Treatment Overview: VP and VA Shunts

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- Colleagues and friends, thank you for joining us for another session of the Neurosurgical Atlas Virtual OR. My name is Aaron Cohen. Our guest today is Dr. Mark Hamilton from the University of Calgary. He is also the chairman of the Adult Hydrocephalus Clinical Research Network Group. He has had tremendous contributions to neurosurgery, in addition to his work on hydrocephalus. We had a lecture from him recently about how we can improve the outcome of normal pressure hydrocephalus. This lecture is more of a technical lecture in terms of how to minimize complications, complications from shunt placement, including VP and VA shunts, and also managing and troubleshooting these shunts. So Mark, I really thank you for being with us. It's an honor to have you for the second time and look forward to learning from you. Please go ahead.

- Well, thank you very much, Aaron, and really appreciate the opportunity. Always like to share information about hydrocephalus. So, the topic is an overview of VP and VA shunts. A lot of these principles that we'll cover will be also relevant to lumboperitoneal shunts. I'll give you a brief outline of what we're gonna do. I'm gonna do an overview of CSF-shunts, talk about the concept of shunt failure, go through some ways to reduce shunt failure. And this is relevant, or not a exclusively to all these different shunts types, but most of them. I have a video during this section demonstrating a VP shunt insertion. We'll talk about then briefly VA shunts. So, I've got a video of converting a VP shunt to a VA shunt, which illustrates the main technical issues associated with doing of VA shunt. So, let's get into shunts. So, we all know that shunts are the mainstay of treatment for hydrocephalus. It's a simple concept, but a complicated function. The goal is to divert CSF to another body cavity. Just as a reminder, endoscopic third ventriculostomy is used in a lot of adult patients, but to reemphasize some of what we talked about with iNPH as very limited role in elderly patients. I also like to remind people that adult hydrocephalus is not one type of disorder, but many. And this is a pragmatic system that we use in the Adult Hydrocephalus Clinical Research Network. There are those that were treated as a child, and they're referred to as transitional patients. There are those that had no treatment as a child, but probably have had big disorder all their life. There are those that have acquired hydrocephalus for a number of etiologies, and then idiopathic normal pressure hydrocephalus, as relevance to their clinical presentation as relevance to the treatment options. For instance, all the first three all have potential role for ETV, whereas iNPH has a very limited role, as I just mentioned. So, the three most common types of shunts, VP shunts, VA shunts, lumboperitoneal shunts. And we're gonna go through mostly VP and VA shunts. So a simple cartoon illustrating the VP and VA shunt. In fact, we come to talk about the VA shunt. We'll look at the length of the catheter in the positioning relative to the atrium. And this diagram is well into the atrium. And that's something that we can discuss more detail if you have time. So of these shunts, there's no evidence that any of them are better than another. So, I think the most common shunt done in North America and Europe is the VP shunt. Lumboperitoneal shunts are done more commonly in Japan and Asia. They are done for in some centers for IIH in North America. But the LP shunt has not taken off in a major way. There is never been a well-designed shunt to shunt randomized trial to compare the outcomes for the different type of shunts. There is an important issue though, relating to different types of shunts, and that's that you should really have the ability to do more than one type of shunt. Not everybody can have be treated with a VP shunt, so you might need to have another type of shunt in your back pocket. So, one of the difficulties with adulthood hydrocephalus and shunt treatment is that shunt surgery is often perceived of as a simple operation. And if you look at the basic way that shunts are done, not a lot has changed in the last probably 60 years now. There certainly are things that have changed, but the basic sort of concepts haven't changed. And so we're left with shunt failure. Now, how common is shunt failure? I've talked to people who indicate they don't have very high rates of shunt failure. Shunt failures are less common in adults. So, just to put things in perspective as we start down this pathway, this is a paper that was published by Joe Piatt, and they looked at data from 2015 from the Nationwide Readmissions database. So in this study, they started with a lot of admissions with coded for hydrocephalus, and they ended up going down to about 8,000, 8,500 operations. It's really important here to look at the number of adults and elders. There's still this perception that hydrocephalus is pediatric disease. In actual fact, when you look at what's happening across, for example, in the United States, adults and elders actually have more shunt surgery than children. This is a failure rate. And so this should put things into perspective. This is a failure rate for children, elders, adults, and infants. And the failure rates are quite, quite bad. I mean, these are, these are bad numbers. You look at the bottom, you're looking at really just past one year. You're looking at in adults about a 50% failure rate. When you look through the, now, the general community, and you know, if this is using the surrogate measure of a shunt reoperation as an indicator of shunt failure. But this is quite disturbing. And adult neurosurgeons are not doing on the whole better than the pediatric neurosurgeons when you look at this information. Now, we recently undertook systematic review and meta-analysis of adult shunt failure. So, failure associated with adult shunt insertion surgeries. We looked at data from about 38,000 patients. So, this is important. When you look at the number of, this is a PRISMO diagram. You