79 - Late Permissive Hypercapnia and Respiratory Stability among Extremely Preterm Infants: A Randomized Clinical Trial

Poster Board #: 79
Publication #: 1908-HP-QA.79

Background: Permissive hypercapnia increases respiratory drive and may thereby decrease apnea and intermittent hypoxemia among preterm infants. Alternatively, decreasing respiratory support may result in respiratory instability.


Objective: Test the hypothesis that targeting higher transcutaneous CO₂ (TcCO₂) compared with lower TcCO₂ improves respiratory stability among extremely preterm infants on positive pressure respiratory support.


Design/Methods: This trial was conducted at the University of Alabama at Birmingham (NCT03333161). Extremely preterm infants on positive pressure respiratory support after postnatal day 7 were randomized to 2 different levels of permissive hypercapnia targeting 5 mmHg changes from baseline TcCO₂ in one of two sequences with four sessions lasting 24 hours or 96 hours total: baseline-increase-baseline-increase or baseline-decrease-baseline-decrease. We collected high-resolution (1 Hz) cardiorespiratory data and evaluated episodes of intermittent hypoxemia (oxygen saturations (SpO₂) <85% for ≥10 sec), severe intermittent hypoxemia (SpO₂ <80% for 10 sec), bradycardia (heart rate <100 bpm for ≥10 sec), and the duration of cerebral (<55%) and abdominal hypoxemia (<40%) on near-infrared spectroscopy using MATLAB.


Results: We enrolled 25 infants with a gestational age of 24w 5d ± 10d (mean+SD) and birth weight 658±147 grams on postnatal day 14±3. There were no differences in episodes of intermittent hypoxemia (5.2±3.1 vs 4.3±4.3 per hour; p=0.25), severe intermittent hypoxemia (1.7±1.5 vs 1.5±1.1 per hour; p=0.48), or bradycardia (0.5±0.7 vs 0.6±0.9 per hour; p=0.75) between higher and lower TcCO₂ target groups. The proportion of time with SpO₂ <85% (8±6% vs 7±6%; p=0.70), SpO₂ <80% (3±3% vs 2±3%; p=0.86), cerebral hypoxemia (26±30% vs 21±29%; p=0.52), or abdominal hypoxemia (3±4% vs 16±56%; p=0.31) did not differ between groups. TcCO₂ values (55.9±6.4 vs 54.6±7.6; p=0.97) and once daily blood gas values did not differ between groups suggesting that TcCO₂ targets regressed to the mean. There was moderate negative correlation between mean TcCO₂ and episodes of bradycardia (r=-0.54; p<0.001) [Figure 1] but no correlation between TcCO₂ and intermittent hypoxemia, cerebral hypoxemia, or abdominal hypoxemia.

Conclusion(s): Targeting higher TcCO₂ did not alter respiratory stability among extremely preterm infants on positive pressure respiratory support although the intended TcCO₂ separation was not achieved. Higher levels of TcCO₂ were associated with fewer episodes of bradycardia.


Figure 1: Correlation between number of episodes of bradycardia per day and mean TcCO₂. There was moderate negative correlation between TcCO₂ and episodes of bradycardia (r=-0.54; p<0.001).

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Authors/Institutions: Colm Travers, University of Alabama at Birmingham, Birmingham, Alabama, United States; Waldemar Carlo, University of Alabama at Birmingham, Birmingham, Alabama, United States; Arie Nakhmani, The University of Alabama at Birmingham College of Arts and Sciences, Birmingham, Alabama, United States; Inmaculada Aban, The University of Alabama at Birmingham College of Arts and Sciences, Birmingham, Alabama, United States; Namasivayam Ambalavanan, University of Alabama at Birmingham, Birmingham, Alabama, United States