Impaired ex vivo lipopolysaccharide-stimulated whole blood tumour necrosis factor production may identify patients in the intensive care unit with ‘sepsis’ and multiple system organ failure

Abstract

Abstract Background There is currently no reliable diagnostic test to identify patients with sepsis in the intensive care unit (ICU) or patients with multiple system organ failure (MSOF). It was previously found that in vitro pretreatment of monocytes with lipopolysaccharide (LPS) induced blunted tumour necrosis factor (TNF) release to LPS rechallenge. It was hypothesized that patients exposed to LPS or septic stimuli in vivo would produce less TNF when stimulated ex vivo with LPS. This preliminary study sought to determine whether impaired ex vivo TNF release was associated with measurable differences in clinical outcome. Methods Heparinized whole blood was obtained from 27 ICU patients and five healthy controls, and incubated immediately with or without LPS 10 ng ml−1 at 37°C for 3 h, then centrifuged to recover serum. Serum TNF levels were measured using an enzyme-linked immunosorbent assay and expressed as mean(s.e.m.). Clinical data, such as ICU length of stay (LOS), duration of mechanical ventilation, white blood cell count and positive cultures, were obtained retrospectively. Quartiles (I, 0–25 per cent; II, 26–50 per cent; III, 51–75 per cent; and IV, 76–100 per cent) were identified on the basis of the distribution of plotted LPS-stimulated whole blood TNF values. Statistical analysis was by χ2 and Student's t tests. Results A wide range of LPS-stimulated whole blood TNF production was observed in ICU patients (5·1(0·7) ng ml−1) and controls (6·6(1·0) ng ml−1). Patients identified in the lowest quartile (n = 6) of TNF producers (less than 2 ng ml−1) had significantly lower TNF production and a higher incidence of infection (83 versus 38 per cent), and longer LOS (21·8 versus 9·0 days) and duration of mechanical ventilation (18·3 versus 6·0 days) than patients in quartiles II–IV (n = 21). Patients in the lowest quartile had significantly lower TNF production (1·1(0·2) ng ml−1) than normal controls (6·6(1·0) ng ml−1) (P < 0·05) or ICU patients in any other quartile (quartile II: 2·9(0·2) ng ml−1, quartile III: 5·3(0·3) ng ml−1, quartile IV: 10·4(1·3) ng ml−1) (P < 0·05). Conclusion The lowest levels of ex vivo LPS-stimulated whole blood TNF production were associated with a prolonged ICU stay, a higher incidence of positive cultures and a prolonged need for mechanical ventilation. Impaired TNF release may be a manifestation of monocyte endotoxin tolerance and may be a marker of monocytic dysfunction. Determination of whole blood ex vivo LPS-stimulated TNF production could be useful in the diagnosis of severe sepsis and MSOF in patients in the ICU.