The performance of the heart rate variability‐derived Newborn Infant Parasympathetic Evaluation Index as a measure of early postoperative pain and discomfort in infants—A prospective observational study

BACKGROUND: The heart rate variability‐derived Newborn Infant Parasympathetic Evaluation (NIPE™) Index is a continuous noninvasive tool for the assessment of pain and discomfort in infants. Little is known about its performance in the early postoperative setting, where assessment of pain/discomfort is usually based on discontinuous observational scoring systems or personal experience of medical staff. AIMS: To investigate the performance of the NIPE as a measure of early postoperative pain and/or discomfort in infants. METHODS: The potential of the NIPE to detect pain/discomfort, as assessed by two clinical scoring systems (FLACC and COMFORT‐B scale), was investigated in postoperative infants (0–2 years). RESULTS: Receiver operating curve (ROC) analyses investigating the power of the NIPE to distinguish between comfort and pain/discomfort, revealed areas under the curve (AUC) of 0.77 for the FLACC, 0.81 for the COMFORT‐B score, and 0.77 for a combination of FLACC & COMFORT‐B. Logistic regression analysis provided initial evidence that the NIPE is an independent predictor of a FLACC score ≥4 and/or a COMFORT‐B score ≥17, though R (2) values were below .2. NIPE values associated with a FLACC ≥4 (48 [45–56]), a COMFORT‐B score ≥17 (47 [42–53]), and a FLACC ≥4 & COMFORT‐B ≥17 (47 [42–57]) were lower than NIPE values associated with a FLACC <4 (60 [53–68], 95% CI of difference −14 to −8, p < .0001), a COMFORT‐B score <17 (61 [54–68], 95% CI of difference −16 to −10, p < .0001), and a FLACC <4 & COMFORT‐B score <17 (60 [53–68], 95% CI of difference −15 to −8, p < .0001). We found no evidence of a predictive value of the NIPE regarding the occurrence of pain. CONCLUSIONS: The NIPE detected pain and discomfort in infants after general anesthesia with reasonable areas under the ROC curve (±0.8), whereas it was not predictive of clinically detectable pain or discomfort.