This past week, Canada lost a rock icon in Gord Downie of the Tragically Hip. My late high school, university and medical school days seem to have him and the band forever enmeshed in memories from that time. In honour of his passing I thought it suitable to pay tribute to him by using one of the band’s famous song titles as the title for this post. No this isn’t a post about the band but rather a controversial ventilation strategy. While CPAP has been around for some time to support our infants after extubation, a new method using high frequency nasal ventilation has arrived and just doesn’t want to go away. Depending on your viewpoint, maybe it should or maybe it is worth a closer look. I have written about the modality before in High Frequency Nasal Ventilation: What Are We Waiting For? While it remains a promising technology questions still remain as to whether it actually delivers as promised.
Better CO2 elimination?
For those who have used a high frequency oscillator, you would know that it does a marvelous job of removing CO2 from the lungs. If it does so well when using an endotracheal tube, why wouldn’t it do just as good a job when used in a non-invasive way? That is the hypothesis that a group of German Neonatologists put forth in their paper this month entitled Non-invasive high-frequency oscillatory ventilation in preterm infants: a randomised controlled crossover trial. In this relatively small study of 26 preterm infants who were all less than 32 weeks at delivery, babies following extubation or less invasive surfactant application were randomized to either receive nHFOV then CPAP for four hours each or the reverse order for the same duration. The primary outcome here was reduction in pCO2 with the goal of seeking a difference of 5% or more in favour of nHFOV. Based on their power calculation they thought they would need 24 infants total and therefore exceeded that number in their enrollment.
The babies in both arms were a bit different which may have confounded the results. The group randomized to CPAP first were larger (mean BW 1083 vs 814g), and there was a much greater proportion of males in the CPAP group. As well, the group randomized first to CPAP had higher baseline O2 saturation of 95% compared to 92% in the nHFOV group. Lastly and perhaps most importantly, there was a much higher rate of capillary blood sampling instead of arterial in the CPAP first group (38% vs 15%). In all cases the numbers are small but when looking for such a small difference in pCO2 and the above mentioned factors tipping the scales one way or the other in terms of illness severity and accuracy of measurement it does give one reason to pause when looking at the results.
No difference was found in the mean pCO2 from the two groups. As expected, pCO2 obtained from capillary blood gases nearly met significance for being higher than arterial samples (50 vs 47; p=0.052). A similar rate of babies had to drop out of the study (3 on the nCPAP first and 2 on the nHFOV side).
In the end should we really be surprised by the results? I do believe that in the right baby who is about to fail nCPAP a trial of nHFOV may indeed work. By what means I really don’t understand. Is it the fact that the mean airway pressure is generally set higher than on nCPAP in some studies? Could it be the oscillatory vibration being a kind of noxious stimulus that prevents apneic events through irritation of the infant?
While traditional invasive HFOV does a marvelous job of clearing out CO2 I have to wonder how the presence of secretions and a nasopharynx that the oscillatory wave has to avoid (almost like a magic wave that takes a 90 degree turn and then moves down the airway) allows much of any of the wave to reach the distal alveoli. It would be similar to what we know of inhaled steroids being deposited 90 or so percent in the oral cavity and pharynx. There is just a lot of “stuff” in the way from the nostril to the alveolus.
This leads me to my conclusion that if it is pCO2 you are trying to lower, I wouldn’t expect any miracles with nHFOV. Is it totally useless? I don’t think so but for now as a respiratory modality I think for the time being it will continue to be “looking for a place to happen”
This is becoming “all the rage” as they say. I first heard about the strategy of feeding while on CPAP from colleagues in Calgary. They had created the SINC * (Safe Individualized Feeding Competence) program to provide an approach to safely introducing feeding to those who were still requiring CPAP. As news of this approach spread a great deal of excitement ensued as one can only imagine that in these days when attainment of oral feeding is a common reason for delaying discharge, could getting an early start shorten hospital stay? I could describe what they found with the implementation of this strategy but I couldn’t do it the same justice as the presenter of the data did at a recent conference in Winnipeg. For the slide set you can find them here. As you can imagine, in this experience out of Calgary though they did indeed find that wonderful accomplishment of shorter hospital stays in the SINC group. We have been so impressed with the results and the sensibility of it all that we in fact have embraced the concept and introduced it here in both of our units. The protocol for providing this approach is the following.
