[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.