Blood gases are helpful in determining the adequacy of respiratory function of the baby (oxygenation and ventilation) as well as the baby acid/base balance. Blood gases can be performed from arterial (either a stab or via an arterial line), venous (through an intravenous cannula) or capillary (heel prick) specimens. Repeated arterial stabs are strongly discouraged, as they are painful and do not represent oxygenation as well as pulse oximetry. Arterial stabs may be taken from the radial artery (provided there is also a palpable ulnar pulse) or from the brachial artery, although this is in close proximity to the median nerve. All three specimens will give a good assessment of acid/base status and pCO2, whereas arterial specimens are required to assess pO2. It is always important to note the  (percentage inspired oxygen) when interpreting blood gases. Each unit should have their own reference ranges

source=Newborn Emergency Transport Service, Victoria.