Shuang Du,1,* Ke Lin,2,* Jing Li,3 Xin Zhou,4 Chaolan Wang,2 Jun Liu,3 Na Li,2 Jian Chen2 

1Department of Rehabilitation Medicine, The First People’s Hospital of Jin Tang County, Chengdu, Sichuan, 610400, People’s Republic of China; 2Traditional Chinese Medicine Department, The First People’s Hospital of Jintang County, Chengdu, Sichuan, 610400, People’s Republic of China; 3Department of Respiratory and Critical Care Medicine, The First People’s Hospital of Jintang County, Chengdu, Sichuan, 610400, People’s Republic of China; 4Department of Laboratory Medicine, West China Hospital of Sichuan University, Chengdu, 610041, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Jian Chen, Traditional Chinese Medicine Department, The First People’s Hospital of Jintang County, Chengdu, Sichuan, 610400, People’s Republic of China, Tel +86-10-18908176456, Email chenjian792@163.com

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