ABG’s Flashcards
When should an ABG be done?
•The acutely unwell patient, including:
• Respiratory distress
• Sepsis
• Low GCS
• Seizure
• Head/neck injury
How to do an ABG?
• Confirm patient details
• Confirm current oxygen therapy
• Ensure correct PPE
• Allen’s test
• Position patient appropriately – access to radial artery, wrist extended with hand at 45 degrees
• Palpate the radial artery
• Insert needle with the bevel facing upwards at 45 degrees – if in the artery, the syringe will self-fill
• Remove needle, cover with gauze, apply firm pressure for 3 minutes
Normal ranges when looking at an ABG
pH 7.35 – 7.45
pCO2 4.5-6.0
pO2 11 – 14
Bicarbonate (HCO3-) 22-28
Base Excess -2 - 2
ABG interpretation
pH
Low - acidosis
High PCO2 respiratory acidosis
Low HCO3- metabolic acidosis
High pH- alkilosis
Low PCO2 respiratory alkalosis
High HCO3 - metabolic alkalosis
Type 1 respiratory failure
Low oxygen (hypoxia)
Causes could be:
Pneumonia
PE
ILD
Type 2 respiratory failure
High carbon dioxide
Sometimes low oxygen also
Causes could be:
Opioids
COPD
Coma
ABG taken on RA
pH= 7.27
PaO2= 7.6kPa
PaCO2= 7.7 kPa
Bicarbonate= 26.5mmol/L
Base Excess= +1.0
SATs= 89%
Respiratory acidosis
As low ph and high co2
Type 2 reps failure could be as a result of COPD
ABG taken on RA
pH= 7.59
PaO2= 11.3kPa
PaCO2= 5.4 kPa
Bicarbonate= 35.6mmol/L
Base Excess= +7.1
SATs= 97%
Metabolic alkalosis
As pH is high and so is bicarb
ABG taken on RA
pH= 7.61
PaO2= 15.8kPa
PaCO2= 2.3 kPa
Bicarbonate= 23.1mmol/L
Base Excess= -1.5
SATs= 99.6%
Respiratory alkalosis
High pH and low CO2
ABG taken on RA
pH= 7.14
PaO2= 14.6kPa
PaCO2= 2.7 kPa
Bicarbonate= 12.4mmol/L
Base Excess= -7.6
SATs= 99%
Metabolic acidosis
ABG taken on RA
pH= 7.36
PaO2= 7.7kPa
PaCO2= 7.9 kPa
Bicarbonate= 38.1mmol/L
Base Excess= +6.7
SATs= 90%
Respiratory acidosis with full compensation
As pH is normal
Type 2 compensated reps failure
ABG taken on 35% venturi mask
pH= 7.24
PaO2= 11.7kPa
PaCO2= 8.2 kPa
Bicarbonate= 36.3mmol/L
Base Excess= +6.5
SATs= 96%
Respiratory acidosis with partial compensation
As pH is low, CO2 is high
Partial as bicarb has increased but pH hasn’t gone back to normal
ABG taken on RA
pH= 7.14
PaO2= 7.6kPa
PaCO2= 7.7 kPa
Bicarbonate= 12.4mmol/L
Base Excess= -7.6
SATs= 86%
Mixed respiratory and metabolic acidosis
Eg type 2 COPD resp failure with sepsis
Normal anion gap range
12-16mmol/L= Normal (including Potassium)
• 8-12mmol/L= Normal (without Potassium)
Potential causes for raised anion gap and normal anion gap
• Raised Anion Gap: Ketoacidosis, AKI, Lactic Acidosis, Ethylene glycol, Aspirin, Methanol
• Normal Anion Gap (ie. bicarbonate loss):Vomiting, Renal tubular acidosis