Christopher Duntsch, the so-called Dr. Death, will probably spend the rest of his life in prison, having lost his appeal in the Fifth District Court of Appeals in Dallas.

A former neurosurgeon based in Dallas, Duntsch worked in four hospitals over a two-year period. His 2017 trial centered on Mary Efurd, who was 74 in 2012 when she underwent an operation with Duntsch wielding the scalpel at Dallas Medical Center. She lost a third of her blood and the full use of her legs but survived. Duntsch was convicted on a charge of injury to an elderly individual.

During the trial, jurors also heard from the husband of Kellie Martin, a 54-year-old Garland schoolteacher who died in 2012 after Duntsch performed back surgery on her at a Baylor hospital in Plano.

A Dallas jury sentenced Duntsch to life in prison in 2017 after hearing how he'd deliberately maimed patients who had sought his care because of back problems.

Christopher Duntsch (Dallas County Sheriff's Department)

Dubbed "Dr. Death," Duntsch recently became the focal point of a highly rated podcast. Laura Beil, an award-winning medical writer formerly with The Dallas Morning News, reports the content of the show and narrates the podcast, which has generated more than 20 million downloads.

Dr. Death made headlines for a different reason in September, when a billboard promoting the show abruptly disappeared near Baylor Scott & White Medical Center in Plano, one of several hospitals where Duntsch operated on patients.

At the time, Dr. Death was the No. 1 podcast distributed by Apple, with over 2 million listeners. In its latest rankings, toppodcast.com lists Dirty John as the most highly rated podcast in the country. It has something in common with Dr. Death: Both are produced by a California-based company, Wondery. Dr. Death has been described as "a story about a charming surgeon, 33 patients and a spineless system."

Beil said late Wednesday that the reaction to the show has exceeded her wildest expectations — especially, she said, "the way the story has resonated with people."

In a 2-1 decision dated Dec. 10, the Dallas appeals court affirmed Duntsch's conviction.

The defendant had appealed his conviction and sentence, arguing that the trial court had abused its discretion by admitting evidence of his alleged extraneous conduct into evidence and alleging that prosecutors had failed to prove his culpable mental state beyond a reasonable doubt.

The Fifth District Court of Appeals concluded that the trial court did not abuse its discretion by admitting evidence of Duntsch's alleged extraneous offenses.

Prosecutors cited an email Duntsch sent to a girlfriend seven months before the surgery that led to his criminal charge. In the email, Duntsch characterized himself as a "cold blooded killer."

"You, my child, are the only one between me and the other side. I am ready to leave the love and kindness and goodness and patience that I mix with everything else that I am and become a cold blooded killer," Duntsch wrote in the email.

"What I am being is what I am, one of a kind, a mother [expletive] stone cold killer that can buy or own or steal or ruin or build whatever he wants," Duntsch's email continued.

The appeals court rejected Duntsch's claim that the email was irrelevant. One of three appeals judges hearing the case did, however, offer a dissenting opinion, which is printed here.

Duntsch has 15 days to appeal to the Texas Court of Criminal Appeals, which doesn't always agree to hear the cases presented to it.