Name: electrophysiological measurement of noxious-evoked brain activity in neonates using a flat-tip probe coupled to electroencephalography
Uploaded: 2017-11-29T15:00:00
Description: Watch this Scientific Journal Video about Electrophysiological Measurement of Noxious-evoked Brain Activity in Neonates Using a Flat-tip Probe Coupled to Electroencephalography at JoVE.com

The authors would like to acknowledge Caroline Hartley and Rebeccah Slater (Department of Paediatrics, University of Oxford, UK) for critical reviewing our paper and Walter Magerl (Department of Neurophysiology, Center of Biomedicine and Medical Technology Mannheim (CBTM), University of Heidelberg, Germany) for supporting us with technical equipment and knowledge.

The study was approved by the Competent Ethics Committee of Northwestern Switzerland (EKNZ 2015-079) and informed written parental consent for the participant was obtained before the measurement.
1. Preparation
<ol>
	<li>Make sure the baby is settled. It should be quiet and settled, without sucking motions during the recording because of movement artefacts. The baby can be asleep9.</li>
	<li>Measure the neonate&#39;s head circumference with a measuring tape to define ...

<ol>
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The approach presented here shows how noxious-evoked brain activity in neonates can be measured in an objective way using EEG recording and flat-tip probe stimulators to apply experimental noxious stimuli. This technique can be used in various clinical settings to detect nociception, e.g. in non-verbal persons such as neonates. The complete study can be done within 15 min, including placing the baby, identifying, preparing and mounting the electrodes, and finally applying and recording the 50 noxious stimuli. Th...

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage1. The inability to communicate verbally does not negate the possibility that an individual is experiencing pain but makes it very challenging to assess pain-relieving treatment, for example in newborn infants2. Several behavioral and physiological indicators are used to assess pain in non-verbal patients. Different scales have been developed over the years, the choice depends on the type of stimulus, gestational age and the environment in which the neonates are embeded3,4,5. These pain assessment tools either rely on the rater&#39;s interpretation or they demand secondary physiological indicators.
In this video, we present a method to assess nociception with electrophysiological recordings optimized for use in newborn infants. Nociception is defined as the neural process of encoding noxious stimuli. Thus, quantitating nociception is an elegant and objective method to determine the neural input in a non-verbal person. Moreover, cortical activity detected by electroencephalography (EEG) is correlated with the intensity of noxious events5,6.
The method presented here combines EEG recording with noxious stimuli produced by a mechanical stimulation with a flat-tip probe, also called a pinprick7, which is not skin-breaking and does not cause behavioral distress6. It has been shown, that nociception following punctuate stimulation is predominantly mediated by A&#948;-fibers, does not need a skin breaking lesion8 and the magnitude of the nociceptive-specific potential is not dependent on sleep state9. The probe is well accepted also by parents when applying this method in a study setting with neonates. The probe is electronically linked to the EEG recording system enabling the EEG recording to be precisely tagged when the probe contacts the skin. This greatly simplifies the process of time locking and is the premise for all subsequent EEG analyses. In order to minimize preparation time of the infant EEG recording we used a modified international 10/20 electrode placement system where we reduced the number of electrodes to the minimum requirement of three electrodes (Figure 1). The central vertex Cz electrode, where the noxious-evoked brain activity is maximal9,10,11, was used together with one reference and one ground electrode.

<table>
	<tbody>
		<tr>
			<td>Easycap</td>
			<td>EASYCAP GmbH</td>
			<td>AC-32-C</td>
			<td>EEG caps for infants sizes 34 and 36</td>
		</tr>
		<tr>
			<td>actiCAP</td>
			<td>Brain Products GmbH</td>
			<td>BP-04243-SIG</td>
			<td>active electrodes</td>
		</tr>
		<tr>
			<td>ImpBox</td>
			<td>Brain Products GmbH</td>
			<td></td>
			<td>impedance measurement</td>
		</tr>
		<tr>
			<td>V-Amp</td>
			<td>Brain Products GmbH</td>
			<td></td>
			<td>EEG recording device</td>
		</tr>
		<tr>
			<td>Contact trigger for pinprick stimulation</td>
			<td>MRC Systems GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PinPrick stimulator set</td>
			<td>MRC Systems GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EEG prepping paste</td>
			<td>USB Pharmacy</td>
			<td></td>
			<td>contains sodium chloride, pumice stone, propylene glycol</td>
		</tr>
		<tr>
			<td>SuperVisc</td>
			<td>EASYCAP GmbH</td>
			<td></td>
			<td>Electrolyte-Gel for active electrodes</td>
		</tr>
		<tr>
			<td>Brain Vision Recorder</td>
			<td>Brain Products GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Brain Vision Analyzer</td>
			<td>Brain Products GmbH</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MATLAB using EEGLAB
			
			
			
			
			
			</td>
			<td>Swartz Center for Computational Neuroscience, University of California San Diego</td>
			<td></td>
			<td>For EEG processing, including averaging of all EEG epochs
			
			
			
			</td>
		</tr>
	</tbody>
</table>

electrophysiological measurement of noxious-evoked brain activity in neonates using a flat-tip probe coupled to electroencephalography

Pain is an unpleasant sensory and emotional experience. In non-verbal patients, it is very difficult to measure pain, even with pain assessment tools. Those tools are subjective or determine secondary physiological indicators which also have certain limitations particularly when exploring the effectiveness of analgesia. As cortical processing is essential for pain perception, brain activity measures may provide a useful approach to assess pain in infants. Here we present a method to assess nociception with electrophysiological brain activity recordings optimized for the use in newborn infants. To produce highly standardized and reproducible noxious stimuli we applied mechanical stimulation with a flat-tip probe, e.g., PinPrick, which is not skin-breaking and does not cause behavioral distress. The noxious-evoked potential allows the objective measurement of nociception in non-verbal patients. This method can be used in newborn infants as early as 34 weeks of gestational age. Moreover, it could be applied in different situations such as measuring the efficacy of analgesic or anesthetic drugs.

