Given the variety of palliative care settings within which symptom distress must be assessed, development of a valid and reliable clinical tool that can be simply ...
JOURNAL OF PALLIATIVE MEDICINE Volume 14, Number 3, 2011 ª Mary Ann Liebert, Inc. DOI: 10.1089/jpm.2010.0412
Measuring Symptom Distress in Palliative Care: Psychometric Properties of the Symptom Assessment Scale (SAS) Samar M. Aoun, B.Sc.(Hons), M.P.H., Ph.D.,1 Leanne Monterosso, BNurs(Hons), Ph.D.,2 Linda J. Kristjanson, B.N., M.N., Ph.D.,1 and Ruth McConigley, B.Sc., MNurs, Ph.D.3
Abstract
Given the variety of palliative care settings within which symptom distress must be assessed, development of a valid and reliable clinical tool that can be simply applied in every day practice is needed. The Symptom Assessment Scale (SAS) uses a 0–10 numerical scale with zero being no symptom and 10 being the worst possible. The key symptoms included in the scale are breathing, bowel problems, appetite problems, pain, insomnia, nausea and fatigue. The instrument is structured to allow either the patient, family member or nurse to assess the symptoms. The scale was tested on 572 cancer patients recruited from five palliative care services in Western Australia. Results indicated that the instrument was brief, clinically useful and was administered with minimal missing data. Internal consistency reliability estimates of the scale ranged from 0.64–0.92 as measured by the Cronbach’s alpha coefficient. Test-retest reliabilities of 0.84–0.92 were obtained using Pearson’s correlation co-efficient. The instrument does not provide an in-depth assessment of individual symptoms, but serves as a screening tool to identify troublesome symptoms that warrant attentive and immediate investigation and comprehensive assessment.
Introduction
P
atients living with cancer and other life-limiting illnesses may experience myriad complex symptoms, such as pain, nausea, breathlessness, and insomnia, requiring monitoring and management. Assessing and monitoring changes in a patient’s symptoms can pose considerable difficulties for clinicians. However, it is widely accepted that impeccable symptom assessment is required if good symptom management is to be achieved.1 In response to this concern, a number of palliative care–specific assessment tools have been developed, including a number of patient self-report rating scales for symptom assessment, most of which report sound psychometric properties.2–4 Although the empirical literature describes the use of these instruments for research purposes, less has been written about the extent to which these tools have been adopted for use in clinical practice. The purpose of this article is to describe the development and testing of one such tool suitable for both clinical and research purposes, the Symptom Assessment Scale (SAS). The most commonly used of such instruments is the Edmonton Symptom Assessment Scale (ESAS), which has been
used extensively in clinical and research settings. Two recent reviews showed that the ESAS is a reliable symptom assessment tool, although there is a need for further validity testing to support use of the ESAS in a variety of settings.5,6 Chang and colleagues7 also noted that some patients found it difficult to understand and complete the visual analogue scales of the ESAS. A more recent study on the routine use of the ESAS8 reported challenges such as lack of clarity about frequency of assessments and difficulty interpreting the symptom rating scale. The Memorial Symptom Assessment Scale (MSAS) is a patient-rated instrument that captures patient-rated severity, frequency, and distress associated with 32 highly prevalent physical and psychological symptoms. In its complete form it can be time consuming to complete.9 Other instruments are also described in the literature. The Support Team Assessment Schedule (STAS) consists of 17 items that are used to evaluate a wide range of patient, family, and service issues.3 With the exception of pain and anxiety, all other symptoms are aggregated under one item labelled ‘‘symptom control.’’ This limits the sensitivity of the tool in terms of identifying and measuring distress caused by a specific symptom and the evaluation of interventions targeted
1 Western Australian Centre for Cancer and Palliative Care, Curtin Health Innovation Research Institute, Curtin University, Perth, Western Australia, Australia 2 School of Nursing, The University of Notre Dame Australia, Fremantle, Australia. 3 School of Nursing and Midwifery, Curtin University, Perth, Western Australia, Australia. Accepted October 14, 2010.
