Functional Evaluation of Microcirculation in Response to Fluid Resuscitation in Hypovolemic Adult Post-cardiac Surgical Patients

Objectives: Microcirculation is bound to be altered during cardiac surgery due to multiple factors, mainly the intense systemic inflammatory response syndrome which peaks in the first 24-h postoperatively. Decreased microvascular flow associated with increased postoperative morbidity has been reported. The literature suggests a potential independence of macrocirculation and microcirculation during fluid loading. The present study was conducted to assess thenar muscle tissue oxygen saturation (StO2) changes during vascular occlusion test (VOT) in response to hypovolemia and to assess the dynamic responses of the StO2 variables post-volume expansion (VE). Material and Methods: Thirty-five adult post-cardiac surgical patients, with stroke volume (SV) variation >12% were included in the study. Fifty-two fluid challenges were studied. Functional evaluation of microcirculation using VOT and near infrared spectroscopy (NIRS) variables along with monitoring of macrocirculatory indices was performed before and after VE. Statistical analysis was done using Student t-test. Results: Post-VE, 34 were responders with increase in SV ≥15% and 18 were non-responders (SV P = 0.0293 vs. P = 0.1480). However, macrocirculatory indices including cardiac output, SV, and delivery of oxygen showed significant improvement in both responders and non-responders. Conclusion: Preload dependence is associated with significant change in the StO2 recovery slope measured at the thenar eminence in volume responders. Functional evaluation of microcirculation using VOT and StO2 can be a useful complimentary tool along with the macrocirculatory indices for optimal fluid rescuscitaion in adult post-cardiac surgical patients.