Figure 1 is the diagrammatic representation of the electrode positioning using the modified international 10/20 electrode placement system. Figure 2 shows the EEG activity recorded shortly before and after application of one single noxious stimulus using a flat-tip probe with 32 mN force, stimulation occurred as described in the protocol to the neonate&#39;s right hand (Figure 2A). The noxious-evoked...

Watch this Scientific Journal Video about Electrophysiological Measurement of Noxious-evoked Brain Activity in Neonates Using a Flat-tip Probe Coupled to Electroencephalography at JoVE.com

Electrophysiological Measurement of Noxious-evoked Brain Activity in Neonates Using a Flat-tip Probe Coupled to Electroencephalography

Measuring pain in non-verbal patients is a challenge. In this study we combine EEG recording with stimulation using a flat-tip probe to detect noxious-evoked brain activity in an objective manner.

Pain is an unpleasant sensory and emotional experience. In non-verbal patients, it is very difficult to measure pain, even with pain assessment tools. ...

The overall goal of this electrophysiological measurement is to objectively asses nociception in newborn infants. This method can help answer key questions in the neonatal field such as how non-verbal patients perceive pain and how it differs in response to different conditions. The main advantage of this technique is that it can be used in neonates born at term or late pre-term starting at 34 weeks of gestational age.The implications of this technique extends toward investigation of pain because it is the first objective measurement of nociception in non-verbal patients. Generally, individuals new to this method will struggle because experience with EEG is required. We first had the idea for this method when we observed after delivery different pain responses in neonates born spontaneously as compared to those born by elective ceasarean section.But also at the neonatal intensive care unit, babies are exposed to so many potentially painful procedures. You don't know how much they perceive even when they are under analgesic drugs. Now we can objectively measure their noxious response.Before starting, ensure the baby is quiet and settled. The baby can be asleep but sucking motion should be absent during the recording because of movement artifacts. Measure the neonate's head circumference with a measuring tape to define the size of the EEG cap.Then identify the active electrode position by marking the middle point between nasion and inion and the middle point between left and right pre-auricular point with a skin marker pencil. A schematic of the electrode positions is shown here. Identify the positions for the ground electrode on the right forehead and for the reference electrode over the left mastoid.Clean the three electrode sites using a cotton swab soaked in skin disinfectant. Then gently scrub the electrode sites with EEG prepping paste to lower the impedance and place the EEG cap with the electrodes attached on the neonate's head. Next, use a syringe with a short plastic needle to inject conductive EEG gel into the electrodes to optimize the contact between the electrodes and the scalp.Then to ensure the impedance is below 50 kilo ohms, connect an impedance meter to the electrodes and set it below 50 kilo ohms. The light will turn green if the impedance is below 50 kilo ohms. After this, connect the electrodes to the amplifier.Position a camera to record the neonate's facial expressions. Then connect the flat-tip probe to the contact trigger device which is fixed to the EEG recording device. Begin by choosing a new work file.Set the sampling rate to 2, 000 Hertz. Set the low cutoff filter to a frequency of one Hertz. Set the high cutoff filter to 70 Hertz and the notch filter to 50 Hertz.Select a study name to store the data. Start the EEG and the video recording. Whilst the neonate's right hand is held in a horizontal position, record background EEG activity.Annotate the EEG recording manually to record periods where no stimuli are applied and the infant is resting. Once the background EEG is stable, administer the required amount of flat-tip probe stimuli to the neonate's right hand. Be careful to use the flat-tip probe perpendicularly to the neonate's hand so the tip does not bend and the correct force is applied.When the flat-tip probe reaches the nominal force on the skin, a trigger signal is generated by the contact trigger device. This signal is sent to the computer tagging the EEG recording with the trigger mark. After the stimuli are administered, stop all the recordings and document the experimental setting details.After taking off the electrodes at the infant's head, clean the scalp with a wet towel to remove any residuals. A flat-tip probe stimulus of 32 millinewtons was applied to the right hand of one patient. The shaded region shows the time window of interest which occurs 200 to 500 milliseconds after the stimulus.After a single stimulus, the noxious-evoked response is visible at approximately 300 milliseconds post stimulus onset. The principle peak at 250 milliseconds is indicated with an arrow. This trace demonstrates the average response of 50 stimuli applied with a force of 32 millinewtons to the same patient.Note that the noxious-evoked potential is clearer if more stimuli are applied. Woody filtering can be used to adjust for slight variability in the response latency. The predefined template shown in red is projected onto the EEG to calculate the magnitude of the noxious-evoked response.Once mastered, this technique can be done in 15 minutes if it is performed properly. While attempting this procedure, it's important to remember to wait to apply the stimuli until the infant is calm. After watching this video, you should have a good understanding of how to objectively measure nociception at bedside.

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