From December 2008 to December 2023, a total of 915 patients underwent prolonged weaning at the weaning centre of the Thoraxklinik of the University of Heidelberg. 130 patients were excluded from the analyses due to exclusion criteria. A total of 785 patients, 313 women and 472 men were included in the final analyses. The median age of the patients was 67 years, the mean BMI was 26 kg/m [2] and 14.4% of the patients had a BMI below 20 kg/m [2]. The most common cause of invasive ventilation was COPD exacerbation with 29.7% of cases, followed by pneumonia 20.1% and postoperative acute respiratory insufficiency (ARI) 17.8%. Other recorded causes were: COVID, trauma, restrictive lung disease, sepsis, obesity hypoventilation syndrome (OHS), heart failure and others. Among the comorbidities recorded in the database, cardiopulmonary diseases and obesity were particularly common: COPD in 55.4% of cases, arterial hypertension in 50.1%, heart failure in 38.3% and CHD 29.8% obesity in 28.9%. The patient characteristics stratified for men and women are shown in Table 1.

Compared to the male patients, females were smaller (160 vs. 175 cm; p < 0.001), but had a significantly higher BMI (29.5 vs. 24.4 kg/m [2]; p < 0.001). The duration of IMV before transfer to the weaning centre did not differ between the sexes, but men had a longer hospital stay in the weaning centre than women (38 vs 32 days; < 0.001). With regard to the causes of IMV, pneumonia was more frequently reported as a reason for IMV in men (16.0% vs. 22.9%; p = 0.018) and obesity hypoventilation syndrome (OHS) in women (8.0% vs. 2.3%; p < 0.001). But there were no differences between the sexes for the other causes. In terms of comorbidities, there were differences in the diagnosis of obesity in 39.9% of women and 21.6% of men (p < 0.001), in line with the recorded BMI values, and women were more likely to have pulmonary hypertension. Men were more likely to have oncological diagnoses (14.6 vs. 8.6%; p = 0.014) and delirium (16.7 vs. 10.2%; p = 0.012), see Table 1.

Overall, 244 (77.9%) women and 356 (75.4%) men were successfully weaned from invasive ventilation (p = 0.440). Those women who were successfully weaned were more likely than men to require non-invasive ventilation (category 3b; 44.7% vs. 34.3%; p = 0.004) and men were more likely to be discharged without NIV (category 3a; 41.1% vs. 33.2%; p = 0.029). There were no significant sex differences in discharge with IMV (17.3% of women and 17.4% of men; p = 1,000) and death in the weaning centre (4.8% of women and 7.2% of men; p = 0.179). The weaning outcomes for men and women are shown in Fig. 1.

Weaning outcomes for men and women N = 785. According to German guidelines, patients were categorised as follows: category 3a: successful prolonged weaning from mechanical ventilation without the need for subsequent long-term non-invasive ventilation (NIV); category 3b: successful prolonged weaning from mechanical ventilation with the continuation of NIV and from mechanical ventilation; category 3cI: failed weaning, patients who continued to receive mechanical ventilation as an outpatient; and category 3cII: failed weaning, patients who died during weaning. The figure shows the number of patients in the individual categories as a percentage. *p < 0.005

In the group comparisons, older age and BMI ≤ 20 kg/m [2] were identified as risk factors for weaning failure in men but not in women. The duration of prior IMV was a relevant factor only in women. Women and Men with unsuccessful weaning also had longer stays in the weaning unit (42 vs. 31.5 days; p = 0.002 and 47 vs. 36 days; p = 0.009). Women with unsuccessful weaning were more likely to have critical illness polyneuropathy (40.6 vs. 18.9%; p < 0.001) and delirium (17.4 vs. 8.2%; p = 0.040), whereas there were no disadvantageous group differences in these comorbidities in men see Table 2.

The cox regression analyses performed with the outcome parameter weaning failure, revealed that sex had no effect on the outcome variable in the population. In the overall study population, age ≥ 65 years (HR 1.73, 95% CI 1.20–2.50; p < 0.005), IMV before transfer to the weaning centre (HR 0.001, 95% CI 1.00–1.00; < 0.001), pre-existing NIV (HR 1.81, 95% CI 1.15–2.84; p = 0.010), were relevant independent risk factors for weaning failure. Please refer to Fig. 2 and the supplementary Tables S1 for further details.

Results of Cox regression analysis for Risk factors for weaning failure in the study population N = 785. The figure shows the results of the Cox regression analysis with weaning failure as outcome variable. The plot shows the Hazard Ratios with their corresponding 95% confidence intervals corresponding to the numerical values given in supplementary Table S1. IMV Invasive mechanical ventilation before transfer to the centre, CIP Critical illness polyneuropathy, BMI body mass index, NIV non-invasive ventilation

Subsequently, regression analyses were conducted on the same set of covariates, with the results stratified by sex. In females, the duration of IMV prior to transfer (HR 1.01, 95% CI 1.00–1.01; p < 0.001), CIP (HR 1.82, 95% CI 1.03–3.23; p = 0.040) and delirium (HR 2.50, 95% CI 1.18–5.27; p = 0.017) were identified as relevant risk factors, while pneumonia was identified as a favourable factor (HR 0.40, 95% CI 0.18–0.93; p = 0.032). For men, only age ≥ 65 years (HR 2.38, 95% CI 1.42–3.99; p < 0.001) and IMV prior to transfer (HR 1.01, 95% CI 1.01–1.01/; p < 0.001 were identified as relevant risk factors. However, it is noteworthy that delirium had the opposite effect for men and proved to be a favourable factor for weaning success in the subgroup of men (HR 0.21, 95% CI 0.21–0.88; p = 0.020). Please refer to Fig. 3 and the supplementary Table S2 and 3 for further details.

Results of Cox regression analysis for Risk factors for weaning failure women and in men. The figure shows the results of the Cox regression analysis with weaning failure as the outcome variable, which were carried out separately for women (A) and men (B). The plot shows the Hazard Ratios with their corresponding 95% confidence intervals corresponding to the numerical values given in supplementary Table S 2 and 3. IMV = Invasive mechanical ventilation before transfer to the centre, CIP Critical illness polyneuropathy, BMI body mass index, NIV non-invasive ventilation