look at the second lying down, you've got about 5,000 documents, 5,000 publications before the duplicates are removed. But by the time you get down to what you can actually extract, we had only 65 papers, and that something will come just in a few seconds to talk about. The quality of the way we report this is really, really a concern. The general take homes from this, where the distal failures are more common in adults than in children. Shunt revision is often used as a shunt failure definition. There's more to it I think than that. And the reporting quality is very poor for the details of shunt failure. So this paper was published in the April issue of "Neurosurgical Focus," and in that we included a list of recommendations on how to report trend failure in adult patients. A study design demographics technique, and it's giving specifics. Without the specifics, we can't understand what the problems are. If we can't understand what the problems are, we can't change the outcomes. So, here are a list of the big issues. So, shunt infection, shunt failure, which means basically ventricular catheter issues, peritoneal catheter issues or valve failure, and shunt over drainage. And we're gonna talk about, and valve failure sometimes gets linked into shunt over drainage. But you can actually have mechanical failure of valves, and we're not gonna talk much about that, but we'll talk about the other ones. So infection rates in adults, infection rates are, you know, quite high, 6 to 10%. It has a lot of morbidity and mortality. It requires repeat surgery. The only way to know about infection rates is to track your infection rates with a local IPC. And I wanna just address the issue of anabolic impregnated catheters, because this is an, I think antibiotic impregnated catheters should not be used as a crutch for shunted infection reduction. There are other techniques we're gonna talk about that are equally, if not more important. So, this study was published in 2019. It's called a BASICS trial. It's a marvelous trial. It was great neurosurgical trial done in the United Kingdom. It was comparing, in a randomized fashion, to a use of a catheter type. They enrolled 3,500 patients. They had pediatric patients, adults in the middle range patients, and elderly patients. And you can see that a substantial number of these were over, elderly patients up to the age of 91. The general take home message is that from the paper, when you put this all together, is that standard infection rates are about 6%. So, that's similar to what we just talked about. Antibiotic impregnated catheters dropped that down to 2%. And silver catheters are the same as standard. So that, again, there's a recommendation we should be using antibiotic impregnated catheters in patients. I'd like you to just to look at the difference between peds and adults. So this is a table in the supplementary data region. So, if you look at the first group, those are the pediatric patients. They have most of the infections. So, the infection rate requiring revision is about 8%. If you go down to the elderly patients, the infection rate requiring revision is about 1%. So, the ability to detect a difference and the significance of that difference is that when you're looking at elderly patients who probably mostly had iNPH, the role of antibiotic pregnant catheters is, I don't think definite as a recommendation for this paper, from this paper. However, you may or may not want to add that into your armamentarium. I would like to stress that technique is extremely important. The Hydrocephalus Clinical Research Network devised a protocol, and they first published this in 2011. It was published a number of times since. And a protocol, as we all know, it's like a a bundle. So, it's structured methods that we put together that we think will help reduce a risk of something they're done in the ICU for central line insertions and use evidence-based practices to look at patient outcomes. So, this is an example of one. There are very, very few in adult hydrocephalus care. This is from Okamura, published in 2020, and they had 124 versus 52 patients who had the bundle. It's very, again, very challenging to do randomized clinical trials. But these are quality improvement trials with consecutive patients. They drop their infection range from 7.3% to 0. The bundle included injection of antibiotics into the reservoir, which was actually part of the first HCRN bundle. So a bit more invasive than some people may want to be. So this is a paper that we published in August of 2022, and it's looking at the standardized infection prevention bundle. And this is without antibiotic and impregnated catheters. So we started from that, going along with the idea that we could add it if we needed it, but we wanted to assess what technique could do without it. We collected prospective data. This was over a nine-year period. These were consecutive patients. All infections were adjudicated by the local IPC, myself, nobody in my group determined if somebody had an infection. And we used criteria. That's another important element. The criteria we use were CNISP, from the Canadian Nosocomial Infection Surveillance Program. The CTC also has criteria. Again, no antibiotic and impregnated catheters. And this summarizes the bundle. This is not expansive. This is not bringing new major changes in technique or a new equipment. But we'll just go through some of these to illustrate. So, we divided into preoperative optimization, the operative field, the operating staff, and the shunt system. So, you don't want the patient to be hyperglycemic; that's at the top line. They administer antibiotics, and there's good evidence for prophylactic antibiotics 30 minutes prior to the first skin incision. There is zero evidence to support more than one dose of antibiotics. And in fact, there's evidence to suggest that you probably increase the risk of C. difficile if you continue with their antibiotics. You limit operating room traffic. Initially we used a providing mix, and I'll show you, when we switched to a Chlorhexidine alcohol skin prep, it made a huge difference. Fundamentally, you