Arterial Blood Gas



The review used to assess the amount of haematosis in respiratory diseases, whether acute or chronic.


It involves measuring blood pressure O2 and CO2, the bicarbonate ion concentration and arterial blood pH.

Arterial Blood GasTechnique:

Sampling 3 mL of arterial blood via the femoral or radial puncture into a heparinized syringe sealed.

It is essential to ensure that the sampling is carried out in an artery and not into a vein.

If successive samples are needed, we can put in place a microcatheter.

By scarification, it is possible to take a sample at the ear lobe or heel in infants.

In any case, absolutely avoid air bubbles that distort the result.


Normal values to 30 years:

– PO2 (arterial oxygen pressure):> 90 mmHg;

– PCO2 (arterial pressure of carbon dioxide): 38-42 mmHg;

– SaO2 (O2 saturation): 95 to 98%;

– PH: 7.38 to 7.42.

PO2 decreases with age, and it is 75 mmHg to 80 years.

Pathological changes:

– Hypoxemia without hypercapnia (pressure drop in O2 but no CO2 pressure increase); the total “+ PO2 PCO2” is less than 130 mmHg in case of:

  – pulmonary embolism,

  – Pulmonary shunt effect with a poorly ventilated area,

  – Alveolocapillary block (loss of permeability of the capillary cell);

– With hypercapnia hypoxemia (decreased oxygen, increased carbon dioxide); the total “PCO2 PO2 +” is between 130 and 150 mmHg in the case of:

  – Depression of the respiratory centers (acute poisoning, head trauma, encephalitis)

  – Paralysis of respiratory muscles,

  – Chronic bronchitis with obstruction.

Hypoxia is severe, if PO2 is less than 40 mmHg and SaO2 less than 75%.



Practical advice:

If venipuncture, we quickly realized the error handling to the following results: PO2 40 mmHg; PCO2 45 mmHg; SpO2: 75%; pH 7.35, which are those of a venous and arterial not.


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