Hyperventilation during EEG workup, a common practice to elicit interictal epileptiform discharges, helps to diagnose and classify seizure disorders, and is rarely associated with adverse events, according to a British investigation published online in Seizure – European Journal of Epilepsy.
The International League Against Epilepsy and other groups recommend hyperventilation (HV) as part of a standard EEG, but there has been uncertainty about the risks of triggering a seizure with HV and its diagnostic value, and about what to tell patients about the risk-benefit ratio.
Dr. Nick Kane, a neurophysiologist at Frenchay Hospital in Bristol (England), and his associates evaluated 3,475 patients hyperventilated for a median of 3 minutes during EEG. Among the patients, 3,170 (91%) were referred for epilepsy or possible epilepsy, 102 (3%) had possible psychogenic nonepileptic seizures, and 203 (6%) had other diagnoses. Patients ranged from infants to nonagenarians and were split evenly between the sexes.
Among the 3,170 suspected-epilepsy cases, HV during EEG elicited interictal epileptiform discharges (IEDs) in 95 patients (3%) who did not have them at rest and exacerbated IEDs in another 292 patients (9.2%). In other words, HV directly or indirectly diagnosed epilepsy and helped to classify seizure type in 12.2% of cases (Seizure 2014;23:129-34).
HV triggered seizures in 69 suspected-epilepsy cases (2.2%), but it’s "worth bearing in mind that in our survey, the vast majority [of provoked seizures] were generalized absences in children without any apparent sequelae. Indeed, provocation of this seizure type is the intention of HV," the team said.
Only one patient had a generalized tonic-clonic seizure.
The findings are in keeping with previous investigations and "confirm that HV in selected patients is a valid activation technique in diagnostic electroencephalography, where the potential benefits outweigh the risks, and also provide information that may assist the informed consent process," the investigators concluded.
The 69 seizures included 59 generalized attacks (86%) – 54 of them absences in children about 10 years old – plus 8 focal seizures (12%) mostly in adults and 2 unspecified seizures.
Twenty-five of the children with absence seizures did not have them at rest, meaning that "HV gives a nearly twofold increase in generalized absence seizures" for diagnostic purposes, Dr. Kane and his team noted.
In the overall group of 3,475 patients, there were no significant cardiovascular or respiratory events, just wheezing in 1 patient with asthma and tachycardia in 1 patient with psychogenic nonepileptic seizures. Both problems ended when the patients stopped hyperventilating.
Thirty-one patients (0.9%) had psychogenic nonepileptic seizures, which involved rhythmic jerks and twitches without EEG abnormalities.
"There are clinical situations where HV is best avoided altogether, particularly when there is a risk of cerebral vasospasm-induced transient ischemic attack or stroke, a recognized complication of HV in patients with sickle cell and moyamoya disease. ... [And] it is sensible to avoid HV in patients with known recent cerebrovascular events (including cerebral infarction, subarachnoid and intracerebral hemorrhage) and significant coronary artery disease," they wrote.
The investigators had no disclosures. The British Society for Clinical Neurophysiology and Association of Neurophysiological Scientists funded the work.