First-Month Adherence to Home Non-Invasive Ventilation in Stable Hypercapnic COPD: Associations with BMI and Bicarbonate Levels.

INTRODUCTION: Long-term home non-invasive mechanical ventilation (NIV) is widely used in patients with hypercapnic chronic obstructive pulmonary disease (COPD). However, its efficacy is heavily dependent on patient adherence. Body mass index (BMI) can influence tolerance and ventilatory load, but its impact on adherence remains unclear. Additionally, NIV for later use at home is frequently initiated during hospitalization to facilitate early discharge, and its ongoing necessity varies. METHODS: This retrospective cohort study included patients with stable hypercapnic COPD prescribed home NIV between 2017 and 2025 at a tertiary respiratory intensive care unit outpatient clinic. Demographics, arterial blood gases, spirometry, ventilator settings, and first-month NIV usage data were extracted from the patients' medical records. We used correlation analyses and Poisson regression modeling to evaluate factors associated with daily hours of NIV use. RESULTS: A total of 413 patients were included. The mean partial pressure of carbon dioxide was 48 ± 7 mmHg. The mean forced expiratory volume in the first second was 28%, indicating severe airflow limitation. Overall adherence was very poor, with approximately 80% of patients using NIV for <4 hours a day, regardless of their BMI category. We found no significant linear correlation between BMI and NIV adherence. A large proportion of the low-adherence group had elevated bicarbonate (HCO3 -) levels (≥27 mmol/L), suggesting chronic compensated hypercapnia. Multivariable analysis found BMI to predict slightly higher adherence (risk ratio [RR] 1.01; p = 0.050), whereas higher HCO3 - was associated with lower adherence (RR 0.96; p = 0.020). DISCUSSION: BMI was not a major determinant of first-month NIV adherence, whereas elevated HCO3 - levels may help identify patients at increased risk of poor early NIV adherence.