Anesthesia for Neurosurgery Flashcards
During all neurosurgery cases, how will the head be in relation to anesthesia?
90* away from you
How many fingers should you leave between the mandible and sternum and/or clavicle to ensure proper venous drainage?
2 fingers to avoid kinking of jugular veins
Generally speaking, the tube goes too deep or becomes too shallow after positioning?
Too deep
With C spine flexion, where does the tip of ETT migrate to?
Caudally, or towards carina
causes endobronchial intubation
With C spine extension and/or rotation, where does the tip of ETT migrate to?
Cranially
closer to the vocal chords so could extubate
What are some of the rules concerning blood loss in neurosurgery?
- Blood loss difficult to estimate
- - Can lose lots of blood during closing
With IV fluids in neurosurgery, what must be taken into account?
- -Minimal third spacing
- Minimal evaporation
- Only give enough to maintain cardiac stability
- Avoid hyperglycemia
- Avoid hyper/hypo natremia
What are the two main diuretics that are used to decrease the brain’s water content?
Mannitol
Lasix
Of the hyper and hypo natremia (which are things to avoid during neurosurgery) which is the detrimental to the patient?
Hyponatremia
(water movement in/out of the brain is controlled by Na shifts, hyponatremia causes large amounts to enter, thus resulting in brain edema)
The brain looks at what aspect of IV fluids to determine effect?
Osmolarity
brain does not care about the oncotic pressure of fluids
What is the normal value for osmolarity of human plasma?
295 mOsm / L
What is the IV fluid we give that is 273 mOsm / L ?
Lactated ringers
Normal saline has what osmolarity?
308 mOsm / L
20% mannitol has what osmolarity?
1098 mOsm / L
What is the IV fluid we give that is 290 mOsm / L ?
Albumin
Is brain tissue sensitive to pain?
NO
Because brain tissue is not sensitive to pain, when are the only times that anesthesia needs to be deep?
Opening and closing
Ideally, the patient needs to be fully awake and full consciousness how long after closing of tissue?
20-30 min
What is CBF?
Cerebral blood flow
CBF accounts for how much of CO?
20%
How much does average human brain weigh?
1500 grams
What is the average CBF of an adult?
40-50 ml/100gram/minute
What is known as critical CBF?
18 mL / 100 gm
What percentage of CBF does grey matter receive?
White matter?
G M: 80%
W M: 20%
What is the new target for EtCO2 ?
Low 30’s
Between what MAP values ensures the brain is adequately perfused?
50 - 150 mmHg
For the normal autoregulatory curve associated with MAP and CBF, what causes a right shift?
Choric hypertension
For the normal autoregulatory curve associated with MAP and CBF, what causes a left shift?
Vasodilators such as inhaled anesthetics
What 2 types of ischemia can occur in brain?
Global
Focal
What is known to cause global ischemia?
- Cardiac arrest
- Severe hypotension
- Hypoxia (normal BP but without O2
How is focal ischemia defined or described?
- Temporary or permanent
- - Partial or complete arterial obstruction
A stroke is a kind of what focal ischemia?
Permanent
A TIA is a kind of what focal ischemia?
Temporary
What is known to cause focal ischemia?
- Stenosis
- Vasospasm
- Embolus
- Clip
What is the best inhaled anesthetic because it decreases CMRO2 while not affecting CBF?
Isoflurane
Halothane used to be used as an inhaled anesthetic until it was found to have what effect?
Large increase in CBF that caused brain to become congested and full
What is the only IV drug given that decreases CMRO2 but increases CBF?
Ketamine
so do use this drug during brain surgery
When treating a hypertensive patient during neurosurgery, what is best drug to use?
Labetolol
When treating a hypertensive patient during neurosurgery, what 2 drugs do you not want to use?
Nitroglycerine
Nitroprusside
Both increase ICP - CBF ratio
What is ICP?
Intracranial pressure
What is a normal ICP?
10 - 15 mmHg
What is the reference point for measurement of ICP?
