Inferior Vena Cava Oxygen Saturation during the First Three Postnatal Days in Preterm Newborns with and without Patent Ductus Arteriosus

In neonatal medicine, it is important to assess tissue oxygenation due to hypoxia, as hyperoxia can have adverse effects. Usually, measurements of arterial oxygen tension (PaO2) and arterial oxygen saturation (SaO2) are used for clinical decisions regarding oxygen therapy in neonates. However, this approach cannot explain the complete physiological economy of oxygen (1–3). Some recommend measuring venous oxygen to evaluate tissue perfusion and response to therapy (1, 3–8). Umbilical venous catheters are widely used in neonatal intensive care units for medication, fluid and nutrition administration. Mixed venous oxygenation can be measured by inserting an umbilical venous catheter into the inferior vena cava (IVC) (3). The advantages of measuring IVC oxygenation are not affected by atrial right-left shunting (3, 4). Monitoring of mixed venous oxygen saturation (Svo2) shows the residual oxygen after tissue oxygen extraction and also represents the combined sufficiency of arterial oxygen content, cardiac output and tissue oxygen consumption (2, 9, 10). Right atrial SvO2 was used for monitoring, in contrast to using SaO2 alone in an animal model (7). True mixed venous blood is derived from a pool of blood entering the pulmonary artery via the great veins in the chest. It contains blood that has passed through all systemic capillary beds capable of extracting oxygen, and is thoroughly mixed in the right ventricle (11). However, catheterization of the pulmonary artery or right atrium is hazardous for neonates and is not routinely applied (3, 12). Umbilical venous catheters are frequently used in neonatal intensive care units due to their lower complication rates. Umbilical venous catheterization is not affected by intracardiac shunting that leads to mixing of systemic and pulmonary venous blood (3, 4, 13). The measurement of venous oxygen saturation has been used in several studies of sepsis and septic shock, and during the perioperative period of major surgery because it shows major derangements in oxygen balance (13–16). Umbilical venous oxygen saturation pointed a great similarity to arterial oxygen saturation in some premature infants in our clinical practice that it was hypothesized as a sign of severe ductal shunt predicting patent ductus arteriosus (PDA). In this study, on the basis of this clinical observation, the course of IVC oxygen saturation was measured in preterm infants as an indicator of mixed venous oxygenation in the first three days of life; and differences between infants with and without PDA were investigated.