In other levels of care, pulse oximetry plus transcutaneous carbon-dioxide measurement is a less invasive, alternative method of obtaining similar information.

[citation needed] An ABG test can indirectly measure the level of bicarbonate in the blood.

Many blood-gas analyzers will also report concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin, and methemoglobin.

ABG testing is mainly used in pulmonology and critical-care medicine to determine gas exchange across the alveolar-capillary membrane.

Combinations of disorders can be complex and difficult to interpret, so calculators,[2] nomograms, and rules of thumb[3] are commonly used.

Arterial blood for blood-gas analysis is usually drawn by a respiratory therapist and sometimes a phlebotomist, a nurse, a paramedic or a doctor.

[4] Blood is most commonly drawn from the radial artery because it is easily accessible, can be compressed to control bleeding, and has less risk for vascular occlusion.

Other syringes may need to be heparinised, by drawing up a small amount of liquid heparin and squirting it out again to remove air bubbles.

[8] If a plastic blood gas syringe is used, the sample should be transported and kept at room temperature and analyzed within 30 min.

If prolonged time delays are expected (i.e., greater than 30 min) prior to analysis, the sample should be drawn in a glass syringe and immediately placed on ice.

[10] The machine used for analysis aspirates this blood from the syringe and measures the pH and the partial pressures of oxygen and carbon dioxide.

Whenever there is poor pulmonary ventilation, the carbon dioxide levels in the blood are expected to rise.

As carbon dioxide concentrations continue to increase (PaCO2 > 45 mmHg), a condition known as respiratory acidosis occurs.

[citation needed] Respiratory alkalosis (Pa CO2 < 35 mmHg) occurs when there is too little carbon dioxide in the blood.

[citation needed] In general, it is much easier to correct acute pH derangement by adjusting respiration.

In such case, lowering the carbon dioxide abruptly means that the bicarbonate will be in excess and will cause a metabolic alkalosis.