A comparison of transcranial Doppler with near infrared spectroscopy and indocyanine green during hemorrhagic shock: a prospective experimental study

Abstract

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.

Figure 1

Calculation of the blood flow index. Typical indocyanine green (ICG) measurement in a pig during stable hemodynamics (black line) and at hemodynamic decompensation (orange line).

Figure 2

Blood flow velocity by transcranial Doppler ultrasound and bood flow index (BFI) by near infrared spectroscopy at the different experimental stages (BL, baseline; BL Th, start therapy; Th + 10 min, after 10 minutes of therapy; Th + 40 min, after 40 minutes of therapy; Th + 90 min, after 90 minutes of therapy). Data are given as mean ± standard error of the mean; *p < 0.001 versus baseline; ^#p < 0.001 versus baseline therapy; ^‡p < 0.01 versus baseline therapy; ^†p < 0.05 versus therapy + 90 minutes. FVmean, mean blood flow velocity in the right middle cerebral artery.

Figure 3

Correlation between blood flow velocity by transcranial Doppler ultrasound and blood flow index (BFI) by near infrared spectroscopy. FVmean, mean blood flow velocity in the right middle cerebral artery; r = 0.62; p < 0.0001. n = 76 measurements in 20 animals.

Figure 4

Correlation between cardiac output (CO) and blood flow index (BFI) by near infrared spectroscopy. r = 0.71; p < 0.0001. n = 76 measurements in 20 animals.

Figure 5

Correlation between cerebral perfusion pressure (CPP) and blood flow index by near infrared spectroscopy. r = 0.66, p < 0.0001. n = 76 measurements in 20 animals.

Figure 6

Cerebral perfusion pressure (CPP) and near infrared spectroscopy derived interval time. n = 76 measurements in 20 animals.

Figure 7

Cerebral perfusion pressure (CPP) and near infrared spectroscopy derived rise time. n = 76 measurements in 20 animals.

Figure 8

Receiver-operator curve using near infrared spectroscopy derived interval time for a threshold of cerebral perfusion pressure <25 mmHg. Area = 0.95 (95% confidence interval 0.92 to 0.99), p < 0.0001.