Question about zeroing lines

When you're zeroing your lines, what you're really doing is calibrating the transducer to the atmospheric pressure in the room. The transducer is the electronic interface between the pressure wave produced by the patient's heart which is transmitted through the fluid-filled rigid column of the tubing and the monitor; it translates that pressure wave into numbers. Calibrating it to the atmospheric pressure in the room removes that factor from the equation. So it really doesn't matter where the level of the transducer is at that point. BUT... for the reading that you're obtaining from the transducer to be meaningful and accurate the transducer must be level with the phlebostatic axis, at the 4ICS. If the transducer is too high the pressure wave traveling through the fluid in the line will have to go "uphill" against gravity and therefore the number you get will be falsely low and vice versa. Does that make sense?

Too funny, harryalex! I think we work in the same unit... I've asked many people what they're doing when they zero their lines and they can't tell me. When I ask them how turning their patient from the left side to the right side has changed the atmospheric pressure in the room and get a blank look. And when I point out that the only entity that can change the pressure in the room is Mother Nature (via the weather), well... it's priceless. Don't get me started about EVDs. That's a horse of a totally other colour!

I'm game if you are!

Yes you do need to relevel with position changes to ensure you're still measuring your pressures at the phlebostatic axis. But there are some situations where you would want to rezero your transducers during your shift. This would include disconnecting the cable (some monitors will "lose" the transducer when you do that, even if it's just for a second), Changes in the weather (from stormy to clear or vice versa, because the atmospheric pressure will change with it) and with any sudden and unexplained change in the pressures you're seeing on the monitor. For example: your patient is well-sedated, has been unmoving for some time, is not bleeding or dumping urine, all infusions are topped up and running appropriately, other vital signs are stable, there are no visible bubbles in the tubing but abruptly has become hypotensive. A cuff BP should be done while you're troubleshooting, and if that doesn't correlate even remotely and there's no apparent reason for the change, rezeroing might be necessary. Mechanical things don't always work perfectly and you want to be sure that you're not treating a mechanical issue with meds or fluid. But raising the head of the bed, or raising the bed itself will not change the atmospheric pressure in the room and thus will not result in the need to recal your transducers. The one exception to this is the external ventricular drain with transducer, which typically by policy are rezeroed every 4 hours. The rationale for this is that even small changes in ICP can cause great damage to the brain and there must be close attention paid to ensuring the numbers we're seeing are as accurate as they can be. Makes sense??