Valid and reliable assessment of pain is essential for effective clinical care and research. Pain assessment is necessary to determine the type of pain, whether pain management is adequate, whether analgesic or analgesic dose changes are required, and whether additional interventions are warranted, including whether specialty consultation is needed [1▪▪]. Although pain is universally acknowledged to be a complex subjective multidimensional experience, one-dimensional tools are often used as the main assessment method in the management of acute pain.
Campaigns of the 1990s to make pain ‘the fifth vital sign’ did much to increase the needed visibility and attention to pain assessment, prompting routine screening for pain and the development of organizational policies that demanded timely reassessment. Unfortunately, the heavy emphasis on use of simple pain intensity scales resulted in a number of unintended negative consequences. Reliance on numeric ratings of pain intensity to guide treatment decisions became linked to reports of serious adverse events [2,3]. Vila et al.  reported the incidence of opioid over sedation per 1000 000 inpatient hospital days increased from 11 to 24.5 (P < 0.001) following use of an acute pain treatment algorithm guided by a numerical pain rating. Empirical evidence has not been able to connect improved compliance with regular pain assessments to better pain treatment or patient outcomes [4–6,7▪▪]. This may, in part, be explained that documentation of pain is treated as a regulatory nuisance and no action is taken in response to the assessment data. Regardless, an explicit approach to the methods and documentation of pain assessment using valid and pragmatic methods is warranted to facilitate communication and well tolerated and effective pain management.
The aim of this review was to highlight current challenges and trends in acute pain assessment tools and methods.
Although ‘objective’ measures such as pain-related behaviors or vital signs may, at times, be useful to determine the presence or intensity of pain, the gold standard for pain assessment is self-report. For brief episodes of acute pain with an obvious source, assessment of location and intensity may suffice in clinical practice. The two major domains assessed in acute pain trials are pain intensity and pain relief . The most commonly used pain assessment tools for acute pain in clinical and research settings are the Numerical Rating Scales (NRS), Verbal Rating Scales (VRS), Visual Analog Scales (VAS), and the Faces Pain Scale-Revised (FPS-R) [9,10]. The VAS and NRS are equally sensitive and function best for a patient's subjective feeling of the intensity of pain . Categorical scales such as mild, moderate, and severe pain may also be useful; however, a systematic literature review of studies comparing NRS, VRS, and VAS in adults suggests that a scale with only three response options offered little opportunity for discrimination and that there is relatively little gain in precision with more than seven options and hardly any above nine . The same review reported the VRS was preferred by the less educated and the elderly and the NRS was the instrument of choice in an age-mixed population and in patients with chronic pain . In analgesic trials, a change of at least 2 on a 0–10 pain intensity scale, or 33% pain intensity difference appears to represent patient-determined clinically important relief .
Regardless of the tool used, the intensity of acute pain is best assessed both at rest (important for comfort) and during movement (important for function and risk of postoperative complications) . Movement evoked pain is more intense and less responsive to opioid treatment . Assessment of the impact of pain on physical and emotional function and sleep are also critical in acute pain management. Although pain intensity ratings have been associated with impairments in function and quality of life, a nonlinear relationship between opioid dose and the visual analog scale has been demonstrated .
ASSESSMENT IN COGNITIVELY IMPAIRED ADULTS INCLUDING UNCONSCIOUS OR SEDATED PATIENTS
The American Society for Pain Management Nursing position statement on pain assessment in patients unable to self-report  recommends a hierarchy of techniques beginning with attempts to obtain self-report, then searching for potential causes of pain, observing patient behaviors, followed by obtaining proxy reporting of pain behavior and activity changes from family members, parents, unlicensed, and professional caregivers.
Five different pain assessment tools have been examined for use with unconscious or sedated intensive care patients . All five tools include behavioral indicators and three include physiological indicators. The Critical-Care Pain Observation Tool  and the Behavioral Pain Scale  have superior reliability validity and reliability testing compared with other adult intensive care tools including the Pain Assessment and Intervention Notation (PAIN) algorithm , the Nonverbal Pain Assessment Tool , and the Adults Nonverbal Pain Scale  although all would benefit from further testing [22,23].
Of note, caution is needed when using a behavior pain tool as an instrument developed for persons in one context (e.g., dementia) may not be appropriate for patients in another (e.g., sedated patients in the ICU). Also, a summed behavioral pain score is not the same as a self-reported pain intensity rating as it may only indicate the presence of pain and may not be sensitive to pain relief.
ASSESSMENT TOOLS FOR CHILDREN
Eleven self-report and 20 observer-rated tools exist to assess pain in children without cognitive impairment and four for children with cognitive impairment . Strong evidence supports the use of the behavioral variables of facial expressions and body movements and the physiologic variables of heart rate and oxygen saturation to assess acute pain in infants . Of the 20 observational pain scales for children aged 3–18 years, the Pediatric Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials group [26,27] recommended use of either the Face, Legs, Activity, Cry, Consolability (FLACC)  or the Children's Hospital of Eastern Ontario Pain Scale  for assessing pain intensity associated with medical procedures and other brief painful events. The FLACC is recommended as first choice for postoperative pain in hospital and the Parents’ Postoperative Pain Measure  is recommended for postoperative pain following discharge. The COMFORT scale  is recommended for pain in children in critical care as the only well studied instrument that makes explicit accommodation for constraints placed on the behavioral expression of pain by mechanical ventilation and physical restraint.
