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Anesthesia Principles: Cerebral Aneurysm
Anesthetic management of the patient with Cerebral Aneurysms
100
Medical
Graduate
06/12/2010

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Term
How much oxygen does the brain uptake at rest?
Definition
20%
Term
What is the CMRO2 of the brain?
Definition
3.54mL/100g/min
Term
How quickly are oxygen stores depleted in the brain?
Definition
*Less than 10 seconds
Term
At what O2 level will unconsciousness occur?
Definition
PaO2 <30mmHg
Term
How quickly are ATP stores depleted?
Definition
*5-8 minutes
Term
What is normal Cerebral blood flow?
Definition

*50mL/100g/min

*750mL/min or 15-20% of cardiac output

Term
When can impairment occur with CBF changes?
Definition

*15-20mL/100g/min= Impairment

*6-15mL/100g/min= isoelectric EEG

*<6mL/100g/min= neuronal death

 

Term
How are cerebral blood flow and CMRO2 related?
Definition
*They are coupled.  Regional blood flow and metabolic rate of the brain can change dramatically; when metabolic rate goes up in a region of the brain, the blood flow to that region also increases
Term
What is the formula for cerebral perfusion pressure?
Definition
*CPP=MAP-ICP (CVP)
Term

What is a normal CPP?

Where are neurological changes seen with decreases in CPP?

Definition

*80-100mmHg

*50mmHg is acceptable low

*<50mmHg slowing EEG

*25-50mmHg flat EEG

*<25mmHg brain damage

Term
Changes in what significantly affects CPP?
Definition
*Changes in ICP >30mmHg significantly compromises CPP
Term
What is autoregulation in the context of the brain?
Definition
*The brain's ability to tolerate swings in MAP with little changes in CBF
Term
Where does CBF become pressure dependent as defined by the autoregulation curve?
Definition
*Below 50mmHg or above 150mmHg
Term
What is the Y-axis in the autoregulation curve?
Definition
*mL/100g/min normal= 50mL
Term
What is the X-axis in the autoregulation curve?
Definition
*MAP in mmHg
Term
If in an appropriate range, what parameters will autoregulation maintain?
Definition

*Keeps CMRO2 between 3-5mL O2/100gm/min

*Maintains cerebral blood flow at 50mL/100gm/min (15-20% of CO)

*Keeps cerebral perfusion pressure approximately 80-100mmHg

Term
What is the most potent extrinsic determinant of CBF?
Definition
*PaCO2
Term
How quickly can changes in PaCO2 be reflected in CBF?
Definition
*within 30 seconds
Term
How much does CBF change for a change in PaCO2?
Definition
*CBF changes 1-2mL/100g/min for every 1mm/Hg increase or decrease in CO2
Term
Define luxury flow.  Is this good or bad?
Definition

*Luxury flow is caused by high CO2 levels throughout the brain could steal blood flow from areas that require extra oxygen and produce metabolites.

*Bad

Term
Define Inverse Steal (Robin hood).  Is this good or bad?
Definition

*Cause by deliberate hyperventilation leading to hypocapnea; cerebral vasoconstriction and improved blood flow to ischemic areas

*Gets more blood flow to all areas not just dilated areas, good effect

Term
How does hypothermia and hyperthermia effect CBF?
Definition

*Hypothermia vasoconstricts and decreases CBF by 57% for each 1 degree celcius

*Hyperthermia vasodilates and increases CBF by 5-7% for each 1 degree celcius

Term

Describe the make up of the blood brain barrier.

Which substances are permeable and which are impermeable?

Definition

*BBB are vascular endothelial cells made up of tight junctions.  This type of lipid barrier allows for the selective passive of molecules

*Permeable substances: oxygen, carbon dioxide, water, and lipid soluble molecules like anesthetic agents.

