This prospective, non-interventional observational study will evaluate the risk of reintubation in adult postoperative patients admitted to the intensive care unit after major surgery. Reintubation after extubation is an important clinical problem because it may increase complications, prolong mechanical ventilation, and extend intensive care and hospital stay.

The study will include adult patients who are extubated in the operating room and admitted to the intensive care unit with spontaneous breathing. Within the first hours after ICU admission, bedside ultrasound measurements of diaphragm thickness, parasternal intercostal muscle thickness, and lung ultrasound score will be performed. The ROX index will also be calculated using oxygen saturation, inspired oxygen concentration, and respiratory rate. Perioperative fluid balance will be recorded from anesthesia and patient files.

Patients will be followed for 48 to 72 hours after ICU admission to determine whether reintubation is required. The study aims to assess whether respiratory muscle ultrasound findings, lung ultrasound score, ROX index, and perioperative fluid balance can help predict reintubation risk in postoperative ICU patients. No additional treatment or intervention will be applied as part of the study, and all clinical decisions will be made by the responsible intensive care team according to routine clinical practice.

Inclusion Criteria:

Adult patients aged 18 years and older

Patients requiring postoperative intensive care follow-up after major surgery, including abdominal, vascular, orthopedic, or ear, nose, throat, head and neck surgery

Patients extubated in the operating room and admitted to the intensive care unit with spontaneous breathing

Patients without any clinical condition preventing the planned measurements within the first 0-2 hours after ICU admission (T0 and T1)

Patients for whom written informed consent can be obtained from the patient or legally authorized representative

Patients admitted to the intensive care unit within the specified study period after ethics committee approval and enrolled consecutively

Exclusion Criteria:

Patients younger than 18 years of age

Patients who leave the operating room intubated or are admitted to the intensive care unit while intubated

Patients with a tracheostomy

Patients with a history of diaphragmatic paralysis

Patients with a significant neuromuscular disease, such as ALS, myasthenia gravis, or similar conditions

Patients with conditions that significantly prevent ultrasound measurements, including marked subcutaneous emphysema, large dressings or bandages covering the measurement area, inability to access the measurement site due to drains or the surgical field, or inability to obtain technically adequate images

Patients in whom the planned measurements cannot be performed due to clinical instability requiring emergency intubation immediately after ICU admission

Patients from whom informed consent cannot be obtained, or patients or legally authorized representatives who refuse participation

Adult postoperative patients aged 18 years and older who are admitted to the anesthesia and reanimation intensive care units after major surgery, including abdominal, vascular, orthopedic, and ear, nose, throat, head and neck surgery. Eligible patients will be those extubated in the operating room and admitted to the intensive care unit with spontaneous breathing during the study period after ethics committee approval.