Precautions in Blood Collection

Blood Collection for Blood Gasses Determination

• When collecting venous blood, the patient must not pump their fist, and the tourniquet is only removed after collection.
• If the tourniquet is removed before collection is finished, CO2 increases, HCO3- and pH decrease due to accumulation of metabolic products.
• The patient must be fully relaxed, avoiding stress or anxiety, which can cause hyperventilation and alter blood gas results.
• Avoid using vaccutainer tubes, as oxygen in the tube can alter the results.
• Blood samples should be kept at a temperature between 37°C and 40°C to avoid alterations in pH, pCO2, and pO2.
• Corrected ABG values must be reported to the doctor, taking into account the patient's temperature.

Precautions in Blood Collection

• Use a gas-tight, Li-heparin powder-coated, glass syringe as the reference collection device.
• When using plastic syringes, coat them with silicon from the inside to prevent gas leakage.
• Never expose the sample to air, as it can result in increased pO2, decreased CO2, and increased pH.
• Keep the collected sample buried in normal crushed ice to maintain parameters for up to 2 hours.
• If no ice is available, analyze the sample within 10 minutes to avoid alterations in pH, pO2, and lactic acid.

Blood Gasses Determination

• For infants, use arterialized blood, which is obtained by warming the limb and dilating the capillaries.
• Hemoglobin oxygen saturation (SO2) is the O2 content divided by O2 capacity and is determined by pulse oximetry.
• Decreased pO2 indicates a reduced ability of O2 to diffuse from alveolar to blood, which can be due to hypoventilation or increased venoarterial shunt.
• Low Hb can be due to low red blood cells or abnormal Hb.

Hemoglobin-Oxygen Dissociation

• Hemoglobin-oxygen dissociation is determined by the affinity of hemoglobin, Po2, and oxygen dissociation curve.
• Oxygen dissociation curve shows the relationship between Po2 and SO2.

Additional Precautions

• Gasses can easily escape or diffuse into the blood sample, so ideal samples are arterial whole blood collected in Li-heparin.
• Powder (Li-heparin) is preferred to avoid dilution, evaporation, or spillage problems.
• Arterial blood is more uniform in composition, well oxygenated, and has a more stable pH.
• If lung or respiratory problems are to be assessed, only use arterial blood.
• The radial artery is preferred for collecting arterial blood due to less complication risks and easy accessibility.