Ex 3 - AC for neuro patients Flashcards
Intra-Cranial Pressure (ICP)
The pressure exerted by the fluids and tissues inside on the the fixed compartment of the cranium.
What four parts make up the fluids and tissues inside the cranium?
Blood, CSF, tissue or cells (both brain and otherwise), and ECF (i.e. edema)
CNS (Cerebral) Metabolic Rate
CMR
This refers to the rate of substrate utilization by the CNS tissue.
Substrates include: O2 and glucose, or any other molecules necessary for brain fxn.
CNS (Cerebral) Blood Flow (CBF)
The amount of blood being delivered to the cells and tissues w/in the cranium.
This varies depending on CMR, blood gases, blood viscosity, MAP, and anesthetic drugs
Cerebral Perfusion Pressure (CPP)
The intravascular pressure minus the pressure in the surrounding tissues, generally given the following formulas:
CPP = MAP - ICP
The body will attempt to regulate the CPP to maintain appropriate delivery of O2 and other metabolic substrates to the tissues within the cranium
What are some signs of ICP?
- Papilledema (optic nerve swelling)
- Anisocoria (unequal size of pupil) or dilated and fixed pupils
- Strabismus (misalignment of the eyes)
- Depressed mentation
- Abnormal respiratory pattern
- Opisthotonus (arching as in tetanus)
- Bradycardia and hypertension (Cushing’s reflex - late marker of ICP)
Is it better to prevent ICP or treat ICP?
Better to prevent
What are some measure for prevention of ICP?
- Maintain low normal PaCO2 (30-35mmHg)
- Prevent significant hypoxemia
- Maintain adequate MAP
- Prevent significant alterations in acid-base status
How can you treat ICP?
Mannitol or furosemide
Why should you avoid administration of large volume of crystalloids?
75-90% of the crystalloid volume will be extravasated w/in the first hour after administration, and this increase in interstitial and cellular fluid will also be w/in the tissue inside the cranium.
Instead, you should give colloids and/or blood products –> these remain in the vascular for longer periods of time
How should the patients head be positioned?
above the heart!
If the head is below the level of the heart this can cause venous congestion.
Hyperglycemia in neuro patients
Hyperglycemia is common –> blood glucose should be monitored
What role does BP play?
Hypertension –> increased CBF and thus ICP
Hypotension –> decreased CPP
What role does hyperthermia play?
Increases CMR
hypothermia may be useful to decrease CMR, but severe hypothermia should be avoided <95 degrees
Which drugs decrease both CBF and CMR?
Barbituates, benson, propofol, etomidate, and opioids (to varying degrees)
*respiratory depression w/opioids should be monitored/treated to prevent rises in PaCO2 and rise in CBF
What is the effect of a2 agonists on CMR and CBF?
They also decrease both CMR and CBF, but the significant decrease in CO and peripheral vasoconstriction makes them contraindicated in these patients.
Ketamine
In clinically useful doses, there are small decreases in CBF but much larger INCREASES in CMR
(increases ICP)
Very small doses are controversial, as they may provide some neuroprotective benefit but at a risk for inc ICP
IA - effect on CMR and CBF?
At levels above 1 MAC, CBF will increase –> increase ICP in dose-dependent fashion
*Best to use IA in a balanced anesthetic protocol (so <1MAC doses are used)
What about Propofol?
Can be used to maintain anesthesia, either as an adjunct to IA or as part of a balanced total IV anesthetic protocol.
Propofol preserves CBF/CMR coupling, so is a good choice
What is the most common imaging modality for spinal cord?
MRI
Followed by:
CT, pyelography, rads, and fluoroscopy
Why are patients with spinal pathology often dehydrated?
Even in seemingly acute situations?
They are often very painful and thus don’t eat/drink normally
*malnutrition and electrolyte imbalances are also possible, but less common
How would you treat post-myelopgraphy seizures?
Benzodiazepine or propofol
What is a major concern of PNS surgery?
PAIN management!
The use of local and/or regional analgesia is appropriate in all cases, and in combo with systemic analgesics such as opioids, a2 agonists, ketamine, lidocaine, and others will help prevent significant post-procedural pain.
Which drug prevents wind up?
Ketamine! NMDA antagonist
