Confirmation of spurious hypoxemia using continuous blood gas analysis in a patient with chronic myelogenous leukemia

The stability of blood gases and CO-oximetry under slushed ice and room temperature conditions

OBJECTIVES

Human blood gas stability data is limited to small sample sizes and questionable statistical techniques. We sought to determine the stability of blood gases under room temperature and slushed iced conditions in patients using survival analyses.

METHODS

Whole blood samples from ∼200 patients were stored in plastic syringes and kept at room temperature (22-24 °C) or in slushed ice (0.1-0.2 °C) before analysis. Arterial and venous pO2 (15-150 mmHg), pCO2 (16-72 mmHg), pH (6.73-7.52), and the CO-oximetry panel [total hemoglobin (5.4-19.3 g/dL), percentages of oxyhemoglobin (O2Hb%, 20-99%), carboxyhemoglobin (COHb, 0.1-5.4%) and methemoglobin (MetHb, 0.2-4.6%)], were measured over 5-time points. The Royal College of Pathologists of Australasia's (RCPA's) criteria determined analyte instability. Survival analyses identified storage times at which 5% of the samples for various analytes became unstable.

RESULTS

COHb and MetHb were stable up to 3 h in slushed ice and at room temperature; pCO2, pH was stable at room temperature for about 60 min and 3 h in slushed ice. Slushed ice shortened the storage time before pO2 became unstable (from 40 to 20 min), and the instability increased when baseline pO2 was ≥60 mmHg. The storage time for pO2, pCO2, pH, and CO-oximetry, when measured together, were limited by the pO2.

CONCLUSIONS

When assessing pO2 in plastic syringes, samples kept in slushed ice harm their stability. For simplicity's sake, the data support storage times for blood gas and CO-oximetry panels of up to 40 min at room temperature if following RCPA guidelines.

Leukocytosis and Spurious Hypoxemia

Abnormally low pO2 and oxygen saturations on arterial blood gases (ABGs) test have been reported in the patients who have very high WBC and platelet counts; generally in the setting of hematological malignancies. This is presumably related to the consumption of oxygen by the active cellular elements in the arterial blood sample during the process of ABG analysis. This phenomenon which is also known as "spurious hypoxemia" or "oxygen steal" or "leukocyte/platelet larceny" is suspected when there is no other obvious explanation for hypoxemia on ABG, especially in the setting of normal oxygen saturations by the pulse oximetry. It is important for medical professionals to be aware of this condition so that appropriate workup and triage can be performed on such patients, which may otherwise lead to unnecessary hospitalization and escalation of care.

[Extreme leucocytosis can lead to an erroneous diagnosis of severe hypoxaemia. Description of a case]

The diagnosis and treatment of respiratory failure is a part of the anaesthesist's daily practice, as well as the hypoxaemia that is one of its physiological and analytical consequences. Patients with an extreme leucocytosis secondary to leukaemia can suffer an incorrect diagnosis of hypoxemia, called "pseudohypoxaemia". This is basically due to the rapid in vitro oxygen consumption, and is characterized by a low partial pressure of oxygen in arterial blood (PaO2) despite a normal oxygen saturation (SpO2) measured by pulse oximetry. Pseudohypoxaemia appears in patients with thrombocytosis or hyper-leucocytosis occurring during blastic crisis of a leukaemia. It must be suspected in patients with a discrepancy between the SpO2 measured by oximetry and the PaO2. In this context, pulse oximetry is the most accurate way to establish the diagnosis and to avoid unnecessary actions. We report the case of a patient with chronic myeloid leukaemia and extreme leucocytosis requiring emergency surgery, and diagnosed with pseudohypoxaemia during the perioperative period that led to a delay in the extubation of the patient.

Leukocytotic pseudohypoxaemia

A case of hypoxaemia was concluded to be a pseudo-condition after investigation demonstrated that the hypoxaemia was not related to lung disease, but rather to the time expiring between obtaining and analysing blood samples and to a reduction in the magnitude of the patient's white cell count.

Spurious hypokalaemia and hypophosphataemia due to extreme hyperleukocytosis in a patient with a haematological malignancy

Serious hyperleukocytosis can strongly affect laboratory results of potassium, phosphate and arterial oxygen tension. A 40-year-old woman is presented with an acute myeloid leukaemia and a strongly elevated leukocyte count (310 × 109/L). Apart from this hyperleukocytosis, initial blood tests showed hypokalaemia, hypophosphataemia and serious hypoxaemia without any corresponding complaints. Blood sampled and transported on ice or directly analysed showed no electrolyte abnormalities and hypoxaemia. The observed discrepancy in laboratory results is probably due to the metabolic activity of the leukocytes in vitro. Spurious laboratory results can be a reason for incorrect decisions concerning additional diagnostics and treatment. In conclusion, hyperleukocytosis can cause pseudohypokalaemia, pseudohypophosphataemia and pseudohypoxaemia, which can be prevented by correct sampling and immediate analysis.

Factitious biochemical measurements resulting from hematologic conditions

Factitious laboratory results often lead to unnecessary testing or treatment. This brief review of factitious biochemical results due to preexisting hematologic conditions focuses on the mechanisms underlying the factitious results and suggests ways to prevent them. An observant pathologist identifies these errors, intervenes in a timely fashion, investigates the sources of error diligently, and institutes measures to prevent their recurrence.

Spurious hypoxemia

OBJECTIVE

To discuss the pathophysiology and clinical implications of spurious hypoxemia in the setting of hyperleukocytosis.

DESIGN

Case report and review of the literature.

SETTING

A 22-bed, adult neurosciences critical care unit at a tertiary care hospital.

PATIENT

A 49-yr-old male with chronic myelogenous leukemia.

INTERVENTIONS

Administration of hydroxyurea and imatinib mesylate.

MEASUREMENTS AND MAIN RESULTS

The patient was admitted to the neurosciences critical care unit with an acute nontraumatic subdural hematoma that required emergent surgical evacuation. His clinical course was notable for neurologic deterioration, sepsis, hyperleukocytosis, severe hypoxemia, and prolonged mechanical ventilation. An inverse relationship was observed between arterial oxygen tension and the magnitude of hyperleukocytosis. Hypoxemia resolved after the institution of chemotherapy and normalization of white cell count. Pulse oximeter saturation was normal throughout.

CONCLUSIONS

Patients with hyperleukocytosis are at risk for severe hypoxemia, which may be real or spurious. Failure to recognize spurious hypoxemia can lead to unnecessary diagnostic tests and therapeutic interventions, exposing patients to avoidable risk. A diagnostic algorithm is proposed.