Contribution of the coronary sinus blood to the pulmonary artery oxygen saturation gradient in cardiac surgery patients.

BACKGROUND

The coronary sinus oxygen saturation (SO2) can affect the oxygen saturation of the superior vena cava (superior cava SO2) and the pulmonary artery (pulmonary artery SO2), causing a gradient between the latter two (ΔSO2), as has been observed in different physiological and pathological conditions. The objective of the study was to evaluate the different determinants of ΔSO2 in cardiac surgery patients.

METHODS

An observational, prospective study was carried out on 18 patients undergoing elective cardiac surgery. Blood samples were obtained from the superior vena cava, the pulmonary artery, the inferior vena cava, and the coronary sinus before extracorporeal circulation.

RESULTS

The following measurements were made: superior cava SO2, pulmonary artery SO2, coronary sinus SO2, and inferior cava SO2. The mean values (± SD) were as follows: superior cava SO2=76.4±12.6%; inferior cava SO2=72.7±15.8%; coronary sinus SO2=46.6±17.0%; and pulmonary artery SO2=71.9±12.9%. The ΔSO2 was 4.5±5.5%. The average oxygen saturation (SO2avg=[Superior cava SO2 + inferior cava SO2]/2) was 74.6±13.7%. The superior cava SO2 was significantly higher than the pulmonary artery SO2, and the ΔSO2 was significantly different from zero (P≤0.05). No significant differences were found between the superior cava SO2 and the inferior cava SO2, and both were significantly different from the coronary sinus SO2. The difference between SO2avg and the pulmonary artery SO2 was 2.74±4.4%.

CONCLUSION

The observed ΔSO2 could only be explained by dilution of the superior cava SO2 with blood with a lower SO2. The coronary sinus blood contributed to generate this gradient.