The 7.40 / 40 Club

If you work in respiratory therapy long enough, you start to notice another pattern.

It’s not wheezing.
It’s not shortness of breath.

It’s numbers.

Specifically: pH 7.40 and CO₂ 40.

Somewhere along the way, those two numbers became the holy grail. The center of the universe. The place where all patients are apparently supposed to live at all times, no matter what.

I once had a doctor joke with me—half joking, anyway—that the goal of BiPAP is simple:

“Get the pH to 7.40 and the CO₂ to 40.”

That’s it. Mission accomplished. Everyone go home.

And honestly, once you hear it, you can’t unsee it.

Patient comes in with a CO₂ of 42.

Forty-two.

Two points above perfection.

Next thing you know: “Let’s put them on BiPAP.”

Now, is the patient in distress?
Are they altered?
Are they tiring out?

Eh… details.

The number is 42.

And we all know what that means.

They must be guided—gently, heroically—back to 40.

Because clearly, the human body cannot function at 42. It’s a miracle they made it this far.

So on goes the mask.

Pressures get dialed in.
Alarms start beeping.
The patient gives you that look like, “Was I doing something wrong?”

And in the background, the ABG waits patiently… ready to reveal whether we’ve restored order to the universe.

A couple hours later:

CO₂: 40

And there it is. Balance has been restored. The stars align. The RT exhales. The doctor nods. The number is right where it belongs.

Never mind that the patient felt okay before. Never mind that they feel exactly the same now—just with a tight mask strapped to their face and a machine hissing beside them.

But the number?

Perfect.

Now, to be fair, BiPAP absolutely has its place. When someone is in real trouble—acidotic, tiring out, heading in the wrong direction—it can be a lifesaver. No argument there.

But sometimes… sometimes it feels like we’re not treating patients.

We’re treating decimals.

We’re chasing a version of “normal” that looks great on paper but doesn’t always match what’s happening in front of us.

Because here’s the truth most of us learn eventually:

Not every patient is supposed to be 7.40 and 40.

Some live at 45.
Some live at 50.
Some have been there for years and are doing just fine.

And that’s okay.

The body adapts. It compensates. It finds its own version of balance, even if it doesn’t match the textbook.

But every now and then, you’ll still hear it.

“CO₂ is a little high… maybe we should start BiPAP.”

And you can’t help but smile.

Because deep down, we all know what we’re really chasing.

Welcome to the 7.40 / 40 Club.