During the last 100 laps of the Southern 500 last weekend, Kasey Kahne’s body had already been pushed beyond its limit.

A rapid, extreme dehydration issue he’d been dealing with over the last year had returned in a big way, and Kahne found himself struggling to even keep his eyes open.

His heart rate was high and out of control. Kahne could barely drive or focus; his few thoughts were about trying to lay back in the corners and just make laps, hoping his body would respond.

Kahne finished the race — he still managed to get 24th place — then got out of the car and lay down on the pit wall as medical personnel arrived. But his heart rate was still so sky high, the doctor couldn’t get a measurement on his pulse.

He threw up all the way to the infield care center — right in front of fans. Once there, his arms, chest and neck were so cramped, Kahne indicated he had to be held down to get IVs in both arms.

“It was just a complete mess,” he said.

So if you’re wondering why Kahne won’t be racing this weekend at the Brickyard 400, that’s a sample of the reason. The fact it could happen again means there’s a chance he might not be in a Cup race again anytime soon — depending on what doctors can figure out.

It’s not as if Kahne is an out-of-shape person or hadn’t been getting enough fluids prior to the race. He’s actually in peak physical condition and spent four days hydrating and eating cleanly prior to Darlington — particularly conscious of what could happen.

That’s because this isn’t a new problem. Fans saw a flash of it last year after Kahne won at the Brickyard, but the extreme dehydration has only gotten worse since then. He struggled at Kentucky and Bristol this season as well, and Darlington was the worst yet.

Essentially, Kahne said his body sweats so much that he can’t keep the fluids in. With his slender frame, it’s different from an NFL offensive lineman with a lot of body fat. Ultimately, Kahne can’t keep up with the hydration fast enough and after a couple hours can’t even drink any more fluids without throwing up.

From that point on, his body starts to shut down — particularly on hot days with a high dew point.

Kahne is now working with doctors to try and “find a way to put together a full race and not hurt my body internally at end of these races,” he said.

What puzzles him is he’s had the same body type for all of his time in NASCAR, but the dehydration issue has only started to creep in over the last two seasons. He can only figure it’s age, since nothing else has changed.

“I can’t control the temperature of my body and my heart rate,” he said. “Once it gets to that point, there’s nothing I can do until I can get out of the car.”

It’s different with sprint car races or shorter races, because the dehydration effects don’t begin until Kahne has been sitting in a hot car with little air flow for a couple hours straight. He can do a five-mile run or 15-mile bike ride with no problems and feel great.

But a three- or four-hour Cup race? More and more, those are starting to become more dangerous for his health.

Kahne acknowledged the ongoing problem played a factor in his decision to retire from Cup racing after this season.

As for the immediate future, he’s already eyeing a hot forecast in Las Vegas next week. He’s hoping one of the three doctors he saw this week can help him come up with a solution to help keep his body from getting dangerously depleted.

“It definitely worries me,” he said. “But if we can come up with solution to stay hydrated prior to race and feel comfortable with it, I’ll be in Las Vegas.”