MH Flashcards
What’s the mortality rate from MH in developed countries?
4-10%
How to help identify pts at risk of MH?
personal or FHx probs with anaesthesia
important to know FHx as a MH-susceptible pt may have had several uneventful anaesthetics
wherever possible, pts suspected of being @ risk of MH should have status verified with confirmatory tests (either through genetic testing or a muscle biopsy with in vitro contracture tests of the excised muscle)- can delay elective surgery for this. If a pts family member has been tested for MH, it’s advised that the relevant diagnostic unit be contacted. Unless the line of inheritance for the MH susceptibility trait between the diagnosed family member & the pt isn’t known to be broken by a relative proven not to be susceptible, the pt should be considered at-risk until proven otherwise.
If there was a suspected episode, valuable to know details (eg, timing wrt surgery, clinical features, Rx, Icu, presumed cause.
What conditions, other than MH, have risk of MH susceptibility?
other phenotypes associated with variants in the RYR1 (or STAC3) gene, eg:
- Forms of congenital myopathy such as core myopathies or King-Denborough syndrome, multiminicore disease, periodic paralysis, pts with a congenital myopathy who are yet to receive a genetic diagnosis will require this as part of their pre-op evaluation, to exclude a RYR1 aetiology or the STAC3 gene is also associated with MH susceptibility.
- pts with incidental finding of being a carrier of RYR1 variant of unknown significance
- idiopathic hyperCKaemia (persistently elevated CK levels >2x ULN for >=3/12 in absence of discernible cause)
certain myopathies with RYR1 abnormalities (or STAC3)- central core myopathy or multiminicore disease with a gain of function RYR1 defect, King-Denborough syndrome with a RYR1 defect, periodic paralysis, idiopathic hyperCKemia
conditions associated with rhabdo:
- exertional rhabdoymolysis
- severe statin-induced myopathy
-exertional heat illness
some muscle disorders don’t confer higher risk of MH but are associated with significant rhabdo & hyperkalemia following sux or volatile eg. Duchenne or Becker muscular dystrophy (both X-linked, recessive leading to abnormal formation of dystrophin)- treat with non-triggering agents
What conditions may be mistaken for MH?
- serotonin syndrome (tacchy, ANS instability (typically HTN), hyperthermia, tremor/hyperreflexia/clonus, ocular clonus, dilated pupils, babinski but no nystagmus)- triggering agent (serotonergic, cocaine, MDMA, ketamine, methylene blue, SSRI)
- NMS (tacchy, HTN, hyperthermia, m. rigidity, sweating, rhabdo)
- phaeochromocytoma: (extreme Art BP fluctuations, hyperthermia, sweat, usually no muscle involvement)
- thyroid storm: hyperthermia, no rigidity but may have rhabdo
- central anticholinergic syndrome: delayed emergence, hyperthermia, nystagmus, dilated pupils
- infection/septicaemia (hyperthermia, usually no muscle involvement)
How to manage pts considered MH susceptible?
avoid triggers (volatiles, sux).
ensure anaesthetic machine (rubber & plastic components of machine, ventilator bellows, soda lime, breathing circuit) flushed so that it delvers <5ppm of any potent inhalational- this may take from 5-104mins with FGF 10L/min.
Activated charcoal filters can reduce [] volatile delivered from a contaminated workstation to <5ppm within 3 min. If kept in place, VA [] can be maintained @ <5ppm with a FGF >1L/min for at least 24hrs but recommendations are that FGF stay at 3L/min & that filters are changed after 12hrs.
If inadequate time to flush workstation, remove vaporisers, flush circuit with O2/air max flow rate for 90 secs, insert activated charcoal filters on insp & exp limb, change breathing circuit & soda lime canister for uncontaminated equipment
If time, remove the vaporisers, change circuit & soda lime, flush circuit with max flow rate for workstation-specific time. maintain max FGF.
If a pregnant woman is known to be MH-susceptible, a delivery plan should be made limiting the need for emergency CS under GA- eg. epidural early in labour, have a machine ready in case she needs emergency OT transfer (no sux in the room, volatiles removed, MH trolley in the room)
If the father is MH susceptible, baby has 50% risk so treat the mother like she’s MH-susceptible until the umbilical cord clamped (if risk
Adverse effects of dantrolene?
muscle weakness, nausea
What’s the max occupational exposure limits for sevo & iso? how does this compare to the amount required to trigger MH?
60ppm (environmental [] can approach this during paediatric inhalational induction), 50ppm
the amount to trigger MH is 1-2x greater than these concentrations. environmental [] of sevo in PACU don’t exceed 1ppm.
Has IVCT been validated in pregnancy?
no
What agents use for ECT in suspected MH?
propofol, roc, sugammadex
What’s the FGF rate for flushing workstations to get volatile levels to <5ppm?
10L/min, time varies depending on the model
In ANZ, what’s the minimum weight & age for in vitro contracture test (IVCT)?
30kg
10yrs
What is the accepted safe level of inhalational agent in an anaesthetic circuit?
<5ppm
How rapidly may activated charcoal filters, placed on the insp & exp limbs of a contaminated machine, reduce volatiles to a safe level? how often should they be changed?
2mins
change them hourly
How to set up anaesthetic vaporisers with charcoal filters?
remove vaporiser
flush circuit for 90 seconds with oxygen or air @ 10L/min using ventilator with a 2L test lung
change full breathing circuit & soda lime while maintaining flushing at 10L/min (ventilatory unchanged)
insert activated charcoal filters on insp & exp limbs
maintain FGF of 10L/min for 90 mins from commencement of anaesthetic, after 90 mins, safe to reduce FGF to 3L/min
How many vials of dantrium (20mg dantrolene) or ryanodex (which has 250mg dantrolene & only requires 5mL sterile water for injection)?
a minimum of 24 (36 in remote locations)
a minimum of 2
