Cutaneous ear lobe Pco₂ at 37°C to evaluate microperfusion in patients with septic shock

Tissue hypercarbia is related to hypoperfusion and microcirculatory disturbances in patients with septic shock. Transcutaneous Pco₂ devices using a heated sensor to arterialize the tissue have been used as an alternative method for estimation of Paco₂. This study investigates whether a cutaneous sensor attached to an ear lobe and regulated to 37°C could be used to measure cutaneous Pco₂ (Pcco₂) and evaluate microperfusion in patients with septic shock.

Fifteen stable patients in an ICU were studied as a control group. Forty-six patients with septic shock who were ventilated were enrolled as the study group. The difference of the gradients between Pcco₂ and Paco₂ (Pc-aco₂) and between Pcco₂ and end-tidal Pco₂(Pc-etco₂) were evaluated for 36 h. Variations of the Pc-aco₂ and Pc-etco₂ during fluid challenge were compared with microcirculatory skin blood flow (mBFskin) assessed by laser Doppler flowmetry.

The baseline levels for Pc-aco₂ and Pc-etco₂ were significantly higher in the patients with septic shock than in the control group (14.8 [12.6] vs 6 [2.7] mm Hg and 25 [16.3] vs 9 [3.8] mm Hg, P < .0001, respectively). During the following 36 h, the Pc-aco₂ and Pc-etco₂ for the surviving patients with septic shock decreased significantly compared with the nonsurvivors (P < .01). The evolution of macrohemodynamic parameters showed no differences between survivors and nonsurvivors. At hour 24, a Pc-aco₂ > 16 mm Hg and a Pc-etco₂ > 26 mm Hg were related to poor outcome. Pc-aco₂ and Pc-etco₂ variations during fluid challenge were inversely correlated with changes in mBFskin (r² = 0.7).

Ear lobe cutaneous Pco₂ at 37°C represents a noninvasive technique to assess tissue Pco₂ measurement. Pc-aco₂ and Pc-etco₂ were related to outcome and provide continuous information on microperfusion in patients with septic shock.