The effects of perfluorocarbon dosing strategy on cerebral blood flow when starting partial liquid ventilation: A randomized, controlled, experimental study

Introduction: Partial liquid ventilation may benefit the lung disease in preterm neonates but intratracheal instillation of perfluorocarbon increases cerebral blood flow and may cause brain injury. We aimed to determine if the effects of perfluorocarbon administration on cerebral blood flow vary by dose-volume, rate of administration, endotracheal tube portal of entry, or closely targeting PaCO2. Methods: Forty-two dosing events (in eleven rabbits) were randomised to different dosing strategies, including a sham (i.e., placebo/control) dose of air over 20 min, 20 mL/kg of perfluorocarbon slowly over 20 min, 10 mL/kg of perfluorocarbon slowly over 20 min, 10 mL/kg of perfluorocarbon moderately fast over 10 min, 10 mL/kg of perfluorocarbon rapidly over 5 min, 10 mL/kg of perfluorocarbon slowly over 20 min via the endotracheal tube tip lumen (as opposed to the proximal end of the tube used in all other groups), or 10 mL/kg of perfluorocarbon slowly over 20 min whilst targeting a PaCO2 of 45 - 50 mmHg. Blood gases, haemodynamics, cortical cerebral blood flow and carotid flow were recorded continuously for 30 minutes from the start of each dose. Results: Carotid flow increased with 20 mL/kg perfluorocarbon and cortical cerebral blood flow was significantly more variable. Carotid and cortical cerebral blood flow increased using 10 mL/kg or 20 mL/kg with no difference between the two dose-volumes. There was no difference in cerebral blood flow by rate of administration, but carotid blood flow was more variable during slow administration. There were no differences in the increase in cerebral blood flow by portal of entry. If PaCO2 was maintained between 45 - 50 mmHg there was no increase in cerebral blood flow and there was less variable carotid flow. Conclusions: Cerebral blood flow increases with perfluorocarbon dosing. This occurs regardless of the dose-volume of perfluorocarbon. These effects were mitigated by closely targeting PaCO2.

Carbon Dioxide Levels When Starting High Frequency Ventilation in Neonates

Objective: High-frequency ventilation (HFV) is an effective means to achieve gas exchange in neonates. Adequate carbon dioxide (pCO2) levels are best achieved immediately after starting HFV, avoiding either hypercapnia or hypocapnia. We aimed to determine the initial pCO2 levels after starting HFV, and the time taken to obtain the initial blood gas. Methods: We conducted an observational retrospective study on neonates that required their first episode of HFV. Data included the first blood gas result after starting HFV and when the gas was taken after starting HFV. Results: This study included 112 neonates with a median birth weight of 938 (IQR: 692 - 1549) grams and gestational age of 27.2 (24.6 - 30.7) weeks. The first pCO2 after starting HFV (mean (SD)) was 53.7 (22) mmHg. Of 112, 15 (13.4%) showed initial hypocapnia (pCO2 35 mmHg), and 17 (15.2%) showed hypercapnia (pCO2 > 65 mmHg)—a total of 28.6% unacceptable pCO2 levels. Of 112, the first blood gas was obtained within 30 minutes in 47 (42%) and within one hour in 85 (76%), with a significant delay of two or more hours in eight (7.1%). Conclusion: Many neonates had unacceptable pCO2 levels upon starting first-time HFV. There were significant delays in obtaining the initial gas.