Malignant Hyperthermia – Flashcards
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What is MH?
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Inherited disorder of skeletal muscle that is triggered in susceptible humans or animals by inhalation agents or succ
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What is MH characterized by?
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Hypermetabolism skeletal muscle damage hyperthermia death
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Where are some high incidence areas for MH?
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Wisconsin, Nebraska, West Virginia and Michigan
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What are some common ages for MH? Males or females affected more? Patients with what 2 conditions are more likely to have MH?
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may happen b/t the age of 3 and 60 males Trismus or some musculoskeletal disorders
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Is past history of MH a 100% indicator for MH?
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No
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Name 9 MH triggering agents.
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Iso Des Halo Enflurane Sevo Diethyl Ether Cyclopropane Methoxyflurane Succ
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What are 7 drugs we commonly use that will not trigger MH?
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Nitrous Barbiturates Benzos IV induction agents NM blockers (nondepolarizing) Narcotic and opioid analgesia LA's
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Discuss the physiology of MH.
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-abnormal release of Ca from the SR - leads to sustained muscle contraction, increase in metabolism and heat production -muscle cells eventually depleted of ATP and die, causing hyperK and ventricular arrythmias -myoglobin is also released from the muscle cells and may be toxic to the kidney
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What will happen to ETCO2 with MH? How do you tell the difference b/t MH and faulty unidirectional valves?
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It will increase suddenly, but baseline will come back to zero Faulty unidirectional valves don't return to zero
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What are some other s/s of MH?
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trunk or total body rigidity masseter spasm (trismus) tachycardia/tachypnea mixed respiratory and metabolic acidosis increased temp (may be a late sign) myoglobinuria
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What is another condition that may present like MH?
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young muscular male with infected appendix will produce a TON of CO2
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Will muscle rigidity always be present? Is temp a late or early sign? What is usually the earliest sign? When will MH present?
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not always late sign elevated ETCO2 at any stage during anesthesia or on emergence
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What are some specific signs to MH? 4
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Muscle rigidity increased CO2 Rhabdo Marked temp elevation
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What are some non specific signs? 4
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Tachycardia Tachypnea Acidosis (resp/metabolic) Hyperkalemia
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Fever without rigidity may be caused by what conditions, and mimic MH?
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thyrotoxicosis, sepsis, pheochromocytoma, Iatrogenic overheating, anticholinergic syndrome (atropine and rubinol), faulty equipment, tourniquet
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What are some conditions that may mimic MH d/t fever and muscular rigidity?
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NMS (neuromuscular malignant syndrome) hypoxic encephalopathy ionic contrast agents in CSF cocaine, ecstasy, amphetamine
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What are the s/s of masseter muscle rigidity?
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Trismus Jaw muscles contracted post Succ No immediate fever children ages 4-12 years affected occurs in both sexes increased CK and myoglobinuria acidosis, PVC's common high likelihood of MH with general rigidity no structural muscle changes
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What are some other possible diagnoses of MMR?
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myotonic syndromes other Neuromuscular disorder TM joint dysfunction normal response to succ underdose of succ
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What are the steps to treatment of severe MMR?
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1. stop inhalation agent and give no more succ 2. either awaken pt or continue with nontrigger agents and follow ETCO2 closely 3. consider observation for 24 hrs, check CK/lytes, myoglobin, give dantrolene as needed, get biopsy
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If MH crisis, what lab values may/will be elevated?
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K Ca Mg Lactate Pyruvate LDH Creatinine Myoglobin Glucose CK
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After MMR, what are the discharge criteria?
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if mild increase in jaw tension, observe for 12 hours for s/s of MH if evidence of myoglobinuria, dark cola-colored urine, increase in temp, pulse rate and abnormality of acid base balance, the patient should be admitted and observed overnight
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What are the significant predictors of MH: muscles? elevated CK > than? plasma K? PETCO2 with controlled ventilation? PACO2 with controlled ventilation? PACO2 with spont ventilation? Temp?
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rigid 20000 after anesthesia with succ >6 MEQ/L >55 >60 >65 rapid increase
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How do you treat acute phase of MH?
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d/c offending agents hyperventilate with 100% O2 treat hyperkalemia (bicarb 1-2 mg/kg prn) dantrolene cool patient (gastric lavage, surface, wound) treat arrythmias (NO Ca channel blockers) check venous and arterial blood gasses check lytes and coags
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How do you dose Dantrolene?
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2.5 mg/kg push, repeat PRN
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How do you treat hyperkalemia?
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hyperventilation bicarb 1-2 meq/kg by IV CaCl - 10 mg/kg, gluconate 10-50 mg/kg glucose/insulin infusion - (peds .01 units/kg with 2 ml/kg 25% dextrose) (adult 10 units reg IV and 50 ml D50W or 1 L D10W)
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How is Dantrolene prepared?