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316 at that symptom. Hearn and Higginson10 developed the Palliative Care Outcome Scale (POS), which assesses physical symptoms (pain and other symptoms together) and psychological, spiritual, and practical domains. However, the authors concede that future development of POS should incorporate more symptom information, notably about nausea, weakness, and breathlessness. The Symptom Distress Scale (SDS) was developed by McCorkle and Young11 to assess subjective experiences of distress. The SDS examines the distress caused by 10 common symptoms, measured on a scale of 1 to 5, with ‘‘1’’ indicating little or no distress and ‘‘5’’ indicating great distress. The instrument was tested with a group of cancer patients and a group of individuals who had experienced a myocardial infarction. The tool demonstrated acceptable reliability and validity estimates and was found to be brief and relatively simple to administer. Since then the tool has undergone minor revisions and has been tested with patients with cancer in a variety of settings.12–18 This instrument continues to be used for measuring symptoms in research settings,19–21 but there are less data about its usefulness as a clinical tool. An adapted version, the Adapted Symptom Distress Scale-2, has also been used in the research setting.22,23 The development of the Symptom Assessment Scale (SAS) Kristjanson and colleagues24 undertook a multisite study to pilot test the SDS with the primary aim of determining the extent that the tool would be appropriate for application in the Australian cancer care context. Results from this pilot work suggested the tool was useful; however, some changes were required to simplify the instrument and also adapt it to make it more culturally appropriate to the Australian population. Modifications included the removal of items related to mobility, mood, concentration, and appearance. One item relating to breathing problems was added. The revised instrument was labelled the Symptom Assessment Scale (SAS) (see the Appendix). It comprises the following seven items: pain, insomnia, nausea, bowel problems, appetite problems, breathing problems, and fatigue. Patients rate the degree of distress associated with the symptom using a 0 to 10 Likert-type verbal rating scale with zero being no symptom distress experienced, ‘‘1’’ being minimal symptom distress, and ‘‘10’’ being the worst possible symptom distress. The time frame for rating the symptoms is in the past 24 hours. Clinicians can add other symptoms experienced by each patient as appropriate. The instrument is structured to allow either the patient, family member, or nurse to assess the symptoms. Although frequent assessment of physical symptoms is a necessary and routine practice, the suitability of frequent assessment of psychological well-being of patients was pretested and found in the pilot study to be intrusive. Patients indicated that they were willing to provide information about physical symptoms (e.g., pain, nausea) because something could be offered to assist with these symptoms. However, to inquire about their feelings such as depression on a daily basis was inappropriate and upsetting. Advice provided indicated that this type of question might be better addressed in a different way, allowing more time for discussion about feelings with a staff member with whom they had a closer relationship. This finding may reflect cultural perspectives
AOUN ET AL. with respect to the context within which discussions of psychological issues occurs. A survey of symptom assessment tools used in Australian services found that 28% of services used the SAS compared with 14% that used the ESAS and 2% that used the MSAS (the rest using unvalidated tools), and both ESAS and MSAS include questions related to psychological distress.25 This article reports the reliability and validity testing of the SAS, a short patient-rated scale of symptom distress that is widely used in Australian clinical palliative care settings both as a clinical tool and for monitoring the quality of care provision.26–28 Although the SAS was developed in 1999 and extensive testing of the instrument was undertaken at that time, the results of the testing were never published in a peerreviewed publication. This article reports the findings from the original testing procedures that were completed in 1999 and analysed further in 2009 and provides information regarding the ongoing use and testing of the SAS in subsequent studies. Testing of the SAS The following questions were addressed: 1. To what extent does the SAS demonstrate internal consistency reliability? 