It’s quite simple really. All you have to do is inject 3 cc of air directly into the right atrium of your unsuspecting experimental animal. Yep. It’s as simple as that. And how to do that short of wielding an air-filled syringe and stabbing it directly into the sweet spot?
The handy-dandy device pictured here is a stopcock. It’s used as a valve to allow one catheter to be connected to more than one thing. We use many stopcocks in my study—on the arterial line to allow connection to the blood-pressure-heart-rate-machine-thing with an extra port for blood draws, on the venous line to allow connection to the central-venous-pressure-machine-thing with an extra port for infusion of valium for sedation, and another stopcock on the same venous line to allow saline injection for measurement of cardiac output with the other port used for blood draws. And that’s not even the half of them apparently.
We measure cardiac output using the thermodilution method in which cold saline is injected into the right atrium and the change in temperature measured. I’ve run this measurement many times before in all of my previous failed (for other reasons) experiments. I always double and triple check all of the stopcocks before injecting saline. And I did no different today before starting my measurements.
Here’s what I was thinking as I was taking my readings:
Okay. First reading: 1322 ml/min. That’s a little high (but in the realm of normal for this animal). Let’s run another one…
Uh. Why is there only a flat line tracing (as opposed to the usual curve) and no reading? Well, not to fear. This has also happened before (or maybe not…what I meant was that the cardiac output machine has done funky things before). Let’s just run it again.
Still a flat line.
Hmm…why is the respiratory-machine-thing alarming? Well, that also happens a lot because this animal likes to breathe against the ventilator and the normals are set at human values.
Let’s just hit that “silence alarm” button.
Hmm…why does it say “apnea (which means that breathing has stopped)?” That’s a little odd. But that’s also happened before—when someone stepped on the line connecting the animal to the respiratory-machine-thing. [looks to see if someone is stepping on line] No one’s stepping on the line.
Crap. Are my lack of cardiac output reading and this apnea related? The apnea did seem to start right after that second attempt at a cardiac output reading. Can’t be, because that means I did something wrong and I triple checked all the stopcocks and I flushed out the saline injection line before using it…
At this point, Collaborator-doctor-man finally notices that there just might be a real problem (the alarms go off a lot in our experiments—we’ve become quite adept at hitting that “silence alarm” button). He glances over at the cardiac output machine setup and notices the problem: the stopcock attached to the very end of the saline bag was in the closed position. Which means that no saline was being drawn into the injector-thing. Which means that the injector-thing was injecting AIR instead of saline into the animal when I tried to take my cardiac output readings. Which means I gave the animal an air embolus that probably went straight to its lungs. Which was why it was apneic. Which means that I so just ruined my entire experiment by killing the animal.
The irony. We’re always so careful to flush out every single line with plenty of saline and to check our syringes twice to avoid little tiny air bubbles because the animal we work with is quite sensitive to air emboli. And here I am, injecting not a little tiny bubble or even two, but 3 whole cc of air into the poor animal. All because some weirdo decided to put a stopcock at the end of that saline bag. Who would do such a thing anyway? Leaving it in the closed position no less? It’s almost as if my major professor snuck in when our backs were turned and sabotaged me just so that he can torture me a little longer. I wouldn’t put it past him. Well, I learned my lesson here. Stopcocks are not my friends.
