Sampling Techniques for Arterial Blood Gas Samples
Edward F. Bell, MD
Peer Review Status: Internally Peer Reviewed
0.2 ml of blood is required for arterial blood gas sampling. If the syringe is heparinized, the heparin should be removed as completely as possible before drawing blood into the syringe; excess heparin left in the syringe decreases the pH value, dilutes the sample, and lowers the PaCO2. Before drawing a sample from an indwelling arterial line, the line should be cleared by withdrawing 1 to 2 ml of blood which is returned immediately thereafter.
An infant without an arterial line who is not severely ill can have his oxygenation status monitored by continuous pulse oximetry or by transcutaneous PO2 monitoring. Any infant being monitored by capillary blood gas samples should have arterial sticks done periodically to validate the capillary sample results or should have continuous pulse oximetry or transcutaneous PO2 monitoring.
Arterial sticks are sometimes performed in severely ill neonates who do not have an indwelling arterial line. A percutaneous arterial stick can be performed using the temporal or radial artery. The brachial artery may be use in emergency situations. A femoral arterial stick should be avoided if at all possible, as there is an increased incidence of aseptic necrosis of the femoral head when this site is used for sampling. Since many infants shunt through the ductus arteriosus, the arterial site from which the sample is obtained should be noted on the blood gas sample requisition.
The frequency of sampling is dependent upon the patient's clinical condition. Any changes in ventilator or CPAP setting must be monitored by a blood gas sample within 15-30 minutes. Any acutely ill child in the NICU in an increased ambient oxygen concentration must have at least daily arterial or fingerstick blood gas sampling
Indwelling catheters should not be placed into the temporal or brachial artery.