The use of the Visual Analogue Scale for the assessment of labour pain: a systematic review

Background For most women, labour pain is an inevitable part of childbirth. According to the International Association for the Study of Pain (IASP), pain is defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” (p.250)1. The pain is acute, quickly rising and it correlates with the intensity, duration, and frequency of uterine contraction 2. Dilation of the cervix from 0 to 10cm occurs during the progression of labour 2. Labour pain is a complex experience affected by a range of factors such as culture, ethnicity, emotion, educational level, gestational age and physical characteristics 3-8. Individual variability has made the assessment of pain a challenge. Pain management plays an important role in maintaining parturients’ safety and it also provides optimal labour experience with minimal pain. In spite of understanding pain and pain management, the assessment of pain remains a difficult yet important task 9. The failure to assess pain is the most common barrier to successful pain management 10. Thus, pain assessment is essential for evaluating parturients’ pain experience during the labour process. The ability to quantify pain intensity is crucial because it serves as a guideline for the administration of analgesia during labour. It also helps to monitor the effectiveness of the analgesia. Evidence suggests however, that pain assessment is inadequate for women with labour pain and they are undertreated 5, 11-13. Therefore, there is a need for appropriate, manageable and effective measures for examining labour pain. The quality of a measurement comprises a few components which are reliability, validity, sensitivity and specificity 14. Reliability and validity are two major criteria for evaluating a quantitative measurement. Reliability is the stability and equivalence with which an instrument measures the attribute while validity is the degree to which an instrument measures what it is supposed to be measuring 14. Pain assessment does not commonly stop with only one recording. Regular and repeat assessment for changes in the intensity of the pain are required for effective pain control 10. Sometimes, researchers will consider other qualities such as sensitivity and specificity. An assessment tool’s sensitivity is its rate of yielding ‘true positives” whereas specificity is its rate of yielding “true negatives” 14. In a review of three commonly used pain rating scales, the sensitivity of a pain rating scales was also defined as the ability of the scale to detect change 15. The review will consider reliability, validity, sensitivity and specificity of the assessment tool since these four components reflect the quality of measurement which affects the accuracy of the information obtained. The most frequently assessed component of pain is pain intensity. In research related to labour pain, VAS has been frequently used to assess parturients’ pain intensity. The VAS consists of a 10cm straight line which is labelled “no pain” at one end and “the worst pain possible” at the other. In addition, VAS is a ratio measurement which has properties consistent with a linear scale 16Patients will be asked to mark the line in order to rate their level of pain using the VAS from time to time. It has been argued that when a simple measurement instrument such as the VAS is used, a complex multidimensional phenomenon is reduced to single quantitative dimension of intensity 12. Several studies have mentioned that the VAS is a valid and reliable labour pain assessment tool 6, 11, 17-19, however, these studies do not justify why VAS is valid or reliable at measuring labour pain. Study on childbirth in Kuwait has indicated that the VAS was proved a reliable and valid rating tool for evaluating clinical pain 19, 20. However, the justification is ambiguous since the clinical pain tested was acute dental pain which is different from delivery pain because the origin and transmission of pain stimuli are different 12. Furthermore, several studies on labour pain have made comparison between VAS and other pain measurements. The correlation, validity and reliability of the pain measurements varied across these studies 21-23. There is a need to examine the quality of VAS since it is the only scale which has been used consistently in research related to women’s health 21. Although several studies have discussed the properties and correlation between different rating scales, the effectiveness of VAS for the assessment of labour pain has not been addressed by any other reviews. There are at present no precise recommendations for measuring labour pain in the context of obstetric unit. The obstetric unit follows the standardised pain scale which is widely used in the context of general clinical cases. The existence of an accurate and objective measurement of labour pain remains as a debatable and multifaceted issue 24. Apparently, more information is needed in order to ascertain whether VAS truly measures pain intensity in women in labour. Review Objective The objective of this systematic review is to critically analyse the literature and establish the best available evidence that investigates the effectiveness of VAS for the assessment of labour pain of pregnant women at term (37-42 weeks gestation). More specifically, the review question(s) is/are: 1. What is the validity of visual analogue scale for the assessment of women’s labour pain at term; 2. What is the reliability of visual analogue scale for the assessment of women’s labour pain at term; 3. What is the sensitivity of visual analogue scale for the assessment of women’s labour pain at term; 4. What is the specificity of visual analogue scale for the assessment of women’s labour pain at term? Criteria