Variations of Cutaneous Capnometry and Perfusion Index During a Heating Challenge is Early Impaired in Septic Shock and Related to Prognostic in Non-Septic Shock

In shock, the increase in cutaneous-to-arterial carbon dioxide partial pressure (Pc-aCO2) and the decrease in the perfusion index (PI) are related to macrovascular or microvascular alterations. We hypothesized that inducing cutaneous vasodilation and local perfusion with heat could provide a noninvasive tool to monitor microvascular reactivity.This study aimed to develop a noninvasive approach, the heating challenge (HC), to monitor the microvascular reactivity of patients with shock and to evaluate the potential relationship with outcome.After ethics committee agreement was obtained, 59 shock patients, including 37 septic shock, 22 non-septic shock (14 cardiogenic and eight hemorrhagic), 10 intensive care unit (ICU)-controls and 12 healthy volunteers, were included in this study. The HC consisted of heating the ear lobe PcCO2 sensor from 37° to 45° over 5 min and recording PcCO2 and PI variations (ΔPcCO2 and PImax/min). HC was performed on admission and during the first 48 h of hospitalization.Pc-aCO2 was significantly higher in shock patients than ICU-controls at baseline (P < 0.05). HC led to a decrease in PcCO2 and an increase in PI in the healthy volunteers (ΔPcCO2 = -9.0 ± 4.6% and PImax/min = 5.5 ± 1.9). On admission, non-septic shock patients (cardiogenic and hemorrhagic shocks) had an HC response profile identical to that of healthy volunteers and ICU-controls. In contrast, septic shock patients had a lower ΔPcCO 2 and PImax/min compared to healthy volunteers and all other groups (P < 0.05). After the first day, the combination of a Pc-aCO2 >17 mm Hg with a positive ΔPcCO2 could predict mortality with a specificity of 82% and a sensitivity of 93%.HC appears to be a dynamic test to classify vascular reactivity alterations in shock. At baseline, HC results were impaired in septic patients and conserved in non-septic patients. After the first day, the association between Pc-aCO2 and ΔPcCO2 was strongly related to prognosis in shock patients.