Critical illness with hyponatraemia and impaired cell membrane integrity—the “sick cell syndrome” revisited

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 < 130 mmol/L) and 19 normonatraemic (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.