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Malignant Hyperthermia Clinical Information

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The condition arises only after exposure of susceptible individuals to triggering drugs.
At the present time it is possible to identify such people only by a reaction, by a family history, by a muscle biopsy, or DNA testing.
The anaesthetic drugs that have been definitely implicated are a muscle relaxant called suxamethonium (succinylcholine) and all of the anaesthetic gases in current use (halothane, enflurane, isoflurane sevoflurane and desflurane- not nitrous oxide). It was once thought that other disorders particularly those with musculoskeletal associations e.g. eye squints and hernias had a greater than normal chance of having malignant hyperthermia, but this is now not thought to be so. Central Core Disease and King Denborough Syndrome are the only known associated disorders.  

Other syndromes have a similar clinical picture on presentation

Neuroleptic malignant syndrome- a reaction to another group of drugs that are used for sedation and treatment in psychiatric practice and also for nausea and vomiting. The reaction may lead to high fever and rigidity of the muscles. There is almost certainly no association with Malignant Hyperthermia.
Heat-stroke or exercise-induced muscle breakdown. This is not related to any drugs but the treatment and consequences may be similar.
After exposure to the drugs, usually during an anaesthetic, but it may be within an hour afterwards, there could be rigidity of the jaw muscles making it difficult or impossible for the Anaesthetist to open the mouth, rigidity of other muscles, increased breathing rate and an increased heart rate. The body temperature will usually rise to 39-40oC or even as high as 46oC.
These changes are thought to originate in an abnormal contraction state of the muscles such that they don't relax normally. This causes an increase in metabolic needs and when these can't be met, leads to breakdown of the muscle and the release into the blood stream of chemicals from muscle. These can cause an unstable heart rhythm and cardiac arrest, an inability of the lungs to oxygenate the blood properly so that artificial ventilation is needed and kidney failure requiring dialysis.
Untreated this condition has a very high mortality.

Emergency Management of a Malignant Hyperthermia Reaction

  1. Discontinue potent inhalational agents, hyperventilate with 100% oxygen (full oxygen flow)
  2. Call for assistance
  3. Prepare and administer dantrolene. An initial dose of 2.5mg/kg should be administered. and repeated every 5-10 minutes until ETCO2, tachycardia and temperature start to fall (the latter may lag). There is no limit to a maximum dose. 44mg/kg have been used. The starting dose for children is 2.5mg/kg

Treat life threatening complications

Commence cooling
  1. Intravenous saline at 4oC – 1 litre/10mins. 4-5 litres can be administered in a young adult. 1 litre reduces mean body temperature approx 0.5oC.
  2. Surface cooling – crushed ice most effective. Ice cubes (in bags) applied extensively to exposed surfaces also effective.
  3. Peritoneal lavage if temperature reduction is resistant. (1 litre Normal Saline at 4oC with 10 min cycles)
  4. Badder lavage for young children only
    Note: gastric lavage, forced air cooling not advised


  1. Hyperventilate
  2. Sodium bicarbonate 1-2mmol/kg. To a ph of 7.1


  1. Sodium bicarbonate
  2. 10 mmol i/v calcium chloride
  3. Insulin/glucose (1unit insulin/5gm glucose)

Arrhythmias – usually respond to the treatment of acidosis and hyperkalaemia

  1. Lignocaine 1-2mg/kg
  2. Amiodarone 2mg/kg
  3. Procainamide 7mg/kg (30mg/min)
  4. Verapamil – avoid similtaneous administration with dantrolene

Monitoring and further management

  1. Observe the patient in an ICU for at least 24hrs. Recrudescence develops in 25% patients and can be associated with mortality.
  2. SpO2, ECG, arterial BP monitoring, temperature, ETCO2
  3. Measure ABGs, electrolytes, CK, coagulation
  4. Maintain urinary output (uo) > 1ml/kg/hr. Mannitol in the dantrolene assists uo


  • An infusion of dantrolene (1-2mg/kg/6hrs) is recommended by some units. Other units treat recrudesence with bolus doses (2.5mg/kg)
  • Avoid an afterdrop in temperature

Do not waste time in:

  • Changing the circuit. Use high flows of 100% oxygen. As an alternative to ventilation use a self-inflating resuscitation bag and separate oxygen source
  • Changing the anaesthetic machine – this can be done if necessary after the acute phase. Advisable to remove vaporizer
  • Attempting central line placement at the expense of the above measures.

