Neurosurgery overview Flashcards
Preoperative considerations for neurosurgery include
general assessment- access
normal preoperative evaluation- systems, airway, mobility
neurological assessment- LOC, reflexes, motor/sensory function, evaluate for s/s of increased ICP, document preexisting neurological deficits
Describe preoperative considerations for medications & monitoring.
medications- anticonvulsants (frequency & continue), premedications, antibiotics, diuretics, steroids
monitoring- arterial line & intraoperative neuro monitoring
The types of intraoperative neuromonitoring include
MEP
SSEP
EMG
Describe MEP
used in surgeries where motor tract is at risk
direct & scalp electrodes
more sensitive to ischemia than SSEP by 15 minutes and degree detection
difficult to obtain due to pre-existing conditions or anesthetic conditions
Describe SSEP.
most commonly monitored
stimulation of peripheral sensory nerve
mapping in spinal cord and sensory cortex
ischemia detection in cortical tissue
reduce risk of spinal cord/brainstem- mechanical or ischemic insults
-may use paralytic but it does monitor some motor
Describe EMG
records muscle electrical activity needle pairs- continuous recording, triggered responses
uses- detect nerve irritation, nerve mapping, assess nerve function, monitoring cranial nerves
Stereotactic neurosurgery applies rules of
geometry to radiologic images to allow for precise localization within the brain, providing up to 1 mm accuracy
Stereotactic neurosurgery allows surgeons to
perform certain intracranial procedures less invasively
Smaller brain biopsies may be done
under local/MAC
_____ needs to be used for larger brain resections
GETA
With stereotactic neurosurgery, radiologically small markers are affixed to the scalp and forehead with adhesive and it is important that
these fudicials do not move between the time of imaging and entry into the OR
once in the OR the patient’s head is appropriately positioned & the locations of the fudicials are entered into a computer
Medications commonly found in the crani bag include
cleviprex, mannitol, keppra, phenylephrine, precedex, epi
Drips commonly used in craniotomies include
propofol at 40-100 mcg/kg/min ABW- max 40 mg/kg/min for asleep motor mapping and awake craniotomy
phenylephrine at 0.2 mcg/kg/min
remifentanil @ 0.2 mcg/kg/min IBW- no real max if patient needs it due to low propofol dose
Describe common induction medications for craniotomies.
fentanyl, propofol, rocuronium
Antibiotics for craniotomies include
vancomycin & cefazolin
Analgesics for craniotomies include
tylenol
narcotic (hydromorphone or fentanyl)
Antiepileptics for craniotomies include
keppra 1 g & vimpat
Drugs that decrease ICP in the setting of craniotomies include
decadron- 10 mg
mannitol- 50-100 mg (actual dose 0.25-0.5 g/kg)
+/- lasix
Specific drugs used for awake cranies include
caffeine- adenosine receptor antagonist
physostigmine- anticholinesterase
Types of mass lesions include
congenital
neoplastic (benign vs. malignant)
infectious (abscess or cyst)
vascular (hematoma or arteriovenous malformation)
Typical presentation of intracranial mass lesions include
HA (50-60%) seizures (50-80%) focal neurological deficits (10-40%) sensory loss cognitive dysfunction
Supratentorial masses can be found in
frontal: personality changes, increased risk taking, difficulty speaking
parietal: sensory problems
temporal: problems with memory, speech, perception, and language skills
occipital: difficulty recognizing objects, an inability to identify colors, and trouble recognizing words
Infratentorial/Posterior fossa masses can affect
cerebellar dysfunction: ataxia/poor balance, nystagmus, dysarthria, cannot perform rapid alternating movements, loss of muscle coordination
brainstem compression: cranial nerve palsy, altered LOC, abnormal respiration
edema, obstructive at 4th ventricle
Primary tumors include
glial cells- astrocytoma, oligodendroglioma, glioblastoma
ependymal cells- ependymoma
supporting tissues- meningioma, schwannoma, choroidal papilloma
Major considerations for intracranial mass lesions include
tumor location- determines position, EBL, risk for hemodynamic changes intraoperatively
ICP elevated
Growth rate & size- slow growing tumors are often asymptomatic
Describe anesthetic goals for intracranial mass management
control ICP
maintain CPP
protect from position-related injuries
rapid emergence for neuro assessment
Describe monitoring for intracranial mass lesion
standard monitors
arterial line (zero based on positioning)
foley catheter
+/- central line
PNS: do not monitor on hemiplegic side b/c you may end up overdosing paralytics
+/- ventriculostomy for ICP monitoring (zero at external auditory meatus)
possible IONM monitoring
Describe positioning needs for intracranial mass lesions
anticipate turning HOB 90-180 degrees
ensure ability to access all vital equipment
adequate IV line extensions
long breathing circuit
PNS often on LEs
HOB elevated 10-15 degrees
pt may be supine, lateral, prone, or sitting
anticipate sympathetic response with placement of Mayfield head pins
Preoperative considerations for intracranial mass lesions include:
determine presence or absence of increased ICP
document LOC & neuro deficits
review PMHx and general health status
Review medication regime: pay special attention to anticonvulsants, diuretics
Review lab findings: glucose levels, anticonvulsant drug levels, electrolyte disturbances, H/H
review radiological studies: evidence of edema, midline shift, change in ventricular size
premedications: avoid benzodiazepines/narcotics in pt with increased ICP, continue corticosteroids & anticonvulsants
Describe maintenance for intraoperative mass lesions
no preferred anesthetic technique
hyperventilation (30)
avoid excessive PEEP (<10)
Describe fluid management for intraoperative mass lesions.
glucose free crystalloids or colloids
replace blood loss with blood/colloids
Describe ICP control for intraoperative mass lesions.
