Pseudohypoxemia in a patient with chronic lymphocytic leukemia

Case Studies in Physiology: Untangling the cause of hypoxemia in a patient with obesity with acute leukemia

Diagnosing the cause of hypoxemia and dyspnea can be complicated in complex patients with multiple comorbidities. This "Case Study in Physiology" describes an man with obesity admitted to the hospital for relapse of acute lymphoblastic leukemia, who experienced progressive hypoxemia, shortness of breath, and dyspnea on exertion during his hospitalization. After initial empirical treatment with diuresis and antibiotics failed to improve his symptoms and because an arterial blood gas measurement was not readily available, we applied a novel, recently described physiological method to estimate the arterial partial pressure of oxygen from the peripheral saturation measurement and calculate the alveolar-arterial oxygen difference to discern the source of his hypoxemia and dyspnea. Using basic physiological principles, we describe how hypoventilation, anemia, and the use of a β blocker and furosemide, collaborated to create a "perfect storm" in this patient that impaired oxygen delivery and limited utilization. This case illustrates the application of innovative physiology methodology in medicine and provides a strong rationale for continuing to integrate physiology education in medical education.NEW & NOTEWORTHY Discerning the cause of dyspnea and hypoxemia in complex patients can be difficult. We describe the "real world" application of an innovative methodology to untangle the underlying physiology in a patient with multiple comorbidities. This case further demonstrates the importance of applying physiology to interrogate the underlying cause of a patient's symptoms when treatment based on probability fails.

COVID-19 in a Patient with Chronic Lymphocytic Leukaemia with Pseudohypoxemia

Infection with SARS-CoV-2 causes critical disease in approximately 5% of affected patients, particularly the elderly, hypertensive, obese and immunocompromised. Patients with haematological cancer, including chronic lymphocytic leukaemia (CLL), are particularly at risk of complications. Very rarely, patients with extreme leukocytosis may develop spurious hypoxemia, or pseudohypoxemia, which confuses the diagnosis of complications and can lead to intervention errors. We report the case of a patient with CLL, severe infection with SARS-CoV-2 and pseudohypoxemia.

LEARNING POINTS

Patients with haematological neoplasms are susceptible to viral, bacterial and fungal infections, and are thus at risk of COVID-19.Patients with chronic lymphocytic leukaemia may rarely, due to a high lymphocyte count, present with spurious, or in vitro, hypoxemia.The clinician must identify and properly treat such cases to prevent any unnecessary treatments and their complications.

The influence of delayed sample processing time on PO2 values in critically ill patients with sepsis-induced leucocytosis

Background: The extent of error, from collection to processing, when measuring PO2, PCO2 and pH in arterial blood samples drawn from critically ill patients with sepsis and leucocytosis, is unknown. Methods: Twenty-nine patients with sepsis and a leucocyte count > 12 000/mm3, who had routine arterial blood analysis were included in the study. Blood was drawn into two 1 ml heparinised glass syringes. One syringe was cooled on ice and tested at 60 minutes. The other syringe was used for analysis at 0, 10, 30 and 60 minutes. Differences in measurements, from the Time-0 results, were described. For PO2, linear mixed models estimated the impact of time to processing, controlling for the potentially confounding and moderating effects of Time-0 leucocyte count and fractional inspired oxygen concentration respectively. Results: PO2 exhibited the most pronounced changes over time at ambient temperature: The mean (SD) relative differences at 10, 30 and 60 minutes were -4.72 (8.82), -13.66 (10.25), and -25.12 (15.55)% respectively; and mean (SD) absolute differences -0.88 (1.49), -2.37 (1.89) and -4.32 (3.06) kPa. For pH, at 60 minutes, the mean (SD) relative and absolute differences were -0.27 (0.45)% and -0.02 (0.03) respectively; for PCO2, 6.16 (7.80)% and 0.25 (0.35) kPa. The median differences for the on-ice 60-minute sample for pH and PCO2 were 0.019 and -0.12 (both P < 0.001), and for PO2 0.100 (P: 0.216). The model estimated that average PO2 decreased by 5% per 10 minute delay in processing (95% CI for effect: 0.94 to 0.96; P < 0.001) at the average leucocyte count, with more rapid declines at higher counts, though with substantial inter-patient variation. Conclusion: Delayed blood gas analysis in samples stored at ambient temperature results in a statistically and clinically significant progressive decrease in arterial PO2, which may alter clinical decision-making in septic patients.

Leukocytosis interference in clinical chemistry: Shall we still interpret test results without hematological data?

Background

Extreme leukocytosis is known to induce remarkable variations of some clinical chemistry tests, thus leading to possible clinical misinterpretation. This study aimed to define whether also moderate leukocytosis may influence the stability of glucose and blood gases.

Methods

Blood samples are sent to the local laboratory through a pneumatic tube system. Clinical chemistry testing is routinely performed using Lithium-heparin tubes (for glucose) and heparin blood gases syringes (for blood gas analysis). Stability of glucose (in uncentrifuged blood tubes) and blood gases (in syringes) was hence evaluated in samples maintained at room temperature. Results were also analyzed in 2 subgroups of samples with different leukocyte counts, i.e., those with leukocytes <15 × 10⁹/L and those with leukocytes >15 × 10⁹/L.

Results

An accelerated decrease of pH was observed in blood gases syringes with leukocytosis (i.e., >15 × 10⁹/L), while no difference was noted for other blood gases parameters (PCO2, PO2). Spurious and time-dependent hypoglycemia was noted in uncentrifuged blood tubes of patients with leukocytosis.

Conclusions

The results of our study suggest that even modest leukocytosis (i.e., around 15 × 10⁹/L), which is frequently encountered in clinical and laboratory practice, may be associated with significant variations of both glucose and pH. This would lead us to conclude that results of these parameters shall be accompanied by those of hematologic testing to prevent clinical misinterpretation, namely with leukocyte counts.

Spurious Laboratory Values in Patients With Leukocytosis

Physiological derangements such as hypoxemia and hyperkalemia are medical emergencies that warrant prompt interventions to prevent further patient clinical deterioration. However, in patients with myeloproliferative diseases or malignancies that result in extreme leukocytosis, hypoxemia and hyperkalemia demonstrated in laboratory results could be deceiving due to in vitro reactions and may not reflect actual patient condition. Clinicians have to be familiar with these phenomena so as to not cause harm by treating these spurious laboratory values.