T4 L5: Respiration control and ABG's Flashcards
What is an ABG?
An arterial blood gas test
What is an ABG used for?
To test for the acid/base balance and the ventilatory status
Why is an ABG taken from arteries?
Because the results are more accurate than in veins
What is meant by ‘CO2 isn’t an acid but acts like one’?
When C02 levels go up, the pH goes down because H2CO3 (carbonic acid) is produced
What happens to blood pH when CO2 elimination is insufficient?
[H+] increases so pH decreases
What is the carbonic anhydrase equation?
C02 + H2O = H2CO3 = HCO3- + H+
What is respiratory acidosis?
The build up/ retention of CO2
What are fixed/ non-volatile acids?
Those that can’t be eliminated by exhalation
How does the body get fixed/ non-volatile acids?
By the oxidation of dietary substrates
How are fixed acids eliminated from the body?
Via the kidneys or the liver. They end up in urine
What are the 3 most important buffers in the body?
Carbonate, proteins circulating in the blood that have histamine residue Eg. Albumin, and phosphates
What ion balances out H+?
Cl-
How do we measure the abnormal accumulation of fixed acids?
Through the anion gap
What is the anion gap?
The gap between the uncounted cations an anions. It helps to measure the acid/base balance
What are those most abundant cations in the blood which are used for the anion gap test?
Na+ and K+ plus some uncounted cations
What are the most abundant anions in the blood which are used for the anion gap test?
Cl- and bicarbonate plus some uncounted anions
How is the anion gap calculated?
the uncounted anions - uncounted cations (because there are more uncounted anions than uncounted cations)
What is the normal AG value for Na - (Cl + bicarbonate )?
12
What is ‘GOLD MARK’ used for?
For the main causes of AG acidosis
What does ‘GOLD MARK’ stand for?
Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis (in diabetes)
What is non-anion gap acidosis and how does it occur?
The loss of bicarbonate. The acidosis occurs when the body tries to compensate for the bicarbonate but that also increases the levels of H+
What causes anion gap acidosis?
The addition of acid
How does loss of bicarbonate occur in the kidney tubules?
By failure to absorb HCO3-
How does stool end up at pH6.6 when the stomach has a pH of 3?
The pancreatic ducts produce bicarbonate and secrete it into the lumen
How does a high output of stool cause a rapid loss of bicarbonate if output of stool is high
Bicarbonate is mixed to optimise the pH so a lot of it is used up if the output of stool is high
What are the 4 causes of non-ionic gap acidosis (loss of bicarbonate)?
Renal tubular acidosis (RTA), GI losses, acetazolamide and excessive administration of Cl-
What is Renal tubular acidosis (RTA)?
When the kidneys don’t properly remove acids from the blood into the urine so too much acid remains in the blood. Bicarbonate tries to correct this
What is acetaxolamide?
A medication with the side effect where it can cause metabolic acidosis (loss of bicarbonate)
What is respiratory acidosis?
High PCO2
What is metabolic acidosis?
Low HCO3- (bicarbonate)
What is respiratory alkalosis?
Low PCO2
What is metabolic alkalosis?
High HCO3-
What is acidaemia?
Low blood pH
What is alkalaemia?
High blood pH
How long does metabolic compensation take?
A few days
How long does respiratory compensation take?
Quickly
What is the compensatory response for respiratory acidosis?
Kidneys retain HCO3-
What is the compensatory response for respiratory alkalosis?
Kidneys eliminate HCO3-
What is the compensatory response for metabolic acidosis?
Lungs eliminate CO2
What is the compensatory response for metabolic alkalosis?
Lungs retain CO2 but there is a limit to this
