The changes in the oxygen saturations in the superior vena cava and the pulmonary artery are not the same during cardiac surgery

Abstract

Objective

To evaluate the changes over time (trend) in sign and magnitude for S_SVO₂ and S_VO₂ during and after cardiac surgery.

Patients and methods

A prospective and observational study was conducted on 34 cardiac surgery patients. Venous blood samples were taken simultaneously from the introductory (S_VCO₂) and distal (S_VO₂) port of the pulmonary artery catheter at predefined intervals. Systemic and pulmonary hemodynamic variables were measured at the same time. The trend was calculated as the difference between 2 consecutive measurements (tSO₂). Data were processed with ANOVA for multiple comparisons, Pearson correlation coefficient and Bland–Altman analysis.

Results

There was a significant correlation between S_VCO₂ and tS_VO₂ (R² = 0.55), the mean of the differences was 0.36 ± 7.75%, and the limits of agreement ranged from −15.1 to 15.9%. The sign of the trend was similar in 85.1% of the paired data. However, the magnitude of the changes in tS_VCO₂ and tS_VO₂ were not always equivalent. Between 0 and 5% of the change in the tS_VCO₂ was coincident with only 44.7% of the tS_VO₂. A wide variation was found between both trends when the signs and magnitudes of the changes were taken into account.

Conclusions

When considering the sign and magnitude, the change over time of central venous O₂ saturations were not interchangeable in cardiac surgery patients. Clinical decisions based exclusively on tS_VCO₂ monitoring should be taken with caution.

Resumen

Objetivo

Comparar los cambios de signo y magnitud de las tendencias (tSO₂) de las saturaciones venosas de arteria pulmonar (tS_VO₂) y de vena cava superior (tS_VCO₂) en pacientes sometidos a cirugía cardíaca.

Pacientes y métodos

Realizamos un estudio prospectivo y observacional en 34 pacientes sometidos a cirugía cardíaca. Las medidas hemodinámicas y las extracciones de sangre se realizaron a intervalos predefinidos. Se extrajeron muestras simultáneamente del puerto distal del catéter pulmonar (S_VO₂) y del introductor del mismo (S_VCO₂). Las tSO₂ se calcularon como la diferencia entre 2 medidas consecutivas. Los datos fueron procesados por test ANOVA, correlación de Pearson y análisis de Bland-Altman.

Resultados

Las tSO₂ de ambas variables mostraron una correlación positiva (R² = 0,55), siendo la diferencia de las medias de 0,36 ± 7,75% y los límites de discordancia desde −15,1 a 15,9%. La probabilidad de que un cambio direccional en tS_VCO₂ pueda ser seguido de un cambio similar en tS_VO₂, mostró que el signo de las mismas coincidió en el 85,1%. Sin embargo, la magnitud del cambio coincidió en un porcentaje menor, dependiendo del considerado. Entre 0 y 5% de cambio en la tS_VCO₂, se encontró coincidencia con la tS_VO₂ en el 44,7% de los casos.

Conclusiones

Considerando que el signo y magnitud de las tendencias de ambas SO₂ no son intercambiables, las decisiones terapéuticas basadas en la consideración de estos parámetros deben hacerse con precaución.