Hi and welcome to this webinar, and in this session we will be looking at anaesthesia for the neurology patient and looking at those kind of troublesome spine and brain cases that that we see in the clinic. So my name is Carl Bradbrook, and I am a European specialist in veterinary anaesthesia and analgesia based in the UK. A Little bit of an introduction just to, to get started.
And I, I'd like to really kind of cover the, the aims, the principles of the kind of this sessions, the principles of looking at both anaesthesia and analgesia in. Our spinal disease cases and primarily here thinking about spinal pain, so those dogs and cats that present to us in the clinic with spinal pain, how are we going to manage them as part of their kind of perioperative care? Really, although we're not gonna be focusing on the procedure itself, I will introduce some new bits of literature, some bits of evidence based medicine that we have available to us as to how we can kind of focus our analgesic management and particularly then for those of you that are doing spinal procedures in in your clinical practise.
With regard to those patients with brain injury, we're gonna be looking really in two categories, but we're gonna be focusing around traumatic brain injury and using the principles of that with regard to our clinical cases and then. As well as those trauma cases that we see in, also looking at how that can apply to our patients that have intracranial disease. I'm thinking here about intracranial neoplasia, where we can also apply the principles of neuro anaesthesia to ensure a a good outcome if we're doing diagnostic testing, for example, in those particular cases.
The spinal disease section's gonna be a little bit shorter than the brain disease section, mainly here because as I said, we're gonna be focusing on analgesia and in the brain section we're gonna be focusing on the principles of neuro anaesthesia. To start then, let's just look at some of the considerations that we have for our spine cases, and we're gonna go through looking at some principles of stabilisation. Is blood work appropriate, when should we be performing pre-anesthetic blood testing in the kind of the scenario of the spine?
Few bits of considerations regarding the patients themselves, analgesia, and that's gonna be the focus of this part of the webinar, and also not forgetting about the procedure, the procedure itself is a really important component, what are the considerations surrounding. The procedure be that diagnostic procedure, such as MRI as as our imaging component, or is it a surgical procedure where there are different concerns with regards to our anaesthetic. I think one of the kind of the peculiarities or the very kind of individual things with regards to neuroimaging, and particularly thinking about MRI about magnetic resonance imaging, is our remoteness from the patient.
We're very used to being with the patient, being able to directly palpate, directly monitor our patients, but we put ourselves perhaps into the MRI. Environment and we're not able to, to do that and we have to actually access the room and access the patient. So the pre-anesthetic components are really focused around our patient examination, and this is going to be the same as for all of our patients prior to anaesthesia.
But the focus for the cases I think that we particularly see, that we see on a, on a regular basis in the clinic will be with regard to their spinal pain. And the majority of the dogs, particularly that we, that we see on a regular basis, will be presenting because of spinal pain, plus or minus other neurological deficits that they may have. And it's really an important focus of our pre-anesthetic time to ensure that we're able to manage their pain effectively, particularly if we're thinking about either diagnostic or surgical procedures.
Blood testing in this kind of scenario, we've we've talked about kind of previous aspects of blood testing and when or where we should be performing it. Is it something to do on all cases? Should it be on selected cases?
But with our neuro patients, particularly those that are maybe going to go undergoing surgical procedures. Then having baseline bloods is certainly a useful, a useful part of our pre-anesthetic examination and our pre-anesthetic testing. Really for two bases here.
One is that these patients often require long term, analgesic medications in the postoperative period, and maybe on long term, anti-inflammatory drugs, and having baseline values, particularly for renal and and hepatic function. Is essential so that we can monitor progress in the post-operative period and ensure that we don't, have complications or adverse events, or if we do that, we're aware that there was an underlying disease. The other part that I think is a really useful and really important part of our pre-anesthetic exam and using blood testing is a number of the patients that present with spinal pain have often been non-ambulatory for a period of time.
And I think because of that, their, not only is their food intake reduced, but so is their fluid intake and. Actually being able to assess volume status and assess hydration status prior to anaesthesia is really an an essential part of our pre-anesthetic workup. So, biochemical and hemaological, so CBC testing is, is really useful when we're trying to, Decide on our pre-anesthetic plans, we're thinking about analgesia and about fluid therapy as being kind of our mainstays of that stabilisation, with these cases.
