Based on the assessment above, what procedures and treatments should the nurse anticipate for Mr. T?

Mr. T. is a 58-year-old male admitted to the critical care unit with a diagnosis of cirrhosis. Mr. T. has been experiencing nausea and vomiting for the past 5 days, shortness of breath, and low-grade fever. The morning of admission, he had an episode of passing bright red stools. Mr. T. is drowsy but responsive to both verbal and painful stimuli. His wife stated that he had not been eating well and had difficulty sleeping for several nights. On assessment, Mr. T’s vital signs are oral temperature 100.5° F, blood pressure 105/60 mm Hg, pulse 102 beats/min, respirations 28/min, and oxygen saturation (SpO2) 94% on 2 liters/min by nasal cannula. Lying supine, his SpO2 dropped to 88%.
Mr. T. also has severe abdominal distention, is positive for jaundice, and has flapping tremors on his right hand. His past medical history includes alcohol (ETOH) dependency, hepatitis C, upper gastrointestinal bleeding, hypertension, and depression. Mr. T’s initial laboratory results are as follows:
Sodium 136 mEq/L
Potassium 3.2 mEq/L
BUN 28 mg/dL
Creatinine 1.4 mg/dL
Bilirubin 3.3 mg/dL
Platelets 80,000 cells/microliter
Prothrombin time (PT) 14 sec
Partial thromboplastin time (PTT) 35.6 sec
Ammonia 62 mcg/dL
Glucose 75 mg/dL
White blood cell count 11,000/microliter
Hemoglobin (Hgb) 9.1 g/dL
Hematocrit (Hct) 28.4%
Albumin 3.0 g/dL
Questions:
Why does Mr. T’s oxygen saturation drop when he is lying supine?
Based on the assessment above, what procedures and treatments should the nurse anticipate for Mr. T?
What is the priority nursing diagnosis for Mr. T?
Based on the priority nursing diagnosis, what patient goals are appropriate for Mr. T?