Unit 7 - Neuro - Musculoskeletal Flashcards
patho of myasthenia gravis
Autoimmune destruction of post-junctional, nicotinic ACh receptors at NMJ via IgG
how does myasthenia gravis manifest
skeletal muscle weakness
Key: skeletal muscle weakness becomes worse later in the day
surgery that can relieve myasthenia gravis symptoms
thymectomy
↓ circulating Anti-AChR IgG in most patients
earliest signs of myasthenia gravis
diploplia, ptosis
how does bulbar muscle weakness manifest in myasthenia gravis
dysphagia, dysarthria, difficulty handling saliva
5 things that exacerbate myasthenia gravis symptoms
- pregnancy
- infection
- electrolyte abnormalities
- surgical/psychological stress
- aminoglycoside antibiotics
why might neonates of moms with myasthenia gravis require airway management
Anti-AChR IgG antibodies cross placenta & cause weakness in 15-20% of neonates for 2-4 weeks
1st line treatment of myasthenia gravis
PO pyridostigmine
what is the Tensilon test
To differentiate pyridostigmine overdose vs. myasthenic crisis, admin. edrophonium 1-2 mg IV
If muscle strength improves, pt had myasthenic crisis
immunosuppressants used in treatment of myasthenia gravis
- corticosteroids
- cyclosporine
- azathioprine
- mycophenolate
use of plasmapheresis in myasthenia gravis
temporary relief during myasthenic crisis or before thymectomy
how do pts with myasthenia gravis react to NMBs
Pts have fewer Nm receptors at NMJ
* Increased sensitivity to NDNMBs (reduce dose by 1/3 to 2/3)
* Decreased sensitivity to succs (also d/t impaired efficacy of pseudocholinesterase on pyridostigmine - 1.5-2 mg/kg for RSI)
how do pts with myasthenia gravis react to NMBs
- Increased sensitivity to NDNMBs (reduce dose by 1/3 to 2/3)
- Decreased sensitivity to succs d/t impaired efficacy of pseudocholinesterase on pyridostigmine (1.5-2 mg/kg for RSI)
Pts have fewer Nm receptors at NMJ
Increased risk for postop mechanical ventilation in myasthenia gravis pts
- Disease duration > 6 years
- Daily pyridostigmine > 750 mg/day
- Vital capacity < 2.9 L
- COPD
- Surgical approach: median sternotomy > transcervical thymectomy
how do volatiles cause skeletal muscle relaxation
via action on ventral horn of spinal cord
patho of Eaton-Lambert syndrome
IgG-mediated destruction of presynaptic voltage-gated Ca2+ channel at presynaptic nerve terminal
reduces amount of ACh released into synaptic cleft
patho of Eaton-Lambert syndrome
IgG-mediated destruction of presynaptic voltage-gated Ca2+ channel at presynaptic nerve terminal
reduces amount of ACh released into synaptic cleft
how are postsynaptic nicotinic receptors affected in eaton lambert syndrome
present in normal quantity & function
presentation of eaton lambert syndrome
- Proximal muscles most affected
- Weakness generally worse in the morning and improves throughout the day
- ANS dysfunction
s/s ANS dysfunction in eaton lambert syndrome
- orthostatic hypotension
- slowed gastric motility
- urinary retention
treatment of eaton lambert syndrome
3,4-diaminopyridine (DAP)
increases ACh release from presynaptic nerve terminal & improves strengt
how do pts with eaton lambert syndrome react to NMBs
Sensitive to succs + NDNMBs
volatiles typically provide enough relaxation
diagnosis to consider when patient has suspected lung cancer undergoing mediastinoscopy, bronch, or thorascopy
up to 60% of pts with eaton lambert syndrome have small oat cell carcinoma
region affected by myasthenia gravis vs. eaton lambert sydrome
MG: postsynaptic Nm receptor
ELS: voltage gated Ca channel
ACh in myasthenia gravis vs. eaton lambert sydrome
MG = decreased response to ACh
ELS = decreased ACh release
NMJ region affected by myasthenia gravis vs. eaton lambert sydrome
MG: postsynaptic at motor end plate
ELS: presynaptic neuron
