FLACC Scale

FLACC Scale in Paediatric Pain Trials and Economic Evaluation

The FLACC Scale turns five observed behaviours into a pain score for infants, young children and children with cognitive impairment who cannot give a reliable rating of their own pain. Crellin and colleagues included 52 randomised trials that used the scale to measure an outcome in infants and children in their 2015 systematic review, so a health economist working on paediatric analgesia or anaesthesia often meets FLACC results as the clinical effect that a cost has to be set against. The scale carries no preference weights, which means a change in the FLACC total cannot become a QALY gain without separate evidence on how much the pain state reduces health-related quality of life. Merkel and colleagues first tested the scale after surgery in 89 children aged 2 months to 7 years, and a revised version, the r-FLACC, was later built for children with cognitive impairment.

How the five behaviour categories are scored

The rater watches the child and scores five categories of pain behaviour, which give the scale its name. They are facial expression, leg movement, activity, cry and consolability. Each category is scored 0, 1 or 2, and the five category scores are added to give a total between 0 and 10, with higher totals indicating more pain behaviour.

$$\text{FLACC} = F + L + A + C_{ry} + C_{on}, \qquad F, L, A, C_{ry}, C_{on} \in \{0, 1, 2\}$$

where $F$ is the face score, $L$ the legs score, $A$ the activity score, $C_{ry}$ the cry score and $C_{on}$ the consolability score, so the total runs between 0 and 10.

Merkel and colleagues published the scale in Pediatric Nursing in 1997. Their study observed 89 children aged 2 months to 7 years in the post-anaesthesia care unit after a range of surgical procedures. They examined agreement between raters, tested whether scores fell after analgesics were given and compared FLACC totals with the Objective Pain Scale and with nurses' global ratings of pain. The abstract reports high interrater reliability, a significant fall in FLACC scores after analgesia and agreement with both comparison measures, and the authors described their validity data as preliminary.

Two studies in 2003 extended the early evidence. Manworren and Hynan asked paediatric nurses to score 147 children under 3 years of age on several inpatient units before analgesia, at the predicted onset of the analgesic and at its predicted peak. They concluded that the tool is appropriate for preverbal children in pain from surgery, trauma, cancer or other disease processes. Willis and colleagues compared nurse-scored FLACC totals with self-reports on a faces scale in 30 children aged 3 to 7 years, about 20 hours after surgery. The two scores were significantly and positively correlated in the whole sample and in children aged 5 to 7, but the correlation was not significant in children under 5.

Validation in children with cognitive impairment and the r-FLACC

Children with cognitive impairment often cannot use a self-report scale at any age, so an observer score is frequently the only pain measure available to a trial or audit. Voepel-Lewis and colleagues reported in 2002 on 140 observations from 79 children with cognitive impairment. Nurses scored the FLACC before and after analgesics, parents rated pain on a visual analogue scale, children who could self-report did so, and blinded nurses later scored videotaped observations.

In that study FLACC scores correlated with parents' scores and fell after analgesics, which the authors took as evidence of validity. Correlations between raters were 0.5 to 0.8 for total scores and 0.3 to 0.8 for single categories, exact agreement gave kappa values of 0.2 to 0.65, and test-retest correlations were 0.8 to 0.883.

Malviya and colleagues then revised the tool. The r-FLACC adds more specific descriptors to the categories and lets parents add the individual pain behaviours of their own child. In their 2006 study, published in Paediatric Anaesthesia, 21 parents added individualised behaviours. Two nurses scored pain with the revised scale before and after an analgesic, children self-reported when able, and experienced nurses blinded to analgesic timing later scored the videotapes, giving 80 observations in 52 children aged 4 to 19 years. The authors reported improved reliability and validity for pain assessment in children with cognitive impairment.

Postoperative and procedural evidence

The validity of an outcome measure depends on the setting in which the measure is used, and the FLACC evidence is uneven across settings. Crellin and colleagues reviewed 25 psychometric evaluation studies and 52 randomised trials in 2015. They concluded that sufficient data address postoperative pain assessment in infants and children, that some positive data support use after surgery in children with cognitive impairment, and that data on procedural pain are limited and conflicting. Their overall judgement was that there are insufficient data to support the FLACC scale in all the circumstances and populations in which it is currently applied.

