Tech Spotlight: Bubble CPAP

There's an old saying: The difference between men and boys is the size of their toys. Well Beckett gets to start his life off with some pretty snazzy toys. The NICU has quite a bit of fancy equipment hooked up to our little man, so I thought I would take some time to explain what all of it is. First up: Bubble CPAP.

Note to people who already know about this stuff: Please let me know if I say something wrong so I can correct it. I promise I won't take offense. But don't be surprised if I defriend you on facebook. (j/k)

Back when Ellie was born NICUs didn't favor CPAP quite as much as they do now. They've always figured it's best to give these little babies the least amount of assistance that they need/want to thrive. As far as breathing is concerned, the most assistance they can give is a ventilator which breathes for you. Next is CPAP which creates a seal around your nose (and sometimes mouth) that forces air in at a constant pressure. The next step down is a nasal cannula which blows air into your nose, but doesn't force it down (because there's no seal around the breathing tube).

After Ellie spent a day or two on the ventilator the doctors said she was doing great so they took her all the way down to a high flow nasal cannula. And she never looked back. She spent the rest of her days at the NICU on a nasal cannula until they were ready to wean her off and let her breathe all by herself.

Within the last few years, new research has come out which indicates that CPAP has benefits over the nasal cannula. Beckett's CPAP continuously forces air into his lungs so that even when he exhales there is still some air in his lungs. This prevents his tiny little air sacs from closing. That's a good thing!

In the womb, babies have no need for lungs (but they do still breath in and out amniotic fluid) which is why they are among the last organs to develop. One of the last things they do is produce a surfactant that makes the tiny air sacs slippery so when they close they don't stick to themselves and stay shut. That would be a collapsed lung, and that's no good. That's where CPAP comes in.

So how does it work? First pure oxygen is piped into the room from a convenient wall jack. Right next to the oxygen hookup is an air hookup to provide "room air" and a vacuum hookup which can provide suction. (I'm trying to convince them to put in a wall hookup that provides coffee.) The vacuum hookup isn't used for CPAP (nor is the coffee hookup).

Next the oxygen and "room air" are sent through and oxygen mixer which allows to nurse to control the oxygen percentage. The "room air" contains 21% oxygen already, so 21% is the minimum amount of oxygen Beckett will get. An oxygen analyzer down the line measures and constantly displays the oxygen percentage to make sure the mixer is doing its job and to let you know exactly what mix you're getting. (The dial on the mixer is pretty sensitive between 21%-30%.)

The oxygen analyzer display is always one of the first places my eyes go when I come to see my boy because that tells me how well he's been breathing lately. A high percentage means he was having episodes of reduced heart rate (bradies) or lowered oxygen saturation (desats) so they turned it up. A low percentage means that Beckett is a rock star. In case you're wondering it's currently at 22.7%. Good job rock star. Sleep on.

At the output of the oxygen mixer sits a regulator to control the flow rate. So now you've got the perfect oxygen mixture and a regulated flow. What more could you ask for? Well some heat and humidity would be nice. The next contraption down the line provides both. The water comes from IV-style sterile water bags. The heat comes from ... well, an electric heater. Nothing fancy there. This contraption also has a sensor (and alarm) to detect blockages down the line. Nice touch. (And if you really must know it has a pressure release device and an inlet for the oxygen analyzer.)

The fancy contraption's output, mixed, heated, humidified, regulated and monitored ... gets piped directly to Beckett's mask/prongs inside the blue inlet hose. But we're not done yet! We still need an outlet. We can't just force a bunch of air down his nose without providing an outlet for the excess and for him to exhale.

Now it's time to put our physics hats on. (If you don't have one, you can pick one up really cheap on Amazon. I recommend one with a Richard Feynman quote on it.) Just sayin'. ... Okay so my point is that if you just vent the outlet to the open air, then the pressure at the end of that outlet tube is going to be the air pressure in the room. And if you travel up the tube to his prongs/mask the pressure will still be pretty much the same. So you're not really pushing air into his lungs, you're just blowing it past. You're teasing him! That's not CPAP that's just mean!

So we need some clever way to terminate this outlet tube and control the pressure all at once. Get excited. It's time to put the bubble in bubble CPAP! The clear outlet tube gets put into a container of water. The air flowing into this water of course creates bubbles. This is Ellie's favorite part. (Okay, I didn't really ask her but I'm pretty sure she'd agree with me if I did.) By controlling how deep you put the end of the outlet tube, you control how much pressure pushes back up into Beckett's nose. Just like in scuba diving or even swimming pools, the deeper you go the higher the pressure.

So when they changed Beckett's CPAP pressure down to a "bubble 5" (from "bubble 6") they simply moved the bottom of the outlet tube up from 6cm deep to 5cm deep. Speaking of deep ...

It might seem a little odd to measure air pressure in cm of water. But actually mm of mercury (mm Hg) has been a standard of pressure for years. In fact, standard atmospheric pressure is 760 mm Hg. So Beckett's CPAP pressure is 5cm H2O + 760mm Hg. That's equal to about 1038cm H2O. That seems crazy high. That means they took atmospheric pressure (1033cm H20) and added just a tiny bit to it. It hardly seems worth doing, 5cm is less than 1% of 1033cm. But of course the atmosphere is pushing in on his lungs at 1033cm H2O. The bubble CPAP gives him just a bit (5cm H2O) of extra pressure to keep those lungs open.