Acidosis induced by carbon dioxide insufflation decreases heparin potency: a risk factor for thrombus formation

Since the introduction of CO₂ insufflation during open heart surgery in our hospital, we incidentally observed thrombus formation in the dissected heart, in the pericardium and in the cardiotomy reservoir of the cardiopulmonary bypass system. Furthermore, we measured very high levels of pCO₂, causing severe acidosis, in stagnant blood in the pericardium and cardiotomy reservoir.

In this in vitro study, we assessed the influence of acidosis and hypothermia on heparin potency and thrombin formation.

We assessed heparin potency in function of pH (pH 5.0-7.4) and temperature (24-37°C) by comparing the activated partial thromboplastin time in platelet-poor plasma between samples with and without unfractionated heparin. We measured thrombin formation in platelet-poor plasma by means of fluorescent, calibrated, automated thrombography in function of pH (pH 5.0-7.4) and temperature (24-37°C). The parameters of interest were the endogenous thrombin potential and the peak amount of thrombin generation.

The major finding of this study is the significant decrease in the efficiency of unfractionated heparin in delaying thrombus formation at acidotic (pH 5.0-7.0) conditions (p=0.034-0.05). Furthermore, we found that thrombin formation is significantly increased at hypothermic (24-34°C) conditions (p=<0.001-0.01).

Based on the results of our in-vitro study, we conclude that acidosis may lead to a decreased heparin potency. Acidosis, as induced by CO₂ insufflation, may predispose patients to incidental thrombus formation in stagnant blood in the open thorax and in the cardiotomy reservoir. Hypothermia might further increase this risk. Therefore, we recommend reconsidering the potential advantages and disadvantages of using CO₂ insufflation during cardiopulmonary bypass.