Arterial blood gases tutorial Flashcards
What does the body physiology processes work best at? pH?
Between 7.35 and 7.45
What is the most important extracellular buffer systems in the body to maintain control of the pH of the body?
CO2 + H2O HCO3 + H(+)
What waste products excretion/retiention controlled by the lung?
CO2
For simplicity should CO2 be thought of as an ACID or ALKALI?
ACID
Where is Bicarbonate excreted? (HCO3)
Its an alkali excreted/reabsorbed by the kidneys
Due to the excretion/reabsorption of HCO3 by the kidney is this a fast or slow process?
ITs a slow process and so the change in concentration due to bicarb is slower than CO2
For simplicity should HCO3 be thought of as an ACID or ALKALI?
ALKALI
What is compensation?
The body’s own attempt to correct a pH balance
How does the body do this? (Compensation)
The body can either rapidly gain or lose CO2 (Acid) or more slowly gain or lose HCO3 (alkali)
What can these process do in terms of pH?
They can alter the pH in the right direction but will not return it to normal
Is it possible to overcompensate?
It is not possible to overcompensate
Describe metabolic acidosis - when does it happen?
IT comes about when there is an excess of H+ produced by the body due to disease (lactic acidosis/renal failure/sepsis)
What does the body do in metabolic acidosis?
It tries to counteract the excess H+ and balance the equation by getting rid of the acid - the easiest and fastest way to do this is to get rid of CO2 (CO2 is acid)
What happens in respiratory acidosis?
There is an accumulation of CO2 (ACID) due to a disease of the lungs or a problem with the mechanics of respiration
How does the body counteract the accumulation of acid in respiratory acidosis?
It tries to hold onto Alkali by reabsorbing bicarbonate from the kidneys (SLOW PROCESS)
What would be seen in ACUTE respiratory acidosis?
A reduced pH
Increase in CO2
Little or no change in bicarb
What would be seen in more chronic respiratory acidosis?
Increase in HCO3 - as it has accumulated because the kidneys have had time to reabsorb it to try and counteract the CO2
What is metabolic alkalosis due to?
A net loss of acid from the body leaving an alkali surplus
How does the body counteract the surplus of alkali in metabolic alkalosis?
Tries to hold onto acid by hyperventilating and retaining CO2
(may also vomit - loss of significant amounts of stomach acid)
What is respiratory alkalosis due to?
Lack of acid because of the loss of CO2. This arises due to hyperventilation from anxiety, pain, early sepsis etc
What does the body to in respiratory alkalosis?
It should lose HCO3 - however this a slow process and the causes of resp alkalosis are usually short lived.
What is PaO2?
The partial pressure of O2 in arterial blood.
Give the normal ranges of pH, PaO2, PaCO2 and BE?
pH = 7.35-7.45 PaO2 = 9.3 - 13.3 kPa PaCO2 = 4.7-6 kPa BE = -2 to +2 mmol/l
What does a high PaCO2 indicate?
Respiratory acidosis
