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Grand Rounds-Troubleshooting the Synchromed Infusion Pump

Michael Turner

July 04, 2012


- Hello, this is the third of the three talks. The first talk we talked about patient selection and history of surgical intervention for hypertenicity. The second one were surgical nuances of implanting drug infusion pumps. This third one will be on troubleshooting the SynchroMed infusion system. Again, it's isolated to the SynchroMed system because many of these are specific tricks based on the SynchroMed system. Again, disclosures I've received honorariums from Medtronic for teaching research and consulting on product development. 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 only sharing personal experience and I'm not making any recommendations on behalf of Medtronic. Let's talk about problems with pumps. The first problem is overdosage. Overdose can come as a programming error, a subdural catheter or a thing called pocket fill. Very important to understand that the pump will not, and has never spontaneously overdose the patient. It is designed in such a way that the internally checks the flow rate virtually continuously and shuts the system down if there is an error in flow rate. However, humans program the pump. So the wrong dose can be entered. The wrong drug concentration can be entered and the wrong bolus. Again, we talked in the last one about where is the drug? And there's a big danger with a overdose with catheter revisions. We'll talk about that later. Again, where is the drug? We went over this in the last one. A drug can be in the reservoir, in the internal pump tubing or in the catheter. Baclofen is an effect of neurotransmitter in the brain and the SynchroMed II Pump reservoir holds 20 to 40 mls of drug, which again can be in 2000 to 3000 micrograms in baclofen 25 to 50 micrograms in morphine. If while filling the needle comes out of the reservoir or was inadvertently not in the reservoir, that entire 40 mls of 2000 microgram per mil or 80 milligrams of baclofen can go into the pocket, and that can lead to difficulties with overdose. Much more serious is a pocket fill done with morphine or a narcotic many times there's 25 to 50 milligram per mil drug. 40 mls of that absorb can lead to a significant respiratory depression. There has been reports of rare respiratory depression with pocket fills from baclofen and pocket fills shouldn't happen if good technique is used especially at the end of the refill aspirating back to make sure that you can get drug out easily to ensure that it was all in the reservoir. So when there is an overdose, it's very similar to other GABA agonist, such as a benzodiazepine overdose. So there's progressive decrease in tone to flacid, confusion, hypotension, bradycardia, hypoventilation going on to apnea and coma. The treatment is support; volume, airway, ventilation, pressors. Physostigmine's list was initially listed in the Medtronic literature. I think it has now been taken out. It is not an antidote, it is a cholinergic stimulant. Most of you are familiar with atropine, which is an anti-cholinergic. And you know, that atropine causes increase in heart rate and decrease in oral secretions. Physostigmine is exactly the opposite. So as somebody is lapsing into coma from an overdose, you really don't wanna increase the secretions in their mouth and you don't wanna induce bradycardia. So what is the treatment of overdose? You can turn off the pump. There are two ways to turn off the pump. One is to use the programmer and you can turn it down to minimal infusion. The other way is to take the drug out of the pump. If you stick the middle of the pump into the reservoir and pull all the drug out of the pump, the pump will go round and round thinking it's still working, but no drug will leave the pump, no drug will go into the patient and anybody can effectively stop the pump, including emergency room doctors if the patient is in trouble, many hours from a pump center. The most effective treatment is to remove spinal fluid. The tip of the catheter, where the highest concentration is connected to the catheter access port. You put a 25 gauge needle into there and start aspirating CSF. As you aspirate CSF, you're aspirating the highest concentration of drug, and you can literally wake the patient up. And this is far and away the most effective. If you cannot aspirate drug through this for one reason or another, a lumbar puncture can be done to remove CSF and trying to remove as much drug as possible. The other problem is under dosage. Again can be a programming error. It could be a pump is empty and as the pump volume gets lower and lower, especially if it gets below one to two mils, it will accurately deliver a drug because there is less pressure behind the pump to push the drug out. Patients with pain, neither a fracture, constipation can have increased stimulus and appear to have an underdose situation. Medication changes can