myasthenia gravis

tutorial today by Dr Hari - question was apparently asked in oct 2009

you are an anaesthetist in a rural hospital and the obstetrician calls you regarding an emergency CS for NRFS. She also has a past history of myasthenia gravis

1) how do you go about determining the degree of NRFS

-use of CTG - presence of late or variable decelerations, defined as decrease in HR of more than 15 beats lasting at least 30 s

-use of scalp pH (normal pH of neonate 7.25-7.35), so fetal distress is when scalp pH <7.25

2) how do you go about assessing this patient for op

don't just focus on the obstetric history- placenta praevia, antenatal history, GDM, lie etc, gestation

-history

-clinical exam

-go through relevant investigations

-old notes

history: extent of disease, control, recent exacerbations esp due to pregnancy

medications: pyridostigmine dose, steroids, immunosuppressants, plasmapheresis

autonomic instability

pre op PFT

issues of post op ventilation:

management: pre op aspiration prophylaxis, neonatologist, wedge , warm OT for baby

standard monitoring, airway trolley and difficult airway adjuncts, experienced surgeon, colleague to help with anaesthesia, AU

working IV plug

maintain with 02:n2o:inhalational, use bis to reduce amount of inhalational (potentiate nm weakness), nerve stimulator

pharmaco: duration of action of sux : unpredictable, may require higher dose eg 2mgkg

high dose may cause type 2 blockade, onset delayed

if on regular plasmapheresis, enzyme to metabolise sux may be reduced

increased sensitivity to relaxant

if not given usual meds preop: controversial- give IV neostigmne 1:30mg pyrido or NG pyrido?

non depolarising: give 1/10 of usual dose, titrate to nerve stimulator

• Ensure that the patient is reminded prior to induction of the possibility of a prolonged intubation*

Extubation: performed on awake patients and hopefully close to his/her baseline status. Reinstitute anticholinesterase medication, either by IV infusion or by reimplementation of the patient's oral regimen.

Leventhal criteria: Predictive scoring system for the need for postoperative ventilation

1) duration of disease for 6 years or longer

2) chronic comorbid pulmonary disease

3) pyridostigmine dose >750 mg/d

4) VC <2.9L

5) Other indicators include preoperative use of steroids, and previous episode of respiratory failure.

These predictors have not been widely validated. (1)

Drugs to avoid: Calcium Channel blockers, Magnesium, Aminoglycoside antibiotics as all of these may contribute to muscle weakness

Post-Op Bed: Patients should be monitored in either a ICU or step-down unit but NOT to a conventional surgical ward.

3) MG vs eaton lambert,

tensilon to differentiate

4) baby not breathing , mother not stable

priority is to stabilise mother

baby: SpO2 88% Hr 50, chin lift and BVM (? pressure gauge), towel under shoulders. intubate , start CPR

CVS collapse most likely due to hypoxia

call code blue, adrenaline 10mcg/kg

stop CPR when HR >60

ETT adrenaline 100mcg/kg (other routes IM, umbilical)

resus guidelines :ARC

5) PPH: anaes plan

-defined as? >500ml/24h

-fluid resus

-post partum : assum gastric physiology and aspiration risk still present up to 48h

-issues of recent GA, physiology changes, MG