Individualised Weaning From Mechanical Ventilation in General ICU

Inclusion Criteria: * Patient is expected to be on invasive mechanical ventilation more 24 hours. * Age \> 18 years * Haemodynamically stable (with instability defined by the presence of two or more of the following criteria: acidosis pH \< 7.2, poor urine output \< 0.5ml/kg, use of vasopressors, e.g. noradrenline \> 25 μg/min). * Patient consent or, in the case that the patient is unable, assent from the next of kin or treating physician following understanding and accept of oral and written information describing the study Exclusion Criteria: * The absence of an arterial catheter for blood sampling at study start. * Medical history of home mechanical ventilation which may lead to prolonged stay in the ICU, including long term oxygen therapy and non-invasive ventilation not associated with sleep apnoa. * Clinical conditions requiring treatment with extracorporeal membrane oxygenation, i.e. an inspired oxygen of 100% for more than 24 hours. * Head trauma or other conditions where intra-cranial pressure may be elevated and tight regulation of arterial CO2 level is paramount. * Primary neurological patients (Glasgow coma score \<10, neurologic damage with limited prognosis, stroke hemiplegia). * Severe heart failure, classified as grade 4 of the Association of Cardiology guidelines \[2\]. * End stage liver disease. * Multiple medical ICU admissions, i.e. more than one admission. * Corrective orthognathic surgery. * Esophageal surgery. * Morbidly obese patients defined as eit…