29 Anesthesia for the Patient with Neurologic Disease

Capnograph

What is the most important piece of equipment for neurologic patients?

Intracranial pressure, cerebral perfusion pressure, cerebral blood flow

What factors are important to remember in neurologic patients, for the fact that they deliver O2 to the nervous tissue?

Mean arterial pressure and intracranial pressure

(subtract MAP - ICP)

What two factors determine cerebral perfusion presure?

We are only able to control blood vessel MAP

note: intracranial pressure is the result of the additive effect of the 3 tissues mentioned

Cerebral perfusion pressure is important to maintain. Of the factors that play into it:

1. CSF volume

2. brain tissue volume

3. blood vessel MAP

Which are we able to control to decrease cerebral perfusion pressure?

CO2 is MORE important to maintain

WHY? because PaCO2 increasing rapidly also rapidly increases cerebral blood flow which ultimately increases intracranial pressure and brain compression

Which is MORE important to control for us to maintain cerebral pressure and blood flow, *O2 or CO2*? Why?

As CO2 goes up, there is a rapid increase of intracranial pressure due to increased cerebral blood flow. The opposite is true as CO2 goes down too far. But between these two numbers, cerebral blood flow is static around 50.

Why is it important to maintain PaCO2 around 50-150 mmHg? What happens above or below these points?

cerebral blood flow

What value is PaCO2 linearly related to?

Hypothermic

Is it better for a patient to be *hyperthermic or hypothermic* for cerebral blood flow?

Too much protein? Dehydration? --> blood won't flow as well because it is sludgey --> O2 won't get to brain as well

How does blood viscosity affect cerebral blood flow?

Increases intracranial pressure

What do seizures do to intracranial pressure?

Decrease

Overall, these drugs *increase or decrease* cerebral blood flow and intracranial pressure:

Benzodiazepines, alfaxalone, propofol

These drugs are tricky because they BOTH increase and decrease cerebral blood flow and intracranial pressure, it just depends on the amount and the scenario

Overall these drugs *increase or decrease* cerebral blood flow and intracranial pressure:

acepromazine, opioids, and ketamine

Acepromazine

Which drug do you have to be careful with because there is not reversal?

Increase

Overall these drugs *increase or decrease* cerebral blood flow and intracranial pressure:

vasopressors (NE/E), atipamazole, inhalant anesthetics with MAC over 1.0

Intracranial pressure increases --> too much pressure compresses vessels --> not enough blood can get to the brain causing decreased cerebral blood flow --> increases MAP to combat (hypertension) --> baroreceptors sense inc, cause bradycardia --> brainstem malfunctions as pressure increases = shallow breathing with occasional apnea (cheyne stokes)

Talk about the Cushing reflex:

1. increased BP

2. rapid bradycardia

3. shallow breathing with occasional apnea

What are the three parts of the cushing reflex triad?

This reflex is a sign of increasing intracranial pressure --> brain hernia and DEATH

*THIS IS AN EMERGENCY*

What is DIRE with the cushing reflex?

HYPERventilate the patient to ETCO2 of 30 mmHG

May also give hypertonic saline

note: remember hyperventilation decreases CO2

How do you treat the cushing reflex?

FALSE: do NOT discontinue meds abruptly around anesthesia = keep routine to prevent episodes

TRUE OR FALSE: You are going to need to get a detailed history of epileptic patients so you can make sure they are off their meds around the time of anesthesia

You do NOT want to reverse it = atipamazole

You can give dexmedetomine for a smoother induction with epileptic patients, but what you do have to keep in mind?

Acepromazine has either no effect or slightly lowers intracranial pressure. So, it seems beneficial but you have to be careful since it has a long duration of action and is NOT reversible

Should you use acepromazine in dogs with epilepsy? Why or why not?

GABA agonists (benzos, propofol, alfaxalone)

note: add ketamine to propofol for a great induction because ketamine adds analgesia and is cerebroprotective

What medications are typically included when anesthetizing an epileptic patient?

FALSE: do NOT withhold analgesia. many of them, like ketamine, may actually even improve neurologic outcomes of a TBI

TRUE OR FALSE: you should withhold analgesia from traumatic brain injury patients (concussive injury, fracture) because they are very likely to increase intracranial pressure.

Alfaxalone and propofol

What meds/anesthetics are frequently used for TBI patients because they are very rapid, titratable, decrease intracranial pressure making them cerebroprotective, and decrease seizure activity?

Fluids (avoid overload and vasogenic cerebral edema) and excessive intracranial vasoconstriction with vasopressors

What things should you be careful of/try to avoid with Traumatic brain injury?

MAP 70-80 to keep cerebral perfusion pressure around 60-70 mmHg

note: some literature says MAP over 90 may improve brain oxygenation in head trauma patients

What should you keep blood pressure around for traumatic brain injury patients?

Pupil asymmetry, under anesthesia may see cushing reflex (inc. bp, low hr)

What signs might you see with increased intracranial pressure and traumatic brain injury?

Hyperventilate patient to PaCO2 of 30 mmHg (this is the same for the cushing reflex)

How can you treat TBIs when intracranial pressure is increasing too much?

Hypothermia

Which is more common with small patients *hyper or hypothermia*

hyperthermia

Which is more common with long surgeries *hyper or hypothermia*

Atlantoaxial instability

This problem is common in yorkies, may cause acute death. be VERY CAREFUL at time of induction = *induction time has a great risk for these patients*, prexoygenate

Are often very weak after anesthesia, megaesophagus and dysphagia are huge risk factors so you have to watch out for aspiration pneumonia (extubate with ETT cuff partially inflated)

What risk factors do you need to keep in mind with neuromuscular disease patients and anesthesia?

Premedication

Opioids, benzodiazepines, acepromazine, and dexmedetomidine are all examples of what type of meds?

Induction agents

Propofol, alfaxalone, ketamine, and inhalant anesthetics are all examples of what type of meds?

Opioids, benzodiazepines

Name the RECOMMENDED premedications for neuro patients

Cardiovascular changes

Dexmedetomidine is a premedication. It doesn't have any significant effect on cerebral blood flow or intracranial pressure. So, what do you have to pay attention to?

Hydromorphone

Which opioid do you have to be careful of because it increases intracranial pressure since it causes vomiting?

Decrease

Benzodiazepines *increase or decrease* cerebral blood flow and intracranial pressure

Propofol and alfaxalone

What induction agents are recommended for neuro patients?

Propofol and alfaxalone

These induction agents are great because they decrease cerebral blood flow and intracranial pressure, but they also may cause respiratory depression and apnea

Propofol or alfaxalone

What other drugs do you commonly add ketamine to?

FALSE

TRUE OR FALSE: mask chamber inductions are recommended for neuro patients

under 1

What do you want the MAC of inhalant anesthetics iso and sevoflurane to be at for neuro patients?

Sevoflurane

Which is preferable for patients with raised intracranial pressure, *iso or sevoflurane*