The need for repeated samplings of arterial blood for blood gas analysis in the infant and small child with severe respiratory or circulatory disease leads to technical problems because of the small size of the patient's arteries. On the other hand, blood gas values obtained from arterialized capillary blood correlate poorly with true arterial samples in infants with cardiopulmonary disease.1 Several techniques are available for arterial sampling, including methods of multiple brachial or radial artery sampling.2,3 Umbilical artery catheterization may be used in the first few days of life.4 In older infants, an arterial cutdown may be necessary for placement of an indwelling catheter, while in patients over 15 kg (33 lb) in weight, percutaneous arterial cannulae can usually be placed. It has been established that venous cannulae in situ longer than 48 hours have a far greater incidence of bacterial growth when cultured at time of