Speed of Lung Inflation During Ventilation of Extremely Preterm Infants

Overview

Babies born extremely preterm (\<28 weeks of pregnancy) require support to breathe. Some babies require help to breathe from a breathing machine (mechanical ventilator). While this keeps babies alive, it may damage their lungs. To reduce this damage, doctors and nurses take particular care to try and provide the gentlest breathing support possible. However, evidence is still required to determine how to best support babies' breathing, whilst preventing lung damage and longer-term lung problems. This clinical trial aims to compare two ways of adjusting a common setting on the breathing machine. This setting is called the pressure rise time or PRT. The PRT determines how quickly the breathing machine inflates a premature baby's lungs. A short PRT quickly inflates the lungs. A long PRT inflates the lungs more slowly. Previous research suggests that more slowly inflating the baby's lungs may cause less lung damage and still allow oxygen to be delivered to and carbon dioxide to be cleared from the lungs. However, larger studies are required to determine whether this should become the standard treatment. This study investigates whether inflating the baby's lungs more slowly (long PRT) using the breathing machine is as effective as the PRT setting currently used (short PRT, more quickly inflating the lungs). The main question it aims to answer is: Does how quickly the breathing machine inflates an extremely preterm baby's lung impact their oxygen levels?

The FLOW-VENT trial will investigate if using a long pressure rise time (PRT; thereby reducing the speed of gas flow) compared to a short PRT, during synchronised, patient-triggered, volume-targeted conventional mechanical ventilation in extremely preterm infants within the first postnatal week impacts an infant's oxygenation. All infants born extremely preterm (\<28 weeks' gestation) require breathing support to survive. However, this support can damage their lungs. Rates of bronchopulmonary dysplasia (BPD), the chronic lung disease of extreme prematurity, are increasing. This is despite 'lung protective' respiratory support and ventilation strategies that aim to minimise harm to the preterm lung. Pre-clinical evidence suggests that gas flows lower than currently used during respiratory support of these infants may be a major, and easily modifiable way of reducing preterm lung injury (Tingay 2024; Bach 2012). Current guidelines lack evidence for suggested gas flow settings. Many ventilators now modulate ventilator gas flows by a setting known as pressure rise time (PRT). FLOW-VENT is a prospective, multicentre, unblinded, randomised crossover trial enrolling 68 extremely preterm infants born \<28 weeks gestational age. A long PRT is defined as a PRT set at 75% of the inspiratory time (Ti). A short PRT is defined as a PRT set at 33% of the Ti. Given the crossover design, infants will receive both the long and short PRT setting. Extremely preterm infants will be randomised to a 'sequence' which will determine the order in which they are exposed to the different PRTs; either: * Long-Short PRT Sequence: Long PRT in the first treatment period and Short PRT in the second treatment period, OR * Short-Long PRT Sequence: Short PRT in the first treatment period and Long PRT in the second treatment period. The trial crossover phase (\~10-12 hours) consists of: 1) Preparatory washout period (1 to 2 hours); 2) First treatment period (4-hours); 3) Washout period (1 to 2 hours); 4) Second treatment period (4-hours). Following this, there is a 12-hour follow-up period to monitor for adverse/safety events. The primary outcome (average S/F ratio) is assessed only during the 4-hour treatment periods. Results from this trial will inform the decision to proceed to a larger randomised trial, powered for longer term respiratory outcomes (e.g. time to extubation from mechanical ventilation, BPD at 36 weeks' postmenstrual age).