Use of Tissue Oxygenation Index and Fractional Tissue Oxygen Extraction as Non-Invasive Parameters for Cerebral Oxygenation

Abstract

Objective: To evaluate the relation between cerebral tissue oxygenation index (TOI), measured with spatially resolved spectroscopy (SRS), and the different oxygenation parameters. To evaluate the relation between a new parameter named fractional tissue oxygen extraction (FTOE) and the cerebral fractional oxygen extraction (FOE). Methods: Six newborn piglets were measured at 33, 35, and 37°C and in hypocapnia. Mean arterial blood pressure (MABP), haemoglobin (Hb), peripheral oxygen saturation (S_aO₂) and P_aCO₂ were measured at each step. Cerebral blood flow (CBF) was measured by injection of coloured microspheres into the left atrium. Jugular bulb oxygen saturation (JVS), cerebral arterial and venous oxygen content (C_aO₂ and C_vO₂) and FOE were calculated. TOI of the brain was calculated and FTOE was introduced as (S_aO₂ – TOI)/S_aO₂. The correlation was calculated with an ANCOVA test. Results: There was a positive correlation (R = 0.4 and p = 0.011) between TOI and JVS. No correlation was found with CBF, MABP or Hb. There was a positive correlation between P_aCO₂ and cerebral TOI (R = 0.24 and p = 0.03). FTOE correlated well with FOE (R = 0.4 and p = 0.016) and there was a negative correlation between FTOE and P_aCO₂ (R = 0.24, p = 0.03). Conclusion: The measurement of TOI and FTOE by SRS correlated well with the cerebral venous saturation and FOE, respectively.