cause problems. The pump itself can die and there can be catheter malfunctions. Pain is a very common problem of increasing tone in back of the patients. And this can be from constipation, urinary tract infection, gallbladder tracts, occult fractures in a spinal cord injury, surgery, or decubitus and finding these often can explain a mild to moderate increase in tone. As the pump empties, we talked about this, the force for getting the drug out of the pump into the patient is expanding gas outside this bellows of a reservoir. It compresses the reservoir, the gas is actually what pushes the drug through this and this dispensing rotor rotates and dispenses the drug. The pump itself controls how fast this rotor is going around. And so, again, as the reservoir collapses the space behind it increases, the pressure of the gas behind it decreases, and there isn't as much oomph to get drug out and you can have an underdose from that. Again, the wrong concentration can be programmed into pump. You can program the wrong daily dose, or again, after a surgery, you can incorrectly program the bolus. Medication changes that can be significant, is you can start a new medication and the most often problem is a SSRI anti-depressant, which seems to conflict with the effect of intrathecal baclofen. And you can have an increase in tone with using the SSRI. Somebody else has stopped a medication. Unexpectedly stopped all baclofen or another antispasmodic or made a change in seizure medication. And this can affect the patient's overall tone. The pump can make, have a problem. One is end of service. This is when the pump is expected to die. And SynchroMed II every time you print out, the after a programming, it gives you a line item called the ERI, the effect of replacement interval. And this starts, this is 84 months. It's actually starts at 81, goes down to zero. At zero, you still have three months to replace it. But when that is over, the pump dies and stops functioning. There have been instances of premature battery failure, and you will get a low battery alarm on interrogation. The other one is a rotor stall, rotor stalls occur when that rotor that dispenses it stops or jams that's because it is really a Swiss watch, hooked up to a number of gears and the gears can crack or malfunction. In the SynchroMed II pump, you can see if there's been stalls occurring, the pump knows what's going on and logs the stalls. So when you interrogate the pump, you can ask for it to print out the logs, and then this will show you whether or not the rotor has been stalling. Catheter malfunctions include kinks, microleaks, macroleaks, migration, scarring. All of these can cause difficulty with the catheter. Underdose is a spectrum of severity. Mild can be a slight increase in tone. This could be due to growth or one of those increase in stimuli. Moderate it will have a moderate increase in tone with itching, and severe it can cause severe hypertonia with spasms, itching, and fever. Baclofen withdrawal can be life-threatening there have been two reported deaths, severe reactions reported in several more cases. And obviously there are many unreported or misdiagnosed cases. There is a review article done by an expert panel put together by Medtronic, where we reviewed all of the up to that point reported cases. It was published in 2002 in the Archives of Physical Medicine and Rehabilitation. What did we find in that review that severe withdrawal has been reported in quadriplegic, spinal cord injury, stiff person syndrome, quadraparetic cerebral palsy and dystonia. There have been many cases of documented loss of drug effect without a significant withdrawal syndrome. And there's really not enough data to identify a high-risk population that is gonna have severe reactions. I think the most dangerous patient is a noncommunicative patient in an extended care facility where the persons caring for them may not know they have a baclofen pump. And when they transfer the patient for problems, many times the back of the pump history is not come along. And the emergency room physicians may or may not consider baclofen withdrawal. Withdrawal has been reported as early in 1981 with oral baclofen. There have been case reports of withdrawal after overdose, and there have been case reports after rapid taper of withdrawal. So unlike narcotics, you can have baclofen withdrawal while still getting a baclofen. The death was reported in 1999. And again, by modern standards, there are a number of significant errors made in patient care. And there have been a number of anecdotal reports. So what is the physiology of withdrawal? It's the loss of GABA mediated inhibition. The patient is hypermetabolic. The patient is spastic and rigid. So they have increase in tone and there's a central effect with seizures and hallucinations. And so what's happened is that there has been, within fusion there's been receptor downregulation, so withdrawal can occur even while tapering and even