NPR news and capnography
Last January, a Minnesota man's heart stopped beating for an amazing 96 minutes. Emergency room doctors thought he was dead. But first responders who gave CPR on the scene decided not to give up, in part because of technology that allowed them to see their efforts were working.
It's called capnography, and it measures how much carbon dioxide is being expelled with each breath. This information helps doctors and emergency medical personnel determine whether a patient is hyperventilating or having a heart attack. It also helps them decide how to treat an asthma attack, or determine whether CPR is working.
How It Works
At a fire station in Brook Park, Ohio, medical officers put a tube in my nose and hook me up to the machine to show me how it works.
"OK, that last data stream there is the capnography. Now just breathe normal," Lt. Mark Lynch says, pointing at a graph on the screen that moves up and down when I breathe.
I watch the monitor as I inhale and exhale. "Every time I breathe out, it goes up," I remark.
"Yes. That's the exhalation. Right," Lynch confirms.
There is also a number on the screen that corresponds to the carbon dioxide I exhale — an estimate of carbon dioxide levels in my blood. As I change my breathing, the number changes, too. By breathing rapidly, I blow out carbon dioxide, and the number on the screen goes down. If I hold my breath, it goes up. Lynch explains that if I were unconscious and receiving CPR, the carbon dioxide levels would tell them how efficiently their chest compressions were pumping blood through my lungs and to my organs. Breathing normally, my number is 35.
"Now, during good CPR, this is probably going to be around 25 — if you keep this up in that 25 range, then there's circulation still going on. ... That's where you're going to get a positive outcome," Lynch says.
Capnography is not a new technology. In fact, it's been around for years, used by anesthesiologists to monitor a patient's breathing during surgery.
But these days, the technology is making its way out of hospital operating rooms and into portable devices that are helping first responders make critical — sometimes life-saving — decisions.
Knowing When Not To Quit
That was certainly the case for Howard Snitzer when he collapsed in front of a Minnesota grocery store one cold night last January. After he woke up days later, some of the emergency medical personnel who helped that night told him what had happened.
"They said, 'We were wondering what you remember about your heart attack.' And I said, 'Nothing.' And they said, 'Well, here's what we remember.' And they started telling this story, and I was just blown away," Snitzer recalls.
For more than an hour and a half, Snitzer had no pulse. Emergency room doctors said there was nothing more they could do. But one of the flight nurses who had come with the emergency helicopter had been trained in capnography. Snitzer's carbon dioxide levels suggested that blood was flowing to vital organs like the heart and brain, and the nurse thought Snitzer still had a chance.
The nurse "called the emergency room doctor, who told him that I was dead and that they should walk away," says Snitzer. "And he hung up and he said to the rest of the people in the room, 'Is anyone else here uncomfortable with walking away from this?' And they all said yes. And it was at that point that he called Dr. White."
That's Dr. Roger White, an anesthesiologist at Mayo Clinic. He's the one who finally came up with the solution to get Snitzer's heart beating normally again.
"We just continued believing that the measurement of carbon dioxide pressure said that if we can stop that fatal rhythm, Howard will be OK," White explains.
After shocking Snitzer's heart 12 times and administering intravenous drugs, they finally did manage to stop that fatal heart rhythm. When a pulse and a regular heartbeat had been restored, Snitzer was airlifted to the Mayo Clinic.
White says that before the use of capnography, the only way of assessing blood flow to vital organs was by feeling for a pulse or by looking for dilated pupils. He says those methods are very crude and can fail. Snitzer never had a pulse despite good carbon dioxide readings. Without the information from capnography, he says, it would have been reasonable to stop CPR — and Snitzer likely would have died.
"The lesson that I certainly learn from this is you don't quit — you keep trying to stop that rhythm as long as you have objective, measurable evidence that the patient's brain is being protected by adequate blood flow as determined by the capnographic data," says White.
Capnography is slowly becoming standard equipment for emergency responders. Next year, the fire department in Brook Park will have five new capnography machines — as opposed to the one they have now.
The American Heart Association added capnography to its 2010 guidelines for treating cardiac arrest patients — a sign, says White, that it's a technology that emergency medical teams can no longer do without.