From the Journals

In-hospital mortality increased in COPD patients with acute exacerbations and high serum phosphate levels



An investigation into associations between serum phosphate levels and in-hospital mortality risk among patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) found significantly higher in-hospital mortality among AECOPD patients with high serum phosphate levels. The finding, according to Siqi Li et al. in a preproof HELIYON article, suggests that hyperphosphatemia may be a high-risk factor for AECOPD-related in-hospital mortality.

Phosphorus is key to several physiological processes, among them energy metabolism, bone mineralization, membrane transport, and intracellular signaling. Li et al. pointed out that in patients with multiple diseases, hyperphosphatemia is associated with increased mortality. In the development of COPD specifically, acute exacerbations have been shown in several recent studies to be an important adverse event conferring heightened mortality risk. Despite many efforts, AECOPD mortality rates remain high, making identification of potential factors, Li et al. stated, crucial for improving outcomes in high-risk patients.

The electronic Intensive Care Unit Collaborative Research Database (eICU-CRD) holds data associated with over 200,000 patient stays, providing a large sample size for research studies. To determine the relationship between serum phosphate and in-hospital mortality in AECOPD patients, investigators analyzed data from a total of 1,199 AECOPD patients (mean age, 68 years; ~55% female) enrolled in eICU-CRD and divided them into three groups according to serum phosphate level tertiles: lowest tertile (serum phosphate ≤ 3.0 mg/dL, n = 445), median tertile (serum phosphate > 3.0 mg/dL and ≤ 4.0 mg/dL, n = 378), and highest tertile (serum phosphate > 4.0 mg/dL, n = 376). The Li et al. study’s primary outcome was all-cause in-hospital mortality, defined as survival to hospital discharge. Secondary outcomes included length of stay (LOS) in the intensive care unit (ICU), LOS in the hospital, and all-cause ICU mortality.

The Li et al. analysis of patient characteristics showed that patients in the highest tertile of serum phosphate had significantly higher body mass index (BMI) (P < .001), lower temperature (P < .001), lower heart rate (P < .001), lower mean arterial blood pressure (P = .011), higher creatinine (P < .001), higher potassium (P < .001), higher sequential organ failure assessment (SOFA) (P < .001), higher acute physiology and chronic health evaluation (APACHE IV) (P < .001), and higher ICU mortality (P < .001). Also, patients with higher serum phosphate levels were more likely to receive renal replacement therapy (RRT) (P < .001) and vasoactive drugs (P = .003) than those in the lower serum phosphate group. Such differences were also observed for age (P = .021), calcium level (P = .023), sodium level (P = .039), hypertension (P = .014), coronary artery disease (P = .004), diabetes (P = .017), and chronic kidney disease (P < .001). No significant differences were observed for gender, respiration rate, SpO2, white blood cell count, hemoglobin, platelets, cirrhosis, stroke, ventilation, LOS in ICU, and LOS in hospital (P > .05).

A univariate logistic regression analysis performed to determine the relationship between serum phosphate level and risk of in-hospital mortality revealed that higher serum phosphate level correlated with increased in-hospital mortality (odds ratio, 1.30; 95% confidence interval, 1.16-1.46; P < .001).

Li et al. posited that several mechanisms may explain increased mortality at higher serum phosphate levels in AECOPD patients: increased serum phosphate induces vascular calcification and endothelial dysfunction, leading to organ dysfunction; hyperphosphatemia causes oxidative stress, cell apoptosis, and inflammation, all of which are involved in the pathogenesis of AECOPD, and a higher phosphate diet exacerbates aging and lung emphysema phenotypes; restriction of phosphate intake and absorption relieves these phenotypes and alveolar destruction, which might contribute to the development of AECOPD.

Li et al. concluded: “Reducing serum phosphate levels may be a therapeutic strategy to improve prognosis of AECOPD patients.”

“This large retrospective analysis on eICU database in the U.S. revealed elevated serum phosphate levels with increased in-hospital mortality among patients experiencing acute exacerbation of COPD,” commented Dharani Narendra, MD, assistant professor in medicine, at Baylor College of Medicine, Houston. “This association, previously observed in various chronic conditions including COPD, particularly in men, is now noted to apply to both genders, irrespective of chronic kidney disease. The study also hints at potential mechanisms for elevated phosphate levels, such as inflammation, oxidative stress, and cell apoptosis in AECOPD, as well as a high-phosphate diet.”

She told this news organization also, “It remains imperative to ascertain whether treating hyperphosphatemia or implementing dietary phosphate restrictions can reduce mortality or prevent AECOPD episodes. These demand additional clinical trials to establish a definitive cause-and-effect relationship and to guide potential treatment and prevention strategies.”

Noting study limitations, Li et al. stated that many variables, such as smoking, exacerbation frequency, severity, PH, PaO2, PaCO2, and lactate, were not included in this study owing to more than 20% missing values.

This work was supported by the National Natural Science Foundation of China, Scientific Research Fund of Hunan Provincial Education Department, Hunan Provincial Natural Science Foundation, and Special fund for rehabilitation medicine of the National Clinical Research Center for Geriatric Disorders Clinical Research Fund. The authors declare no competing interests.

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