So ensuring that we have assessed volume status, pack cell volume, total solids, in conjunction with our other testing is going to be a really useful part. And looking at their heart rate and their respiratory pattern as well, so after giving analgesia, does their heart rate remain high, for example, maybe that's indicating in combination with the blood testing that the patient's hydration status or volume status is abnormal. So we're gonna split the kind of procedural part into two sections, so we have our diagnostic section.
And the mainstay of neuroimaging is MRI. And as I've already kind of alluded to, the, the kind of access to the patient and our ability to monitor the patient is, is quite severely limited with this imaging modality. So you can see the setup here where we have a control room that houses the anaesthetic machine and the monitoring equipment and we have a window through there to where the MRI and the scanner is.
So we're not always able to. Be with the patient and to actually access and directly monitor the patient. So to do that, we have to go into the scan room, and that may or may not involve and pauses in scanning or being in there during the image acquisition.
Because of that, our monitoring is reliant on certain aspects. We're limited in certain cases as to the type of monitoring equipment that we have available to us. And it may be that we have something like an esophageal stethoscope plus catography because they're relatively easy to run through.
The scan room, but we have equipment considerations, particularly with regard to, cables that can run into the room. So fibre optic monitoring systems are required for for MRI imaging, or we have to have a, monitor and a slave monitor in the scan room. So because of that, our monitoring can be kind of different to what we would be used to in the kind of prep and surgical areas.
There's sequences that MRI produces or uses to produce the images that we are able to then look at for our, our surgical diagnosis or our or our medical diagnosis can also affect the quality and the interpretation of our monitoring information as well. So. Using something like a an esophageal stethoscope is, is a really useful monitoring tool with this particular setup.
Safety's obviously a really important consideration with regard to MRI, so being aware of that when we're moving patients in and out of the scan room and in and out of the scanner, with regard to the permanent magnetic field and just being aware of the equipment that you're using, the trolleys, etc. With regard to that. So.
That's really the main part of our diagnostic setup is the limitations that are associated with anaesthesia and acquiring those MRI images. The other component then of our neuro anaesthesia with regard to our spines are those surgical procedures, and we have, you know, a number of of sets of considerations and concerns that centre around the the procedures that we are commonly performing. And I think the two that, .
That we do on a, on a daily, on a daily basis are going to be those dorsal approaches to the spinal cord. And this is something that is being performed in, in, in a number of clinics now. And that's the hemilaminectomy, so, relatively.
One of the common neuro spinal procedures. And the second would be the ventral sites so the ventral approach, to the cervical region of the spinal cord. Hemilaectomy being, thoracic and, lumbar, the main areas.
We'll move on in the next few slides to looking at an approach to analgesia, but with the surgical procedures, analgesia is going to be key, and it's likely that we will have performed an MRI imaging prior to to surgery, and we'll have utilised analgesia with that. And I kind of mention that now because when we anaesthetize patients and we position them for for imaging. We've got muscle relaxation associated with analgesia, that is likely to change the kind of the posture and the patient may have been holding a certain posture because of the pain associated with their disease process.
And although MRI itself is not a painful procedure, but no susception associated with the scan, you can see no susception and I think that's particularly evident when we're positioning patients, and then we're holding in that position for a prolonged period of time to acquire images. So analgesia is very often required for imaging of, of the spine. For the surgical procedure, other consideration of the concerns are going to be to be haemorrhage, so associated with the approach to the spinal cord, either dorsally or ventrally.
Certainly with the ventral approach in the, in the neck and the cervical region, there are quite, there are large, vessels that, have to be, retracted to access, the spinal cord. And with regard to the hemilaminectomy and the dorsal approach, then we. Or the dissection through, or the, the, the retraction of muscle off the spinus processes, and then the access to the spinal cord, and to the venous plexus can be associated with haemorrhage as well.
So monitoring haemorrhages, is an important consideration during this procedure. If we're thinking about imaging and a surgical procedure or a lengthy surgical procedure, really important to be monitoring body temperature, hypothermia is a is a common complication associated with these procedures and the likelihood then of additional complications such as bradycardia, hyper. Attention, prolonged recoveries, and can be something that we should be aware of, during the, this kind of this patient experience.
