Endotoxemia, immunocompetence and the responsiveness of neutrophils in critically ill patients

Introduction

Lipopolysaccharide (endotoxin) is a potent inducer of a complex pattern of pre-inflammatory and anti-inflammatory cytokines that generate a predictable pathophysiologic response in animal and healthy human subjects. However, measuring endotoxin in the blood or serum of critically ill patients has been problematic.

We have recently developed an assay for endotoxin in whole blood which is rapid and reliable. Using chemiluminescent technology. primed patient neutrophils mixed with an anti-endotoxin antibody are analysed for respiratory burst activity corresponding to neutrophil recognition of complexes of endotoxin and anti-endotoxin antibody. The chemiluminescent assay provides reliable quantitation of whole blood endotoxin and provides a method of measurement of the in vivo state of activation (cl-max) and immunocompetence (responsiveness) of circulating neutrophils.

Purpose

To validate the utility of the chemiluminescent assay tor simultaneous measurement of endotoxemia, and neutrophil activation and responsiveness in a cohort of critically ill patients.

Methods

Using the chemiluminescent assay, we measured endotoxin levels in whole blood samples from 64 consecutive patients who met the SCCM/ACCP Consensus Conference criteria tor sepsis and 20 non-septic patients in our 36 bed Medical-Surgical ICU. Each patient sample was analysed in duplicate. Anti-endotoxin antibody was added to the first sample to aid in the measurement of endotoxin, then the second sample is challenged with a maximum stimulatory dose of endotoxin (800pg/ml) to allow endotoxin quantitation and measure the state of neutrophil activation is assessed by the maximal chemiluminescent response. The cl-max is proportional to the number of neutrophils and degree of activation. The responsiveness is a measure of the normalized level of activation of neutrophils by a maximal antigen-antibody challenge (LPS-anti-LPS immune complex).

Results

Compared to healthy controls, non-septic patients have a significantly higher cl-max (1.2 ± 0.8 versus 7.1 ± 5.6. P = 0.0001) but similar responsiveness (47.0 ± 14.6 versus 43.5 ± 16.7, P = 0.95). Septic patients were significantly different from controls with regard to el-max and responsiveness but also to critically ill, non-septic patients (see Table). Mean endotoxin levels were significantly different between non-septic and septic patients. Results follow (± SD).

Conclusions

The chemiluminescence assay can identify a group of patients who have significant endotoxemia. Furthermore, the assay contributes information on the state of activation (cl-max) and potential responsiveness of circulating neutrophils. The assay provides a reliable and rapid method to assess neutrophil activation and opsonin dependent immunocompetence and may serve as a clinical tool for selecting patients who may benefit from anti-endotoxin strategies.

Table 1 Table (abstract P016)