Differential Diagnosis

The patient's presentation of coughing up clear sputum, abdominal and back pain, altered mental status, and vital signs indicating tachycardia and hypoxemia, along with a history of recent digestive surgery, gastric ulcer with perforation, and COPD, suggests a complex clinical picture. Here is a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Pulmonary embolism (PE): Given the recent history of surgery, which is a significant risk factor for venous thromboembolism, along with symptoms of cough, abdominal and back pain, and hypoxemia, PE is a highly plausible diagnosis. The altered mental status could be due to hypoxia.

• Other Likely Diagnoses

  • Pneumonia: The patient's history of COPD and recent surgery increases the risk of developing pneumonia, which could explain the cough, fever, and hypoxemia.
  • Anastomotic leak or abscess: Following digestive surgery, especially with a history of gastric ulcer perforation, there's a risk of complications such as an anastomotic leak or abscess, which could cause abdominal pain, fever, and altered mental status due to sepsis.
  • Acute respiratory distress syndrome (ARDS): This could be a complication of severe pneumonia, sepsis, or another critical illness, leading to hypoxemia and altered mental status.

• Do Not Miss Diagnoses

  • Sepsis: Given the recent surgery and history of gastric ulcer perforation, sepsis is a critical diagnosis not to miss. It could explain the altered mental status, tachycardia, and hypoxemia.
  • Cardiac ischemia or myocardial infarction: Although less directly related to the symptoms, cardiac events can cause chest pain, shortness of breath, and altered mental status, especially in a patient with significant comorbidities.
  • Pulmonary edema: Especially if there's a history of heart failure or significant fluid overload post-surgery, pulmonary edema could explain the cough, hypoxemia, and altered mental status.

• Rare Diagnoses

  • Empyema or complicated parapneumonic effusion: Although less common, these conditions could explain the patient's symptoms, especially if there's a history of pneumonia or recent thoracic surgery.
  • Acute aortic dissection: This is a rare but life-threatening condition that could cause back pain, altered mental status, and hypoxemia if there's involvement of the aortic arch or descending aorta affecting blood flow to vital organs.