Monitoring heart rate variability to assess experimentally induced pain using the analgesia nociception index: A randomised volunteer study.
BACKGROUND
Pain assessment using a numerical rating scale (NRS) is considered good clinical practice, but objective assessment in noncommunicating patients is still a challenge. A potential solution is to monitor changes in heart rate variability transformed into the analgesia nociception index (ANI), that offers a noninvasive means of pain quantification.


OBJECTIVE
The aim was to measure magnitudes, descending slopes and time courses of ANI following expected and unexpected painful, nonpainful and sham experimental stimuli and compare these with pain intensity as assessed by NRS in conscious human volunteers. We expected a negative correlation between ANI and NRS after painful stimuli.


METHODS
Randomised stimuli and placebo-controlled, single-blinded study.


METHODS
Experimental pain simulation laboratory, Bochum, Germany.


METHODS
Twenty healthy male students, (mean ± standard deviation; 24.2 ± 1.9 years) recruited via local advertising, were consecutively included.


METHODS
ANI values were continuously recorded. After resting, four stimuli were applied in a random order on the right forearm (unexpected and expected electrical pain, expected nonpainful and sham stimuli). Blinded volunteers were asked to rate all four stimuli on NRS.


METHODS
ANI means (0-100), amplitudes, maxima, minima and slopes with NRS pain intensity scores (0-10).


RESULTS
Resting alert volunteers showed ANI values of 82.05 ± 10.71. ANI decreased after a random stimulus (maximal decrease of 25.0 ± 7.3%), but different kinds of stimuli evoked similar results. NRS scores (median; interquartiles) were significantly (P = 0.008) higher after expected (5.25; 3.5-6.75) compared with unexpected (4.50; 3.0-5.0) pain stimuli. No correlation was found between ANI and NRS.


CONCLUSIONS
ANI did not allow a differentiation of painful, nonpainful or sham stimuli in alert volunteers. Therefore, ANI does not exclusively detect nociception, but may be modified by stress and emotion. Thus, we conclude that ANI is not a specific, robust measure for assessment of pain intensity.
From the Department of Anaesthesiology, Intensive Care Medicine, Palliative Care Medicine and Pain Management, Berufsgenossenschaftliches Universitätsklinikum Bergmannsheil GmbH Bochum, Medical Faculty of Ruhr University Bochum, Bochum (GJ, PKZ, CHM-F), and Department of Anaesthesiology, Intensive Care and Pain Medicine, University Hospital of Muenster, Münster, Germany (EMP-Z).
Gunnar
G
Jess
Esther M
EM
Pogatzki-Zahn
Peter K
PK
Zahn
Christine H
CH
Meyer-Frießem
D000328:Adult; D018592:Cross-Over Studies; D004558:Electric Stimulation; D005858:Germany; D006339:Heart Rate; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods*; D059225:Nociception; D059226:Nociceptive Pain / Q000175:diagnosis* / Q000503:physiopathology; D010147:Pain Measurement / Q000379:methods*; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D016037:Single-Blind Method; D013997:Time Factors; D055815:Young Adult