Christine Allison and her husband, Troy, were watching television in their Columbus, Ohio, home last July when his breathing became erratic. She dialed paramedics and fetched her husband a paper bag to calm him while they waited.

"I'll see you in a minute," she said in those frantic moments when the ambulance arrived. "I'm on my way."

About three hours later, Troy Allison would be dead at the age of 44.

Troy Allison and his wife, Christine Allison.

What happened at Mount Carmel West hospital in that time still baffles Christine Allison. She said her husband, an excavator, had been diagnosed with diabetes after suffering a broken hip from a dump truck accident three years ago — but was not in such declining health that he should have died so suddenly.

Christine Allison, 53, would later learn that he received a 1,000 microgram dose of fentanyl, which is used in hospitals to treat severe pain, although typically in much smaller amounts.

Troy Allison's death and at least 33 others involving Mount Carmel patients from 2015 to 2018 remain part of a wider internal investigation into Dr. William Husel, who treated them, and why the intensive care doctor allegedly ordered "significantly excessive and potentially fatal" doses of pain medication in 28 of the cases, according to the hospital.

Husel's medical license was suspended Friday by the State Medical Board of Ohio, which said the allegations against him were so serious that he was not afforded a hearing prior to the board's vote and can no longer practice medicine in the state.

Yet, key questions remain unanswered: Why such high doses, and were they the result of repeated mistakes — or intentionally meant to be deadly?

Doctors, pharmacists and lawyers who spoke with NBC News say hospitals such as Mount Carmel, one of the largest health systems in Ohio, have multiple safeguards in place that should prevent patients from being overmedicated to death. There are checks and balances allowing those in the chain of command to trigger an alarm, the medical experts added, so that an error can be avoided or reviewed after the fact, including during emergency situations in which dangerous drugs such as fentanyl are used.

"We know that the risk for error goes up in chaotic situations, but hospitals have worked hard to limit these risks and do a very good job protecting safety in fast-paced environments like the emergency room or intensive care unit," said Dr. Daniel Tobin, an associate professor of medicine at Yale University and a leading expert on opioid safety.

At least six wrongful death lawsuits have been filed on behalf of deceased patients, including Troy Allison, alleging Husel ordered the doses either negligently or purposefully in order to hasten the end of their lives.

All Christine Allison knows is that her husband of 11 years, her best friend and a father of two, was taken from her — and she wants Husel to explain why.

"He actually seemed very kind and very compassionate. I trusted him," she said of the doctor. "Now I think he needs to be in prison. The system failed."

'WHY DOES HE NEED PAIN MEDICATION?'

Inside Mount Carmel West, a sprawling 37-acre campus in downtown Columbus, the scene was a blur for Christine Allison and one of her daughters.

"A lot of the time, I didn't know what was going on," Christine Allison said.

Her husband was rushed from the emergency room to intensive care, and she was told he was suffering from multisystem organ failure. Such a condition on its own can be fatal, although in the ICU there is still a chance for survival.

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"When we got to ICU, they told us, 'No, he's dying,'" she said.

She does not believe her husband would have given permission to receive such a high dose of fentanyl because she was told he was unconscious when he arrived at the hospital. And she said no one consulted with her about the need for painkillers.

Dr William Husel WCMH

Attorneys for the Allison family said they were led to believe Troy Allison was going to be brain dead even if he were successfully resuscitated, although no evidence was given to support that conclusion.

"He's unconscious — why does he need pain medication?" Christine Allison asked.

In her brief interaction with Husel, she found him to be understanding. But after she was told her husband was dead, no one debriefed her about what happened or any options that could have saved him.

She stood in the hallway of the hospital with her daughter, in shock, thinking, "What happens next?"

It was five months later, just after Christmas, when a physician administrator from Mount Carmel called Christine Allison to reveal that her husband had been given a potentially lethal dose of fentanyl, and that she may get contacted by detectives investigating his death.

She was stunned. She would never have wanted her husband to be given a deadly amount, and in Ohio and every state but six, physician-assisted deaths are illegal.

"I would have said, 'Let him go naturally. This is between my husband and God now,'" Christine Allison said.

