate is a base and can aid the stabilisation of pH

18
Q

What will differ in the fndings for acute respiratory acidosis vs chronic?

A

Both will have reduced pH and increased CO2

Only chronic wil have increased bicarbonate as this takes a while to accumulate

19
Q

What is metabolic alkalosis?

A

An overall net loss of acid from the body causing a surplus of alkali (bicarbonate)

This could be due to vomiting for example

20
Q

How is metabolic alkalosis counteracted?

A

Hypoventilation - CO2 is retained

21
Q

What will metabolic alkalosis present with?

A
  • Elevated pH
  • Marginal CO2 increase - hypoventilation is an inefficient mechanism
22
Q

What will the findings for metabolic acidosis be?

A
  • Reduced pH
  • Reduced [H+]
  • Reduced bicarbonate
  • Tachypnoea
23
Q

What is respiratory alkalosis?

A

Caused due to excessive CO2 loss from hyperventilation

This is due to pain, stress, anxiety and early sepsis

24
Q

What would be the compensatory mechanism of chronic respiratory alkalosis be if it did occur, which it usually doesn’t?

A

Loss of bicarbonate

This is a slow process and takes a while, whilst respiratory alkalosis is usually a short lived condition

25
Q

What are the findings in respiratory alkalosis?

A
  • Elevated pH
  • Hyperventilation
  • Low CO2
  • Little, if any, HCO3 change
26
Q

In relation to acidosis, what do elevated bicarbonate levels indicate?

A

Chronic respiratory acidosis

Bicarbonate levels take a while to rise as a compensatory mechanism

27
Q

Why can respiratory acidosis ccur when prescribing oxygen to patients with type II respiratory failure?

A

By increasing oxygen the perfusion problem is solved and enough oxygen can enter the blood

Oxyegn displaces carbon dioxide from haemoglobin due to the Haldane effect

However, due to the poor ventilation, carbon dioxide cannot escape and will dissolve in the blood causing acidosis

Effectiviely, administering oxygen in these situations promotes acidosis

28
Q

What is hypoxaemia?

A

Abnormally low amount of oxygen in the blood

This causes cyanosis, dyspnonea, tachypnoea and arrhythmias

29
Q

Why does hyperventilation lead to loss of conciousness?

A
  • Carbon dioxide is removed at a greater rate then it is produced
  • This raises blood pH - respiratory alkalosis
  • This has symptoms of dizziness and collapse
30
Q

What is hypoxia?

A

An abnormally low amount of oxygen reaching tissues

31
Q

Why is oxygen given regardless of the consequences in life threatening conditions such as cardiac arrest, sepsis etc?

A

The effects are of acidosis are minimal compared with certain death

32
Q

What is type I respiratory failure?

A

Hypoxaemia without an increase in carbon dioxide levels in the blood (PaCO2)

Typically, caused by a ventilation/perfusion (V/Q) mismatch - the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lungs

33
Q

What may cause type I respiratory failure?

A
  • Low PaO2 oxygen (high altitude)
  • V/Q mismatch (parts of the lung receive oxygen but not enough blood to absorb it, e.g. pulmonary embolism)
  • Alveolar hypoventilation
  • Diffusion problem (oxygen cannot enter the capillaries due to parenchymal disease, e.g. in pneumonia or ARDS)
  • Shunt (oxygenated blood mixes with non-oxygenated blood from the venous system, e.g. left to right shunt)

The Respiratory System (16 decks)

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