MH & awareness
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MH is an uncommon, but fatal disorder typically caused by .....
exposure to inhaled anesthetics and/or succinylcholine
Incidence in North American and Europe are _______ for adolescents and _____________ for adults.
- Adolescents: 1 in 15,000
- Adults: 1 in 50,000-150,000
For MH, Use of Dantrolene has decreased the mortality rate to less than ___%
5% (down from 70%!)
What is MH defined as?
Sustained hypermetabolic state and abnormalities in skeletal muscle biochemistry
When did MH first happen?
- 1962 when a patient came close to dying after receiving general anesthesia and experiencing an extreme increase in core body temperature.
- The incidence of this case, and many others that appeared around this time was believed to be due to the new development and increased frequency of use of drugs like halothane
What patient population is MH most frequently seen in?
more frequently seen in young men with an average age of 15 and those of Caucasian northern European dissent.
Highest incidence of MH in the US?
MH is extremely dangerous in younger athletic males with large amounts of muscle mass, why?
due to the ability of the muscles to increase body temperature to even greater levels.
Overall incidence during anesthesia is approximately _________general anesthetics in the general population (Barash)
1 in 10,000
TRUE or FALSE. Family history or previous exposure to anesthesia can accurately predict the occurrence of MH.
FALSE. Neither can accurately predict it.
_______of susceptible MH patients manifest the syndrome during their first general anesthetic.
2/3; The other 1/3 manifest during subsequent administration of anesthetics.
What does MH result in?
results in hyperthermia, tachycardia, high end-tidal CO2, skeletal muscle rigidity, and acidosis.
What is more important age or size in terms of risk for MH?
AGE! don't give to an adolescent even if they are a big teenager!
Does MH always manifest itself on the 1st anesthesthetic?
NOPE, 2/3 of the time it will but not ALWAYS
What kind of inherited disorder is MH caused by?
- Autosomal dominant inherited disorder
- Defect is the ryanodine receptor (RYR1)
RYR1 is in a more open resting state than normal that results in an intracellular calcium release rate that is _____ times that in people without MH.
What is the pathophysiology behind MH?
A triggered uncontrolled release of free calcium from the sarcoplasmic reticulum leads to activation of energy producing biochemical pathways and hypermetabolism
What rare non-anesthetic triggers can cause MH?
trauma, exercise, heat, stress, and infection
In MH, what is happening at the cellular level d/t the uncontrolled release of Ca+ from the SR?
- ↑ action between the actin and myosin leading to sustained muscle contractures. The body attempts to restore the calcium, but it is unable to.
- Excessive breakdown of ATP due to this hypermetabolic state.
- Generalized skeletal muscle rigidity, destruction, and rhabdomyolysis
- Excessive metabolic stimulation leads to ↑CO2 production and lactic & respiratory acidosis.
- With the depletion of ATP there is a disruption of the skeletal muscle cell membrane that allows K, Ca, CK, & myoglobin to leak into the ECF.
What causes the hyperkalemia and cardiac arrhythmias in MH?
Loss of potassium from the muscle cells result in hyperkalemia, metabolic acidosis and cardiac arrhythmias.
What causes the renal failure and DIC in MH?
The released myoglobin causes myoglobinuria, disseminated intravascular coagulation, and renal failure. Renal tubules get clogged by myoglobin. Renal failure can be end result.
What is the most sensitive and specific sign of MH?
In the absence of equipment malfunction is increased ETCO2 (can double or triple)
What is the most common cause of death in MH?
- Arrhythmias including V-fib
- Can occur within minutes
Is fever an early or late sign of MH?
Fever is inconsistent, often a late sign (6-24hrs)
Do renal failure and DIC rapidly develop in MH?
YES. If pt. survives initial few minutes, ARF and DIC can rapidly develop
What are LATE complications of MH? (6-24hrs)
skeletal muscle swelling, cerebral edema, hepatic failure & left heart failure
What are the INITIAL S/S of MH?
- Increasing EtCO2 (double or triple), over min. to hrs., or requiring increasing minute vent (or tachypnea) to maintain normal EtCO2
- Masseter Muscle Rigidity (Trismus)
*2 or more of these signs greatly increases risk of MH
What is Masseter Muscle Rigidity?
- Jaw muscle tightness with limb muscle flaccidity after admin of succhinylcholine.
- Keeping in mind that incomplete relaxation or a tight jaw is different from MMR often described as Jaws of Steel.
- Additionally myotonia can cause MMR.
What should you do if you're patient has masseter muscle rigidity?
Safest thing to do if MMR presents is to wake the pt up, as intubation will be unlikely as well.
Masseter muscle rigidity is preductive of MH in up to __% of cases, and is associated with myoglobinuria
After an episode of Masseter Muscle Rigidity, the patient should be observed carefully for a period of _____ hours.
What are the S/S of MH?
↑CO2, perspiration, hyperthermia, ↑HR, dysrhythmias, muscle rigidity, HOT CO2 exhauster, dark brown urine in foley catheter (myoglobinuria)
What lab abnormalities would you expect to see w/MH?
- CK elevated
Pre-op ABCDs of MH
- Ask about personal and family past history of Malignant Hyperthermia Adverse Anesthesia reactions (unexplained fever or death during anesthesia). Aware of clinical signs of MH.
- Body temperature monitoring for all patients undergoing general anesthesia for other than brief procedures.
- Capnographic monitoring for all patients undergoing general anesthesia.
- Dantrolene: have dantrolene available wherever MH trigger anesthetics are used.
ABCDE of emergency treatment for MH
- Ask for Help Ask for the MH cart and for dantrolene. Agents/Anesthesia: Stop anesthesia triggering agents and the surgery.
- Breathing: hyperventilate with 100% oxygen.
