Neuroanaesthesia Flashcards
Acute Spinal Cord Injury
American Spinal Injury (ASIA) Impairment Scale
Considerations
Goals
Conflicts
Acute Spinal Cord Injury
American Spinal Injury (ASIA) Impairment Scale
A: Complete: no motor or sensory function is preserved in the sacral segments S4-5
B: Sensory incomplete: sensory but not motor function is preserved below the neurologic level & includes the sacral segments (light touch or pin prick at S4-5 or deep anal pressure) AND no motor function is preserved more than three levels below the motor level on either side of the body
C: Motor incomplete: motor function is preserved below the neurologic level & more than half of key muscle functions below the neurologic level of injury have a muscle grade <3 (grades 0 to 2)
D: Motor incomplete: motor function is preserved below the neurologic level & at least half (half or more) of key muscle functions below the neurologic level of injury have a muscle grade ≥3
E: Normal: sensation & motor function are graded as normal in all segments & the patient had prior deficits
Considerations
Emergency trauma patient with C/T/L-spine injury:
ATLS approach to identify multisystem life threatening & occult injuries
Potentially difficult airway (full stomach, C-spine, uncooperative)
Hemodynamic instability: neurogenic +/- hypovolemic shock
Hypothermia, coagulopathy, acidosis
Intoxication
Additional injuries: traumatic brain injury (TBI) with ↑ intracranial pressure (ICP) in 25%
Need to prevent secondary spinal cord injury (keep MAP > 85-90)
C-spine precautions & airway protection
Potential for:
Diaphramatic paralysis (C3-C5)
Respiratory insufficiency with injury above T7
Neurogenic shock (hypotension & bradycardia)
Neurogenic pulmonary edema
Severe autonomic nervous system abnormalities
Hypothermia due to loss of thermoregulation
Hyperkalemic arrest with succinylcholine after 24 hrs
Goals
Avoid secondary spinal cord injury:
Spinal cord perfusion pressure: goal MAP > 85-90 (IV fluids, vasopressors)
Prevent hypoxemia, hypotension, hyperglycemia, hyperthermia
Immobilization during airway management & positioning
Manage complications of acute spinal cord injuries
Ventilatory & hemodynamic support as needed
Neurogenic shock:
Fluids/vasopressors
If bradycardic: atropine, external pacer, pharmacologic pacing (dopamine, isoproterenol)
Conflicts
Unstable c-spine, difficult airway +/- TBI (↑ ICP) vs potentially uncooperative patient
Aspiration risk (RSI) vs hemodynamic instability
Aneurysm Coiling
Considerations
Anaesthetic technique
Aneurysm Coiling
Considerations
Unfamiliar/remote environment:
Limited help & specialized tools
Potential prolonged patient transfers
Limited access to patient
Need for absolute immobility (muscle relaxant or remifentanil infusion)
Unsecured aneurysm:
Risk of rupture: need to avoid ↑ transmural pressure
Need to control hemodynamics: possible need for hypotension or sinus pause for coil placement
place external pacing/defibrillator pads
Complications:
Aneurysmal perforation/rupture
Cerebral ischemia due to misplaced coils, clots, vasospasm, dissection
Seizures
Contrast (anaphylactoid reactions, contrast-induced nephropathy, acute kidney injury)
Anesthetic Technique
Pre-induction arterial line is necessary
Maintain cerebral perfusion pressure (CPP) to prevent ischemia, but avoid ↑ transmural pressure to prevent aneurysm rupture
Maintain on sevoflurane & remifentanil OR propofol & remifentanil
Usually heparinized to ACT 2-3X normal
Arnold Chiari Malformation
Background
Considerations
Goals
Arnold Chiari Malformation
Background