So, monitoring body temperature and utilising appropriate methods to warm the patient during the procedure, such as showing on the right hand of the slide here, where we're using the right hand side of the photo, where we are using a warm, a force warm air device, which the patient is lying on. And we're using a heat and moisture exchanging device attached to the breeding system as well. Positioning can be a concern depending on the procedure type.
So for hemiectomy, patients will be positioned in sternal recumbency and the position of the, of the spine for this procedure may result in some additional pain. The positioning for something such as a ventral slots, where the patient is in dorsal recumbency with the neck extended and can stretch the, not just the vasculature, but also the neurovascular bundle in the neck, and that increase and that kind of stretch and retraction of the, the vagal trunk can cause concern during anaesthesia and also can result in haemorrhage as well, associated with that neurovascular bundle. For other procedures, that's commonly performed, such as stabilisation, for cervical instability, requires a, a very flexed neck, kind of kind of a hyperflex neck position, and that in itself can cause problems with our airway, compromise the airway and ensure that we have a patent airway into those procedures, so.
There are considerations associated with positioning. Ventilation, so thinking here about whether we need to intervene with either manual or mechanical ventilation, depending on the analgesic requirements for the procedure and also on the positioning for the procedure, we may need to intervene. So monitoring these patients with regard to catography and anti carbon dioxide concentration will be useful to target ventilation, in these, in these procedures.
So thinking about analgesia and as for our other surgical procedures that are on other our other analgesic options, then the opioids will, will still currently remain kind of like our mainstay of analgesic provision for those patients presenting with spinal pain and. For me, the, the new, agonists such as methadone will be my kind of like first line choice for providing analgesia to those patients presenting with acute or even more chronic spinal pain. The non-steroidals with their analgesic and anti-inflammatory properties are also going to be something that we're going to be utilising.
Although we may have concern in some of the procedures with regards perhaps to haemorrhage, of utilising these in the perio-operative setting, but certainly for. Pooperative analgesia, and maybe even preoperative stabilisation, or if they're not surgical cases, utilising anti-inflammatories in that kind of that post imaging and recovery period. But just being aware of the potential for some of the unwanted effects, the non-steroidals, and when we may have to consider using something else, such as paracetamol.
We're starting to see further evidence about the usefulness of paracetamol, obviously only in dogs, and paracetamol shouldn't be used in cats. There's a little bit of literature to document the use of paracetamol compared to one of the non-steroidals, and perhaps the benefit in those cases, or at least the non-inferiority of paracetamol and to the non-steroidals. But again, we're still collecting evidence and collecting data about the use of paracetamol and the appropriate dose of paracetamol that should be used for pain management in dogs.
The other analgesic which we find useful, I certainly find useful with regard to analgesia in the spinal case is ketamine, and be that in the kind of acute setting, where we have relapses in pain management, and we're trying to deal with breakthrough pain, and ketamines a useful option. And certainly in those surgical cases, the, the use of a ketamine infusion can certainly be, be considered. Using pain assessments will aid in ensuring good analgesia, but also ensuring that the analgesia that you provide is appropriate and when to step that analgesia up or down.
So in dogs using the composite measure pain scale, the short form of the Glasgow pain scale is going to be our choice, and in cats, and the feline acute pain scale, so the Glasgow . Feline version. Or and or even the feline grim scale, so the .
The e and acute pain scale incorporates some of those those facial pain recognition tools associated within that kind of incorporated within that. And the more recently published feline grimace scale, so similar to some of the laboratory animal grimace scales that are already available, and to the baby pain face scale utilised in human medicine, have some additional options there with regard to to scoring, to scoring pain. Wanted to mention at this stage, two bits of literature that have been published looking at firstly here the use of pregabalin, and then secondly we'll look at the use of gabapentin.
These are both studies in dogs. This is a 2020 study looking at the use of pregabalin for analgesia. In dogs undergoing disc surgery, so an intravertebral disc.
Surgery. This 2020 study used pregabalin at 4 milligrammes per kilo, orally 1 hour prior to anaesthesia, and then, 3 times daily for 5 days post surgery, compared to a group where they didn't use pregabalin. The rest of the analgesic and anaesthetic, protocol was the same between the two groups.
