Degradation of the Endothelial Glycocalyx Contributes to Metabolic Acidosis in Children Following Cardiopulmonary Bypass Surgery

Objectives Cardiopulmonary bypass surgery is complicated by metabolic acidosis, microvascular dysfunction, and capillary leak. The glycocalyx-a layer of proteins and sugars lining the vascular endothelium-is degraded during cardiopulmonary bypass. We aimed to describe the kinetics of glycocalyx degradation during and following cardiopulmonary bypass. We hypothesized that cleavage of negatively charged fragments of the glycocalyx would directly induce metabolic acidosis through changes in the strong ion gap (defined using Stewart's physicochemical approach to acid-base chemistry). We also investigated whether glycocalyx degradation was associated with failure of endothelial function and cardiovascular dysfunction. Design Single-center prospective cohort study. Setting Twenty-two bed surgical/medical PICU. Patients Twenty-seven term infants and children requiring cardiopulmonary bypass surgery for the correction/palliation of congenital heart disease. Interventions None. Measurements and main results We recruited 27 patients, 5 days to 57 months old. We prospectively sampled plasma prior to, during, and following cardiopulmonary bypass at predefined time points. We measured plasma concentrations of interleukin-6 (inflammatory marker), heparan sulfate (negatively charged glycocalyx glycosaminoglycan), and syndecan-1 (neutrally charged glycocalyx protein). We defined the following outcome measures: metabolic acidosis (strong ion gap), renal dysfunction (fold change in creatinine), capillary leak (fluid bolus volume), cardiovascular dysfunction (Vasoactive Inotropic Score), and length of ventilation. In linear regression models, maximum measured heparan sulfate concentration (negatively charged) was associated with metabolic acidosis (p = 0.016), renal dysfunction (p = 0.009), and length of ventilation (p = 0.047). In contrast, maximum measured syndecan-1 concentration (neutrally charged) was not associated with these clinical endpoints (p > 0.30 for all). Conclusions Our data show that metabolic acidosis (increased strong ion gap) is associated with plasma concentration of heparan sulfate, a negatively charged glycosaminoglycan cleaved from the endothelial glycocalyx during cardiopulmonary bypass. In addition, cleavage of heparan sulfate was associated with renal dysfunction, capillary leak, and global markers of cardiovascular dysfunction. These data highlight the importance of designing translational therapies to protect the glycocalyx in cardiopulmonary bypass.