1307 RESPIRATORY INFECTIONS IN INFANTS ON MECHANICAL VENTILATION: THE IMMUNE RESPONSE AS A DIAGNOSTIC AID

Abstract

Bronchial aspirates for bacterial and viral cultures and bronchial IgM were obtained weekly in 41 patients receiving artificial ventilation. Mean birth weight 1,680 grams ± 875grams GA 32.6 weeks ±4.4. The mean duration of ventilation was 28 days (maximum 137 days). Weekly blood samples were also obtained for serum IgM and hemagglutination antibodies against O antigens prepared from the patient's own microorganisms. Clinicoradiographic evidence of pneumonia was compared with the demonstration of specific immune responses (rise in titer of at least four fold) or a significant rise in serum or bronchial IgM levels. Significant specific immune response was documented in 24% of the patients studied. Altogether there were 35 clinicoradio-graphic pneumonic episodes. Abnormal serum IgM was found in 60%, bronchial IgM in 42% and specific antibodies in 34% of those episodes. Combining the three parameters studied pneumonia was documented in 30 out of the 35 purported episodes. Patients with severe bronchopulmonary dysplasia had significantly elevated levels of both bronchial (p <.001) or serum IgM (p <.001) even during asymptomatic periods. No correlation was found between paired samples of bronchial and serum IgM (r=0.16). The data on bronchial aspirate IgM are compatible with local production by the lung. We conclude that the immune response of the host is helpful in documenting respiratory infections in infants receiving prolonged respirator therapy.