Ventilatory response to CO₂ in patients with epilepsy

Area of Science:

• Neurology
• Respiratory Physiology
• Epilepsy Research

Background:

• Severe periictal respiratory depression is a suspected risk factor for sudden unexpected death in epilepsy (SUDEP).
• The determinants of periictal respiratory depression, particularly interictal ventilatory control, are not well understood.
• Interindividual differences in hypercapnic ventilatory response (HCVR) may predict severe periictal hypoventilation.

Purpose of the Study:

• To evaluate a method for measuring interictal HCVR at the bedside in an epilepsy monitoring unit (EMU).
• To examine the relationship between interictal HCVR and postictal hypercapnia following generalized convulsive seizures (GCSs).
• To identify potential risk factors for severe respiratory depression and SUDEP in epilepsy patients.

Main Methods:

• Interictal HCVR was measured using a modified rebreathing technique with a respiratory gas analyzer.
• Minute ventilation, tidal volume, respiratory rate, and end-tidal CO2 were continuously recorded.
• Postictal respiratory parameters, including transcutaneous CO2 and oxygen saturation, were monitored during video-electroencephalography (EEG).

Main Results:

• HCVR measurement was well-tolerated, rapid, and safe in the EMU setting.
• HCVR slope was inversely correlated with the duration and magnitude of postictal hypercapnia after GCSs.
• A subset of patients exhibited very low CO2 sensitivity, correlating with increased postictal CO2 levels.

Conclusions:

• Bedside HCVR measurement is feasible and safe in epilepsy patients.
• Low interictal HCVR may identify individuals at increased risk for severe respiratory depression and SUDEP.
• Further research into low HCVR as a SUDEP risk factor is warranted.