Grand Rounds-Implantation of Intrathecal Drug Infusion Pumps: Technical Nuances
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- Hello, this is the second talk on our series. The first talk was patient selection and surgical treatment of hypertonicity. This is a surgical nuances of Pump Implantation and Replacement. Again, the disclosures, I received honorariums for teaching consulting and research and product development from Medtronic. The FDA, the Medtronic has not reviewed, edited or approved this talk. I may discuss procedures or uses for intrathecal baclofen that are not in the FDA labeling. I am sharing personal experience and not making any recommendations on behalf of Medtronic. The first thing to do when implanting a pump is to consider some things about the pump. The first thing is the size. The classic pediatric or smaller pump is one third thinner in thickness. The diameter is identical to the adult pump. It does have a 20 ml reservoir and the minimum weight for children is 25 pounds. The adult pump has a 40 ml reservoir, but again, the minimum weight for implantation is 25 pounds. Again, this is a picture of the 20 ml reservoir, and it's about a third smaller than the adult reservoir. Other things to think about is the patient's size and body habitus, whether or not they have a G-tube or a vesicostomy or other tubes coming out of their colostomies and other as well. What previous operations and scars do they have across their abdomen? Very important in something neurosurgeons aren't likely to think about is when they're seated in chairs, since many of these patients are nonambulatory and spend a good deal of their day in a chair, where are their belts, their straps, and their braces? What style clothing do they wear? Where is their belt line? How do they sit? How do they get around the community? What is their mobility? Subfascial placement is very effective. It has a lower profile, a much better cosmetic appearance, does allow cerebral palsy kids to do a commando crawl, better back brace tolerance with this on if they have to wear a TLSO because of scoliosis. Additionally, there's another layer of tissue over the pump. And when studied has had a lower risk of infection and less risk of skin erosion. However, it's much more surgery to do this. Here's an example of shooting and looking across the abdomen of a patient of mine that I've taken care of for years with a spinal cord injury, she was a woman in her thirties and she did not want a TUNA can sticking out of her belly. And when I told her about subfascial we did this and you can see that you can't see it. The actual location of the pump, the subfascial pump is actually implanted underneath the anterior rectus sheath and the external oblique over in here. And when it's implanted, it's very important when doing this procedure that you first in size down to the fascia horizontally across the rectus, then go across and identify the external oblique. Then putting your finger under the external oblique, separate the external from the internal oblique and lift that up and then put an army navy underneath. That gives you good exposure of the lateral border of the rectus sheath. Within size, the lateral border, this will free up the rectus and allow you to dissect it off things they don't teach you in medical school, or you never really think about is that, that wonderful six pack you worked so hard to get in the gym is all above the umbilicus. So if this is a thin adult making dissection below the umbilicus will be much easier because when you're putting into subfascial pump, that six pack is actually attachments of the anterior to the post rectus sheath and separations of the muscle and you have to take them all down when doing this. Catheter position. Again, we know from early eighties that there was a 4/1 lumbar to cervical concentration gradient. This is from the days when IRB were not so strict and they would ask patients to allow them to do a lateral cervical puncture and sample CSF from the cervical except or the cervical cistern, and also from the lumbar. And these were catheters that were at about T11 in paraplegic and diplegic patients. And they saw that there was 4/1 consecration gradient. What we have learned from animal studies is that much of the drug adheres to the cord into receptors within several centimeters of the holes in the tip of the catheter. So most of the effect is in that area, the drug then also gets into the general circulation of the CSF and does distribute up and down the cord. Clinically we know from that when we moved the tip of the catheter into the higher cervical region that the catheter does, or that the patient with upper extremity hypertonicity does get better control with the intrathecal Baclofen, but they will never get as good a control because in the cervical region, there are more alpha receptors than GABAA receptors for tone control and therefore Baclofen being a GABAA agonist is not as effective as it is in the lumber where most of the receptors for tone control in the spinal cord are GABAA mediated. So in general, I put the catheter up about T1, or I should say in the mid thoracic region or lower thoracic region, maybe about T8 for lumbar control in patients who are paraparetic diplegic and an a pain pump for back and leg pain. I will go up to C7 T1 when I want to get a brainstem effect in patients with dystonia mixed movement disorders, choreoathetosis. And so, again, the other interesting thing is