Maintain anaesthesia for completion of the surgical procedure with TIVA

Elective Management
Management of the malignant hyperthermia susceptible patient.
Patient Groups at High Risk:
  • Patients who have survived an MH reaction and/or have a positive in vitro contracture test (IVCT).
  • Relatives of such patients.
  • Patients with suspected MH reactions.
  • Associated muscle disorders, e.g. central core disease.

Pre-operative Preparation:

  • Inform Consultant Anaesthetist.
  • Discuss options.
  • Benzodiazepine premedication.

Operating Theatre:

  • Unused theatre 15 minutes (>14 fresh air exchanges/hour).
  • Agent-free/’clean machine’ (see technician page).
  • Dantrolene available.
  • MH trolley (see technician page).


General Anaesthesia:
  • ECG
  • Temperature/nasal/axillary
  • SpO2
  • ETCO2
  • ABGs checked intraoperatively only if indicated. E.g. unexplained tachycardia

For Neuraxial/Regional Anaesthesia:

  • ECG- Temperature (axillary)
  • SpO2
  • ETCO2 via nasal prongs


  • Thiopentone/Propofol are safe. Ketamine may cause confusing signs
  • Suxamethonium and potent inhalation agents are contra-indicated
  • Non-depolarising muscle relaxants/narcotics are safe
  • Neostigmine is safe (avoid atropine during an MH reaction – tachycardia, reduced temperature loss)
  • IV fluids – normal saline

Management Post-operatively:


  • Continue monitoring temperature, SpO2, ECG, respiratory rate, PR, BP and ETCO2 (if available)
  • Take four measurements of the above over an hour, i.e. each 15 minutes
  • ABGs measured only if abnormal intraoperatively, or abnormal signs in recovery
  • Monitor in standard recovery area. Safe concentrations of inhalational agents are <5ppm. Not achieved in a well ventilated recovery
  • For a regional procedure standard monitoring period – approximately 30 minutes

Inform Anaesthetist if:

  • HR > 130 bpm
  • SpO2 < 94%
  • Temperature >38.5oC
  • Base deficit > -6mmol/L
  • ETCO2 >55mm Hg


  • Discharge to the DOSA ward after one hour if the above measurements are stable
  • Three groups of measurements at half-hourly intervals, RR, PR, BP, Temperature
  • Contact anaesthetist if PR >130bpm and temperature >38.5oC


  • Patient can then be discharged home if stable
  • Next day contact home/ward to check that there were no complications

Drug Use

Drug use in malignant hyperthermia susceptible patients

  • Depolarising muscle relaxants.
  • Potent inhalational agents (excludes N2O).
  • Long acting cholinergic drugs (Neostigmine is safe).
  • Calcium channel antagonists with simultaneous Dantrolene use.
Use with Caution:
  • Ketamine. Signs may be confused with an MH reaction.
  • Aminophylline and Theophylline related compounds
  • 5 H.T agonists.
Commonly used Drugs that are Safe:
  • Opioids
  • Local anaesthetics
  • N2O
  • Ecbolics
  • Sympathomimetics
  • NSAIDs
  • Antibiotics 

Susceptibility Check

Checking of Names for MH Susceptibility:
Booked Lists cases:
  • As assistants to the anaesthetist, anaesthetic technicians are responsible for the checking of surnames of people having operations the next day, then all names that may be MH related are highlighted. Children have the father and mother's susceptibility checked.
  • The anaesthetists are therefore made aware and obtain the necessary family history from the patient.
  • MH names are found on a comprehensive computer database which is only accessible by the technicians and anaesthetists at Palmerston North Hospital.
  • There is a manual systems still available of extensive family trees in relation to MH as back-up should the computer fail.