while still receiving medication. Withdrawal has progressed in an intrathecal baclofen patient receiving oral baclofen. So to stop baclofen withdrawal on an intrathecal patient may require intrathecal baclofen. Early symptoms are itching, In many times, the patient doesn't really complain of itching or kind of blows it off because they can't imagine why it would be called that when really put to the details, it's more a creepy crawly feeling than a classic poison IV type of itching. And it's over the entire body. The patients feel terrible. They feel, you know, they just feel on edge overstimulated type of feeling. Their tone is significantly improved and cerebral palsy kids who really rarely have spasms can have rather a significant spasms and may even develop some rigidity, you'll then see tachycardia fever and the blood pressure has been reported up and down. So a simple acronym, and this came to me from a spinal cord injured patient in Terre Haute who's very salt of the earth. And after having her second episode of baclofen withdrawal, she looked at me and said, Dr. Turner, I never wanna be itchy, twitchy or bitchy again. And this has always served to be a very good reminder of the symptoms of baclofen withdrawal. Now, baclofen withdrawal is a cascade. There have been articles saying it triggered the autonomic dysreflexia. And I surely have had a patient who went into baclofen withdrawal and presented in our emergency room with a blood pressure too high to measure. In other words, it topped out the cuffs at a systolic over 300, it's been said possibly to trigger the neuroleptic malignant syndrome, but not really sure, maybe triggering a malignant hyperthermia, but it doesn't seem to respond to datrium. Probably it is really triggering the serotonin syndrome because many of the symptoms are almost identical to the serotonin syndrome. More important, it seems to be blunted by giving Cyproheptadine, which is an antiserotonergic agent. And we have found significant improvement in symptoms with periactin. So they, after about 24, 48 hours, they really started to develop hyperthermia, rhabdomyolysis, seizures, multiple organ failure, confusion, hallucination going on to coma as the syndrome progresses. The severe symptoms appear to start about 72 hours after the onset of the first symptoms. Early intervention should be able to prevent, excuse me, prevent progression and restarting baclofen can reverse the symptoms after the start and that's been the experience and all been a rare case. The difficulty is that they are admitted often with a rule-out sepsis or renai colic. And it may be a two to three days waiting for culture results before they realize that the patient is not septic and that Baclofen withdrawal may be a problem. Baclofen withdrawal really is when it occurs is because it wasn't in the initial differential diagnosis and the pump doctor managing the patient wasn't involved and contacted by the ER or intensive care doctors until after the onset of the cascade. The treatment of baclofen withdrawal is baclofen. Resume the prior dose and route as soon as possible. All baclofen has been anecdotally reported to lessen the symptoms. You give a high dose orally, 80 to 120 milligrams in an adult and frequent Q2-Q4 hour administration. As I mentioned earlier, periactin 4-8 milligrams every six hours, which blunts the serotonin response has been very effective in decreasing the severity of the symptoms. And since I started using periactin, we have not really had to have ICU type of care in our post-op patients. So when we think about baclofen withdrawal, there's really a treatment cascade. So when they're very mild symptoms, you may be able to adjust the pump, maybe some PRN Valium or baclofen, and many times a treatment can be initiated at home and then they can come to the office to be evaluated in the office in a elective type of manner. More severe symptoms, the patient needs to be admitted to the hospital, starting oral baclofen at therapeutic doses, periactin starting at four milligrams, Q6 hours. And we use PRN Valium or ativan, IV or by mouth. As it gets worse, severe level one, transfer the patient to the ICU, increase the oral baclofen to the point of sedation, increase the periactin to eight milligrams q6 hours, and then consider a benzodiazepine drip, versed or ativan and titrate to patient comfort, not to flaccidity. If that happens, then you may need to intubate the patient for respiratory depression. If they're still having symptoms and you've intubated them and increased the benzodiazepine, you might consider doing a lumbar puncture and instilling a hundred micrograms of intrathecal baclofen. This may be enough to stop the withdrawal symptoms and allow it to be controlled with the oral baclofen and IV and oral benzos. That doesn't work then place a lumbar drain and continually infuse intrathecal baclofen. In truths, I have never reached level two or level three severity in my practice. So working