Cpot.pdf

The Journal of Pain, Vol 11, No 10 (October), 2010: pp 983-987 Available online at www.sciencedirect.com

Assessing Pain Behaviors in Healthy Subjects Using the Critical-Care Pain Observation Tool (CPOT): A Pilot Study Yannick Tousignant-Laflamme,* Patricia Bourgault,y Ce´line Ge´linas,z,x and Serge Marchand{ * Universite´ de Sherbrooke, School of Rehabilitation, Faculty of Medicine and Health Sciences, Sherbrooke, Quebec, Canada. y School of Nursing, Faculty of Medicine and Health Sciences, Sherbrooke, Quebec, Canada. z McGill University, School of Nursing, Montreal, Quebec, Canada. x Centre for Nursing Research, Jewish General Hospital, Montreal, Quebec, Canada. { Universite´ de Sherbrooke, Departement of Neurosurgery, Faculty of Medicine and Health Sciences, Sherbrooke, Quebec, Canada.

Abstract: The Critical-Care Pain Observation Tool (CPOT) is a behavioral scale recommended by experts for pain assessment in critically ill patients unable to verbally communicate. The main goal of this study was to determine the relationship between self-reports of pain intensity and the CPOT score, and establish the sensibility and the specificity of the CPOT to different levels of pain intensity in healthy subjects. A total of 18 healthy subjects participated in the study (mean age = 37.8 years). All subjects underwent a 2 minutes noxious cold pressor test (CPT) at 7 C. Verbal pain ratings were obtained with a visual analog scale (0-100) while pain behaviors were videotaped. Afterwards, 2 independent evaluators quantified pain behaviors using the CPOT. Interrater reliability was supported with an ICC of 0.963 (95%CI [0.904-0.986]). A moderate positive correlation between the CPOT scores and self-reports of pain intensity during the CPT was found (r = 0.52, p = 0.028). Such result indicates that subjects reporting high level of pain showed a higher number or more intense pain behaviors. A cut-off score >2.5/8 on the CPOT led to a sensibility of 64% and a specificity of 86%. Results from this pilot study support that an increase of CPOT score is correlated with moderate to high levels of pain intensity and further support the clinical use of the CPOT. Perspective: This article presents the psychometric properties of a behavioral pain scale called the CPOT which was developed to assess pain in critically ill adults unable to self-report. Our results in healthy subjects showed that the CPOT behavioral score is significantly correlated with the self-report of pain intensity and supports its clinical use. ª 2010 by the American Pain Society Key words: Pain assessment, cold pressor test, experimental pain, facial expression, sensitivity and specificity.

T

he Critical-Care Pain Observation Tool (CPOT) is a behavioral scale which was initially developed to assess pain in critically ill adults unable to selfreport. It has previously been tested in postoperative, medical, and trauma intensive care unit (ICU) adult patients.1,2 In the validation process of the tool, verbal ICU patients were included in order to evaluate the association between pain behaviors and the gold Received October 13, 2009; Revised December 1, 2009; Accepted January 15, 2010. Address reprint requests to Yannick Tousignant-Laflamme, pht, PhD, Universite´ de Sherbrooke, Faculty of Medicine and Health Sciences, School of Rehabilitation, 3001, 12e avenue Nord, Sherbrooke, Que´bec, J1H 5N4, Canada. E-mail: [email protected] 1526-5900/$36.00 ª 2010 by the American Pain Society doi:10.1016/j.jpain.2010.01.266

standard of pain, ie, the patient’s self-report. The CPOT scores were associated with the presence of pain as reported by patients (ANOVAs, P # .001), and moderate positive correlations were also obtained with selfreports of pain intensity (r = .40–0.71, P # .05). The psychometric properties of the CPOT are supported in ICU patients, which makes this tool specifically recommended by many experts in pain and critical care for the detection of pain in this vulnerable population.6,7,12,16 Although the CPOT is considered as a valid scale for the assessment of clinical pain in critical care, there is still a need to explore its utility in other contexts and populations. As previously reported in a study of Ge´linas et al,4 a CPOT score >2 on an 8-point scale was associated with the presence of pain in postoperative ICU adult patients. Moreover, the CPOT was found to better classify patients 983

