Assistant Professor University of Alabama at Birmingham University of Alabama at Birmingham Birmingham, Alabama, United States
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 enrolled25 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).
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