No abstract

We report changes in arterial blood-gas tensions for up to 5 min of apnoeic oxygenation in 26 anaesthetized paediatric patients (21 children, five infants). Changes in oxygen and carbon dioxide tension were greatest in the first minute of apnoeic oxygenation. In subsequent minutes, rates of change in gas tension were approximately constant. The rate of decline in oxygen tension (31 (95% confidence interval (CI) 20.1-42.2) mm Hg min-1) was more than three times that reported in studies in adults. The rate of increase in carbon dioxide tension (4.2 (95% CI 3.7-4.7) mm Hg min-1) was similar to that reported in adults. After successful preoxygenation, oxygen tension remained greater than 290 mm Hg in all children (age > 1 yr) throughout the study. This was not the case in infants. We found no correlation between changes in blood-gas tensions and age or weight of patients. The small number of infants studied showed rapid decreases in oxygen tension which if sustained would be expected to limit the safe duration of apnoeic oxygenation, unlike adults where apnoeic oxygenation is limited by hypercapnia. Extrapolation of our results suggests that when preoxygenation has been successful, apnoeic oxygenation could continue safely in children for at least 10 min. Infants may become hypoxic after only 2 min.

Uncontrolled studies of avoidance of house dust mite (Dermatophagoides pteronyssinus) by atopic subjects have reported clinical improvement in the severity of eczema. The aim of the present study was to examine the temporal relationship between environmental exposure to the major mite allergen (Der pI) and clinical disease severity in children with chronic atopic eczema. Twelve children were identified as being house dust mite-sensitive on the basis of skin prick test and RAST to Der pI. They were examined on two occasions with a median interval of 63 days. Clinical severity of eczema improved in nine children and deteriorated in two children during this period. Der pI concentration in dust from mattresses changed significantly in only three subjects and there was no correlation between changes in clinical severity and changes in environmental Der pI exposure. Change in RAST against Der pI did correlate positively with change in Der pI exposure (rho = 0.56, P less than 0.05) but these changes were not associated significantly with changes in eczema severity or skin test response to Der pI. It is concluded that the observed changes in clinical severity were unlikely to be due to immediate hypersensitivity responses to natural variations in Der pI concentrations in the personal environments of these subjects.

Background-The effect of inhaled P2 adrenergic drugs on infants with wheezing disorders remains controversial. Salbutamol inhibits the bronchial responsiveness of infants to histamine and nebulised water but whether or not it acts as a bronchodilator in this age group is unclear. The aim of the present study was to determine whether salbutamol can hasten the reversal of histamine induced bronchoconstriction in infants. Methods-Bronchial challenge with histamine was performed in 40 infants aged 12 months or less with no previous history of respiratory symptoms. Response to histamine was assessed by forced partial expiratory flow/volume curves to measure maximal flow at functional residual capacity (VmaxFRC). After a fall of 40% or more from baseline VmaxFRC, each infant was randomly assigned to receive either salbutamol 0-5% or saline 0 9% solution by nebuliser. The rate of recovery of VmaxFRC and the time to reach baseline VmaxFRC were derived by linear regression. Results-Infants who received salbutamol had a significantly faster rate of recovery (geometric mean 8-5 mllslmin) than those who received saline (4.1 mlls/min).Considerable interindividual variation was observed in the time from maximum bronchoconstriction to recovery of baselineVmaxFRC in both groups of subjects. Conclusions-Salbutamol significandy speeds the reversal of histamine induced bronchoconstriction in infants during the first 12 months of life. This observation provides further evidence to support the presence of functional p1 adrenergic receptors in the airways of infants. (Thorax 1993;48:317-323) The effect of inhaled ft2 adrenergic drugs on infants with wheezing disorders remains controversial with many studies showing no improvement in lung function,"A and others showing a decline in function.57 The observed absence of a clear beneficial effect of #2 agonists in wheezy infants is not explained by an absence of #2 adrenergic receptors in the infant lung, as studies have shown a protective effect of inhaled salbutamol on histamine challenge8 and nebulised water challenge9 in recurrently wheezy infants. A study by Tepper'°suggested a therapeutic effect of isoprenaline after methacholine challenge in healthy infants, but this evaluation was neither controlled nor randomised. Histamine and methacholine have different pharmacological effects on the airways" and methacholine has been shown to provoke more central bronchoconstriction than the more peripheral action of histamine.'2 Histamine and methacholine also induce different time courses of bronchoconstriction in adult subjects with more rapid recovery following histamine challenge.'3 Recovery after histamine challenge in infants is also rapid but there is considerable intersubject variation. 14 There is no clear information on the effect of inhaled salbutamol on histamine induced bronchoconstriction. This study was designed to test the hypothesis that, in infants during the first 12 months of life, inhaled salbutamol would lead to a more rapid recovery of baseline lung function ...

A study was undertaken to examine the circadian rhythm of peak flow rate in asthmatic and normal children in the community by means of cosinor analysis. An initial study of 12 matched pairs of asthmatic and normal children was used to determine the mean amplitude of peak expiratory flow (PEF) variability in the two groups (7-8% and 4-4%) and the number of subjects required to show a significant difference. On the basis of this study 37 community based children with asthma diagnosed by questionnaire and 40 control subjects measured PEF four times daily for 14 days. Cosinor analysis of the data produced a significant fit in 20 asthmatic and 18 control children. A small but significant difference in amplitude was observed between the asthmatic (6 2%) and the control (4-2%) children. There was no significant phase difference between the rhythms in the two groups. Cosinor analysis explained 14% of PEF variance. It did not provide a reproducible estimate of phase between week I and week 2; the acrophase changed by more than one hour in 26 of the 37 asthmatic children. The cosinor model may be inappropriate for the investigation of low amplitude circadian rhythms, especially when measurements are made infrequently.