The influence of age and sex on the relationship between heart rate variability, haemodynamic variables and subjective measures of acute post-operative pain.

Background And Objective: Both skin conductance and surgical stress index have been proposed as useful means of assessing pain. Both methods are based on the assessment of the sympathovagal balance, which, according to reports, is influenced by age and sex, and currently neither of the assessments take these factors into account. The aim of this study was to determine the relationship between age, sex, magnitude of acute post-operative pain and haemodynamic and autonomic changes.

Methods: Two hundred twenty patients were asked to quantify their level of pain on a numeric rating scale (NRS) at different time points in the recovery room. Simultaneously, the following measures of heart rate variability were analysed: total power, low frequency, high frequency, low-to-high frequency ratio and ultra-short entropy. Additionally, SBP, heart rate and respiration rate were recorded.

Results: A total of 1098 NRS readings were obtained from 220 participants (123 men, 97 women, aged 40 ± 15 years). For heart rate variability, the low-to-high frequency ratio was significantly higher [mean (SE): 7.7 (0.56) vs. 6.7 (0.47); P < 0.05] and the ultra-short entropy significantly lower [mean (SE): 46.2 (0.8) vs. 47.2 (0.8); P < 0.05] for NRS 5-10 vs. NRS 0-4. Age correlated negatively with blood pressure and heart rate, and all measures of heart rate variability, except the low-to-high frequency ratio. Low-to-high frequency ratio and blood pressure were higher in men.

Conclusion: Acute pain influences the sympathovagal balance. This response is significantly influenced by age and sex.