that we know that we can control tone with increased concentration in many of the meetings where there are multiple doctors who take care of children. I've asked at these meetings, how many have actually revised a catheter for axial growth at the time of a pump replacement. In other words, when the child had a pump put in at three or four, seven years later, there are 10 or 11 have grown significantly. Their catheter is obviously no longer at T1 is pulled down to T4 T5, have they ever had to move it back up. And most of them have not very rarely in fact, our catheters increased because they've been able to maintain control of the upper extremities just by increasing the dose. In choosing the pump location on the abdomen, you have to know that the pump has to be two to three inches from the surface of the skin to program it, again, straps and braces must not chronically rub over the pump. G-tube seemed to leak onto the pump incision immediately after. And so if it's very close would tend to put it on the right side, avoid direct pressure on the bladder by putting it down too low. And the gallbladder and appendix on the right side in these children. Another point is that many of the children have truncal hypotonia and tend to sag when sitting and when they slump their rib cage can come down on the pump and it can be painful. In adults where appearance is important, put it back below the umbilicus so that it's less obvious with tight shirts and dresses. Obese patients are trouble because you have to be near the surface to program it. Many of these patients have 6, 8, 10 inches of fat, and you cannot anchor the pump to fat. The fat will not hold and soon the pump will be flipping around. The secret is to move it up. Another thing they don't tell you in medical school, but when you have beer berries that men have that's because their fat is underneath their abdominal wall. And that smooth beer belly surface is the fat underneath. Their abdominal wall fascia tends to be up near the surface, but it's still very important to put this pump up higher above the umbilicus, and really the tip being near the rib cage, because then the pump is resting on the abdomen. It isn't hanging down from below. And when you put it below the umbilicus on the lower half of this beer belly, the belt rubs and pushes on it. And it becomes very, very painful and disagreeable to the patient. Women are rubenac and they tend to put their food fat outside their abdominal wall, and they layer it. And there can be very difficult. In women again, try to get up near the rib cage because in that area, the fat is thinnest and you can often so down right below the ribs. However, if they are morbidly obese, other sites can be the buttock, in the back. And in the very large women, you can sometimes put it sub co-curricular, unlike the typical pacemaker to try to keep it from becoming mobile when they move. In my side, my default is the left side is the first choice because the gallbladder and appendix are on the right, which would have to be examined. The other thing is, is that it's very important to rotate the catheter access port bump on the pump medial so that it doesn't rub on the rib cage or the iliac crest. If the pump is on the patient's left side, when you rotated medial, the catheters coming up at you, since the catheter comes off clockwise from the pump, if you rotated medial on the right side, the tubing is going away from you and larger patients again, you can on the right side, you can move it more media, the pump more medial, and rotate the catheter access port lateral. Then you can see the pump tubing when you're closing, and there's less risk of catching it in a stitch. In really small children where it won't fit in one half of the abdomen, you actually can elevate the umbilicus. Also in children, you could place it subfascial. You cannot use subfascial in a child or adult who has more than three or four inches of fat outside of the fascia, because it becomes impossible to find the pump for refills. What about infection reduction? There was a guidelines for reduction, a surgical site infection printed in 1999. Although it is somewhat old. Most of the surgical tenants were developed by then. And this is a good article free from the CDC, that talks about evidence for a different surgical scrubs for ventilation systems, for drapes, for a number of factors that have gone through as well as antibiotics. Some evidence based suggestions from there, a preoperative bath for three days with chlorhexidene Hibiclens does reduce the colony count the colony forming units on the skin of patients significantly. actually Dial soap, reduces it some but not as much. There is not a large scale study showing that Hibiclens best actually reduce infection, but reduction of colony count is a good idea. Use of plastic occlusive drapes to cover all exposed skin. It's very important to realize that no matter what prep you use, all of them reduce the colony forming units on the skin, but they never reduce it to zero. So even prepped skin is not sterile and touching the skin can transfer organisms to your glove, which then when you pick up the implant can be transferred. Jim Drake in hospital for sick kids did a very nice study where they monitor a number of factors with pump implant. And at the end of the surgery, the surgical, the study nurse research nurse took the gloves from the patients identified who had the glove on and went to the sink and found that there