- Cooling, if the patient is hot (aggressively down to 38°C): insert large bore IV catheters. Cold intravenous fluids (NS) 15 cc/ kg IV 3 times. Irrigate the wound and stomach with cold saline. Call MH Hotline 1-800 MH HYPER
- DANTROLENE: give dantrolene IV, 2-2.5 mg/kg, and repeat the dose until the signs are controlled.
- Electrolytes, check them, especially potassium.
What is the dose of dantrolene?
- 2-2.5mg/kg Q5min repeat until signs are controlled (more than 10 mg/kg may be given as dictated by clinical circumstances)
- Continue 1mg/kg Q 6hrs x 24-48 hrs.
How much cold IVF should you give in MH?
15cc/kg IV x3
Where should cool for MH?
ice packs to the groin and axilla, gastric, wound, and rectal lavage– of these, gastric lavage is the quickest most practical means for rapid temperature control.
What are the ABCDEF of secondary steps in MH?
- Acidosis? Assess initial and subsequent arterial or venous blood gases.
- Bicarbonate? 1-2 mEq/kg guided by pH and base deficit.
- Circulation/monitoring: consider a-line, CVL, labs: arterial/venous blood gases, myoglobin levels. CBC, Coagulation tests CK,
- Dysrhythmias: generally subside with resolution of the hypermetabolic phase of MH. Diuresis: assure diuresis greater than 1 ml/kg/h.
- Electrolytes: if hyperkalemic, treat with bicarbonate, glucose/insulin, calcium.
- Follow up: Arterial and venous blood gases. Body temperature (core) avoid hyper/hypothermia. End-tidal CO2, CK, coagulation tests. Diuresis (urine output and color). Electrolytes.
How do you treat arrhythmias in MH?
- amiodarone, lidocaine, procainamide, adenosine, or other drugs indicated according to the ACLS protocol.
- Remember impact of hyperkalemia.
What labs would you get as secondary step in managing MH?
- A or V BG
- myoglobin levels
- Coagulation tests
Should you use Ca+ Channel blockers to treat a dysrhythmia in MH?
- NO! Calcium channel blockers should NOT be used
- Verapamil can interact with Dantrolene to produce hyperkalemia (already a problem) and myocardial depression (Barish)
What is Dantrolene?
- Direct-acting skeletal muscle relaxant
- Acts to dissociate intracellular excitation-contraction coupling by binding to Ryr1 Ca++ Channel receptor, interfering with the release of Ca++ from sarcoplasmic reticulum.
How is Dantrolene supplied, how do you prepare it?
- 20mg Dantrolene w/ 3G of Mannitol
- Mixing: Reconstitute with 60ml sterile H2O (non-bacteriostatic) & shake until fully dissolved.
What else can Dantrolene be used for?
Dantrolene can also be used to decrease temp in Thyroid Storm and Neuroleptic Malignant Syndrome
Why is mannitol mixed with the Dantrolene?
- Mannitol causes osmotic diuresis, as well as excretion of K+, Ca++, phosphorous, cloride,Mg++, Urea & uric acid, so ensure foley cath in place.
- Helps keep tubules clear of clogging
How long is Dantrolene good for once mixed?
How should Dantrolene be stored?
Unconstituted Dantrolene should be stored at room temp (59-86 deg F) and avoid prolonged exposure to light
What is the 1/2 life of Dantrolene?
What is the most serious SE of Dantrolene?
- It has hepatic metabolism.
- Hepatotoxicity (incidence of 1:1000)
- Administering the smallest necessary dose is advised, along with following the LFT’s.
What is awareness?
Occurs when a patient becomes conscious during a procedure performed under general anesthesia and subsequently has recall of these events
What is recall?
Ability of the patient to retrieve stored memories
What is EXPLICIT memory?
Ability of the patient to recall specific events, noises, sensations that occur during general anesthesia
What is implicit memory?
- Subconscious changes in behavior or performance without the ability to recall specific events during general anesthesia
- **NOT AWARENESS**
What types of surgeries are at higher risk for awareness?
- Cesarean Section (0.4%)
- Cardiac (not tolerating high anesthetic-1.1% to 1.5%)
- Trauma and emergency surgery (11% to 43% but have decreased with better resuscitation of patients)
What patient characteristics put a patient at risk for awareness?
- Hx Substance abuse (ie. Benzo, opioid, cocaine)
- Difficult intubation
- Chronic pain patient on increased doses opioids
- Limited hemodynamic reserve / ASA 4-5
- History of awareness
- Severe end-stage lung disease
What anesthetic techniques put the patient at risk for awareness?
- Muscle relaxants
- Nitrous oxide-opioid anesthesia
What are a lot of cases of anesthesia awareness attributed to?
- Surgery performed at night – awareness attributed to fatigue of provider
- Most cases of anesthesia awareness are attributed to human error, wrong drug administration, failure of equipment
Why does Bronchoscopy and/or laryngoscopy put a patient at risk for awareness?
w/ bronch or repeat laryngoscopy, you’re losing a lot of gas, volatile out into atmosphere
For awareness, what should you do during the preanesthesia eval?
assess the risk of awareness and incorporate the possibility of awareness as part of the informed consent for all high-risk scenarios
What VERY IMPORTANT step can we take to prevent awareness?
Check all anesthesia equipment (machine, vaporizers, infusion pumps)
What should you do if awareness occurs?
- Interview (take a detailed account of his or her experience, include this in the patients chart)
- Apologize (assure the patient of credibility of his/her account….sympathize
- Explain (possible reasons for occurrence ..light anesthesia 2/2 cardiac instability etc)
- Offer support (psychological or psychiatric support, referral of patient to specialist)
- Notify surgical team
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