Biological inflammatory markers mediate the effect of preoperative pain-related behaviours on postoperative analgesics requirements.

BACKGROUND: The predictive value of an individual's attitude towards painful situations and the status of his immune system for postoperative analgesic requirements are not well understood. These may help the clinician to anticipate individual patient's needs. METHODS: Sixty patients, who underwent a laparoscopic cholecystectomy under standardised general anaesthesia, were included. The total analgesic requirements during the first 48 h were the primary endpoint (unitary dosage, UD). The individual's attitude towards imaginary painful situations was measured with the Situational Pain Scale (SPS). The emotional status was assessed by the Hospital Anxiety and Depression Scale (HADS) and the inflammatory status by the neutrophil-to-lymphocyte ratio (NLR). RESULTS: Univariate analyses revealed a significant association between UD and SPS, HADS and NLR. A negative relationship between SPS and NLR (NLR = 0.820-0.180*SPS;R(2) = 0.211;P < 0.001) and a positive relationship between SPS and HADS (HADS = 14.8 + 1.63*SPS; R(2) = 0.159;P = 0.002) were observed. A multiple linear regression analysis showed that the contribution of NLR to the UD was the most effective. A mediation analysis showed a complete mediation of the effect of SPS on UD (R(2) = 0.103;P = 0.012), by the NLR (SPS on NLR: R(2) = 0.211;P = <0.001), the HADS (SPS on HADS: R(2) = 0.159;P = 0.002). The variance in UD explained by the SPS was indirect and amounts to 46% through NLR and to 34% through HADS. CONCLUSIONS: In this series, preoperative pain-related attitudes (SPS) were associated with the postoperative analgesic requirements (UD) after a cholecystectomy. Eighty per cent of this effect was mediated by the HADS and the NLR.

The fine tuning of pain thresholds: a sophisticated double alarm system.

Two distinctive features characterize the way in which sensations including pain, are evoked by heat: (1) a thermal stimulus is always progressive; (2) a painful stimulus activates two different types of nociceptors, connected to peripheral afferent fibers with medium and slow conduction velocities, namely Adelta- and C-fibers. In the light of a recent study in the rat, our objective was to develop an experimental paradigm in humans, based on the joint analysis of the stimulus and the response of the subject, to measure the thermal thresholds and latencies of pain elicited by Adelta- and C-fibers. For comparison, the same approach was applied to the sensation of warmth elicited by thermoreceptors. A CO(2) laser beam raised the temperature of the skin filmed by an infrared camera. The subject stopped the beam when he/she perceived pain. The thermal images were analyzed to provide four variables: true thresholds and latencies of pain triggered by heat via Adelta- and C-fibers. The psychophysical threshold of pain triggered by Adelta-fibers was always higher (2.5-3 degrees C) than that triggered by C-fibers. The initial skin temperature did not influence these thresholds. The mean conduction velocities of the corresponding fibers were 13 and 0.8 m/s, respectively. The triggering of pain either by C- or by Adelta-fibers was piloted by several factors including the low/high rate of stimulation, the low/high base temperature of the skin, the short/long peripheral nerve path and some pharmacological manipulations (e.g. Capsaicin). Warming a large skin area increased the pain thresholds. Considering the warmth detection gave a different picture: the threshold was strongly influenced by the initial skin temperature and the subjects detected an average variation of 2.7 degrees C, whatever the initial temperature. This is the first time that thresholds and latencies for pain elicited by both Adelta- and C-fibers from a given body region have been measured in the same experimental run. Such an approach illustrates the role of nociception as a "double level" and "double release" alarm system based on level detectors. By contrast, warmth detection was found to be based on difference detectors. It is hypothesized that pain results from a CNS build-up process resulting from population coding and strongly influenced by the background temperatures surrounding at large the stimulation site. We propose an alternative solution to the conventional methods that only measure a single "threshold of pain", without knowing which of the two systems is involved.

How many response levels do children distinguish on faces scales for pain assessment?

Faces scales are one of the most commonly used instruments to assess pain intensity in children. Most available faces scales present five to seven faces. The present research was conducted to investigate the ability of 4- to 7-year-old children to distinguish the response categories of different faces scales. In the first study, 121 children were asked to rate painful situations on a 3- and a 6-level faces scale commencing with a smiling 'no pain' face. Children were divided into two age groups (4-5 and 6-7 years). Investigations of the category functioning were performed with a rating scale Rasch model for each age group. Results revealed the low performances of the 6-level faces scale as compared to the 3-level faces scale and also the difficulty children experienced in scoring the imaginary painfulness of items. Consequently, a second study was conducted. In this second study, 76 children were asked to rate pictures depicting painful situations on a 3-level faces scale beginning with a neutral 'no pain' face. Results of this second study confirmed an improvement in the ability to distinguish the three response categories with age. The 4-5 year-old children could only distinguish two response categories and the 6-7 year-old children were able to discern the three levels of the 3-level faces scale. In conclusion, young children do not distinguish as many faces as proposed by the majority of available faces scales. These results strongly recommend a reduction in the number of response levels of faces scales for pain assessment in children.

Measure of experimental pain using Rasch analysis.

Most common instruments used to assess the painfulness of nociceptive stimuli and the perception of such stimuli are ordinal. This property limits arithmetical operations and statistical procedures that can be applied on their numbers. The Rasch methodology provides mathematical procedures for transforming scores on an ordinal scale into measures on an interval scale. The present paper aims at presenting the basics of this methodology by applying it to the measurement of experimentally induced pain. Six blocks of seven CO(2) laser heat stimuli varying in intensity were delivered on the hand of 100 healthy subjects. They rated their pain perception on a three-level verbal rating scale (not painful, slightly painful, painful). One member of the family of Rasch models, the many-facet model, was applied to the analysis of these ratings. The analysis provided linear measures of the painfulness for each intensity of stimulation, of the pain perception of each subject and of the painfulness of each successive block. All these measures are located on a single pain perception continuum. Advantages and disadvantages of this methodology will be discussed in terms of subsequent possible mathematical analyses, statistical tests and implications for experimental and clinical investigations.