Transcutaneous Blood Gas Monitoring in the Rat

Transcutaneous blood gas (TCBG) analysis is a noninvasive alternative method of estimation of blood gas tensions. The objective of the study reported here was to validate this method against standard blood gas (STBG) analysis in adult and juvenile Sprague-Dawley rats. We sought to establish the optimal TCBG probe site and temperature, to establish probe temperatures that would not cause thermal burns, to evaluate correlations between blood gas values (P_aCO₂ and P_aO₂ ) determined by use of TCBG and STBG, and to evaluate the sensitivity of the TCBG unit to changes in arterial blood gas partial pressures. Our results indicated that: in general, the xyphoid area was the optimal site for probe placement, with 44.5°C being the optimal probe temperature for the highest correlation, but thermal burns may be a problem; probe temperatures of 42.5°C (adults) and 42.0°C (juveniles) do not cause thermal burns when left in place for three hours; probe temperatures of 44°C (adults) and 42°C (juveniles) resulted in moderate correlation between P_a CO_{2 and Ptc} CO₂ ; and the TCBG unit adequately responded to changes in arterial blood gas partial pressures. Neither P_tcCO₂ or P_tcO₂ reflect actual values of P_aCO₂ or P_aO₂, respectively. We concluded that TCBG analysis may be used as an indicator of change in P_a CO₂ with sufficient animal numbers under tightly controlled conditions, but not as an indicator of change in P_aO₂ in adult and juvenile rats.