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Small preterm infants (less than or equal to 1500 g) have only a sustained decrease in ventilation in response to
R Alvaro1, J Alvarez, K Kwiatkowski
1Department of Pediatrics, University of Manitoba, Winnipeg, Canada.
Insights
Smaller preterm infants (<=1500g) show a blunted ventilatory response to low oxygen (15% O2), unlike larger infants. This suggests their respiratory control is more fetal-like, with no initial breathing increase during hypoxia.
Area of Science:
- Neonatal Physiology
- Respiratory Control
Background:
- The classic biphasic ventilatory response to hypoxia (15% O2) was previously observed in larger preterm infants.
- Current neonatal intensive care units (NICUs) manage smaller preterm infants (<=1500g) who may exhibit different physiological responses.
Purpose of the Study:
- To investigate the ventilatory response to 15% oxygen in smaller preterm infants (<=1500g).
- To test the hypothesis that smaller preterm infants exhibit a fetal-like respiratory response, characterized by an absence of initial hyperventilation.
Main Methods:
- Studied 14 healthy preterm infants (<=1500g) during rapid eye movement (REM) and quiet sleep.
- Measured ventilation using a nosepiece and flow-through system.
- Defined sleep states using EEG, electro-oculogram, and body movements; infants breathed 15% O2 for 5 min after a 3-min control period in 21% O2.
Main Results:
- In REM sleep, minute ventilation significantly decreased from control values after 1 minute of 15% O2 exposure (p=0.03) and continued to decrease through 5 minutes (p=0.004).
- In quiet sleep, minute ventilation also significantly decreased from control values after 3 minutes of 15% O2 exposure (p=0.03) and remained decreased at 5 minutes (p=0.04).
- No initial increase in ventilation was observed in either sleep state, supporting the fetal-like response hypothesis.
Conclusions:
- Healthy preterm infants weighing <=1500g demonstrate a depressed ventilatory response to acute hypoxia (15% O2).
- This response pattern, lacking an initial hyperventilatory phase, is consistent with a more immature or fetal-like respiratory control system in smaller preterm infants.
Abstract:
The classic "biphasic" ventilatory response to 15% O2 was previously observed in preterm infants who were large compared with those in the intensive care nursery today. We hypothesized that in the smaller infant (less than or equal to 1500 g) the response might be closer to that of the fetus, with no initial increase in ventilation. Thus, we studied 14 healthy preterm infants less than or equal to 1500 g [birth weight 1200 +/- 63 g (mean +/- SEM); gestational age 29 +/- 0.4 wk; postnatal age 17 +/- 3 d] during rapid eye movement and quiet sleep. Ventilation was measured using a nosepiece and a flow-through system. Sleep states were defined using EEG, electro-oculogram, and body movements. After a control period in 21% O2 (3 min), infants breathed 15% O2 for 5 min. In rapid eye movement sleep, minute ventilation decreased from 0.186 +/- 0.020 (control) to 0.178 +/- 0.021 (30 s), to 0.171 +/- 0.017 (1 min; p = 0.03), to 0.145 +/- 0.016 (3 min; p = 0.002), and to 0.129 +/- 0.011 l.min-1.kg-1 (5 min; p = 0.004). In quiet sleep, it decreased from 0.173 +/- 0.019 (control) to 0.164 +/- 0.019 (30 s), to 0.166 +/- 0.019 (1 min), to 0.148 +/- 0.013 (3 min; p = 0.03), and to 0.146 +/- 0.012 l.min-1.kg-1 (5 min; p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)