Transcutaneous blood gas CO2 monitoring of induced ventilatory depression in mice

We assessed a simple, noninvasive method of monitoring transcutaneous partial pressure of CO 2 (Ptcco 2 ) in mice to determine whether it would provide an accurate and reproducible method to assess ventilatory depression in mice. To this end, Ptcco 2 and Paco 2 (partial pressure of arterial CO 2 ) measurements were performed on isoflurane-anesthetized male C57Bl/6 mice breathing differing percentages of CO 2 or fentanyl, a known ventilatory depressive drug. All doses of fentanyl produced a sharp increase in Ptcco 2 values within 20 min with difference in Ptcco 2 values between saline and all fentanyl groups being statistically significant (P < 0.0001). A good correlation between Paco 2 and Ptcco 2 values was established (r 2 = 0.91). A Bland-Altman analysis likewise found that Ptcco 2 measurements in the mice reliably and accurately reflected their Paco 2 values. Therefore, under controlled conditions, Ptcco 2 measurements were found to reliably reflect Paco 2 values in mice. Consequently, the Ptcco 2 method can be used as a means to rapidly and quantitatively assess the ventilatory depressive properties of a wide spectrum of drugs, under varying conditions in numerous mouse models.