up to SynchroMed pump, why are my spasms worse? The first is to take a good history. Is it a pump malfunction? So find when the pump was implanted, when is the elective replacement interval, interrogate the pump, look at the logs to see if there's some indication of frequent stalls. Is there a low reservoir volume? Ask when the pump was last refilled and when is the pump supposed to be refilled. Has there been a programming error? When was the last dosage adjustment? When was the last time the pump was programmed? Have there been any change in medications, an anticonvulsant, an antidepressant, tone control, benzodiazepines? Is there increased tone and again, without increased tone, it is not baclofen withdrawal. Is there itching? Is there a fever and how bad? Constitutional symptoms, is there associated nausea, vomiting or diarrhea? How bad is the pain? Where is it located? And is there a relationship to pain and the tone increases? Interrogate the pump, look at the alarm date when it should be refilled. Look for any alarms occurring, a low battery alarm, a stall alarm, a low reservoir volume alarm. And look at the elective replacement interval, is the pump due to be replaced? In terms of imaging, the first thing we do is a KUB and an AP and lateral lumbar spine. It's very important to put on the requisition to include all pump and pump tubing because the x-ray techs are taught to cone down and cone out the fat, and that will cone out most of your pump tubing. And when you're looking for a fracture. Catheter fractures often occur at the nipple here or at connectors in the back, or if it was a midline placement between the spinus processes. In the old pump connector, there was always a gap here. This is not a fracture, but this is the neural sutureless connectors that have been used for the last several years. Don't have that gap. Although this isn't the world's greatest film, this is a spinus process. This is a spinus process, here's the catheter coming out, and you can see a gap where the catheter was torn by the interspinus ligament from the midline implantation. And this is a hundred percent preventable by doing the shallow angle or blank approach. This is a migration where the catheter walks out of the spine. The important thing to remember is this occurs in the first weeks after implantation. Once the catheter has scarred in, it is unlikely to walk out. So again, in our algorithm, we do plain films. If the plain films are abnormal showing a fracture, disconnection or migration, the patient needs to go to surgery for a catheter revision. If it's normal, then we do a catheter access port aspiration. When we do this, this is the catheter access port. It only will allow a 25 or 24 gauge needle to get into it. That's a safety feature because the reservoir port is filled with 20 and 22 gauge needles. And that prevents an inadvertent, putting the entire reservoir volume on a refill into the catheter access port. The catheter access port has no access to the drug within the pump or the reservoir. When you aspirate you're aspirating CSF from here, when you're injecting, you're injecting into the catheter, you're have nothing to do with the pump. A normal functioning pump, you should easily be able to aspirate three to four milliliters of CSF. The catheter is sitting freely in the spinal CSF and when the catheter was implanted, right after implantation, there was good spontaneous flow of CSF. And we should be able to aspirate if a patient is having problems with drug delivery, especially severe problems, and you cannot aspirate after the catheter access port, then the patient goes directly to surgery. There's no need for further testing. So what if the catheter access port is normal? What options do you have? One is to just take the patient to surgery and explore and plan to replace the entire catheter, again, an assumption that the pump interrogation has been normal. Imaging studies you can do after that, is a catheter access port injection with fluoroscopy, an indium scan, a spiral CT scan, and an MRI scan. The catheter access port injection with fluoroscopy, you aspirate the catheter access port. Again, if you cannot aspirate three milliliters stop, do not inject, this can lead to a bolus of baclofen or morphine being given to the patient. And there are several reported cases of respiratory arrest in the radiology department. You then will inject ionic contrast medium. Most people inject somewhere between five and 15 milliliters. You look for leaks at the connectors and you watch the flow from the catheter tip. False negatives are very common with this and the reason is the pump only pumps out an average of 0.1 to 0.5 and the vast majority, maybe one milliliter over 24 hours. With this test, you're injecting five to 15 mils in less than a minute. That's significantly different pressures, significantly different flows. And then you have no axial imaging only AP and lateral. So you may or may not be able to pick