Malignant hyperthermia

Characteristics of MH

 An uncontrolled rise in myoplasmic calcium results which causes a hyper-metabolic response

• Leads to increased CO2 production, oxygen consumption, fever, tachycardia, tachypnea, acidosis, hyperkalemia, myoglobinuria, increased CPK, cyanosis and death

pathophys of MH

• An abnormal structure and function of a calcium channel within their skeletal muscle. 

• When exposed to the agent, an abnormal Ca released, causing sustained muscle contraction, abnormal increase in energy utilization and heat production.

Muscle cell eventually runs out of energy and dies releasing large amounts of K and myoglobin into the bloodstream, leading to arrhythmias and kidney failure.

clinical S&S of MH

• Unexplained tachyarrhythmia- compensatory mech (96% of cases) & HTN [ EARLY SIGN ] 

• Increased end-tidal CO2 [ EARLY SIGN ]

• Hypoxemia [ EARLY SIGN ]

• Acidosis (80%) [ EARLY SIGN?- on the powerpoint as early but Zhang said it was a later sign b/c compensatory mech fail- for exam purposes just choose the BEST answer..]

• Masseter rigidity (common in early phase)

• Unexplained tachypnea (85% of cases)

• General muscle rigidity – late sign

• Cyanotic or mottled skin – generally starts with a generalized flush (70%) [late sign] 

• Rapid, sustained increase in body temperature – late sign only 30% of cases. Temperature can be as high as 110°

• Cola-colored urine due to rhabdomyolysis (late sign)

lab findings with MH

• ABGs: Respiratory & Metabolic Acidosis: Arterial hypoxemia

• Decreased pH ; Decreased PO2; Increased PCO2

• Serum K greater than 6mEq/L

• Creatine Kinase greater than 20,000units/L

• Serum myoglobin greater than 170mcg/L

• Urine myoglobin greater than 60mcg/L

Predisposing factors of MH

• Most common between ages 2 – 42

• 2/3 cases are men

• 1st degree relative of someone who has had MH or MH susceptible is at greater risk

• Higher risk in someone with a muscle disorder

  • Central Core disease

  • Multi-minicore disease

  • King Denborough syndrome

• 2/3 of susceptible patients manifest this syndrome during their first anesthetic

• Gene for MH: chromosome 19, the genetic coding site for Ryanodine receptors (calcium release channel) of skeletal muscle sarcoplasmic reticulum. 

• 2 genetic mutations have been identified as predisposing a patient to MH:

• RYR1: encodes the Ryanodine receptor, 

• & CACNA1S [ hopefully not testing on this one]

DX of MH

• caffeine halothane contracture test (CHCT).

• Done with thigh muscle biopsy

Drugs considered trigger of MH

• Known triggers: 

• Volatile anesthetics - sevoflurane, isoflurane, and desflurane

• Inhaled anesthetics (except nitrous oxide)

• Muscle relaxant – succinylcholine

Definitive treatment for MH and MOA

dantrolene

• Reduces contraction of skeletal muscle by a direct action on excitation-contraction coupling

• Contains Mannitol (converts hypotonic solution to isotonic)

• Can potentiate [ inc] NDNMBs – does not affect reversal

differential dx for MH

o   Is depth of anesthesia adequate? hypovolemic ?

o   Is pain addressed?

o   Esmolol?

o   Check for rigidity- check TOF to assess NMB

• could it be NMS?

• thyroid storm?

• pheochromocytoma?

• is there a CO2 leak from insufflation?

steps when MH is suspected

-       Stop triggering agent – give propofol

-       Call for help [ MDA or chief CRNA ]

-       Alert surgeon- close up if possible

-       Ask someone to get MH cart

-       Change CO2 absorber/ breathing circuit

-       Turn baer hugger to ambient and Ask for chilled IVF [ also ask for ice packs —> gastric lavage also good for rapid temp control- stop when temp is <38]

o   If pt does NOT have foley, place one now to monitor UOP and color

-       Inc FiO2 to 100% and hyperventilate [#1 according to Zhang] the patient

o   This will help blow off CO2 and improve acidosis if present

o   If pt has an a-line, get an ABG- administer Bicarb if acidotic

§  1-2mEq/Kg

-       Calculate and administer dantrolene

Does patient have peaked T waves?

o   Could indicate high K

o   CaCl to stabilize the heart 

o   Give 10 units insulin + 1-2 amps of D50

o   Hyperventilate [ already doing that ]

o   Na biacarb [ might already be given ]

o   Albuterol – 8-12 puffs

If pt still have arrythmias after K tx:

o   Amiodarone 150mg IV

o   Lidocaine 1.5 mg/kg

Check labs

o   CK

o   Electrolytes

o   Coagulation studies?

-       Admit to ICU

• DO NOT USE Calcium Channel Blockers in presence of Dantrolene- WHY ?? and which med specifically

• Verapamil can interact with Dantrolene to produce hyperkalemia and myocardial depression

Dantrolene management (initial, infusion and postop)

2.5 mg/kg IV [ max 10mg/kg]

• Continue IV Dantrolene for 24 - 48 hrs = 1 mg/kg every 6 hrs or 0.25mg/kg/hr to prevent recrudescence (relapse) of symptoms

Dantrolene ___mg in one vial. How to constitute

20

• Mix with Sterile Distilled Water = 60ml H2O /20mg Dantrolene per ampule

• Clear yellow to yellow/orange color 

• DO NOT use bacteriostatic water 

• Requires at least 2 providers -- labor intensive [ does not dissolve easy ] 

• Do not use iced fluid to dissolve Dantrolene

Ryanodex

: more expensive -$6,900/ vial

• Approved by FDA for use in Malignant Hyperthermia patients on July 23, 2014

• 250 mg mixed in 5ml of Sterile Water

in this list of drugs, which are considered SAFE and not a trigger for MH?

• local anesthetics

• barbiturates

• Benzodiazepines

• Succ

• etomidate

• Ketamine

• Sevoflurane

• nitrous oxide

• Nondepolarizing muscle relaxants

• Isoflurane

• propofol

• Desflurane

  
  

• local anesthetics

• barbiturates

• Benzodiazepines

• Succ

• etomidate

• Ketamine

• Sevoflurane

• nitrous oxide

• Nondepolarizing muscle relaxants

• Isoflurane

• propofol

• Desflurane

preparation for a patient with known susceptibility to MH

• 1st case of the day

• Avoid triggering agents 

• Remove vaporizers, or tape in “OFF” position

• Change CO2 absorber, replace breathing system & reservoir bag

• Flush the anesthesia machine with O2 set at >10L/Min

• Review & know your machine’s recommendation

• Older machines require only 20 minutes

• Newer machines may require up to 104 minutes of O2 flushing

• Keep fresh gas flow at 10L/min during case to prevent rebound phenomenon

• Place activated charcoal filters on inspiratory & expiratory limbs

• Know where MH cart is 

• Know where crushed ice for OR is to cool pt

• 3L refrigerated/cold IV solution

• Monitoring for signs of MH

• Ensure all OR personnel are informed of treatment protocol