*ABG Basics* Flashcards

1
Q

Normal ranges for all values?

A
pH = 7.35-7.45
pO2 = 11-13 (>10)
pCO2 = 4.7-6.0
HCO3- = 22-26
BE = -2 to +2
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2
Q

What is normal pO2 and how is it calculated in patients on administered oxygen?

A

Normal should be >10 on room air (RA)

  • normal for patients on delivered oxygen is calculated as roughly 10kPa below the %oxygen being administered
  • e.g. patient on 20% oxygen should be at pO2 10kPa
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3
Q

What are the abnormal pO2 states defined as?

A

Hypoxaemia = pO2<10

Severe hypoxaemia/respiratory failure = pO2<8

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4
Q

What are the 2 types of respiratory failure and how are they defined?

A

Type 1 - hypoxaemia (<8) with normocapnia (<6)

Type 2 - hypoxaemia with hypercapnia (>6)

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5
Q

What is type 1 respiratory failure caused by and how does it form?

A

Ventilation/perfusion mismatch (V/Q mismatch)

  • volume of air flowing in/out of the lungs does not match the flow of blood to the lung tissue
  • as a result of the mismatch, pO2 falls and pCO2 rises (remember these are in the blood, not the lungs)
  • the rise in pCO2 triggers an increase in the patients alveolar ventilation which corrects the pCO2 but not the pO2 (different dissociation curves)
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6
Q

Examples of V/Q mismatch?

A

Reduced ventilation with normal perfusion = pulmonary oedema, bronchoconstriction (e.g. severe asthma)

Reduced perfusion with normal ventilation = pulmonary embolism

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7
Q

What is type 2 respiratory failure caused by and how does it form?

A

Caused by alveolar hypoventilation

  • patient can’t adequately oxygenate, and eliminate CO2 from, their blood
  • pCO2 rises as it isn’t cleared
  • pO2 falls as less is absorbed into the blood form the lungs
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8
Q

What are the causes of alveolar hypoventilation (i.e. causes of type 2 respiratory failure)?

A
  • Increased resistance due to airway obstruction (COPD)
  • Reduced compliance of the lung tissue/chest wall (pneumonia, rib fracture, obesity)
  • Reduced strength of respiratory muscles (Guillain-Barré syndrome, motor neurone disease)
  • Drugs acting on the respiratory centre reducing overall ventilation (opiates)
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9
Q

Evidence for source of pH derangement?

A

Imbalance in HCO3- = metabolic
Imbalance in pCO2 = respiratory
- these are the buffers the body uses to correct the pH if one of them is causing a deranged pH

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10
Q

What is a typical pH, pCO2, and HCO3- appearance for respiratory acidosis with no compensation?

A

pH - decreased (acidic)
pCO2 - increased (CO2 retention)
HCO3- - normal

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11
Q

What is a typical pH, pCO2, and HCO3- appearance for respiratory alkalosis with no compensation?

A

pH - increased (alkalotic)
pCO2 - decreased (hypocapnia)
HCO3- - normal

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12
Q

What is a typical pH, pCO2, and HCO3- appearance for respiratory acidosis with partial/complete metabolic compensation?

A

pH - low/normal (partial/complete comp)
pCO2 - increased
HCO3 - increased

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13
Q

What is a typical pH, pCO2, and HCO3- appearance for respiratory alkalosis with partial/complete metabolic compensation?

A

pH - high/normal (partial/complete comp)
pCO2 - decreased
HCO3 - decreased

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14
Q

Incomplete so will come back to this but GeekyMedics quiz link on back of this and in Practice Paper 3

A

https://geekyquiz.com/learn/quiz/336440/

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