*Impermeable solutions are proteins, ionic compounds and high molecular weight substances such as Mannitol

Term
List some examples of what can disrupt the BBB.
Definition

*Severe HTN

*Tumor

*Trauma

*Stroke

*Infection

*Hypoxia

*Hypercapnea

*Sustained Seizure

Term
How do the gradients change once the BBB is disrupted?
Definition
*The membrane changes from an osmotic to a hydrostatic gradient.
Term
Where do cerebral aneurysms predominately occur?
Definition
*At a branch of a large cerebral artery where they balloon out by a thin neck (d/t turbulent flow)
Term
Where in the brain do aneurysms most commonly occur?
Definition
*Commonly located in the base of the brain in the anterior Circle of Willis
Term
Although aneurysms can form in many shapes, which shape is the most common?
Definition
*Saccular (berry aneurysm)
Term
After the age of forty who is affected more by aneurysms? At what age are individuals most commonly dx with an aneurysm?
Definition

*Women

*40-60

Term
Most often, what is the cause of aneurysm formation?
Definition
*From a congential, or developmental defect in the tunica media adn adventitia of a vessel wall.
Term
What are some causes of aneurysm formation?
Definition

*Congenital/developmental defect

*Brain trauma

*Infection

*Atherosclerosis

*Abnormal rapid cell growth (neoplastic disease)

*Certain rare diseases of the connective tissue: 

-Marfan's Syndrome

-Psuedoxanthoma Elasticum

-Ehlers-Danlos Syndrome

-Fibromuscluar dysplasia

-Polycystic Kidney Disease

Term
What increases the risk of rupture?
Definition

*Increased risk is caused by an increase in the transmural pressure (TMP) inside the aneurysm.

*Transmural pressure is the difference between the MAP and the ICP.  A liner relationship exists, any significant change that increases the difference can lead to rupture. (increase in MAP or decrease in ICP).

Term
What are some other risks for rupture?
Definition

*Increase in transmural pressure

*Aneurysm size 2.5cm or larger in diameter although smaller aneurysms also rupture

*Cigarette smoking

*Excessive alcohol consumption

*Recreational drug use

Term
What are some symptoms of a cerebral aneurysm?
Definition

*Pupil dilation

*Drooping eyelid

*Pain above or behind the eye

*Headache

*unsteady gait

*a temporary problem with sight

*Double vision

*numbness in the face

*Photophobia

Term
90% of aneurysms are detected following rupture.  What symptoms present with a ruptured cerebral aneurysm?
Definition

*Sudden, extremely severe headache typically described as the worst headache of the victims life

*N/V

*Short loss of consciousness or prolonged coma

*25% experience specific neurological problems linked to specific areas of the brain

*Hydrocephalus (d/t decreased CSF absorption in arachnoid villi)

*Seizure

Term
What are some complications of ICH?
Definition

*Intracranial HTN

*Rebleed

*Vasospasm

*Hydrocephalus

Term
How are cerebral aneurysms diagnosed?
Definition

*H&P

*CT, MRI

*LP

*Angiography

*

Term
How are cerebral aneurysms graded?
Definition
*Hunt and Hess Classification of Patients with subarachnoid hemorrhage
Term
Describe the Hunt and Hess scale
Definition

*Grade O: Unruptured aneurysm

*Grade I: Asymptomatic, or minimal headache and slight nuchal rigidity

*Grade II: Moderate to severe headache, nuchal rigidity, no neurologic deficit other than cranial nerve palsy

*Grade III: Drowsiness, confusion, or mild focal deficit

*Grade IV: Stupor, moderate to severe hemiparesis, early decerebration, vegetative disturbance

*Grade V: Deep coma, decerebrate rigidity, moribund 

 

Term
What is the goal of emergency treatment of a cerebral aneurysm?
Definition

*Early diagnosis

*Airway management d/t disordered breathing that can occur from cerebral compromise

*Control of ICP

*Hemodynamic stabilization

Term
After identification, how is a cerebral aneurysm medically managed?
Definition

*Seizure prophylaxis (Dilantin, Phenobarbital)

*Intubation

*Mannitol

*Corticosteroids (Decadron)

*Beta Blockers

*Ca Channel blockers (Nimodipine)

*Early surgical intervention following a major rupture ahd been found to improve outcome

Term
What are the advantages of early surgical intervention of a cerebral aneurysm (less than 72 hours from bleed)?
Definition

*Less change of rebleed

*Removal of subarachnoid blood

*Secure aneurysm

*Less bed rest with associated complications (earlier mobility)

