Dynamic near-infrared spectroscopy measurements in patients with severe sepsis correlate with invasive hemodynamic measurements

Introduction

Near-infrared spectroscopy (NIRS) has recently been utilized to monitor tissue perfusion in hemorrhagic shock. NIRS has also demonstrated changes in tissue perfusion in severe sepsis. NIRS combined with arterial and venous occlusion cuffing can be used to noninvasively measure thenar and systemic oxygen delivery (DO₂I), and oxygen consumption (VO₂I). We hypothesized that DO₂I and VO₂I measured by NIRS in patients with severe sepsis will be associated with severity of illness and will correlate with DO₂I and VO₂I measured invasively and by metabolic cart.

Methods

Septic patients (n = 10) were selected for the study who met criteria for severe sepsis, had a pulmonary artery catheter, and had family able to give written consent. Normal age-matched control patients (n = 9) were enrolled for comparison. We measured the mean arterial pressure (MAP), serum lactate, plasma hemoglobin, mixed venous oxygen saturation (SVO₂), and systemic oxygen consumption via metabolic cart (metVO₂I), and calculated systemic oxygen consumption and delivery via pulmonary artery catheter (paVO₂I, paDO₂I), thenar oxygen delivery (nir.thenarDO₂I), thenar oxygen consumption (nir.thenarVO₂I), systemic oxygen delivery (nir.sysDO₂I), systemic oxygen consumption (nir.sysVO₂I), and mixed venous oxygen saturation (nirSVO₂) in patients with severe sepsis in a surgical ICU. The same data, without invasive hemodynamic measurements, were measured once in volunteers. NIRS data were collected from the thenar eminence using the Inspectra system (Hutchinson Technology, Hutchinson, MN, USA). A poor outcome was defined by multiorgan dysfunction 7 days after the development of severe sepsis, death within 28 days of severe sepsis, or both.

Results

Healthy volunteers and septic patients were similar with respect to age and sex. MAP and hemoglobin were decreased and serum lactate increased in septic patients compared with healthy volunteers. In septic patients, nirSVO₂correlated with SVO₂ (P < 0.001), nir.sysVO₂I correlated with metVO₂I (P = 0.017), and nir.sysDO₂I correlated with paDO₂I (P < 0.001). Interestingly, paVO₂I did not correlate well with metVO₂I (P = 0.435). Of these patients, 4/10 developed poor outcome. Patients with poor outcomes had significant elevations of paDO₂I (P < 0.001), nir.thenarDO₂I (P = 0.005), nir.sysDO₂I (P < 0.001), and SVO₂(P < 0.001) compared with patients who did not develop poor outcomes.

Conclusions

NIRS measurements of SVO₂ and DO₂I correlated with invasively measured values in patients with severe sepsis. Interestingly, nir.sysVO₂I correlated more closely to metVO₂I than did paVO₂I. Dynamic NIRS values were predictive of outcomes. This suggests a role for NIRS measurements of SVO₂, DO₂I, and VO₂I in patients in severe sepsis.