Urea clearance can be used as a relatively simple method to estimate blood flow changes during microdialysis of vasoactive substances, in particular when the tissue is preconditioned in order to enhance the contrast between baseline and the responses to the provocations. Our results support that, in the model described, urea clearance was superior to the optical methods as it detected both the increases and decrease in blood flow, and the returns to baseline between these periods.

Background Questions remain about long-term outcome for COVID-19 patients in general, and differences between men and women in particular given the fact that men seem to suffer a more dramatic course of the disease. We therefore analysed outcome beyond 90 days in ICU patients with COVID-19, with special focus on differences between men and women. Methods We identified all patient ≥ 18 years with COVID-19 admitted between March 6 and June 30, 2020, in the Swedish Intensive Care Registry. Patients were followed until death or study end-point October 22, 2020. Association with patient sex and mortality, in addition to clinical variables, was estimated using Cox regression. We also performed a logistic regression model estimating factors associated with 90-day mortality. Results In total, 2354 patients with COVID-19 were included. Four patients were still in the ICU at study end-point. Median follow-up time was 183 days. Mortality at 90-days was 26.9%, 23.4% in women and 28.2% in men. After 90 days until end of follow-up, only 11 deaths occurred. On multivariable Cox regression analysis, male sex (HR 1.28, 95% CI 1.06–1.54) remained significantly associated with mortality even after adjustments. Additionally, age, COPD/asthma, immune deficiency, malignancy, SAPS3 and admission month were associated with mortality. The logistic regression model of 90-day mortality showed almost identical results. Conclusions In this nationwide study of ICU patients with COVID-19, men were at higher risk of poor long-term outcome compared to their female counterparts. The underlying mechanisms for these differences are not fully understood and warrant further studies.

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