And they used pain scoring using the short form of the Glasgow acute pain scale for dogs, and they used mechanical noise receptive threshold testing. To look for evidence of of neuropathic pain. So a positive outcome in this piece of work, where the dogs in the pregabalin group had lower pain scores and they had higher mechanical no receptor threshold testing.
Thresholds when pregabalin was used, so a positive outcome for the incorporate for incorporating, pregabalin into your analgesic protocol, in this particular surgical scenario. The The second study that I wanted to mention here, which is an older study, there's there's been no follow up to with regard to the use of gabapentin in this scenario yet. Again, thinking about neuropathic pain and the use of gabapentin and for that, so this study again in dogs, monitoring post-operative pain after intervertebral disc surgery, used gabapentin at 10 milligrammes per kilo.
They used it BID prior to anaesthesia, and I think, you know, one thing to mention here with regard to no effect is we have, subsequent evidence that gabapentin likely needs to be dosed 3 times daily in dogs to ensure, or at least to try and get a positive analgesic effect. So the half-life does not, in dogs mean that gabapentin can be used twice daily, in the majority of cases. In this study, they assessed outcome using again the short form the Glasgow pain scale and they used a visual analogue scale as well, and they measured cortisol levels.
Between the two groups again the rest of the analgesic protocol was the same between the two groups, so a gabapentin group and a group that didn't receive gabapentin. And unfortunately they were not able to to document a a positive effect, or at least an increased analgesic effect of using gabapentin on top of a methadone formulation that was utilised to provide analgesia. So the dosing, and the, the, the dose, sorry, and the dosing interval are likely to be two aspects in this study that means that it wouldn't, that it should be repeated, perhaps at TID dosing to see whether we do get a positive effect.
So, pregabalin, we have some evidence there at gabapentin, we would like more evidence that these drugs are useful in this particular type of surgical pain. The last part of the kind of kind of an ultimate like an update on analgesia that I was gonna include here just thinking that this would be, this was a useful aspect to to put in. Is a a a newly described or relatively newly described local anaesthetic technique for providing analgesia for dogs undergoing haul laminectomy so both primarily thoracic hemilaminectomy but also lumbar hemilaectomy, and this is the ESP or the erectal spine a plane block.
This is a technique that requires ultrasound imaging of the transverse spinal process, and then installation of our local anaesthetic solution and within, or kind of below the muscle within this plane that's associated with the ESP requires ultrasound imaging and the use of er an ultrasound. Needle. Something that we've been utilising for around 1, maybe 1.5 years now.
And provides excellent analgesia when this block is effective and we get excellent analgesia for the surgical procedures for for these cases. It's gonna show a short video here. So we are imaging the spinal process you can see the needle coming through on .
You see the needle as it passes through the tissues, we're aiming for this very hyperrechoic component of the of the lateral of, of the transverse process. And then we're aiming to deposit local anaesthetic along that plane above the transverse process. You can see the needle coming in from the left of the screen dorsally, at the top of the screen, coming in at an angle.
Sorry, I'm just gonna go back one there, so. Really kind of conclusion with this technique is this is going to be kind of moving forward as we incorporate, we, we aim to incorporate local anaesthesia within our surgical procedures. This technique has been shown to reduce the consumption of other analgesics during the procedures and primarily thinking here about opioid analgesia plus other analgesics, improve, surgical conditions and allow for better cardiovascular stability during what can sometimes be quite a lengthy surgical procedure.
So, this is certainly a procedure, a technique that we will be continuing to improve on, and I'm sure there will be further literature to support the use of this, in dogs. Yeah. So from a conclusion point of view, just to kind of summarise this first section on spinal disease, then we want to consider, I mentioned our patient's volume status, so thinking about their hydration status at presentation, have they been able to eat and drink normally prior to their arrival at the clinic.
Good analgesia. And then thinking about the procedure, is it, is it a diagnostic procedure such as MRI? What are the considerations with regard to that, or is it a surgical procedure, thinking about the considerations that we've been through and for that part as well.
So we'll move on and look then at some of the brain diseases that we are presented with, and I'm gonna we're gonna separate these into two, into two parts, so those that present with traumatic brain injury, having had some sort of head trauma. And our concerns here with regard to things like blood loss and the risk of regurgitation and aspiration because of abnormal and cranial nerve reflexes and and abnormal ability to maintain a patent airway. Ocular and dental injuries, again very common in cats to see them with facial injuries that may involve the eyes and the jaw, and then also soft tissue and trauma as well.