just need to make sure that the stuff dries. I've seen draping done when there's still pools of prep on the skin. And we use IO band to the surgical field, 'cause it holds down the drapes, and then it's contact with the surgical field. The operating staff were asked to do full hand scrubs. We don't use alcohol-based scrubs. There was some evidence, one of the HCRN studies that that might be a risk factor. All participants double gloved. And then after draping, everybody changes their outer layer. There's evidence that holes in gloves are common, and if there is spec- I think reasonable speculation that the highest probability time to contaminate your gloves is during draping. We only open the shunts when they're needed. So just at that time, don't let it sit out on the table. We avoid con- or minimize contact of the shunt device with the drapes, the operative drapes. And we try to minimize shunt device handling. In pediatric practice, there's often a name to have the no- this refer as a no touch technique. I use sort of a minimal touch technique. So, this is what happened in this study. So, this is 621 consecutive surgeries for shunt insert and shunt revision. If you look at the first part of the graph, starting in 2013, the shunt infection rate was about 6.8%. And that's before, that's information we collected prospectively. And using the IPC to validate it before we instituted any protocol. The first protocol was with IV providing, and you can see the infection rate dropped to above 4%. And then when we switched to the alcohol solution, it dropped to 0%. And extending out into 2023, there has been 1 infection with about 800+ operations. So, it's doable if you pay attention to the surgical technique in the details. So in summary, I think it's, you know, OR behavior is essential. So it's the operating environmental, environment culture. Everybody's tuned into what we're trying to do, what we're trying to prevent. A protocol or a bundle, I think is essential. You have to have a careful follow-up regarding the infections. It's essential if you're gonna be able to look at your infection numbers. And iNPH, I think the evidence for AICs is weak and infection rates should be achievable less than 1 or 2%. So shunt failure. So again, just to remind you, this is the graph, the survival curve for all the different age groups from Joe Piatt's paper. And you can see that there is significant problems. As I mentioned, the surgical techniques, the basic approach hasn't changed or evolved a lot in most centers. And this is one of my favorite quotes, the definition of insanity from Albert Einstein: "Doing the same thing over and over again and expecting different results." We've all seen that happen. It didn't work that time; it's gotta work this time. So innovation doesn't mean you have to wait for a new device. Technique, again, matters. So I used a quality improvement methodology. I had been collecting data perspectively, I was concerned about shunt failure rates. The more shunts I did, the more shunt revisions I did. And I was using the standard practices, tech practice techniques that I had been taught. So I looked at what could be, what those problems were. And then I instituted changes to try and overcome those problems. Particular catheter placement. Traditional methods are based on landmarks for entry, it's posterior inferior. There's little evidence to support which is better. There was a pediatric randomized trial recently that did not support one over the other. And there's been no such study in adults. Tip location, where in the ventricle it should land. There's no ways to support that one location's better. And in the literature, incorrect placement occurs about 1 to 20% of the time. So we, or I started with using frameless image guidance to place the ventricular catheter and also to select the entry type, the entry location, and the patient tracker has evolved over time. This is an image of a typical screen that we're looking at and the patient beside it. So we, I select the entry point to align with the ventricle. In elderly patients, if they can't turn the neck, you can adjust the entry point to accommodate that. The catheter does not have to end up at the frontal horn. You don't, you just mainly don't want it in the brain. You don't want it upright against the penal surface, if you can avoid that. So, we track the catheter in real time. I'll show you that in the video. The peritoneal catheter problems are the most common issue in adults. You know, in pediatrics, it's proximal catheter. Proximal catheter, that's the biggest area where issues occur. And adult patients is the opposite. You can sometimes see this with scarring in the tip by a fat, and I'll show you an example of that or scar. But in iNPH patients, I think it's often just blocked by getting tangled up in the omentum. And this could be 20 to 50% in the first year. So this is an example of- two examples of catheters that had debris in them. And you notice these are slit catheters. They're slit tips. So, they have an open end, but they have fenestrations along the side. It's usually four fenestrations. I would advocate not using this type of catheter. I think they're more prone to obstruction. That's a personal bias. There's some literature that points to that, but I've had more problems with that and many less problems with a just a simple open tip catheter. I also talk about that when you get to deviations. So, this is an example of a peritoneal catheter that never made it to the abdomen. It's in the abdominal wall. And that's another potential risk of failure. So now I'm gonna show you a video that illustrates this. It's about 8 to 10 minutes long, and there's an audio overlay. It was published in JOVE. It's open access. It was an opportunity to lay out from beginning to end every aspect of doing a VP shunt insertion. This is of course using the techniques that I've outlined, and I'm not able to say that my techniques are better than some other techniques. I'm simply saying that the techniques we did used here resulted in a dramatic drop in shunt failure. So we're gonna start the video.