Acute Cases:

  • Patients who come for acute surgery have their names checked by the Technician on duty and if the name is associated with MH, the Anaesthetist is informed and they check out susceptibility.
  • If an association is suspected, and agent free Anaesthetic Machine is available and used.
  • With monitoring the appropriate equipment a Trigger free anaesthetic is given.
  • People with MH Negative Biopsies are given a normal anaesthetic.

Malignant Hyperthermia Susceptible:

  • People who have positive muscle biopsy results have their medical notes labelled and a National Health Index alert is placed on their notes.
  • Patients with positive muscle biopsy results are advised to contact their GP to obtain a medic alert bracelet.
  • If any assistance is required in regard to Malignant Hyperthermia susceptibility, Contact: Palmerston North Hospital, Operating Theatre on (06) 350-8500 and ask for the Consultant Anaesthetist on call.

Susceptible Parturient

Suggested protocol for the management of the malignant hyperthermia susceptible parturient and postnatal care of infants at risk.

Notification & Counselling
  • Antenatal
    • Specialist referral (anaesthetist/obstetrician). This applies even if the partner is MHS, and not the patient.
    • Patient counselled by anaesthetic staff at the same or subsequent antenatal visit. Check family tree, discuss labour management, physical examination.
    • Base Hospital management (ideally).
  • Labour (Delivery Suite)
    • Notify anaesthetic staff immediately patient is in labour or delivery proposed. Consultant Anaesthetist should be informed of any MHS patient in labour or undergoing surgical procedure.
    • Preparation of theatre for possible use (anaesthetic technician):
      - unused for 15 minutes
      - vapour free machine available
      - MH trolley available
      - Dantrolene available
    • Notify anaesthetic technician if patient in labour or delivery proposed.
    • Paediatrician informed.

Management During Labour

  • Blood tests - should be taken early in labour (Hb, urea & electrolytes, creatine kinase (CK), calcium).
  • Pain relief - epidural early in labour as first option pain relief to minimise stress and activity – helpful for baby.
  • Monitoring - pulse / BP hourly temperature (oral / axillary) hourly. If temp >38.5oC - radial line for ABG’s ? - Sp02
  • Monitoring - the mother should have continuous CTG monitoring during labour.

Observations - see Table A

TABLE A Frequency Notify Specialist Anaesthetist
Blood pressure Hourly If rising
Pulse Hourly If > 120 beats/min
Oral Temperature Hourly If > 38.5oC:
Measure SpO2
Measure arterial blood gases (notify on call specialist anaesthetist if base deficit >8mmol/L)
Radial artery line may be indicated
  • Ranitidine - 150mg orally and repeat 8 hourly
  • Fluids - use normal saline or Dextrose / Saline (avoid Hartmans).
  • Post-partum maternal observations:
    - after delivery 1 hourly RR, pulse and temperature for 4 hours, then discontinue if satisfactory.
  • Creatine Kinase - measure 14-24 hours postpartum
  • Transfer - to another unit after 4 hours if required
  • Note - Adrenalin containing solutions, syntocinon or ergometrine are not contraindicated.

At Risk Newborn

  • Positive partner:
    If the father is positive and the mother is normal, intensive monitoring of the mother is not required. However, the foetus may be susceptible, so foetal monitoring is indicated, and continued after delivery (see below).
  • Post-partum:
    All newborn of either a susceptible mother or father are to have vital signs recorded hourly for 4 hours after delivery (pulse, respiratory rate, temperature). Contact the anaesthetist on call if recordings are abnormal. (See table B)

TABLE B Frequency Notify Specialist Anaesthetist
Respiratory rate Hourly >60/min
Pulse Hourly >180 bpm
Temperature Hourly >37.5oC :
Measure SpO2
Measure ABG’s

Emergency Caesarean
Anaesthetic for caesarean section for the MH susceptible parturient.
Care before Anaesthetic:
  • Notify anaesthetist.
  • Operating theatre (see labour protocol for preparation).
  • Notify paediatrician.
  • Blood tests (FBC, renal profile, CK, Ca++) – not required for a woman whose partner is MHS.
  • Dantrolene prophylaxis no longer used.
  • Antacid prophylaxis (important for MHS women as risk may be increased without the use of Suxamethonium).
  • Elective Caesarean patients receive Ranitidine 150mg orally at 2100 hours the night before, and 150mg orally at 0700 hours on the day of surgery.
  • Emergency Caesarean patients receive 150mg orally 12-hourly or 50mg IV 8-hourly during labour, or 50mg IV once decision has been made to perform Caesarean section.
  • 30mls Sodium Citrate 0.3 molar is given 10 minutes before surgery.
  • IV fluids – Normal saline.