2. To what extent does the SAS demonstrate stability over time? 3. To what extent does the SAS demonstrate construct validity? 4. To what extent does the SAS demonstrate sensitivity to changes in patient’s condition over time? Approval to conduct this study was obtained from the human research ethics committees of Edith Cowan University and each study setting. The study was undertaken between January and December 1998 and documented in a report in 1999.24 Methods Sample and setting A consecutive sampling of mainly cancer patients receiving palliative care in five services in Perth, Western Australia over a 12-month period was obtained. These services were all major services existing at the time of the study. This population was selected because of the high incidence of symptom distress associated with palliative care. Hence, the sample was able to provide useful data regarding the consistency, stability over time, and construct validity of the instrument. Participants were recruited from five palliative care services covering three different settings: consultative palliative care services (n ¼ 2), inpatient palliative care units (n ¼ 2) and home care service (n ¼ 1). The inpatient units had a combined total of 48 beds, with an occupancy rate of approximately 90%. The home care service provided palliative care to patients throughout the metropolitan area of Perth, both in the home and in residential aged care settings, with an ongoing caseload of approximately 400 patients. The two consultative palliative care services received approximately 12 new referrals per week. Symptom assessment was performed daily for each patient by the bedside nurse and recorded on a Symptom Assessment Recording Form. Training was undertaken to ensure
MEASURING SYMPTOM DISTRESS IN PALLIATIVE CARE consistency in administering the tool. Patients were asked to assess the degree of distress they were experiencing with respect to seven symptoms of the SAS. Patients indicated verbally, or by pointing to the number on the scale, the level of severity of symptom distress. SAS scores were reported for each patient on at least five occasions, allowing for testing of sensitivity of the SAS to changes in symptoms over time. Statistical analyses Descriptive statistics were used to describe the sample in terms of demographic characteristics, clinical characteristics, and symptom distress variability. Internal consistency reliability was assessed using Cronbach’s standardized a coefficient. A criterion of at least 0.70 was preset as the minimum for internal consistency, which is considered acceptable for a newly developed instrument.29 As well, Carmines and Zeller30 suggested that 50% of item-tototal correlation should be between 0.40 and 0.70. Scores above 0.70 indicate redundancy of items, and scores below 0.40 indicate that the item may not contribute information about needs parallel with other scale items. The intraclass correlation coefficient was used to determine stability of the SAS over time. This statistic allowed for an assessment of the extent of agreement across the two time points while correcting for possible chance agreement. A correlation of at least 0.70 was preset as the criterion for satisfactory test-retest reliability.29 Construct validity was evaluated using the ‘‘known group validity’’ technique and was assessed by comparing symptom assessment scores of patients with different cancer diagnoses. An analysis of variance (ANOVA) was used to test for differences in the Time 1 (T1) scores with a Sheffe post hoc test used to test for statistical differences between the groups, based on comparisons of scores across cancer diagnoses known or hypothesized to score differently. We hypothesized that the SAS would be able to discriminate individual symptom distress scores between patients with different cancer