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with severe pain. However, it is still unknown if the CPOT is capable of detecting other levels of pain intensity. The main objective of this pilot study was to determine the relationship between self-reports of pain intensity and the CPOT score in healthy adults exposed to experimental pain, and to establish the sensibility and the specificity of the CPOT to different levels of pain intensity. Part of this work was presented at the 28th annual conference of the American Pain Society.19

Methods Participants After approval from the Local Research Ethics Committee (Ethics committee of the Etienne-LeBel Clinical Research Centre of the Centre Hospitalier Universitaire de Sherbrooke), healthy volunteers were recruited by a research assistant through local ads. We collected data from 18 volunteers, 9 men and 9 women (mean age 37.8 6 8.7 years); all were French-speaking communitydwelling individuals. None of the participants were suffering from any known diseases and none were taking medications that could alter pain perception. The entire experimental procedure lasted about 30 minutes and took place at the Clinical Research Centre of the Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Quebec, Canada. All participants gave their written informed consent for their participation in the study and received a $20 compensation.

Experimental Pain Procedure The experimental pain procedure consisted of a cold pressor test (CPT). During this procedure, the subjects were asked to immerse their right arm (above the elbow) in circulating cold water maintained at 7 C for 2 minutes. Although subjects were told that they could remove their arm at any moment, all tolerated the 2-minute immersion. Previous studies showed that the CPT adequately elicits a strong and prolonged pain sensation in healthy subjects18 or chronic pain patients.9 Furthermore, this type of experimental pain was shown to better mimic clinical pain than brief stimuli.15

Measures Self-Reports of Pain Intensity Pain intensity ratings were assessed during the experimental pain procedure every 15 seconds using a verbal numerical rating scale (VNRS) which ranged from 0 (absolutely no pain) to 100 (worst pain imaginable). It was previously shown that this scale has good ratio properties.8

Pain Behaviors Assessment Tool Pain-related behaviors were assessed using the CriticalCare Pain Observation Tool (CPOT), a tool including 4 typical behaviors (facial expressions, body movements,

muscle tension, compliance with the ventilator for mechanically ventilated patients or vocalization for verbal patients).1 Each behavior is rated on a 0 to 2 scale for a possible total score ranging from 0 to 8 (see Table 1 for a description of each behavior; refer to Ge´linas et al1 for a more detailed description of the tool). The CPOT was tested and validated in different ICU groups including postoperative cardiac surgery patients,1 trauma, other postoperative, and medical patients.2 Both the French version and the English version of the CPOT showed good psychometric properties. Weighted kappa from .52 to .88, and ICC from .80 to .93 were obtained for interrater reliability. Discriminant validity was supported with higher CPOT scores during a nociceptive procedure (eg, turning with or without other care) compared with rest or a nonnociceptive procedure (noninvasive blood pressure) (P # .001). As previously described, the CPOT score was found to be associated with the patient’s self-report of pain, the gold standard in pain measurement, which supports the criterion validity of the tool. A CPOT cut-off score >2 showed a sensitivity of 86%, and a specificity of 78% for the presence of pain during turning procedures in postoperative cardiac surgery ICU patients.4 While the CPOT appears to be a reliable and valid scale to measure the presence of pain in ICU patients unable to self-report, it must be noted that it cannot be used if the patient is unresponsive (eg, paralyzed, under neuromuscular blocking agents, or heavily sedated). Also, the CPOT is intended to support the detection of the presence of pain by the number and intensity of exhibited behaviors, and is not considered as a painintensity scale.

