Fig. 1. Minimum alveolar concentration (MAC), physiologic variables, and survival during 4-h isoflurane in rats. MAC was determined using the response to tail clamping of ten or more simultaneously anesthetized rats. A second order polynomial fit was applied to the MAC data of postnatal day (P)7 rats ( A ). Blood withdrawn blindly from the left cardiac ventricle under general ( isoflurane groups ) or local anesthesia ( control ) was analyzed in a blood gas analyzer and oxygen tension ( B ), glucose concentration ( C ), carbon dioxide tension ( D ), and pH ( E ) were determined. Only one sample was obtained per P7 rat, whereas four blood samples were drawn from every P60 cardiorespiratory control rat (n = 6). Data are medians and interquartile ranges except glucose concentrations (median, range) and survival ( F ); mean, 95% confidence interval). Only those rats that awoke from anesthesia were considered survivors. Two rats in the P7 isoflurane group survived 4 h of isoflurane but died before awakening from anesthesia. None of the unanesthetized control animals died (not shown). FiO2= fraction of inspired oxygen; PCO2= partial pressure of carbon dioxide; PO2= partial pressure of oxygen.
