Early detection of microcirculatory changes using simultaneous heated and unheated transcutaneous blood gas monitoring: a proof-of-concept study in a porcine lipopolysaccharide model of systemic inflammation.

INTRODUCTION: Early detection of microcirculatory failure in septic patients has the potential to improve clinical outcomes. The microcirculation regulates the oxygen (O2) supply and carbon dioxide (CO2) washout in tissues and changes early during severe inflammation and sepsis. Transcutaneous blood gas sensors measure tissue O2 and CO2 levels at the skin surface, or when warmed use the vasodilatory response to approximate arterial levels. In addition to differences in measured O2 and CO2 values, systemic inflammation is likely to affect this vasodilatory effect of skin warming. This study investigated whether continuous comparison of heated and unheated transcutaneous blood gas monitoring could early detect microcirculatory changes using a porcine lipopolysaccharide (LPS) model of systemic inflammation. METHODS: Thirty female Yorkshire x Norwegian Landrace pigs were subdivided into three study groups (control, LPS, and LPS with fluid resuscitation) and received LPS or saline control. Transcutaneous CO2 (tcPCO2) and O2 (tcPO2) were continuously and simultaneously measured using a heated (43 °C) and unheated (37 °C) transcutaneous sensor (Sentec OxiVenT™) at the porcine ear. Arterial blood gas measurements (PaCO2 and PaO2) were performed at baseline and 1, 2, and 3 h after LPS administration. At each time point, tcPCO2, tcPO2, and differences between transcutaneous and arterial blood gas measurements were determined. In addition, the unheated-heated tcPCO2 difference and the ratio between heated tcPCO2 and tcPO2 (tcPCO2/tcPO2) were calculated. RESULTS: After LPS administration, a significant increase in heated tcPCO2 and a significant decrease in tcPO2 and tcPO2/tcPCO2 were observed. This resulted in a significant decrease in the unheated-heated tcPCO2 difference from 22.1 [18.8-33.2] to 0.7 [-8.3-8.8] mmHg in the LPS group, and from 23.0 [16.9-23.9] to -1.2 [-6.6-2.0] mmHg in the resuscitation group, while it remained 6.5 [3.1-9.8] mmHg in the control group. PaCO2 and PaO2 did not show large changes. CONCLUSION: Heated tcPCO2, tcPO2, unheated-heated tcPCO2, and tcPO2/tcPCO2 as observed using transcutaneous blood gas monitoring are promising parameters for early detection of microcirculatory changes during severe infections. In future studies, simultaneous heated and unheated transcutaneous measurements should be further explored in both healthy and septic patients.