Febrile seizures occur in 2-5% of the population and are typically limited to children between 3 months and 5 years-of-age. The pathophysiological link between increased body temperature and increased seizure susceptibility is unsolved in humans. In a mouse model it has been shown that young animals had a tendency to hyperventilate thereby causing intra-cerebral hypocapnia / alkalosis and a decrease of their seizure threshold. This effect was not observed in older animals. Redressing the pCO2 (carbon dioxide partial pressure) by breathing carbon dioxide enriched air instantly stopped the seizures.

In this study the investigators want to investigate the respiratory physiology in children with febrile seizures and compare it to children who have fever but did not have febrile seizures.

The investigators hypothesize that in children with febrile seizures the rising body temperature triggers a larger increase of respiratory rate (hyperventilation) and subsequent drop in pCO2 levels.

This study could provide the basic physiological data for an interventional trial to test the efficacy of carbon dioxide inhalation to interrupt febrile seizures.

The aim of the study is the continuous non-invasive monitoring of

• body temperature
• respiratory rate
• transcutaneous pCO2
• heart rate
• pulsoxymetric SaO2 (arterial oxygen saturation) during a febrile illness
• in children without febrile seizures and
• in children who had suffered a febrile seizure during the actual febrile illness.

Children will be recruited from the emergency units of the Charité University Hospital and a large Community Hospital, matched according to age, gender and the cause of their febrile illness and their data will enter final analysis if their body temperature rose at least once to or above 38.0 degree C and changed more than 1.0 degree C during the observational period.

Inclusion Criteria:

• Febrile illness with body temperature ≥38.0 degree C
• 50% of study population: never had a febrile seizure
• 50% of study population: simple or complex febrile seizure within one day of investigation
• Change of body temperature of ≥1.0 degree C during the monitoring period
• Provision of written informed consent by the parents or guardians of the child
• Artefact-free simultaneous measurement of respiratory rate, pCO2 (transcutaneous probe), body temperature (rectal probe), and heart rate during change of body temperature of ≥1.0 degree C.

Exclusion Criteria:

• Past history of afebrile seizures
• Past history of neonatal seizures
• Retarded psychomotor development
• Chronic respiratory disease
• Cardiologic disease
• Severe other organ disease
• Permanent medication for chronic disorder
• Therapeutic increase of inspiratory oxygen concentrations during the observational period

Children with febrile illness between 3 months and 5 years of age with a body temperature of >38.0 during the monitoring period.