Acta Paediatr 81: 832-5. 1992
Persistence of respiratory symptoms into the second year of life: predictive factors in infants born preterm B Yuksel and A Greenough Department of Child Health, King’s College Hospital. London, U K
Yuksel B, Greenough A. Persistence of respiratory symptoms into the second year of life: predictive factors in infants born preterm. Acta Paediatr 1992;81:832-5. Stockholm. ISSN 0803-5253 Preterm infants frequently suffer from recurrent respiratory symptoms in the first year of life. Our aims were to assess if such respiratory morbidity persisted beyond the first year and to define the predictive factors. One hundred and sevenfeen infants (median gestational age 29 weeks) were followed prospectively for two years. Thirty-eightinfants had symptoms only in the first year (group A) and in a further 20 infants, symptoms were present in both years (group B). Comparison of these two groups revealed no significant difference in birth weight or gestational age, but the duration of ventilation and increased inspired oxygen concentration were significantly longer in group B. Significantly more infants in group B had had an air leak in the neonatal period, and airways resistance at six months of age was also significantlyhigher in group B. We conclude that infants with severe neonatal respiratory distress are likely to have persisting respiratory morbidity and that respiratory function measurements at six months of age provide the most accurate predictor of chronic respiratory symptoms. 0 Lung function, neonatal ventilation, respiratory symptoms
B Yuksel, Department of Child Health, King’s College Hospital, London SE5 9RS. U K
Recurrent respiratory symptoms occur frequently during the first year of life amongst preterm infants following discharge from neonatal intensive care (1). The prevalence of respiratory symptoms amongst preterm infants appears to be twice that found in infants born at term, but of similar socioeconomic background and ethnic origin (1). Such symptoms are an important cause of respiratory morbidity as they are associated with an increased readmission rate for chest-related disorders (2, 3). We have prospectively followed preterm infants consecutively admitted to our neonatal unit. Our aim was to assess the effect of increasing postnatal age on the occurrence of respiratory symptoms. We also hoped to determine which factors were predictive of chronic respiratory morbidity as evidenced by persistence of respiratory symptoms into the second year of life.
Patients and methods Infants born preterm at King’s College Hospital whose parents lived locally were followed prospectively following discharge from the neonatal intensive care unit. All those with birth weights less than 1500 g and, in addition, those with birth weights less than 2000 g and who required mechanical ventilation in the neonatal period were recruited into the study. On discharge from the neonatal unit parents kept diary cards in which they recorded their infant’s symp-
toms of cough and/or wheeze during the day or night. From the diary cards infants were defined as having recurrent respiratory symptoms if they wheezed and/or coughed for at least three days following all upper respiratory tract infections and wheezed and/or coughed on more than three days per week over a fourweek period per year. Two groups of infants were then identified, those who were symptomatic in the first year of life only (group A) and those who had persistent respiratory morbidity, that is, those who were symptomatic in both the first and second year of life (group B). To determine possible predictive factors of persistent respiratory morbidity, we examined the infants’ neonatal notes to assess the duration of assisted ventilation (IPPV), requirement for an increased concentration of inspired oxygen support and the occurrence of pulmonary interstitial emphysema or pneumothorax (air leak). We also assessed lung function at six months of age. The infants were sedated with oral choral hydrate solution and airways resistance (Raw) measured using a whole body plethysmographic technique (4). The measurements were made in the Paediatric Respiratory Laboratory, where a medical history was obtained and height and weight measured. The infants were then sedated with oral chloral hydrate solution 80-100 mg/kg. Raw was measured using a whole body plethysmograph. The infant breathed through a face mask, which was sealed around the infant’s nose and mouth using silicone putty to ensure an airtight seal. The face mask was connected to the re-breathing bag via a heated pneumotachograph.
