Technique:
(1) A warming device is applied to the skin:
(1a) a warm, moist towel (can encase the covered foot in a plastic bag to avoid soaking the bed)
(1b) a "heel warmer" commercial device
(1c) a heating lamp should NOT be used
(1d) a skin irritating ointment or lotion should NOT be used
(2) The maximum temperature should not exceed 42°C. A higher temperature can cause a burn. The temperature of any makeshift skin warmer should be tested before being applied to the infant's skin.
(3) After several minutes the skin should be erythematous, reflecting the increased blood flow.
Problems that can a failure to achieve arterial-like results:
(1) The presence of a right-to-left cardiac shunt can reduce the PaO2 and increase PaCO2 in arterial blood. An infant with a patent ductus arteriosus or foramen ovale can develop a transient shunt if crying.
(2) poor blood flow through the skin (shock, etc)
(3) edematous skin
(4) hemolysis of the blood sample
Accuracy of blood gas results according to Banister:
(1) The pH of arterialized capillary blood is similar to that of arterial blood.
(2) The base deficit of arterialized capillary blood is similar to arterial blood unless the foot is edematous.
(3) The PaCO2 of arterialized capillary is similar to that of arterial blood up to 85 mm Hg. The PaCO2 of arterialized capillary blood above 85 mm Hg could be significantly higher than that of the arterial blood.
(3) The PaO2 of arterialized capillary often underestimates (is lower than) that seen in the arterial blood by 2 to 10 mm Hg (lower in 10 of 12 samples).