up an abnormality. The indium scan when done it should show a normal myelogram of the canal and pump and tubing. It can show disconnections, it can show a non-functioning pump. It is the only physiologic evaluation of the system. However, it takes at least 48 hours to perform this test. And because indium has to be made in a cyclotron, in most centers nuclear medicine doesn't work on the weekends, you can only inject these studies on Tuesday and Wednesday, making it very difficult to do an expeditious workup of a patient in severe withdrawal. Because of that, we went to the CT catheter study. It's very important when doing this study that the patient is on the CT scanner bed. And the injection is with the patient on the bed. You cannot inject the patient fluoro or do a typical fluoro test and then transfer to CT, the resolution will be lost. So you then do a side port aspiration. You ensure that at least three Ccs of CSF has been aspirated. Again, if you don't, don't inject. You then inject only two to three mls is the lowest we can do to get visualization, Inject it slowly, and then do a spiral CT scan of the entire catheter in pump and increase the field of view over the pump to see the catheter enter the pump. This is what a normal scan should look like. The contrast is heavier than CSF and in the area of the thoracic kyphosis, will layer, you should see a perfect oil-water type of meniscus and it should be absolutely level. And when you're looking at this, look at the top of the column and the bottom of the column, that's where the abnormalities are seen easiest. We have seen cases where we can actually see the contrast extravasated into the subcutaneous spaces. Here's a classic subdural catheter where you see the contrast climbing up along the way. Again, the only way it can climb like this is if there's a membrane on each side. So the contrast must be in the subdural space. Here's something we discovered once we started doing these, and these are catheter tip loculations. You can actually see fluid levels, but the drug doesn't flow out freely, it's actually loculated here in the CSF. And again, because the pump only pumps a 10th of a mil a day or half a mil a day, this can hold a whole a day supplier drug. So what do you do when you're on call? Well, the role of the ER doctor is to evaluate for other causes and symptoms, looking for other infections, other causes of increased stimulus, respiratory problems, constipation. They can order the APN lateral, lumbar spine and KUB, and they also help triage by evaluating the severity of the symptoms. And if they're severe initiate treatment for an overdose valium, underdose, give some valium ativan for an overdose. Again, make sure the ABCs are being initiated. Role of the primary on-call team. Many of you have no experience with baclofen pumps or morphine pumps. Get the detailed history we went over earlier and then collect the data so decisions can be made. What are the patient's vital signs? What is this tone like? Are they having spasm? What is their level of consciousness? How uncomfortable are they? What laboratories have been done? And then what is the ER workup done? And then evaluate again, the severity of the spasms. Cause that's the triage that will decide whether or not the patient could be sent home on oral baclofen or worked out and needs to be admitted and worked up as an emergency. The pump call team or the person who's taking pump call. I worked with a primary call team to determine whether this is underdose, overdose, and if it's even has anything to do with the pump, is there a severity of symptoms? Is there a necessity for emergent reprogramming? In other words, an overdose stopping the pump. And then medications for treatment of symptoms in withdrawal syndromes usually there's not much gain by coming in the middle of the night to interrogate the pump because many times not much will be done, unless there's a question by history that the pump... the patient needs a refill and the pump is dry. Then the pump team can come in and refill the pump. Most of the pump workup can be done the next day when x-ray is available. Again, important to remember that baclofen lowers the tone. If a patient comes in and they're lethargic or confused and their tone remains high or normal, it isn't the pump. If the patient is febrile, in pain and tone is at baseline, it isn't the pump. We never turn off the pump to see if it's the cause of the problem. You can't do that because you'll put the patient in acute withdrawal. If it must be done, the drug must be tapered, but again, the pump never goes crazy and in general it has never been reported to overdose a patient without there being an intervention. And so if the patient's been on a stable dose for weeks or months, again, there's very little to be gained by turning off the pump. Oral baclofen must be continued after the pump is implanted or revised. All baclofen crosses a blood-brain barrier and gets deep into