A critical appraisal of assessment tools in children characterized the quality of literature as poor and commented that many of the papers presenting new tools were simply adding to or modifying existing and already validated tools . Contextual influences on pain expression must also be considered in the assessment of children. Healthcare providers and parents may actively discourage children from displaying their pain and children have varying development capacity to feign, exaggerate, or suppress outward signs of pain .
CONCEPTUAL SHIFT AWAY FROM NUMBERS TO ASSESSMENT AS A SOCIAL TRANSACTION
Pain assessment clearly involves more than just quantifying the intensity of pain. Pain is a biopsychosocial experience that involves both sensory and emotional feelings. A more comprehensive assessment can help determine the type of pain (e.g., neuropathic, visceral, somatic, muscle spasms), how the pain affects function, what interventions have been effective and patient fears and misconceptions about pain management. Validated multidimensional tools including the Brief Pain Inventory  and the McGill Pain Questionnaire  are designed for chronic pain and can be challenging to administer during an acute pain event in part because of length . Similarly, multidimensional tools specifically designed for acute pain, such as the American Pain Society Patient Outcome Questionnaire  and the International Pain Outcomes Questionnaire , are intended for purposes other than direct care and are not suitable for frequent reassessments often required in minute to hour intervals demanded by acute pain. A number of nonvalidated multidimensional mnemonic tools, however, can be found in clinical practice to direct a more comprehensive initial pain assessment [37–39] (Table 1). Assessment domains that are common in these tools include location, quality, severity, temporal characteristics, and aggravating and alleviating factors with notable absence of items that assess impact of pain on physical or emotional function or sleep.
In reality, clinical assessment is rarely based solely on self-reported pain intensity ratings and has been described as a social transaction with adults  and children . This means assessment is a more complex communication process between the patient and clinician composed of diverse interpersonal and intrapersonal dimensions that interact and affect each other. A study of patients with chronic pain  identified a number of factors patients considered consciously and unconsciously when making a pain rating. This includes among other things the impact of pain on their activities, their level of distress and fatigue, a comparison of current pain with their usual and worst pain, and what the clinician might think of a given pain rating. Of note, over half the respondents stated that they found it difficult to separate the different dimensions of pain, and there was a tendency to feel fraudulent if pain were rated at a low level but they required help. The authors concluded that a pain rating is better conceptualized as an attempt to construct meaning, influenced by a range of internal and external factors and private meanings.
CLINICALLY ALIGNED PAIN ASSESSMENT TOOL
The need for a conceptual shift away from simple pain intensity ratings has resulted in at least one new tool named the Clinically Aligned Pain Assessment (CAPA) tool  (Table 2). The local impetus for designing the tool included patient and staff frustration with repeatedly having to equate the experience of pain as a number from 0 to 10. Instead, the CAPA tool functions as a conversation guide to gather categorical information during the course of a more natural conversation. Similar to a mnemonic, the tool provides a framework for the clinician to elicit questions but with a distinct focus on how comfortable a patient is, whether discomfort is improving or worsening, whether the patient is able to participate in recovery activities, and if pain is interfering with sleep. The clinician then codes and documents the conversation. At no point, does the patient rate any scale or check boxes of responses.
In a 4-week quality improvement study on four inpatient units that covered surgery, medicine, cancer, and orthopedic services with more than 12 000 total pain assessment observations, statistical data analysis revealed both patients and nursing staff members strongly preferred CAPA to NRS . The probability of correctly classifying clinical pain states (defined as severity and effectiveness of pain management) was 81% for CAPA compared with 42% with NRS. The study also revealed improvements in staff satisfaction and the patient satisfaction, including the Hospital Consumer Assessment of Healthcare Providers and Systems postdischarge survey question ‘How well was your pain controlled’. The creators concluded that having brief natural conversations about what patients were feeling seems to have greater pragmatic validity and acceptance, while providing more precise, consistent, accurate measurement than the NRS. Clearly, more study is needed, but the CAPA offers a pragmatic and innovative shift away from one-dimensional pain intensity ratings.
A fundamental acknowledgement is that no single tool can be broadly recommended for assessing acute pain in all contexts. A plethora of similar assessment tools suitable to age and cognitive ability are available, but little is known about clinical utility in terms of timing, frequency, and clinician response. The optimal frequency of reassessment is likely to depend on a number of factors, including the type or surgical procedure, the adequacy of initial pain relief, the presence of side-effects, presence of comorbidities, and changes in clinical status. The selection of a particular pain assessment tool should be based on factors such as developmental status, cognition and level of consciousness, educational level, and likely cultural differences. Pain assessment should be considered a process, rather than a tool. New methods such as the CAPA that help translate the patient experience into more than a number would be useful.
The author wishes to thank and acknowledge Gary Donaldson, PhD, Professor and Director Pain Research Center, Department of Anesthesiology at the University of Utah, for permission to share the CAPA tool and review of this manuscript.
Financial support and sponsorship
Conflicts of interest
The author has received honorarium past 12 months for participation in Advisory Boards for Pacira, Zogenix, and Janssen Pharmaceutica.
There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
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