The same group reported in 2018 on 100 children aged 6 to 42 months filmed during a procedure, with 26 clinicians independently scoring the video segments. Interrater and intrarater reliability coefficients were high (0.92 and 0.87), but the authors stated that concerns remain about the specificity and design of the scale. Crying, struggling and difficulty in consoling a child can also reflect fear or distress, which makes specificity hard to establish during procedures.

The PedIMMPACT consensus, reported by McGrath and colleagues in 2008, listed the FLACC among measures of pain intensity for children aged 1 year and over, for procedural pain and for postoperative pain. The core outcome domains the same consensus set for acute paediatric pain trials are pain intensity, global judgement of satisfaction with treatment, symptoms and adverse events, physical recovery, emotional response and economic factors. A trial designed on these lines records the costs alongside the FLACC result.

Where FLACC scores enter trials and economic models

A FLACC result can enter an economic evaluation in three standard ways. The first is as the effect measure in a cost-effectiveness analysis in natural units, such as the cost per child kept below a chosen FLACC score or the cost per point of mean score reduction. That ratio can compare two analgesic regimens for the same procedure, but the ratio cannot be set against a QALY threshold or compared with programmes that improve other outcomes.

The second is as the rule that defines states in a decision tree or other model. A trial result such as the proportion of children with a FLACC score at or above a cut point within the first day after surgery can set the probability of a moderate or severe pain state, and that state can carry costs such as rescue analgesia or a longer recovery stay. The cut point is the analyst's choice and should be stated, because a different cut point changes the probabilities in every arm.

The third is as the starting point for a cost-utility analysis. Here the FLACC result only classifies the child, and the health state utility value attached to each pain state has to come from somewhere else, for example a preference-based measure for children such as the CHU9D or a published utility for a comparable state. A mapping function that predicted utilities from FLACC totals would need a dataset in which the FLACC and a preference-based measure were recorded for the same children at the same time.

Why a FLACC total cannot serve as a utility

A QALY weight has to sit on a scale where 1 is full health and 0 is dead, and its values have to reflect preferences between health states. The FLACC total meets neither condition. A total of 0 means no observed pain behaviour, which says nothing about the child's other health problems, and a total of 10 is not anchored to death. The categories are also scored on an ordinal scale, so the step between 2 and 4 is not known to matter as much as the step between 6 and 8, and dividing a FLACC total by 10 does not produce a utility.

Time matters as well. Most FLACC results describe pain over minutes or hours after surgery or during a procedure. Even a large utility decrement held for a day or two yields a very small QALY difference, so a cost-utility result for short-term pain relief is driven almost entirely by the assumed decrement and duration, and those numbers do not come from the FLACC itself.

Illustrative worked example of an analgesic comparison

All numbers in this example are illustrative and do not come from any trial. Two postoperative analgesic regimens are compared in children after day-case surgery, with 200 children in each arm. The analysts define a pain episode as any FLACC total of 4 or more in the first 24 hours, a cut point chosen for the illustration and not taken from a validated band.

1. Episode rates. Under the standard regimen 80 of 200 children have a pain episode, a rate of 80 / 200 = 0.40. Under the new regimen 50 of 200 do, a rate of 50 / 200 = 0.25. The difference is 0.40 − 0.25 = 0.15 episodes avoided per child.

2. Cost per episode avoided. The new regimen costs GBP 15 more per child once rescue analgesia and nursing time are included.

$$\frac{\Delta C}{\Delta E} = \frac{15}{0.15} = 100$$

where $\Delta C$ is the incremental cost per child in GBP and $\Delta E$ is the number of pain episodes avoided per child. The result is GBP 100 per pain episode avoided, a natural-unit ratio that a commissioner can judge only against other ways of avoiding postoperative pain in children.

3. Turning episodes into QALYs. Suppose an episode reduces utility by 0.2 for 0.005 years, a little under two days. Each episode then costs 0.2 × 0.005 = 0.001 QALYs, and the regimen gains 0.15 × 0.001 = 0.00015 QALYs per child.

$$\text{ICER} = \frac{15}{0.00015} = 100000$$

where 15 is the incremental cost per child in GBP and 0.00015 is the QALY gain per child. The ICER is GBP 100,000 per QALY gained.