were holes in over 30% of the gloves. And if the person wearing the glove touched the shunt, there was a significant increase in shunt infection. This seems to lend, the solution to this is double gloving. Although there has not been a large scale study that shows a double gloving does significantly decrease surgical site infection. It does make a lot of sense. Also, the idea of wound minors. We have published a study using a foam wound liner to cover these, the wound edges. When you make an incision in the skin, the exposed epidermis on each edge of the incision that you've made can have sweat glands and hair follicles with germs in that exposed area. And again, covering that when you're trying to slide an implant over it makes sense. The other thing that that article makes a good point is that when you have an implant or a foreign body and incision, be it a silk suture or any implant, the number of organisms to start a clinically significant infection is 100 organisms 10 to the two without an implant it takes 10 to the five organisms to get a clinical infection. What about prophylactic antibiotics? There are multiple studies showing that prophylactic antibiotics given within one hour before the surgery, especially within 30 minutes, make a significant reduction in infection. The evidence also suggests that the only dose that's truly significant is the dose prior to incision, and that it is very important to have therapeutic levels in the tissue at the time of contamination. And there's a lot of preclinical data that supports that. There is no evidence to support use for greater than 24 hours postoperative. The CDC article did recommend Kefzol or Cefazolin is the medication of choice. The reason because it has very rapid tissue penetration, and it would given even within 30 minutes prior to the surgery, very rapid, almost instantaneous high concentrations in the tissue. However, it is not MRSA. It does not kill amoxicillin resistant staph aureus, Zinacef has better CSF production or penetration, and also does not have penicillin cross-reactivity and makes it an option, especially in patients where CSF is involved. Vancomycin does kill MRSA. However, it takes over one hour to diffuse. And because it's a large molecule takes another hour to get adequate tissue levels so that it probably is not an effective prophylactic antibiotic unless given more than two hours pre-op and we have re-implanted patients who have been ex-planted with pumps with MRSA. We have actually admitted those patients the night before and started them on vancomycin that night. So they have high tissue levels of vancomycin and again, a small series, but seems to be able to decrease the risk of reinfection. In positioning, the lateral position with the side the pump is gonna be on up is very important. It's very important that this back is perpendicular to the floor so that you get the, your anatomy is straight on x-ray and then you bend the knees to open up the spinous process. And lots of tape is used to secure the patient in the lateral position. You then identify the iliac crest, the spine, the umbilicus anteriorly for planting the pump implant and the costal margin. It's very helpful to keep the pump warm, the older pumps. It was essential. It's still a good idea in the sink too, because it makes it much easier to aspirate out the water that it's packaged with into fill it. You put it in warm saline or water, lying on the OR table will cool the pump and make it difficult. You do not need to purge the pump. And again, a point for an infection reduction is not to have the implant lying out on the table for dust or other infected particles to land on it. Keep it covered when not actively using it. The lumber puncturing positioning is everything. Fluoroscopy is absolutely essential. The entry point preferred is L2-3. So the needle enters under the L2 lamina. The reason for that is that maximum motion of the lumbar spine is that L4-5 and L5 S1. And it's very important to keep the catheter as far away from that flection and extension motion to prevent migration and stress on the catheter. The obliged paramedian approach is very important when doing this, and there'll be a video in a second showing this. Catheter insertion. Once you put the catheter in, if it runs into an obstruction and backs up or coils, you cannot pull the catheter back through the current needle, because the top of the opening on the tier needle, will cut or damage the catheter leading later on to micro leaks. However, you can cut down on the needle to the fascia, removed the needle, and at the level of the catheter at the level of the fascia, you can pull the catheter back and forth and steer it. Here is a video on the paramedian oblique approach. There are really two ways to put a needle into the lumbar spine for a catheter. The classic has been the midline approach going between the spinous processes. We have all come around to identifying that the paramedian of black approach has significant advantages for catheter implantation, and is really the method of choice. When you do a midline approach, the angle is really quite sharp approaching it almost a 90 degree angle so that you can get between the spinous processes. This makes the catheter leaves the needle at a very sharp angle, often leading to difficulty steering the catheter, and actually even getting the catheter out of the needle tip. And it's much more difficult to advance and to steer that. When coming in you do