Group of disorders that are defined by anatomic anomalies of the cerebellum, brainstem, and craniocervical junction, with downward displacement of the cerebellum, either alone or together with the lower medulla, into the spinal canal
Four major types (I-IV)
Considerations
↑ ICP/hydrocephalus
C1-2 instability, dens may impinge on brainstem
Association with meningomyelocele:
Hypovolemia (fluid & blood loss from defect)
Infection
Heat loss
If adult: risk with neuraxial from direct injury, herniation
↑ risk of latex allergy
↑ perioperative risk:
Brainstem dysfunction: stridor, apnea, aspiration
Autonomic instability: arrhythmias, bradycardia, labile BP
Seizures
Goals
Avoid ↑ ICP, maintain CPP
Avoid brainstem herniation
Latex-free environment
Rapid emergence for postoperative neurological examination
Autonomic Hyperreflexia
Background
Considerations
Management
Pregnancy Considerations
Autonomic Hyperreflexia
Background
Spinal cord injury above T6
Frequency variable: 20-70% of patients
Above lesion: reflex bradycardia & vasodilation (flushed)
Below lesion: unopposed sympathetic stimulation (vasoconstriction/hypertension)
Common clinical manifestations:
Headache, diaphoresis,↑ BP, bradycardia
Flushing, piloerection, blurred vision, nasal obstruction, anxiety, nausea
Consequences of event:
Bradycardia, AV block, PACs, PVCs
Severe headache, seizures, subarachnoid hemorrhage, ↓ level of consciousness
Dyspnea, LV failure, pulmonary edema
Blurred vision
Anxiety, agitation
Chest pain/myocardial ischemia
Considerations
Potential for hypertensive emergency with end-organ damage
Considerations of chronic SCI
Need for invasive monitoring
Difficult to assess success of neuraxial technique
Management
Discussion with surgeon regarding plan for procedure
Remove potential triggers (e.g., full bladder, foley insertion, full rectum, surgical stimulus)
General anesthetic vs neuraxial technique (if GA, consider a deep anesthetic)
Management of hypertensive event:
Consider deepening level of anesthesia if under GA
If epidural, consider top-up
Treat severe hypertension with fast-acting titratable agents:
Nitroprusside 0.5-3mcg/kg/min or nitroglycerin 5-200mcg/min
Hydralazine 10-20mg IV prn
Phentolamine 5mg IV prn
Look for evidence of end-organ involvement & treat accordingly
Pregnancy Considerations
Multidisciplinary discussion regarding plan for labor & delivery
Consider scheduled elective cesarean section
If vaginal delivery:
Admit early to monitored bed with telemetry
Need continuous BP monitoring with arterial line
Remove all preventable triggers of autonomic hyperreflexia (vaginal exams, full bladder = foley insertion)
Start early epidural to prevent hypertensive episodes from contractions
Difficult to assess success of epidural:
May need larger test dose to rule out subarachnoid placement
Chestnut suggests two ways to assess level of epidural
Sensory block cephalad to level of spinal cord lesion
Evaluating segmental reflexes below level of the lesion: lightly stroke each side of the abdomen above & below the umbilicus, looking for contraction of the abdominal muscles & deviation of the umbilicus toward the stimulus (reflexes are absent below the level of the block)
If cesarean delivery:
Either general anesthetic or neuraxial technique:
Must have arterial line
Vasodilators drawn up & ready
Succinylcholine contraindicated
Severe respiratory insufficiency or technical difficulties with neuraxial anesthesia may necessitate the use of general anesthesia
Craniotomy
Considerations
Goals
Conflicts
Craniotomy
Considerations
Limited airway access
Need to treat ↑ ICP & optimize surgical exposure
Maintenance of cerebral perfusion pressure (CPP):
Retractor pressure
Clipping/flow interruptions
Neuromonitoring