The FLACC result supplied only the episode rates in step 1. The decrement of 0.2 and the duration of 0.005 years came from outside the trial, and halving either would double the ICER. A regimen that looks good value per episode avoided can look poor value per QALY, which reflects the short duration of the pain and not a failure of the regimen.

How the FLACC differs from nearby measures

A self-report pain scale, such as a numerical rating scale or a faces scale, asks the child to rate the pain and so yields a patient-reported outcome. The FLACC records what an observer sees, so the scale sits among the other kinds of clinical outcome assessment. Whether a particular FLACC rating counts as a clinician-reported outcome or an observer-reported outcome depends on who scores the rating, a trained nurse or a parent or carer, and a trial report should say which.

The FLACC also differs from generic measures used in children. The PedsQL describes health-related quality of life across several domains without preference weights, and the CHU9D adds preference weights so that its scores can feed a QALY calculation. The FLACC covers a single construct, pain behaviour at the time of observation, and like the PedsQL the FLACC is a non-preference-based measure. In paediatric economic evaluation the three can sit side by side in one trial, each answering a different question.

Limitations and common misreadings

A common error in using FLACC results is to read the score as more general than the evidence allows. Several forms of misreading recur.

• A high score shows pain behaviour, and in a procedure the same behaviours can come from fear. Crellin and colleagues found limited and conflicting evidence for procedural pain, so a trial of a procedural intervention that reports only FLACC may be measuring distress as much as pain.
• The 1997 validation covered children aged 2 months to 7 years after surgery, and Willis and colleagues found no significant link with self-report in children under 5. Use in older children or outside the postoperative setting rests on later and thinner evidence.
• The r-FLACC adds descriptors and individual behaviours to the original, so pooled results should say which version each trial used.
• A mean change of 1 point does not represent the same amount of pain at every level, and a responder definition based on a cut point is often easier to interpret.
• The responsiveness of the FLACC to analgesia says nothing about the value of the change, which has to come from preference-based evidence.

Sources

• Crellin DJ, Harrison D, Santamaria N, Babl FE. Systematic review of the Face, Legs, Activity, Cry and Consolability scale for assessing pain in infants and children: is it reliable, valid, and feasible for use? Pain. 2015;156(11):2132-2151. doi:10.1097/j.pain.0000000000000305
• Crellin DJ, Harrison D, Santamaria N, et al. The psychometric properties of the FLACC scale used to assess procedural pain. Journal of Pain. 2018;19(8):862-872. doi:10.1016/j.jpain.2018.02.013
• Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes. 4th ed. Oxford University Press; 2015.
• Malviya S, Voepel-Lewis T, Burke C, Merkel S, Tait AR. The revised FLACC observational pain tool: improved reliability and validity for pain assessment in children with cognitive impairment. Paediatric Anaesthesia. 2006;16(3):258-265. doi:10.1111/j.1460-9592.2005.01773.x
• Manworren RCB, Hynan LS. Clinical validation of FLACC: preverbal patient pain scale. Pediatric Nursing. 2003;29(2):140-146. https://pubmed.ncbi.nlm.nih.gov/12723828/
• McGrath PJ, Walco GA, Turk DC, et al. Core outcome domains and measures for pediatric acute and chronic/recurrent pain clinical trials: PedIMMPACT recommendations. Journal of Pain. 2008;9(9):771-783. doi:10.1016/j.jpain.2008.04.007
• Merkel SI, Voepel-Lewis T, Shayevitz JR, Malviya S. The FLACC: a behavioral scale for scoring postoperative pain in young children. Pediatric Nursing. 1997;23(3):293-297. https://pubmed.ncbi.nlm.nih.gov/9220806/
• Voepel-Lewis T, Merkel S, Tait AR, Trzcinka A, Malviya S. The reliability and validity of the Face, Legs, Activity, Cry, Consolability observational tool as a measure of pain in children with cognitive impairment. Anesthesia and Analgesia. 2002;95(5):1224-1229. doi:10.1097/00000539-200211000-00020
• Willis MHW, Merkel SI, Voepel-Lewis T, Malviya S. FLACC Behavioral Pain Assessment Scale: a comparison with the child's self-report. Pediatric Nursing. 2003;29(3):195-198. https://pubmed.ncbi.nlm.nih.gov/12836995/