Procedures During the CPT, all subjects were videotaped in order to observe and assess their pain-related behaviors. Individual videotapes were viewed by 2 independent evaluators (different than the experimenter who gathered data during the CPT) in order to verify interrater reliability of the CPOT. Both evaluators were trained to use the CPOT by the author of the tool (CG) who explained the content of the CPOT and its scoring method. Both evaluators also practiced scoring pain behaviors with the CPOT by viewing educational videotapes of ICU patients prior to the conducting of the study. Since the subjects in our sample were not intubated, the vocalization item was used instead of ‘‘compliance with the ventilator.’’ Regarding muscle tension, the evaluators rated this indicator according to their perception about how relaxed or tense the subjects appeared during the CPT. For instance, foot tapping was considered as very tense (score of 2) whereas making a fist with the hand was considered as tense (score of 1).

Data Analysis Descriptive statistics (means, standard deviations) were obtained for pain intensity and pain behaviors (CPOT). Interrater reliability between the 2 evaluators of the CPOT scores was examined using interclass correlation coefficient (ICC). We used correlation coefficient to

Tousignant-Laflamme et al Table 1.

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Frequencies (n) of Individual Behavioral Indicators of the CPOT During the CPT

Facial expression Body movements Vocalization Muscle tension

SCORE OF 0

SCORE OF 1

SCORE OF 2

Relaxed, neutral 4 (22%) Immobile, normal position 9 (50%) Normal tone or no sound 11 (61%) Relaxed 7 (39%)

Tense 7 (39%) Protection movements 9 (50%) Sighing, moaning 6 (33%) Tense or rigid 5 (28%)

Grimacing 7 (39%) Restlessness 0 (0%) Crying out, sobbing 1 (5%) Very tense 6 (33%)

examine the relation between self-reports of pain intensity and CPOT scores. Sex differences in regards to CPT pain intensity and CPOT scores were assessed using a Mann-Whitney test for independent samples in order to make sure no sex differences were present. Finally, ROC curve analysis was used to calculate the sensitivity and the specificity of the CPOT to pain intensity.

Results Self-Reports of Pain Intensity and CPOT Scores The mean pain intensity during the CPT was 74.8 6 21.1 and no gender difference was observed (T = 91.5, P = .60). A percentage of 72% of subjects rated their pain as severe (70–100/100), 17% as moderate (40–69/100), and only 11% as mild (1–39/100). The mean CPOT score for all subjects was 2.83 6 2.35 (see Table 1 for frequencies of individual items) and again no gender difference was found (T = 95.5, P = .39).

CPOT Interrater Reliability Interrater reliability of the CPOT scores was supported with high interclass correlation coefficients (ICC = .963, 95%CI [.904–.986]), suggesting that both evaluators reached similar ratings of pain behaviors when viewing the videotapes.

Correlation, Sensibility and Specificity of the CPOT to Pain Intensity During the CPT, a significant moderate positive correlation was obtained between the CPOT scores and the self-reports of pain intensity (r = .52, P =. 028). Sensibility (Se) and specificity (Sp) were calculated using Receiver-Operating Characteristic (ROC) curve analysis. To allow determination of sensitivity and specificity of the CPOT, the subject’s self-report of pain intensity was used as the gold-standard criterion. Since pain intensity was a continuous variable (0–100), they were dichotomized as above or below 60/100 which refers to moderate pain, and also above or below 40/100 for mild pain. For verbal pain ratings greater than 60/100, the threshold for best Se (81%) and Sp (86%) was found to be a score >1 on the CPOT. The AUC was significant and indicated moderate-to-good discriminative properties (AUC: .799; P = .004). Regarding a cut-off score >2.5 on the CPOT, which would be consistent with previous findings in postoperative ICU patients,4 the Se was 63% and Sp remained at 86% (See Table 2 for complete results).

The AUC remained unchanged (AUC = .786; P = .015) indicating good discriminating properties. Finally, using a gold-standard criterion of 40/100 on the NVRS, the best cut-off score on the CPOT was >1 with Se of 62.5% and Sp of 100% (AUC = .86, P > .001). However, Se was lower (50%) at a cut-off score >2.5 on the CPOT (See Table 3 for complete results). Again, the AUC was significant and indicated good discriminative properties (AUC: .89; P = .001).