Tragus of ear
Moderately increased ICP is what?
20-40 mmHg
What is any ICP that is > 40 mmHg?
Severely increased ICP
What is the most aggressive and invasive way to measure ICP?
Ventriculostomy
What is the least aggressive means to measure ICP and is used with patients with coagulopathic disorders?
Subdural bolt
What to mechanisms regulate ICP?
- Shift of CSF from cranium to spinal cord
- - Shift of blood from cranium to spinal canal
What risks does an elevated ICP present?
- Decrease in CPP
- Herniation of brain tissue
- Inadequate exposure
- Retractor’s Ischemia
What is CPP?
Cerebral perfusion pressure
How is CPP determined?
CPP = MAP - ICP
Of the 4 most common sites for herniation, what is the most often occurring?
– number 4
herniation out of opened skull either from trauma or surgical removal
Of the 4 most common sites for herniation, what is the most deadly?
– number 3
Herniation of cerebellum
What is the main goal of ICP management?
Prevention of further increases in ICP
What is brain tissue called?
Parenchyma
What is brain tissue?
Parenchyma
What does parenchyma consist of?
- Brain cells and myelin
- Intracellular fluid
- Extracellular fluid
Which component of parenchyma responds well to steroids?
Extracellular fluid
What are the three main components of intracranial contents?
- Parenchyma
- Blood
- CSF
What are the 2 types of components of intracranial contents that respond and compensate to changes in pressure very quickly?
- Blood
- - CSF
An increase in intracellular fluids is due to what?
- Acute hyponatremia
- - Physical cellular damage
An increase in interstitial water (extracellular fluid) is due to what?
- Venous engorgement
- Hypertension
- Hypervolemia
What causes both intra and extra cellular fluid decreases?
- Diuretics (mannitol)
- Encouragement of venous drainage
- Decadron (only for tumors)
How does mannitol increase urine output?
Mannitol stays in the vasculature and is filtered by the kidneys so has no reuptake. This causes an increase in urine because filtered mannitol takes large volumes of fluid with it
T OR F? Cerebral blood flow and cerebral blood volume are not the same
TRUE
What is CBV?
Cerebral blood volume
What is normal CBV?
150 mL
75% of which is in venous system
What helps determine amount of venous drainage from the head?
- Gravity
- Head position
- Intra-thoracic pressure
Will ICP increase or decrease with jugular compression?
Increase
If you have a venous obstruction, what will happen in the acute setting?
An increase the CBV and subsequently will increase ICP (monitor closely)
If you have a venous obstruction, what will happen long term?
Increase edema which will lead to a decrease in CSF absorption to decrease ICP
What is the normal CSF?
75 - 100 mL
What are the basic principles concerning drugs used during neuroanesthesia?
- Want prompt recovery
- Minimal barbiturates
- Propofol good
- Short acting narcotics
- Moderate concentrations of inhalational anesthetics
- Avoid Succyinycholine in patients with hyperkalemia and recent strokes (because succ will increase ICP)
What are the other basic principles to follow besides drugs in neuroanesthesia?
- Proper positioning to encourage venous drainage
- Clear airway
- Proper use of muscle relaxants
- Proper IV Fluids
What is the cutoff to treat hyperglycemia?
nothing over 180
What are the goals for emergence ?
- No coughing
- No hypertension
- Prompt recovery and awakening
- Minimal hypercarbia
What would be some reasons for a neurosurgical patient to not wake up?
- SUrgical problems such as hemorrhage, tension pnemocephalus, seizures, strokes
- Hypercarbia ( Anything over 70)
What patients are not expected to wake up quickly?
- Acute subdural hematoma
- Closed head injury
- Surgery on frontal lobe
- Surgery around brain stem
Intracranial Aneurysms are what and occur most often where?
– Dilation of the blood vessel that tends to be located around bifurcation of arteries
– Are in 2% of population
What is SAH?
Sub arachnoid hemorrhage
when the aneurysm ruptures
What 2 detrimental outcomes are brought on by a SAH?
