DISCUSSION
The present study was conducted to assess the prognostic utility of GNRI in patients with aspiration pneumonia, mainly comprising older individuals. Multivariate analysis revealed that male sex, a history of CHF and malignancy, disease severity evaluated using the A-DROP scoring system, lower GNRI score, and an initial antibiotic change were negative prognostic factors. To the best of our knowledge, this is the first study demonstrating the prognostic value of GNRI in patients with aspiration pneumonia.
Aging is an irreversible biological process characterized by decreased organ system reserve and weakened homeostatic control.20 In older adults, these changes may lead to decreases in food intake and absorption caused by impaired gastrointestinal function, resulting in undernutrition. Furthermore, underlying disease and inadequate dietary habits may negatively affect nutritional status. Consequently, undernutrition leads to decreased activity and weakened immune function, resulting in the further deterioration of organ function and nutritional status.21 Undernutrition is associated with weakening of swallowing muscles and skeletal muscles and is a significant risk factor for aspiration pneumonia.6, 21Several studies have reported the utility of serum albumin levels and BMI as prognostic factors for older patients with pneumonia.23-26 Nevertheless, despite the ease of evaluating these indicators, they may be influenced by various factors.
This study demonstrated that lower GNRI was a significant prognostic factor for older patients with aspiration pneumonia. GNRI is calculated based on serum albumin levels and a physique-based index. This nutrition-related index is easily assessed without the need for complex procedures such as the measurement of grip strength or limb circumference. Our ROC analysis indicated that the AUC value for GNRI was greater than that for albumin and BMI, and a significant difference was observed with albumin. Serum albumin is affected by extracellular fluid volume, dehydration status, and inflammatory dynamics.27 BMI, a physique-based index, is also affected by recent dehydration status. Thus, GNRI, which is derived from serum albumin levels, height, and body weight, may have optimized the deviation caused by these factors.
Recent studies have highlighted the prognostic significance of GNRI in various diseases. According to seminal reports, GNRI < 98 was defined as nutrition risk.10 In our cohort, more than 70% of patients had GNRI < 98 (even in the survivor group), suggesting that most patients with aspiration pneumonia in our cohort were at nutritional risk. Thus, establishing a cut-off value for GNRI in patients with aspiration pneumonia is critical and warrants resolution.
The multivariate analysis revealed several independent prognostic factors other than GNRI, including male sex, CHF, history of malignancy, and higher A-DROP score. CHF is a risk factor for hospitalization with pneumonia.28 In patients with heart failure, alveolar flooding may disrupt immune function in the alveoli, including effective opsonization and macrophage function, consequently affecting microbial clearance and increasing the risk of pneumonia.29 In addition, patients with impaired cardiac function may fail to meet the increased demand for cardiac output owing to hemodynamic changes associated with pneumonia.30 A current or latent history of malignancy can adversely affect the clinical course of patients with aspiration pneumonia. Cancer-related inflammation causes exhaustion, which leads to undernutrition and inactivity. Systemic cytotoxic chemotherapy or radiotherapy may attenuate immunity owing to impaired bone marrow function, dysfunction of immunocytes, and prolonged gastrointestinal dysfunction. The prognostic utility of scoring systems such as CURB-65, A-DROP, and pneumonia severity index for older patients with pneumonia remains controversial owing to heterogeneity in older adults.31-33 These scoring systems comprise age, gender, vital signs, laboratory findings, and comorbidities but lack nutritional indicators. Moreover, an initial antibiotic change may represent treatment failure and/or lead to the development of side effects. Though dissecting this factor is challenging, an initial antibiotic change may lead to prolonged treatment duration and result in further deterioration in general condition and patient outcomes. As stated above, similar to previous reports, we conjectured that the prognostic evaluation of older patients with aspiration pneumonia requires comprehensive assessments of patient status, disease severity, and microbiological and/or antibiotic components.
This study had some limitations. First, this was a retrospective study at a single institute. Patient characteristics and backgrounds may differ between countries and/or local regions. Thus, the generalizability of our findings to other populations may be limited. Second, the diagnosis of aspiration pneumonia was conducted based on clinical symptoms, test results compatible with pneumonia, and findings regarding aspiration assessed by the ST and trained nurse. Given the lack of consensus on diagnostic criteria for aspiration pneumonia, this issue warrants further discussion. Third, this study did not precisely investigate the cause of death, which may include mortality events other than aspiration pneumonia. Notably, unlike CAP in younger patients, some patients developed aspiration pneumonia in the course of senility and exhibited fatal outcomes. Despite these limitations, this study employed a relatively large sample size compared with previous studies on patients with aspiration pneumonia.
In conclusion, the assessment of nutrition, disease severity, microbiological findings, and antibiotic factors in older patients with aspiration pneumonia is crucial for predicting prognosis. In particular, GNRI is easy to calculate and may have a greater prognostic value than conventional nutritional indicators. Further investigations are warranted to validate the results of the present study.