Arterial Blood Gas Measurement Flashcards
What does ABG measure? (5)
Partial pressure of oxygen
Partial pressure of carbon dioxide
pH
Plasma bicarbonate
Base excess
What does PO2 measure?
The partial pressure of oxygen: This variable indicates how much oxygen is dissolved in the arterial blood, and if it is particular low it can suggest inadequate gas exchange in the lungs.
What does PCO2 measure?
The partial pressure of carbon dioxide: This variable indicates how much carbon dioxide is dissolved in arterial blood, and if it is particularly high it can suggest inadequate gas exchange in the lungs.
What does pH measure?
The ‘power of hydrogen’: This variable describes the acidity, neutrality or alkalinity of the blood. The pH of arterial blood is finely tuned, and small deviations can affect oxygen transport and delivery.
What does plasma bicarbonate measure?
This variable describes the concentration of bicarbonate dissolved in arterial blood. If plasma bicarbonate is higher or lower than normal, this could be evidence of gas exchange imbalance.
What does base excess measure?
This variable describes the concentration of bases (predominantly bicarbonate) compared with the ‘expected concentration’. An exact match is 0, an excess of base is positive, and a base deficit is negative.
What is the oxygen saturation of mixed venous blood?
75%
How does oxygen bind to haem groups within erythrocytes?
Through cooperative binding
What is oxygen flux?
The amount of oxygen delivered to peripheral tissue per minute
What is pulmonary transit time?
The amount of time it takes for a molecule to cross the gaseous exchange surface 0.75s, oxygen can equilibrate within this length of time
What decreases pulmonary transit time?
• Carbon dioxide is soluble within plasma, therefore enabling ability to dissolve quickly into the alveoli. Cardiac output increases during exercise -Decreases pulmonary transit time (Improves ability to increase oxygen saturation of haemoglobin, oxygen loading is faster).
What is an acid?
Acids have the ability to donate hydrogen ions (Weak association). H+ (protons Valency of +1 has no electrons or neutrons). A greater concentration of H+ ions - Lower pH.
What is a base?
Base: Anionic (negative charged ions) molecule capable of reversibly binding protons, reducing the available dissociated H+ ions within the plasma.
H+A-⇌H++ A-
Which enzyme catalyses the formation of carbonic acid within RBCs?
Carbonic anhydrase
What is the fate of carbonic acid within RBCs?
Dissociates into respective hydrogen and bicarbonate ions
Which transporter regulates bicarbonate-chloride exchange?
AE1 transporter
How is carbon dioxide primarily transported through circulation?
As bicarbonate
As carbaminohaemoglobin
Dissolved in plasma
What is alkalaemia?
Refers to elevated blood pH in respect to standard
What is acidaemia?
Refers to lower than standard blood pH
What is alkalosis?
Describes circumstances that will decrease [H+] & increase pH.
What is acidosis?
Describes circumstances that will increase [H+] and decrease pH.
What is respiratory compensation?
Changes in ventilation can stimulate a rapid compensatory response to alter carbon dioxide elimination, therefore altering the pH.
What is metabolic compensation?
Changes in HCO3- & H+ retention/secretion in the kidneys can stimulate a slow compensatory response to pH change Metabolic compensation
- An acidosis will need an alkalosis to correct
- An alkalosis will need an acidosis to correct
What is the following diagnosis for:
Low pH
High Carbon dioxide
Normal Base excess
Uncompensated respiratory acidosis
What is the following diagnosis for:
High pH
Low Carbon dioxide
Normal Base excess
Uncompensated respiratory alkalosis
What is the following diagnosis for:
Low pH
Normal Carbon dioxide
Low BE
Uncompensated metabolic acidosis
What is the following diagnosis for:
High pH
Normal Carbon dioxide
High Base excess
Uncompensated metabolic alkalosis
What is the following diagnosis for:
Low pH
High Carbon dioxide
Low Base excess
Uncompensated mixed acidosis
What is the following diagnosis for:
High pH
Low Carbon dioxide
High Base excess
Uncompensated mixed alkalosis
What is the following diagnosis for:
Low pH
High Carbon dioxide
High Base excess
Partially compensated respiratory acidosis
What is the following diagnosis for:
High pH
High Carbon dioxide
High Base excess
Partially compensated metabolic alkalosis
What is the following diagnosis for:
Low pH
Low Carbon dioxide
Low Base excess
Partially compensated metabolic acidosis
What is the following diagnosis for:
High pH
Low Carbon dioxide
Low Base excess
Partially uncompensated respiratory alkalosis
What is the following diagnosis for:
Normal pH
Low Carbon dioxide
Low Base excess
Fully compensated respiratory alkalosis/ metabolic acidosis
What is the following diagnosis for:
Normal pH
High Carbon dioxide
High Base excess
Fully compensated respiratory acidosis/metabolic alkalosis