Smooth & crisp emergence for postoperative neurological assessment
Complications:
Venous air embolism
Hemorrhage
Arrhythmias & hemodynamic instability
Goals
Cerebral protection:
Minimize ↑ ICP
Maintain CPP
Neuroprotection: temperature, barbiturates
Minimize use of long acting sedatives to facilitate post-operative neurological evaluation
Facilitate intraoperative neurological monitoring
Conflicts
Full stomach vs. ↑ ICP
Difficult airway vs. ↑ ICP
Pituitary Surgery
Considerations
Goals
Pituitary Surgery
Considerations
Mass effects:
Neurologic impairment (bitemporal hemianopsia, cranial nerve palsies)
Potential ↑ ICP (rare, secondary to obstructive hydrocephalus)
Neurohormonal effects/endocrinopathies:
Non-functional adenomas
Hypersecretory tumors (60%):
Prolactin > GH > ACTH, TSH rare
Cushing’s, acromegaly
Endocrine deficiencies secondary to mass:
Hormone production impaired in the following order
GH, LH, FSH, TSH, ACTH, prolactin (“Go Look For The Adenoma Please”)
Panhypopituitarism
Surgical Issues/complications:
Shared airway
Head up positioning:
Poor patient & airway access
Bleeding into pharynx (coroner’s clot)
Venous air embolism
Systemic absorption of cocaine from mucosa → HTN, arrhythmias
Neurologic injury
Massive, difficult to access hemorrhage (cavernous sinus or carotid)
Post-operative endocrine dysfunction
CSF leak/meningitis risk
Diabetes insipidus
Rapid smooth emergence
Goals
Optimize perioperative endocrine function (stress dose steroids), consult endocrinology
Avoid further ↑ in ICP (if hydrocephalus)
Provide a still field for microscopic surgery
Minimize long acting sedatives (crisp emergence for neurological evaluation)
Controlled emergence (minimize bucking/coughing/vomiting to ↓ risk of bleeding and CSF leak)
Monitor for postoperative complications:
Diabetes insipidus (~40%)
SIADH (usually delayed)
Adrenal insufficiency & CV collapse (steroid coverage)
Bleeding → ↑ ICP, brainstem compression, cranial nerve dysfunction
CSF leak (risk of meningitis)
Hypothalamic injury
Cerebal ischemia
Stroke
Posterior Fossa Surgery
Background
Considerations
Goals
Posterior Fossa Surgery
Background
Posterior fossa contains: brainstem, cerebellum & cranial nerves IV to XII
Pathology requiring surgery usually includes: congenital lesions (e.g. Arnold-Chiari malformation), tumours, acoustic neuromas, vascular lesions
Considerations
Indication for procedure & status/complications of neurological disease (↑ ICP)
Considerations of patient positioning & potential complications (lateral, prone, sitting)
Anesthetic modifications for neuromonitoring: TIVA anesthesia, no paralysis
Facilitation of brain relaxation: TIVA, SjvO2 for titration, mannitol, hyperventilation
Complications:
Hemorrhage
Venous air embolism (VAE)
Hemodynamic instability from brainstem manipulation
Limited access to patient (foresight required in planning airway, access, monitoring)
Goals
Maintenance of CPP
Facilitation of neuromonitoring
Optimal brain relaxation for surgical exposure
Rapid & smooth emergence
Stable hemodynamics on emergence
Vigilance & monitoring for VAE if high risk position
Spina Bifida
Background
Considerations
Pregnancy
Spina Bifida
Background
Failure of the developing spine to completely enclose the neural elements in a bony canal
May be associated with Chiari II malformation
Spina bifida occulta:
Failed fusion of the neural arch without herniation of the meninges or neural elements
Defect limited to a single vertebra (typically L5 or S1)
Very common (5% to 36% of the population), can be considered a normal variant
Spina bifida cystica:
Failed closure of the neural arch with herniation of the meninges (i.e., meningocele) or the meninges & neural elements (i.e., myelomeningocele) through the vertebral defect