effectiveness of AChE inhibitors in region affected by myasthenia gravis vs. eaton lambert sydrome
MG: adequate
ELS: poor
patho of guillain barre syndrome
- Peripheral polyneuropathy characterized by immunologic destruction of myelin in peripheral nerves
- AP can’t be conducted
presentation of Guillain-Barre Syndrome
- Flu-like illness usually precedes paralysis by 1-3 weeks
- Typically persists ~2 weeks, full recovery in ~4 weeks
common etiologies of Guillain-Barre Syndrome
- Common: Campylobacter jejuni bacteria, EBV, CMV
- also: vaccinations, surgery, and lymphomatous disease
treatment of guillain barre syndrome
plasmapheresis and IVIG
steroids and interferon do NOT improve
s/s guillain barre syndrome
- flaccid paralysis that begins in distal extremities and ascends bilaterally towards proximal extremities, face, & trunk
- ANS dysfunction common
sensory deficits in guillain barre syndrome
paresthesia, numbness, pain
major anesthesia concerns with guillain barre syndrome
skeletal muscle denervation, impaired ventilation, ANS dysfunction
NMBs and guillain barre
- Avoid succs (risk hyperkalemia from proliferation of EJRs)
- Sensitivity to NDNMBs
why are guillain barre pts at high risk for HD instability under GA, position changes, PPV, and blood loss
ANS dysfunction
guillain barre pt response to indirect acting sympathomimetics
- Exaggerated response d/t upregulation of postjunctional adrenergic receptors
patho of Familial Periodic Paralysis
Characterized by acute episodes of skeletal muscle weakness accompanied by changes in serum K+ concentration
Disorder of skeletal muscle membrane (↓ excitability), not NMJ
type of Familial Periodic Paralysis that’s a calcium channelopathy
hypokalemic periodic paralysis
type of Familial Periodic Paralysis that’s a sodium channelopathy
hyperkalemic periodic paralysis
how is Hypokalemic Periodic Paralysis diagnosed
if skeletal muscle weakness follows a glucose-insulin infusion (weakness with ↓ serum K+)
AVOID in Hypokalemic Periodic Paralysis
- glucose containing solutions
- K+ wasting diuretics
- beta 2 agonists
- succs
why should D5W be avoided in Hypokalemic Periodic Paralysis
D5W = insulin spike = K+ shifted into cells = hypokalemia
how is Hyperkalemic Periodic Paralysis diagnosed
if skeletal muscle weakness follows oral potassium admin (weakness after serum K+ increases)
AVOID in Hyperkalemic Periodic Paralysis
- succs
- K+ containing solutions like LR
treatment of Familial Periodic Paralysis
acetazolamide for both forms
why is acetazolamide used in treatment of familial periodic paralysis
creates non-anion gap acidosis
protects against hypokalemia & facilitates renal K+ excretion (protects against hyperkalemia)
AIs of familial periodic paralysis
- Avoid hypothermia at all costs (even when on CPB)
- Serum K+ monitoring indicated
how is MH characterized
disordered calcium homeostasis
how does Ca2+ enter myocyte when T-tubule is depolarized in MH
via dihydropyridine receptor
receptor activated by MH that instructs SR to release too much calcium
RyR1
why is there a substantial amount of ATP consumed in MH
More Ca2+ to engage with contractile elements + cell attempts to return excess to SR via SERCA2 pump
what causes hyperkalemia and myoglobinemia in MH
Sarcolemma breakdown = K+ and myoglobin to enter systemic circulation
effects of increased intracellular calcium in myocyte
- Rigidity from sustained contraction
- Accelerated metabolic rate, rapid ATP depletion
- Increased O2 consumption
- Increased CO2 and heat production
- Mixed respiratory and lactic acidosis
- Sarcolemma breaks down
- K+ and myoglobin leak into systemic circulation
only 3 conditions definitively assoc with MH
- King-Denborough syndrome
- Central core disease
- Multiminicore disease
why should volatiles and succs be avoided in DMD
