The formation of platelet microvesicles in septic pigs treated with different kinds of volume replacement

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Introduction

Bacterial lipopolysaccharide (LPS) is believed to be one of the major pathogenic factors of Gram-negative sepsis. Sepsis may be accompanied with thrombocytopenia, platelet activation and elevated platelet-derived microvesicles. Higher formation of microvesicles has been associated with higher mortality in endotoxemic pigs.

Design

Prospective, randomized animal laboratory study.

Methods

Twenty anesthetized pigs divided in four groups received feces (1 g/kg body-weight) installed in the abdomen to induce sepsis. Group 1 was treated with ringer's solution (RS), group 2 with 6% hydroxyethyl starch 200/0.5 (HES), group 3 with modified fluid gelatin 4% (MFG4) and group 4 with modified fluid gelatin 8% (MFG8), each to maintain a central venous pressure of 12 mmHg. Before induction of sepsis (baseline) and after 2 (+2 h), 4 (+4 h), and 8 (+8 h) h, a citrated blood sample was drawn. Flow cytometry was used for determination of microvesicles. Platelets and microvesicles were identified with an anti-platelet-mAb (Donor: DH Sachs, Charlestown, USA) and a secondary antibody labeled with phycoerythrin (goat-anti-mouse, Dako SA, Denmark). Microvesicles were determined as smallest 1-3% positive cells in forward scatter.

Results

Baseline values were considered as 100%. In the RS-group sepsis was associated with an increase of microvesicles to 137± 58% (Mean ± SD) after 2 h, leading to 179± 45% (+4 h) up to 210± 121% (+8 h). In group 2 (HES) there was an increase at +2 h (109± 25%) and a decrease at +4 h (89± 26%) and +8 h (73± 19%). In Group 3 and 4 a decrease of microvesicles after induction was revealed at +2 h (51± 25%, MFG4 and 45± 16%, MFG8) +4 h (62± 10%, MFG4, 79± 58%, MFG8) and +8h (63± 41%, MFG4, 53± 17% MFG8). Formation of microvesicles was significantly higher in the RS treated group compared to all colloid groups (P<0.05).

Conclusion

In this porcine sepsis model, volume replacement with colloid solutions seemed to reduce the detectable number of platelet derived microvesicles, which could be seen after the use of ringers solution. This may be a sign of less activation with colloids.