When our 5-month-old kitten, Jasper, went into kidney failure a few years ago, letting him die wasn’t an option. We rushed him to our veterinarian, who drew his blood, X-rayed him, and cultured his urine. She told us he might have just a few days to live. So we drove him to an emergency clinic on the outskirts of Baltimore, where he saw an internist, then a nephrologist. He spent three days in the intensive care unit, hooked up to a catheter and intravenous antibiotics, while he underwent ultrasounds, urinalyses, and blood-chemistry profiles. Slowly, he began to recover. It took a while for our bank accounts to do the same. We had adopted Jasper for next to nothing from a shelter, but a few days of emergency veterinary care had cost us more than $3,000.

Twenty years ago, we couldn’t have spent that much money if we wanted to. The fancy machines, the complex diagnostics, even the veterinary specialists just weren’t available. Thanks to advances in veterinary medicine, our pets are living longer, healthier lives than ever before. But it has also become much harder to let them go. When our dogs and cats used to get very sick, we could justify putting them to sleep because it was the only option. Now, in an age of kidney transplants for cats and chemotherapy for dogs, euthanasia has begun to seem like a cruel way out.

Yet not everyone can afford to save their pets. And some go bankrupt trying. Meanwhile, vets themselves are struggling with whether to offer such expensive services to clients they know can’t afford them. Every year, our pets become more like family, and in some cases virtual children. Indeed, as I write in my new book, Citizen Canine: Our Evolving Relationship With Cats and Dogs, we have become closer to our pets than at any point in human history. But just how far should we go to save them?

That’s not a dilemma early veterinarians wrestled with. The American vet of 150 years ago was more of a mechanic than a physician. He focused solely on economically valuable creatures like cows and horses, administering strong laxatives or cauterizing open wounds with a red-hot iron so that these animals could continue to produce milk and pull freight. Healing a dog or cat would have made about as much sense as bandaging up a pet rock.

But as livestock disappeared from cities at the turn of the 20th century, vets turned to pets to save their profession. Cats and dogs had begun to move indoors; owners were springing for pet food and fancy toys, and they sought out doctors who would treat their pets like any other member of the household. Vet schools began teaching companion animal medicine, and practitioners transformed their clinics into small-animal hospitals. Dank horse stables became comfy waiting rooms. Grungy aprons were shed for white coats. And red-hot irons gave way to leading-edge therapies. “If you were an ailing dog,” stated a 1951 article in Science News Letter, “you’d probably be treated with essentially the same techniques that medical doctors use on human patients.”

By the mid-20th century, the number of veterinarians in the United States had quintupled, and pets had become their most reliable source of income. But a far more significant transformation had taken place. What was once an economic relationship between human and beast had become a sentimental one. The owners of cows and horses would never have spent more money on their animals than they were worth, but cat and dog owners did—sometimes in a single visit. Far more than toys or pet food, the vet clinic provided an outlet for people to express their true devotion to their pets: They were no longer just spoiling them; they could now save their lives. Meanwhile, by providing humanlike medicine, vets signaled to society that pets were worthy of such care, elevating their status above that of any other animal. The behavior of owners, combined with the services offered by veterinarians, helped turn pets into true family members. Owners became parents. And vets, far from their days as the mechanics of livestock, became the pediatricians of fur babies.

Today, veterinarians belong to one of the most respected professions in the country, ranking just behind doctors and nurses. And we’re shelling out more on medical care for our pets than ever before, in excess of $15 billion this year in the United States alone. A lot of that comes from owners willing to spend anything—or almost anything—to delay the inevitable. A recent poll found that nearly two-thirds of people would pay up to $1,000 to save their animals, with another quarter ready to fork over $3,000 or more. Hang out in a veterinary clinic, and you won’t have a hard time finding men and women sobbing as they write in their checkbooks or pull second credit cards from their wallets. After all, how do you put a price on a member of the family?

All of this might seem like good news for vets, but they’re struggling with the issue. “It’s wonderful that people are willing to spend $10,000 or $20,000 to deal with their sick pet, but ethically it puts us in quicksand,” says Douglas Aspros, the former president of the American Veterinary Medical Association and the manager of a veterinary clinic in White Plains, New York. “If a client wants me to do a $20,000 surgery on a cat, the practicality has to go beyond, ‘There’s someone willing to pay for it.’ As a society, should we be promoting that?” Some vets, says Aspros, have started to use companies that offer credit to people with marginal incomes—just so they can afford their vet expenses—and the pet owners end up paying very high interest rates. “How much responsibility do we have for getting them into that?”

Owners too may need to start asking themselves how much is too much. We live in a society that increasingly allows us to spend our way out of almost any dilemma. Yet no matter how hard we try, we can’t make our pets live as long as we do. Attempting to do so could put us in the poor house. At some point, the sentimental relationship we have with our pets has to become an economic one. If we do make that ultimate decision, however, we can console ourselves with having given our animals the best life possible. After all, any cat or dog that has escaped living on the street or in a cage in a shelter has won the lottery, regardless of whether we spring for that kidney transplant.

For now, I’m thankful to have Jasper by my side. He’s almost 9 now, and still frisky. Luckily, we were able to weather the financial storm he put us through. And we’d do it again. Jasper may have put a dent in our savings, but it’s still the best money we’ve ever spent.