- [Narrator Of Video] Introduction. We described the case of a 72 year old male who was diagnosed with idiopathic normal pressure hydrocephalus or iNPH, who met the criteria for insertion of a ventricular peritoneal shunt. The patient presented with a one year history of progressive gait and cognitive impairment and intermittent urinary incontinence. His past medical history was significant for hypertension and the surgical treatment of bladder cancer. A magnetic resonance imaging or MRI of the brain showed ventriculomegaly with an evidence index of 0.41. An MRI evaluation completed four years earlier did not demonstrate ventriculomegaly and had an evidence index of 0.29. His neurological examination confirmed he had a wide based shuffling gait with low steppage and an abnormally slow gait velocity of 0.83 meters per second. He had no signs of myelopathy. His Montreal Cognitive Assessment or MoCA was 22 out out of 30, which confirmed his mild to moderate cognitive impairment. A three day external lumbodrain also known as an ELD trial with hourly CSF removal was done to test CSF removal symptom responsiveness. After the ELD trial, his gait velocity improved to 1.2 meters per second and his MoCA score increased by three points. Given the positive response to temporary CSF removal, the patient was offered ventricular peritoneal shunt surgery. The protocol and videos presented follow the guidelines of the University of Calgary Conjoint Health Ethics Research board and informed media consent was obtained, and the patient provided written consent to this publication. Protocol. The surgical approach presented here can be performed for any ventricular peroneal shunt insertion surgery. Positioning and pre-procedure set up. Place the patient's supine on a donut headrest with the head turned towards the contralateral side, and then place a shoulder roll to augment exposure of the occipital region. Obtain a preoperative cranial MRI or computer tomography or CT with an appropriate neuro navigation protocol. Upload the patient's preoperative cranial MRI or CT, and register to the neuro navigation system, and complete the neuro navigation workstation planning. Select an entry point and target for the proximal catheter. Mark the selected entry site location on the patient's skull. By standard, a right sided posterior approach is preferred, and as precluded by the patient's circumstances. Mark an inverted U-shaped or horseshoe shaped incision to incorporate the entry point. Shave any hair surrounding the incision with a clipper. Infiltrate the scalp incision with a local anesthetic. Prep the entire surgical field with a 2% chlorhexidine gluconate and alcohol solution. A strict infection prevention protocol, often referred to as a bundle, must be adhered to. Prior to operative draping, all scrubbed surgical staff must double glove and change their outer gloves for a new pair after draping the patient has been completed. Drape the entire surgical field with an antimicrobial and size drape, which can also help hold the drapes in place and reduce surgical team direct contact with skin. Apply a standard laparoscopic drape and extend the opening in a cranial direction to the edges of the draping to allow exposure of the cranium and the chest surgical fields. Cranial exposure. Use a number 15 scalpel to score the horseshoe shaped incision. Use a fine tip monopolar cautery to deepen the incision, making sure to preserve the periosteal layer. Retract the skin edges with a retractor and make a cruciate periosteal incision in the center to expose the skull using monopolar cautery. Make an approximately two centimeter burr hole in the center of the periosteal exposure, ensuring the underlying dura is preserved. Subcutaneous distal catheter placement. Make a para midline sub incision down to the perifacial fat layer. Blunt dissect the subcutaneous tissue for two to three centimeters in the cranial direction. Carefully guide a tunneling stylet within its encasing plastic sheath within the subcutaneous layer, and pass it toward the cranial incision, taking every caution to stay above the ribs and clavicle and avoid piercing the skin. Once the inferior aspect of the cranial incision is pierced by the tunneler, withdraw the stylet leaving the plastic sheath in place. Create a subgaleal pocket at the inferior edge of the cranial tissue around the plastic sheath that will be sizable enough to bury the shunt valve. Use monopolar cautery and blunt dissection with the Kelly forceps. Remove the distal catheter from the sterile packaging and place it in sterile saline. Thread the distal catheter through the tunnel plastic sheath from the cranial to the caudal direction, minimizing contact of the shunt components to the drapes, and then remove the plastic sheath. Prime the system with sterile saline to remove any air. Valve attachment. If a programmable shunt valve is used, it should be programmed to the desired setting before it's removed from the packaging and before it's passed into the operative field. Just before use, remove the valve from its sterile packaging and place it into sterile saline, and prime it with the sterile saline. Attach the distal port of the valve to the proximal end of the distal catheter. Secure the catheter twice with silk ties and prime the system with sterile saline to remove any residual air. Ventricular or proximal catheter insertion. Just before it's needed, remove the ventricular catheter from a sterile packaging and place it into sterile saline. Create a small centrally located circular durotomy, equivalent to the diameter of the proximal catheter that incorporates the underlying pia and arachnoid. Use the fine tip or needle tip monopolar cautery to do this. Place the navigation stylet within the proximal catheter, and pass the catheter into the ipsilateral ventricle using real-time navigation along the pre-program trajectory to the target depth. Often there is CSF flow at about five centimeters of depth, however it is appropriate to advance the catheter to a depth of approximately 8 to 10 centimeters. Once at the target depth, remove the stylet from the particular catheter and confirm that there is free flow of CSF. At this point, clamp the catheter with the snap using booties to protect the catheter. Trim the proximal catheter leaving about two centimeters extra from the edge of the outer table of the skull. Attach the distal end of the proximal catheter to the proximal outlet of the valve and secure it with two silk ties. Carefully place the valve into the subgaleal pocket and anchor the valve sleeve to preserve periosteum with 4-O silk suture. Apply gentle traction on the distal catheter at the abdominal incision to ensure no catheter kinks exist. Confirm spontaneous CSF flow at the distal and vision system. Intraabdominal or distal catheter placement. The distal catheter is placed laparoscopically within the peritoneal cavity, ideally by a general surgeon. Make a colinear periumbilical incision with a 15 blade scalpel, followed by blunt dissection down to the abdominal wall fashia. Grasp the fascia on each side with Kocher forceps, and inside it in a vertical fashion to ensure entry into the peritoneal cavity. Place number two polydioxanone stay sutures through the incised fascia on our side. And then insert a blunt Hasson trocar. Insert a 30 degree angle laparoscope through the Hasson trocar access port. Place a five millimeter port in standard fashion under direct vision, usually on the left. But this position may vary depending on the density and position of the interperitoneal adhesions. Perform any lysis of adhesions that may be required. Make a small hole in the ligament from the left side of the ligament using a combination of electrocautery and laparoscopic Metzenbaum scissors. The hole in the ligament must be made as close to liver and diaphragm as possible to allow adequate and proper positioning of the catheter. Using the electrocautery hook, create a transverse abdominal tunnel through the previously created subsidy sternum incision where the distal BB catheter exits through the subcutaneous space. Insert the distal peritoneal shunt catheter into the peritoneal cavity through the path created with an 11 French peel-away sheath Introducer. Once the catheter is visualized in the abdominal cavity with the laparoscope, grasp it and position it through the hole in the ligament. The catheter should be trimmed laparoscopically to fit the patient's anatomy and position the catheter as described. It should be noted that there is no predetermined length of the catheter. The catheter's final resting place must be in the retro hepatic space. The final position of the catheter should ideally be inferior to the diaphragm and superior and posterior to the mobilized liver. It should be immediately superior to the right pericolic gutter. CSF flow through the catheter can be confirmed by direct visualization with the laparoscope. Remove the residual trimmed portion of the catheter through the five millimeter port. Deflate the abdomen slowly and cautiously to ensure no migration of the catheter occurs. Then remove all the instruments. Wound closure.

