Learning your lines

I was recently asked “what is a line infection?” and I realized that it would take more than 140 characters to explain everything about it. I also figured it would be a good topic to educate on, since as a whole line infections are very badly managed.

Briefly, a line infection refers to a bacterial (or fungal) infection of a central line, usually in a vein but an arterial line could get infected too. The classic case is a catheter tip infection with bacteria in the bloodstream. The patient may have a fever, and may be quite sick indeed.

One might ask; “How the heck does that happen??!!”. Actually, surprisingly easily.

Lines can be infected from two ends – the outside end is open to the air and is accessed every time a medication or IV nutrition is put through it. If sterile technique is not used bacteria can get into the line. Heck, even with sterile technique bad luck plays a part too. These bugs are often skin bacteria that are normally fairly wimpy or considered “contaminants” when grown in blood cultures (meaning they were picked up from the skin as the needle went in, not that the lab contaminated them!). The inner end is safely inside a blood vessel, which is sterile, but if bacteria get into the bloodstream for other reasons they can stick to the plastic line, since bacteria as a rule LURVE to stick to non-biologic stuff. These can be any kind of bug, but are more likely to be bacteria from the gut who wandered off accidentally in the bloodstream and find a home there before the immune system can kill them off.

Once a line infection is established, we have a problem. Plastic lines have no bloodstream and no immune system. Bacteria can produce slimely stuff (called a biofilm) that coats the infection and acts as a barrier to the immune system, and some antibiotics. Imagine smearing peanut butter on a table, then trying to get it off with your finger. Even after a good swipe you’ll leave a smear behind. Now imagine trying to clean it off by dripping detergent onto it. That’s what it’s like trying to clear a line of a line infection. The only way to guarantee clearing a line is to pull it out and put a new one in.

Pulling a line is not a lightly-undertaken job though. If someone has a line they probably have a reason for it – long-term nutrition, chemotherapy, antibiotics etc. If you pull that line you may interrupt their usual doses, for days at a time. Line sites get scarred and if you do this enough you can run out of new sites to use! So it’s paramount to diagnose a line infection properly.

Imagine the following: a kid with a line gets a fever. They come to the hospital and blood cultures are drawn from the line. They grow a staph aureus. OH NO! He has a staph aureus line infection right? Not necessarily. Blood drawn from the line is just blood – this could be any other staph bacterial bloodstream infection, such as from a bone or joint infection, endocarditis (infection in the heart) or something else. We need to know whether the line has more bacteria than the rest of the blood stream.

This is where most people go wrong – you MUST MUST MUST draw multiple cultures, including a culture from some place else (and yes, this means sticking a needle in someone – suck it up). Ideally you need quantitative cultures, where you draw a fixed volume of blood then plate it out and count the colonies. If the line cultures grow significantly more than the periphery, it’s a line infection. If it’s the same, it is a bacterial bloodstream infection, but not a line infection. BIG difference. If you can’t do “quants” you can time how long the cultures take to turn positive in the lab. Most experts consider a difference of a few hours to be significant.

Once you know it is a line infection, you can think about what you’re doing. Most people get started on broad-spectrum antibiotics to cover all the likely bacteria. Once you know your bug though, you can tailor therapy. Non-Aureus staph for example may actually be cleared using a couple of weeks of antibiotics. Enterococcus or staph aureus are tougher, gram-negative bacteria from the gut are even worse. Pseudomonas or candida/other fungi are practically impossible to clear, don’t even try.

What’s the harm in trying? Time. You waste time. You have a kid sitting in the hospital getting IV antibiotics. You may send them home…and you may be able to show that the blood cultures turn negative….but you stop those antibiotics and WHAM the peanut butter smear you didn’t quite clean off has grown back into a big old dollop of yuck again. You’ve wasted 2 weeks at least, several days of hospital time AND now you’re back at square one and you have to pull the line you should have pulled two weeks ago.

The two biggest errors I see people try with line infections are: not correctly testing for line infection with sufficient blood cultures; trying to salvage an unsalvageable line. People are fooled into thinking they have cleared a line infection, when in fact they may have been treating a bacteremia from another source and just THOUGHT they were treating a line infection. This reinforces the incorrect belief that clearing line infections is easy…

I get consulted on these kids. I can rarely offer specific guidance unless the correct workup has been done. I have seen kids get lines out that I am sure were not infected, and I have seen kids treated for weeks for an infection that could have been cured with a 30 minute procedure to pull the line out. There are evidenced-based guidelines on this issue published by the Infectious Disease Society of America – ID docs KNOW how to manage line infections – and yet our guidelines, and our specific advice, is often ignored.

Best reason I was ever given for not removing an infected line? “We can’t take it out, we’re using it for the dopamine”. Yeah, well maybe if you stopped using it the patient wouldn’t be in shock any more…

Screenshot of the most critical table from the IDSA guidelines.
20120528-084530.jpg

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