The blood gas analysis [BGA] is a method to measure the gas distribution [partial pressure] of oxygen, carbon dioxide as well as the pH-value and acid-base balance in the blood. Patients have seen this method at their lung specialist: firstly, a special balm is applied to the earlobe which stimulates the blood flow. The earlobe becomes hot. This procedure is necessary because actually arterial blood is necessary to determine blood gases precisely. It has been discovered that the increased blood flow [hyperaemisation] caused by the balm yields quite informative results. The painful punctuation of an artery remains an exception. After a short application time one is pricked and the blood is collected in a small tube and then usually put into an analyser. Two statements can be deducted from the blood gas results:

  • How much oxygen enters the blood stream (determined by measuring partial oxygen pressure [paO2]). This value determines if the patient needs extra oxygen. Insufficient oxygen in the blood is medically referred to as hypoxaemia or as being hyposaemiac.
  • How much carbon dioxide is in the blood (determined by measuring partial carbon dioxide pressure [paCO2]). If too much carbon dioxide is retained in the body [retarded] or not breathed out, one speaks of hypercapnia or of being hypercapnic..

The different combinations of not having enough O2 and having too much CO2 are assigned to different technical terms. You do not have to know those values by heart or even be able to interpret the results of your blood gas analysis but you should be familiar with both of these terms.

Partial pressures of O2 and CO2 and classification of gas exchange disorders
  Normal Mild Moderate Severe
paO2 > 65-70 60-65 55-60 < 55
paCO2    36-44 45-48 49-54 > 55
Hypoxia without hypercapnia Low paO2 at normal and decreased arterial paCO2
Hypoxia with hypercapnia decreased paO2 and increased (retained) paCO2 The hypoxia with hypercapnia might be caused in the terminal stage of COPD and of the lump emphysema.