I have to admit, while I have only experienced this approach for a short time the results do seem to be impressive. Although anecdotal a parent even commented the other day that she felt that SINC was instrumental in getting her baby’s feeding going! With all this excitement around this technique I was thrown a little off kilter when a paper came out suggesting we should put a full stop to feeding on CPAP!
What caused my spirits to dampen? This study enrolled preterm infants who were still on CPAP at ≥ 34 weeks PMA and were taking over 50% of required feeding volumes by NG feeding. The goal was to look at 15 patients who were being fed on CPAP +5 and with a mean FiO2 of 25% (21-37%) using video fluoroscopic swallowing studies to determine whether such patients aspirate when being fed. The researchers became concerned when each of the first seven patients demonstrated abnormalities of swallowing function indicating varying degrees of aspiration. As such they took each patient off CPAP in the radiology suite and replaced it with 1 l/min NP to achieve acceptable oxygen saturations and repeated the study again. The results of the two swallow studies showed remarkable differences in risk to the patient and as such the recruitment of further patients was stopped due to concerns of safety and a firm recommendation of avoiding feeding while on CPAP was made.
|Table 2. Percentage of all swallows identified with swallowing dysfunction
|Variable Mean ± s.d.
||Mean ± s.d.
||Mean ± s.d.
|Mild pen. %
|Deep pen. %
|| 25 (18.2–32)
|Nasopharyngeal reflux %
Taking these results at face value it would seem that we should put an abrupt halt to feeding while on CPAP but as the saying goes the devil is in the details…
CPAP Using Ram Cannulae
Let me start off by saying that I don’t have any particular fight to pick with the RAM cannulae. They serve a purpose and that is they allow CPAP to be delivered with a very simple set of prongs and avoid the hats, straps and such of more traditional CPAP devices. We have used them as temporary CPAP delivery when moving a patient from one area to another. As the authors state the prongs are sized in order to ensure the presence of a leak. This has to do with the need to provide a way for the patient to exhale when nasal breathing. Prongs that are too loose have a large leak and may not deliver adequate pressure while those that are too tight may inadvertently deliver high pressure and therefore impose significant work of breathing on the patient. Even with appropriate sizing these prongs do not allow one to exhale against a low pressure or flow as is seen with the “fluidic flip” employed with the infant flow interface. With the fluidic flip, exhalation occurs against very little resistance thereby reducing work of breathing which is not present with the use of the RAM cannula.
A comparison of the often used “bubble CPAP” to a variable flow device also showed lower work of breathing when variable flow is used.
The Bottom Line
Trying to feed an infant who is working against a constant flow as delivered by the RAM cannulae is bound to cause problems. I don’t think it should be a surprise to find that trying to feed while struggling to breathe increases the risk of aspiration. Similarly, under treating a patient by placing them on nasal prongs would lead to increased work of breathing as while you may provide the needed O2 it is at lower lung volumes. Increasing work of breathing places infants at increased risk of aspiration. That is what I would take from this study. Interestingly, looking at the slide set from Calgary they did in fact use CPAP with the fluidic flip. Smart people they are. It would be too easy to embrace the results of this study and turn your nose to the SINC approach to feeding on CPAP. Perhaps somewhere out there someone will read this and think twice about abandoning the SINC approach and a baby will be better for it.
* SINC algorithm and picture of the fluidic flip courtesy of Stacey Dalgleish and the continued work of Alberta Health Services
I had a chance recently to drive a Tesla Model S with autopilot. Taking the car out on a fairly deserted road near my home I flicked the lever twice to activate the autopilot feature and put my hands behind my head while the vehicle took me where I wanted to go. As I cruised down the road with the wheel automatically turning with the curves in the road and the car speeding up or slowing down based on traffic and speed limit notices I couldn’t help but think of how such technology could be applied to medicine. How far away could the self driving ventilator or CPAP device be from development?
