Arterial Blood Gases Flashcards
What is the bloods normal pH range?
7.35 - 7.45
What is the most important buffering system to maintain blood pH?
CO2/HCO3
What is the equation linking CO2 and HCO3?
What controls the retention and excretion of CO2 in this system?
Lungs
What controls the excretion and retention of HCO3 in this system?
Kidneys
What should CO2 be thought of as, in ABGs?
An acid
What should HCO3 be though of as, in ABGs?
A base
What is compensation?
The body’s efforts to correct pH imbalances
How far can compensation go?
Compensation will change pH in the right direction but will never be able to over compensate
What is meant by a metabolic acidosis (Acidaemia technically) ?
This is a condition in which there is an excess of H+ and thus not enough HCO3 to balance
What are some conditions that can lead to metabolic acidosis?
Lacticacidosis - Exercise
Renal failure
Sepsis
Diabetic ketoacidosis
How does the body compensate for a metabolic acidosis?
Too much acid on one side means that the body needs to get rid of acid on the other, by blowing off CO2, so respiratory rate increases
What are some signs of metabolic acidosis?
Increased H+
Reduced pH
Tachypnoea
HCO3 levels low
What is respiratory acidosis?
This is an increase in pH caused by an accumulation of CO2, due to a decrease in lung function or problem with the mechanics of respiration
How does the body compensate for respiratory acidosis?
As there is now too much acid, the body increases levels of base, so the kidneys reabsorb more bicarbonate, back into the blood, this is a slow process
What are some signs of acute respiratory acidosis?
Reduced pH
Increased pCO2
Little change in bicarbonate concentrations (Slow)
What are some signs of chronic respiratory acidosis?
Slightly reduced pH
Increased pCO2
Increased bicarbonate levels
What is metabolic alkalosis?
This is a decrease in H+ levels due to a net loss of acid from the body, causing a surplus of base that can’t react
How does the body compensate for metabolic alkalosis?
The body tries to hold on to extra acid, as CO2, so causes hypoventilation to retain CO2
What is the most common cause of metabolic alkalosis?
Vomiting
What are some signs of metabolic alkalosis?
Elevated pH
Small increase in CO2 (Hypoventilation is relatively ineffective)
What is respiratory alkalosis?
This is a lack of acid, due to a loss of CO2, usually caused by hyperventilation, as more CO2 is blown off
What are some common causes of respiratory alkalosis?
Anxiety leading to hyperventilation
Pulmonary embolism
CNS disorders: stroke, subarachnoid haemorrhage, encephalitis
Altitude
Pregnancy
How does the body compensate for respiratory alkalosis?
Hyperventilation is usually only short lived, so the body doesn’t usually have time to compensate by excreting bicarbonate