Arterial Blood Gases

Arterial blood gases (ABGs) is a collective term applied to three separate measurements—pH, P co 2, and P o 2—generally made together to evaluate acid–base status, ventilation, and arterial oxygenation. Oxygen (O2) and carbon dioxide (CO2) are the most important respiratory gases, and their partial pressures in arterial blood reflect the overall adequacy of gas exchange. Pa o 2 is affected by age and altitude. Pa co 2 by altitude. Therefore, Pa o 2 must be individually calculated for each patient, and both determinations must be interpreted against local normal values. Hydrogen is not present in blood as a gas and, therefore, does not exert a partial pressure. However, pH, which measures hydrogen ion activity, is a conventional part of every arterial blood gas determination. The normal range for blood pH is 7.35 to 7.45.Some calculated or derived variables may be reported with the ABGs. The bicarbonate concentration, which can be calculated from the pH and P co 2, is the most useful of these. Others, such as base excess and base deficit, are not essential and may be confusing.