High Carbon Dioxide Levels in Blood at Myasthenic Crisis Onset Linked to Increased Mortality Risk, Study Suggests

High levels of PCO₂ — a measure of the amount of carbon dioxide gas dissolved in blood — may be a useful biomarker for higher mortality risk in people with myasthenia gravis undergoing acute respiratory crisis, a study suggests.

The study, titled “Myasthenic crisis treated in a Chinese neurological intensive care unit: clinical features, mortality, outcomes, and predictors of survival,” was published in the journal BMC Neurology.

One of the most serious complications of myasthenia gravis is known as myasthenic crisis, in which patients experience significant respiratory muscle weakness, leading to acute respiratory failure that requires mechanical ventilation (assisted breathing).

Myasthenic crisis occurs in approximately 10–20% of people with myasthenia gravis over the course of their disease. It can be quite dangerous, though mortality rates have been significantly reduced since the development of intensive care techniques.

To understand more about the clinical characteristics, management, and outcomes of patients who go through myasthenic crisis, a group of Chinese researchers conducted a retrospective study. The study included 113 people who had been admitted to a neurological intensive care unit (ICU) for such a crisis.

The researchers sought to identify clinical and other factors at the time of the onset of the myasthenic crisis that might predict outcomes and survival for these patients.

First, they determined that the mortality rate at time of onset of myasthenic crisis upon admission into the neurological ICU was 18.6%.

When examining different factors that could predict outcomes for these patients, researchers found that both the PCO_2, and the score on the Myasthenia Gravis–Activities of Daily Living scale, at onset of myasthenic crisis correlated with both duration of ventilation and length of ICU stay. The MG-ADL is a measure of disease activity.

Additionally, the results showed that, compared with patients who had good outcomes, those with intermediate or poor outcomes tended to be older at first myasthenic crisis onset. Those with intermediate or poor outcomes also had lower pH, or high acidity in blood, and lower PO_2, or oxygen dissolved in blood. They also had higher PCO₂ before intubation, which is the process of inserting a breathing tube.

Statistical analysis identified pre-intubation PCO₂ levels as an independent predictor of survival. Higher PCO₂ levels likely indicated the presence of chronic respiratory acidosis, a medical condition in which decreased breathing increases the concentration of carbon dioxide and acidity in blood.

“Therefore, in MC patients with extremely high PCO₂ level before intubation may obtain poorer prognosis, especially in patients with older age,” the researchers said.

Additional statistical analysis identified that age at first myasthenic crisis onset was significantly associated with mortality.

“Our results suggest that PCO₂ before intubation and MG-ADL [Myasthenia Gravis–Activities of Daily Living] score at MC [myasthenic crisis] onset may be useful indicators of more severe disease likely to require extensive respiratory support and ICU management,” the researchers said.

“Timely and effective treatment for chronic respiratory acidosis before ICU admission may help prevent exacerbation and improve outcomes,” they added.