want to make the needle parallel to the ligamentum flavum fibers, and then you feed it in. The other thing about the midline approach is the inner spinous ligament. Your catheter is in the middle of the inner spinous ligament. And over time that ligament buckles every time there's flection and extension, that puts a lot of stress on the catheter, and it has been shown to tear the catheter. And in my experience, these patients always present at three o'clock on Friday afternoon. The peer median approach, however, comes in in a much shallower angle, the guidelines or the, what you're looking for is the needle wants to go in at the level of the fuzz sets down below and come in about just below that, you now have a much shallower angle for the catheter to go in, making it much easier to advance the catheter and much easier to try to manipulate the catheter. Again, you want the needle tip to be parallel or the bevel to be parallel. And then when you enter, you will see a flashback of CSF. Then you can fit the catheter in very easily, and it will go down and fit in very nicely. The other advantage is that the catheter is going through about three inches of muscle. And this muscle acts as a very efficient washer to prevent backtracking of CSF along the catheter and leading to CSF collection subcutaneously, we have not had to use per strings sutures or other such events to do to prevent CSF. The other obvious advantage of this is there is no inner spinous ligament to tear the catheter. It's making a point here that you do not want to pull the catheter back in the needle through either approach. Now, again, when we're doing a lumbar puncture, it's very important to do the lumbar puncture under fluoroscopy so that you make only one puncture with a 14 gauge tier needle. It's very important before the puncture to make sure that your visualization on fluoroscopy shows that the spinous processes midline between the two pedicles so that your angulation of your x-ray beam is correct and your actually got no parallax. Then you make the pump pocket and you make the pocket deep enough that the incision doesn't cross the pump, the incision should be above the pocket, not across the middle of the pocket. And again, subfascial implantation is an option. If you're doing a two-piece catheter, you can tunnel from the small incision in the back, up to the front and pass the pump segment back. If you're doing a one-piece catheter, you have to anchor first, then tunnel from the abdomen to the back and pass the one-piece catheter up to the front. And this tunneling is dead subcutaneously. The V wing anchor is a method of anchoring the catheter. It goes on to the catheter. It must anchor at the fascia. A tip is that it's much easier to manipulate and work with the V wing anchor. If you put it in a simple hemostat or a dandy clamp, that gives you a handle to hold onto while you're manipulating. Likewise, if you're doing a two-piece catheter, the pin connector is much easier to deal with and hold on to while you're putting it on the catheter if you put it in a simple hemostat. When we anchor, we want to make very sure that the fascia comes all the way to the tip of that V wing anchor. So in this, although the catheters on top of it, the V wing anchor is anchored here, and it's right up against the fascia. If you tie it down and realize that it is not there, then it's important to tie a cuff of tissue over that. So that there's not catheter visualized between the fascia and the anchor. If there is when the patient flexes that distance increases, more catheter comes out. And then when the patient extends again, if this is open, the catheter can buckle out and this can lead to migration. 'Cause in many most cases, when there is migration, the catheter has migrated out in front of the anchor. It's also very nice to have a second anchor after a loop in the incision to hold right there. This allows that tension from rotation, flection extension is not directly transmitted to the anchoring suture. Lets skip that. You tie the anchor with 2-O silk. And again, this is showing very important that it there's no catheter visible. You have the strain relief loop. You check for CSF flow at the other end of the catheter once you're done all your anchoring sutures, to make sure that the sutures have not occluded the catheter at all. This is from a expert panel that went over a number of things for implantation. Again, you should anchor here. The anchor needs to be against the fascia. There should be a strain relief loop, and then a second anchor here to diffuse motion and energy from a rotation. Likewise, there should be a loop of tubing behind the pump. So that motion intention are not pulling directly on the nipple of the pump right here, leading to tears. And again, you want to rotate this bump media so that it doesn't rub against the ribs. And this catheter here is not underneath the ribs. You then aspirate water from the pump and we fill it with 500 microgram per mil Baclofen. When I'm doing subcutaneous implantations I do use a Dacron pouch. This one we soaked in Betadine. At one time, we no longer do that. We have not had significant increase in infection. The advantage of the pouch is that you do not have to precisely place your sutures to hit the suture anchors. If you're gonna use one of the four suture anchors, you have to have sutures in at least three, so that you don't have an axis of rotation that can lead to dislodgement. If you have the