So there's a whole kind of myriad of injury that presents to us with those head trauma cases. On the other hand, we have patients presenting with intracranial disease. Both dogs and cats probably present with these, but in dogs and cats, neoplasia, so a space occupying lesion and in cats primarily, but in in dogs as well, abscessation associated also with being a space occupying lesion.
And then we have those inflammatory brain diseases such as amyosis and meningitis and encephalitis as well, which, Can, be incredibly debilitating and rapidly progress and we will be focusing on those kind of neuro anaesthesia principles over the rest of this webinar, looking at how we can manage those cases effectively if we will require anaesthesia for diagnostic testing. Similar to what we just mentioned, but just to kind of summarise those two, so head trauma really, road traffic accidents and falls from height, . Dog versus dog, big dog versus little dog, kick injuries, we see those cases where dogs are kicked by horses, intentionally, but the horses, the dogs are running around and, and they are injured that way.
Intracranial disease obviously can be related to trauma. Neoplasia and inflammatory disease are our two main, types of intracranial disease. When we think about traumatic brain injury, mortality is high, some of these patients don't make it to the clinic and post their injury.
And the primary injury is that injury to the brain itself from the trauma. And the secondary injury is often what results in that high mortality rate, if the primary injury does not result in death, it's the secondary injuries that result in a high mortality morbidity associated with brain injury. And that can be hypo or hypertension, hyperglycemia, hypoxemia.
And the inflammatory changes and the changes in intracranial pressure. With regard to some physiology, I think it's important to remember that the cranial vault of the cranium is a is a box in which we have the brain, we have the cerebrospinal fluid, and we have blood as well. And none of these components are compressible.
We can change the volume of the CSF and the volume of the blood within the cranial vaults. But because of that, there's minimal volume compensation amongst those components. So as soon as we have an injury, perhaps like a bleed, where we get an increase in blood volume, eventually we're going to get to a point where the brain, becomes, becomes compressed.
Our intracranial pressure is rising, and it's that change that's going to lead to those other physiological components of secondary brain injury. So if you think about the, the brain, as we mentioned, we've got the blood, the brain tissue itself, and the CSF. Useful to think about those three things within that enclosed space, so we only have the ability to reduce our CSF volume, but as soon as our intracranial pressure starts to rise, then we're not able to compensate anymore, and that's going to have a compromising effect on brain function.
So our normal in we're able to measure intracranial pressure in a clinical setting, our normal intracranial pressure is between 5 and 12 millimetres of mercury. And we're we're aiming to avoid increases in our intracranial pressure by maintaining our our cerebral perfusion pressure and preserving our cerebral blood flow. And a way to think about this and and this will make more sense as we go through some of the monitoring changes that we might see or we anticipate seeing and how we're going to manage those, but the cerebral perfusion pressure is equal to the mean arterial pressure minus the intracranial pressure.
And auto regulation maintains this response and we'll we'll focus a little bit more as to why that is important. What about our cerebral blood flow? Obviously we need to maintain blood flow to ensure that we maintain that coupling between flow and metabolism.
So the cerebral tissue requires a has a high oxygen demand and has a high metabolic rate. So our cerebral blood flow is equal to our perfusion pressure, divided by the vascular resistance within the cerebral system. So we're aiming in our neuro cases to maintain aminoteral pressure that's perhaps higher than we would normally aim for, so over 60 millimetre mercury in the normal patient, in our, in our brain patients, in our neuroanaesthesia cases, we should be aiming for a mean terial pressure of 70 to 80 millimetres of mercury.
We should be maintaining or controlling a normal carbon dioxide level, because carbon dioxide is important in the cerebral vasculature with maintaining vascular resistance. If we let CO2 rise, then we're going to cause cerebral vasodilation. We need to maintain oxygenation as well, and to ensure that and we meet the oxygen demand of the cerebral tissues.
Auto regulation is important as it is in the renal vasculature, it's important in the cerebral vasculature as well, so an increase in mean arterial pressure, results in vaso constriction and a and a decrease in immunoarterial pressure and results in vasodilation. With regard to arterial carbon dioxide concentrations or tensions, an increase in CO2 also results in vasodilation, and a decrease in CO2 results in basal constriction. So we can utilise those principles, we are aiming for as normal pressure.