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dissolve 20 mg/bottle with 60 ml sterile bacteriostatic water shake vigorously give 2.5 mg/kg STAT repeat as needed may need 10-12 mg/kg Dantrolene 1 mg/kg IV q 4-6h and continued for 24-48 hours
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What is the MOA of Dantrolene?
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binds to the Ca channel site in the muscle restores the balance b/t Ca release, entry and uptake
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What are Dantrolene precautions?
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may cause muscle weakness with pre-existing muscle disease sterile phlebitis may follow administration - give in largest vein possible with CCB's (dilt and verapamil) may produce life threatening hyperkalemia and myocardial depression does not interfere with muscle relaxants or reversal
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What labs must be checked to monitor MH?
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blood gases CK q 12 hrs Myoglobinuria Clotting factors (PT, PTT, INR, fibrin split products) Liver enzymes BUN
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What are the steps to treatment of MH post acute phase?
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observe patient in ICU Continue Dantrolene Continue patient monitoring Counsel patient and family Complete the adverse metabolic reaction report and submit to the North American MH Registry
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Post Crisis, how is Dantrolene dosed? How many hours do you give Dantrolene total?
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1 mg/kg every 4-6 hours for 24 hrs 36 hours
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What are the 5 most common causes of mortality from MH?
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Acidosis Hyperkalemia Organ failure d/t hyperthermia DIC Renal failure d/t myoglobinuria
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If you are dealing with a MH susceptible patient, what are the most impt things you should have prepared and avoid? monitor?
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-avoid inhalation agents, avoid sux -have dantrolene available -dantroline is NOT necessary preoperatively -monitor Temp -PACU monitoring for a minimum of 1 hour and vitals q 15 mins at least
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What needs to be done to the anesthesia machine if you are going to have a susceptible patient on the OR table?
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-shut down vaporizers -flow O2 at 10L/min for 20 minutes through the machine and vent, and place breathing bag on Y and turn on ventilator during flushing -Change CO2 absorbent
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Do newer anesthesia machines need a longer flush time? How long?
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yes 27-85 mins of 10L/min FGF
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Is there a way to speed up the process of clearing the machine?
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yes - charcoal filter can clear it within 2 mins
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What is the Regimen for anesthesia in MH susceptible patients?
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Anxiolytic Ketamine Propofol/opioid induction NDNMJB Nitrous/narcotic/prop Reverse muscle relaxant Observe for 3-4 hours
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What are the required meds on the MH cart?
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dantrolene - 36 vials sterile water sodium bicarb dextrose mannitol furosemide
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What does the AANA preparedness statement say needs to be done in prep for MH?
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-Providers should be prepared to treat MH -Personnel should be trained in the recognition/treatment of MH -MH cart should be available in anesthetizing and recovery areas -Written treatment plan should be posted with cart -24 hours MHAUS hotline # should be posted on cart
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What is the genetic inheritance of MH?
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inherited in an autosomal dominant fashion - must look at both your patients family and his/her family members medical hx
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Why is diagnostic testing not recommended as a screening tool for the general population?
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b/c the test usefulness depends on the pre-test probability that the patient is MH susceptible
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What is the Caffeine Halothane Contracture Test (CHCT)?
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Test for MH: uses a muscle biopsy and is the GOLD Standard! -It assesses muscle contractile properties upon exposure to Ryanodine receptor agonists (Caffeine, Halothane) -Abnormally high levels indicate MH susceptible -extremely accurate
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Causative mutation in what gene indicates MH susceptible?
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RYR1 gene
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What are some indications for doing a CHCT test?
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-patient has relative who is MHS -patient with MHS family member -patient with past suspected MH event -patient with severe MMR during anesthesia with a triggering agent -patient with moderate to mild MMR with evidence of rhabdo -patient with unexplained rhabdo during or after surgery -patient with exercise induced rhabdo -signs suggestive of but not definitive for MH -if military service is desired, patients with suspicion of MHS are required to undergo CHCT
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What are the cons of CHCT?
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-patient must undergo invasive surgical procedure, with 2-7 days of disability to get the biopsy -testing can only be performed in specialized biopsy centers -expensive
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What are some Pros to genetic testing?
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less expensive than CHCT less invasive than CHCT no need to travel if positive - won't need a CHCT
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What are some cons to genetic testing?
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-absence of a causative mutation does not rule out MH -expensive -insurance may not cover
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Which is more expensive, CHCT or genetic testing?
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CHCT - covered by most insurance companies Genetic testing may or may not be covered...MHAUS may be able to help
