OBJECTIVE To compare "central venous pressure" in pediatric patients in a clinical setting as measured from catheters in the infrahepatic inferior vena cava and the right atrium. METHODS Prospective, unblinded study. METHODS Cardiothoracic intensive care unit of a tertiary care university hospital. METHODS Thirty-three pediatric cardiac surgical patients, 2 days to 92 months of age (mean 24 +/- 4 months). METHODS All patients had intraoperative placement of an 8-cm, double-lumen, femoral venous catheter and a transthoracic right atrial catheter. Patients were studied for 0 to 2 days after surgery. RESULTS Measurements were obtained during mechanical and spontaneous ventilation. Although not statistically identical, measurements of "central" venous pressure in the inferior vena cava and right atrium correlated well (r2 = .87 for mechanical ventilation; r2 = .83 for spontaneous ventilation). Of 31 data pairs in mechanically ventilated patients, the absolute difference in pressures was as large as 3 mm Hg in three patients and <3 mm Hg in all the rest. In 15 spontaneously breathing patients, there were only three data measurements where the difference in pressure was 2 mm Hg and none of the differences was greater. In spontaneously breathing patients, the phasic changes due to respiratory variations in venous pressure were in phase in both the intrathoracic and intra-abdominal catheter positions. CONCLUSIONS We conclude that while "central" venous pressures measured in the inferior vena cava and in the right atrium are not statistically identical, any differences are well within clinically important limits. Placement of central venous pressure catheters in the inferior vena cava by the femoral venous approach is a reliable alternative to cannulating the superior vena cava in pediatric patients without clinically important intra-abdominal pathology and with anatomic continuity of the inferior vena cava with the right atrium. Relatively short femoral vein catheters allow adequate measurement of central venous pressure without concern for exact catheter tip position and without the risk of right atrial perforation, intracardiac arrhythmias, and inadvertent puncture of carotid and intrathoracic structures. Unlike previously reported results in neonates, we found that the phasic changes of venous pressure with the respiratory cycle were similar in both intrathoracic and intra-abdominal recordings, making this an inappropriate clinical indicator of venous catheter tip position.