Inclusion Criteria  Main study  Data will be collected from patients who fulfil all the following inclusion criteria:  1. Standard ICU arm:  All male or female aged ≥18 years admitted to a participating Intensive Care Units who are invasively mechanically ventilated for more than 12 hours will be included. Patients admitted with medical, surgical, trauma, burns, neurological and neurosurgical clinical problems. Admitted to ICU prior to the COVID-19 surge in the specific country.  COVID-19 sub-study  Data will be collected from patients who fulfil all the following inclusion criteria:  COVID-19 ICU arm:  All male or female aged ≥18 years admitted to a participating Intensive Care Units who are invasively mechanically ventilated for more than 12 hours will be included.  Patients admitted with pneumonia and/or acute respiratory failure and a diagnosis of COVID-19.  The accepted criteria for the diagnosis to COVID-19 includes one of the following: 1) RT-qPCR is positive for SARS-CoV19 nucleic acid; 2) the viral gene identified by gene sequencing; or 3) presence of COVID-19-specified IgM and IgG antibodies.  Non-COVID-19 ICU arm:  All male or female aged ≥18 years admitted to a participating Intensive Care Units who are invasively mechanically ventilated for more than 12 hours will be included. Patients admitted with medical, surgical, trauma, burns, neurological and neurosurgical clinical problems. No confirmed or suspected COVID-19 disease.  Exclusion Criteria  Main study  Data will not be collected from patients who fulfil the following exclusion criteria:  1. Standard ICU arm:  • Patients admitted to non-acute care units  COVID-19 sub-study  Data will not be collected from patients who fulfil the following exclusion criteria:  COVID-19 ICU arm:  Patients with confirmed diagnosis of COVID-19 but admitted to ICU for indications different than pneumonia and/or acute respiratory failure (incidental positive COVID-19) Patients admitted to non-acute care units  Non-COVID-19 ICU arm:  Patients admitted to non-acute care units