Common ABG values

1.8 Common ABG values


The following parameters are commonly found on ABG reports and are provided for reference (normal ranges in brackets):


H+ (35–45 nmol/L) < 35 = alkalaemia, >45 = acidaemia


Concentration of free hydrogen ions: this is a measure of how acidic or alkaline a solution is.


pH (7.35–7.45) < 7.35 = acidaemia, >7.45 = alkalaemia


Negative log of the H+ ion concentration: this is a common representation of the H+ concentration. Due to the logarithmic nature of the scale, small changes in the pH actually represent large changes in the H+ concentration.


PO2 (>10.6 kPa or >80 mmHg in arterial blood on room air)


Partial pressure of O2: can be thought of as the drive for O2 molecules to move from one place to another. PO2 is not a measure of O2 content but it does determine the extent to which Hb is saturated with O2. PaO2 refers specifically to the partial pressure of O2 in arterial blood.


PCO2 (4.7–6.0 kPa or 35–45 mmHg in arterial blood)


Partial pressure of CO2: can be thought of as the drive for CO2 molecules to move from one place to another and (unlike PO2) is directly proportional to the amount of CO2 in blood. PaCO2 refers specifically to the partial pressure of CO2 in arterial blood.


So2 (>96% on room air)


O2 saturation of haemoglobin: the percentage of O2-binding sites on Hb proteins occupied by O2 molecules. This is a measure of how much of the blood’s O2-carrying capacity is being used. SaO2 refers specifically to the O2 saturation of arterial blood.


HCO3 act (22–28 mmol/L)


Actual bicarbonate: the plasma bicarbonate concentration calculated from the actual PCO2 and pH measurements in the arterial blood sample. High bicarbonate levels signify a metabolic alkalosis and low levels signify a metabolic acidosis.


HCO3 st (22–28 mmol/L)


Standard bicarbonate: the plasma bicarbonate concentration calculated from the PCO2 and pH measurements in the arterial blood sample after the pCO2 in the sample has been corrected to 5.3 KPa (40 mmHg). The authors recommend using this measurement of bicarbonate in ABG analysis.


BE (−2 to +2)


Base excess: a calculation of the amount of base that needs to be added to, or removed from, a sample of blood to achieve a neutral pH, at 37°, after PCO2 has been corrected to 5.3 KPa (40 mmHg). A positive BE indicates that there is more base than normal (metabolic alkalosis) and a negative BE indicates that there is less base than normal (metabolic acidosis).


Lactate (0.4–1.5 mmol/L)


An indirect measure of lactic acid: high levels of lactic acid are a sign of tissue hypoxia.


Hb (13–18 g/dL men, 11.5–16 g/dL women)


Plasma haemoglobin concentration: this effectively determines blood’s capacity to carry O2.


Na (135–145 mmol/L) Plasma sodium concentration.


K (3.5–5 mmol/L) Plasma potassium concentration.


Cl (95–105 mmol/L) Plasma chloride concentration.


iCa (1.0–1.25 mmol/L) Plasma ionised calcium concentration.


Glucose (3.5–5.5 mmol/L if fasting) Plasma glucose concentration.


Related posts:

  1. When and why is an ABG required?
  2. ABG sampling technique
  3. Making ABG interpretation easy
  4. Acid–base balance: the basics

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Dec 18, 2016 | Posted by in CARDIOLOGY | Comments Off on Common ABG values

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