Patients

Clinical and ventilator data were collected from all infants transferred by the Neonatal Emergency and Transport Service of the Peter Cerny Foundation (NETS-PCA, Budapest, Hungary) over a 29-month period (between 20 March 2017 and 4 September 2019) who received invasive or noninvasive respiratory support during interhospital transport using a fabian + ncpap evolution neonatal ventilator (Acutronic Medical Systems, Hirzel, Switzerland, software version: 4.0.1). The transport team comprised a fully trained neonatologist experienced in neonatal transport and an experienced neonatal transport nurse practitioner. Respiratory management, including the choice of ventilator mode and settings, was at the discretion of the transport team without an explicit protocol.

Of the 667 infants transferred during the period, we enrolled babies who were born after 36 completed weeks of gestation, received therapeutic hypothermia for HIE and were ventilated via an endotracheal tube during the transfer which lasted for at least 15 min (n = 49). Eligibility criteria for introducing therapeutic hypothermia was in accordance with the total body hypothermia for neonatal encephalopathy trial protocol [21]. Prior to transfer all infants received passive hypothermia at the referring unit which included reducing or turning off the heat source of the incubator or the resuscitation equipment and monitoring the rectal temperature. We excluded two infants who had major congenital abnormalities and one atypical case where hypothermia and transfer happened after a postnatal collapse at 20 h of age. Of the remaining 46 infants, we analyzed clinical and ventilator data from those receiving synchronized intermittent mandatory ventilation (SIMV) with VG (n = 28) or without VG (n = 8). The transport service’s guideline suggests the use of SIMV in infants suffering from HIE; the choice of whether to use VG or not was left to the clinician during the study period. When VG was used, the guideline was to use 4–6 mL/kg as target tidal volume, but clinicians could reduce that below 4 mL/kg if needed to avoid or reduce hypocapnia. The ten infants ventilated with other modes (SIPPV with or without VG or SIMV-VG with pressure support) were excluded. The study was approved by the Scientific and Medical Research Council Ethics Committee of Hungary (reference number: 40158/2018/EKU). All procedures were performed in accordance with the ethical standards of the Research Ethics Committee and the amended Helsinki Declaration (1983).