- Rebleeding
- - Vasospasm’s
What are optimal days you can operate on a SAH patient?
- 1 to 3 days after initial hemorrhage
- > 14 days after hemorrhage
(because of vasospasm likelihood, you cannot operate between 3-14 days)
What grading scale is used for classifying neurological status?
Hunt grading scale
1 = good
5 = Very bad
What hunt grades can you extubate the patient?
Hunt scales 1-2
What hunt grades are not extubatable?
Grades 4-5
What hunt grade allows practitioner to use judgement and clinical signs as to whether to extubate the patient or not?
Grade 3
What are some important pre-anesthetic evaluation things to remember for aneurysms?
- Hunt grade
- Number of aneurysms
- Vasospasms or not
- Hydrocephalus
- Serum sodium levels
There are 2 types of hyponatremia that could present, what are they?
– SIADH
– Cerebral Salt Wasting Syndrome
What is SIADH?
Hyponatremic state in which patient is making too much ADH which causes patient to retain fluid and dilute Na.
–Goal is to restrict fluids
What is Cerebral Salt Wasting Syndrome?
Hyponatremic state in which patient is secreting too much water and thus secreting Na.
– Goal is to give fluids
What type of monitors are needed for aneurysm clippings?
–ASA std
– 2 16g IVs
– A line
– CVP or SG catheter
(double lumen is better for giving fluids because has 2 14 gauges compared to the triple lumen which has 1 16g and 2 18g)
– Intra-op angiography
What is the one main thing you want to avoid in patients presenting for aneurysm repair?
HYPERTENSION
How much will a 1*C drop equate to loss in CBF?
5-7%
Focal ischemia will always occur during what clipping phase?
Placement of temporary clips
What do you want to give/do during a temporary clip placement?
- Hypertension
- CNS depressant
- Mild hypocarbia
Aneurysm ruptures occur in how many cases?
15-20%
What is the goal when an aneurysm ruptures?
- Keep up with blood loss
- Controlled hypotension
- Barbiturates (particularly propofol)
- Adenosine (to stop heart if surgeon cannot control bleeding and needs no flow for short period of time)
What things can we do to decrease O2 consumption of the brain to protect it?
- Induced hypothermia (~34*C)
- - Drugs (Isoflurane, Propofol)
What things can we do to increase focal blood flow of the brain to protect it?
- Hypertension
- - Hypocarbia
What is the 2nd leading cause of morbidity and mortality and has an incidence of 30 - 45%?
Vasospasm
What drugs are given to treat cerebral vasospasm?
- Nimodipine (Ca blocker)
- Mg. Sulfate
- Hypervolemia, Hypertension, Heamodilution after clipping
What is an alternative approach to aneurysm repair that is much less invasive and is done in Interventional radiology?
Thrombogenic wire placement
Coiling
Who are not candidates for the coiling procedure?
- Pt with wide neck aneurysm
- - Pt who has no access to neck of aneurysm
What is an AVM?
Arterio-venous malformation
Where are most AVM’s found?
90 % supratentorial
mostly in the cortex
What is AVM?
Where the arteries and veins are directly connected without having capillaries and capillary beds between them
What are some signs and symptoms of AVM?
- Headaches (number 1 symptom)
- Seizures
- Bleeding
- Focal ischemia
What are the courses of treatment for AVM?
- Embolization to make less bloody
- Followed by resection
– Gamma knife used for unresectable locations (uses targeted focused radiation to knock out AVM)
What are some general assumptions for AVM?
- Protracted and massive blood loss
- No vasospasm
- Bleeding occurs into parenchyma
- Hyperperfusion (b/c body must compensate for lack of area around resected AVM)
- Want to keep Blood pressure low post -op
- Want to have normal blood volume post -op
What are some general assumptions for aneurysms?
- Blood loss minimal unless rupture
- High incidence of vasospasm
- Bleeding occurs into sub arachnoid space
- No incidence of hyperperfusion
- Want to keep blood pressure high post -op
- Want to keep blood volume high post -op
