We can always learn and we can always do better. At least that is something that I believe in. In our approach to resuscitating newborns one simple rule is clear. Fluid must be replaced by air after birth and the way to oxygenate and remove CO2 is to establish a functional residual capacity. The functional residual capacity is the volume of air left in the lung after a tidal volume of air is expelled in a spontaneously breathing infant and is shown in the figure. Traditionally, to establish this volume in a newborn who is apneic, you begin PPV or in the spontaneously breathing baby with respiratory distress provide CPAP to help inflate the lungs and establish FRC.
Is there another way?
Something that has been discussed now for some time and was commented on in the most recent version of NRP was the concept of using sustained inflation (SI) to achieve FRC. I have written about this topic previously and came to a conclusion that it wasn’t quite ready for prime time yet in the piece Is It Time To Use Sustained Lung Inflation In NRP?
The conclusion as well in the NRP textbook was the following:
“There are insufficient data regarding short and long-term safety and the most appropriate duration and pressure of inflation to support routine application of sustained inflation of greater than 5 seconds’ duration to the transitioning newborn (Class IIb, LOE B-R). Further studies using carefully designed protocols are needed”
So what now could be causing me to revisit this concept? I will be frank and admit that whenever I see research out of my old unit in Edmonton I feel compelled to read it and this time was no different. The Edmonton group continues to do wonderful work in the area of resuscitation and expand the body of literature in such areas as sustained inflation.
Can you predict how much of a sustained inflation is needed?
This is the crux of a recent study using end tidal CO2 measurement to determine whether the lung has indeed established an FRC or not. Dr. Schmolzer’s group in their paper (Using exhaled CO2 to guide initial respiratory support at birth: a randomised controlled trial) used end tidal CO2 levels above 20 mmHg to indicate that FRC had been established. If you have less CO2 being released the concept would be that the lung is actually not open. There are some important numbers in this study that need to be acknowledged. The first is the population that they looked at which were infants under 32 6/7 weeks and the second is the incidence of BPD (need for O2 or respiratory support at 36 weeks) which in their unit was 49%. This is a BIG number as in comparison for infants under 1500g our own local incidence is about 11%. If you were to add larger infants closer to 33 weeks our number would be lower due to dilution. With such a large number though in Edmonton it allowed them to shoot for a 40% reduction in BPD (50% down to 30%). To accomplish this they needed 93 infants in each group to show a difference this big.
So what did they do?
For this study they divided the groups in two when the infant wouldn’t breathe in the delivery room. The SI group received a PIP of 24 using a T-piece resuscitator for an initial 20 seconds. If the pCO2 as measured by the ETCO2 remained less than 20 they received an additional 10 seconds of SI. In the PPV group after 30 seconds of PPV the infants received an increase of PIP if pCO2 remained below 20 or a decrease in PIP if above 20. In both arms after this phase of the study NRP was then followed as per usual guidelines.
The results though just didn’t come through for the primary outcome although ventilation did show a difference.
|Duration of mechanical ventilation (hrs)||63||204||0.045|
The reduction in hours of ventilation was impressive although no difference in BPD was seen. The problem though with all of this is what happened after recruitment into the study. Although they started with many more patients than they needed, by the end they had only 76 in the SI group and 86 in the PPV group. Why is this a problem? If you have less patients than you needed based on the power calculation then you actually didn’t have enough patients enrolled to show a difference. The additional compounding fact here is that of the Hawthorne Effect. Simply put, patients who are in a study tend to do better by being in a study. The observed rate of BPD was 33% during the study. If the observed rate is lower than expected when the power calculation was done it means that the number needed to show a difference was even larger than the amount they originally thought was needed. In the end they just didn’t have the numbers to show a difference so there isn’t much to conclude.
What I do like though
I have a feeling or a hunch that with a larger sample size there could be something here. Using end tidal pCO2 to determine if the lung is open is in and of itself I believe a strategy to consider whether giving PPV or one day SI. We already use colorimetric devices to determine ETT placement but using a quantitative measure to ascertain the extent of open lung seems promising to me. I for one look forward to the continued work of the Neonatal Resuscitation–Stabilization–Triage team (RST team) and congratulate them on the great work that they continue doing.