Time course of severe respiratory syncytial virus infection in mechanically ventilated infants

The time course of intensive care for severe respiratory syncytial virus (R SV) lower respiratory tract illness may be predicted by the severity of gas exchange during the first 48 h of mechanical ventilation. To test this hyp othesis, two studies were undertaken in RSV-positive mechanically ventilate d patients who did not have chronic lung disease, congenital heart disease or immunodeficiency. First, a retrospective criteria-generating review of 4 5 infants was carried out. In these infants, more severe lower airway disea se, as demonstrated by four-quadrant consolidation on chest X-ray, was asso ciated with 'best' alveolar arterial oxygen gradients (AaDO(2), torr) and m ean airway pressure (MAP,cm H2O) values as follows: first 24 h, AaDO(2) > 4 00 and MAP > 10 (positive and negative predictive values 100% and 97%, resp ectively); second 24 h, AaDO(2) greater than or equal to 300 and MAP > 10 ( positive and negative predictive values 91% and 100%, respectively). The se cond study, a prospective, hypothesis-testing, analysis of length-of-stay i n 44 infants stratified according to the above AaDO(2) and MAP criteria dem onstrated that the duration of intensive care was longer in the severe grou p. median (interquartile range in days) 17 (15-39) vs 7 (4-8) (p < 0.01). We suggest that, in mechanically ventilated infants with RSV, the time cour se of intensive care is predictable based on early clinical features and re spiratory parameters, Therefore reports on the effectiveness of special the rapies using intensive care stay as a measure of outcome should be interpre ted with respect to these observations before drawing conclusions about eff icacy.