Low Platelet Count

I had a 16 year old patient recently who was the victim of a GSW to the L groin. It lacerated his L femoral artery. The artery was repaired with a graft. I received him in the ICU and he developed compartment syndrome in his abdomen and L thigh. He ended up with an open abdomen and thigh with wound vacs in place. A couple days later his kidneys failed and he ended up on CRRT. His leg was dying although he had a good pulse in it. They did an AKA. He was still in critical condition when I left with high lactate and still on CRRT. The plan was to do a disarticulation in a few days. He had an extremely low platelet count, which bottomed out at 5,000 the morning of the AKA and he was given around 6- 6 packs of platelets to get his count up to 63,000 so he could go to surgery. By that night his count was back at 13,000 and when given a 6 pack went up to 25,000. No one could really figure out why his platelet count was so low and kept dropping down. This had gone on for several days of dropping and then getting platelets and coming up to about 20-30 and then right back down under 15,000. Some said that CRRT will chew up platelets but I have had other patients on CRRT that that was not a problem. Just wondering if anyone has any ideas why such a low platelet count that just kept dropping down even when given platelets.