- [Mark] I'm just going to move past this and then just come to-

- [Narrator Of Video] 25 sub particulars-

- [Mark] Gonna to pause that. Going to go to the, yeah-

- [Narrator Of Video] The patient presented in this video.

- So, we, we'll just move on to- so with this, these techniques, the rationale for putting the catheter in the peri hepatic space was to keep it away from the omentum. And we did this as a quality improvement trial. We had a grading system for a ventricular catheter placement. We used system of- grade one in the ventricle, grade two in the ventricle, but touching the appendema and grade three, not in the ventricle, in the brain. We, as part of our protocol, looked at distal catheter placement after the procedure. So this first example on the right is an example of it where, you see the catheter in the peri-haptic space, the one in the middle with free floating. And just for reference, the one in the on the far right shows a malposition. The catheter's actually in subcutaneous tissue. And that one wasn't part of this series. So this was, again, a consecutive series of patients. There were 115 patients before this was instituted. There were 129 after it was instituted. And by instituted that meant that we were not only doing shunt infection prevention, but we were doing the laparoscopic insertion and the ventricular catheter placement with the image guidance. So you can see again, that most of the failures in both group were in the distal catheter. But the big difference is the percentage and number of distal catheter failures drop substantially. So if you look at the etiology of failure, it was mostly mechanical obstruction. And if you look at a Kaplan-Meier curve for the groups, the red line illustrates the group that had the bundle used to change in the surgical technique. And the blue was the group that did not, that had the standard technique. The decrease in failure was substantial and sustained. And the bottom axis is years, not months. So, at three years we were dealing with about a 75% success rate. About 25% of catheters or shunts were failing. So, we haven't fixed all the problem, but I think we improved it a lot. And there's a couple other things we noticed. When we subdivided the groups that where the catheter was put behind the liver, but then sort of popped out into the abdomen, which occurs about 10% of the time, that group then mimics what you see in the blue line, their failure rate. It just wasn't- the numbers weren't significant, weren't high enough to allow us to do any real comparison. But the trends were quite interesting. So then when we look over time at shunt revisions, and you look at the far left is basically the shunt failure rate. The line dividing down the middle is when the ShOut outcomes protocol, which included the laparoscopic and image guidance and infection control that was instituted, and the infection, the shunt failure rate dropped, and the shunt failure rate continued to drop and drop and drop. So while I had perceived that we were doing at one point more shunt revisions than insertions, that has totally reversed. And we follow all of these patients. You know, we all these patients are followed in our clinic, and we have a series of definitions to use for shunt failure and a series of steps we use to evaluate shunt failure. So, that's an important technical issue that can improve patient outcome. And I wanna touch on shunt over drainage, which is really a difficult concept or a difficult issue to deal with. This recent literature review not only reviewed the literature, but also asked a group of people to comment on what they thought the etiology and definitions were for over drainage. In the literature that is summing this whole process up, over drainage patients was basically defined as "a persistent condition with clinical manifestations as postural dependent headache, nausea, and vomiting, and/or radiological signs of slim ventricles and subdural hygromas or hematomas." So in practical terms, that means you can get orthostatic headache. It's more common than people think. There's also orthostatic hearing loss. It's referred as to as hypacusis or hypoacusis. This basically means the same thing. And then subdural effusions or chronic subdural hematomas in 10 to 20%. So, hyperacusis is not well documented with regards to frequency, but I think it does occur. And with programmable shunts, you can make it actually disappear. This is what I think most of us dread with a shunt. It's the subdural fusion that becomes a chronic subdural hematoma. And we look at some literature published on this. This is a paper from Sweden. They have an iNPH network of multiple centers. And they looked at the frequency of subdural hematomas in 1,846 patients, and subdural hematomas occurred in 10%. So, that's a significant number. It means that we have a lot of work to do to fix this. And the reason for this, it comes down to the fundamental way that most junk valves work. They're differential pressure valves. Most of us heard that term. They have an opening pressure. But when they're used, we also have to add in the hydrostatic pressure, the length of the catheter, and then the drainage cavity pressure. So, the term siphoning occur is how we describe this. It certainly is a significant issue in some patients, and it's the underlying event that leads to the symptoms we just discussed. So if you're trying to prevent this, there are quite a number of issues to address. Patients with bigger ventricles, are they more prone to this? We asked whether headache with CSF removal, either by LP or ELD caused a headache. The very, the number of iNPH patients who get headache with ELDs is quite small, but we wonder whether that might indicate something that puts them at higher risk. The position of the distal catheter tip relative to the ventricular system. So, if you had a catheter that was positioned in the right atrium, that would be a shorter length than