Day #125 - Polycythemia and Hypoxemia

Today we discussed a case of a patient with polycythemia and acute hypoxemia. The most likely diagnosis was pulmonary embolism and the discussant detailed an excellent approach to the diagnosis of PE.

I have previously blogged about DVT and PE here. The article the discussant mentioned is available here

I wanted to focus on the approach to polycythemia in more detail (review article here):

Definition: Hemoglobin greater than 165 in women (hematocrit 48%) or 185 in men (hematocrit 52%).

Relative polycythemia, related to volume contraction, needs to be differentiated from absolute polycythemia in which there is an increased red cell mass.

Primary

• Polycythemia vera
• High oxygen affinity hemoglobins
• Epo receptor activating mutations
• Other

Secondary

• Chronic hypoxemia from:
  
  • Cyanotic heart disease
  • Right to left shunts (i.e. AVMs in HHT, other)
    
  • Chronic hypoxemic lung disease
  • Obstructive sleep apnea
  • Pickwickian syndrome (obesity hypoventillation)
  • Living at altitude
  • Chronic carbon monoxide poisoning! (Including smoker's polycythemia)
    
• EPO overproduction (think highly vascular tumors):
  
  • Renal cell carcinoma
  • HCC
  • Uterine cancer
  • Hemangioblastoma
    

Uptodate has a good algorithm for the diagnosis of polycythemia (adaped below):


Treatment of PRV:

• ASA to prevent ischemic events
• Phlebotomy to hematocrit less than 45% in men and 42% in women
• Failing phlebotomy add hydroxyurea
• Add allopurinol in patients with symptomatic hyperuricemia or very high uric acid excretion (greater than 1100mg/day)