Continuous Central Venous Oxygen Saturation Monitoring under Varying Physiological Conditions in an Animal Model

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We compared saturations from a paediatric central venous oximetry catheter with co-oximetry values with changes in drug infusions, intravascular blood volume and hypoxia in an animal model. Piglets (large white) were anaesthetised, intubated and mechanically ventilated. PediaSat oximetry catheters were placed in the superior vena cava via jugular vein cut-down and in the inferior vena cava percutaneously via the femoral vein. A carotid arterial catheter was placed via cut-down for blood sampling and pressure monitoring. Anaesthesia was maintained with continuous thiopentone and supplemental morphine. Haemodynamics (heart rate, mean arterial blood, central venous pressure), fibreoptic ScvO2 (ScvO2-inferior) from inferior vena cava, fibreoptic ScvO2 (ScvO2-superior) from superior vena cava and blood gas oximetry (ScvO2-co-ox) were measured simultaneously at predetermined intervals during increasing adrenaline and sodium nitroprusside infusions and during increasing hypoxia and hypovolaemia. There was good agreement of both superior vena cava and inferior vena cava ScvO2 catheters with co-oximetry during adrenaline and sodium nitroprusside infusions. During the hypoxia study there was good agreement between the co-oximeter to ScvO2-superior catheter but poor agreement with to the inferior vena cava catheter samples. In the hypovolaemic phase of the experiment there was good agreement between the measured co-oximetry value and ScvO2-superior catheter until the mean blood pressure reached 43 mmHg. The oximetry catheter is capable of identifying changes in ScvO2 under physiological conditions usually encountered in clinical medicine but was less accurate at the extremes of physiology and when placed in the inferior vena cava catheter especially during hypovolaemia and hypoxia.