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DOI: 10.1055/s-2005-862041
Inspite of platelet activation eptifibatide effectively inhibits hypothermia induced platelet aggregation (HIPA) during cooling and rewarming
Objectives: Recently we showed that GP IIb/IIIa inhibitors avoid HIPA under conditions of deep hypothermic circulatory arrest (DHCA). It remains unclear, however, whether hypothermia induced aggregates dissolve during rewarming.
Material and Methods: Heparinized blood of healthy volunteers (n=6) was left untreated as control or was treated with 2.5µg/ml of the GP IIb/IIIa inhibitor eptifibatide (Integrilin®) both at 37°C. Samples of these were cooled in stasis for 30 minutes to 18°C to simulate DHCA. Rewarming to 37°C followed over 20 minutes. Using flow cytometry platelet aggregates were identified by their size employing CD41-antibody binding. Platelet activation percentage was measured by P-selectin antibody (flow cytometry). To control the influence of time, aggregates and P-selectin in hypothermia-exposed samples were compared with samples constantly kept at 37°C within the same time-frame. Data are reported as median and interquartile range. Group comparisons were performed using the Wilcoxon matched pairs test.
Results: There is a time-related decrease of aggregate-formation and an increase of P-selectin expression in all samples. In untreated samples hypothermia-exposure induced significantly formation of aggregates (cooling: 1.5-fold; rewarming: 2.9-fold) and expression of P-selectin (cooling: 3-fold; rewarming: 7.9-fold). In eptifibatide-treated samples the number of aggregates was not altered significantly by hypothermia or by rewarming as compared to control. P-selectin expression was significantly induced by hypothermia (cooling: 11-fold; rewarming: 10-fold) in eptifibatide-treated samples.
|
|
Untreated (30min) |
Untreated (+20min) |
Eptifibatide-treated (30min) |
Eptifibatide-treated (+20min) |
|
Aggregates control – (const. 37°C) [n/10000 events] |
2121 (1680–2488) |
615 (406–1172) |
1942 (1209–2386) |
437 (387.5–680.5) |
|
Aggregates – hypothermia exposed [n/10000 events] |
cooling: 3240 (2607–5261) |
rewarming: 1813 (1030–2329) |
cooling: 2325 (1833–3309) |
rewarming: 453 (395–837.5) |
|
p-value |
p=0.0313 |
p=0.0313 |
p=0.0938 |
p=0.5625 |
|
P-selectin control (const. 37°C) [% ab-postive] |
2.6 (1.8–4.1) |
4.6 (3.8–6.4) |
2.0 (0.8–3.3) |
3.9 (1.9–6.5) |
|
P-selectin – hypothermia exposed [% ab-positive] |
cooling: 7.9 (4.6–15.9) |
rewarming: 36.4 (18.8–51.2) |
cooling: 22.0 (5.5–39.7) |
rewarming: 39.0 (19.1–54.0) |
|
p-value |
p=0.0313 |
p=0.0313 |
p=0.0313 |
p=0.0313 |
Conclusions: The persistent elevation of aggregates in hypothermia-exposed untreated blood-samples after rewarming, indicates that hypothermia induced platelet aggregates are still present. Although eptifibatide does not inhibit hypothermia induced platelet activation, it effectively inhibits HIPA in-vitro and may thus prevent microthrombembolic disease in patients operated on in DHCA.