MH Dantrolene Flashcards by Joe Susco

Temp regulation centers

Hypothalamus-
Gain center-posterior
Loss center-anterior

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1 degree change in temp will alter BMR by

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Most heat loss is by

Radiation (40%)
Convection (30%)
Burn pts lose most via evaporation

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Hypothermia phys changes

Increase SVR, decrease CO, myocardial depression, increases blood viscosity, Left shift, impaired coags, decrease CO2 production, decrease O2 consumption

Shivering increase cardiac work, O2 consumption

Drug elimination slowed

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MH signs and symptoms

Hypercarbia
Tachycardia/pnea
Hyperthermia (1-2c q5min)
HTN
Dysrhythmias
Acidosis
Skeletal muscle rigidity (Masseter muscle spasm after succs in children CPK >20,000 confirms)
Myoglobinuria
Hypoxia

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MH incidence, genetics

1 in 15,000 anesthetics in children
1 in 50,000 anesthetics in adults
Dominant pattern of inheritance

Ryanodine receptor mutation found in 50% of MH families and 20% of all MH patients

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Triggers

Full episodes- Halothane, Enflurane, Isoflurane, Desflurane, Sevoflurane, Succinylcholine

MIld episodes- Exercise in hot conditions, neuroleptic drugs, ETOH, infection

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MH patho

Increased myoplasmic Ca+

Muscle spasms–> rhabdomyolysis

Heat production–>fever–> hypermetabolism

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MH clinical features

Skeletal muscle involvement
SNS hyperactivity
Hypercapnia
Hyperthermia

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Masseter muscle rigidity

May be normal sign after succs, but- if sustained immediately check a K+ and blood gas. Clinical MH occurs about 20% of the time after this.

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Skeletal muscle in MH

Pain
Myoglobinuria
Cardiac arrhythmias

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CPK in MH

> 20,000

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What is the main concern with rapid rhabdomyolysis in MH

Rapid increase in K+

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SNS hyperactivity

Tachy, acidosis, ATP depletion, hypoxemia, heat production, hyperventilation, CV instability

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Labs

Get an A-line

Decreased PaO2, increased PaCO2
High lactate and low pH

CPK very high, up to 100,000
Elevation correlates best with rhabdomyolysis, less well with fever and acidosis
Resting CK mildly increased

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MMR

Continue with agents that will not trigger MH or postpone elective surgery

Unless MH manifests, dantrolene is not recommended

Pts should be closely observed for 24 hours for signs of MH

Discuss muscle biopsy with MH expert

MH testing

Halothane contracture test- gold standard

Caffeine contracture test- not reliable, many false positives

MH treatment

Must be identified early

Call for Help/MH cart

Stop all volatile agents and succs, change circuit/soda lime, change to new machine if possible

Hyperventilation on 100% O2

Dantrolene 2.5mg/kg bolus followed by 2mg/kg IV q5 minutes to a total of 10mg/kg

Bicarb for acidosis

Monitor temp, aggressively cool to under 38C

Maintain 2ml/kg/hr UO with fluids, lasix

Tx for dysrhythmias and hyperkalemia in MH

No Ca channel blockers

Other standard antiarrhythmics ok (Procainamide 15mg/kg IV)

Correction of hyperkalemia and acidosis correct most problems. Hyperventilation, dantrolene, and bicarb may be sufficient.

Treat hyperkalemia with glucose, insulin, and calcium

MH care once initial episode is controlled

ICU for 36 hours (25% recrudescence rate)
Continue dantrolene for at least 24 hours, 1mg/kg q6 hrs

No K+ fluids, avoid LR
Follow coags as DIC may occur

Measure CK q6h until normal after pt has improved/stabilized
CK may remain elevated for 2 weeks

MH cart drugs

36 vials of dantrolene, 20mg each with 60ml sterile water for each vial (1000ml x 2)
8.4% bicarb 50ml x 5
Lasix 40mg/amp x 4 amps
D50 50ml vials x 2
CaCl 10% 20ml vial x 2
Regular insulin 100units/ml x 1 (must be refrigerated)
Lidocaine HCl 2% 1 box = 2 grams or 10ml/100mg preloaded vial

MH cart equipment

Syringes 60ml x 5 to dilute dantrolene
Mini-spike IV additive pins x 2 and multi-ad fluid transfer sets x2 (to reconstitute dantrolene)
Angiocaths 20g-2inch, 22g-1inch, 24g-3/4inch (4 each)
D5W 250ml x1, Microdrip IV set x 1
NG tubes
Irrigation tray with piston syringe x 1
Toomy irrigation syringes 60ml x 2

MH monitoring

Core temp probes

CVP kits

A-line/CVP transducers

Additional MH stuff

Large sterile drap
Three-way irrigating foley
Urinometer 
Rectal tubes
Plastic bags for ice, large and small
Bucket for ice

MH lab supplies

6 abg kits CK myoglobine, SMA 19 (LDH, e-lytes, thyroid), PT/PTT, fibrinogen, fibrin split products, CBC, lactic acid (2 adult, 2 peds) Urine cup x 2 myoglobin Urine dipstick hemoglobin

Dantrolene MOA

Reduces muscle tone and metabolism- prevents Ca release from sarcoplasmic reticulum. Restores Ca balance. 10-15h half-life

Does dantrolene potentiate NDMR? Interfere with reversal?

No. No. Do make sure muscle strength has returned prior to extubation.

Dantrolene cautions

Significant muscle weakness in those with muscle diseases Phlebitis is common Ca channel blockers and dantrolene may produce life-threatening hyperkalemia and myocardial depression Oral dantrolene may be used for several days after the acute phase has been controlled

Who needs to have dantrolene stocked? How much?

Any place administering MH triggering agents must have a minimum of 36 vials of dantrolene at all times Must be kept close to the OR and sterile water must be available for mixing

Testing

11 North American centers Muscle biopsy with halothane test is highly sensitive 30 mutations identified, but 50% of MH pts have no such mutations

Machine prep for pt with MH

Remove vaporizers Change absorbent 10L/m flow O2 for at least 20 minutes, change all circuit components at this time Charcoal filter

Management of known MH pt

No triggering agents Dantrolene pretreatment not recommended Treatment plan should be available, reviewed Minimum 4 hr observations suggested Can still be discharged same day if anesthetic is uneventful

Diseases associated with MH

Central core disease, muscular dystrophy, Na channel forms of myotonia

Diseases that mimic MH

Neuroleptic malignant syndrome- muscle rigidity, fever, autonomic instability, cognitive changes, such as delirium, and CPK increases. Pts are on antipsychotics- haldol, prolixin, thorazine

Succs in children

Best avoided Only for emergencies, special situations Sudden hyperkalemic cardiac arrest in pts with undiagnosed myopathies- young males, 40 cases since 1990, 50% mortality

Tx for sudden unexpected cardiac arrest

CaCl Bicarb Insulin/Glucose Hyperventilation May require dialysis and CPB Hyperkalemia treatment is key to good pt outcome, even with prolonged resuscitation effort DON'T use succs in kids unless you have a really good reason!