Cerebral oxygenation for pain monitoring in adults is ineffective: A sequence-randomized, sham controlled study in volunteers.

BACKGROUND: Pain assessment by Numeric Rating Scale (NRS) is considered to be good clinical practice, but objective pain assessment is still a challenge. Near infrared spectroscopy (NIRS) measures cerebral tissue oxygen saturation (SctO2) that increases with cortical-neuronal activity and may provide point-of-care bedside pain monitoring. Analogous to promising studies in newborns, we hypothesize that different levels of SctO2 can probably quantify pain intensity. SctO2 may increase following painful in contrast to non-painful or sham stimuli and may correlate with pain intensity as assessed by NRS in volunteers. METHODS: Twenty healthy male students (24.2±1.9 years), recruited via local advertising, were consecutively included in a sequence-randomized, sham-controlled, single-blinded study. SctO2 was recorded continuously with two NIRS sensors on the forehead. After resting, four stimuli were applied in a random order on the right forearm (unexpected and expected electrical pain, expected non-painful and sham stimuli). Blinded subjects were asked to rate each stimulus on NRS. STATISTICS: RM-ANOVA; Wilcoxon or paired Student t-test; Spearman's rank correlation; P<.05. RESULTS: Resting volunteers showed SctO2 of 72.65%±3.39. SctO2 significantly increased for about 60 to 70s until a maximum after unexpected painful (74.62%±3.9; P=.022) and sham stimuli (74.07%±3.23; P=.014). Expected painful (P=.139) and non-painful stimuli (P=.455) resulted in no changes in SctO2. NRS scores (median, IQR) were rated significantly higher after expected (5.25, 3.5 to 6.75) than after unexpected (4.5, 3 to 5; P=.008) pain. No strong correlation was found between NRS and SctO2. CONCLUSIONS AND IMPLICATIONS: Contrary to our expectations, measuring SctO2 via a two-channel NIRS is not able to remediate the lack of objective bedside pain assessment under standardized experimental conditions in alert adults. TRIAL REGISTRATION: DRKS 00011575 (retrospectively registered).

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. OBJECTIVES: 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. DESIGN: Randomised stimuli and placebo-controlled, single-blinded study. SETTING: Experimental pain simulation laboratory, Bochum, Germany. PARTICIPANTS: Twenty healthy male students, (mean ±â€Šstandard deviation; 24.2 ±â€Š1.9 years) recruited via local advertising, were consecutively included. INTERVENTION: 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. MAIN OUTCOME MEASURES: 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 ±â€Š10.71. ANI decreased after a random stimulus (maximal decrease of 25.0 ±â€Š7.3%), 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. CONCLUSION: 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.