Differential Diagnosis

The patient's symptoms of fluctuating blood pressure, elevated heart rate, low-grade fevers, chest pressure, sharp pains, and significant drops in blood pressure upon standing, along with other symptoms like headaches, night sweats, nausea, fatigue, and shortness of breath, suggest a complex clinical picture. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Dehydration and Orthostatic Hypotension: The patient's symptoms of fluctuating BP, drops in BP with standing and activity, and improvement with IV fluids suggest dehydration and orthostatic hypotension as a primary concern. The presence of nausea, fatigue, and headaches further supports this diagnosis.

• Other Likely Diagnoses

  • Anemia: Slightly lower RBC, hemoglobin, and hematocrit levels could indicate anemia, which might contribute to the patient's fatigue, shortness of breath, and possibly the orthostatic hypotension.
  • Infectious Disease: Low-grade fevers and night sweats could suggest an underlying infectious process, such as endocarditis, tuberculosis, or a viral infection, which needs to be considered given the patient's overall clinical presentation.
  • Autonomic Dysfunction: The significant fluctuations in blood pressure and heart rate, along with orthostatic hypotension, might indicate autonomic nervous system dysfunction, which could be primary or secondary to another condition.

• Do Not Miss Diagnoses

  • Septic Shock: Although the patient's oxygen levels are mostly stable, the presence of low-grade fevers, tachycardia, and significant hypotension with activity could be indicative of early septic shock, which is a medical emergency.
  • Cardiac Tamponade: Chest pressure and sharp pains, along with hypotension, could suggest cardiac tamponade, a life-threatening condition that requires immediate intervention.
  • Pulmonary Embolism: Shortness of breath, especially worsening with activity, and chest pain could indicate a pulmonary embolism, which is a critical diagnosis not to miss.

• Rare Diagnoses

  • Pheochromocytoma: This rare tumor of the adrenal gland could cause fluctuating blood pressure, tachycardia, and orthostatic hypotension, along with headaches and sweating.
  • Addison's Disease: Although less common, Addison's disease (primary adrenal insufficiency) could explain the orthostatic hypotension, fatigue, and possibly some of the other symptoms like nausea and low-grade fevers.
  • Mitral Valve Prolapse with Significant Regurgitation: This condition might lead to symptoms such as palpitations, shortness of breath, and chest discomfort, but it would be less likely to cause the significant fluctuations in blood pressure and orthostatic changes seen in this patient.