Introduction

Health-related quality of life (HRQoL) is one and possibly the most important follow-up measure that is used to assess outcome after critical care [1, 2]. A decreased HRQoL has repeatedly been shown for former ICU patients both short and long term after critical care and compared with a general population [3–5]. Focus in such studies has been directed at factors believed to be important for this outcome. The most commonly stressed are age, sex, duration of stay on the ICU, Acute Physiology And Chronic Health Evaluation (APACHE) II score and time on ventilator [1]. Also, it has recently been claimed that pre-existing disease is more important than the others listed and of a magnitude comparable to these factors taken together [6]. This finding was made when a large control population was used and adjusted for co-morbidities. In that study approximately 50% of the decrease in HRQoL was ascribed to co-morbidities together with the other factors (age, sex, duration of stay on the ICU, APACHE II score and time on ventilator).

It may then be concluded that yet more factors must contribute to the HRQoL situation for these patients. In HRQoL research outside the field of critical care, it has been shown that factors such as social integration, coping and socio-economic factors (marital state, education, immigrant status) also may be important for the HRQoL experience [7–9].

The concept of availability of social integration (AVSI) was primarily developed in the mid-1970s with the emergence of a new field of scientific research and initially was used in the mental health literature [10]. From this research, the role of social relationships, especially integration, was emphasised as a buffer against negative health effects, and furthermore it was argued that social integration maintains or sustains the organism by promoting adaptive behaviour of neuroendocrine responses in the face of stress or other health hazards. Risk factors of importance for the lack of social integration and health include the following: younger age, older age in women, lower occupational grade, less education, lower social class, immigrant status, more symptoms of ill health, smoking, and more frequent use of alcohol [11, 12]. More socially isolated or less socially integrated individuals are less healthy, both psychologically and physically, and are more likely to die [7, 13]. Research has indicated that psychosocial counselling during and after stressful procedures, such as critical care, can decrease the associated level of stress and improve the recovery process [14, 15]. Recently this has become a focus of research interest during intensive care [16, 17], however, it is not widely used for this purpose after the period of intensive care and discharge from the hospital.

The aim of this study was to examine to what extent social integration patterns affect HRQoL outcome in the 6 month follow-up of critically ill patients and to examine if the effects differ between the ICU patients and the general population.

Materials and methods

Design

This prospective, multicenter study took place in three mixed medical-surgical ICUs, one university and two general hospitals, in south-east Sweden. They have a regional referral area covering roughly 1 million people.

Patients with primary coronary disease, those recovering after heart surgery and neurosurgery, neonates, or patients with burns are treated in other specialised units and were excluded from this study. The ICUs admit 500–750 patients annually and nearly all admissions are emergencies. The most common primary diagnoses are multiple trauma, sepsis, and disturbances in respiratory or circulatory systems.

Participants

This study is part of a large study previously published [6, 18]. In short, all patients aged 18 years and older who were consecutively admitted to the ICUs between 2000 and 2004, remained in the ICU for more than 24 h, were alive 6 months after discharge from hospital, and consented to participate in the study were included. Patients who were readmitted were included only on their first admission. We sent information and a request to participate to each patient by mail, together with a structured questionnaire and a preaddressed and prepaid envelope. Patients who had not responded within about 10 days were contacted by telephone by one of the investigators (L.O., E.S. or C.B.), which was predetermined. If telephone or first mailing achieved no answer, two reminders were sent out (at 3 and 6 weeks). The clinical databases in each hospital were used to extract patient data.

Data from a public health survey of the county of Östergötland were used for comparison of availability of social integration, HRQoL and comorbidity. This reference group consisted of a random sample of the general population living in the uptake area of the hospitals. That survey was undertaken for the purpose of monitoring the general health of this population in a different study and was completed during 1999 [12].

The study was approved by the Committee for Ethical Research at the University of Health in Linköping.

Questionnaires and instruments

A set of structured questionnaires was mailed to the study population 6 months after discharge from hospital. The questionnaire contained questions about the patients’ background [(civil state, children living at home, born in Sweden or not, education, employment before and after admission to the ICU, sick leave before and 6 months after discharge from the ICU and hospital, and pre-existing disease (self-reported diagnosis)]. The questionnaire asked, “Have you had any significant illness, reduced body function or other medical problem and did you have it for more than 6 months prior to the ICU period?” with the answer either “yes” or “no”. Further, this question also had the following specified illness alternatives: “cancer; diabetes; heart failure; asthma/allergy; rheumatic-gastrointestinal, blood, kidney, psychiatric, neurological disease; thyroid or any other metabolic disturbance; or any other long term illness”. The last alternative was an open question with a slot for free text.

