Ethane production rates and minute ventilation

Ethane quantitated in the expired alveolar gas is a noninvasive measure of free radical activity. This method has been criticized for lack of control of minute ventilation (V̇E) in spontaneously breathing animals, although ethane, which is poorly soluble in tissues, should not be affected by changes in V̇E. We measured ethane elimination rates in six strain 13 guinea pigs (GP13) during spontaneous room air breathing and in six room air breathing, pentobarbital-anesthetized, tracheostomized, externally warmed, mechanically ventilated GP13s at various levels of V̇E. In the ventilated animals, weight^{0. 75}/V̇E (metabolic activity corrected for V̇E) was a linear function of arterial CO₂ tension (Pa(CO₂)) drawn from arterial line (r = 0.72, P < 0.005). However, weight^0.75/V̇E did not correlate with ethane elimination rates (r = 0.12, not significant). The mean (± SD) ethane elimination rates in the spontaneously breathing animals was 3.15 ± 0.96 pmol · min^-1 · 100 g^-1 and was not significantly different from the mean rate in the mechanically ventilated animals (3.11 ± 1.37) over a range of V̇E's. These data demonstrate that ethane elimination rates are not affected by changes in V̇E and are unaffected by pentobarbital anesthesia.