The crude mantra “you’re not dead until you’re warm and dead” has guided paramedics for years, but advances in resuscitating frozen patients are improving the odds for hypothermia victims, whether they are oil rig workers who fall into the North Sea or Minnesotans who pass out in the cold.

Promising approaches have emerged in a partnership between Mayo Clinic and the University Hospital of North Norway, which, located above the Arctic Circle, has gained expertise on saving hypothermic skiers, adventurers and outdoor workers. Its work is identifying new, safer methods to rewarm frozen patients to improve on the existing survival rate of 30 to 40 percent.

“As long as you can continue to maintain circulation,” frozen and pulseless patients stand a chance, said Gary Sieck, a Mayo physiology professor taking part in the research. “And that’s where CPR really becomes important.”

In Minnesota, it also has become controversial.

A lawsuit filed late last year is questioning whether paramedics are taking advantage of the improving lifesaving techniques. The case involves the death of Jake Anderson, a 19-year-old University of Minnesota student found in December 2013 along the Mississippi River. The suit alleges that medics didn’t follow their own practices when declaring him dead without examining him or taking him to a nearby hospital.

“The fact of the matter is, they didn’t check,” said attorney Robert Hopper, who filed the federal lawsuit against the police, fire, paramedic and coroner agencies involved. “You want to hope it’s an anomaly.”

Medics in the Minneapolis area are guided by the Hennepin County EMS Advisory Board, which recommends that first responders use lifesaving efforts for hypothermic patients even if they don’t have discernible heartbeats. The exceptions are victims who have been underwater for more than 90 minutes, show obvious signs of death such as traumatic injuries, or have been frozen so badly that ice has coated their throats or stiffened their chest walls.

Aggressive lifesaving efforts are otherwise warranted because the same extreme cold that can cause someone’s heart to stop can also have a preservative effect on the body, making it possible to revive the patient, said Dr. Rade Vukmir, a hypothermia expert at Temple University in Philadelphia.

In this hibernation-like state, a patient can have a slow pulse that is hard to find, which is why rescuers are supposed to take at least 30 seconds to try to find it and to proceed with lifesaving efforts, he noted.

“We always try and ensure patients are adequately warmed before we cease resuscitative efforts,” he said.

Twenty years ago, hospitals had little chance of saving patients with severe hypothermia, especially those without heartbeats. The Norway researchers reviewed 10 cases before 1999 in which they used heart-lung bypass machines to circulate blood outside the bodies of patients in cardiac arrest to warm it up. None survived. Since that time, however, this approach at North Norway has saved nine of 24 patients, with most having “favorable” recoveries.

Sieck said a key is figuring out the best pace and methods for rewarming patients, because that process in and of itself can shock patients and produce cardiac arrests.

But Sieck also said that hospitals have been inconsistent. A 2010 study of hypothermia treatment found that doctors tried 14 different methods of rewarming in just one hospital.

“How you rewarm patients seems to be critical,” said Sieck, who is studying the cellular activities that cause cardiac arrests during rewarming and how to prevent them.

Sieck said he believes most rescuers are doing their best. “The EMS people I’ve met are up to speed and doing a good job. We just have to give them the right tools.”

One famous rescue case involved a Swedish radiologist who survived a skiing accident in 1999 that left her trapped in freezing water for 80 minutes and dropped her body temperature to 56.7 degrees.

Survival stories have emerged in Minnesota as well. University of Minnesota Duluth student Alyssa Lommel was saved — although amputations of her hands and portions of her feet were necessary — after she fell asleep outside in subzero temperatures for several hours in December 2013 and her body temperature dropped to 79.

A Star Tribune review of state death records suggests that there is at least the potential for more lifesaving attempts. Among 41 Minnesota patients with hypothermia listed as a cause of death last winter, only nine were listed as having been pronounced dead in hospitals.

Six were involved in vehicle accidents or falls that could have made their deaths obvious at the scene. It’s possible that doctors coded the places of death as taking place at accident scenes even if victims received CPR and were taken to hospitals.

But the data and the potential lack of hospitalizations bother some experts. Even if the odds of survival are remote, the default has to be to perform CPR and get hypothermic patients to hospitals, said Bob Pozos, a hypothermia expert who conducted research at UMD and later for the U.S. Navy in San Diego.

“People are going to say, ‘What are the chances?’ But you can’t play that game with cold because you just don’t know,” he said. “The science at least says you bring them back and there’s a possibility they might survive. I don’t think it’s a gray area.”

Whether Anderson could have been saved is unclear. Hopper argued that rescuers at least needed to try, per their own policies, by thoroughly checking Anderson’s pulse and examining his airway to see if CPR was possible.

The Minneapolis firefighters who were first to respond found what they believed to be obvious signs of death and called off HCMC paramedics, who conducted a brief check on Anderson’s body, the lawsuit states. Anderson had been in the cold for more than eight hours between the time he left a party and when he was found near the 10th Avenue Bridge.

The rescue agencies are fighting the case, and in a motion this week asked for the suit to be dismissed.

Pozos believes the death toll could go down with more aggressive EMS efforts.

“I personally talked to a young kid who drowned in a lake in Chicago,” he said. “The boy actually came out and he was dead — hypothermia, no pulse, no heart rate. He spoke English and Spanish. And when we went to visit him [after he was resuscitated] he spoke both beautifully. And he had been completely dead.”