Saline locks

vintagemother, BSN, CNA, LVN, RN · Mar 13, 2016

Blood doesn't come back up the catheter, usually, and I think that's due to the pressure of the blood in the vessels keeping the saline in place.

I typically see the catheters to be filed with NS, and usually not pink tinged.

When you flush the Cath, you push the saline using force. It doesn't drip in by gravity.

I'm pretty sure that seeing blood in a SL IV is an indication to flush it with NS because pooled blood can clot and occlude which would defeat the whole purpose of leaving in a SL for IV access.

I hope that's clear. If not ask some more questions!

Flushing PRN and Q shift also help keep blood from pooling in the catheter line.

Here's a link to a detailed explanation from the much missed Daytonite on AN:

https://allnurses.com/general-nursing-student/how-to-maintain-314391.html

**NICU Guy, BSN, RN** · Mar 13, 2016

It is physics. Once you clamp the tubing after you flush the line, it creates negative pressure. Same thing when you put a straw in a glass of soda. If you place your thumb over the top and pull the straw out. The soda doesn't drain out.

nfeese · Mar 13, 2016

ok so the catheter inside the vein remains full of NS or hep whichever is ordered? Like it remains in the catheter without dripping out into the vein? That's what's got me a mess...

nfeese · Mar 13, 2016

Btw the straw example is grrreeeaaattt love it. I have to ahave clear understanding of concepts and that straw reference is going in my back pocket. I'm gonna share that with my teacher.

Double-Helix, BSN, RN · Mar 13, 2016

Yes, ideally the NS or heparin flush stays in the catheter.

It's all about pressure. There are neutral pressure caps and positive displacement caps. Neutral caps DO allow the reflux of blood if the pressure in the vein is greater than that in the catheter. You might witness this in the PIV of a toddler who is crying, or when a tourniquet is placed on the extremity with the IV. In order to prevent the reflux of blood, the line is clamped, ideally while the flush is being pushed through the line. This helps create a little more pressure in the catheter that prevents blood reflux (like the straw and drink example).

Positive displacement caps are most likely to be found on PICC lines or other central lines. For these devices, the closure of the cap is what creates the positive pressure in the line, preventing blood reflux. The line is only clamped AFTER the syringe is removed from the cap, otherwise you're deactivating the positive pressure system. Clamping these lines is really more to prevent air embolus in the event of cap dislodgment than it is to prevent blood reflux.

nfeese · Mar 14, 2016

So say a patient has a periphereal IV removed and saline locked wouldn't it have a positive pressure cap at the end? So basically the positive pressure cap acts as your finger would over a straw? And the clamp... how will it defeat the purpose or mess it up? Sorry to be asking so much and I appreciate your feedback and wisdom.

Double-Helix, BSN, RN · Mar 14, 2016

It has to do with the mechanism of the design of the caps. The short answer is that clamping a line or most regular caps aren't positive pressure, they are neutral pressure. When you clamp, the pressure in the line stays the same as before you clamp it, all you're doing is cutting it off, preventing flow between each side of the clamp. A positive pressure cap places additional force into the line when nothing is attached to it. Accessing the cap with a syringe deactivates that mechanism, allowing flow for injection or aspiration of fluid/blood. If you clamp the line while the cap is accessed, it becomes a neutral pressure system.