Mild nocturnal hypoxemia and sympathetic nervous system activation in infants with viral bronchiolitis

Introduction and Aims: Current guidelines suggest that oxygen may not be administered to infants with bronchiolitis and SpO2 >90%. However, the pathophysiological consequences of acute hypoxemia in infants are unknown. We hypothesized that even mild nocturnal hypoxemia is associated with increased pulse rate. Methods: Hospitalized infants with bronchiolitis and diurnal SpO2 >90% underwent nocturnal oximetry before discharge. Primary outcomes were: (i) nocturnal average pulse rate; (ii) pulse rate index = [(average pulse rate)-(95th percentile value in active sleep for age)] X 100/ (95th percentile value in active sleep for age). Explanatory variables were: (i) group assignment i.e. bronchiolitis with nocturnal basal SpO2 >90% and <95% vs. bronchiolitis with SpO2 ≥95% vs. controls without lung disease; and (ii) the cumulative nocturnal hypoxemia score (Acta Paediatr 2015;104:e106). Results: Infants with bronchiolitis and hypoxemia (n=24; median age [IQR] 2.6 [1.7-3.6] months) had significantly higher average pulse rate than infants with bronchiolitis and no hypoxemia (n=16; 2.6 [1.7-4.7] months) or controls (n=25; 2.8 [1.6-4.8] months): 138.1±11.8 vs 126.5±13.9 vs 123.4±9.2 bpm; P=.008 and P<.001. Pulse rate index correlated significantly with nocturnal hypoxemia score (r2=0.26; P<.001). After oxygen administration to 13 infants with bronchiolitis and hypoxemia, average pulse rate and pulse rate index decreased significantly (mean: -9.5 bpm; 95% CI: -3.8 to -15.1; P=.003 and -6.5%; 95% CI: -2.5% to -10.5%; P=.004, respectively). Conclusion: Infants with bronchiolitis and mild nocturnal hypoxemia have increased pulse rate which decreases after administration of oxygen.