In the field of emergency medical care, we often experience a situation in which we cannot measure pulse oximetric saturation (SpO₂) or blood pressure due to circulatory failure associated with shock. However, as we can measure rSO₂ values of the brain even in patients with shock, we hypothesized that we could evaluate the oxygen supply-demand balance between brain and muscle tissue by simultaneously measuring regional oxygen saturation (rSO₂) values of the brain and muscle tissue of patients with shock.
We attached a TOS-OR rSO₂ monitor (TOSTEC CO., Tokyo, Japan) to 10 healthy volunteers and measured the rSO₂ values of their brain and muscle for 3 minutes. The rSO₂ values of their brain cerebral regional oxygen saturation (crSO₂) and muscle regional oxygen saturation (mrSO₂) were 77.6±1.6% and 76.2±1.3% (mean ± SD). There was little difference between crSO₂ and mrSO₂ (cerebro-musculoskeletal difference in regional saturation of oxygen; c-mDrSO₂). However, there were discernible amount of c-mDrSO₂ in three cases with shock, Case 1 showed a prolonged shock state due to septic shock caused by bacterial pneumonia. Her crSO₂ values was always higher than her mrSO₂ value, and there was a c-mDrSO₂. Case 2 showed a decrease in mean arterial pressure (MAP) with the development of septic shock caused by intestinal perforation. His crSO₂ value was higher than that of his mrSO₂, and c-mDrSO₂ increased with the decrease of his MAP. Case 3 had a low MAP due to hemorrhagic shock caused by postpartum hemorrhage. Her crSO₂ value was higher than that of her mrSO₂ and a c-mDrSO₂ was present. After resuscitation, the c-mDrSO₂ decreased with the increase in her blood pressure.
We evaluated the usefulness of simultaneous measurement of crSO₂ and mrSO₂ as an objective and non-invasive method in shock management. Even if SpO₂ or blood pressure could not be measured due to circulatory failure associated with shock, it was possible to measure the values of crSO₂ and mrSO₂, which changed in real time with fluctuation of the blood pressure. Unlike previous monitoring devices, the rSO₂ monitor may continuously and clearly reflect the changes in local oxygen supply-demand balance.