Critical illness with hyponatraemia and impaired cell membrane integrity - the "sick cell syndrome" revisited.

Abstract Objective: To determine whether impaired cell membrane permeability exists in critically ill patients with “sick cell” type hyponatraemia. Design and methods: A 36 year old male patient was identified in an intensive care unit (ICU) with liver disease and multi-organ failure. His initial serum sodium (Na) was 101 mmol/L and osmolar gap + 35 mmol/L. A flow cytometric system was used to assess lymphocyte membrane integrity using fluorescein diacetate (FDA) and propidium iodide (PI). Following this, similar studies were carried out in 17 hyponatraemic (Na  136 mmol/L) ICU patients. Results: Flow cytometry in the index patient showed two clear populations of cells—one was normal (with identical characteristics to a healthy control) and the other had dysfunctional cell membrane integrity. The extended patient series, however, revealed only 2 other patients with similar flow cytometric patterns—one hyponatraemic and one normonatraemic. Conclusions: Cell membrane studies in the index patient demonstrated supportive evidence for the “sick cell syndrome” in critically ill patients. The extended series revealed that 3/37 (8%) had this abnormality, which was however not consistently associated with hyponatraemia.