• Paediatric anaesthesia · Jul 2018

    Time to consider the contact force during photoplethysmography measurement during pediatric anesthesia: A prospective, nonrandomized interventional study.

    • Ji-Hyun Lee, Seungman Yang, Jonghyun Park, Hee Chan Kim, Eun-Hee Kim, Young-Eun Jang, Jin-Tae Kim, and Hee-Soo Kim.
    • Department of Anaesthesiology and Pain Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea.
    • Paediatr Anaesth. 2018 Jul 1; 28 (7): 660-667.

    BackgroundRespiratory variations in photoplethysmography amplitude enable volume status assessment. However, the contact force between the measurement site and sensor can affect photoplethysmography waveforms. We aimed to evaluate contact force effects on respiratory variations in photoplethysmography waveforms in children under general anesthesia.MethodsChildren aged 3-5 years were enrolled. After anesthetic induction, mechanical ventilation commenced at a tidal volume of 10 mL/kg. Photoplethysmographic signals were obtained in the supine position from the index finger using a force sensor-integrated clip-type photoplethysmography sensor that increased the contact force from 0-1.4 N for 20 respiratory cycles at each force. The AC amplitude (pulsatile component), DC amplitude (nonpulsatile component), AC/DC ratio, and respiratory variations in photoplethysmography amplitude were calculated.ResultsData from 34 children were analyzed. Seven contact forces at 0.2-N increments were evaluated for each patient. The normalized AC amplitude increased maximally at a contact force of 0.4-0.6 N and decreased with increasing contact force. However, the normalized DC amplitude increased with a contact force exceeding 0.4 N. ΔPOP decreased slightly and increased from the point when the AC amplitude started to decrease as contact force increased. In a 0.2-1.2 N contact force range, significant changes in the normalized AC amplitude, normalized DC amplitude, AC/DC ratio, and respiratory variations in photoplethysmography amplitude were observed.ConclusionRespiratory variations in photoplethysmography amplitude changed according to variable contact forces; therefore, these measurements may not reflect respiration-induced stroke volume variations. Clinicians should consider contact force bias when interpreting morphological data from photoplethysmography signals.© 2018 John Wiley & Sons Ltd.

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