Non-invasive assessment of the microcirculation in ICU patients

Introduction

Microcirculation is severely affected in sepsis. The non-invasive evaluation of microcirculation and its association with the severity of sepsis has not been sufficiently studied.

Objective

To compare microcirculation parameters with sepsis severity.

Methods

We studied 23 patients of a general ICU (age 56 ± 21 years) and 11 healthy volunteers (age 28 ± 4 years). Severity of sepsis was assessed with the SOFA score (5 ± 2), APACHE II score (13 ± 5) and sepsis severity category (SIRS n = 15, severe sepsis n = 4 and septic shock n = 4). An InSpectra^® near-infrared spectrometer was used to measure the thenar muscle tissue oxygen saturation (StO₂) before, during and after a 3-min occlusion of the brachial artery. For the occlusion we used a brachial cuff and raised the pressure 50 mmHg above the measured systolic blood pressure. For the StO₂ curve analysis we used the InSpectra^® Software Analysis program. For the statistical analysis we used SPSS 11.5 for Windows^® and applied one-way ANOVA.

Results

The StO₂ baseline value was significantly lower in patients with severe sepsis when compared with healthy controls (65 ± 15 [49, 85] vs 83 ± 6 [72, 93], P = 0.009). During the 3-min occlusion of the brachial artery the StO₂ decrease rate was significantly lower in the septic shock group compared with healthy controls (15.5 ± 6.3 [6.5–21.4] vs 38.7 ± 10.3 [22.1–52.9], P < 0.001) as well as compared with the SIRS group (15.5 ± 6.3 [6.5–21.4] vs 25.4 ± 7.2 [17.8–43.4], P = 0.036). The StO₂ decrease rate was also significantly lower in the severe sepsis group when compared with healthy controls (15.0 ± 0.6 [14.4–16.0] vs 38.7 ± 10.3 [22.1–52.9], P < 0.001) as well as compared with the SIRS group (15.0 ± 0.6 [14.4–16.0] vs 25.4 ± 7.2 [17.8–43.4], P = 0.028). After the release of the occlusion, the StO₂ increase rate was significantly lower in the SIRS, severe sepsis and septic shock groups when compared with healthy controls (402.1 ± 140.1 [206.2–653.5] vs 643.8 ± 241.4 [389.0–1275.0], P = 0.002; 322.4 ± 162.6 [185.5–520.5] vs 643.8 ± 241.4 [389.0–1275.0], P = 0.005; and 219.3 ± 136.3 [82.4–404.5] vs 643.8 ± 241.4 [389.0–1275.0], P < 0.001, respectively).

Conclusion

Tissue oxygen saturation is related to the severity of sepsis. Additionally, tissue oxygen consumption is significantly lower in patients with septic shock or severe sepsis compared with healthy subjects or patients with SIRS. The lower StO₂ increase rate in ICU patients may indicate affected endothelium reactivity.