Regional Anaesthetic – Care in Operating Theatre / Recovery:

  • Regional Anaesthesia
    • Regional anaesthesia (spinal or epidural) is preferred
    • Any local anaesthetic may be used
    • Adrenalin containing solutions of local anaesthetic are not contraindicated.
    • Other sympathomimetics are not contraindicated
    • Ephedrine can be safely used if required for hypotension
  • For a Woman who is herself at risk of Malignant Hyperthermia
    • ECG, Non-invasive Blood Pressure (NIBP), Pulse Oximetry (SaO2) are always measured at Caesarean Section.
    • Axillary/oral temperature measurement.
    • End Tidal Carbon Dioxide (ETCO2) by nasal prongs is monitored intraoperatively.
  • Ecbolics
    • Syntocinon is safe, Ergometrine can be used if necessary
  • Arterial Blood Gases (ABG’s)
    • Taken during Caesarean Section if indicated by:
      - Sustained tachycardia >120 beats/min
      - Rising temperature >38.5oC
    • Serial ABG’s indicated (site an arterial line), if abnormal signs/results at any stage, especially Base Deficit >8 mmol/L or temperature >38.5oC.
  • Post-Anaesthetic Care Unit (Recovery Ward)
    • Remains in Post-anaesthetic Care Unit for standard recovery time after Caesarean Section (monitor temperature, SpO2, NIBP and BP for thirty minutes)

General Anaesthetic – Care in Operating Theatre / Recovery:

  • Suxamethonium and all volatile agents must be avoided in all MHS women and partners of MHS men,as these can cross the placenta to the foetus (Suxamethonium crosses the placenta in small quantities).
  • There must be careful assessment of the airway and ability to intubate: - Awake oral fibreoptic intubation recommended if any difficulty anticipated.
  • Rocuronium 1mg/kg can be given 30 seconds before induction agent to provide rapid intubating conditions:This will last a long time, so ventilation must be possible. Alternatively Atracurium 1mg/kg after induction has slower onset. Remifentanil 4mcg/kg can be used for intubation without any muscle relaxant. It may cause respiratory depression in the neonate, it may cause hypotension and bradycardia in the mother. It will wear off quickly if intubation fails.  
  • For Woman who is Herself at Risk of Malignant Hyperthermia- ECG, SpO2, ETCO2, nasal temperature probe is placed for continuous temperature monitoring intraoperatively and for one hour afterwards in Recovery.
  • Induction of Anaesthetic -Induction is with Propofol and non-depolarising muscle relaxant/remifentanil as above. Alfentanil and/or Fentanyl may also be used (notify Paediatrician)
  • Maintenance of Anaesthetic - Maintenance is with Propofol infusion, Nitrous Oxide, and Opioids.
  • Arterial Blood Gases (ABGs) - Taken during Caesarean Section if indicated by: - Sustained tachycardia > 120beats/min -Rising temperature > 38.50C. Serial ABGs indicated (site an arterial line), if abnormal signs/results at any stage, especially base deficit >8mmol/l or temperature >38.50C
  • Ebolics - Syntocinon is safe. Ergometrine can be used if necessary
  • Reversal - Neostigmine/atropine can be used
  • Post-Anaesthetic Care Unit (Recovery Ward)- Observe for one hour with continuous ECG, temperature, SpO2, ETCO2 via nasal prongs, RR, BP (4 measurements over one hour). ABG’s indicated if abnormal signs/results at any stage, especially Base Excess >8mmol/L or temperature >38.50C. Repeat creatine kinase 14-24 hours post-delivery.
  • For woman who herself is not at risk of Malignant Hyperthermia- Induction and intubation as above. Maintenance with propofol infusion, nitrous oxide and opioids as above. After delivery of the baby volatile agents can be used in the normal way. No extra monitoring is required after delivery or in the postoperative period.