diagnoses. For example, we hypothesized that patients with lung and head and neck cancers would have higher distress scores for breathing than patients with other cancer diagnoses. Likewise, patients with breast cancer would have higher pain scores than patients with other cancers. A repeated measures general linear model was used to determine the sensitivity of the SAS to changes in symptom scores over five time points. This was an important requirement to determine whether the SAS was a useful tool that could be used in the clinical setting to detect expected changes in a patient’s condition over time. For example, it was hypothesized that distress related to pain would decrease over time as the palliative care team implemented effective symptom management of this problem. Results Sample characteristics We recruited 572 patients from five different palliative care specialist services in Western Australia. Data from 18 recruited participants were not included in the analysis for the following reasons: patient was deceased prior to data collection (n ¼ 8), no submission of data (n ¼ 7), patient was diagnosed as terminal after recruitment (n ¼ 1), patient was
317 discharged prior to data collection (n ¼ 1), or the patient decided not to participate (n ¼ 1). (See Table 1.) Clinical characteristics A wide range of cancer diagnoses were included in the sample; most patients had metastatic disease and had undergone some form of cancer treatment, and 22% continued to have active treatment. Only 5% of patients had a diagnosis of nonmalignant disease. (See Table 2.) Instrument Testing Symptom intensity. (See Table 3.) The possible SAS score range for each symptom was 0 to10 (0 ¼ no problems to 10 ¼ worst possible problem). The range of mean SAS scores was 2.30 (nausea) to 5.83 (fatigue). Internal consistency. The SAS achieved an internal consistency estimate as measured by Cronbach’s a of 0.62 ( p < 0.001) using T1 SAS scores. This estimate was just below the preset criterion of 0.70 and indicated a moderate degree of internal consistency. The total score on the SAS was also correlated with each symptom score. All seven symptoms (100%) achieved item-to-total correlations between 0.40 and 0.70. This was well above the preset range of at least 50% of items within this range. Construct validity. (See Table 4.) As hypothesized, patients with breast cancer had the highest scores for appetite problems, nausea, bowel problems, and pain of any cancer group. Patients diagnosed with lung cancer had higher breathing scores than other cancer groups. Post hoc tests showed patients with head and neck and lung cancers had significantly higher breathing scores than patients diagnosed with colon cancer ( p ¼ 0.005), leukemia ( p ¼ 0.001), Table 1. Demographic Profile of Patients (n ¼ 572) Gender Male Female Age 25–60 61–70 71–80 81–98 Marital Status Married/de facto Never married Divorced/separated Widowed Country of birth Australia UK Other Preferred language English Other Palliative care service type Consultative service Home care service Inpatient unit
n (%) 333 (58) 237 (42) 117 112 220 119
(21) (20) (39) (21)
324 48 44 142
(58) (9) (8) (25)
349 (63) 114 (21) 91 (16) 526 (92) 46 (8) 91 (16) 196 (34) 285 (50)
AOUN ET AL.
Symptom Appetite Bowel Breathing Fatigue Insomnia Nausea Pain
n
Mean
SD
544 542 545 539 544 548 540
4.72 3.80 3.14 5.83 3.48 2.30 3.98
3.166 3.139 3.191 2.772 2.914 2.826 3.054
SD, standard deviation.
Other 6.16 (2.76) Colon 5.73 (2.51) Prostate 5.72 (2.77) Gastric 5.67 (2.62) Breast 5.65 (2.97) Head/neck 5.54 (2.81) Lung 5.46 (3.05)
Fatigue Breathing
Lung 4.54 (3.38) Head/neck 3.27 (3.21) Breast 2.93 (3.09) Colon 2.49 (3.00) Gastric 2.46 (2.96) Other 2.35 (2.86) Prostate 2.31 (2.86) SD, standard deviation.
Table 3. Mean SAS Scores for Each Symptom
Breast 4.89 (3.30) Prostate 4.47 (3.2) Other 4.12 (3.24) Gastric 3.52 (3.23) Lung 3.48 (2.96) Colon 3.09 (3.02) Head/neck 2.72 (2.65)
