Electrolyte Imbalance and Its Prognostic Impact on All-Cause Mortality in ICU Patients with Respiratory Failure

<i>Background and Objectives</i>: Chronic obstructive pulmonary disease (COPD) and acute respiratory failure are critical clinical conditions associated with high mortality rates in intensive care units (ICUs). Electrolyte imbalances are significant variables that may influence all-cause ICU mortality in this patient group. In this retrospective study, we aimed to investigate the relationships between the serum levels of sodium (Na⁺), chloride (Cl^-), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) and all-cause ICU mortality in patients admitted with respiratory failure. Additionally, we conducted a detailed mortality analysis on the basis of sodium quartiles and pathological absolute sodium thresholds to reveal their associations with ICU mortality from all causes. <i>Materials and Methods</i>: A total of 1109 patients were analyzed between January 2022 and January 2024. The electrolyte levels measured at ICU admission, demographic data, APACHE II and SOFA scores, arterial blood gas results, BUN and creatinine levels, need for noninvasive mechanical ventilation, length of ICU stay, and survival outcomes were assessed. Statistical analyses were performed via Kaplan-Meier survival analysis and the Cox regression method. <i>Results</i>: Our findings revealed that patients with low potassium and calcium levels had significantly higher mortality rates (<i>p</i> < 0.05). When sodium levels were divided into quartiles, mortality risk markedly increased in both the lowest (Q1) and highest (Q4) quartiles. Cox regression analysis revealed that the mortality risk in hyponatremic patients was 2.2 times greater than that in normonatremic patients (<i>p</i> = 0.005). In the hyponatremic group, the increased mortality risk was statistically borderline significant (<i>p</i> = 0.06). In the logistic regression analysis conducted to evaluate ICU mortality, which included all electrolyte levels and clinical scoring systems, higher APACHE II and SOFA scores were identified as significant risk factors for ICU mortality. Conversely, the presence of COPD was found to be relatively protective compared with other underlying causes of respiratory failure in terms of mortality. <i>Conclusions</i>: Electrolyte imbalances are important predictors of mortality in patients with respiratory failure. Sodium levels exhibit a "U-shaped" relationship with mortality, with hyponatremia emerging as a prominent risk factor. Careful assessment of electrolyte imbalances is crucial in the clinical management of these patients.