Term
What are the disadvantages of early surgical intervention of a cerebral aneurysm?
Definition

*Operating on a freshly injured brain with impaired autoregulation (often why surgery is delayed)

*May not have a good H&P and subsequently may not be as "tuned-up" as they could be for surgery

Term
What are the advantages of delayed surgical intervention for a cerebral aneurysm (10-14 days)?
Definition

*Recovery from SAH

*Vasospasm resolved

*Co morbidities can be identified and managed

Term
What are the outcomes comparing early and late surgical intervention?
Definition
*Overall outcome found to be similar 6 months after surgery.
Term
What is cerebral vasospasm, why does it occur, and what are the symptoms caused by?
Definition

*Cerebral vasospasm is the spasm of affected or associated arteries close to the rupture site.

*Believed to be caused by the oxyhemoglobin portion of blood

*Symptoms are caused by cerebral ischemia and infarction

Term
What is the incidence and when does cerebral vasospasm occur?
Definition

*Occurs in 30% of patients

*4-14 days after bleed

Term
What are the symptoms of cerebral vasospasm?
Definition

*Change in LOC

*Hemodynamic instability (HTN)

*Lethargy

*Coma

Term
What is the prevention and treatment of cerebral vasospasm?
Definition

*Prevention is taking Nimodipine (a CCB).  Nimodipine is not effective in treating a vasospasm

*Treatment with triple H therapy (Goal is to treat ischemia with an increase in CPP)

*Hypertension (pressors if needed)

*Hemodilution (33% hematocrit)

*Hypervolemia volume expansion with

-Crystalloids 0.9NS (avoid dextrose and LR)

-Colloids

-Aim for PAWP of 12-18 and

-CVP 10-12

Term
What are important things to assess in a patient undergoing an aneurysm clipping preop?
Definition

*Thorough neurological assessment

*Identify and document neurological deficits

*Hung and Hess classification of SAH

*Identify coexisting diseases that may be aggravated by induced hyper/hypotension (Ex: carotid stenosis)

*Other Co Morbidities (CVA, DM, Respiratory impairments)

*EKG (Arrhythmias are common with elevated ICP, SAH)

*Electrolyte abnormalities (D/t diuretic administration, volume status)

 

Term
What are some measures that can lead to hypokalemia in the pt undergoing a cerebral aneurysm clipping?
Definition

*Diuresis

*Hyperventilation

Term
What should be avoided preoperatively?
Definition
*Limit sedation to avoid hypercapnea, or obscure deterioration in condition
Term

What are some important preoperative considerations for the patient undergoing a cerebral aneurysm clipping?

Definition

*Line placed in Preop as patient tolerates, may need to postpone until after induction for CVP/PA cath.

*Best to have arterial line for induction

*2 large bore IVs

*T&C 2 units PRBCs

*Prepare to be far away from the head of the patient

-Long circuit

-IV extensions

-Plenty of body padding

Term
What should the anesthetist prepare for immediately following induction?
Definition

*A massive adrenergic response to intubation stimulus, followed by a long non stimulating shave/prep time

 

Term
Where should the BP be maintained post induction, HR?
Definition

*BP should be 15-20% below baseline

*Avoid tachycardia

Term
What is the induction agent of choice?
Definition

*Pentothol 3-5mg/kg

*Propofol however is an appropriate choice 2-3mg/kg (being used as first choice d/t pentothol shortage)

Term
When should a second dose of induction agent and narcotic be administered?
Definition
*For mayfield tong placement
Term
What are acceptable choices for NDMR?  What should be avoided and why?
Definition

*Vecuronium 

*Pancuronium if HR stable

*Succinylcholine should be avoided due to increased ICP associated with its use.  Precurarize if necessary.

Term
Why does succinylcholine increase ICP?
Definition
*Arousal phenomenon.  Transient increase in CBF attenuated by STP (or induction agent), Precurare
Term
What vasoactive agents can be used to decrease blood pressure?
Definition

*Short acting beta blocker- Esmolol 0.5mg/kg

*Nicardipine 0.5-1.0mg boluses to effect

Term
What agents are used to blunt laryngoscopy?
Definition

*Lidocaine 1.0-1.5mg/kg

* Opioids (Fentanyl 7-10mcg/kg front-loaded to blunt effects of laryngoscopy)

-Sufenta bolus of 0.5-1.0mcg/kg/hr throughout case. 

