Introduction: The present study was designed to compare cerebral hemodynamics assessed using the blood flow index (BFI) derived from the kinetics of the tracer dye indocyanine green (ICG) with transcranial Doppler ultrasound (TCD) in an established model of hemorrhagic shock.
Methods: After approval from the Animal Investigational Committee, 20 healthy pigs underwent a simulated penetrating liver trauma. Following hemodynamic decompensation, all animals received a hypertonic-isooncotic hydroxyethyl starch solution and either arginine vasopressin or norepinephrine, and bleeding was subsequently controlled. ICG passage through the brain was monitored by near infrared spectroscopy. BFI was calculated by dividing maximal ICG absorption change by rise time. Mean blood flow velocity (FVmean) of the right middle cerebral artery was recorded by TCD. FVmean and BFI were assessed at baseline (BL), at hemodynamic decompensation, and repeatedly after control of bleeding.
Results: At hemodynamic decompensation, cerebral perfusion pressure (CPP), FVmean and BFI dropped compared to BL (mean +/- standard deviation; CPP 16 +/- 5 mmHg versus 70 +/- 16 mmHg; FVmean 4 +/- 5 cm x s(-1) versus 28 +/- 9 cm x s(-1); BFI 0.008 +/- 0.004 versus 0.02 +/- 0.006; p < 0.001). After pharmacological intervention and control of bleeding, FVmean and BFI increased close to baseline values (FVmean 23 +/- 9 cm x s(-1); BFI 0.02 +/- 0.01), respectively. FVmean and BFI were significantly correlated (r = 0.62, p < 0.0001).
Conclusion: FVmean and BFI both reflected the large variations in cerebral perfusion during hemorrhage and after resuscitation and were significantly correlated. BFI is a promising tool to monitor cerebral hemodynamics at the bedside.