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Moving Beyond the 0–10 Scale for Labor Pain Measurement

2016; Lippincott Williams & Wilkins; Volume: 123; Issue: 6 Linguagem: Inglês

10.1213/ane.0000000000001641

1526-7598

Brendan Carvalho, Jill M. Mhyre,

Pregnancy-related medical research

When laboring women request epidural analgesia, many expect complete pain relief. Despite best intentions and great efforts by anesthesia providers, this expectation often is unmet, and breakthrough pain on the labor and delivery unit is common. Rapid and accurate diagnosis and targeted treatment of breakthrough pain are cornerstones of high-quality obstetric anesthesia care; however, it can be tempting to dismiss women with breakthrough pain as unrealistic, naive, or "high-maintenance." Sadly, unmet expectations for pain relief appear to be most acute among nonwhite women with low levels of education, literacy, and numeracy.1 The importance of effective treatment for breakthrough pain has been obscured by the fact that pain control in labor is only moderately predictive of maternal satisfaction with childbirth.2 Provided that neonatal outcome is good, maternal satisfaction is often high irrespective of labor pain scores or analgesia provided. Personal expectations, caregiver-patient relationships, peripartum support, and patient involvement in decision making often override the influence of pain when women evaluate their childbirth experience.3 Indeed, for a subset of women with robust coping skills, self-efficacy, support, and a strong desire to avoid neuraxial analgesia, pain scores and the quality of any pain relief bear little relationship to satisfaction.4,5 In fact, many women seeking unmedicated birth prefer if clinicians not even ask about pain.6 For laboring women who desire complete pain relief, the quality of analgesia achieved bears a more direct relationship with maternal satisfaction with analgesic services.2 For example, among women receiving epidural analgesia, breakthrough pain requiring top-ups by the anesthesiologist is among the strongest predictors of dissatisfaction with analgesic services.7 Earlier requests for analgesia and greater analgesic requirements in early labor, however, have been associated with dysfunctional labor and eventual need for cesarean delivery.8 Maternal requests for epidural rescue boluses also may predict future failed epidural anesthesia top-ups for cesarean delivery.9 One of the real barriers to effective diagnosis and targeted treatment for breakthrough pain is an absence of high-quality labor pain measurement tools. Analog pain intensity scores such as the verbal rating scale (none, mild, moderate, and severe), numerical rating scales (NRS 0–10, 0 = no pain and 10 = worst pain imaginable), and visual analog scales (0–100, presented as a 100-mm long line, from 0 = no pain to 100 mm = worst pain imaginable) are used ubiquitously in a clinical and research settings to measure labor pain and determine analgesic efficacy.10 Despite their widespread use, particularly the NRS, these scales are unidimensional, measuring only the intensity of pain, and lack many characteristics of an ideal psychometric pain instrument in a labor setting. The dynamic and progressive nature of labor pain is poorly captured by analog pain intensity scales.11 Mathematical analysis of pain scores in the first stage of labor indicates a sigmoidal relationship between cervical dilation and reported pain scores but with substantial intersubject variability.12 It is possible that this sigmoidal relationship is an artifact of the tool used to measure pain rather than characteristic of the underlying phenomena it seeks to describe. As labor progresses and the true magnitude of pain is revealed, women's understanding of "severe" or "worst pain imaginable" often shifts. These scales have an inherent "ceiling" because of the 10- or 100-mm limit, and women in qualitative studies have called for the ability to rate pain that is beyond "worst imaginable." Because of constraints within the 11-point NRS, the calibration of each incremental increase in analog score becomes increasingly distorted. Specifically, pain ratings close to the 10- or 100-mm limit increase by a smaller amount than pain scores further down the scale, and pain beyond the original score or scale limit still get recorded as 10 or 100 mm. Translation of these continuous analog scores to categorical descriptors (eg, none, mild, moderate, and severe pain) also may vary significantly among individuals. In one study, patients' 95% confidence interval ranking of moderate and severe pain was 15 to 83 mm and 39 to 100 mm, respectively.13 The experience of childbirth pain is multidimensional and complex. Analog pain intensity scales do not account for interactions among the intensity of contraction, the presence of any rest between contractions, the relative duration of that rest, the total duration of labor pain, and the influence of coping, intrapartum support, and sleep deprivation. Laboring and recently delivered women place more importance on pain intensity than duration (eg, stating that pain intensity of 5/10 for 2 hours is preferable to 10/10 for 1 hour).14 Cognitive and emotional factors, including women's expectations and fears surrounding pain relief, impact both the experience of labor pain and the use of pain measurement instruments.15 For the purpose of diagnosing and optimally managing breakthrough labor pain, it is particularly problematic that analog scales do not differentiate the nature or location of pain. Labor pain may change from intermittent visceral