The Severe Respiratory Insufficiency Questionnaire was valid for COPD patients with severe chronic respiratory failure

Abstract

Objectives

The Severe Respiratory Insufficiency (SRI) Questionnaire has recently been developed and validated for the assessment of health-related quality of life (HRQL) in patients with severe chronic respiratory failure resulting from a broad spectrum of underlying disorders. The present study was aimed at reexamining the internal structure of the SRI specifically for chronic obstructive pulmonary disease (COPD) patients.

Study Design and Setting

Cross-validation was performed in two COPD groups (N = 78 and N = 84), each receiving home mechanical ventilation in addition to long-term oxygen therapy. The internal consistency reliability was calculated using Cronbach's α coefficient. Explorative Factor Analysis was performed followed by Confirmatory Factor Analysis to establish construct validity.

Results

In the total group (N = 162) Cronbach's α ranged from 0.73 to 0.88. Only one factor could be established which explained 58.5% of the total variance confirming one Summary Scale (SRI-SS). For each of the seven subscales, Confirmatory Factor Analysis revealed two factors, which were substantially correlated (r = 0.43–0.80). All scale scores covered a broad range of the questionnaire's scaling range (0–100). The mean SRI-SS score was 52 ± 17 indicating a homogenous scaling distribution.

Conclusion

The SRI is a multidimensional and highly specific tool with high psychometric properties for HRQL assessment in COPD patients with severe chronic respiratory failure.

Introduction

The evaluation of health-related quality of life (HRQL) in patients with chronic and noncurable disorders is becoming more essential in health care practice and research because it provides an important means of evaluating the human and financial costs and benefits of modern medical treatment modalities [1], [2], [3]. In clinical studies, questionnaires are the most frequently used tool for the assessment of HRQL; here, disease-specific questionnaires are postulated to be more sensitive than generic questionnaires to changes and, therefore, to be most appropriate for clinical trials in which specific therapeutic interventions are being evaluated [1].

Noninvasive positive pressure ventilation (NPPV) has been increasingly used to treat hypercapnic chronic respiratory failure (CRF) that can arise from various underlying disorders such as chest wall deformities, neuromuscular disorders, obesity hypoventilation syndrome, or chronic obstructive pulmonary disease (COPD) [4], [5]. Healing is not possible in the vast majority of CRF patients who receive life-long NPPV as a means of home mechanical ventilation (HMV). Therefore, the assessment of HRQL is extremely important in these severely ill patients.

There is overwhelming evidence to suggest that physiological parameters such as blood gases, survival, and even HRQL increase in patients with chest wall deformities or neuromuscular disorders after the implementation of HMV [6], [7], [8], [9], [10]. In contrast, there are conflicting data about patients with COPD [11], [12], [13], and the survival benefits of adding HMV to long-term oxygen therapy (LTOT) have not yet been documented [14], [15]. In addition, longitudinal studies have indicated only minor and inconsistent changes of HRQL after NPPV in stable hypercapnic COPD [15], [16], [17], [18], [19]. Although this might be due to selection bias, failing effectiveness of HMV or differences in sample size in different studies, inconsistent results might also be confounded by the different methodologies used to assess HRQL.

Well-validated health measures that specifically address HRQL in patients with severe CRF and primarily focus on COPD patients do not exist. Accordingly, if inappropriate measures are used, all conclusions regarding the impact of HMV on HRQL must be deemed premature. This calls for more appropriate studies on HRQL that are specifically tailored to better indicate the role of NPPV in patients with stable hypercapnic COPD. Recently, we developed the Severe Respiratory Insufficiency Questionnaire (SRI), which was shown to be appropriate for clinical trials aimed at assessing HRQL in CRF patients receiving HMV treatment [20]. However, the SRI has been validated for a broad spectrum of patients with CRF rather than specifically for COPD. Therefore, the aim of the present study was to reexamine the internal structure of the SRI for patients with CRF that was induced exclusively by COPD, thus providing a suitable instrument that reliably allows the longitudinal assessment of HRQL in these patients.