can have MH-like syndrome from rhabdo (not true MH)
absence of dystrophin destabilizes sarcolemma - more calcium can enter c
why should volatiles and succs be avoided in DMD
can have MH-like syndrome from rhabdo (not true MH)
patho of MH type reaction in DMD patients
- Absence of dystrophin destabilizes sarcolemma during muscle contraction, ↑ membrane permeability
- Extracellular Ca2+ free to enter cell (can ↑ rate of metabolism)
- Intracellular K+ is free to exit cell (can result in hyperkalemic cardiac arrest)
- Myoglobin free to exit cell
MH risk factors
- Geography: families from Wisconsin, Nebraska, West Virginia, & Michigan at ↑ risk
- Male sex
- Youth
early s/s MH
- tachycardia
- tachypnea
- masseter spasm
- warm soda lime
- irregular HR
late signs of MH
- muscle rigidity
- cola-colored urine
- coagulopathy
- irregular HR
- hyperthermia
most sensitive indicator of MH reaction
EtCO2 that ↑ out of proportion to Vm
what is trimus
tight jaw that can still be opened (normal response to succs)
what is masseter rigidity
tight jaw that can’t be opened
what causes masseter spasm
↑ Ca2+ in myoplasm
site of action distal to NMJ so NMB will not relax jaw
gold standard for diagnosing MH
Caffeine-Halothane Contracture Test
who should have a Caffeine-Halothane Contracture Test
Anyone who has experienced MH or masseter spasm should be tested
who should have a Caffeine-Halothane Contracture Test
Anyone who has experienced MH or masseter spasm should be tested
MH differential
- thyroid storm
- neuroleptic malignant syndrome
- sepsis
- pheochromocytoma
- serotonin syndrome
- heat stroke
- metastatic carcinoid
- cocaine intoxication
how long should the machine be flushed for MH risk patient
20-100 min high flow (time depends on model)
charcoal filter prep for MH risk patient
Place Vapor-Clean charcoal filter on inspiratory and expiratory port of machine & flush with high FGF (>10 L/min) for 90 seconds prior to using machine on patient
external parts of machine that should be removed & replaced for MH risk patient
CO2 absorbent, circuit, bag
1st thing you should do with suspected MH reaction
Discontinue triggering agent (volatile or succs)
convert to TIVA
why should you hyperventilate when MH reaction suspected
facilitates CO2 elimination, enhances O2 delivery, drives K+ into cells
100% O2 at minimum FGF 10 L/min
why should you hyperventilate when MH reaction suspected
facilitates CO2 elimination, enhances O2 delivery, drives K+ into cells
100% O2 at minimum FGF 10 L/min
purpose of charcoal filters
Maintains halogenated anesthetic concentration < 5 ppm for up to 12 hours with FGF of 3 L/min
how often should Vapor-clean be changed during MH crisis
every hour
MOA of dantrolene
1) Reduces Ca2+ release from RyR1 receptor in skeletal myocyte
2) Prevents Ca2+ entry into myocyte, which ↓ stimulus for Ca2+ -induced- Ca2+ release
dantrolene dosing
- 2.5 mg/kg IV repeated q5-10 minutes
- Continued in ICU: 1 mg/kg q6H or 0.1-0.3 mg/kg/hr for 48-72 hours
common side effect of dantrolene admin
venous irritation
concentration & admin of Dantrium
20 mg/vial
reconstitute with 60 mL water
concentration & admin of Ryanodex
250 mg/vial
dilute in 5mL sterile water
when should you stop cooling pt with MH reaction
stop at 38 degrees C
treatment for lactic acidosis in MH
Bicarb 1-2 mEq/kg titrated to ABG and base deficit
treating hyperkalemia in MH
5-10 mg/kg CaCl
0.15 units/kg insulin + 1 mL/kg D50
how to prevent against dysrhythmias in MH
Class 1 antiarrhythmics
15 mg/kg procainamide, 2 mg/kg lidocaine
do NOT give CCBs
how to prevent against dysrhythmias in MH
Class 1 antiarrhythmics
15 mg/kg procainamide, 2 mg/kg lidocaine
do NOT give CCBs
desired UOP in MH
>2 mL/kg/hr
Protects against renal injury from free myoglobin
IV hydration, 0.25 mg/kg mannitol, 1 mg/kg Lasix