perhaps in the peritoneum. If you had a catheter tip that was placed at a jugular bulb, that would be even a shorter length. And then if you have a catheter that's in the abdomen, patient height may come into it. So that's extra length of catheter. And then finally, the risks depend on what kind of shunt you're using. Is it a fixed or programmable valve? It's not necessary that programmable valves decrease the rate of over drainage, but they certainly allow you to treat it without surgical intervention with greater ease. And then whether you use an anti-siphon or flow restriction device. So these are all, the fact- not all, but most of the factors that play into how people end up with over drainage. Programmable shunt valves, as I mentioned, I think are extremely important in the adult patients. It gives you the ability to alter the opening pressure, which can also then correct for almost all of the symptoms that we described. However, the ultimate goal is to try and prevent over drainage while not allowing under drainage. So it's trying to find this balance of treatment, but not the side effects that we can see. And just, this is the only thing I'm gonna mention about anti siphon devices, because it's a complicated topic. Partly because of the taxonomy. There are fixed anti siphon devices and programmable anti siphon devices. The pressure controlled diaphragm-type anti siphon device such as with the Medtronic Delta valve is one type. The siphonguard for Codman Integra is a different mechanism. It's a flow controlled device, and some people actually don't refer to it as an anti siphon device, 'cause it's not exactly the same. And then there's a gravity controlled anti siphon device systems that are quite different. And so we need to develop better strategies, we need to have better understanding of how to deal with this. I'll show you one example of an attempt to do this with a randomized trial. This was a paper published in 2014 by Carsten Wikkelso and Gothenburg. They did a very interesting protocol where they, it was double blind, randomized. They had 68 patients in two groups. In one group, they started with the pressure at 200 fixed and then dropped it down to 40 over a series of changes over six months. And they use the cognitive king valve. The upper limit is 200 of the water. And the other group was set at 120 and left there. So the interesting thing was that there was no major difference in over drainage symptoms or subdurals. However, if you started lowering the drain below about 120, over drainage started to increase. The symptoms started to increase. So very interesting, but doesn't lead us to a definitive answer of how to avoid this. So if you're gonna treat over drainage, which is the, you know, but it happens, I think it is a series of questions you have to ask, what's the clinical status of the patient? Is this patient having a symptom of headache or is it patient with subdural fusions or is the patient with actually chronic sub hematoma, bilateral hematomas? So if the patient's an extremist, it changes the type of approach you might need for that patient. The same with hypacuis. So, a lot of it comes down to what is the symptom and how's the patient doing? And then a secondary thing is whether they're on anticoagulants or antiplatelet agents. And this is another confounder, in the elderly patients anticoagulants are very, very frequently used. So, I don't want anybody to use this, but just an example of tinkering, trying to figure out an approach to different valves using some of these ideas and using them in a consecutive fashion to see if it makes a difference. And also how to manage chronic subdural hematomas if they occur in a patient. So I've actually altered this a bit since this was first put together, but to give you a look at the first look at sort of what we saw and before the protocol, we were looking at about a 17% risk of subdural effusions or chronic subdural hematomas. When we put this protocol in using different sort of standards for a particular size, we would increase the resistance. If somebody had very big ventricles, it would increase the setting if they had the resistance, if they had headache with their drainage procedure and increase the drainage if they have, if they're tall and they're gonna have a VP shunt. So the number of over drainage incidents dropped down to about 10%. This is just an initial look at this. This is again, an ongoing process, and I don't think we have narrowed this down to a series of steps that's definitive. It is just trying to make a dent in this significant clinical problem. And you look at the number of shunt surgeries required to deal with over drainage, it's actually not a huge number, 1.5 to 1.7%. And that's usually for somebody with a chronic sub hematoma. At least with the programmable valves, we rarely have to tie off the catheter and change the valve to a higher resistance valve. So, that's a review of the major issues. Now I mentioned I was gonna touch on VA shunts. I think again, everybody needs to have a backup shunt system, and there are a lot of different ways to insert a VA shunt. I'm gonna show you one that we started using in our institution, because looking at the other methods, they were all indirect ways of assessing the tip location. As I mentioned, you need other strategies. There are other shunts which I'm not gonna cover, such as ventriculoperitoneal shunts. People have put shunts into virtually every body cavity that exists. But I think the VA shunt actually serves a really good purpose. If there's abdominal pathology, then the VA shunt is usually a good option. And I think there's a lot of work that needs to be done to, as I mentioned at the beginning, comparing different shunts to find out if there are, what the pluses and negatives are in a systematic fashion. So again, cartoon just illustrating this, but now just to remind me to mention that the tip of the catheter in this diagram is in the