Term
What should be used for intraoperative monitoring?
Definition

*Foley catheter

*CVP 

-To treat VAE, monitor fluid status

*Pulmonary artery catheter

*Arterial line

*Precordial dopplar (2nd-3rd ICS righ of the sternum)

*PNS

*Temperature with warming modalities

Term

What inhalational agent should be used for maintenance and why?

Definition

*Isoflurane 0.7-1.0% (around a MAC).  Iso is shown to provide slightly more decrease in CMRO2 with less cerebral vasodilation than the others 

Term
At what %ET of isoflurane will a patient wake up?
Definition
*Around 0.28-0.27
Term
What should a maintenance of propofol infusion run at and why is it utilized?  How does it compare to Pentothol?
Definition

*75-100mcg/kg/min

*To decrease CMRO2, cerebral blood volume and metabolism

*Similar to barbiturates but not as cerebroprotective

Term
If there will be temporary occlusion of a cerebral artery, what should be used for cerebral protection?
Definition
*STP drip 20-30mg/kg over 2 hours if brain protection is necessary.
Term
How does Etomidate compare to STP?  Any differences?
Definition

*Offers cerebral effects similar to barbiturates but to a lesser degree.

*Offers hemodynamic stability

Term
What NDMRs are a good choice for cerebral aneurysm clipping?
Definition

*NDMRs do not cross BBB

*Vec, Pav, Roc are a safe choice (lack histamine release)

Term
Why is BP maintained 15-20% below baseline? 
Definition

*To prevent vasospasm

*Decrease EBL

*Allow for surgical exposure and visualization

Term
Where should PaCO2 be kept?
Definition
*Mild hyperventilation to produce a mild hypocapnea of 25-30mmHg (closer to 30)
Term
How can PaCO2 be managed?
Definition
*By changing respiratory rate
Term
Below what PaCO2 can cause significant cerebral ischemia?
Definition
*PaCO2 below 22mmHg
Term
What can be given for slack brain?
Definition

*Mannitol 1gm/kg

*Loop diuretics Lasix 0.5mg/kg

Term
What can be used as an infusion intraop to keep BP 15-20% below baseline?
Definition

*Nitroprusside

*NTG

Term
When might surgeon ask for a temporary increase in blood pressure?
Definition

*May ask for temporary increase in MAP to 80-100mmHg if a feeder vessel is clamped for a short period to allow for clipping of aneurysm

*Increased MAP during clipping will increase tributary perfusion

Term
What should be used to provide a brief increase in MAP without dysrhythmias?
Definition
Phenylephrine
Term
What will mild hypothermia do for the brain?
Definition

*Mild hypothermia around 33 degrees will

-Decrease CMRO2

-Brain size

-increase the brain's ability to tolerate ischemia

Term
How much will 1 degree Celsius increase or decrease CMRO2?
Definition

*1 degree decrease will decrease CMRO2  7%

 

Term
How much fluid should be administered during anesthesia for a cerebral aneurysm clipping?
Definition

*4-5mL/kg/hr plus losses (urine and blood)

*Fluids must be given to avoid further hypovolemia and hypotension, sudden boluses should be avoided

 

Term
Why does relative hypovolemia usually result in the patient undergoing a cerebral aneurysm clipping?
Definition
*Volume depletion from overnight fasting and volume redistribution from vasodilation of anesthetic agents result in relative hypovolemia.
Term
What may occur after brain is exposed regarding fluid status?
Definition
*Increases in intravascular volume may cause swellin gof normal brain, which the surgeon is attempting to retract.
Term
Why should isosmolar fluid be chosen for the patient undergoing a cerebral aneurysm clipping and glucose containing fluids be avoided?
Definition

*Glucose, which increases osmolarity, has a large volume of distribution pysiologically, and glucose- containing fluids are hypotonic and very likely to cause brain edema in regions where the blood brain barrier is impaired.  