EVD/lumbar drain
increases in cerebral blood flow
Emergence for intraoperative mass lesions must be
slow & controlled- straining or bucking can cause ICH or worsen cerebral edema
aggressive BP management (SBP <140 or <160)- risk for hemorrhage or stroke- clevidipine, labetalol, esmolol
surgical team will do neuro exam immediately after extubation; prior to OR departure
Postoperative considerations for intracranial mass lesion
admit to ICU for observation transport with HOB elevated- 30 degrees manage hypertension O2 for transport minimal pain post craniotomy observe for seizures, neuro deficits, increased ICP
Describe an awake-awake craniotomy.
no infusions until closing
propofol or remi for pins
Describe an asleep-awake craniotomy.
start under GA with LMA/ETT (don’t get them back breathing)
wake the patient up once tumor is exposed
propofol drip 40 mcg/kg/min ABW
remifentanil drip 0.2-0.4 mcg/kg/min IBW
Describe an asleep craniotomy
TIVA-IONM, asleep motor mapping
GETA: no IONM
Awake craniotomies are used for
epilepsy surgery and resection of tumors in frontal lobes & temporal lobes when speech and motor are to be assessed intraoperatively
Patient considerations for awake craniotomies include
airway
temperature
anxiety
Additional considerations for awake craniotomies include
asleep with LMA for exposure
awake for cortical mapping & tumor resection
sedated for iMRI deployment- evaluate resection
when tumor resection complete use appropriate anesthetic to keep comfortable
Safety hazards for personnel in iMRI include
magnetic field strength
cold hazards
acoustic noises
Monteris medical “LITT” may be used to intervene for
epilepsy
glioblastomas
recurrent brain metastases
radiation necrosis
MR thermography uses
phase change to calculate real time temperature data at and around probe
thermal dose confirmed in real time using bio-thermodynamic theory
Describe what the white line, blue line, and yellow line
white line- vaporized
blue line- dead
yellow line recoverable
The contents of the posterior fossa include
cerebellum- movement and equilibrium
brainstem- autonomic nervous system, CV & respiratory centers, RAS, motor/sensory pathways
cranial nerves I-XII
large venous sinuses
Brainstem injuries can be a result of
bradycardia & hypertension-trigeminal nerve stimulation (Cushing’s reflex)
bradycardia & hypotension- glossopharyngeal or vagus nerve stimulation
respiratory centers may be damaged and necessitate mechanical ventilation postoperatively
tumors around glossopharyngeal and vagus nerves may impair gag reflex and increase risk of aspiration
cranial nerves IX, X, and XI control pharynx and larynx
Anesthetic considerations for posterior fossa surgery include
preoperatively- same considerations as those with intracranial lesions
positioning- may be sitting, modified lateral, or prone
Sitting position advantages include
improved surgical exposure- more anatomically "correct" less retraction and tissue damage less bleeding less cranial nerve damage better resection of the lesion access to airway, chest, extremities
Disadvantages relating to CV compromise as a result of the sitting position include
postural hypotension
arrhythmias
venous pooling
Describe nerve injuries related to the sitting position
ulnar compression-arms across abdomen, pad elbows
sciatic nerve stretch- pillow under knees
lateral peroneal compression- pad knees
brachial plexus stretch- pad under arms to support shoulders
Describe pneumocephalus related to the sitting position.
open dura–> CSF leak–> air enters
after dural closure, air can act as a mass lesion as CSF reaccumulates
usually resolves spontaneously
tension pneumocephalus- Burr holes to relieve
symptoms include delayed awakening, HA, lethargy, confusion
if using N2O, discontinue before dural closure
A venous air embolism occurs when
pressure in a vein is subatmospheric
level of incision is >5 cm higher than the heart
patients with PFO can have air enter arterial circulation
The incidence of venous air embolism is
potentially lethal
sitting position 25-50%
prone, lateral supine: 12%
Paradoxical air embolism is when
air enters left side of heart & travels to systemic circulation
occurs when right heart pressure is greater than left
common in patients with PFO
Signs & symptoms of venous air embolism include
decreased ETCO2 decreased PaCO2 decreased SaO2 spontaneous ventilation mill-wheel murmur detection of ET nitrogen increased PaCO2 hypotension dysrhythmias
Monitoring for VAE is through
capnography
CVP/PA line
precordial doppler
** do not rely on one monitor alone to diagnose VAE. use monitors with different sensitivities to confirm
Sensitivity for monitoring of VAE from most sensitive to least
TEE (5-10x more sensitive than doppler) precordial doppler ETCO2- decreases with 15-25 mL of air PAP- increased with 20-25 mL of air CVP PaCO2 MAP
Treatment for venous air embolism includes
100% O2, discontinue N2O
notify surgeon to flood field or pack wound
call for help
aspirate from CVP line (have stopcock close to insertion site, aspirate with 30-60 mL syringe)
volume load
inotropes/vasopressors
jugular vein compression
PEEP
position patient LLD with slight Trendelenburg
CPR if necessary
Craniocervical decompression is when
the cerebellum protrudes through foramen magnum- compresses brainstem and cervical spinal cord
types I-IV
syringomyelia
Anesthetic considerations for chiari malformation include
position- prone or sitting
EBL- large venous sinuses
vital sign instability due to brainstem manipulation
postoperative: pain management
