Features of pseudohypoxemia:
(1) high white blood cell count: in CLL > 100,000 per µL
(2) arterial PaO2 reduced, yet pulse oximetry oxygen saturation normal
(3) alternatively, the pulse oximetry oxygen saturation may be reduced
(4) clinical hypoxemia absent, or not as severe as expected based on test results
Proposed mechanism:
(1) for arterial blood gases: If a delay occurred between collection and testing, then oxygen may be consumed by the leukemic cells. This may become more marked if the specimen was not placed on ice during transportation.
(2) for pulse oximeter: increased methemoglobin, causing error in the calculation of oxygen saturation. Some equations assume that methemoglobin is <= 0.4% (Gartrell, 1993, page 918), while patients with hyperleukocytosis may have methemoglobin levels of 15-21%.
Actions:
(1) test blood gases immediately after collection (have blood gas instrument at the bedside)
(2) measure methemoglobin levels if performing pulse oximetry
(3) compare results of pulse oximetry with arterial blood gas findings
(4) chemotherapy with cytoreduction
(5) pulmonary function testing