Dacron pouch, you can anchor several places. The tissue will in-growth into the pouch and hold it very clearly. You suture the pouch with a heavy non-absorbable. We closed the wound in three layers. There is a deep layer of micro or absorbable sutures that obliterates all dead space around the pump to decrease risk of seroma, that a second layer to close fat and tissue above that. And then we closed the skin all with absorbable suture. We do use on Q pump to infuse marketing into the pocket at two milliliters per hour. And we've been able to especially with the subfascial to have decreased post-op pain and earlier ambulation, we're also using argaelas dressings, which are silver ion release that antiseptic. And again, we've published some data showing improvement in our infection rate with pumps. There's a lot of data in cerebral vascular surgery that that dressing does decrease wound infections. And again, this is a typical on Q pump catheter with an argaelas dressing over it. This is the argaelas dressing. Maxorb is another dressing that has ionic silver. That is an antiseptic. After the pump is implanted, you have to program a continuous dose plus a bolus dose. The continuous dose is what the patient will be getting every day. And generally this is equal to twice the effect of test dose. So the patient had a 50 microgram, test dose. We will start at a hundred micrograms per day unless the patient had a prolonged effect from their test dose or became too flacid. Then we will either use, we will decrease the dose. We have to bolus to cab the pump to fill the tubing inside the pump and to fill the catheter. When we do a into service revision, we remove the old pump. If there is a pouch, don't remove old pouch, just slip the bivalve and slip the pouch itself, pull the old pump out and put the new pump in the old pouch and close it up. We always check catheter flow. Number one, to make sure we've emptied all of the drug out of the catheter, making programming much easier. And if there's no flow, we will often revise the catheter. Then you have to program the pump correctly. The question you always have to ask yourself is where is the drug? When the pump is filled, the drug goes into a reservoir. The drug then comes out of the reservoir into the internal pump tubing, where this rotates and dispenses drug it then comes through the internal pump tubing, which is about 0.2 milliliters in volume then goes out to the catheter. The catheter volumes are usually in the range of 0.15 to 0.2 milliliters. So you have to program drug to go from here, through here and out here. The time to do that when the catheter is, when the pump is brand new, and the bolus is run as fast as it could is about 20 minutes plus, or minus a couple of minutes. So again, in a new implant, there's drug only in the reservoir. There is water that's furnished with the pump and their CSF in the catheter. And again, you have to program it to go all the way through. So you have the pump tubing volume, which is about 0.199 ml in the increment tube pump. And then the catheter volume, the bolus time should be around 20 minutes, 18 to 24 minutes. When you're doing just a catheter revision, not replacing the pump. Remember there then is drug in the reservoir and drug in the pump tubing. There is no drug in the catheter. So you're programming a much smaller volume, just to 0.2 milliliters to fill the catheter. The time for that should be in the range of about eight milliliters. I mean, eight minutes. When you're doing an end of service replacement, again, it's important. Again, you fill the pump with drug, you're gonna hook the catheter up and then program it. If you have not drained the drug out of the catheter, you then have a situation of drug, water, drug, and that's impossible to bolus. So it's much easier if you drain the catheter, you then have drug, water, water. If you don't drain the catheter, you then have to purge the pump on the back table to pull the drug through the pump tubing and out to this point so that you will have correct programming. Post-op care for children, where they lay flat in bed overnight and up in the chair in the morning, if they don't have a spinal headache are able to sit in their chair for two hours, they can tolerate a diet. They can go home. Same for the adults. Again, flat in bed. They can go home when they can sit up for two hours, tolerate their diet. Many of the Baclofen pump patients are going on to rehab. And so therefore they have to be in the hospital for three days to qualify for inpatient rehab. But that's primarily a social issue, not a post-op issue. Routine wound care instructions should be given to the patients to call for swelling around the insertion. And especially for any fluid leakage out of the wound call for orthostatic headache. Very important before the patient goes home, to understand when their pump needs to be refilled, where it's gonna be refilled, they need to have the emergency numbers to call if they're having problems. And they need to know when to call the surgeon and when to call the managing physician, if they're not the same and also should have their post-op appointment with the surgeon, post-op appointment with a spasticity clinic, and a very clear knowledge of when the pump needs to be refilled. That's the end of this segment, the next segment will be on troubleshooting the Baclofen pump, the things you need to know when taking calls.
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