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

Summary

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.

Abstract

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.

Introduction

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 embeded

Protocol

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

1. 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.
2. Measure the neonate's head circumference with a measuring tape to define the size of the EEG cap.
3. Identify the active electrode position: Cz / vertex position by marking the middle point between nasion and inion a....

Results

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's right hand (Figure 2A). The noxious-evoked.......

Discussion

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.......

Materials

List of materials used in this article

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