Association Between the Serum Phosphate Levels and Hospital Mortality as Well as 90-Day Mortality Among Critically Ill Patients with Chronic Obstructive Pulmonary Disease: A Retrospective Cohort Study

Purpose: COPD patients frequently have abnormal serum phosphorus levels. The objective of this study was to examine the correlation between serum phosphorus levels with hospital and 90-day mortality in critically ill patients with COPD. Patients and Methods: The MIMIC IV database was used for this retrospective cohort analysis. We extracted demographics, vital signs, laboratory tests, comorbidity, antibiotic usage, ventilation and scoring systems within the first 24 hours of ICU admission. Restricted cubic splines and multivariate cox regression analysis models were used to evaluate the connection between serum phosphorus with hospital and 90-day mortality. We assessed and classified various factors including gender, age, renal disease, severe liver disease, the utilization of antibiotics and congestive heart failure. Results: We included a total of 3611 patients with COPD, with a median age of 70.7 years. After adjusting for all other factors, we observed a significant positive association between serum phosphate levels with both hospital mortality (HR 1.19, 95% CI: 1.07– 1.31, p< 0.001) and 90-day mortality (HR 1.15, 95% CI: 1.06– 1.24, p< 0.001). Compared to the medium group (Q2 ≥ 3.15, < 4.0), the adjusted hazard ratios for hospital mortality were 1.47 (95% CI: 1.08– 2, p=0.013), and 1.31 (95% CI: 1.06– 1.61, p=0.013) for 90-day mortality in the high group (Q3≥ 4.0). Hospital mortality decreased at serum phosphate levels below 3.8 mg/dl (HR 0.664, 95% CI: 0.468– 0.943, p=0.022), but increased for both hospital (HR 1.312, 95% CI: 1.141– 1.509, p< 0.001) and 90-day mortality (HR 1.236, 95% CI: 1.102– 1.386, p< 0.001) when levels were above 3.8 mg/dl. Subgroup and sensitivity analyses yielded consistent results. Conclusion: In critical ill COPD patients, this study demonstrated a non-linear association between serum phosphate levels and both hospital and 90-day mortality. Notably, there was an inflection point at 3.8 mg/dl, indicating a significant shift in outcomes. Future prospective research is necessary to validate this correlation. Keywords: COPD, serum phosphate, mortality, MIMIC-IV, critically ill