Interaction of mental comorbidity and physical multimorbidity predicts length-of-stay in medical inpatients

Abstract

Background: Mental comorbidities of physically ill patients lead to higher morbidity, mortality, health-care utilization and costs.

Objective: The aim of the study was to investigate the impact of mental comorbidity and physical multimorbidity on the length-of-stay in medical inpatients at a maximum-care university hospital.

Design: The study follows a retrospective, quantitative cross-sectional analysis approach to investigate mental comorbidity and physical multimorbidity in internal medicine patients.

Patients: The study comprised a total of n = 28.553 inpatients treated in 2017, 2018 and 2019 at a German Medical University Hospital.

Main measures: Inpatients with a mental comorbidity showed a median length-of-stay of eight days that was two days longer compared to inpatients without a mental comorbidity. Neurotic and somatoform disorders (ICD-10 F4), behavioral syndromes (F5) and organic disorders (F0) were leading with respect to length-of-stay, followed by affective disorders (F3), schizophrenia and delusional disorders (F2), and substance use (F1), all above the sample mean length-of-stay. The impact of mental comorbidity on length-of-stay was greatest for middle-aged patients. Mental comorbidity and Elixhauser score as a measure for physical multimorbidity showed a significant interaction effect indicating that the impact of mental comorbidity on length-of-stay was greater in patients with higher Elixhauser scores.

Conclusions: The findings provide new insights in medical inpatients how mental comorbidity and physical multimorbidity interact with respect to length-of-stay. Mental comorbidity had a large effect on length-of-stay, especially in patients with high levels of physical multimorbidity. Thus, there is an urgent need for new service models to especially care for multimorbid inpatients with mental comorbidity.

Fig 1. Length-of-stay in relation to number of mental comorbidities.

μ: mean length-of-stay, plotted as diamonds; ci: 95% confidence interval; N: number of cases. The number of mental comorbidities on the x-axis is displayed up to 5, as the number of cases with 6 or 7 mental comorbidities is less than 10. The y-axis is cut-off at 140 days for better discernability of the boxes. S1 Fig displays the plot with all outliers.

Fig 2. Length-of-stay differentiated by mental comorbidity spectrum.

μ: mean length-of-stay, plotted as diamonds; ci: 95% confidence interval; N: number of cases that have a diagnosis in the respective F-category (ICD-10 range starting with the characters F0-F6). Cases that have mental comorbidity diagnoses in several F-categories are counted in each one separately and are therefore represented in multiple boxes. The y-axis is cut-off at 60 days for better discernability of the boxes. S2 Fig displays the plot with all outliers.

Fig 3. Length-of-stay differentiated by age group and presence of mental comorbidity.

Age group naming: 10 encompasses age at hospitalization 18–19 years, 20 encompasses 20–29 years, 30 eoncompasses 30–39 years etc. The numerical values matching this figure are in Table 2. Error bars indicate the 95% confidence interval.

Fig 4. Length-of-stay for increasing Elixhauser score with and without mental comorbidity.

The Elixhauser score on the x-axis is displayed up to 10, as the number of cases with higher scores were ≤ 20. The numerical values matching this figure are shown in S3 Table. Error bars indicate the 95% confidence interval.