Myelomeningocele:
Progressive neurologic disease that eventually produces orthopedic, neurologic & genitourinary complications
Occult spinal dysraphism:
Intermediate group of conditions wherein the bony defect is associated with one or more anomalies of the spinal cord, including: intraspinal lipomas, dermal sinus tracts, dermoid cysts, fibrous bands & diastematomyelia (split cord)
These lesions are differentiated from the more benign spina bifida occulta
May have no neurologic symptoms or may have minor sensory, motor & functional deficits of the lower limbs, bowel & bladder; they also may have orthopedic issues, such as scoliosis, limb pain & lower extremity abnormalities
Patients with cord abnormalities have cutaneous stigmata in 50% of cases & 70% have tethered spinal cord
Considerations
Need for neuroimaging/detailed neurological history & physical exam prior to neuraxial anesthesia:
Look for hair tufts, dimples, hyperpigmented lesions, cutaneous lipomas over the spine & if present send for imaging prior to neuraxial or do GA only
CNS:
Hydrocephalus & risk of ↑ ICP, many have VP shunt
Flaccid paralysis usually high lumbar/low thoracic
Potential for autonomic hyperreflexia if lesion between T5-T8
Bowel & bladder control dysfunction
Respiratory:
Scoliosis with restrictive lung disease, risk of pulmonary hypertension/RV failure
Cardiovascular: possible congenital heart disease
↑ incidence of latex allergy
Pregnancy
Spina bifida occulta:
Neuraxial is generally safe
Recommend to insert needle remote from site of malformation seen on imaging
Patients are at higher risk of post dural puncture headache
Meningocele & myelomeningocele:
If spinal level involvement T11 or higher, likely will have painless labor
Epidural & spinal has been performed in literature, so NOT absolute contraindication but will be difficult & may be unreliable
May need epidural in situ to avoid autonomic hyperreflexia during labour
Spine Surgery
Considerations
Goals & Conflicts
Spine Surgery
Considerations
Surgical indication (instability, tumour, kyphoscoliosis, decompression/fusion, infection, congenital)
Potential for difficult airway with C-spine disease
Risk of blood loss, hypovolemic shock, massive transfusion → perioperative blood conservation strategies
Potential neurological deficits, spinal cord injury
Neuromonitoring considerations
Prone positioning complications:
Venous air embolism
Nerve injury
Postoperative visual loss
Airway swelling
Postoperative pain management
Patient considerations:
Trauma, malignancy, chronic pain, spinal shock, respiratory insufficiency
Scoliosis (lung disease, pulmonary hypertension, RV failure)
Goals & Conflicts
Careful airway assessment & management
Perioperative blood conservation:
Preoperative: iron, erythropoietin, preoperative autologous donation, correction of coagulopathy
Intraoperative: acute normovolemic hemodilution, cell saver, anti-fibrinolytics (tranexamic acid), surgical techniques, anesthetic techniques (patient positioning, normothermia, controlled hypotension)
Postoperative: transfusion targets
Anesthetic technique:
Neuromonitoring (TIVA, avoid neuromuscular blocking drugs)
Opioid sparing (ketamine, lidocaine, dexmedetomidine)
Careful securement of ETT, lines, monitors
Assessment for airway swelling prior to extubation
Subarachnoid Hemorrhage
Considerations
Goals
Conflicts
Pregnancy management of Acute Intracranial bleed
Subarachnoid Hemorrhage
Considerations
Emergency, full stomach
Unsecured aneurysm with potential for rebleeding:
Avoid hypertension & changes in transmural pressure
Potential massive hemorrhage
