Submitted by deb on Mon, 06/27/2011 – 19:16
Periodic Paralysis Patients at Increased Risk of MH
Patients with Hyperkalemic periodic paralysis and Paramyotonia Congenita are at increased risk for Malignant Hyperthermia (MH) during surgery.
Patients with all types of periodic paralysis often become paralyzed during or after surgery, from stress, chilling in the OR and the use of IV solutions which contain sodium and/or glucose. Patients report long periods of increased weakness after surgical anesthesia, and may experience paralysis or significant reduction of muscle strength in the days following surgery. There is a increased risk of falls and embolus in the days following surgery, if a post-surgical attack is not treated.
MH is one of the leading causes of death with anesthetics. Malignant hyperthermia susceptibility (MHS) is usually a dominantly inherited trait. Studies indicate that MHS is due to a malfunction in the mechanisms regulating sarcoplasmic calcium-ion fluxes. For further information see: Anesthesia in Hypokalemic Periodic Paralysis and Anesthesia in Hyperkalemic PP and Paramyotonia Congenita.
Individuals at risk should be screened through in vitro muscle contracture testing (IVCT). Chromosome analysis is in early stages and is not yet a reliable diagnostic tool but is performed at research centers such as Royal Perth Hospital (Aus). Genetic testing is able to identify the already known mutations and research continues to identify other possible mutations. IVCT requires a fresh specimen of vastus medialis approximately 3 x 1 x 1 cm. This is usually performed under femoral nerve block with minimal or no sedation required. For more information on how the procedure is performed read Current Diagnostic Testing for Malignant Hyperthermia, from the American Society of Anesthesiologists. This includes a contact which physicians may use to learn where they may send tissue samples for contracture tests.
Genetic Testing for MH
Genetic mutations in the RYR1 gene on chromosome 19 (the gene for the calcium release channel of the sarcoplasmic reticulum of skeletal muscle) have so far been identified in about 30% of affected families worldwide. It is likely that so far unidentified mutations account for another 20-30% of cases. Mutations in the adult muscle sodium channel alpha subunit gene (SCN4A) on chromosome 17 and the alpha subunit of the dihydropyridine receptor gene (CACL1A3) on chromosome 1 have been identified in a small number of families. We have specimens from IVCT proven cases from 20 families. Six of these families have been shown to carry known mutations in the RYR1 gene. In those families not carrying an identified mutation, cDNA from affected individuals is being analyzed for new mutations segregating with the disease. Blood from MH suspects can be tested from anywhere in Australia. Enquiries should be directed to Mark Davis, Neuroscientist at email@example.com.
Management of Perioperative Rise in Temperature
Temperature rise perioperatively may be due to:
- Inadvertent overheating by warming devices
- Systemic inflammatory response to major trauma
- Fat embolism
- Head injury
- Spinal cord injury
- Light anaesthesia and volatile anaesthetic induced shivering
- Transfusion of mismatched or infected blood products
- Drug reactions with or during anaesthesia (neuroleptic malignant syndrome, MAO inhibitors, ACE inhibitors, SSRIs, cocaine, ecstasy, atropine, scopolamine.)
- Malignant Hyperthermia
Manifestations of MH
Unexpected Increase in CO2 Production with rise in end tidal CO2 and arterial PCO2. Tachypnoea will occur in spontaneously breathing patients. The CO2 absorber may become rapidly exhausted. Muscle Rigidity manifesting initially as masseter muscle spasm but spreading to involve truncal and limb muscles. Tachycardia, arrhythmias, and hemodynamic instability occur as hypercarbia, hypoxemia, hyperkaliemia and acidosis become significant. Cyanosis, skin mottling and falling O2 saturation reflect the onset of hypoxemia. Hyperthermia and sweating may be a late manifestation however core temperature may rise as rapidly as 1 degree C every 5 minutes.
Abnormal Laboratory Values
- Metabolic and/or respiratory acidosis.
- Elevated serial blood CKs
- Myoglobinaemia and myoglobinuria
Treatment of MH
If Malignant Hyperthermia is suspected in Theatre:
- Withdraw volatile anaesthetic agents and substitute with TIVA
- Notify the Surgeons and Nurses and terminate the surgical procedure as quickly as possible
- Check the monitors (end tidal CO2, temperature)
- Check the ECG
- Check O2 saturation
- Insert an arterial line and draw an ABG, measure K+, CK
- Consider inserting a central line
If Malignant Hyperthermia is suspected in Recovery Room
As above but also consider chest X-ray, blood cultures and cranial CT depending on the clinical picture.
When the Diagnosis of Malignant Hyperthermia is made
- Declare an MH emergency
- Call for Anaesthetic assistance
- Hyperventilate with 100% O2 (3-4 x normal minute volume )
- Increase fresh gas flow to more than 10 L/min.
- Exclude the Sodalime absorber from the circuit
- If using rubber circuitry, change to a fresh set
- If using silicone or plastic hoses do not change at the expense of maintaining hyperventilation
- CALL FOR DANTROLENE SUPPLY, a sterile mixing bowl and a 1 litre bag of water for Injection
- Assign 2 people to mix Dantrolene. This is best performed by removing the tops of the vials with a bottle opener, emptying the contents into a sterile bowl and adding water drawn up with a syringe into the bowl. Each vial must be reconstituted with 60 mL of water.
- Administer Dantrolene via a central line at an initial dose of 2.5 mg/kg over 5 min. Further doses of the same amount can be administered according to the response of heart rate, arterial CO2, rigidity and temperature fall at intervals of 10 min. After a total dose of 10 mg/kg ventilatory support may be necessary if the patient is not already ventilated.
- Stop using any heating devices, remove covering garments or linen where possible and reduce operating theatre temperature.
- Initiate cooling if temperature is elevated. If appropriate, administer ice cold saline via a large peripheral cannula. Pack axillae and groins with plastic bags full of crushed ice.
ARRHYTHMIAS, ACIDOSIS, AND HYPERKALEMIA
Hypoxia, hypercarbia, acidosis and hyperkalaemia will produce tachyarrhythmias and ectopy which are best treated with Beta blockers (Metoprolol, Esmolol) or Lignocaine or Calcium. Acidosis in a ventilated patient can be treated with Sodium Bicarbonate. Caution should be used in the non ventilated case. THAM, which does not produce CO2, might be preferable if it is available. Hyperkalaemia should be treated with an Insulin/Dextrose infusion if the rise in Potassium is rapid or ECG signs of hyperkalaemia become evident.
- Insert a urinary catheter.
- Take a sample of urine for Myoglobin assay.
- Promote a diuresis with fluids (normal saline) and Furosemide.
- Extra Mannitol may be given in addition to that already in the Dantrolene (3 mg per vial).
- Take a sample for coagulation studies.
- Order platelets and FFP if clinical evidence of a coagulopathy is present.
- Take a sample for coagulation studies.
- Repeat blood gas and biochemistry tests frequently.
- Evidence of ongoing rigidity, rhabdomyolysis, elevated temperature, and continued hypercarbia will necessitate further doses of Dantrolene.
- Monitor haemodynamics and urine output for signs of developing renal failure.
- Arrange transfer to intensive care.
AT A LATER DATE
Review family history if available and refer to an MH testing centre.
Credits / Additional Information
The content on this page is used with permission. It essentially mirrors that found at Australian & New Zealand College of Anesthetists. Also see the excellent website of the Malignant Hyperthermia Association of the USA.