Endotoxaemia detected during cardiopulmonary bypass with a modified Limulus amoebocyte lysate assay

Cardiopulmonary bypass (CPB) is associated with blood heparin level fluctuations and a reduction in haematocrit due to crystalloid haemodilution. The effect of these changes on the reliability of the Limulus amoebocyte lysate (LAL) chromogenic microassay for the measurement of plasma endotoxin was assessed in vitro. It was shown that the assay could be significantly compromised by twofold haemodilution which can occur during CPB. The interference effect on the assay caused by CPB-associated heparin was not significant if a comparatively large amount of heparin (25 IU/ml) was added to the blood at the time of sampling. The effect of haemodilution was counteracted by prediluting plasma samples with crystalloid by a factor dependent on the sample haematocrit (to ensure that the proportion of plasma was similar in all samples). A correction was then required to determine the endotoxin level in the original sample. The modified assay was used to determine sequential plasma endotoxin levels in 14 patients under...