Infant EEG Changes During Sevoflurane Wash-out
Infant EEG Changes During Sevoflurane Wash-out
Background: Few electroencephalography (EEG) data are available in anaesthetized infants. This study aimed to identify EEG characteristics that might warn of awakening (AW) from sevoflurane anaesthesia in infants.
Methods: Twenty intubated infants [aged 39–77 weeks post-menstrual age (PMA)] were studied after surgery during sevoflurane wash-out. EEG was recorded at the end of surgery and throughout emergence. Changes in EEG time and frequency domains were described.
Results: At the end of surgery, mean end-tidal sevoflurane concentration was 2.3% (range 1.5–3.5) before wash-out and reduced to 0.3% (0.1–0.6) when AW began. On AW, movement artifacts made signals difficult to interpret. Before awakening, most power was within frequencies ≤4 Hz, but trends over time were variable. Summated power in frequencies between 20 and 70 Hz was almost always <5 µV. During anaesthesia, there were two common power spectra: infants >52 weeks PMA had obvious summated power in the frequency range 5–20 Hz (P5–20 Hz) (mean 308, median 320, range 110–542 µV), which decreased before awakening began [mean decrease 252 µV (95% CI 153–351)], whereas younger infants had low P5–20 Hz throughout. P5–20 Hz during anaesthesia increased with age; power in this frequency band of ~100 µV separated infants younger and older than 52 weeks PMA.
Conclusions: During sevoflurane wash-out, decreasing P5–20 Hz might warn of impending AW in infants >3 months old, but not in younger infants.
An assessment of the effect of anaesthetic agents on the depth of anaesthesia is important in infants as in older patients. If, in order to avoid excess anesthesia, the dose is minimized, it would be desirable to have a monitor of anaesthesia depth that could warn of unintended awakening (AW). Electroencephalography (EEG), including monitors of processed EEG, might be suitable but few data are available in anaesthetized infants. The data from adults might not be applicable because EEG characteristics in infants are known to differ from those in adults.
In their review of EEG in children, Constant and Sabourdin state that, typically, a sedative dose (or concentration) of sevoflurane increases beta activity and as the dose increases to cause anaesthesia, high-amplitude low-frequency oscillations appear. If the dose is increased further, there is EEG suppression with intermittent bursts (burst suppression) followed by EEG silence. EEG changes during sevoflurane wash-out and emergence are assumed to be the same but in reverse. The evidence, however, for these changes occurring in infants is limited. There are four published data sets of EEG effects of sevoflurane in infants and small children: one during induction, two during emergence, and one during surgery.
Induction was studied by Constant and colleagues in children aged 2–12 yr. An increase in dose was associated with an increase in total spectral power especially in low-frequency bands, and 14–30 Hz oscillations were common.
Of the emergence data sets, Davidson and colleagues studied toddlers and children (anaesthesia also involved opioids and some had isoflurane), and Lo and colleagues studied children aged 22 days to 3.6 yr emerging from either sevoflurane or isoflurane alone. Both studies found that during steady-state anaesthesia, infants <6 months old have low EEG power, but in older infants, as in adults, there is appreciable power in frequencies between 2 and 30 Hz. However, their observations on EEG changes associated with emergence conflict. In one study, the power within the 2–20 Hz range decreased, and in the other, power within the 8–30 Hz range increased.
Hayashi and colleagues studied processed EEG variables in 62 neonates and infants having surgery (some had fentanyl and a caudal block) during steady sevoflurane concentrations between 0.5 and 2%. In children aged 6 months to 2 yr, spectral edge frequency (SEF90) was inversely related to sevoflurane concentration, but this was less so in younger infants. Below ~3–5 months of age, the SEF90 was always low.
We studied the EEG, both in time (i.e. visual appearance of the 'raw signal') and frequency domains, in infants during emergence from sevoflurane to determine characteristics that could be used to warn of potential AW. In a pilot study before this project, infants would frequently remain immobile during wash-out unless they were stimulated and then often awaken suddenly. This has been observed by others. We considered that it was necessary to provoke AW and therefore needed a stimulus that could be repeated without causing distress. During natural sleep in infants, McNamara and colleagues showed that tickling the foot caused a reproducible sequence of AW behaviour. First there was a withdrawal response of that limb, then a change in heart rate or breathing pattern, followed by a startle and EEG responses coincident with AW. These may relate to activation of the spinal reflex, then the brain stem, followed by the sub-cortical nuclei and finally the cerebral cortex.
This observational study describes the changes in the EEG of infants during wash-out of sevoflurane with AW provoked by gentle cutaneous stimulation.
