The importance of sensor contacting force for predicting fluid responsiveness in children using respiratory variations in pulse oximetry plethysmographic waveform

Predicting fluid responsiveness is crucial for adequate fluid management. Respiratory variations in pulse oximetry plethysmographic waveform amplitude (ΔPOP) are used to predict fluid responsiveness, but show inconsistent results when used for children. Contacting force between the measurement site and sensor can affect the ΔPOP value, thereby hindering its reliability as an indicator. We studied the influence of contacting force on the efficacy of ΔPOP as a fluid responsiveness indicator in children. In total, 43 mechanically ventilated children aged 1 month–5 years were studied. After anesthetic induction, mechanical ventilation began with a tidal volume of 10 ml/kg. ΔPOP was calculated for five different contacting force groups (0–0.3N, 0.3–0.6N, 0.6–0.9N, 0.9–1.2N, and 1.2–1.5N) and individually adjusted contacting force. Pulse pressure variation (PPV), and ΔVpeak were recorded before and after volume expansion. Subjects were considered as fluid responders if volume expansion increased the stroke volume index (SVI) by > 15%. Data from 38 patients were finally analyzed. A significant difference between the responders and non-responders was found only in ΔPOPs at 0.9–1.2N contacting force (P = 0.002) and individually adjusted contacting force (P < 0.000), while other contacting force groups did not show significant differences. ΔVpeak predicted a 15% increase in SVI (P = 0.008), whereas PPV did not. The ability of ΔPOP to predict fluid responsiveness depends on the contacting force in mechanically ventilated children. When contacting force is controlled to an adequate degree, the ability of ΔPOP to predict fluid responsiveness can be improved.