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Metabolic response of preterm infants to variable degrees of respiratory illness
T M Wahlig1, C W Gatto, S J Boros
1Division of Neonatology, Children's Hospital of St. Paul, MN.
Insights
Preterm infants with respiratory distress syndrome show increased oxygen consumption and lactate levels linked to illness severity. Their nitrogen balance is mildly negative and not tied to illness severity, suggesting adequate amino acid intake.
Area of Science:
- Neonatal Physiology
- Pediatric Critical Care
- Metabolic Response to Illness
Background:
- Severe illness in older individuals increases oxygen consumption (VO2), lactate, cortisol, and negative nitrogen balance.
- Understanding the metabolic response in preterm infants to respiratory illness severity is crucial for appropriate care.
- Preterm infants with respiratory distress syndrome (RDS) require mechanical ventilation, posing metabolic challenges.
Purpose of the Study:
- To investigate the metabolic response of preterm infants to varying degrees of respiratory illness.
- To correlate physiological instability markers with respiratory illness severity in mechanically ventilated preterm infants.
Main Methods:
- Studied twelve 2-day-old preterm infants with RDS requiring mechanical ventilation.
- Measured oxygen consumption (VO2) and carbon dioxide production via indirect calorimetry.
- Analyzed nitrogen balance, urinary 3-methyl-histidine and norepinephrine, and serum lactate and cortisol levels.
Main Results:
- VO2 was directly correlated with the ventilatory index (VI), indicating increased oxygen demand with greater respiratory illness.
- Serum lactate levels also showed a direct correlation with VI and VO2.
- Nitrogen balance was mildly negative but not significantly related to VI or VO2; cortisol and norepinephrine levels did not correlate with VI.
Conclusions:
- Preterm infants with RDS exhibit elevated VO2 and serum lactate concentrations directly proportional to respiratory illness severity.
- These infants typically experience a mild negative nitrogen balance, independent of illness severity.
- While increased energy may be needed, current amino acid intake appears sufficient, suggesting no need for excessive supplementation.
Abstract:
In older children and adults, physiologic instability associated with severe illness causes increased cellular oxygen consumption (VO2), increased serum lactate and cortisol levels, and more negative nitrogen balance. To determine the metabolic response of preterm infants to severity of respiratory illness, we analyzed VO2, nitrogen balance, urinary 3-methyl-histidine and norepinephrine concentrations, and serum levels of lactate and cortisol as a function of ventilatory index (VI). Twelve 2-day-old premature infants who were appropriate in size for gestational age (mean +/- SEM birth weight: 1460 +/- 251 gm) and who required mechanical ventilation for respiratory distress syndrome had VO2 and carbon dioxide production measured by indirect calorimetry and blood and urine samples obtained concurrently. All infants received amino acids, 1.0 gm/kg per day, and a mean energy intake of 27 +/- 3 kcal/kg per day, provided as a parenteral dextrose solution. The resting energy expenditure exceeded energy intake in all infants. The VO2 value ranged from 5.5 to 9.2 ml/kg per minute and was directly correlated with VI (r = 0.79; p = 0.002). Nitrogen balance ranged from -160 to 53 mg/kg per day (mean: -33 +/- 21 mg/kg per day) but was not dependent on VI (r = 0.04) or VO2 (r = 0.01). The serum lactate level correlated directly with VI (r = 0.82; p = 0.002) and VO2 (r = 0.60; p = 0.05), but cortisol and urinary norepinephrine levels did not. We conclude that preterm infants with respiratory distress syndrome have increased VO2 rates and serum lactate concentrations directly related to the degree of respiratory illness. They are generally in a state of mildly negative nitrogen balance, the degree of which is not related to severity of illness. Although these infants may require increased energy delivery during illness, they do not appear to require excessive amounts of amino acids.