Is low socioeconomic position associated with mortality among mechanically ventilated patients in Denmark?

Background: Mechanically ventilated patients have high mortality. Low socioeconomic position (SEP) is associated with poor health in many vulnerable populations. Whether SEP is associated with mortality in frail patients such as those receiving invasive mechanical ventilation (MV) is unclear, especially outside of the COVID-19 pandemic.

Objectives: To examine whether low SEP is associated with mortality among Danish adults on MV.

Methods: We conducted a population- and registry-based cohort study of all non-surgical patients aged ≥25 years receiving incident MV from January 2005 to March 2019 in Denmark. Three SEP indicators were defined as low, medium, or high: highest education (1 yr pre-admission); mean annual disposable household income in those <65 years (3 yrs pre-admission); and mean liquid assets in those ≥65 years (3 yrs pre-admission). Another SEP indicator, employment status, was defined as unemployed, outside workforce, or employed in those <65 (1 yr pre-admission). Demographics were identified at MV start and comorbidities within 5 years pre-admission. The outcomes were 30-day and 1-year mortality. We performed propensity score (PS) weighting using average treatment effect among the treated weights to compare mortality between SEP groups, by age. Cox proportional hazards regression was used to compute hazard ratios (HR).

Results: We identified 19,472 patients aged 25-64 years and 25,327 aged ≥65 years. Baseline differences in measured confounders across SEP groups were balanced by PS weighting.
Among 25-64-year-olds, unweighted 30-day mortality for low, medium, and high income groups was 32%, 33%, and 31%, respectively. PS-weighted HRs for the low income group were increased for 30-day and 1-year mortality compared with the medium income group (HR 1.07 [95% confidence interval (CI) 1.00-1.14]; HR 1.07 [95% CI 1.01-1.14]) and the high income group (HR 1.40 [95% 1.13-1.72]; HR 1.39 [95% CI 1.14-1.68]). Patients with low educational level had higher 30-day and 1-year mortality than those with high level (HR 1.27 [95% CI 1.13-1.42]; HR 1.28 [95% CI 1.16-1.42]). Unemployed patients had higher 30-day and 1-year mortality than those who were employed (HR 1.21 [95% CI 1.05-1.39]; HR 1.18 [95% CI 1.03-1.35]).
Among patients ≥65 years, unweighted 30-day mortality for the low, medium, and high income groups was 51%, 53%, and 51%, respectively. There was a slightly increased risk of 30-day and 1-year mortality for those with low vs high liquid assets (HR 1.06 [95% CI 0.99-1.15]; HR 1.12 [95% CI 1.05-1.19]).

Conclusions: Despite Danish residents having access to tax-funded healthcare, we observed differences in mortality risk by SEP indicators among non-surgical patients on invasive MV, particularly in adults <65 years.