Discussion In this pilot study, a moderate positive correlation was found between the self-reports of pain intensity and the CPOTscores while subjects were exposed to an experimental painful procedure, the cold pressor test (CPT). This result suggests that the higher the level of pain, the higher was also the CPOT score, and this is consistent with previous findings in critically ill adult patients.1,2 Such information is crucial in clinical settings. When a patient is unable to self-report pain, valid behavioral pain scales should be used as an alternative measure for the detection of pain and the evaluation pain management. This is in fact recommended in the clinical guidelines of the American Society of Pain Management Nursing (ASPMN) for pain assessment in nonverbal populations.7 Facial expression and muscle tension were the behaviors for which a higher proportion of the subjects (>60%) received a CPOT score of 1 or 2. On the other 2 behavioral indicators, most subjects (>90%) received a score of 0 or 1. Such observations are consistent with previous studies in critical care. In fact, in the study of Ge´linas et al,3 facial expression and muscle tension were found to be significantly related to the patient’s self-report of pain (n = 141). Similar findings were obtained in the

Se and Sp for Overall CPOT Scores: Pain Cut-Off $ 60/100

Table 2. CRITERION $0 >0 >0,5 >1 >1,5 >2,5 >3 >4 >5,5 >7

SENSITIVITY

95% CI

SPECIFICITY

95% CI

100,00 90,91 90,91 81,82 72,73 63,64 54,55 45,45 9,09 0,00

71,3 - 100,0 58,7 - 98,5 58,7 - 98,5 48,2 - 97,2 39,1 - 93,7 30,9 - 88,8 23,5 - 83,1 16,9 - 76,5 1,5 - 41,3 0,0 - 28,7

0,00 14,29 28,57 85,71 85,71 85,71 85,71 85,71 100,00 100,00

0,0 - 41,1 2,4 - 57,8 4,5 - 70,7 42,2 - 97,6 42,2 - 97,6 42,2 - 97,6 42,2 - 97,6 42,2 - 97,6 58,9 - 100,0 58,9 - 100,0

Abbreviations: Se, sensitivity; Sp, specificity; CI, confidence intervals.

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Se and Sp for Overall CPOT Scores: Pain Cut-Off $ 40/100

Table 3. CRITERION $0 >0 >0,5 >1 >1,5 >2,5 >3 >4 >5,5 >7

SENSITIVITY

95% CI

SPECIFICITY

95% CI

100,00 93,75 87,50 62,50 56,25 50,00 43,75 37,50 6,25 0,00

79,2 - 100,0 69,7 - 99,0 61,6 - 98,1 35,5 - 84,7 29,9 - 80,2 24,7 - 75,3 19,8 - 70,1 15,3 - 64,5 1,0 - 30,3 0,0 - 20,8

0,00 50,00 50,00 100,00 100,00 100,00 100,00 100,00 100,00 100,00

0,0 - 80,7 8,2 - 91,8 8,2 - 91,8 19,3 - 100,0 19,3 - 100,0 19,3 - 100,0 19,3 - 100,0 19,3 - 100,0 19,3 - 100,0 19,3 - 100,0

Abbreviations: Se, sensitivity; Sp, specificity.