LAYERS OF SAFETY CHECKS

Troy Allison wasn't the only patient to get as many as 1,000 micrograms of fentanyl, according to the lawsuits filed against Mount Carmel and Husel.

Lawyers say up to 100 micrograms of the synthetic opioid would be normal for a patient, depending on their size and the circumstances.

According to three physicians in Ohio, ordering an opioid at most hospitals works this way: The doctor writes the order to the pharmacist, who's usually located elsewhere in the hospital, via an electronic system. (Gone are the days of doctors writing on note pads.) The pharmacist then reviews the order and signs off. That allows a nurse to get the order and retrieve the medication, often through an automated machine that dispenses the amount requested. (Also gone are the days of unassigned vials of medicine lying around.) Then, the nurse administers the drug.

Dr. Iahn Gonsenhauser, who oversees quality and patient safety efforts at the Ohio State University Wexner Medical Center, said that at numerous points, someone who believes the medication dosage is too high can raise a red flag. A pharmacist has the ability to check in with a doctor to ensure the amount is what they wanted and to stop it if they believe it to be incorrect. Nurses, too, before administering a drug can refuse or signal to their supervisor that the amount appears to be wrong.

Electronic ordering systems are also built-in with notifications that will alert users at the point of order if the medication being requested appears off.

In emergency situations, there are overrides in place for nurses to access the drugs even if the medication amount may be questionable, Gonsenhauser said, but that should usually send an immediate notification to the pharmacy team, which can later review what happened.

Dr. Ted Parran, who specializes in addiction treatment at St. Vincent Charity Medical Center in Cleveland, said medications at hospitals are counted to make sure they're not being abused and in the event regulators want to perform an audit.

He said hospitals have made significant strides in the past 20 years to avoid medical errors and patient harm.

"Errors can happen," Parran added, "but systematic or repetitive ones shouldn't."

Neil MacKinnon, dean of the University of Cincinnati James L. Winkle College of Pharmacy, said pharmacists routinely push back at doctors, especially in hospitals, when a medication request doesn't appear right.

"Physicians are very pleased when they get a call alerting them about it," he said. "They say, 'You saved my butt.'"

Lawyers for the families of patients who died at Mount Carmel say they are still trying to determine how Husel may have ordered the potentially deadly doses of painkillers, and where any breakdowns may have occurred amid the layers of protocol.

Husel may have been charming and persuasive enough to get his medication orders fulfilled, and colleagues working late nights with him may not have felt they could overrule him, said Gerry Leeseberg, an attorney for Christine Allison and other families.

Hospital officials said that Husel, 43, was fired Dec. 5 after five years with the facility, and that 20 other employees, including nurses and pharmacists, have been removed pending further investigation.

"As we learn more, we will share our findings with each affected family," Ed Lamb, Mount Carmel Health System's president and CEO, said in a statement Thursday. "We are committed to being open and honest about what happened, and what we are doing to ensure it never happens again."

NBC News has been unable to reach Husel for comment and it's unclear if he has an attorney.

The Franklin County Prosecutor's Office said it is investigating allegations in the cases along with the Columbus police's homicide unit, but no formal charges have been made.

David Austin with his wife, Bonnie, in an undated photo. Courtesy David Austin

In an interview Thursday with WOSU radio, Ohio's new attorney general, Dave Yost, had urged the state medical board to suspend the doctor's license. "It looks like we've got a serial killer on the loose with a medical license and access to fentanyl," he added.

The case has drawn national attention because of the high numbers of deaths.

David Austin — whose 64-year-old wife, Bonnie, was treated by Husel last September after she went in suffering chest pains and had difficulty breathing — said everything at the hospital happened so fast. His wife died about 35 minutes after she was given 600 micrograms of fentanyl and Versed, a sedative, through an IV, according to her medical records.

Austin said he would have wanted Husel to do anything in his power to save his wife of 36 years — not give her a potentially deadly dose of a painkiller. Now, he said, he wants justice.

"When the doctor came out, he said she was brain dead — her heart wasn't working," Austin said, his voice breaking. "Of course, of course I wanted my wife to survive."