right atrium, and that's probably not required, but I'll go over this in a second. If the catheter's too long and is into the mitral valve, it can actually do a quite significant injury to the patient. The way to put VA shunts has changed dramatically. We don't do cut down techniques except in rare circumstances. We use a Seldinger technique which I'll illustrate in the video. It's less invasive, small incision, and it's just a marvelous way to pass the catheter. The concerns people have had with VA shunts have been complications. I think many of these are from past techniques and past issues when they're being used in pediatric patients, where you get arrhythmias, micro embolization, pulmonary hypertension, catheter coiling. And how do you manage shunt failures in these patients? I think pulmonary hypertension is very rare. My experience with VA shunts is just a, you know, in current series is a little under 100, and I've not seen that. Clotting at the catheter tip is rare. The issue of micro embolization has not been settled. And that's something we could discuss if there were questions regarding that. So again, indirect methods, you have no certainty where the catheter is. You have a ballpark area. When I started doing VA shunts, I was taught to put them somewhere, the tip somewhere routine about T-4 and T-6. That didn't really tell me exactly where it was. Other people used the parina, other people used other techniques such as ECG changes, pressure changes. So, we started using transesophageal echo, very easy to access for use in the OR. It eliminates the need for x-rays. And this was a series we published in "Operative Neurosurgery," just mainly to show the technique. And what you've got basically is the transesophageal echo coming down where you get, you know, usually excellent visualization of the heart and the vena cava. It does two things. One, when we pass the cannula, the wire through the cannula, we can actually verify the wire is in the right atrium. But before we pass the catheter down. Whereas if you weren't doing this, you might miss or be unaware that the catheter might have flipped up into the brachial until you'd done more x-ray imaging. So this is a still photograph. I'll show you the video in a sec. So this is the right atrium, this is the vena cava, this is the cava atrial junction. This is the catheter tip. Well, here's a short video. There's no audio with this, so I'll just talk a bit. The patient's position, just like you saw on the other one, this is a patient who has a VP shunt whose abdomen had a tremendous amount of scar and the shunt, we decided to convert him to a VA shunt. So we make a linear incision at the junction of the peritoneal catheter in the valve. Then we extract the peritoneal catheter, basically pull it up out of the peritoneal cavity. And then the next step is confirming that there's flow, so that we know that the proximal portion of the shunt is definitely working. And then we use ultrasound for the technique approach. I think using ultrasound to tap- to gain access to the internal jugular is essential to decrease risks. Then through the needle, we're passing a wire, the needle is removed, and then a small incision is made to expand it. At this point I tunnel, so that I'm not doing a lot of manipulation once we've got the catheter into the inferior cava. So I leave that plastic sheath in place, then we pass the catheter down through the sheath. It'll eventually be shortened at the top end, and the distal end will be positioned using the esophageal echo for localization. A dilator and a eight French Peel-Away are passed over the guidewire, and the guidewire will be removed after the Peel-Away sheath is fully inserted, and it's important to use a Peel-Away sheath, because you need to extract this from the wound. And if you do not have a Peel-Away sheath, that's going to be impossible without disrupting your operation. So we pull out the dilator, and then we pass the catheter down. Now at this point, the anesthesiologist gets involved in a major way. We localize the position of the catheter, we then shorten the length, and this is a video with the arrow showing the catheter in the cavoatrial junction. We can do a bubble test during this with saline injection into the catheter to verify the tip location and actually some of those little dots after the catheter tip represent that. The beauty of this is you know exactly where the catheter tip is. The question that has never been answered is where should the catheter tip be? Is it okay if it's up higher in the superior cava? Is it okay if it's in the atrium? So, when doing this procedure, we at least knew what we were doing in terms of location in consecutive patients. So the conclusion of what we found doing this, there were a couple of, I think technical jewels. One is that this is feasible. It's a beautiful way to do these procedures. In this initial report, the shunt revision rates were equivalent to what we had seen in VP shunt surgery prior to that. What we learned was that I was using a closed tip catheter with slits. I surveyed a number of neurosurgeons, found that about half were using those and about half were using open tip catheters. The major reason for failure was clotting of the distal tip. When we pull the catheter out to replace it, we'd see clot up to the top of the slits and then that would be the end of it. So by eliminating that part of the shunt, we've eliminated, virtually eliminated the risk of distal clotting, and we have not seen any problems related to having an open tip catheter. So there's more that needs to be done. As I mentioned, what is the optimal location for the catheter tip? We have been using low-dose aspirin after shunt insertion for the VA shunts. This is based on some other literature, but has never been conclusively sorted out. So there are lots of questions. But in the meantime, this is a very good shunt approach to have as your backup shunt. Thank you.

