Evaluation of criteria for chronic lung disease in surviving very low birth weight infants. Newborn Lung Project.

Criteria in common use for the diagnosis of chronic lung disease of prematurity or bronchopulmonary dysplasia in the neonatal period have not been sufficiently compared and validated against indicators of later respiratory complications. In this study of all 680 infants < or = 1500 gm birth weight admitted to six perinatal centers August 1, 1988, to July 31, 1990, 524 were alive and had no major congenital anomalies at 5 years old. Of 419 who had given permission to release their names and addresses, 272 were located and participated in a follow-up study. The following diagnostic criteria for bronchopulmonary dysplasia and chronic lung disease of prematurity were used during the initial hospitalization: (1) use of supplemental oxygen on day 30 of life, (2) a comprehensive bronchopulmonary dysplasia severity score applied at 25 to 35 days of life developed by a clinician panel to adjust for practice variation in ventilatory support and blood gases, (3) use of supplemental oxygen on day 30 of life with radiographic evidence consistent with bronchopulmonary dysplasia between days 25 and 35 of life, (4) radiographic evidence consistent with bronchopulmonary dysplasia alone, and (5) use of supplemental oxygen at 36 weeks' postconceptional age. These criteria were assessed against use of bronchodilators or steroids during the first 2 years of life, diagnosis of asthma, and hospitalizations for respiratory causes up to age 5. Although all criteria were significantly associated with all the outcomes, radiographic evidence was most predictive. These results indicate that, during a period when 21% of neonates were exposed to antenatal steroids, 24% received surfactant and 9% received postnatal corticosteroids, radiographic evidence was more predictive of long-term respiratory outcome than other commonly used criteria.

Multivariate assessment of traditional risk factors for chronic lung disease in very low birth weight neonates. The Newborn Lung Project.

All neonates (n = 581) with birth weights less than 1501 gm admitted to seven neonatal intensive care units in Wisconsin and Iowa were candidates for a study aimed at the multivariate assessment of risk factors for chronic lung disease while controlling for baseline severity of respiratory disease. Data from 361 neonates were analyzed for all risk factors except fluids; only neonates weighing less than 1200 gm were included (n = 220). Information on traditional risk factors for chronic lung disease was abstracted. A total of 110 (30%) of the analyzed neonates were oxygen dependent on day 30 of life. The following baseline factors were associated with increased risk of oxygen dependence in a joint multivariate model: lower birth weight (odds ratio 1.4/100 gm), higher baseline severity score (odds ratio 2.7/doubling at 32 weeks gestational age), lower gestational age (odds ratio 2.4/week at severity 0), Apgar score at 1 minute (odds ratio 1.6/2 points), male gender (odds ratio 1.9), and nonblack race (odds ratio 2.2). After adjustment for all baseline factors, patent ductus arteriosus, ventilator pressure at 96 hours, oxygen at 96 hours, and fluid intake were associated with oxygen dependence. Neonates with a low baseline severity score who remained oxygen dependent had a higher intake of fluid relative to output, whereas neonates with a higher baseline severity score had higher fluid intake and output. Lack of weight loss was associated with increased severity but not with oxygen dependence. The results of this study generally confirm the significance of previously reported risk factors for chronic lung disease in a multivariate setting but show that risk factors may not have the same impact in neonates with different baseline severity.

Intravenous energy and amino acids in the preterm newborn infant: effects on metabolic rate and potential mechanisms of action.

