Anesthesia in the News
  • Skin Conductance for Gauging Pain in Mechanically Ventilated Infants

    Skin conductance (SC) provides good validity for assessing pain in critically ill infants requiring mechanical ventilation, according to a cross-sectional observational study recently published in the European Journal of Pain.

    The measurement of SC is a physiological approach to assessing pain, which is predicated on the sympathetic nervous system’s response to stress. When pain occurs, the stress induces sympathetic excitation and causes emotional sweating at an infant’s foot or hand area.

    Cohort and exclusions

    The study cohort was comprised of 55 infants up to 12 months of age who were mechanically ventilated at either a level-three neonatal intensive care unit (NICU) within a tertiary referral pediatric hospital in Canada or a level-three pediatric intensive care unit (PICU) within the same hospital between October 2017 to November 2018.

    Infants receiving high doses of cholinergic activating/blocking drugs were excluded until 8 hours after these medications were given because such drugs may influence SC responses.

    Procedures measured

    All patients were subjected to both painful and non-painful procedures. Painful procedures were defined as intrusive interventions that entail skin-breaking procedures, such as heel lance or venipuncture, or non-tissue breaking painful procedures like nasogastric and orogastric tube insertion. Non-painful procedures were routine care requiring direct contact between the caregivers and the infants without any invasiveness, such as diaper change or positioning.

    Painful and non-painful procedures were divided into three phases: before the procedure (the first 30 seconds of the 3 minutes prior to either procedure); during the procedure (the first 30 seconds following either procedure; and after the procedure (the final 30 seconds of the 3 minutes after completion of either procedure).

    The separation of observation periods before and after the procedure ensured that infants were less likely to be handled for preparation before the procedure or settling after the procedure; thus the data collected during these two time windows would more likely represent the infant’s conditions during baseline and recovery.

    SC findings

    The number of SC waves per second was statistically significantly higher during painful procedures than during non-painful procedures: a median of 0.27 (interquartile range 0.2 to 0.4) vs. a median of 0 (interquartile range 0 to 0.09), respectively.

    SC during painful procedures was also statistically significantly higher than before and after painful procedures: a median of 0 (interquartile range 0 to 0.07) vs. a median of 0 (interquartile range 0 to 0.07), respectively.

    In addition, SC demonstrated moderate statistically significant positive correlations with the referent pain measurement Premature Infant Pain Profile-Revised (PIPP-R)  (Spearman’s rho = 0.4 to 0.62) and the four-item Neonatal Facial Coding System (NFCS) (Spearman’s rho =0.31 to 0.67) before, during and after painful or non-painful procedures.

    Furthermore, SC showed excellent performance, with area under the receiver operator curve (ROC) of 0.979, along with an impressive sensitivity of 92.31%, a specificity of 95.42%, and a negative predictive value of 99.21%.

    However, there was only a sufficient positive predictive value of 66.67% to discriminate moderate-to-severe pain.

    Provisos and next steps

    Despite SC showing promising results for measuring pain, further research is needed before the technique can be recommended for routine clinical use, according to the authors.

    Meanwhile, the values of SC need to be cautiously interpreted, as there are imperfect correlations with the referent pain measurements and low positive predictive value. Pain assessment with SC also requires considering the status of the individual infant, the infant’s personal expression and pain-related context.

    As long as infants are able to respond behaviorally to pain, SC in combination with other pain scales that provide a different dimension of pain in infants than SC could be useful. This strategy might also exclude the false positive cases found with SC only.

    Being able to discriminate between pain and non-painful distress offers immense clinical benefit, according to the authors. They recommend that future studies test the validity of SC for pain assessment in relation to the intensity of ongoing pain or non-painful distress in infants.

    The authors also advocate an interdisciplinary collaboration between technologists and pain scientists to advance the technology of measuring SC.

    Find the full study, Hu J, Harrold J, Squires JE, Modanloo S, Harrison D. The validity of skin conductance for assessing acute pain in mechanically ventilated infants: A cross-sectional observational study. Eur J Pain. 2021 Jun 8. at