We don't want to be too vailated and we don't want to be too vasoconstricted either. So you can see that cerebral blood flow is maintained over quite a wide blood pressure range, but as soon as our blood pressure either falls below a mean of 50 or is greater than a mean of 150, then cerebral blood flow will either will significantly reduce with a linear reduction. In, blood pressure, or we get a linear sorry, a linear reduction in blood flow or we get a linear increase in blood flow.
So we should be aiming to maintain blood pressure in this range here. Having said that, I think we are aware that auto regulation is also impaired when we have significant brain injury. How are we gonna decide that intracranial pressure is raised, we need to look at our clinical signs, our mentation, and we can look at pupillary changes as well.
If intracranial pressure does rise, then the delivery of oxygen and the delivery of nutrients to the cerebral tissue to the brain itself is going to be compromised and maintaining that perfusion pressure is important. This kind of fits in nicely then to Cushing's response or Cushing's triad, so we if we get an increase in intracranial pressure, our cerebral blood flow decreases. We get an increase in carbon dioxide.
Tension, we get an increase in mean arterial pressure to try and maintain perfusion pressure and we get a reflex bradycardia. So patients may deteriorate suddenly. Monitoring is really important.
If we monitor an increase in blood pressure, followed by a reduction in heart rate, we may be seeing this Cushing's response, and that was likely to indicate that intracranial pressure is increasing, and we need to be able to manage that. The blood brain barrier itself is a selectively permeable membrane. With a protective function obviously to maintain the brain outside of the vascular system.
We can have compromise to the blood brain barrier with trauma, and that may mean that some of the drugs that we give have a different effect, usually a greater effect than we would expect in the patient with a healthy brain. And in those cases where we've got an inflammation such as meningitis or encephalitis, then that also means that we may see differences in the effect of the drugs that we administer as part of both our analgesic and our anaesthetic protocol. Just thought we introduce here, just very, very short kind of case study looking at, so we've got a 14 year old domestic short hair with with a recent history of seizure activity, aggression.
Otherwise, the patient is quiet with a poor appetite. On physical examination they are obtunded, and the heart rate's about 200 beats per minute. And they've got a reduced menace response and the clinical examination, the neuro examination is suggestive of a of a forebrain lesion.
Go back and just think about which are our primary injuries, so the injury to the brain itself and which are the secondary injuries that we need to be thinking about with regard to our anaesthetic management. Just something to kind of think about at this time, which, which pre premedication would you use for magnetic MRI so magnetic resonance imaging in this case? Do we need to provide analgesia?
Do we need high doses? Do we need to think about moderating our doses, and you can question in this case whether we should use a low dose of morphine, methadone, sorry, not, we should not be using morphine, not within like to induce vomiting. We want to avoid anything that's going to further increase intracranial pressure.
And vomiting is one of those reflexes that can increase ICP. Low dose of methadone likely then to be sparring on the other drugs that we require to maintain anaesthesia, or should we think about something like tool? Reasonable sedation, poor analgesia, likely to be shorter acting, may be, may require to be topped up during the procedure.
Those aspects of assessing intracranial pressure that we mentioned earlier, so the quiet mentation, dull mental status, obscured propillary changes, important to assess with regard to raise in ICP. So in this case, we should be assuming that intratrinal pressure could be raised. And therefore we need to consider those principles of neuro anaesthesia that we have been discussing.
So what can we do? Our priorities similarity with our spinal patients, stabilisation, analgesia, if appropriate, fluid therapy, oxygen supplementation to ensure oxygen delivery to the cerebral tissues, and a baseline blood testing assessment. We, although we don't want to over volume resuscitate, ensuring that patients are not dehydrated and ensuring normal and adequate volume status is essential in these cases.
We want to do everything that we can to maintain our cerebral perfusion pressure. Looking at electrolytes, concentrations, particularly if we're going to think about utilising something like Manitol or hypertonic saline, when we're managing rays intracranial pressure, ensuring that potassium is not low, supplementing if appropriate, assessing for any evidence of coagulopathy. And ensuring that glucose is regulated within the normal reference range.
