This large national cohort study, including over 500,000 patients, where around 5% are treated with continuous renal replacement therapy (CRRT) , aims to evaluate the association between time to initiation of CRRT and intensive care unit (ICU) length of stay (LOS).

This large national cohort study, including over 500,000 patients, aims to evaluate the association between time to initiation of continuous renal replacement therapy (CRRT) and intensive care unit (ICU) length of stay (LOS).

The investigators hypothesize that earlier start of CRRT is associated with shorter length of stay among critically ill patients.

CRRT is seen as a costly intervention, and after studies failing to demonstrate a mortality benefit from earlier initiation, the trend is to push, or postpone the start of CRRT. In Sweden the additional cost of CRRT amounts to around 5000 SEK, approximately 500 dollars/euros per 24 hours. However, the 24-hour cost of staying in the ICU is around 58000 SEK or 5800 dollars/euros.

Inclusion Criteria:

• Patients with critical illness
• Admitted to Swedish ICUs from 2010-2023
• Adult (18 years or older)

Exclusion Criteria:

*Patients under 18 years of age

All adult critically ill patients in Swedish ICUs from 2010-2023, with- and without the need of CRRT forms this cohort.

Within the cohort, a nested case-control type of study can be performed. Two groups:

Group 1: Patients with CRRT initiation time less than 30 hours (early CRRT) Group 2: Patients with CRRT initiation time 30 hours or more (late CRRT)

Swedish law prohibits IPD sharing using extracted quality register data, when this has not been stated in the primary ethics application. However, other researchers can theoretically apply for data extraction from the Swedish Intensive Care Register.