Distribution of fluids between body compartments following fluid therapy in cardiac surgery

Intravenous fluids are commonly used to resuscitate cardiac surgery patients in the operating room and ICU, assuming they expand the intravascular compartment. However, the quantitative information for their distribution and shift between the tissue compartments is still lacking. This study aimed to assess how administered fluids distribute across compartments and their effects on micro- and macrocirculation during the long term of cardiac surgery.

Thirty-three consecutive patients undergoing major cardiac surgery were prospectively enrolled. Information regarding the body fluid distribution [total body water (TBW), extracellular water (ECW), intracellular water (ICW)], sublingual microcirculation total vessel density (TVD), per-fused vessel density (PVD), and proportion of perfused vessel (PPV)], and hemodynamics were collected before surgery (T0), on the day of discharge from the intensive care unit (T1), and on the third day at the ward (T3). Correlations of the changes in microcirculatory and macrocircula-tory parameters were determined by linear regression.

Twenty-four patients were included in the analysis with available data. Body weight significantly increased from 86.0 ± 13.6 kg to 91.6 ± 13.3 kg at T1 and decreased to 87.8 ± 12.9 kg at T3 (p< 0.001). While TBW and ECW varied in parallel with body weight, ICW showed a continuous decrease throughout the study process. TVD, PVD, and PPV significantly decreased at T1, then increased at T3, but all remained lower than baseline (p< 0.001 for TVD and PVD, p= 0.034 for PPV). A cut-off point of a 5% increase in body weight predicted a 10% decrease in TVD with a sensitivity of 0.833 and specificity of 0.666. Besides, a cut-off point of a 4% increase in body weight predicted a 10% decrease in PVD with a sensitivity of 0.94 and specificity of 0.75.

Administering fluid during operation and intensive care stay significantly reduces ICW and causes microcirculatory disturbances in cardiac surgery patients. Long-term microcirculation disturbances correlate with ECW and TBW in these patients.