*Glucose at the time of neurologic insult correlates strongly with a poor outcome.

Term
What is the most common complication of Cerebral Aneurysm Clipping?  What is closely correlated with this complication? 
Definition

*Vasospasm

*The amount of blood in the subarachnoid space and the extent of vessel narrowing are closely correlated.

Term
When vasospasm occurs post op, what therapy should be used?  What is used for prevention?
Definition

*Triple H 

-Hypertension

-Hemodilution (33% Hct)

-Hypervolemia

*Nimodopine (CCB)

Term
What is the time frame that a rebleed occurs after cerebral aneurysm clipping?
Definition
*Most often in the first 24 hours post op
Term
What diagnostic test is often done before transfer from the OR if complications are suspected?  What drugs should you take?
Definition

*CT

*STP, airway management tools, resuscitation drugs

Term
What is a treatment alternative for cerebral aneurysm coiling?  What is the goal of treatment?
Definition

*Endovascular Therapy (Guglieimi Detachable Coil- GDC)

*Goal of treatment is to prevent the flow of blood into the aneurysm sack by filling the aneurysm with coils and thrombus. Interruption of flow will prevent rupture.

Term
What is the procedure of a cerebral aneurysm coiling?
Definition

*A standard cerebral arteriogram is performed to locate the aneurysm

*Another catheter is passed though the first up to the aneurysm neck.

*A platinum coil is advanced into the aneurysm and coils until the aneurysm is completely occluded

*Low voltage is passed into the tip of the coil to release it into the aneurysm

*A post procedure arteriogram is completed to verify complete occlusion of the aneurysm. 

Term
What are the advantages of endovascular therapy?
Definition

*Shorter hospital stay

*Less anesthetic requirements

*Fewer surgical complications, minimally invasive

*Uncomplicated positioning, supine without external fixation of head (head fixed with tape instead of tongs)

Term
What are the disadvantages of cerebral aneurysm clipping?
Definition

*Aneurysm rupture

*Vasospasm

*Stroke

*SAH

*Supture

*Reexpansion of original aneurysm

*Incomplete coiling requiring more coil to be placed

*Long-term follow up of aneurysm is suggested at this time.  (The aneurysm is not clipped so there is a chance of expansion or bleed).

Term
What are the anesthetic implications of cerebral aneurysm clipping?
Definition

*GA with complete muscle paralysis to allow for a completely still patient

*minimal narcotic, painless procedure requiring fast wake up and assessment

*Short duration 2-3 hours

*Arterial line perfered

*Induction and emergence same as clipping

*Isoflurane/NDMR maintenance (need to be completely still)

*Minimal to no blood loss

*Heparin may be used (ACT 200-250)

Term
Which has less risk traditional craniotomy cerebral aneurysm clipping or an endovascular coiling?
Definition
Endovascular coiling
Term
What is Arteriovenous Malformation?
Definition
*An AVM is a congenital abnormality that involves a direct connection form an artery to a vein devoid of a pressure modulating capillary bed.  This irregular resistance to the cerebral vasculature leads to ischemia surrounding brain tissue and high risk of SAH or intracerebral hemorrhage.
Term
What is the treatment for AVM?
Definition

*Intravascular embolization alone or followed by surgical excision

*Surgical excision

*Radiation

 

Term

Who is more at risk for AVM?

Definition

*Males>Females

*Present at any age but bleeding most common in age 10-30

*Usually healthy without comorbidities 

 

Term
Why should fluid volume status be considered in the angiography suite for a AVM?
Definition
*Related to dye load and mannitol administration in angiography suite
Term
Is there potential for blood loss with an AVM surgery?
Definition
*Yes, more potential for significant blood loss 
Term
What does loss of autoregulation in the pt with an AVM cause at the site of injury and excision? How is this controlled?
Definition

*Loss of cerebral autoregulation leading to hyperemia and swelling.

*Tight hemodynamic control

*Beta blockers, SNP, NTG, Phenylephrine

Term
What are the post op complications of AVM sugery?
Definition

*Neurological deficits

*Cerebral edema 

*Increased ICP

*Intracerebral hemorrhage

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