Giving lungs the DELUX treatment

Giving lungs the DELUX treatment

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 DELUX study

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.

The Reveal

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.

What is the optimal depth of chest compressions to achieve return of spontaneous circulation (ROSC)

What is the optimal depth of chest compressions to achieve return of spontaneous circulation (ROSC)

If you work in Neonatology or in Pediatrics for that matter there is no doubt that at some point you took the neonatal resuscitation program (NRP). Ideally you should be recertified every year or two years depending on your profession. In the course you are taught that the depth of chest compressions required to achieve the best chances of ROSC is 1/3 the diameter of the chest. The evidence to support this comes from a CT evaluation of neonatal thoraces in the paper Evaluation of the neonatal resuscitation program’s recommended chest compression depth using computerized tomography imaging. In this study the authors found that using a mathematic model the 1/3 chest compression recommendation should in theory yield the best hemodynamic outcome.

What about ROSC?

Hemodynamics is one thing in a model but what about real life? I don’t think you could reasonably do an RCT these days with the outcome of interest being ROSC in humans. What research ethics board would allow you to randomize to the outcome of death in babies and deviate from an international organizations recommendations for best practice? My former colleagues in Edmonton had an answer to this issue though by using a piglet model to test the hypothesis that 33% is indeed better than either 12.5%, 24% or 40% chest compression depth. Their paper Assessment of optimal chest compression depth during neonatal cardiopulmonary resuscitation: a randomised controlled animal trial tackles just that question.

How did they do it? In an animal lab that is equipped with a mechanical device to simulate chest compressions they were able to instrument piglets and after asphyxiating them with an occluded ETT they began the process of trying to revive them. After being asphyxiated they initiated a combination of PPV with a neopuff and gave epinephrine (0.02 mg/kg/dose) intravenously2 min after the start of positive pressure ventilation and every 3 min until ROSC with a maximum of three doses, with a maximum resuscitation time of 10 min. The groups were divided in the following manner.

What did they find?

Two very interesting things came out of the study. The first was that they abandoned the 12.5% group early in the study when it became apparent that no piglet would survive using this depth. The other thing they found in support of greater depths of 33 and 40% compression depth is shown in the following graph.

The authors found that in terms of systolic and diastolic blood pressure the best chances in particular for systolic blood pressure were the 33 and 40% compression depths. Looking at the bottom right figure it is also evident that cerebral blood flow increases with increasing depth of compression.

With respect to the primary outcome they found this:

The median (IQR) time to ROSC was 600 (600–600) s, 135 (90–589) s, 85 (71–158)* s and 116 (63–173)* s for the 12.5%, 25%, 33% and 40% AP depth groups, respectively (p<0.001 vs 12.5% AP depth group). The number of piglets that achieved ROSC was 0 (0%), 6 (75%), 7 (88%)** and 7 (88%)** in the 12.5%, 25%, 33% and 40% AP depth groups, respectively (*p<0.05 and **p<0.005 vs 12.5% AP depth group).

Of note, one of the piglets randomized to 40% depth of compression had pulmonary contusions at autopsy.

Putting it all together

The article supports the use of 33-40% chest compression but it raises an important point in my mind. The study used a mechanical device to ensure the percentage compression and it is clear that if you fall below these numbers the ROSC and hemodynamics is impaired while if you go to high you run the risk of damaging the lungs (I know it was just one but a previous study demonstrated harm at 50% compression depth as well).

This raises the question about failed resuscitations. Do we know how deep we are actually compressing during these situations? Sure, everyone can recite that we should be compressing to 1/3 of the chest diameter but what are we actually doing? In some cases are we not doing enough and in other cases doing way to much? I would imagine the answer to this question is yes. I do wonder as we continue to automate so much in our world through advances in technology if doing the same in neonatal resuscitation is not that far off. When our hands are sweaty and tremulous with adrenaline coursing through our veins how good are we really at controlling the precise depth of compression. Time will tell what happens but what is clear to me is that precision matters and really how precise can we be?