clinical blood gases Flashcards by Freya Balcombe

how is haemoglobin saturation measured

absorption spectrometry using a finger probe

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what is most healthy peoples oxygen saturation

97%

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2 different ways of measuring arterial blood gases (ABG)

single arterial puncture technique
in-dwelling arterial catheter or A-line

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which artery is most commonly used for ABG measurement and which other 2 are used less often

radial artery
less commonly used:
femoral artery
brachial artery

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what does a blood gas measure

PaO2
PaCO2
Hydrogen ion/pH
Bicarbonate
may also measure electrolytes and Hb

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difference between PA and Pa

PA - partial pressure in alveolus
Pa - partial pressure in arterial circulation

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normal blood gas values: H+

36-44nmol/l

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normal blood gas values: PO2

12-15kPa

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normal blood gas values: PCO2

4.4-6.1

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normal blood gas values: HCO3 (bicarbonate)

21-27.5

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what is BE

base excess (to do with metabolic blood gases)

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normal blood gas values: BE

+2 to -2 mmol/l

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difference between PAO2 and PaO2 values and why

PaO2: 12-15kPa
PAO2: 14-15kPa
oxygen dilution

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what do carbon dioxide levels tell us about

ventilation

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what happens to pCO2 and pO2 during hyperventilation

pO2 same, low pCO2

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what happens to pCO2 and pO2 during hypoventilation

low pO2, high pCO2

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what does increase of CO2 in blood lead to

acidosis

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what is carbon monoxide (CO) produced from

incomplete combustion (mainly faulty gas boilers)

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what does CO form when it binds to haemoglobin

carboxyhaemoglobin

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how does CO damage the body

higher affinity to haemoglobin than oxygen so displaces it
also toxin to mitochondria

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carbon monoxide treatment

high concentration oxygen - this displaces CO from haemoglobin

what is respiratory failure

low oxygen level in the blood
PaO2<8kPa

what is respiratory failure caused by

V/Q mismatch or hypoventilation

what is the name for low oxygen levels in the blood

hypoxaemia

type 1 respiratory failure blood gas levels

low PaO2 normal (or low) CO2

what is type 1 respiratory failure caused by (mainly)

V/Q mismatch

type 1 respiratory failure example

pneumonia

what is V/Q mismatch

not enough oxygen or not enough blood being oxygenated

what are other causes of type 1 respiratory failure

lung diseases affecting parenchyma interstitial lung disease bronchiectasis obstructive airways disease (asthma, COPD - but can also cause type 2) pulmonary embolism

type 1 respiratory failure treatment

treat with oxygen while treating underlying cause

type 2 respiratory failure blood gas levels

low PaO2 high PaCO2

what is type 2 respiratory failure caused by

hypoventilation

what is gas levels in type 2 respiratory failure due to and what can they lead to?

low O2 level due to hypoventilation high CO2 due to increased levels in alveolar space and less removed from blood acute rise in blood CO2 leads to respiratory acidosis

other causes of type 2 respiratory failure

hypoventilation opiate toxicity neuromuscular disease COPD acute severe asthma

asthma and respiratory failure - what suggests significant asthma attack

hypoxaemia

COPD and respiratory failure - difference between type 1 and type 2

earlier stage - mucus and patches of emphysema, type 1 more severe - type 2 could be acute or chronic

acidosis - equation

CO2 + H2O <-> H2CO3 <-> H+ + HCO3-

what is H+ increased by

increase in pCO2 (respiratory acidosis) increase in acid production or decrease in excretion (metabolic acidosis)

acidosis - acute vs chronic type 2 respiratory failure

acute - yes chronic - maybe not

why does chronic type 2 respiratory failure often not have acidosis

low CO2 for so long that body compensates, raises bicarbonate levels to buffer this, therefore no acidosis

acute type 2 respiratory failure - blood gas levels

low oxygen high carbon dioxide high H+ normal bicarbonate

chronic type 2 respiratory failure - blood gas levels

low oxygen high carbon dioxide normal H+ high bicarbonate

problem with chronically high CO2 levels?

high CO2 levels normally stimulates breathing, if it is chronic it is compensated for so will no longer to this therefore become dependant on hypoxia to stimulate breathing

why could oxygen therapy for patients with chronic type 2 respiratory failure be bad? how should they be treated?

because CO2 levels will rapidly rise higher making them more hypoxemic because of the effects of CO2 narcosis. treated with controlled oxygen, monitor response.

which type of respiratory failure could oxygen therapy be bad for?

chronic type 2 respiratory failure

what is respiratory alkalosis caused by

hyperventilation

respiratory alkalosis blood gas levels

low PCO2 and low H+

conditions causing excess production of acid

lactic acidosis diabetic ketoacidosis

what is a classic sign of acidosis

kussmal breathing - breathing more quickly and deeply to try get rid of acid

what blood gas level is a sign of metabolic acidosis

high acid, LOW bicarbonate

what does standard bicarbonate mean?

no metabolic component to illness