[alice md]

myasthenic crisis is not a rare complication of MG. It is estimated to occur in 20% of patients and probably much more in MuSK.

I therefore think it is important that patients will know this:

There are more and more studies that show that 70% of patients with myasthenic crisis can be managed with non-invasive ventilation, without the need for intubation.

An important parameter for the success of NIV is the level of CO2 and bicarbonate in the blood.
a level of CO2 above 45 (which is marginally above normal levels for normal people) decreases the success rate significantly. (this goes with what Annie said, regarding CO2 levels in MG, and there is surprisingly sparse data regarding levels of CO2 in patients with MG at baseline).
More important is a bicarbonate of over 30. This means that the patient has been having relatively high levels of CO2 (compared to his normal) for a significant time. to the extent that his body started compensating for it.

the fact that 30% of patient do require intubation because of high levels of CO2 and bicarbonate means to me that those patients have arrived late. And possibly if they came earlier they would have done much better.

None of this comes as a surprise, because the same is true for any other illness. eg-asthma, myocardial infarction, sepsis etc. We know that once your body has to start compensating for the damage it is very late in the game, and intervention should have been done much earlier. This has a significant effect on morbidity and even mortality.

So, I think the bottom line is that patients with MG should learn to recognize early signs of respiratory failure, and also insist on having a trial of NIV. They also need to explain to their physicians that treatment should be started before there is a change in their CO2 level. The best parameters to follow are the negative inspiratory pressure and maximal expiratory pressure. which should be above 20-30 and 40 respectively. The vital capacity which is being used in many neurology wards around the world has been shown to be a very poor parameter.

Also, patients who have respiratory involvement should have a peak flow meter (like the one used by asthma patients), know their baseline and check it when they are experiencing respiratory symptoms.

I can tell you (from my own experience) that a timely treatment with NIV can lead to such a rapid and dramatic improvement that it looks "impossible" to some neurologists who have very little understanding in respiratory physiology.

alice