Abstract and Introduction
Abstract
Background: Few electroencephalography (EEG) data are available in anaesthetized infants. This study aimed to identify EEG characteristics that might warn of awakening (AW) from sevoflurane anaesthesia in infants.
Methods: Twenty intubated infants [aged 39–77 weeks post-menstrual age (PMA)] were studied after surgery during sevoflurane wash-out. EEG was recorded at the end of surgery and throughout emergence. Changes in EEG time and frequency domains were described.
Results: At the end of surgery, mean end-tidal sevoflurane concentration was 2.3% (range 1.5–3.5) before wash-out and reduced to 0.3% (0.1–0.6) when AW began. On AW, movement artifacts made signals difficult to interpret. Before awakening, most power was within frequencies ≤4 Hz, but trends over time were variable. Summated power in frequencies between 20 and 70 Hz was almost always <5 µV. During anaesthesia, there were two common power spectra: infants >52 weeks PMA had obvious summated power in the frequency range 5–20 Hz (P5–20 Hz) (mean 308, median 320, range 110–542 µV), which decreased before awakening began [mean decrease 252 µV (95% CI 153–351)], whereas younger infants had low P5–20 Hz throughout. P5–20 Hz during anaesthesia increased with age; power in this frequency band of ~100 µV separated infants younger and older than 52 weeks PMA.
Conclusions: During sevoflurane wash-out, decreasing P5–20 Hz might warn of impending AW in infants >3 months old, but not in younger infants.
Introduction
An assessment of the effect of anaesthetic agents on the depth of anaesthesia is important in infants as in older patients. If, in order to avoid excess anesthesia, the dose is minimized, it would be desirable to have a monitor of anaesthesia depth that could warn of unintended awakening (AW). Electroencephalography (EEG), including monitors of processed EEG, might be suitable but few data are available in anaesthetized infants. The data from adults might not be applicable because EEG characteristics in infants are known to differ from those in adults.
In their review of EEG in children, Constant and Sabourdin state that, typically, a sedative dose (or concentration) of sevoflurane increases beta activity and as the dose increases to cause anaesthesia, high-amplitude low-frequency oscillations appear. If the dose is increased further, there is EEG suppression with intermittent bursts (burst suppression) followed by EEG silence. EEG changes during sevoflurane wash-out and emergence are assumed to be the same but in reverse. The evidence, however, for these changes occurring in infants is limited. There are four published data sets of EEG effects of sevoflurane in infants and small children: one during induction, two during emergence, and one during surgery.
Induction was studied by Constant and colleagues in children aged 2–12 yr. An increase in dose was associated with an increase in total spectral power especially in low-frequency bands, and 14–30 Hz oscillations were common.
Of the emergence data sets, Davidson and colleagues studied toddlers and children (anaesthesia also involved opioids and some had isoflurane), and Lo and colleagues studied children aged 22 days to 3.6 yr emerging from either sevoflurane or isoflurane alone. Both studies found that during steady-state anaesthesia, infants <6 months old have low EEG power, but in older infants, as in adults, there is appreciable power in frequencies between 2 and 30 Hz. However, their observations on EEG changes associated with emergence conflict. In one study, the power within the 2–20 Hz range decreased, and in the other, power within the 8–30 Hz range increased.
Hayashi and colleagues studied processed EEG variables in 62 neonates and infants having surgery (some had fentanyl and a caudal block) during steady sevoflurane concentrations between 0.5 and 2%. In children aged 6 months to 2 yr, spectral edge frequency (SEF90) was inversely related to sevoflurane concentration, but this was less so in younger infants. Below ~3–5 months of age, the SEF90 was always low.
We studied the EEG, both in time (i.e. visual appearance of the 'raw signal') and frequency domains, in infants during emergence from sevoflurane to determine characteristics that could be used to warn of potential AW. In a pilot study before this project, infants would frequently remain immobile during wash-out unless they were stimulated and then often awaken suddenly. This has been observed by others. We considered that it was necessary to provoke AW and therefore needed a stimulus that could be repeated without causing distress. During natural sleep in infants, McNamara and colleagues showed that tickling the foot caused a reproducible sequence of AW behaviour. First there was a withdrawal response of that limb, then a change in heart rate or breathing pattern, followed by a startle and EEG responses coincident with AW. These may relate to activation of the spinal reflex, then the brain stem, followed by the sub-cortical nuclei and finally the cerebral cortex.
This observational study describes the changes in the EEG of infants during wash-out of sevoflurane with AW provoked by gentle cutaneous stimulation.
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