Extubation is a regular occurrence in the NICU. We do our best to predict who will succeed and who will fail but it isn’t always easy to figure out who they are in advance. We use techniques such as looking at oxygenation histograms and using thresholds for PIP, PEEP or MAP but in the end sometimes it works and other times it doesn’t. In an effort to improve on intubation success, some creative researchers in Switzerland employed a technique called end-expiratory lung impedance or EELI to measure lung volume before, during and after the extubation process. The use of EELI is based on the impendance of the lung changing with the distribution of tissue and air and by placing electrodes one can generate a cross sectional volume that has been shown in neonates to be representative of total lung volume. The EELI technique creates an image like this which is use to generate the estimate of lung volume.
The researchers in this study were seeking to do a quality improvement project and use EELI to estimate lung volume at different time points in an extubation. The time points were all 30 seconds including, immediately before first handling of the infant (baseline), tracheal suctioning (suction), start and end of adhesive tape removal (adhesive tape begin and adhesive tape end), pulling the endotracheal tube (extubation), initiation of non-invasive ventilation (NIV), immediately before and after turning the infant to prone position (supine and prone, respectively), and 10 min after turning to prone position (prone10). As per unit policy all babies were ventilated with Draeger VN500 ventilators and if <28 weeks went on to NIPPV when extubated or if 28 weeks or more straight CPAP. The purpose of this quality initiative was to determine using EELI at what point in the extubation process infants might be losing lung volume and then based on the information see if they could ultimately use this to improve the chances of successful extubation in the future.
What makes this study interesting is that the infants were found to lose volume but at a time when I would not have expected it.
Below is a graphical depiction of EELI and estimates of FRC during the different time points. The changes in electrical impedance by EELI were converted on the right Y axis to an FRC in mL/kg.
What is surprising at least to me here is the loss of volume occurs not with extubation but rather when the tape removal process happens. With the placement of the prongs on the infant at extubation the FRC gradually rises and recovery occurs. Moreover as shown in the 12 patients included in this study, the recovery once non-invasive ventilation is provided is quite rapid and evident within 1-2 breaths.
A couple other things to note. The loss of FRC during tape removal was about 10 mL/kg and if typical FRC in a preterm infant is 20-25 mL/kg you can see the impact this would have on lung volume and reserve. As this was a small study it could not detect a threshold at which extubation would fail but one infant who developed a pneumothorax and required reintubation did not get back to their baseline FRC.
What is this signaling?
Yes this is a small study but it did look at about 3000 breaths so there is a fair amount of data to look at. What the paper demonstrates I think is that there is a vulnerable time during tape removal where likely due to the fact that we use uncuffed ETTs in neonatology it is possible for these infants to lose lung volume. It may be that as they strain and bear down the ventilator may not be as effective at delivering volume to them. Measures that might help during this time could be skin to skin care, breastmilk drops or scent, sucrose or a variety of other non-pharmacologic measures to keep them calm. This might help to minimize such volume loss. Secondly, knowing the significant risk of volume loss it underlines the importance of placing nasal prongs on as quickly as possible during the transition from invasive to non-invasive ventilation as recovery of lung volume is possible. It think it also suggests that if we are “peepaphobic” and use an insufficient amount of support at extubation these infants may be vulnerable to experience significant volume loss as well.
While EELI may not be perfect, this study is the first of its kind and may shed some light into why some infants fail after extubation. While usually I say less is more, I do wonder if in the case of extubation, this study gives some evidence to support starting with a higher PEEP than you think you need non-invasively and then backing off after one has successfully extubated. This may be the first study I have seen on this but I am certain it won’t be the last.