gasometria

Gasometria, or arterial blood gas analysis, is a laboratory test used to assess the balance between acidity and base in the blood as well as the efficiency of gas exchange. It measures pH, partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2), bicarbonate concentration (HCO3-), base excess, and oxygen saturation. Some laboratories also report lactate and electrolytes as part of the assessment.

Indications for gasometria include evaluation of respiratory function and acid–base status in acutely ill patients, monitoring of patients in intensive care or under mechanical ventilation, assessment before anesthesia, and investigation of suspected metabolic or respiratory disorders such as sepsis, shock, COPD, or asthma exacerbations.

Sampling and types of specimens: arterial blood gas (ABG) is the preferred test for assessing oxygenation and ventilation; venous blood gas (VBG) can provide information on acid–base status but is less reliable for oxygenation. Capillary samples may be used in newborns or difficult access situations. Proper preanalytic handling is essential: sample collection with heparinized syringes, avoiding air bubbles, gentle mixing, and timely analysis. ABG samples are usually kept on ice if delayed, and analyzed promptly to ensure accuracy.

Interpretation: begin with the pH to determine acidosis or alkalosis, then examine PaCO2 for respiratory components and HCO3- for metabolic components. Determine primary disorder and assess compensatory response. The base excess and lactate can support the assessment and help gauge tissue perfusion. Clinical context is essential, as many patients have mixed or evolving disturbances.

Limitations: results depend on proper technique and timely analysis; peripheral or equipment issues can affect accuracy. ABG values may not reflect whole-body oxygenation in certain conditions, and venous samples should not be used to infer arterial oxygenation.