Histamine provocation in young, awake children with bronchial asthma, using a fall in oxygenation as the only indicator of a bronchial reaction D Holmgren 1 , S Redfors 2 , G Wennergren 3 and G Sten 2 Departments of Pediatric Cardiology 1 , Pediatric Clinical Physiology 2 and Pediatrics 3 , Sahlgrenska University Hospital/O ¨ stra, Go ¨ teborg, Sweden Holmgren D, Redfors S, Wennergren G, Sten G. Histamine provocation in young, awake children with bronchial asthma, using a fall in oxygenation as the only indicator of a bronchial reaction. Acta Pædiatr 1999; 88: 545–9. Stockholm. ISSN 0803–5253 Bronchial provocation with histamine was performed in 11 boys and 6 girls, age range 2.7–7.4 y, with unspecific respiratory symptoms or bronchial asthma, using a fall in oxygenation as the only indicator of a bronchial reaction. In addition to transcutaneous oxygen tension (tcPO 2 ), transcutaneous carbon dioxide tension (tcPCO 2 ) was continuously monitored during the provoca- tion procedure in order to identify possible changes in ventilation. A fall of 20% or more in the tcPO 2 below a “floating” baseline value, defined as the highest tcPO 2 value between the inhalations of histamine up to that point, was regarded as indicating a significant bronchial reaction. One child was excluded from the study because of an “early, false-positive” reaction due to hyperventilation during the inhalation, verified by a decrease in the tcPCO 2 followed by a compensatory period of hypoventilation, resulting in a fall of more than 15% in the tcPO 2 after the inhalation of saline. In the vast majority of the children, however, the tcPO 2 values remained stable during the first dose stages of saline and histamine, with either a gradual fall immediately before or a distinct fall in conjunction with the reaction. The mean reaction concentration was significantly lower in the group of children with clinical asthma, 0.74 mg/ml, compared with the group of children with unspecific respiratory symptoms, 2.00 mg/ml (p = 0.03). In conclusion, a 20% fall in the tcPO 2 can be used as the only indicator of a bronchial reaction during bronchial provocation tests in young, awake children. Changes in ventilation evaluated by monitoring tcPCO 2 , makes it possible to distinguish between a fall in oxygen tension due to an early, “false” reaction as a result of hypoventilation and a “true” bronchial reaction. & Asthma, bronchial provocation, oxygenation, young children D Holmgren, Department of Pediatric Cardiology, Sahlgrenska University Hospital/O ¨ stra, SE-416 85 Go ¨teborg, Sweden (Tel. 46 31 343 40 00, fax. 46 31 845029) In recent years, several studies have shown that the airway response to bronchial provocation can be evaluated by monitoring the transcutaneous oxygen tension (tcPO 2 ) (1–7). The transcutaneous technique for blood gas monitoring is advantageous, as it is non- invasive and almost independent of active co-operation from the child, thereby making it potentially applicable to studies of very young children. However, only one previous study has so far been reported in which a fall in oxygenation was the only indicator of a significant bronchial reaction during bronchial provocation in young, awake children (8). The reason for the hesitation about using the tcPO 2 as the only indicator of a bronchial reaction may be explained by methodological problems, such as difficulty creating “stable” baseline values in the transcutaneous blood gases due to the fact that the oxygenation may be affected by changes in the breathing pattern (9) and by the state of activity in the awake, young child (10). The aim of the present study was to evaluate the use of tcPO 2 as the only indicator of a bronchial reaction during bronchial provocation in young, awake children with bronchial asthma. Materials and methods Seventeen children, 11 boys and six girls, with a median age of 5.1 y (age range 2.7–7.4 y), were investigated consecutively after referral from the Pediatric Allergy Department at our institution. The children were investigated during an asymptomatic period without current or recent respiratory infection. Informed consent was obtained from the children and/or from one or both of their parents. The study was approved by the local medical ethics committee. The severity of the disease was evaluated according to a four-degree scale based on clinical criteria such as  Scandinavian University Press 1999. ISSN 0803-5253 Acta Pñdiatr 88: 545±9. 1999