Availability of social integration (AVSI)

The instrument AVSI [19] was used to assess social integration patterns. AVSI was developed in the beginning of the 1980s and has been validated and found reliable (internal consistency 0.71; test re-test 0.75; stability of scores over time 0.84–0.87, range 4–12 months) [19] and used repeatedly in examinations of social structure in patient populations [20–22]. Furthermore one of these studies [22] involves the reference group also used in the present study. This instrument is one of four subscales in the extensive instrument known as the Interview Schedule for Social Interaction (ISSI) [19]. AVSI has been translated into Swedish and has been found to be a reliable instrument in this context as well [11]. In the Swedish setting it has been used in epidemiological research [12]. It comprises seven questions. In six of them, respondents are asked how many persons they receive support from, for example “These days, how many people with similar interests do you have contact with?” with six answer alternatives ranging from no one to more than 15. One question is to be answered yes or no: “Other than those at home, do you have someone you can turn to if you are in trouble? Someone that you can meet easily and that you trust and that really can help you when you have hard times?” The questions generate a summed score index with a scale ranging from 6 (the worst score) to 36 (best score).

Health-related quality of life

The Medical Outcome Short Form 36 (SF-36) was chosen for the evaluation of HRQoL [23, 24]. The instrument is internationally well known and has often been used [25]. SF-36 has previously been applied in intensive care [6, 26–28] and has recently been recommended as one of the best-suited instruments for measuring HRQoL in trials in critical care [29].

SF-36 has been translated into Swedish and validated in a representative sample [30]. It has 36 questions and generates a health profile of eight sub-scale scores [24, 30]. These eight scores were aggregated to form two commonly used summary scores: the physical component (PCS) and the mental component (MCS).

Statistics

Data are presented descriptively (mean, 95% confidence intervals) using parametric statistics (one-way analysis of variance) and non-parametric statistics (Pearson’s chi-squared test). Linear regression analysis, adjusted for sex and age, was used to evaluate the independent effects of APACHE II scores on admission, length of stays in ICU and hospital, diagnoses on admission, time on ventilator, marital state, level of education, born in Sweden or not, age, sex, social support and pre-existing disease on HRQoL (component summary scores) among the patients. Only standard statistical methods were used [31]. Further, when ICU survivors were compared with the reference group, survivors older than 74 years were excluded since the reference population did not include subjects older than 74 years.

The Statistical Package for the Social Sciences (SPSS, version 17.0, Chicago, IL, USA) was used for the statistical analyses. Probabilities of <0.05 were accepted as significant.

Results

Clinical and socio-demographic characteristics of the patients

During the study period, 5,306 patients were admitted to the ICUs. Of these a total of 1,663 (31%) patients met the inclusion criteria. After two reminders, 980 patients (59%) answered the questionnaire (Fig. 1).

Fig. 1
figure 1

Outline of the study protocol

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The group who did not respond at all in the study [n = 683 (41%)] differed from the group who responded in that there were fewer men (p = 0.02), higher average APACHE II score (p = 0.04), shorter length of stay in the ICU (p < 0.0001), shorter time on ventilator (p < 0.0001) and fewer gastrointestinal diagnoses on admission (p = 0.02) (Table 1).

Table 1 Clinical characteristics on admission of the patients in the study group and the non-responders group
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For the reference group, questionnaires were initially sent out to 10,000 people. After two reminders, 6,093 (61%) had responded [12]. Apart from lower percentages of immigrants and single households, the responders in the reference group differed only marginally from the reference population of the county [12]. The reference group was younger (p < 0.001), included more women (p < 0.001), had a higher rate of marriage/cohabitation (p < 0.001) and employment (p < 0.001), and had a lower rate of comorbidity (51%) (p < 0.001) than the ICU group, after adjusting for age in the ICU group (age < 74 years) [n = 780 (80%)] (Table 2).

Table 2 Socio-demographic characteristics of patients in the study group <74 years and the reference group
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Availability of social integration

The former ICU patients reported significantly lower mean scores in availability of social integration than the reference group, 19.8 (SD 6.3) compared with 20.7 (SD 5.8) (p < 0.001). In Table 3 the comparison between the individuals with or without comorbidity in each study group is shown. The ICU patients with pre-existing diseases reported significantly lower mean scores in availability of social integration compared with the ICU patients who were healthy before the intensive care period. For the reference group there were no differences in availability of social integration between the individuals with comorbidity or not. Significant differences in availability of social integration were also seen between the ICU patients with pre-existing diseases compared with the reference group with comorbidity. Between the healthy former ICU patients and the healthy reference group, there were no differences in availability of social integration (Table 3).

Table 3 Comparison of social support (mean score) between ICU patients <74 years and the general population with or without comorbidity
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Health-related quality of life

The reference group scored a significantly higher HRQoL than the ICU patients for all eight dimensions of the SF-36 (p < 0.001) and for the summary component scores, with mean score differences between 6.9 (mental health) and 34.8 (physical health).

