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Abstract
Introduction: Instability of peripheral oxyhemoglobin saturation (SpO2) in preterm infants is correlated with late disability and is poorly understood. We hypothesised that a reduced ventilation to perfusion ratio (VA/Q) is the key predisposing factor for SpO2 instability. Methods: We first used a mathematical model to compare the effects of reduced VA/Q or shunt on SaO2 stability (SaO2 and SpO2 are used for model and clinical studies respectively). Stability was inferred from the slope of the SaO2 vs. inspired oxygen pressure (PIO2) curve as it intersects the 21 kPa PIO2 line (breathing air). Then, in a tertiary neonatal intensive care unit, paired hourly readings of SpO2 and PIO2 were recorded over a 24 h period in week old extremely preterm infants. We noted SpO2 variability and used an algorithm to derive VA/Q and shunt from the paired SpO2 and PIO2 measurements. Results: Our model predicted that when VA/Q < 0.4, a 1% change in PIO2 results in >8% fluctuation in SaO2 at 21 kPa PIO2. In contrast, when a 20% intrapulmonary shunt was included in the model, a 1% change in PIO2 results in <1% fluctuation in the SaO2. Moreover, further reducing the VA/Q from 0.4 to 0.3 at 21 kPa PIO2 resulted in a 24% fall in SaO2. All 31 preterm infants [mean gestation (±standard deviation) 26.2 (±1) week] had VA/Q < 0.74 (normal >0.85) but only two infants had increased shunt at 1.1 (±0.5) weeks’ postnatal age. Median (IQR) SpO2 fluctuation was 8 (7)%. The greatest SpO2 fluctuations were seen in infants with VA/Q < 0.52 (n = 10): SpO2 fluctuations ranged from 11%–17% at a constant PIO2 when VA/Q < 0.52. Two infants had reduced VA/Q and increased shunt (21% and 27%) which resolved into low VA/Q after 3–6 h. Discussion: Routine monitoring of PIO2 and SpO2 can be used to derive a hitherto elusive measure of VA/Q. Predisposition to SpO2 instability results from reduced VA/Q rather than increased intrapulmonary shunt in preterm infants with cardiorespiratory disease. SpO2 instability can be prevented by a small increase in PIO2.
Original language | English |
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Article number | 1112115 |
Journal | Frontiers in Physiology |
Volume | 14 |
DOIs | |
Publication status | Published - 7 Feb 2023 |
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Reducing global mortality and severity of disease in newborn infants through innovation and holistic interventions
Pillow, J. (Investigator 01)
NHMRC National Health and Medical Research Council
1/01/21 → 31/12/25
Project: Research
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Improving the Immediate and Longer-Term Health Outcomes of Preterm Infants
Pillow, J. (Investigator 01), Simmer, K. (Investigator 02), Patole, S. (Investigator 03), Strunk, T. (Investigator 04), Moss, T. (Investigator 05), Burgner, D. (Investigator 06), Whitehouse, A. (Investigator 07), Prescott, S. (Investigator 08), Tingay, D. (Investigator 09) & Gill, A. (Investigator 10)
NHMRC National Health and Medical Research Council
1/01/13 → 30/09/21
Project: Research
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Bronchopulmonary Dysplasia - Identifying Cardiorespiratory Consequences & Targets for Prevention & Intervention
Pillow, J. (Investigator 01), Hall, G. (Investigator 02), Hantos, Z. (Investigator 03) & Gill, A. (Investigator 04)
NHMRC National Health and Medical Research Council
1/01/13 → 31/12/18
Project: Research