arterial blood gas Flashcards
what 2 things do arterial blood gases look for?
- acid base balance
- ventilatory status
what percentage of the acid in our body is carbon dioxide?
> 90%
what happens to the equation for carbon dioxide elimination is insufficient?
retained carbon dioxide will drive the equation to the right thereby increasing [H+] and decreasing the pH
what is respiratory acidosis?
the build up or retention of carbon dioxide
what are fixed/non volatile acids?
products from the oxidation of dietary substrates
what do you have to do with fixed acids?
physically eliminate them from the body, usually by the kidneys or the liver
what prevents the acid we produce daily from lowering our pH too much?
buffers
what are the 3 most important buffers?
bicarbonate, proteins and phosphate
what volume of Na + K should you have in the blood?
144 mEq/L
what volume of Cl + bicarbonate should you have in the blood?
128 mEq/L
what is the anion gap?
the uncounted ions minus the counted cations
what are the 2 equations for measuring the anion gap?
anion gap = (Na + K) - (Cl + Bicarbonate)
anion gap = Na - (Cl + bicarbonate)
what are the main causes of an anion gap?
hint GOLD MARK
Glycols (ethylene and propylene) Oxoproline L-lactate D-lactate Methanol Aspirin Renal failure Ketoacidosis
what are the 2 categories for metabolic acidosis?
1) addition of acid (anion gap acidosis)
2) loss of bicarbonate (non anion gap acidosis)
what methods do you lose bicarbonate from the body?
- renal tubular acidosis
- GI losses
- acetazolamide
- excessive chloride administration (intravenous fluids with NaCl)
what are the 6 steps to interpreting an arterial blood gas?
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
what value shows full compensatory?
around 7.35 or 7.45
what are clues that a mixed disorder exists?
- 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
what does the dorsal respiratory group do?
control quiet breathing, trigger inspiratory impulses
what does the ventral respiratory group do?
trigger inspiratory and expiratory impulses during exercise or other times of active exhalation
what does the respiratory centre control?
controls inspiratory and exhalation efforts
which efferent nerves are linked to inspiratory muscles?
- diaphragm: phrenic nerves, C3-C5
- external intercostal muscles: thoracic nerves T1-T11
- sternocleidomastoid: XI cranial nerve
- scalene muscles: C3-C8
which efferent nerves are linked to muscles of exhalation?
- abdominal wall: T5-T12
- internal intercostal muscles: T1-T12
which inputs can modify the respiratory rhythm?
- emotional inputs from the cerebral cortex
- lung receptors
- chemoreceptors (central and peripheral)