I have written about automatic saturation adjustments in a previous post but this referred to those patients on mechanical ventilation. Automatic adjustments of FiO2. Ready for prime time? Why is this goal so important to attain? The reasoning lies in the current design trends in modern NICUs. We are in the middle of a large movement towards single patient room NICUs which have many benefits such as privacy which may lead to enhanced breastfeeding rates and increased parental visitation. The downside, having spoken to people in centres where such designs are already in place is the challenge nursing faces when given multiple assignments of babies on O2. If you have to go from room to room and a baby is known to be labile in their O2 saturations it is human nature to turn the O2 up a little more than you otherwise would to give yourself a “cushion” while you are out of the room. I really don’t fault people in this circumstance but it does pose the question as to whether in a few years we will see a rise in oxygen related tissue injury such as CLD or ROP from such practice. In the previous post I wrote about babies who are ventilated but these infants will often be one to one nursed so the tendency to overshoot the O2 requirements may be less than the baby on non- invasive ventilation.
A System For Controlling O2 Automatically For Infants on Non-Invasive Ventilation
This month in Archives Dr. Dargaville and colleagues in Australia provide two papers, the first demonstrating the validation of the mathematical algorithm that they developed to control O2 and the second a clinical report outlining how well the system actually performed on patients. The theoretical paper Development and preclinical testing of an adaptive algorithm for automated control of inspired oxygen in the preterm infant. is a challenge to comprehend although validates the approach in the end while the clinical paper at least for me was easier to digest Clinical evaluation of a novel adaptive algorithm for automated control of oxygen therapy in preterm infants on non-invasive respiratory support.
The study was really a proof of concept with 20 preterm infants (mean GA 27.5 weeks, 8 days of age on average) included who each underwent two hours of manual control by nursing to keep saturations between 90-94% and then 4 hours of automated control (sats 91 – 95%) then back to manual for two hours. The slightly shifted ranges were required due to the way in which midpoint saturations are calculated. The essential setup was a computer equipped with an algorithm to make adjustments in FiO2 using an output to a motor that would adjust the O2 blender and then feedback from an O2 saturation monitor back to the computer. The system was equipped with an override to allow nursing to adjust in the event of poor signal or lack of response to the automatic adjustment.
The results though demonstrate that the system works and moreover does a very good job! The average percentage of time that the saturations were in the target range were significantly better with automated control (81% automated, 56% manual). As well as depicted in the following figure the amount of time spent in both hypoxic and hyperoxic ranges was considerable with manual control but non-existent on either tail with automated control (defined as < 85% or > 98% where black bars are manual control and white automatic).
From the figure you can see that the amount of time the patients are in target range are much higher with automatic control but is this simply because in addition to automatic control, nurses are “grabbing the wheel” and augmenting the system here? Not at all.
“During manual control epochs, FiO2 adjustments of at least 1% were made 2.3 (1.3–3.4) times/hour by bedside staff. During automated control, the minimum alteration to FiO2 of 0.5% was being actuated by the servomotor frequently (9.9 alterations/min overall), and changes to measured FiO2 of at least 1% occurred at a frequency of 64 (49–98) /hour. When in automated control, a total of 18 manual adjustments were made in all 20 recordings (0.24 adjustments/hour), a reduction by 90% from the rate of manual adjustments observed during manual control (2.3/hour).”
From the above quote from the paper it is clear that automated control works to keep the saturation goal through roughly 7 X the number of adjustments than nursing makes per hour. It is hard to keep up with that pace when you have multiple assignments but that is what you need I suppose! The use of the auto setting here reduced the amount of nursing interventions to adjust FiO2 by 90% and yields tighter control of O2 saturations.
Dare to Dream
Self driving oxygen administration is coming and this proof of concept needs to be developed and soon into a commercial solution. The risk of O2 damage to developing tissues is too great not to bring this technology forward to the masses. As we prepare to move into a new institution I sincerely hope that this solution arrives in time but regardless I know our nurses and RRTs will do their best as they always do until such a device comes along. When it does imagine all of the time that could be devoted to other areas of care once you were able to move away from the non-invasive device!
This may sound familiar as I wrote about this topic in the last year but the previous post was restricted to infants who were under 1000g. High Flow Nasal Cannula be careful out there had a main message that suggested the combined outcome of BPD or death was more prevalent when HFNC is used alone or with CPAP than when CPAP is used alone. The question remains though whether this applies to larger infants. Without looking at the evidence for that combined outcome most people would say there is unlikely to be a difference. Larger more mature babies have a much lower risk of BPD or death so proponents of HFNC would say it is simpler to use and helps prevent nasal breakdown as well. The question remains as to whether all outcomes are the same in larger infants and that is the point of this post.
