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module 103 - theme 4 > arterial blood gas > Flashcards

arterial blood gas Flashcards

1
Q

what 2 things do arterial blood gases look for?

A
  • acid base balance

- ventilatory status

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2
Q

what percentage of the acid in our body is carbon dioxide?

A

> 90%

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3
Q

what happens to the equation for carbon dioxide elimination is insufficient?

A

retained carbon dioxide will drive the equation to the right thereby increasing [H+] and decreasing the pH

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4
Q

what is respiratory acidosis?

A

the build up or retention of carbon dioxide

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5
Q

what are fixed/non volatile acids?

A

products from the oxidation of dietary substrates

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6
Q

what do you have to do with fixed acids?

A

physically eliminate them from the body, usually by the kidneys or the liver

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7
Q

what prevents the acid we produce daily from lowering our pH too much?

A

buffers

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8
Q

what are the 3 most important buffers?

A

bicarbonate, proteins and phosphate

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9
Q

what volume of Na + K should you have in the blood?

A

144 mEq/L

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10
Q

what volume of Cl + bicarbonate should you have in the blood?

A

128 mEq/L

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11
Q

what is the anion gap?

A

the uncounted ions minus the counted cations

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12
Q

what are the 2 equations for measuring the anion gap?

A

anion gap = (Na + K) - (Cl + Bicarbonate)

anion gap = Na - (Cl + bicarbonate)

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13
Q

what are the main causes of an anion gap?

hint GOLD MARK

A 
Glycols (ethylene and propylene)
Oxoproline
L-lactate
D-lactate
Methanol
Aspirin
Renal failure
Ketoacidosis
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14
Q

what are the 2 categories for metabolic acidosis?

A

1) addition of acid (anion gap acidosis)

2) loss of bicarbonate (non anion gap acidosis)

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15
Q

what methods do you lose bicarbonate from the body?

A
  • renal tubular acidosis
  • GI losses
  • acetazolamide
  • excessive chloride administration (intravenous fluids with NaCl)
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16
Q

what are the 6 steps to interpreting an arterial blood gas?

A

1) examine the pH, PCO2 and HCO3-
2) determine the primary process. Does the patient have an acidaemia or alkalemia based on the pH? if so what type?
3) if metabolic acidosis is present, calculate the anion gap
4) identify the compensatory process
5) determine if a mixed acid-base disorder is present
6) determine the cause

17
Q

what value shows full compensatory?

A

around 7.35 or 7.45

18
Q

what are clues that a mixed disorder exists?

A
  • the anion gap should be similar in value to the reduction of bicarbonate
  • an anion gap is present but the pH is alkalaemic
  • incomplete compensation for any primary process
19
Q

what does the dorsal respiratory group do?

A

control quiet breathing, trigger inspiratory impulses

20
Q

what does the ventral respiratory group do?

A

trigger inspiratory and expiratory impulses during exercise or other times of active exhalation

21
Q

what does the respiratory centre control?

A

controls inspiratory and exhalation efforts

22
Q

which efferent nerves are linked to inspiratory muscles?

A
  • diaphragm: phrenic nerves, C3-C5
  • external intercostal muscles: thoracic nerves T1-T11
  • sternocleidomastoid: XI cranial nerve
  • scalene muscles: C3-C8
23
Q

which efferent nerves are linked to muscles of exhalation?

A
  • abdominal wall: T5-T12

- internal intercostal muscles: T1-T12

24
Q

which inputs can modify the respiratory rhythm?

A
  • emotional inputs from the cerebral cortex
  • lung receptors
  • chemoreceptors (central and peripheral)
25
Q

what do central chemosensors do?

A
  • detect [H+]

- [H+] is in the CSF reflects blood [H+], PaCO2 and CSF CO2 but these are not directly sensed by central chemoreceptors

26
Q

what is the carotid body?

A

bundle of cells outside the bifurcation of carotid arteries

27
Q

what is the aortic body?

A

bundle of cells within the aortic arch

28
Q

what do the carotid and aortic bodies do?

A

they are backups for each other and they both respond to PaO2 and PaCO2 however the carotid bodies do the bulk of the peripheral sensing and also detect the pH

29
Q

what happens to the ventilatory response in response to PCO2?

A
  • the body increases ventilation if PaCO2 builds up in the blood
  • the body is very sensitive to even small changes in the PaCO2 an the VE can be increased a great deal
30
Q

what do opioids do?

A

they blunt the sensitivity to PaCO2

31
Q

what is one of the most common causes of acute hypercarbic respiratory failure?

A

opioid ingestion

32
Q

what happens to the ventilatory response in response to PO2?

A
  • normally an increase in ventilation only occurs when PaO2 drops significantly
  • however, sensitivity to PaO2 is altered by PaCO2
  • compared to PaCO2 the body is much less sensitive to changes in PaO2
  • this is due to the dual role of CO2 as a by-product of respiration as an acid; the body is highly engineered to keep the blood pH constant

module 103 - theme 4 (19 decks)

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