the brain. Intrathecal baclofen diffuses less than a quarter inch into the brain and so the deep areas of the brain do not get intrathecal baclofen. And if you acutely stop oral baclofen patients very frequently have hallucinations and other symptoms of withdrawal. We're now going to talk about the syndromes of catheter malfunction. We talk about symptoms of catheter malfunction because again, patients come in with typical syndromes and they're very helpful in trying to figure out what's going on with the patient. Again, I receive honorariums for teaching and consulting. And as we said earlier in this talk, Medtronic has not reviewed, edited or approved this talk. So again, patients present with complaints. When you have similar symptoms and signs, this constitutes a syndrome. The first syndrome we identified again, it was in a CP patient and mother was always right, and the syndrome is tone control that seems to be very good when the patient wakes up in the morning and tone control gets worse as the day goes on and they have varying symptoms. And again, this first patient that I had was exactly that man said when he wakes up in the morning, he's fine. He gets put into his wheel chair, sits in his wheelchair all day, and by the end of the day, as soon afternoon, he's got markedly high tone. We worked at everything. X-rays are normal, side port aspiration was normal, CT catheters studies were normal, we even explored the first patient and could find nothing on exploration. And we did an LP test dose and he got an excellent response to the baclofen by the test dose. The pathology is there's a minute tiny hole in the tubing. When the patient is lying down, there is no back pressure on the pump and so the drug goes the end of the pump holes. If there is a hole in the dural edge or in the connector in the back, when the patient then gets upright in the wheelchair, the catheter has to be... the pump has to pump against gravity to get to the tip. And this extra back pressure leads to the drug dripping out. And again, you only need to lose 0.1 to 0.5 mls over 24 hours to lose the entire day supply of drug. So then when the patient was up, all of the drug was going out to his pinhole and none of it was going out the end of the catheter and the patient was having withdrawal symptoms. It's diagnosed at surgical exploration, how we do it and to test, I opened up the back of the patient over the catheter, then aspirate the cath... Put a needle in the catheter access port anteriorly, aspirate CSF and then I pinch the tubing at the fascia and inject. If there is a leak between in the pump tubing, between the pump and the spine, there'll be able to inject some fluid. And then you open up looking for that. If with pressure, there is no fluid going out of the syringe that you're injecting with. Then you know that it's not a problem there. We then go ahead and replace the entire spinal segment of the catheter. We don't tend to routinely remove the spinal catheter because we have a lot of difficulty with spinal leak from removing that hole. Occasionally, you will see water spraying out of a leak site in the back. If the leak was near the near the connector in a tubing system, and then you have to replace the catheter. The subdural catheter symptom there's vacillating tone control, random changes in control from overdose syndrome to underdose syndromes. And what happens is the catheter goes through the arachnoid and the drug delivery is in the subdural space. So a puddle of drug forms and reflux is back in the CSF with cough or strain or valsalva. The amount getting into the spinal fluid is unpredictable. Our index patient for this was another cerebral palsy child the mom had exactly the opposite history of our previous patient. In that whenever he went to school, the nurses were calling and saying that they couldn't arouse him after lunch. He would be dead asleep and unarousable. All of us who have been through medical school, pathology lectures after lunch, know that it's easy to fall asleep, but he was basically unarousable. So we brought him into the hospital and put him in bed rest. And after two days sitting in bed, he had no symptoms at all, no problems at all. And then mom being says well he's always in his chair. We said, well, let's put them in his chair. And mom said, okay. And so her method of transporting him is to do a big bear hug with him sitting on the bed and bear hug transfers him into the chair. And about two to three hours later, the patient is unresponsive. What happens again the catheter gets through the arachnoid and drug is being delivered into the subdural space not freely. So it's puddling out here and you're getting a rather large puddle of drug, but the entry point is still open. So when a valsalva occurs, when this mother grabbed this kid, the intraspinal pressure increases, pushes against the arachnoid and dispenses an uncontrolled amount of drug into the CSF, leading to an overdose system. Again, the