for considering studies for this review Types of Studies This component of the review will consider any randomised controlled trials (RCT) that examine the effectiveness of visual analogue scale and other measurements for the assessment of labour pain in pregnant women in terms of the assessment scale’s reliability, validity, or sensitivity. In the absence of RCTs other research designs, such as non-randomised controlled trials and before and after studies, will be considered for inclusion in a narrative summary to enable the identification of current practice and possible pain measurement tools for examining labour pain effectively. The review will focus on publications that have appeared over the last 15 years, from 1994 to 2009. Only papers published in English will be included. Types of Participants This component of the review will consider all studies that included pregnant women at term (37-42 weeks gestation) with labour pain. Only parturient who delivered in the hospital setting will be included. Parturient who had cervical dilatation from 0 to 10cm will be included. Subjects who received labour analgesia during the labour process will also be included. Types of Interventions This component of the review will consider studies that include the following interventions: Using Visual Analogue Scale (VAS) to assess labour pain intensity; Using other pain assessment tools to assess labour pain intensity. Types of Outcome Measures The main focus of this systematic review is the quality of the assessment tools. Thus, this component of the review will consider studies that include the following outcomes: Validity of the assessment tools Reliability of the assessment tools in terms of the stability and equivalence aspects Sensitivity of the assessment tools Specificity of the assessment tools Exclusion Criteria For the purposes of this review, studies focusing on adults with pain other than labour pain will be excluded from the review. Studies that included parturients who delivered out of the hospital setting will be excluded. Papers published before 1994 will be excluded in order to examine latest and current pain measurement used in the hospital setting. Search Strategy for identification of studies Prior to commencing the review, an initial search was carried out in order to identify current activity related to the review topic from Joanna Briggs Institute (JBI) Library of Systematic Reviews, Cochrane Library, Evidence Based Medicine, and Database of Abstracts of Reviews of Effects (DARE). The search strategy aims to look for published studies and papers. The search will be limited to English language reports. A three-step search strategy will be utilised in each component of this review. An initial limited search of MEDLINE and CINAHL will be undertaken followed by an analysis of the text words contained in the title and abstract, and of the index terms used to describe the article. A second search using all identified keywords and index terms will then be undertaken and will extend to other relevant databases. Thirdly, the reference list of all identified reports and articles will be searched for additional studies. The databases to be searched include: Medline; CINAHL; PubMed; ScienceDirect; Wiley-Interscience; OvidSP; SpringerLink; PsycINFO; Scopus Google Scholar; Database of Abstracts of Reviews of Effects (DARE); Evidence Based Medicine; Cochrane Library; JBI Library of Systematic Reviews; The search strategy will be limited to the following years 1994 to 2009. Initial Keywords to be used for the three review components will be: Pain Parturients Pregnant women Obstetric patients Labour pain Labor pain Obstetric pain Intrapartum pain Birth pain Childbirth pain Delivery pain Pain measurement Pain assessment Pain scale Pain tool Labour pain score Pain rating Pain rating scales Numerical rating scale Visual analogue scale Verbal rating scale Simple descriptor scale Verbal descriptive scale Pain matcher McGill Pain Questionnaire Psychometric properties Pain intensity assessment Validity Reliability Sensitivity The combination search of key terms in databases such as Scopus, Wiley-Interscience, SpringerLink, PsycINFO, and OvidSP will follow the search strategy elicited from CINAHL, PubMed and ScienceDirect (Appendix I). Methods of Review Critical Appraisal Papers selected for retrieval will be assessed by two independent reviewers for methodological validity prior to inclusion in the review using the standardised critical appraisal instruments from the Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI-MASTARI) (Appendix II, III, IV). Any disagreements that arise between the reviewers will be resolved through discussion with a third reviewer. Data Extraction Data will be extracted from papers included in the review using standardised data extraction tools from the Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI-MASTARI) (Appendix V). Any disagreements that arise between the reviewers will be resolved through discussion with a third reviewer. Data Synthesis Where possible quantitative research study results will be pooled in statistical meta-analysis using Joanna Briggs Institute Meta Analysis of Statistics Assessment and Review Instrument (JBI-MASTARI). All results will be double entered. Odds ratio (for categorical data) and weighted mean differences (for continuous data) and their 95% confidence intervals will be calculated for analysis. Heterogeneity will be assessed using the standard Chi-square. Where statistical pooling is not possible, the findings (Appendix VI) will be presented in narrative summary in the study findings section of the review. Conflicts of interest There are no conflicts of interest regarding this systematic review.

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