Fluid column for epidurals

[Urzuz]

Hi everyone,

First time poster around these parts. For some background, I'm a second year anesthesiology resident right now.

I had a question regarding columns during epidural placement. I feel like I should know the answer to these questions, but I figured I would just confirm what I think the answers are!

When using a fluid column after getting the Tuohy needle into the epidural space, I understand that you are looking for the fluid column to drop when you open it to atmosphere, because the epidural space is at a lower pressure than atmosphere. My question is, what are the different things you can see to tell you that you AREN'T in the epidural space, and where do those things imply you are? If you don't see it drop at all, I think that could mean you could be anywhere from the subcutaneous tissue all the way down to the ligamentum, right? If you are intrathecal, what would you see? I know you would theoretically get a wet tap so that would tip you off, but if you did hook a fluid column up, what would happen? Also, I've seen some of my attendings ask patients to take a deep breath while the column is dropping. What are they looking for?

Thanks in advance for the replies!

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[Gas you down]

Hi everyone,

First time poster around these parts. For some background, I'm a second year anesthesiology resident right now.

I had a question regarding columns during epidural placement. I feel like I should know the answer to these questions, but I figured I would just confirm what I think the answers are!

When using a fluid column after getting the Tuohy needle into the epidural space, I understand that you are looking for the fluid column to drop when you open it to atmosphere, because the epidural space is at a lower pressure than atmosphere. My question is, what are the different things you can see to tell you that you AREN'T in the epidural space, and where do those things imply you are? If you don't see it drop at all, I think that could mean you could be anywhere from the subcutaneous tissue all the way down to the ligamentum, right? If you are intrathecal, what would you see? I know you would theoretically get a wet tap so that would tip you off, but if you did hook a fluid column up, what would happen? Also, I've seen some of my attendings ask patients to take a deep breath while the column is dropping. What are they looking for?

Thanks in advance for the replies!

they seem to be using the "hanging-droplet technique". just look that up and check it out.

 

[cchoukal]

If you were intrathecal, what you would see would depend on the ICP and the height of your fluid column. ICP is typically 5-15, so if the height of your column were above that, you might still see the column drop. If the height were below that, you might see fluid rise up and out of the column.

 

[RussianJoo]

what "fluid column" are you talking about? I've never hooked up any columns or been asked to hook up any columns when doing epidurals.I use a column if I am measuring opening pressures for an LP. Could you please explain what you mean by fluid column?

 

[lushmd]

what "fluid column" are you talking about? I've never hooked up any columns or been asked to hook up any columns when doing epidurals.I use a column if I am measuring opening pressures for an LP. Could you please explain what you mean by fluid column?

RJ, you can use the epidural catheter itself for this purpose. Next time you do an epidural, try this: connect the luer connector, bolus a small volume (<0.5 mL) of saline (if you're less confident) or local anesthetic (more confident), remove the luer connector, and lift the catheter up such that it's tip is well above the site of epidural insertion. If the catheter is in the epidural space, you should observe that the fluid column falls.

 

[RussianJoo]

Do you mean after threading the catheter? I've done that once before and saw it go down, didn't really know that's what the OP meant because one attending only had me do that once no one else has ever asked me to do that, I guess I haven't done enough epidurals because I am pretty sure I know if I am in or not if I do both get the loss and thread the catheter. And don't need other tricks to tell if I am in the space or not. Ultrasound might be a good way to check catheter placement too.

 

[fakin' the funk]

Ultrasound might be a good way to check catheter placement too.

Tell us more.

 

[somedumbDO]

Do you mean after threading the catheter? I've done that once before and saw it go down, didn't really know that's what the OP meant because one attending only had me do that once no one else has ever asked me to do that, I guess I haven't done enough epidurals because I am pretty sure I know if I am in or not if I do both get the loss and thread the catheter. And don't need other tricks to tell if I am in the space or not. Ultrasound might be a good way to check catheter placement too.

I only use U\S if they are super fat and need to find midline, otherwise especially in PP huge waste of time and money

 

[RussianJoo]

Tell us more.

I have one attending who wants us to scan the back and measure how far the epidural space is and basically mark our space before doing the epidural. That way we know when the LOR should happen and know that we're not in the right location if we're beyond that distance with our needle. The same technique can probably be used once the catheter is in to see if it's in the space or not.

Like the person above said, this is really only needed for super obese pts where you can't feel anything but back fat. But it can be done on normal sized pt's too, and will probably take even less time to do, than with the super morbid obese.

 

[fakin' the funk]

I have one attending who wants us to scan the back and measure how far the epidural space is and basically mark our space before doing the epidural. That way we know when the LOR should happen and know that we're not in the right location if we're beyond that distance with our needle. The same technique can probably be used once the catheter is in to see if it's in the space or not.

Yeah I'm with you on finding midline and ID'ing depth to LF. It's the bold part I don't buy. There are, like, some bones in the way, plus you're trying to imagine an object that is nearly in the same plane as your U/S beam.

 

[RussianJoo]

We can see 22G needles when doing US guided blocks, and guide wires inside blood vessels when doing central lines, so I figured we should be able to image a catheter inside the epidural space, especially in the transverse section between the transverse processes, which is the image I use to measure the distance to the LF. it will just be a dot in that view but it theoretically should be visible. Next time I have extra time when placing an epidural pre-op for post-op pain I'll grab an ultrasound and take a look after I am done placing the epidural. This might not be anytime soon since I am not in the main OR for the next couple of months. I'll try to post a picture here when I do get an image.

 

[Mr Wizard]

what "fluid column" are you talking about? I've never hooked up any columns or been asked to hook up any columns when doing epidurals.I use a column if I am measuring opening pressures for an LP. Could you please explain what you mean by fluid column?

In my experience, this is usually done more frequently with thoracic epidurals because of technical difficulty and patient population/procedures which can make reliable catheter function paramount post-operatively.

This is achieved by addition of an IV tubing extension/stopcock set on your field. You fill the tubing with saline, close or occlude while attaching to the luer lock on the tuohy. Then you raise the tubing, open to air and watch to see if the saline drops.

This is just extra confirmation/confidence of correct placement if your LOR was not that good. Deep respirations would cause variation in the rate of saline fall.

 

[Mman]

We can see 22G needles when doing US guided blocks, and guide wires inside blood vessels when doing central lines, so I figured we should be able to image a catheter inside the epidural space, especially in the transverse section between the transverse processes, which is the image I use to measure the distance to the LF. it will just be a dot in that view but it theoretically should be visible. Next time I have extra time when placing an epidural pre-op for post-op pain I'll grab an ultrasound and take a look after I am done placing the epidural. This might not be anytime soon since I am not in the main OR for the next couple of months. I'll try to post a picture here when I do get an image.

I bet the time it takes to find an epidural catheter in the epidural space on ultrasound is longer than the time it takes me to walk in the room, consent the patient, prep them, place the epidural, bolus it, and place the dressing and have finished charting.

You can see a 22 g needle on ultrasound because it's metallic. And it's also at a pretty shallow angle to the ultrasound probe and relatively superficial. You can see a guidewire on ultrasound for the same reason when doing an IJ, plus that is floating in a nice fluid filled space.

A plastic epidural catheter sitting in a potential space that is probably at least 5+ cm deep and surrounded by bone? You'd spend days on some patients trying to find it. The baby would already be delivered and you'd still be confirming catheter placement.

An epidural shouldn't be made more difficult.

 

[Deanmonster]

Ultrasound can't see through bone or air. So you won't be able to see your catheter very well in the epidural space.