The effects of intravenously administered amino acids and of varying amounts of energy on metabolic rate were studied and potential mechanisms examined in 19 healthy 4- to 6-day-old preterm (30 to 32 weeks gestation) infants. The infants were randomized to three groups. Group 1 (n = 6) received nonprotein energy 38 kcal/kg/d; group 2 (n = 5), 64 kcal/kg/d; and group 3 (n = 8), 64 kcal/kg/d plus 1 to 2 g/kg/d crystalline amino acids. Thirty-six hours after beginning the infusion, oxygen consumption (VO2) was measured by indirect calorimetry for 5 to 6 hours. Simultaneously, urine was collected for urinary norepinephrine excretion, which was determined using liquid chromatography with electrochemical detection. Serum thyroxine (T4) and triiodothyronine (T3) concentrations were determined by radioimmunoassay. Group 1 had lower VO2 and urinary norepinephrine excretion than did groups 2 and 3, which did not differ. T4 and T3 were not different among the three groups. The demonstrated simultaneous changes in VO2 and norepinephrine excretion with varying energy intakes independent of age supports energy intake as a modulator of the sympathetic nervous system, which in turn controls metabolic rate. Moderate amounts of intravenously administered amino acids do not appear to play an active role in this process; nor do they alter T3 and T4 valves. When VO2 increased with increasing energy intake, T3 and T4 were unaffected, supporting a passive role for thyroid hormones in diet-induced thermogenesis.

Estimating the completeness of reporting of adult deaths in populations that are approximately stable.

PIP: An elaboration of Preston's (Preston and Hill, 1980) procedure for determining the completeness with which deaths are recorded in approximately stable populations is presented. Both the procedures of Preston and that of Brass are conventionally limited to mortality beyond early childhood, to mortality above age 5 or age 10. The method considered here is based on characteristics of stable populations, i.e., populations that have been subject for a long time to little variation in age-specific mortality schedules or in overall levels of fertility. The essential features of a stable population are maintained even if fertility has changed. This is the case as long as no strong trend in fertility existed more than 15 or 20 years before the date at which the population is observed. Recent changes in fertility may affect the structure of the population at adult ages, but the effect on estimates of completeness of death records can generally be kept within tolerably narrow limits. Prior to showing how explicit estimates of the relative completeness of recording of numbers of deaths and persons can be derived from counts of deaths and persons by age, it is noted that a life table for a stable population can be constructed directly from the recorded distribution of deaths by age, or from the recorded distribution of persons. The procedures described are applied to several different populations in order to illustrate the computational steps necessary to estimate the completeness of death records at ages above childhood in populations that are approximately stable.^ieng

The effects of thermal environment on heat balance and insensible water loss in low-birth-weight infants.

To define the neutral environmental temperature and assess the effects of deviation from that temperature on insensible water loss and heat balance, 12 premature infants were studied in a conventional incubator at four different predetermined ambient temperatures. Our method combines insensible water loss measured by a continuous read-out electronic scale with heat production as determined by open circuit measurement of oxygen consumption. An increase of 1 to 2 degrees C, to an ambient temperature above or near the top of the neutral zone, produced a significant rise in insensible water loss, from 1.90 +/- 0.76 to 3.08 +/- 1.19 ml/kg/hour (mean +/- SD), a corresponding rise in evaporative heat loss, and a fall in nonevaporative heat loss. A decrease of 1 to 2 degrees C, to a slightly subneutral ambient temperature, resulted in an increase in oxygen consumption from 5.82 +/- 0.92 to 7.45 +/- 1.50 ml/kg/minute, and an increase in total heat loss, but no change in insensible water loss and evaporative heat loss. The increased total heat loss was judged to be due entirely to a greater nonevaporative heat loss, both by convection and by radiation. The data confirm that ambient temperature is an important determinant of the magnitude and the partition of heat loss in low-birth-weight infants.

Heat balance in premature infants: comparative effects of convectively heated incubator and radiant warmer, with without plastic heat shield.

Insensible water loss, oxygen consumption, and carbon dioxide production were measured in eight premature infants under four different conditions: in conventional single-walled incubator with and without plastic heat shield, and under radiant warmer with and without heat shield. IWL was greater under the radiant warmer (3.40 +/- 1.50 ml/kg/hour, mean +/- SD) than in the incubator (2.37 +/- 1.15 ml/kg/hour) when both were compared without heat shield. Addition of the heat shield reduced IWL in the incubator (2.13 +/- 0.76 ml/kg/hour) but not under the radiant warmer (3.37 +/- 0.94 ml/kg/hour). There were no significant differences in VO2 or respiratory quotient between any two of the four study conditions.