ACTA PRDIATR 81 (1992)
A heated, humidified re-breathing system was used to avoid box pressure changes due to the heating and cooling of respired gas. Raw was measured at two-thirds maximum inspiratory flow by the classical techniques of Dubois et al. suitably modified for infants (5). Raw was calculated from at least 10 breaths. All measurements were corrected for the resistance of the apparatus (8 cmH2O/l/s, measured at flows of between 5 and 15 I/ min). Traces were analysed blind of clinical details. The reproducibility of Raw was determined in 16 children of similar gestational and postnatal age to the study population. Measurements of Raw were performed before and after infants had been removed and returned to the body plethysmograph. The coefficient of variation of Raw was 9%. One hundred and seventeen preterm infants (56 girls and 61 boys) with a median birth weight of 1 192 g (range 506-2000 g) and gestational age of 29 weeks (range 2335 weeks) were studied. Ninety-five infants had a birth weight less than 1500 g. The majority of the infants (90%)had suffered from respiratory distress syndrome (RDS) in the neonatal period and had required respiratory support. The median duration of mechanical ventilation was 1.5 days (range 0-75 days) and duration of supplementary oxygen was 5 days (0-340 days). None of the infants had suffered from bronchopulmonary dysplasia (BPD), that is, persistent oxygen dependency with a chest radiograph appearance demonstrating hyperexpansion and cystic-looking lungs (6). Ethical permission for this study was granted by the King's College Hospital Ethics Committee. Statistical analysis Differences between the groups were assessed for statistical significance using either the Wilcoxon rank sum test or Fisher's exact test. The sensitivity and specificity of the possible predictive factors were calculated.
833
Chronic respiratory morbidity of preterm infants
Table I . Characteristics of the two groups (median (range and interquartile range)).
Gestational age (weeks) Birth weight (g)
Duration of ventilation (days) Duration of oxygen dependency (Jays) Airway resistance at 6 months (cm HzO/l/s)
Group A (n= 38)
Group B (n = 20)
29 (26-34) (28-30.5) 1204 (562-1988) (866-1459) 2 (0-32) (0.2-5) 3.5 (0-82) (0.6-1 1) 43 (22-82) (3 1 4 9 )
28 (24-32) (26.4-30.5) I138 (656- 1690) (813-1326) 6 (049) (0.7- 19.5) 10 (0-340) (3-65.5) 52 (27- 100) (50-60.5)
only became symptomatic after their first lower respiratory tract infection, which occurred in all cases in the second year of life. There was no significant difference in gestation age or birth weight between groups A and B. The 95% confidence intervals of the difference of the means of group A (29 weeks, 1255 g) and group B (28 weeks, 1 109 g) were -4.78 to 2.63 weeks and -325 to + 3 3 g, respectively. The infants in group B were ventilated for longer (p
Persistence of respiratory symptoms into the second year of life: predictive factors in infants born preterm B Yuksel and A Greenough Department of Child Health, King’s College Hospital. London, U K
Yuksel B, Greenough A. Persistence of respiratory symptoms into the second year of life: predictive factors in infants born preterm. Acta Paediatr 1992;81:832-5. Stockholm. ISSN 0803-5253 Preterm infants frequently suffer from recurrent respiratory symptoms in the first year of life. Our aims were to assess if such respiratory morbidity persisted beyond the first year and to define the predictive factors. One hundred and sevenfeen infants (median gestational age 29 weeks) were followed prospectively for two years. Thirty-eightinfants had symptoms only in the first year (group A) and in a further 20 infants, symptoms were present in both years (group B). Comparison of these two groups revealed no significant difference in birth weight or gestational age, but the duration of ventilation and increased inspired oxygen concentration were significantly longer in group B. Significantly more infants in group B had had an air leak in the neonatal period, and airways resistance at six months of age was also significantlyhigher in group B. We conclude that infants with severe neonatal respiratory distress are likely to have persisting respiratory morbidity and that respiratory function measurements at six months of age provide the most accurate predictor of chronic respiratory symptoms. 0 Lung function, neonatal ventilation, respiratory symptoms
B Yuksel, Department of Child Health, King’s College Hospital, London SE5 9RS. U K
Recurrent respiratory symptoms occur frequently during the first year of life amongst preterm infants following discharge from neonatal intensive care (1). The prevalence of respiratory symptoms amongst preterm infants appears to be twice that found in infants born at term, but of similar socioeconomic background and ethnic origin (1). Such symptoms are an important cause of respiratory morbidity as they are associated with an increased readmission rate for chest-related disorders (2, 3). We have prospectively followed preterm infants consecutively admitted to our neonatal unit. Our aim was to assess the effect of increasing postnatal age on the occurrence of respiratory symptoms. We also hoped to determine which factors were predictive of chronic respiratory morbidity as evidenced by persistence of respiratory symptoms into the second year of life.