A Non-Inferiority Trial
First off it is important to understand what this type of trial is. The first requirement is that the two treatments have both been compared to a placebo and found to be both effective. Once you establish that you have a choice between two treatment options then you eliminate the placebo and compare them head to head. What you are looking for in this type of trial is to determine not whether one is better than the other but that there is no difference in a clinical outcome of interest. If you find no difference then the next step is to look at other outcomes that might be of interest and see if there are any benefits to picking one versus the other. In the case of CPAP vs HNFC, if a non-inferiority trial showed no difference in an important outcome such as length of stay but nasal breakdown was less with HFNC it might lead a unit to use HFNC for their infants. Okay, now that we have that cleared up we can move on to an actual study examining this very subject.
This was an interesting study with a great name (The HIPSTER trial) that enrolled infants > 28 weeks and 0 days with none of the infants receiving surfactant but either being randomized to HFNC or CPAP after delivery. These infants were your typical modern day cohort of babies who may avoid intubation and surfactant by establishing FRC early with positive pressure applied to the nose through one of these devices. The end point for the study was treatment failure within 72 hours. If an infant failed in the HFNC they could have a trial of CPAP whereas in the CPAP group they were intubated. For each infant in the HFNC group flow was set from 6-8 l/min and for CPAP 6-8 cmH2O.
Treatment was considered to have failed if an infant receiving maximal support (high-flow therapy at a gas flow of 8 liters per minute or CPAP at a pressure of 8 cm of water) met one or more of the following criteria:
- FiO2 of 0.4 or higher
- Arterial or free flowing cap gas with a pH of 7.2 or less plus a pCO2 > 60 mm Hg obtained at least 1 hour after starting treatment
- Two or more episodes of apnea requiring positive-pressure ventilation within a 24-hour period or six or more episodes requiring any intervention within a 6-hour period.
- Infants with an urgent need for intubation and mechanical ventilation.
So what happened?
The trial randomized 583 infants (278 HFNC, 286 CPAP) but was halted by the data and safety monitoring committee after an analysis of the first 515 revealed that the outcome was worse in the HFNC group (25.5% failure rate vs 13.3 for CPAP). Interestingly treatment failures were more common in babies below and above 32 weeks so it was not just the smallest infants who failed.
Another interesting finding was that the most common reason for treatment failure was criteria 1 (FiO2 > 40%) while intubation was higher for all infants but did not reach statistical significance. Curiously what did reach a significant difference was criteria #4 (18.4% urgent intubations in the CPAP group vs 5.6% in the HFNC group). You might be tempted to therefore ponder which is worse, a little O2 or being intubated but you need to recall the trial design which was set up to provide this kind of result. If you failed HFNC you were placed on CPAP whereas if you failed CPAP you were intubated. In the HFNC group, 78 infants were deemed to have failed but 28 of them were in fact “rescued by CPAP”. It therefore isn’t a fair comparison when it comes to urgent intubation since if you failed CPAP there wasn’t another option.
Not a total loss
Nasal trauma was indeed much lower in the HFNC group, occurring only 8.3% vs 18.5% of the time with CPAP. Pneumothorax was also found to be significantly different with none of the patients in the HFNC group having that complication vs 2.1% in the CPAP group. What this study tells us is that as a primary modality to treat newborns with RDS who have not received surfactant it is preferable to use CPAP in the first 72 hours. Some of you may say it might not say that at all but consider the impact of having more babies exposed to high FiO2. We know from other studies that high FiO2 can be quite damaging to preterm infants and this study was certainly not powered to look at all those important outcomes such as ROP, PVL and BPD. The authors report them and found no difference but without adequate power to show a difference I wouldn’t take much comfort in those findings.
I think were things may settle out though is what to do in more mature infants. There is no question that for those on chronic respiratory support there is some risk of nasal breakdown. Although I don’t have much experience with HFNC I would think that for the older patient who either already has BPD at 36 weeks or is close to that point but reliant on +4 or +5 CPAP that HFNC might help “give them a break”. As such I don’t see this as a total loss but rather an option to try when CPAP for whatever reason is not tolerated.
