Does ice directly over an open wound inhibit clotting?

Answer 1

No. Ice on an open wound actually HELPS clotting.

Lowering the local temperature, ice stimulates a heat-loss reflex that significantly reduces blood flow by constricting arterioles. (This causes the cold tissue to appear light in color. And it's also why ice is helpful in first aid for closed injuries, to prevent swelling.) The reduced blood flow allows the clot to form and stick without washing away.

You might guess ice would inhibit clotting, because low temperature decreases two processes important in clotting: release of clotting factors by blood platelets, and the enzyme reactions that actually convert liquid blood into a clot. However, these two reactions are only slightly affected by cold, while local blood flow is dramatically reduced by cold.

In contrast to ice, mild heat inhibits clotting by increasing local blood flow.