Abstract
The auditory evoked potential (AEP) is correlated to anaesthetic depth. The AEP has been used in rats, pigs, dogs and humans to assess anaesthetic depth. This study was undertaken to determine whether the AAI Index derived from the AEP correlated with changes in end tidal isoflurane concentration in dogs. The average AAI Index was 21.8 +/- 10.5 and isoflurane concentration was 1.7 +/- 0.4%. Data were divided into 0.5% intervals of end tidal anaesthetic agent concentration (ETAA). When ETAA values were higher than 2.5% the AAI values were 2.1-2.5%, 1.6-2.0% and 1.1-1.5% higher than AAI values although not statistically different. The 2.1-2.5 % interval was statistically different from the 1.1-1.5% and <1.1% interval. The 1.6-2.0% interval was statistically different from the 1.1-1.5% and the <1.1% intervals. The 1.1-1.5% interval was statistically different from the <1.1% interval. The correlation between the AAI Index and isoflurane was -0.176 and was statistically significant (P = 0.0009). A linear regression between the AAI Index and isoflurane revealed the following relationship: AAI = 29.074 - (4.2755 x isoflurane) with a power of 0.913. The polynomial regression relationship was AAI = 53.334 - (35.715 x isoflurane) + (10.322 x isoflurane2) - (0.43646 x isoflurane3) with a power of 0.999. The AAI Index was found to correlate with changes in isoflurane concentration.
Highlights
The auditory evoked potential (AEP) has been described as a method to control the delivery of isoflurane[13]
When end tidal anaesthetic agent concentration (ETAA) values were higher than 2.5 % the AAI values were 2.1–2.5 %, 1.6–2.0 % and 1.1–1.5 % higher than the AAI values, not statistically different
This study showed that the isoflurane concentration is correlated with the AAI Index
Summary
The auditory evoked potential (AEP) has been described as a method to control the delivery of isoflurane[13]. The AEP has been used for assessment of anaesthetic depth in rats[1,2,8], pigs[10] and dogs[9,13,15]. It consists of a set of electrical impulses (brain waves) that are formed when a sound is delivered at the external auditory meatus. As the electrical impulses move from the brain stem to the cortical structures, an early and late cortical response can be seen[17]. The early cortical response occurs within 10–80 ms of the stimulus and is referred to as the middle
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