This study will address two specific research questions simultaneously:

1. validation of the GastroIntestinal (GI) Dysfunction score (GIDS).
2. description of epidemiology, risk factors, and management of phosphate disorders.

The aim is to recruit 20 ICUs and 1500 ICU patients. Sites will recruit all consecutive adult patients to a maximum of 120 patients or a maximum recruitment period of 8 weeks, whichever comes first. Daily data collection on gastrointestinal signs and symptoms as well as phosphate values and management will be collected during ICU stay for maximum of 7 days. 28 and 90 day mortality and days free of organ support will be the main outcomes. Secondary outcomes include prevalence of hypo- and hyperphosphatemia and description of their management.

Patient population All consecutive adult patients that are admitted to participating ICU during a recruitment period of maximum 8 weeks.

Duration of the study for the individual patient:

1. Study period of a maximum of 7 days
2. Follow-up period of a maximum of 90 days All patients will be included in the Part A of the study validating GIDS, patients from sites with routine serum phosphate measurements will be included also in the Part B of the study where additional data on serum phosphate levels and management of phosphate disorders will be collected. There will be no additional measurements due to study participation, daily routine is documented.

Baseline characteristics will be collected at ICU admission/study inclusion Daily data include routine data on organ dysfunctions and organ support therapies and specific data on phosphate where available.

Outcome data include 28 and 90 days mortality, and days free of organ support by day 28.

Inclusion Criteria:

• Admission to ICU during the study period
• Age ≥18 years

Exclusion Criteria:

• Age <18 years;
• Patients with restrictions of care such as "no intubation" or "no renal replacement therapy" on ICU admission and patients admitted for treatment as organ donors;
• Continuous chronic home ventilation for neuromuscular disease;
• Declined participation or informed consent (if the local ethics committee requests the latter for this non-interventional study);
• Readmission to ICU during the study period

All consecutive adult patients that are admitted to participating ICU during a recruitment period of maximum 8 weeks. In all included patients data on organ dysfunctions will be collected, in patients from sites with routine serum phosphate measurements additional data on phosphate values and management will be collected (inclusion in the Phosphate part of the study).