Hyperglycemia is a negative prognostic indicator in those patients that present with brain injury. Avoiding everything that we can to further raise intracranial pressure and the other components important here, but if we are blood sampling is to avoid you taking blood samples from from the neck. Jugular occlusion again is likely to raise intracranial pressure.
Fluids options, . Use of isotonic fluids for volume of resuscitation is likely to be the first line of treatment. If we're thinking about volume replacement and also thinking about cerebral blood flow and reduction in ICP requirements, then the use of hypertonic saline could be considered.
Colloids may be appropriate for significant volume resuscitation if we don't want to use large volumes of of crystalloid fluids and then worry about them redistributing into the interstitial space. In patients that are anaemic as a result of trauma, blood products may be, may be required. Application and monitoring equipment prior to anaesthesia is going to be really really useful and important in those patients that present that are still obtunded but improving in mentation.
So we're able to look at their ECG we're able to see heart rate changes during induction of anaesthesia, monitoring blood pressure. Checking blood glucose monitoring for hyperglycemia. And looking for heart rate and blood pressure changes that suggest a raise or a rise or a high intracranial pressure.
What are our options if we suspect that intracranial pressure is high? Manatol, Manol being used then to decrease blood viscosity and promote an osmotic diuresis. There is some thought behind using repeated doses of Manatol and certainly we seem to get the best or most appropriate clinical effects on the first administration, maybe a second administration can be utilised, but prolonged administration or repeated administration may result in accumulation within.
The cerebral tissue itself and worsening of cerebral edoema. We're going to give a bolus over around 10 to 20 minutes. We should be checking volume status and the electrolytes prior to use to ensure that it's appropriate to give mantle, and the peak effect takes around 30 minutes.
Fruzammide may be used in addition to Manito on the basis of its reduction in its ability to reduce CSF production, reduce brain volume, again, ensuring that the patient is normally bulimic prior to the administration of for reason wide. With hypertonic saline, there's certainly the, the long term evidence in human medicine is unclear about whether we should use, whether we should use Manitol or 7.2% hypersonic saline or even 3.6% or 4.8% hypertonic saline.
In terms of long term outcome, there's no evidence to suggest that one is more superior to the other. With regard to long term outcome. With hypersonic saline, we should be giving isotonic crystalloids first and cautious about using it if the patient is already hypernatremic.
If we're still concerned about volume stasis, about blood pressure and we are hypotensive, we may need to then intervene with the use of a vasopressor or an ionotrope. With regard to premedication, it, it may be in a number of these cases that an opioid alone is going to provide sufficient premedication, be that methadone at low doses. Brophenol, incorporating that with perhaps a benzodiazepine for induction.
Aromazine we tend, we would usually avoid because of the long duration of action, the vasodilatory effects of aromazine, and then the effect in the, in the postoperative or the post anaesthesia period in terms of patients neurological status. I think there's been a bit of a shift, although dexam melatoninine we should be cautious when raised where ICP is raised, primarily because it can mimic that Cushing's response, that Cushing's triad, and we might misinterpret that. But certainly low doses of dexaminotomidine used as an infusion in in human ICU patients with neurological disease, can be considered, so it might be something that we see.
And more literature on, in the coming years. Pre-medication is best going to be administered IV using low doses to get the effect that we want topping up as required. And these are definitely patients where pre-oxygenation is going to be important and if we have a prolonged induction and if we have a difficult intubation, pre-oxygenation will be essential.
The IV routes of induction are going to be most appropriate, propofol, olfaxolone, and the inhalational technique or inhalational induction should be avoided, in, in cases where we have an unknown brain status. Avoid a cough, or intubation, and we have some evidence that a lidocaine bolus prior to use of propofol, or alfaxolone can be considered. Intubation should be done once the patient is at an appropriate depth of anaesthesia, and we should be aiming to maintain an anti CO2 at the lower end of the normal reference range based on those principles of neuro anaesthesia that we that we previously discussed.
What are we going to do then if we see our Cushing's response or our Cushing's triad at induction. The most important thing at this time is going to be then to secure the airway and to, In instigate mechanical ventilation or manual ventilation to reduce our carbon dioxide levels down to the lower end of our normal reference range and start to monitor from that point. So that's going to be the most useful emergency intervention at that time, ensuring the patient's not apneic, ensuring that the patient is oxygenated and ventilated appropriately.