cramping pain with uterine contractions to sharp and/or continuous somatic pain closer to delivery.16 Given all the aforementioned limitations of analog pain scales, we are encouraged that this edition of Anesthesia and Analgesia includes a publication by Angle et al17 in which they examine the Angle Labor Pain Questionnaire (ALPQ) during initiation of epidural analgesia in early active labor. These authors have developed and validated a multidimensional psychometric questionnaire that measures the most important dimensions of women's labor and childbirth pain experiences. The ALPQ measures 5 key dimensions (enormity of the pain, fear/anxiety, uterine contraction pain, birthing pain, and back/long haul pain) previously found to be important in the childbirth pain experience. The scale appears to be sensitive to change after epidural analgesia pain relief, showed no floor or ceiling effects, and demonstrated internal consistency, reliability, and concurrent validity.17 Unfortunately, even with the help of experienced investigators, the ALPQ took 3.5 minutes for the average laboring women to complete before induction of epidural analgesia and 2 minutes to complete after induction of epidural analgesia. Demographic characteristics of the participants reflected a population that should have the least trouble with such an instrument (ie, white, college-educated English speakers). Half of the women approached for the study also refused to participate, many because of pain. The relative complexity of this measurement tool will likely limit the use of this pain questionnaire in routine clinical practice. The widespread appeal of the NRS 0 to 10 relates to its simplicity and how rapidly it can be understood and performed for people in pain. Even among analog scales, the NRS is associated with better compliance, applicability, and responsiveness compared with the visual analog scale 0 to 100 mm, a slightly more cumbersome scale.18 The McGill Pain Questionnaire (MPQ) was developed similarly to improve on analog pain intensity scales.19 In addition to pain intensity, the full MPQ presents 78 adjectives clustered in 20 categories, including verbal pain descriptors and affective components related to pain. The lack of widespread clinical and research application of the MPQ in a labor setting is likely because of its inherent complexity and time-consuming nature. Many of the 78 adjectives bear little relationship to most women's experience of labor pain. The scoring system (the total number and rank order of adjectives selected) offers little information about potential solutions to improve analgesia and treat labor pain. In contrast, the ALPQ has several characteristics that suggest its added complexity might be useful. Of the 28 items on the ALPQ, 13 adjectives also are included on the MPQ, including all items within the subscales for uterine contraction pain and the enormity of pain. The instruments diverge within subscales of fear/anxiety, back pain/long haul, and birthing pain, which are domains and specific items that were derived from years of qualitative work with delivering women at Sunnybrook Health Sciences Center. Used in combination with the Angle Pictoral Pain Mapping and Pain Ranking Tools,17 it is possible that this instrument, despite its complexity, will help women communicate what exactly is driving their NRS of 9 or 10. It is, however, also possible that women whose pain is out of control will lose the capacity to interact with an instrument this complex. The use and utility of the ALPQ in vulnerable populations (ie, those who speak languages other than English, those with low education, literacy, or numeracy) also must be explored further. Ultimately, for the ALPQ to find a place in clinical medicine, future studies will need to demonstrate a relationship between use of the pain questionnaire and important clinical outcomes. If the ALPQ improves diagnosis and treatment of breakthrough pain, helps better maintain optimal labor analgesia, or enhances maternal experience of analgesic care, then women's and clinicians' tolerance for a more time-consuming and complex pain questionnaire will be extended. In conclusion, we want to congratulate Angle et al17 on the development and implementation of the ALPQ. This multidimensional psychometric questionnaire is an improvement over the analog pain intensity scores that dominate labor pain assessments, and address important dimensions of women's labor and childbirth pain experiences. The complexity and time needed to administer the ALPQ will likely limit implementation, and its fate may be restricted to a research tool much like the MPQ. Measuring labor pain accurately is important to optimize the care of women and facilitate appropriate analgesic use, as well as allow different analgesic techniques, drugs, and doses at different stages of labor to be compared. A simple and easy-to-perform pain measurement tool that correlates with meaningful obstetric outcomes and maternal satisfaction with obstetric analgesic services is needed. Whether the ALPQ meets these objectives remains to be determined. Regardless, we wholeheartedly agree about the urgent need to move beyond analog pain scores and embrace all the dimensions of the labor and childbirth experience to improve maternal satisfaction and obstetric outcomes. DISCLOSURES Name: Brendan Carvalho, MBBCh, FRCA. Contribution: This author wrote, reviewed, and approved the final manuscript. Name: Jill M. Mhyre, MD. Contribution: This author edited, contributed, and approved the final manuscript. This manuscript was handled by: Jean-Francois Pittet, MD.