and prostate cancer ( p ¼ 0.008). Patients with gastric cancer had significantly lower pain scores than patients diagnosed breast cancer ( p ¼ 0.029). There were significant differences between cancer diagnosis and bowel symptom scores (F ¼ 2.334, p ¼ 0.018), breathing symptoms scores (F ¼ 7.540, p < 0.001) and pain (F ¼ 4.326, p < 0.001). Post hoc tests show patients without cancer had significantly higher breathing scores than patients diagnosed with colon ( p ¼ 0.006), gastric ( p ¼ 0.019), genitourinary ( p ¼ 0.006), and other cancers ( p ¼ 0.006). Patients with lung cancer had significantly higher breathing scores than patients diagnosed with colon cancer ( p ¼ 0.005), leukemia ( p ¼ 0.001), and genitourinary cancer ( p ¼ 0.008). Patients with gastric cancer had significantly lower pain
Breast 2.90 (3.12) Other 2.55 (2.79) Colon 2.4 (2.80) Gastric 2.3 (2.99) Prostate 2.07 (2.70) Lung 1.79 (2.65) Head/neck 1.72 (1.90)
(9) (16) (3) (5) (17) (34)
Breast 5.16 (3.08) Head/neck 4.76 (3.44) Other 4.74 (3.27) Colon 4.69 (3.27) Lung 4.66 (3.04) Prostate 4.34 (3.08) Gastric 4.28 (3.08)
49 91 17 26 96 196
Bowel
44 (8) 67 (12) 13 (2)
Nausea
175 (31) 225 (40) 248 (44)
Appetite
(29) (8) (20) (13) (25)
Insomnia
162 43 112 73 141
Pain
n (%) 41 (7) 92 (16) 46 (8) 26 (5) 121 (21) 62 (11) 149 (26) 29 (5) 33.3
Table 4. Mean SAS Scores Ranked by Cancer Diagnosis (SD)
Primary diagnosis Breast Colon Gastric Head/neck Lung Prostate Other Not cancer Average time since diagnosis (months) Secondary involvement Bone Brain Liver Lung Other Previous treatment Chemotherapy Radiotherapy Surgical Current treatment Chemotherapy Radiotherapy Surgical Comorbidity Arthritis Chronic lung disease Cognitive impairment Neurological conditions Symptomatic heart disease Other
Prostate 3.67 (2.99) Other 3.65 (2.95) Colon 3.56 (3.07) Lung 3.50 (2.94) Head/neck 3.44 (2.62) Breast 3.08 (3.02) Gastric 2.80 (2.73)
Table 2. Clinical Profile of Patients (n ¼ 572)
Breast 5.03 (2.94) Head/neck 4.92 (2.73) Prostate 4.44 (2.92) Lung 4.03 (3.14) Colon 3.71 (2.88) Other 3.41 (3.01) Gastric 2.33 (2.46)
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MEASURING SYMPTOM DISTRESS IN PALLIATIVE CARE scores than patients diagnosed with breast cancer ( p ¼ 0.029). Stability over time. (See Table 5.) A subsample of patients participated in the test-retest reliability assessment (n ¼ 60). Participants completed the SAS at T1 and 2 hours later at time two (T2). This time frame was chosen to minimize variations in symptom distress over time, allowing testing of the reliability of the instrument. Research staff also confirmed that no pain medication or symptom intervention was administered during this time interval. Results indicated a significant level of agreement among participants ranging from r ¼ 0.84 for nausea and breathing to r ¼ 0.94 for pain. Sensitivity to change over time. (See Table 6.) Repeated measures over five time points demonstrated the SAS is sensitive to changes in symptom distress over time as shown in the symptoms of appetite, insomnia, nausea, and pain. Bowel symptoms, breathing, and fatigue scores did not change significantly over time. The average time between symptom assessments was 2.35 days, ranging from 1.4 to 17.1 days. Discussion This study tested the SAS in a variety of Western Australian palliative care settings: inpatient, consultative, and community based. Results indicate the SAS is easy to administer, in terms of its brevity and the short time required to administer it and with minimal missing data. It is likely to be a useful tool to guide clinical care. The SAS does not provide an in-depth assessment of individual symptoms, but serves as a screening tool to identify troublesome symptoms that warrant more attentive and immediate clinical investigation and comprehensive assessment. Internal consistency reliability and stability over time of the SAS were found to be acceptable. The SAS demonstrated construct validity by discriminating changes in expected symptoms among patients with different cancer diagnoses. The SAS also demonstrated sensitivity to detect changes in symptom distress over time. The variation in internal consistency as measured by Cronbach’s a suggests the different symptoms assessed by the instrument are not necessarily correlated in this population. This is expected because each cancer type and related treatment cause comorbidities and symptoms that are
Table 5. Symptom Test-Retest Reliability
Symptom Appetite Bowel Breathing Fatigue Insomnia Nausea Pain
n
r
p
60 59 59 60 60 60 60
0.92 0.90 0.84 0.87 0.92 0.89 0.94