↑ ICP & prevent secondary injury:
Avoid cerebral ischemia: CPP 60-70/MAP 80-90 mmHg
↓ ICP
↓ CMRO2: barbiturate coma, burst suppression, mild hypothermia
Maintain euglycemia, normocapnia
Neurologic complications:
Rebleed
Cerebral vasospasm
Obstructive hydrocephalus
Seizures
Medical complications:
Neurogenic pulmonary edema
Myocardial dysfunction, arrhythmias
Electrolyte imbalances (hyponatremia due to cerebral salt wasting, SIADH)
Goals
Hemodynamic control & monitoring:
Minimize transmural pressure to avoid rebleed
Avoid acute hypertensive episodes (essential because rebleed is often fatal)
Keep SBP < 160 mmHg (AHA guideline 2012) & keep MAP > 85 mmHg (to prevent ischemia)
Facilitate surgical exposure/control ICP
Protect from secondary brain injury:
CPP 60-70/MAP 80-90 mmHg
↓ ICP
Normocapnia
↓ CMRO2: mild hypothermia, barbiturates, DHCA (deep hypothermic circulatory arrest)
Euglycemia: glucose < 11 mmol/L
Prevent vasospasm (nimodipine, pravastatin)
Conflicts
Aspiration risk (RSI) vs tight hemodynamic control to prevent rebleed/cerebral ischemia (titrated induction)
Minimize transmural pressure (deep induction to prevent rebleed) vs maintain CPP (hemodynamic support to prevent ischemia)
Pregnancy Management of Acute Intracranial Bleed
Decision to proceed with surgery:
If 3rd trimester (>32 weeks)
Consider simultaneous procedure, or cesarean section first followed by intracranial procedure
If pre-term viable (24-32weeks):
Do intracranial surgery, then wait for fetal maturity
Deliver if fetal distress
If pre-term non-viable (<24weeks):
Do intracranial surgery, then wait for fetal maturity
Induction:
Titrated to protect against rebleed vs secondary brain injury
Accept aspiration risk
Mannitol:
Risk of fetal dehydration
If tight head → give
If non urgent indication → discuss with neurosurgery, avoid if possible
PaCO2 management:
Maintain around 30 mmHg
Consider maintaining in high 20’s if tight head
Traumatic Brain Injury
Considerations
Neurosurgical considerations
Goals
Conflicts
Treatment of ↑ ICP
Traumatic Brain Injury
Considerations
Trauma/ATLS approach
Possible C-spine injury
Monitoring & managing ↑ ICP:
Risk of cerebral ischemia & brain herniation
Prevention of secondary brain injury:
Avoid hypoxia, hypercarbia
Maintain adequate CPP (60-70)
Avoid hyperglycemia, hyperthermia
Multisystem complications:
CNS: herniation, seizures
CVS: myocardial dysfunction and ST changes, arrhythmias
Pulmonary: neurogenic pulmonary edema
DIC (disseminated intravascular coagulopathy)
DI (diabetes insipidus), SIADH (syndrome of inappropriate ADH), CSW (cerebral salt wasting)
Neurosurgical Considerations
Limited airway access
Optimization of surgical exposure
Invasive monitoring
Complications:
Venous air embolism
Hemorrhage
Arrhythmias and hemodynamic instability
Goals
Assess severity of TBI
Prevent secondary brain injury:
Hypoxia (PaO2 > 60 mmHg)
Hypercarbia (PaCO2 35mmHg)
Hypotension, maintain CPP ~ 60 mmHg (MAP ~ 80)
Avoid abrupt ↑ in BP & ICP (< 20-25mmHg)
Avoid hyperthermia & hyperglycemia
C-spine precautions
Hct > 30
Conflicts
Full stomach vs. ↑ ICP
Hemorrhage/hypovolemia vs. ↑ ICP
Difficult airway vs. ↑ ICP
Treatment of ↑ ICP
Elevate HOB
Loosen collars, ETT ties to promote venous drainage
Decrease intrathoracic pressures (change ventilator settings, decrease PEEP)
Hyperventilation to PaCO2 30 for a brief period only of ~30 min
Sedate
Analgesia
Paralysis
Barbiturate coma (1-5 mg/kg sodium thiopental then 1-3 mg/kg/hr)
Hypothermia (or at least normothermia)
Mannitol (0.5-1 g/kg)
Furosemide (0.25-0.5 mg/kg)
Hypertonic saline 6-8 ml/kg of 3% saline
Correct sodium and osmolality
CSF drainage
Surgical decompression (head, abdomen)