Patients and methods Infants born preterm at King’s College Hospital whose parents lived locally were followed prospectively following discharge from the neonatal intensive care unit. All those with birth weights less than 1500 g and, in addition, those with birth weights less than 2000 g and who required mechanical ventilation in the neonatal period were recruited into the study. On discharge from the neonatal unit parents kept diary cards in which they recorded their infant’s symp-
toms of cough and/or wheeze during the day or night. From the diary cards infants were defined as having recurrent respiratory symptoms if they wheezed and/or coughed for at least three days following all upper respiratory tract infections and wheezed and/or coughed on more than three days per week over a fourweek period per year. Two groups of infants were then identified, those who were symptomatic in the first year of life only (group A) and those who had persistent respiratory morbidity, that is, those who were symptomatic in both the first and second year of life (group B). To determine possible predictive factors of persistent respiratory morbidity, we examined the infants’ neonatal notes to assess the duration of assisted ventilation (IPPV), requirement for an increased concentration of inspired oxygen support and the occurrence of pulmonary interstitial emphysema or pneumothorax (air leak). We also assessed lung function at six months of age. The infants were sedated with oral choral hydrate solution and airways resistance (Raw) measured using a whole body plethysmographic technique (4). The measurements were made in the Paediatric Respiratory Laboratory, where a medical history was obtained and height and weight measured. The infants were then sedated with oral chloral hydrate solution 80-100 mg/kg. Raw was measured using a whole body plethysmograph. The infant breathed through a face mask, which was sealed around the infant’s nose and mouth using silicone putty to ensure an airtight seal. The face mask was connected to the re-breathing bag via a heated pneumotachograph.
ACTA PRDIATR 81 (1992)
A heated, humidified re-breathing system was used to avoid box pressure changes due to the heating and cooling of respired gas. Raw was measured at two-thirds maximum inspiratory flow by the classical techniques of Dubois et al. suitably modified for infants (5). Raw was calculated from at least 10 breaths. All measurements were corrected for the resistance of the apparatus (8 cmH2O/l/s, measured at flows of between 5 and 15 I/ min). Traces were analysed blind of clinical details. The reproducibility of Raw was determined in 16 children of similar gestational and postnatal age to the study population. Measurements of Raw were performed before and after infants had been removed and returned to the body plethysmograph. The coefficient of variation of Raw was 9%. One hundred and seventeen preterm infants (56 girls and 61 boys) with a median birth weight of 1 192 g (range 506-2000 g) and gestational age of 29 weeks (range 2335 weeks) were studied. Ninety-five infants had a birth weight less than 1500 g. The majority of the infants (90%)had suffered from respiratory distress syndrome (RDS) in the neonatal period and had required respiratory support. The median duration of mechanical ventilation was 1.5 days (range 0-75 days) and duration of supplementary oxygen was 5 days (0-340 days). None of the infants had suffered from bronchopulmonary dysplasia (BPD), that is, persistent oxygen dependency with a chest radiograph appearance demonstrating hyperexpansion and cystic-looking lungs (6). Ethical permission for this study was granted by the King's College Hospital Ethics Committee. Statistical analysis Differences between the groups were assessed for statistical significance using either the Wilcoxon rank sum test or Fisher's exact test. The sensitivity and specificity of the possible predictive factors were calculated.
833
Chronic respiratory morbidity of preterm infants
Table I . Characteristics of the two groups (median (range and interquartile range)).
Gestational age (weeks) Birth weight (g)
Duration of ventilation (days) Duration of oxygen dependency (Jays) Airway resistance at 6 months (cm HzO/l/s)
Group A (n= 38)
Group B (n = 20)
29 (26-34) (28-30.5) 1204 (562-1988) (866-1459) 2 (0-32) (0.2-5) 3.5 (0-82) (0.6-1 1) 43 (22-82) (3 1 4 9 )
28 (24-32) (26.4-30.5) I138 (656- 1690) (813-1326) 6 (049) (0.7- 19.5) 10 (0-340) (3-65.5) 52 (27- 100) (50-60.5)
only became symptomatic after their first lower respiratory tract infection, which occurred in all cases in the second year of life. There was no significant difference in gestation age or birth weight between groups A and B. The 95% confidence intervals of the difference of the means of group A (29 weeks, 1255 g) and group B (28 weeks, 1 109 g) were -4.78 to 2.63 weeks and -325 to + 3 3 g, respectively. The infants in group B were ventilated for longer (p
