Renovascular reactivity measured by near-infrared spectroscopy

Abstract

Hypotension and shock are risk factors for death, renal insufficiency, and stroke in preterm neonates. Goal-directed neonatal hemodynamic management lacks end-organ monitoring strategies to assess the adequacy of perfusion. Our aim is to develop a clinically viable, continuous metric of renovascular reactivity to gauge renal perfusion during shock. We present the renovascular reactivity index (RVx), which quantifies passivity of renal blood volume to spontaneous changes in arterial blood pressure. We tested the ability of the RVx to detect reductions in renal blood flow. Hemorrhagic shock was induced in 10 piglets. The RVx was monitored as a correlation between slow waves of arterial blood pressure and relative total hemoglobin (rTHb) obtained with reflectance near-infrared spectroscopy (NIRS) over the kidney. The RVx was compared with laser-Doppler measurements of red blood cell flux, and renal laser-Doppler measurements were compared with cerebral laser-Doppler measurements. Renal blood flow decreased to 75%, 50%, and 25% of baseline at perfusion pressures of 60, 45, and 40 mmHg, respectively, whereas in the brain these decrements occurred at pressures of 30, 25, and 15 mmHg, respectively. The RVx compared favorably to the renal laser-Doppler data. Areas under the receiver operator characteristic curves using renal blood flow thresholds of 50% and 25% of baseline were 0.85 (95% CI, 0.83-0.87) and 0.90 (95% CI, 0.88-0.92). Renovascular autoregulation can be monitored and is impaired in advance of cerebrovascular autoregulation during hemorrhagic shock.

Relationship Between the Ambulatory Arterial Stiffness Index and the Lower Limit of Cerebral Autoregulation During Cardiac Surgery

“…Cerebral arterioles match CBF and cerebral metabolic requirements by vasodilation and constriction despite changes in cerebral perfusion pressure 24, 25. This action is referred to as cerebral pressure autoregulation.…”

Renal Failure and Heart Surgery

“…During hypoperfusion, renovascular autoregulation is compromised earlier and more severely than cerebrovascular autoregulation [27]. Innovative technology to determine the lower limit of the cerebral autoregulation threshold has been developed and validated at Hopkins.…”

Defining oliguria during cardiopulmonary bypass and its relationship with cardiac surgery–associated acute kidney injury

“…17 Although activation of these systems ensures CBF as long as BP is within the autoregulation range, the resulting compensatory vasoconstriction can severely compromise renal blood flow. 7 In porcine experiments, MAPs at the limits of renal autoregulation were higher than MAPs at the limits of CBF autoregulation. 7 In those studies, renal blood flow was only 25% of baseline before CBF became pressure passive.…”

“…7 In porcine experiments, MAPs at the limits of renal autoregulation were higher than MAPs at the limits of CBF autoregulation. 7 In those studies, renal blood flow was only 25% of baseline before CBF became pressure passive. Unfortunately, there are presently no clinical monitors of renal blood flow for adults undergoing CPB.…”

“…6 Similar to the brain, blood flow to the kidney is autoregulated to ensure perfusion over a range of blood pressures (BPs). 7 Our group has evaluated whether monitoring of cerebral blood flow (CBF) autoregulation provides a more precise approach for determining mean arterial pressure (MAP) targets during CPB than empirical targets. [8][9][10][11] We have found that the lower limits of CBF autoregulation vary widely between individuals and that the magnitude that MAP is below the lower limits of autoregulation influences the risk for AKI.…”