A sustained inflation at birth of an asphyxiated lamb which lasts 30 seconds leads to much more rapid restoration of heart rate and blood pressure than either conventional ventilation or a series of shorter sustained inflations of 5 seconds each. This new study from the same group (Sobotka KS, et al. Single Sustained Inflation followed by Ventilation Leads to Rapid Cardiorespiratory Recovery but Causes Cerebral Vascular Leakage in Asphyxiated Near-Term Lambs. PLoS One. 2016;11(1):e0146574) shows that cardiac contractility, carotid artery flow and cerebral oxygen delivery also increase much more rapidly.
But, wait a minute, is that necessarily a good thing? What is important is the eventual re-establishment of a stable circulation, and a reduction in cerebral injury, and injury to other organs. One of the reasons we have switched to room air resuscitation (at least for full term infants) is that re-oxygenation injury is reduced compared to 100% oxygen resuscitation, maybe increasing cerebral perfusion and oxygen delivery very quickly might also have some harmful effects.
In this new study the authors also performed brain histopathology of the lambs after resuscitation, mostly looking at how many blood vessels in each of 3 sections of the brain were surrounded by extravasated serum. There were significantly more disrupted blood vessels and extravasations in the sub-cortical white matter of the single prolonged inflation lambs than the other 2 groups, and slightly more in the gray matter and the periventricular white matter also. Exactly why this occurs, what the potential impacts are and whether it might also occur in babies exposed to different kinds of sustained inflations is unknown, but will need to be investigated.
Two fairly recent randomized trials have concentrated on pulmonary outcomes:
In the first, nearly 300 infants from 25 to 29 weeks gestation were randomized, Lista G, et al. Sustained Lung Inflation at Birth for Preterm Infants: A Randomized Clinical Trial. Pediatrics. 2015;135(2):e457-e64. They either were placed on CPAP, or had a sustained lung inflation (25 cmH2O for 5 seconds) followed by CPAP. The SLI group were more likely to avoid mechanical ventilation during the first 72 hours of life, but the number ever intubated, the proportion who developed BPD and survival were not different. As the babies were not necessarily asphyxiated, this was really a trial of SLI as a lung protective strategy, which did not really show any benefit; other complications of prematurity, including IVH and PVL, were not different between groups.
The second study enrolled nearly 200 infants of 34 to 36 weeks gestation, Mercadante D, et al. Sustained lung inflation in late preterm infants: a randomized controlled trial. J Perinatol. 2016;36(6):443-7. They described the intervention as follows :
after oropharyngeal and nasal suctioning, a prophylactic pressure-controlled (25 cmH2O) inflation was sustained for 15 s using a neonatal mask and a T-piece ventilator, followed by the delivery of 5 cmH2O CPAP. In the following 6 to 10 s, CPAP was discontinued in the absence of signs of inadequate respiratory effort (that is, apnea or gasping) or heart rate 4100 beats per min (b.p.m.). In the presence of signs of inadequate respiratory effort and/or whenever the heart rate was between 60 and 100 b.p.m. despite CPAP, a SLI maneuver with the same parameters was repeated. If the heart rate was <100 b.p.m. after the second SLI maneuver, the infant was resuscitated according to the recommendations of the American Academy of Pediatrics (AAP).
This study showed no benefit of the procedure, and 3 babies in the SLI group, but none of the controls, developed a pneumothorax.
It seems to me we should be being very careful with this intervention, and I say this as someone who has done it intermittently for many years. I think I’ve mentioned before on this blog that Anthony Milner showed years ago in depressed full-term babies who were intubated before their first breath, that a prolonged (5 seconds) slow-rise inflation pressure, up to 30 cmH20 eliminated the apparent opening pressure of the lungs and led to rapid establishment of an FRC. My anecdotal experience is that sometimes when I take over ventilating a baby who the junior staff is having difficulty with, and I apply that kind of a long inflation, often the lungs will be easy to inflate, and then assisted ventilation is much easier, often with a recovery of other clinical signs.
I’m somewhat less convinced of the value of SLI as a lung-protective strategy for preterm infants, and certainly the clinical data so far do not support it. As a part of a resuscitative strategy for depressed babies, I think there is more promise; but it now looks like we will have to carefully examine potential neurologic compromise.