The PCS summary component score mean was 39.1 (SD 12.7) for the ICU patient group and 50.0 (SD 9.6) for the reference group (p < 0.001). The MCS summary component score was 45.0 (SD 13.4) for the ICU patient group and 49.0 (SD 10.6) for the reference group (p < 0.001). The summary component scores were used in a multiple linear regression analysis to evaluate the effect of availability of social integration (AVSI score), APACHE II score at admission to the ICU, length of stay in ICU and in hospital, diagnoses on admission to the ICU, time on ventilator, marital status, education, born in Sweden or not, gender, age and pre-existing disease (Table 4). The results demonstrate that availability of social integration significantly affected HRQoL both physically and mentally to a greater extent than age, sex, years of education, marital state or immigrant status, but to a lesser extent than pre-existing diseases. Further availability of social integration significantly affected HRQoL to a greater extent than ICU-related factors, APACHE II score, length of stay in ICU or time spent on ventilator. Of the ICU-related factors examined, only the ICU admission diagnoses affected HRQoL more than the availability of social integration.

Table 4 SF-36 summed score multiple regression analysis, (linear) final model (95% confidence interval for B) (n = 980)
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ICU patients with lower mean AVSI scores and younger age had lower physical and mental component scores. The magnitude of this effect was smaller compared with the effects of pre-existing diseases. Longer duration of stay in the hospital was associated with lower physical component score, and being single/widow/widower was associated with a lower mental component score (Table 4).

Discussion

The new and important finding of this study is that availability of social integration patterns affects HRQoL for former ICU patients, and this effect, albeit smaller than that of pre-existing diseases, needs to be acknowledged in studies trying to comprehensively picture HRQoL in former ICU patients.

The cohort used in this study is a part of a large study that has previously been examined from several different perspectives [6, 18, 26]. Health-related quality of life has been examined short and long term. In these investigations, the cohort was found to be comparable to other general ICU follow-up studies in Scandinavia and in northern Europe. Also the background characteristics (APACHE II, LoS, diagnoses) are similar in comparison [3, 27, 32]. It may therefore be assumed that the findings presented in this study regarding the effects of social support are valid also for other units in this part of the world.

Although in the present study the APACHE II scores were higher in the non-responders group, LoS in ICU and time on ventilator were higher in the study group. This suggests that the study group comprises patients with relevant ICU-related illnesses.

Very interestingly, when comparing the availability of social integration values of the present ICU groups with a control population from the uptake areas of the ICU units, it is evident that the ICU population has a significantly decreased (approximately 10%) AVSI score. As anticipated we found a significant effect on AVSI score of age but not sex [7]. Thus, it needs to be appreciated that a significant, and most probably the largest, effect on the AVSI score for this patient group is the effect of pre-existing disease. This was also evident as an interaction in the statistical analysis. Despite this, a significant effect of AVSI score on HRQoL remained after controlling for the effect of pre-existing disease and age. This finding suggests that AVSI score has an effect on HRQoL beyond what is registered due to effects of pre-existing disease. This stresses that AVSI score is important when a comprehensive HRQoL examination is being done on former ICU patients or any other population. Furthermore, of the socio-economic factors examined, only marital state (living alone) was found to have an effect on HRQoL, and this effect was small.

There are a number of factors that may affect the conclusions of this study. First is the number of patients studied. Although done in a less populated area of Sweden, 980 patients were recruited to this study, which makes it a very large study in this field of research.

Second, from a social perspective Sweden is a homogenous country [12]. This leads to the fact that variations in AVSI scores in populations examined are rather small as was experienced also in this study [11, 12]. The relevance of the present findings may then be larger in countries with larger social differences where adjustments of the effects of social network on the outcome of HRQoL may be more important [33]. The fact that the reference group was examined a few years prior to the study group may have influenced the results. Also this effect is most probably minor in the Swedish setting.

Third, another confounding factor is that it is difficult to examine the effects of socio-economic factors in this rather homogenous population. However, although we did not have specific income data, other often-examined socio-economic variables, i.e., marital status, education, employment, immigrant status and sick leave, were examined and adjusted for.

Fourth, and very importantly, when examining effects of the availability of social integration patterns there is as yet no consensus as to what measure to use [34, 35]. This makes it difficult to compare the outcomes of different studies. For example the AVSI score instrument used in the present study is a quantitative measure of social integration. It does not assess the quality of the social relationships and the corresponding support provided. However, those assessing quantitative aspects of social integration have claimed this approach to be more readily applicable, and the questions are more easily and quickly understood and answered. They have also found that the data predict physical illness in prospective studies. The psychometric properties, however, are unknown [36].

Fifth, a complicating fact is that many factors of the population studied are known to affect AVSI score and possibly the opposite applies as well. That is, pre-existing disease, age, sex and marital state are all known to be important for the social integration pattern [11, 12]. It is difficult then to know which effect is cause–effect-related as all of these are known to affect social integration, while at the same time several of them have strong effects on HRQoL. We believe however, that when adjusting for such effects by multiple regression techniques, the conclusions are still valid.

Last, a limitation of the present study is the response rate of 59%, which on one hand is an acceptable rate for postal questionnaires, but on the other hand there is a risk that the non-responders could include more individuals with lower social integration. The latter is at least in theory plausible.

Conclusions

The novel finding in this study is that the social integration patterns among former ICU patients were found to affect HRQoL, and therefore social integration needs to be examined in parallel when comprehensive studies on HRQoL in these populations are undertaken. Furthermore, this effect is larger than that of any of the ICU-related factors but smaller than that of pre-existing diseases.