Post-General / Regional Anaesthetic care in Postnatal Ward:

  • Infant -Monitor infant of Malignant Hyperthermia susceptible father or mother hourly for the first four hours following delivery:- Heart rate, Respiratory rate and Temperature.Notify on call Specialist Anaesthetist if there is an increasing trend or abnormal finding in any of the above (temp>37.50C, HR >180 bpm, RR > 60/min).
  • MHS mother- Check creatine kinase 14-24 hours after delivery

Post Anaesthetic Care Unit

Management of MH Susceptable Patients
The traditional management of MH susceptible patients has consisted of administering an anaesthetic free of MH triggering agents, and monitoring for 4-6 hours in the post-anaesthetic care unit (PACU). The disadvantages are increased costs and disruption of nursing staff, particularly if a young child has to be managed in PACU for four hours.
We looked at reducing this time, and initially a literature review showed that almost all MH reactions developing in PACU within one hour of transfer to recovery, including those with triggering and non-triggering anaesthetics.
Also, a retrospective review of all PACU data in MH patients was undertaken about the same time to identify any particular problems that may be occurring. PACU data in MH susceptible or related patients was reviewed between 1991 and the end of 2000, showing that no significant problems were evident.
As a result of the two reviews, the monitoring period in PACU was changed to one hour, and below is the protocol followed:

Patient population:

Patients included are MHS and MHE tested according to the European MH Work Protocol. Also included are a large group who are related to MHS individuals but have not been tested for various reason, often because they are too young.


On transfer to recovery, a set of measurements are taken immediately (table 1) and then at 15 minute intervals for one hour.
If the patient is stable, he/she is then discharged either to the ward if an overnight stay is required, or to a step-down unit where a further set of three observations are taken at half-hourly intervals, excluding end-tidal CO2 (ETCO2). If the patient is stable they can then be discharged home, but if the procedure is short or the patient is looking particularly well they can be discharged at any time within the step-down unit period, and this occasionally tends to happen.
On discharge the caregiver is given a note with advice to contact the Duty Anaesthetist if the temperature is >38oC, or the patient passes dark urine. The PACU nursing staff check the patient by telephone the following day.


This prospective study so far involves 68 patients, aged 1 to 68 years, mean age of 24 years. Anaesthesia time is 15 minutes to 2 hours 40 minutes, with a mean of 49 minutes.
Fig 1 represents the MH status and anaesthetic preference of the 68 procedures – 27 MHS, 37 NBD (no biopsy done), but these were all direct relatives of MHS individuals, and 5 MHE patients. Only 19% had regional anaesthesia, and all others had General Anaesthesia.
Fig 2 details the range of surgical procedures undertaken. General procedures such as appendices, incision and drainage of abscess, hernia repair, etc, counted for about 25% of the procedures, muscle biopsy 20%, and others are indicated. 
Diagrams to be added
The PACU data is shown in table 2. The numbers refer to the peak recording for each parameter. Mean values are bracketed. There have been few significant findings. Five patients had ETCO2 greater than 50mm, probably secondary to hyperventilation, five had SPO2 less than 95% readily corrected with supplemental oxygen. No patient had significant hyperpyrexia, and although there were a few increased respiratory rates and tachycardias, these were mainly in anxious younger children. No patient achieved >3 on the MH Clinical Grading Scale (MHCGS), there was no evidence of MH, and Dantrolene was not used.
Only minor problems such as tachycardia and increased respiratory rate were reported in the step-down unit. 72% were managed as day-stay patients, and nursing staff followed up 97% the following day, and no problems relating to MH were reported.


This is a small but ongoing study, but there is no evidence of MH caused by the stress of anaesthesia in surgery. A one-hour period of close monitoring in PACU has not resulted in any missed reactions or risk to the patient. Even that time may be able to be reduced in the future.

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