This systematic review evaluated the results of 17 studies for risk factors for admission or readmission in COPD patients who had experienced an exacerbation. Variables including using long term oxygen therapy, having low health status or poor health related quality of life and not having routine physical activity were all associated with an increased risk of admission and readmission to hospital.
was shown to be an independent risk factor for hospital admission for an acute exacerbation of COPD. Higher levels of PaCO2
likely represents a marker of disease severity or less likely that patients with chronic hypercapnia, and hence raised actual bicarbonate, are probably more easily symptomatic than normocapnic patients because of their rapid and shallow breathing pattern (Ringbaek et al 2002
), resulting in earlier and more frequent need for acute care.
In this review, three predictive factors: “previous hospital admission”, “dyspnea” and “oral corticosteroids” were all found to be significant risk factors of readmissions. Oral corticosteroids are often used in the treatment of acute exacerbations of COPD. In contrast, studies of the utility of inhaled corticosteroids in COPD patients who require hospital admission or emergency department treatment provide conflicting results, with some studies reporting improvement and others reporting no effect. This inconsistency suggests that the results of ongoing clinical trials, designed to look at the specifically possible benefits of inhaled corticosteroids on the risk of exacerbation, should be awaited before recommending their routine use in COPD patients. The most recent such study, paradoxically showed an increased risk of pneumonia in patients with COPD (Calverley et al 2007
In some studies use of long-term home of supplemental oxygen (LTOT) was independently associated with admission or shorter time to first readmission for acute exacerbations of COPD. However in other studies, this association was not significant or it did not remain significant after adjustment, indicating that LTOT could be probably a marker of severity in those patients.
The negative association between current smoking and hospital admission was explained by Anthonisen (2000)
in that many severely ill patients with COPD spontaneously quit smoking in response to their symptoms and disability, and it is hardly surprising that these patients do not do well afterwards. For this reason studies of patients with well established disease have often not shown a reduction in admission with smoking cessation.
Prospective studies including a wider range of COPD severity would be helpful to clarify this issue.
Low body mass index (BMI) was associated with admission and non elective readmission and consistently with its relation to prognosis of COPD in three studies (Kessler et al 1999
; Pouw et al 2000
; Garcia-Aymerich et al 2001
). It is not clear whether the observed relationships between both low body weight on admission and early readmission are causal relationships or whether these parameters represent epiphenomena of more severe disease. There is a hypothesis that tissue depletion in patients with COPD may be related in part to a systemic catabolic response induced by inflammation, which cannot completely be reversed by nutritional support only (Schols et al 1998
). Further studies are indicated to confirm this hypothesis.
In this review, the presence of coexisting comorbidites was not associated with an increased probability of frequent exacerbations, but with an increased risk of admission. This suggests that comorbidity does not appear to be a risk factor for frequent exacerbations, but a risk factor for severe life threatening exacerbations that can provoke admission. We believe that potentially all co-morbidities are important contributing factors to COPD morbidity, and special attention should be paid to the diagnosis of coexisting disease and its association with COPD admission.
Patients with COPD who perform a relatively high level of physical activity in their daily life have been shown a substantially reduced risk of readmission due to exacerbation (Garcia-Aymerich et al 2001
; Lau et al 2001
).The explanation could be that exercise engages cardiovascular system and helps the body to deliver oxygen to respiratory muscles more efficiently. In addition, endurance training can reduce exercise induced lactic acidosis and improve the oxidative capacity of the muscles in patients with moderate to severe COPD. Therefore such muscles would be more able to tolerate a COPD exacerbation than untrained muscles.
Being managed by a respirologist was also associated with higher risk of readmission, contrary to what might have been expected, and it was not totally removed after adjustment for previous admission, suggesting that other mechanisms may be operating. However, in another study (Wilkinson et al 2004
), it has been demonstrated that prompt treatment by a physician is associated with better outcomes.
Patients who habitually fail to seek therapy for their exacerbations have worse health-related quality of life and are more likely to be hospitalized for the management of an exacerbation. Patients with more symptoms at exacerbation onset tended to present earlier for treatment, and those exacerbations with more symptoms were indeed more severe, as they took longer to recover. Therefore, the milder and less symptomatic exacerbations were in fact presenting slightly later, and when this effect is taken into account, the benefit of early treatment became more pronounced.
In conclusion, our results for this systematic review suggest that there are a number of potential modifiable factors that are independently associated with the higher risk of COPD exacerbation requiring admission/readmission to hospital. Identifying these factors and the development of targeted interventions could potentially reduce the number and severity of such exacerbations.