- Nicely done. Very much appreciate it, Mark, really like your technique, how you put the catheter into the space between the diaphragm and the retro hepatic space. I've never been as sort of, I would say careful about putting it right at that location, but it gives me some ideas. Maybe doing it would be much better rather than just placing it somewhere in the abdomen where there's a lot of free space. I do agree that using the endoscopic technique to place it in a very good location is a significant advantage. I think there's still many centers, very advanced centers in the country that actually place the catheter through a small incision. They just blindly pass it through. God knows if it is ends up in a small cavity. And then when you have a shunt issue, we really don't know where it's coming from. Is it because of the abdomen? It's because of somewhere else? So, it's really a great practice to use general surgery colleagues in my case, to have them put the distal catheter in a very favorable location. That's a great learning point that I want to emphasize. Do you have any other thoughts there, Mark?

- I think that you're correct. I think a lot of places still do the small hole incision, micro or mini laparotomy. I did that for quite a long time. When I started collecting real-time data on my patients, I was a little bit horrified at the failure rates and that's when I looked for other alternatives. But there was one paper that was published doing not, I was thinking about laparoscopy, but there were papers where they had done studies where they had done laparoscopy and the failure rates distally were still high. So I wanted to do this technique, and I think it's not just the laparoscopy that helps, it's the combination of everything, and it's like, I look at this like a shunt insertion bundle and other things may be added. I think by reducing infection, by making sure the catheter works, we don't have proximal catheter problems. It makes the shunt function better. And then keeping it in, if you can keep it in the liver, in the perihepatic space, the failure rates are very, very small. Most of the people who we find fail eventually, because the catheter pops out, and we put it back. Now another thing, another pearl was that we started just doing a, as we started doing this, we did a shunt, an intraabdominal adhesion score. One to five, one nothing, five severe, they couldn't even do the operation. And we also started looking at whether there was momentum up over the liver, because that's another variation. It has not shown us that shunts won't work if you have a lot of adhesions. But if their shunts are failing, they have lot of adhesions. I don't persist, I just go to a VA shunt. And I think persistence is not the answer to repeated shunt failures. It's trying to figure out what's going on or go elsewhere.

- Well said. As you said, Albert Einstein said stupidity is doing the same thing expecting a different result. I think shunts are one procedure that if you stick with your every consistent and invariable technique, you really make sure you have a protocol of how everything you're doing can be extremely helpful. The other issue is I use a reservoir at the, I use the reservoir with the valves, with the reservoir, so I can always, or burr hole cover, you may call it the reservoir, because I can tap the shunt easier and assist the status of the shunt. You don't do that. Can you tell me what's the reason for you not doing it? Because I thought you should never do it without it, because then you have no idea how to tap this shunt. So, tell me what your thoughts are there.

- So, I actually, I use the valves I use have a reservoir.

- Okay.

- I don't put it over the burr hole. I'm not a fan at all of burr hole valves per say, but I understand people use reservoirs, and like Rickham reservoirs and other types.

- Yes.

- In pediatric, when I did pediatric, I did a lot of pediatric neurosurgery. And what I used to see is small ventricles with a burr hole valve, and a real challenge trying to deal with catheter problems, the ventricular catheter problems. But so the valves I do are tapable. And one of the ways I investigate whether a patient has shunt function is I like to use radio nuclei tests. They're not the be all and end all, but they are a part of the process we use. You have to have experience in how to interpret them. The value comes if you find the shunt is completely blocked. And sometimes that's hard to determine clinically. You're trying to figure out what other things could be going on, differential diagnosis. So the assessment of shunt failure is something that you should have a series of steps to go through. I find it's great way to teach residents, because residents learn technique very, very well when you do it over and over again. And they see that, they learn very fast that way. And I think it spreads in terms of reducing the risk of failures.

- If you have a shunt infection instead of externalizing the shunt, treating it and then coming back later, the other option I have seen people do is they treat with antibiotic, leave the shunt in 100%. And then when the CSF is cleared, they come back, one surgery, take out the shunt, put a new shunt and they're done. What are your thoughts about that practice?

- I'm not a huge fan of it. When I've seen people, I've seen examples where that's been done. And I think the reinfection rate's very high. The approach that most, the standard approach that I take is if the patient doesn't require a drain to a particular drain for survival, then we remove the entire shunt system, treat them, and then put the shunt back in. That might be for an iNPH patient. If it's patient who needs a drain to manage their intracranial pressure, then I will start treating the patient. I'll usually change the drain out at some point. And then I will, when their CSF is clear, and it's been clear for about five days, then I'll go back and put their shunt back. There's a lot of that we need to learn about what is the best approach. That is simply be the approach I prefer to use. And it's based on seeing these patients with higher risks of recurrent infections.

- I really appreciate your input. Excellent lecture as always, Mark, look forward to having you with us for the third ventriculostomy lecture soon. And again, thank you for all your contributions again.

- Oh, and thank you for the opportunity.

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