Thunder Project II14 in which grimacing and rigidity were the most frequent behaviors in critically ill patients who experienced procedural pain (n = 4,278) compared with those without procedural pain (n = 1,558). Facial expression (predominantly brow lowering, orbit tightening, levator contraction and eye closure)13 has also been found to be the best predictor of pain in both experimental10 and clinical studies.11 There is strong evidence that these facial responses constitute the core of the ‘‘pain face’’ and support our findings and the results obtained in critical care. Although our experimental pain procedure was brief, it did cause important levels of pain where over 70% of the subjects reported experiencing severe pain (>70/ 100). This is in accordance with previous studies which showed that this tonic painful stimulus produces a high level of pain.5,17 In this sample of healthy subjects exposed to an experimental pain procedure, the threshold associated with maximization of the sums of sensitivity and specificity using gold-standard criteria of both mild (40/100) and moderate pain (60/100) was found to be a score greater than 1 on the CPOT. However, better results were obtained using moderate pain (60/100) as a gold-standard criterion. This is consistent with previous findings in postoperative ICU patients which showed that the CPOT could adequately classify patients with higher levels of pain.4 In fact, even if subjects’ self-reports of pain intensity and pain-related behaviors measured with the CPOT are moderately correlated, these 2 methods of assessing pain are complementary in nature, referring to the sensory and the behavioral components of pain. Moreover, in the clinical recommendations of the ASPMN,7 experts strongly highlight that behavioral scores are not accurate reflections of pain intensity and should not be translated into categories of pain levels but should rather be used for the detection of the presence of pain. On the other hand, evaluating the sensitivity and the specificity of a behavioral scale is quite useful for clinicians as it provides them with valuable information to guide their practice. Regardless of the gold-standard criterion (mild or moderate pain intensity) used to establish sensitivity and specificity of the CPOT, specificity showed

higher values (85.7% and 100% respectively). In other words, high specificity would help to adequately rule in patients in pain, and to avoid administering an analgesic to a patient who does not need it (what is commonly feared in clinical practice). It must be noted that the best cut-off score on the CPOT was >1 in this sample of healthy subjects as compared with postoperative (ie, cardiac surgery) ICU patients (n = 99) for whom the best CPOT cut-off score was >2.4 In another study by Ge´linas and Johnston2 with 30 critically ill adults with various diagnoses (trauma, postoperative, medical), the best cut-off score on the CPOT was found to be >3 with a sensitivity of 66.7% and a specificity of 83.3%. This smaller ICU group represented critically ill patients who were sicker than cardiac surgery ICU patients. Moreover, this sicker group received higher doses of analgesic or sedative agents. The use of such medication may have an impact on the behavioral reactions to painful procedures and on the CPOT scores as well. Indeed, healthy subjects were not receiving any medication and the best CPOT cut-off was found to be the lowest documented so far. However, the cut-off score >2.5 on the CPOT in this healthy group showed acceptable results of sensitivity and specificity, and appears to be more realistic for the detection of pain in a clinical context. Furthermore, such criteria would be consistent with results from the Thunder Project II in which critically ill patients without procedural pain exhibited less than 2 behaviors, and in which patients with procedural pain were at least 2 times more likely to have increased behaviours.14

Limitations We had a relatively small sample size and our painful procedure mostly produced high (severe) levels of pain intensity. However, since the distribution of perceived pain intensity was not equivalent for mild, moderate and severe pain, this might have influenced the results. Furthermore, since pain-related behaviors were assessed using videotapes, the evaluation of muscle tension substantially differs from the initial method (use of passive flexion and extension of upper limbs)—this might have led the evaluator to underscore this particular aspect. However, this observation might be counterbalanced by the fact that the evaluators were aware of the verbal pain ratings of the participants during the CPT, which might have led them to overscore this aspect. Finally, pain behaviors in healthy subject may differ from those who are critically ill and may not reflect the situation observed in the ICU. Based on this, the psychometric properties of a tool cannot be generalized to any patient or subject groups, and should be examined in different groups and specific settings.

Conclusions This is the first study in which the CPOT was used to assess pain behaviors in healthy adult subjects exposed to experimental pain. No matter the context (clinical versus experimental pain) or the participant sample, it seems

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that the CPOT behavioral score is significantly correlated with the self-report of pain intensity. Even if acceptable results of sensitivity and specificity were obtained, a cut-off score on the CPOT cannot be fixed at this time. Further research with larger samples and in various context or procedures is still needed.

Acknowledgments

References

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There are no financial or other relationships that might lead to a conflict of interest. The authors would like to thank Miss Kathya Daigle for her enthusiastic involvement in this project.

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