Blodgas

Blodgas, commonly known as blood gas analysis, is a laboratory test that measures the acidity–base balance and gas tensions of arterial blood to assess oxygenation, ventilation, and metabolic status. It is used to evaluate patients with respiratory failure, shock, or other critical conditions. The test can be performed on arterial blood (arterial blood gas, ABG) or, less commonly, on venous blood (venous blood gas, VBG).

What is measured includes pH, partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2), bicarbonate (HCO3-), base excess, and oxygen saturation (sO2). Some analyzers report additional parameters such as lactate, electrolytes, and hemoglobin oxygen content. These values help describe the patient’s acid-base status and level of oxygenation, and they guide treatment decisions in acute and critical care settings.

Collection and handling: arterial samples are typically drawn from arteries such as the radial, brachial, or femoral artery, using a heparinized syringe. Samples should be kept on ice and analyzed promptly to minimize changes from gas exchange with air or tissue during handling. Pre-analytical variables, including sampling technique, transport time, and temperature, can significantly affect results. Venous samples are easier to obtain but provide different reference values and are less reliable for assessing oxygenation in real time; ABG remains the gold standard for many ventilatory assessments.

Indications and interpretation: blodgas is used to evaluate respiratory function, guide ventilator management, and diagnose or monitor metabolic or respiratory acid-base disorders. Interpretation follows a stepwise approach, starting with pH to identify acidosis or alkalosis, then PaCO2 and HCO3- to determine whether the disturbance is respiratory or metabolic, and whether compensation is present.