ABGs Flashcards
How can you determine whether an acid base disturbance is respiratory or metabolic?
If the pH and pCO2 are moving in the same direction (either both high or both low) then it is metabolic. If they move in opposite directions then it is a respiratory cause.
How can a metabolic acidosis occur?
DKA, lactic acidosis, aspirin overload or renal failure. Diarrhoea
What are some causes of metabolic alkalosis?
GI losses of H+ (vomiting mainly, sometimes diarrhoea),
Renal loss of H+ ions (diuretics).
Explain how sepsis affects ABGs
Sepsis can cause reduced end organ perfusion which will cause tissue hypoxia. This results in anaerobic respiration with accumulation of lactic acid. Resulting in lactic acidosis.
Explain how DKA affects ABGs
Absence of insulin, causes reduced glucose into cells so there is release of FFA which are converted into ketone bodies which causes the blood to become more acidic.
What are some causes of mixed respiratory and metabolic acidosis?
Cardiac arrest and multi-organ failure
What are some causes of mixed respiratory and metabolic alkalosis?
Liver cirrhosis and diuretic use,
hyperemesis gravidarum,
excessive ventilation in COPD
What are the normal ABG values?
H+ = 36-43mmol/L
pH = 7.35-7.45
PaCO2 = 4.6-6.0 kPa
PaO2 = 10.5-13.5 kPa
HCO3 = 23-30 mmol/L
What is type 1 respiratory failure and some causes
Low O2 with normal/low CO2. Aim for O2 sats of 94-98%
Causes: pneumonia, PE, pulmonary oedema, pulmonary fibrosis
What is type 2 respiratory failure and what are some causes?
Low O2 with a high CO2. Aim for O2 sats of 88-92%.
Causes include COPD, neuromuscular disease and obesity hypoventilation.
What is the normal anion gap and when is it useful?
It is useful in determining the cause of a metabolic acidosis Normal = 8-16mmol/L
What are some causes of a raised anion gap metabolic acidosis?
- renal failure, DKA, lactic acidosis, toxins
What are some cause of a normal anion gap metabolic acidosis?
Renal tubular acidosis, diarrhoea, carbonic anhydrase inhibitors and ureteric diversion
