Optical biomarkers for sepsis-related microcirculatory impairment

Sepsis is a dysregulated host reaction to infection leading to life-threatening organ failure. Microcirculatory impairment manifesting as exaggerated vasomotion (i.e., low-frequency oscillations in arteriolar tone, independent of heartbeat and respiration) is an early indicator of sepsis, which precedes organ injury and septic shock. The objective of this study was to assess the sensitivity of various non-invasive optical biomarkers quantifiable with near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) to the onset of sepsis-related microcirculatory impairment. 14 Sprague-Dawley rats (4 control), equally divided into male and female, were used for this study. NIRS and DCS probes were secured to the hind limb and head of each animal to simultaneously monitor the peripheral and cerebral microcirculation. Control animals received an intraperitoneal injection of saline while experimental animals received fecal slurry to induce sepsis. To quantify vasomotion power, continuous wavelet transform was applied to the NIRS measures of oxyhemoglobin (𝐻𝑏𝑂), deoxyhemoglobin (𝐻𝑏), total hemoglobin (𝐻𝑏𝑇), and oxygen saturation (𝑆𝑡𝑂₂), as well as relative blood flow (𝑟𝐵𝐹) from DCS. Effect size (Cohen’s d) between control and septic animals for vasomotion power in each parameter at the onset of microcirculatory impairment (i.e., 2.5 to 4 hours post injection) was computed. The results reveal that while the brain is still partly protected, the peripheral microcirculation is the most sensitive target for detecting this sepsis-related phenotype, with peripheral 𝐻𝑏 oscillations exhibiting the greatest effect size (Cohen’s d = 3.30). Immediate future work will include applying these techniques to monitor microcirculatory regulation in diverse ICU patients.