Comparative effects of halothane, isoflurane, sevoflurane and desflurane on the electroencephalogram of the rat

Abstract

SummaryInhalant anaesthetic agents are commonly used in studies investigating the electroencephalographic (EEG) effects of noxious stimuli in animals. Halothane causes less EEG depression than isoflurane, however, the EEG effects of halothane, isoflurane, sevoflurane and desflurane have not been compared in the same model. This study aimed to compare the EEG effects of these inhalational agents in the rat.Forty male Sprague-Dawley rats were assigned to four groups and anaesthetized with halothane, isoflurane, sevoflurane or desflurane. EEG was recorded from the left and right somatosensory cortices for 5 min at three different multiples of minimal alveolar concentration (MAC) (1.25, 1.5 and 1.75). Median, 95% spectral edge frequency and total power were derived and a single mean value for each was calculated for the first 60 s of each recording period. When the raw EEG contained burst suppression (BS), the BS ratio (BSR) over 60 s was calculated. No BS was found in EEG recorded from the halothane group at any concentration. BS was present at all concentrations with the other anaesthetic agents. BS was almost complete at all concentrations of isoflurane, whereas BSR increased significantly with increasing concentrations of sevoflurane and desflurane. No significant differences were found between the BSR due to the 1.75 MAC multiple of isoflurane, sevoflurane or desflurane. Halothane causes significantly less depression of cortical activity than the newer inhalant agents at equivalent multiples of MAC. These data support the hypothesis that halothane has a fundamentally different mechanism of action than the other inhalant agents.

Effects of halothane on the electroencephalogram of the chicken

“…In contrast, Murrell et al . (2008) reported a variable increase in F50 and no change in F95 in rats anaesthetized with halothane over the range 1.25–1.75 MAC. This study differed, however, in that electrical recordings were made from the cortical surface using surgically implanted electrodes located over the left and right primary somatosensory (S1) cortices.…”

“…2003; Murrell et al . 2008). However, in this study, burst suppression was not evident until halothane concentration was increased to 2 MAC, and occurred in one‐third of chickens at this concentration.…”

“…2006; Murrell et al . 2008), less is known about the effects of different anaesthetics on the avian EEG. The effects of halothane on the avian EEG are of particular interest, as this agent has been widely used to study nociception and analgesia in mammals (Murrell & Johnson 2006).…”

“…Such EEG changes may be quantified, for example, by calculating variables such as the median frequency (F50), spectral edge frequency (F95) and total power (Murrell et al . 2008). Furthermore, at high concentrations some anaesthetic agents cause burst suppression (BS), identified as periods of isoelectric EEG interspersed with high‐voltage bursts of activity (Steriade et al .…”

“…2006; Murrell et al . 2008). In addition, the EEG effects of increasing MAC multiples have been shown to vary between agents and species (Johnson & Taylor 1998; Antunes et al .…”