We generally see an carbon dioxide concentrations are lower in cats, so that is likely to mean that we should maintain a lower CO2 in the cat than we do in the dog. And our interventions, as I mentioned, will be mechanical ventilation, maintaining oxygenation, maintaining ventilation. We may then want to intervene with one of the fluid therapy types that we discussed previously with regard to also reducing intracranial pressure.
If we've got significant edoema and inflammation, we may want to think about other interventions to manage that before we then consider recovering the patient from anaesthesia at the end of the procedure. I think for me, I, if we have a suspicion, a significant suspicion of raising crial pressure, the use of ventilation, mechanical or manual, is very, very useful, allows us to maintain depth of anaesthesia, allows us to maintain ent the carbon dioxide. With, again, the use of an inhalation agent, so I, so sevofurane may have some benefit over isolorane with regard to its ability to maintain auto regulation and that flow metabolism coupling that we talked about earlier on.
Both ISO and Zivo are likely to decrease intracranial pressure. There may be evidence that an IV maintenance agent, such as a propofol infusion is beneficial over the use of the inhalation agents because it tends to cause less vasodilation, but it will cause more respiratory depression than the inhalation agent. So ventilation is going to be essential if an IV protocol is used.
Monitoring will centre, sorry, the recovery, sorry, monitoring will centre around all of the body systems. But considering other aspects such as haemorrhage, analgesia, ventilation, and the management of any arrhythmias that may be associated, particularly if you've got brain stem disease. So if we've got significant brain stem inflammation and edoema, plus or minus herniation of the brain stem as well, we may also see arrhythmias that will require management if they're affecting.
Particularly affecting cardiac output and blood pressure, but also, if they are affecting. Sorry, if they all become a malignant arrhythmia as well. A smooth and a calmest recovery period as possible, ensuring analgesia is appropriate, seizure management, if that is required.
And it's a time to consider in that immediate postoperative period that we minimise the effects of any secondary injury, so maintaining normal blood pressure, normal glucose, ensuring the patient is adequately oxygenated. And maintaining our ability to monitor for any signs of raised intracranial pressure. This is a question that often comes up about the evidence or the benefits of utilising corticosteroids.
So there's little evidence to support a positive benefit for traumatic brain injury. And the hyperglycemia that I mentioned earlier is certainly a negative prognostic indicator, with regard to outcome. Other negative effects, they can increase increase infection, they may affect the immune response, and later on we will not be able to use non-steroidals.
If there is inflammatory disease, or neoplasia, and we've got edoema associated with that, they may have, there may be a benefit to the use of steroids in that scenario, particularly if they want to recover the patient from anaesthesia. The modified Glasgow Coma Scale, for dogs has been documented in head trauma and it may be a useful indicator in the postoperative period or the post anaesthesia period with regard to monitoring function and looking at whether the the interventions that we put in place are effective. This is a scale so that it goes from 3 to 18 with 3 categories.
If you have a a Glasgow Coma Scale score of 18, that's normal, you're a normal patient, and at 3, you're unresponsive with a very grave prognosis. So it, it can be a useful prognostic indicator of of patients that have suffered head trauma. So just to, just some conclusions from the the the the brain section of this webinar.
Apply the principles of neuro anaesthesia in cases where you suspect, you have clinical suspicion of raising intracranial pressure of, you know, head trauma, traumatic injury, or those patients are present as a mentally obtunded. Maintain meaning arterial pressure and therefore our cerebral perfusion pressure, maintain normocapnia and maintain nor so hypothermia to ensure as good an outcome as possible. And then finally, to just to kind of summarise that the, the principles of analgesia and anaesthesia.
There are some similarities for both the spinal and the brain disease patients, but the spinal, the patient presenting with spinal disease, then I think kind of the pain is one of the main aspects that we should be focusing on and managing in an appropriate and effective way with those cases. And the brain disease patients are gonna really they're gonna be split into two aspects. Those patients who present with traumatic brain disease and those that present with intracranial disease that's not traumatic in origin.
But the principles of neuro anaesthesia for those will be very, very similar based on . Looking for and managing those secondary brain injury effects as a result of the, the primary injury. So, thank you for attending and listening to this webinar and.
Please send any questions through that come up that crop up as as you go through this session.