diagnose catheter access port, if all the holes of the catheter in the subdural space, you may not be able to aspirate, but we'd been able to aspirate in that because you're aspirating pure drug, which looks identical to CSF. An indium scan is reported at one time to see a puddle at the tip of the catheter. The injection dye studies are very dangerous 'cause the dye can flush a baclofen from the subdural space so if you cannot aspirate, again don't inject. The low volume CT scan safely identifies this because again we aspirate and here again is the contrast marching up the side and a patient with a subdural catheter. This is the normal CSF view. The other thing we started to see is catheter tip loculations. This is probably the reason you get no flow. When you're getting... When you do a side port aspiration or a poor response to drug, what is happening is arachnoid is scarring around the catheter tip, whether it was from bleeding at the time of insertion, a partial subdural catheter, irritation by high concentration of drug. And again, these are what the loculations look like. They're just pockets where drug is collecting in the pocket. Although some drug may get out in the CSF when you're injecting two to three mils over a brief period of time in normal physiology, very little of the drug gets out into the CSF. Catheter migration, again, occurs before the wound heals in two to three weeks. So if a patient is complaining that they never got the effect of the drug that they got at the test dose, or they come back at their one month followup and have had no response to the drug, take an x-ray. You can see very quickly that the catheter has pulled out of the spine and it's a problem. As long as the patient has a seroma in their back, they're at a risk. Once the back is healed flat, the risk of migration decreases if the catheter has been anchored correctly. If the catheter has not been anchored, then again, they can pull out later. There's a very interesting relationship between hydrocephalus and VP shunts in patients with pumps. Baclofen is removed from the spinal fluid solely by bulk flow through arachnoid granulations. It is not absorbed by the dura, it is not broken down. A functioning VP shunt will divert CSF out of the ventricles and into the shunt. Therefore, the volume of spinal fluid getting into the spinal canal is decreased and the flow rate is decreased. So therefore, the concentration of baclofen in the CSF increases. Insertion of a new shunt or revision of a shunt that's malfunctioning in a patient with a stable dose of baclofen will require a decrease in the dose of baclofen to achieve the same effect. A malfunctioning shunt may present as an increase in spasticity, due to decrease in CSF into the shunt and therefore an increase of CSF in the spinal canal. Most important that you have to decrease the dose after the shunt has been improved. Our first patient for this was again, a girl who lives three hours away, her pump is programmed and filled by a home health service. And her mother called and said that this patient has had a little bit of increase in clonus, nothing big, and she wanted an increase. So we ordered a 10% increase. That worksheet, they called back a week later and said, the symptoms are worse can you increase again? We said, well, you have to come in, but we'll increase you. She couldn't get in for a couple of weeks so she had three increases of 10% to 20% and then when she came in to see me finally, after three weeks, she had headaches and an obvious shunt malfunction. When we revised the shunt and recovery room, we did not remember to decrease the dose back to the one before the shunt malfunction started. And she was very difficult to arouse in recovery. So again, diagrammatically in the normal patient, they make 350 to 500 mils. It comes out of the ventricles down through the spinal component back out, and we're dripping 200 micrograms per day, let's say, into the spinal canal and you have a certain concentration. When you then put a shunt in, or in our case revise the shunt. All of a sudden, much more CSF is leaving the ventricles and going into the shun and not coming down. So now you have much less CSF going down, but you haven't changed the flow rate, so you have a marked increase in concentration and the patient has an overdose situation. The important thing to remember about this situation is that many times the patient with a shunt malfunction will have increased tone before they have other symptoms. And therefore the shunt, the person increasing the concentration and increasing the daily dose is usually not the pediatric neurosurgeon or the neurosurgeon who's gonna revise the shunt. So if you have a patient with a shunt malfunction and a pump prior to revising the shunt and make sure there has not been any adjustments in the dose to theoretically treat the need for more drug due to the shunt malfunction. Thank you.

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