Room to breathe, room to vent

by Lorien E. Menhennett

Of the dozens of patients I encountered the summer I worked in an ICU in the Chicago area, the person I remember the best is Mr. Chesterfield.* Rather, I remember Mrs. Chesterfield — her husband was on a ventilator and was unconscious and unable to talk the whole time I was there. But Mrs. Chesterfield and I had some lovely conversations while I stocked the nurse’s cart in Mr. Chersterfield’s room, brought in new boxes of gloves, and changed the sharps box. She even sent me a thank-you note, telling of her appreciation for how I had encouraged and comforted her during that difficult time.

At the time, I knew the machine hooked up to Mr. Chesterfield was pumping his lungs full of air, breathing for him. But I had no idea how it worked, or what damage such a life-saving device could potentially cause. Until today’s lab meeting.

Clearly, if someone cannot breathe on his or her own, having a machine do it is a good thing. There are several problems with using a ventilator, however. One is that using a ventilator at “high-tidal volume” — which is sometimes required, when a person’s lung capacity is diminished (from what I understand) — can “hyperinflate,” or overstretch, the lungs. This excessive stretching breaks the cell-cell junctions (sticky stuff that keeps the cells together). This necessary (but damaging) overstretching results in a condition called “volutrauma.” In this condition, the permeability of the lung cells (specifically, alveolar epithelial cells) increases, which affects gas (i.e., oxygen and carbon dioxide) exchange, the spread of micro-organisms (and infection/inflammation), and the build-up of fluid. When volutrauma is taken to the extreme, according to one person in my lab meeting, you basically drown to death because your lungs fill with fluid. Not good.

Of course, when you breathe normally, you are also stretching your lungs — perhaps about 8 percent. High-tidal volume ventilation might stretch your lungs about 20 percent instead. With that extra stretch comes increased permeability and the cell-cell gaps that create all the problems.

What one of my fellow researchers has found is that decreased levels of a particular protein seem to be linked with those cell-cell gaps and increased permeability. Increased levels of that protein may be associated with fewer gaps, called a “partial rescue.” This means the protein could be a “therapeutic agent” for ventilator-induced lung injury. Which would be a huge deal, especially considering that many ventilator patients are older, and that the ratio of elderly people in the overall population in the United States is about to jump sky high.

Of course, there are plenty of issues to work out with this research. (I won’t even start on those.) This is basic science, not even close to a clinical trial. But it’s exciting to see how something happening in the lab next door could potentially save lives a few years (or decades) down the road.

And who knows? Maybe by the time I’m an anesthesiologist (a thought that has occurred to me more than once) this is a treatment I’ll be using.

*Name has been changed to protect the patient’s privacy.