As a primary therapy for non-invasive management RDS I will keep my CPAP for all babies thank you.
On occasion two articles will be published in short succession and have discrepant findings. This appears to be one of those times. Hishikawa K in Japan published a paper in September entitled Pulmonary air leak associated with CPAP at term birth resuscitation while Calebi MY from Turkey published Impact of Prophylactic Continuous Positive Airway Pressure on Transient Tachypnea of the Newborn and Neonatal Intensive Care Admission in Newborns Delivered by Elective Cesarean Section in August of this year.
The findings as we will discuss were quite discrepant which on the surface leaves the practitioner in a quandry. How do I best treat my patients? The key difference between the two studies was the finding of an increased rate of pneumothorax in the study by Hishikawa when CPAP was used in term infants with respiratory distress after delivery. Curiously prophylactic CPAP of +5 was used in both studies but the populations under study were quite different. The study by Calebi targeted infants between 34 0/7 weeks and 38/6/7 weeks vs term infants in the study from the Japanese group.
Another important difference is the utilization of CPAP which in the study by Calebi involved prophylactic administration within twenty minutes of birth and in the Japanese cohort the indication was the development of symptoms. Thinking about this for a moment, these two groups are actually quite different. A newborn with TTN has an increased amount of interstitial fluid that has not made it’s way to the hilum for reabsorption in the lymphatic system. The lungs of these infants are heavier with fluid than comparable infants without such pathology and therefore are also less compliant. Non compliant lungs are prone to microatelectasis as the infants progressively experience alveolar collapse. The longer the clinician waits to start supportive CPAP the more the lungs collapse and greater negative pressure is required to open these closing alveoli. Furthermore if there is fluid in the airway itself there is the potential for a ball valve mechanism to come into effect whereby air is able to pass through the dilated airways during inspiration but on expiration the collapse leads to air trapping. Such trapping places the infant at risk for air leak. CPAP is used to establish an adequate functional residual capacity (FRC) as indicated in this picture. Failure to do so results in atelectasis.
The Japanese study examines the impact of CPAP after a change in guidelines in 2010 suggesting that CPAP should be utilized in the delivery suite for those infants with ongoing respiratory distress. The study by Calebi really examines a different patient group being those who are near term patients with TTN who have early CPAP implemented. The early administration of CPAP may be the technique that prevents alveolar collapse as mentioned above and avoids the requirement by the infant to generate such high negative pressure with its inherent risk of air leak.
Is All CPAP The Same?
Another important distinction between the two papers is the way in which CPAP was administered. The Japanese utilized a flow inflating bag with a pressure valve and manometer while the study by Calebi employed a T-piece resuscitator. When it comes to maintaining CPAP there is no question having used both devices that I find the T-piece resuscitator much easier to use and over longer periods the reliability of the pressure delivered by the T-piece would be superior to that with the flow inflating bag. The Neopuff T-Piece Resuscitator possesses a pressure relief valve which could help during an instance when the patient is crying or breath holding. The constant flow without a relief valve could lead to airleak which is precisely the situation that may occur during the use of a flow inflating bag.
Yes there was over a three fold increase in airleak at near term gestational age in the Japanese cohort but this was not seen at all in the Turkish study in which CPAP was implemented early. So the message here is that if you start CPAP early enough you can prevent airleaks from occurring. This in and of itself is worth implementing.
Can CPAP Reduce Hospital Admission to NICU?
There is more to the story however. The Turkish group demonstrated a significant difference in admission rates to the NICU as shown in the following figure. The results here although just achieving significance should not be minimized. Avoiding progressive atelectasis decreases admission rates. The conclusion here is that there is little benefit in adopting a wait and see approach to those kids born by elective c-section. While it is true that you may be treating a significant number of healthy patients between 34 0/7 – 38 6/7 weeks with CPAP it is for a brief period and makes a significant difference in frequency of admission.
We live in an era of bed shortages and I would argue that anything we can do to reduce admissions and moreover keep babies with their parents is worth exploring. From my perspective treating these kids with the appropriate CPAP device for twenty minutes after birth is well worth it. Perhaps your unit should consider the same.