ARDS occupies a curious place among life’s insidious threats. Not just because of its very high mortality rate, though that is sobering enough. (It kills upwards of 50,000 people in the United States each year, more than breast cancer.) Thirty years ago, the mortality rate from ARDS was more than 60 percent, so progress has been made. But still:
It’s insidious because there are so many pathways that can lead to its onset, because it strikes with appalling speed, and because it is so damnably difficult to treat. Furthermore, it’s “an equal-opportunity disease,” says Jason Christie, associate professor of medicine and epidemiology, and section chief of medical critical care at HUP. “Doesn’t matter the gender or ethnicity. It affects everybody, everywhere.”
The New England Journal of Medicine has warned that ARDS and its understudy, ALI, represent a “serious public-health issue,” especially given the “looming expansion of the elderly population.”
And yet, outside of the medical world, it seems that the only people who have heard of it are those who have lost, or almost lost, someone to it.
“ARDS is clearly reported in the scientific literature,” says Barry Fuchs, associate professor of medicine, director of the medical ICU, and medical director of respiratory care services at HUP. “But it’s definitely underappreciated by and underreported to the lay public.”
Part of the problem, Fuchs adds, is that “unlike cancer and heart disease, the public and the politicians don’t hear [enough] about the heart-wrenching stories to really have an impact.” Adding to its stealth is the fact that “ARDS is a syndrome, not a specific diagnosis. It’s caused by so many things. You could get it from a blood transfusion, an infection, aspiration—it’s an ICU thing that people get sick from and die of. This is nebulous to patients and families.”
“You have to have something bad happen to you” to come down with ARDS, says Christie. “And that’s hard because people don’t walk down the street and get it, or they don’t get it for three months and are sitting thinking about how they can battle it. They get it really quickly, and then they live or die.”
Take a deep breath. Then take a moment to savor that simple act. We breathe from the time we’re first slapped on the butt in the delivery room, tens of thousands of times a day, every day. Until we don’t.
Without oxygen, the cells in our bodies can’t function. When we inhale air, oxygen is brought into the alveoli, the air sacs in our lungs, where it is transported to the surrounding blood vessels; the oxygenated blood is then delivered to our bodies’ cells. The alveoli are also responsible for the magical exchange in which carbon dioxide is exhaled as a waste gas.
A lot of things can cause the intense inflammation of lung tissue that characterizes ARDS. Among the most common are sepsis, pneumonia, trauma, aspiration, pancreatitis. But the end result is that the alveoli lose their ability to exchange oxygen and carbon dioxide with the blood, owing to a collapse of the air sacs and leakage of fluid (edema) into them. As the lungs try to heal the damage, scar tissue is formed, adding to the problem.
“In ARDS, basically your lungs leak like a sieve,” says Anthony Dal Nogare, a physician specializing in pulmonology and critical-care medicine at Rocky Mountain Heart and Lung in Kalispell, Montana. (Note: He’s been patiently explaining things to this writer on and off since our elementary-school days.) “The function of lungs is to exchange gas. And for that to happen you have to have a very thin membrane between the blood—where the oxygen and carbon dioxide go in and out of—and the alveoli, where the air comes down. So in a normal lung, there’s just a few micrometers separating those two.”
With ARDS, “that barrier gets broken down, and the capillaries become permeable, and fluid just leaks out of the blood space and into the alveolar space,” he adds. “So now you’ve replaced that beautiful, fine, thin structure with just a bunch of fluid and cells, and you can’t exchange gas anymore.”
ARDS has really only been on the medical radar since the 1960s, when ICUs—and ICU-related illnesses—became a regular part of Western hospitals. (It’s sometimes referred to as Adult Respiratory Distress Syndrome, to distinguish it from the version that afflicts infants.) In the early days the syndrome was known as Shock Lung, or White Lung (from the near-total whiteness of the lungs when viewed on X-rays), or Da Nang Lung (from the site of the Vietnam hospital where so many young soldiers succumbed to it after they had seemingly survived their battle wounds).
“People have traced it back to World War I, when forensic physicians doing autopsies on soldiers killed on the battlefield would find their lungs filled with fluid,” says John Hansen-Flaschen, a Penn professor of medicine and chief of the pulmonary, allergy, and critical-care division at HUP, and a prominent figure in the field. “They called it Drowned Lung, and it was recognized also in World War II as a post-mortem finding in soldiers who were severely injured but didn’t die right away.”
Why some people develop ARDS and some don’t is still a mystery; it’s like some terrible Borgesian lottery, where the winning ticket may get you a viper. This susceptibility is the part of the dark puzzle that Penn researchers are trying to solve.
“One of the most striking features of acute lung injury and ARDS is that it’s very hard to predict which patients will get it,” says Nuala Meyer, an assistant professor of medicine whose research focuses on identifying genetic and molecular risk factors for acute lung injury and organ dysfunction during critical illness (see “Evolution, Inflammation, and ARDS”). “I’ve seen very sick septic patients who never required more than 30 or 40 percent FiO2, which is an amount of oxygen from the ventilator. And yet I’ve seen other people with what seems like a controllable infection that still seems to flood their lungs.
“I think some patients are predisposed to flood their lungs,” she adds. “And some of the genetic variants we’re looking at may have been evolutionarily selected to help you respond to injury or inflammation in ancient times, when the biggest threat to life was infection or trauma.”
There’s a similar variation on the treatment-response side, she points out. “Some people go from being impossible to oxygenate for an hour or two, to coming down to 50 percent within a day or two, whereas others just stay at 100 percent and require high amounts of PEEP [positive end-expiratory pressure]—another ventilator maneuver we can use for oxygenation. There’s a lot of heterogeneity, both in who’s susceptible to it and in how patients respond to our therapy.”
For the families and loved ones of patients, “dealing with that uncertainty is tough,” says Paul Lanken, professor of medicine and former director of the medical ICU and Intermediate Medical Care Unit at HUP. “Thirty percent mortality—who is that 30 percent? When they first come in, I can’t tell.”
Mar|Apr 2012 Contents
Download this article (PDF)
page 1 | 2 | 3 | 4 | 5