Minimum alveolar concentration of isoflurane in green iguanas and the effect of butorphanol on minimum alveolar concentration

Abstract

Results suggest that the MAC of isoflurane in green iguanas is 2.1% and that butorphanol does not have any significant isoflurane-sparing effects.

Minimum Alveolar Concentration of Isoflurane and Arterial Blood Gas Values in Anesthetized Green Iguanas, Iguana iguana

“…In the latter study, gas was sampled from the face mask and this may have led to overestimation o f the concentration o f isoflurane. The mean minimum alveolar concentration value in this study is lower but overlaps, within one standard deviation, with that o f Mosley, et al, 2003, andBarter, et al, 2006, values. A lower m inim um alveolar concentration value m ay reflect either m inor, undetected differences in m ethodology, or reflect intraspecific variation combined with a relatively small sam ple size. This study used seven animals, Mosley, et al, 2003 used ten animals, andBarter, et al, 2006 used six animals.…”

“…In one stu d y , M o sley, e t al, fo u n d tw o sim ila r v alu e s o f M A C is o f lu ra n e , 2.0± 0.6% and 2 .1± 0.6% in the same iguanas, when measured at least 6 days apart (Mosley, et al, 2003). In the other study, Barter, et al, repeated M A C is o f lu ra n e determi nations three times in the same individuals in one protracted (> 1 0 h r) an esth etic event (B arter, et al, 2006).…”

“…While this may reflect some degree o f interspecific variation in susceptibility to isoflurane, there should be m inim al intraspecific variation and yet the two prior isoflurane anesthesia studies in green iguanas yielded different minimum alveolar concentrations. Two minimum alveolar concentration determinations studies conducted six or more days apart on the same experimental group o f igua nas yielded minimum alveolar concentration values o f 2.0 ± 0.6% and 2.1 ± 0.6% (Mosley, et al, 2003). In a different study, M A C is o f lu r a n e determinations made on the same ani m als d u rin g a sin g le a n e s th e s tic e p is o d e th a t la s te d approximately 10 horns, yielded the following results: 2.4 ± 0.7%, at about four to fives hours post induction (PI), 2.1 ± 0.5 % at eight to nine hours PI, and 1.8 ± 0.3% at 10 -11 hr PI; (Barter, et al, 2006).…”

“…Furthermore, reptiles possess a single ventricle and dual aor tic arches, so that arterial blood gas values will vary with the collection site Sonnenschein, 1964, Oldham andSmith, 1975). In this study, we determined blood gas values in green iguanas for samples obtained from the right common carotid artery, a direct branch o f the right aortic arch, and compared values to those o f arterial blood collected from the left carotid artery (Barter, et al, 2006), the femoral artery (M osley, et al, 2004), and the ventral coccygeal vessels (Mosley, et al, 2003, Mosley, et al, 2004 under similar con ditions. The purpose o f this study was therefore two-fold: to provide additional data and insight pertaining to the minimum alveolar concentration o f isoflurane and arterial blood gas values in green iguanas and to compare results with those o f previous publications.…”

“…The anatomical unit o f gas exchange in reptiles is the faveolus (Maina, 2000) and while minimum faveolar concentration or MFC may repre sen t m ore a c c u ra te term in o lo g y , m in im u m a lv e o la r concentration is traditionally adopted in prior reptilian anes th e tic s tu d ie s an d w ill be u sed h ere fo r co n sisten cy . Minimum alveolar concentration values should be consistent across mammalian species (Quasha, et al, 1980), but seem to be more variable across reptile species even when maintained within their respective preferred optimal temperature range (Mosley, et al, 2003).…”