Dark green gastric residuals are gross but may be part of a systemic logical fallacy in Neonatology

Dark green gastric residuals are gross but may be part of a systemic logical fallacy in Neonatology

In recent years we have moved away from measuring and reporting gastric residuals. Checking volumes and making decisions about whether to continue feeding or not just hasn’t been shown to make any difference to care. If anything it prolongs time to full feeds without any demonstrable benefits in reduction of NEC. This was shown in the last few years by Riskin et al in their paper The Impact of Routine Evaluation of Gastric Residual Volumes on the Time to Achieve Full Enteral Feeding in Preterm Infants. Nonetheless, I doubt there is a unit in the world that has not had the following situation happen. It is 2 AM and the fellow on call is notified that they need to come and see a patient. On arrival the bedside nurse shows them a syringe that contains dark green murky fluid. The fellow is told that NG tube placement was just being checked and this is what was aspirated. The infant is fine in terms of exam but the question is asked “What should I do with this fluid”. The decision is made that the fluid looks “gross” and they discard it and then decide to resume feedings with a fresh batch of milk. Both parties feel good about discarding what looked totally unappealing for anyone to ingest and the night goes on. If this sounds familiar it should as I suspect this happens frequently.

Logical Fallacy

A colleague of mine introduced me to this concept and I think it may apply here. Purdue University’s writing lab defines a Logical Fallacy in this way “Fallacies are common errors in reasoning that will undermine the logic of your argument. Fallacies can be either illegitimate arguments or irrelevant points, and are often identified because they lack evidence that supports their claim.”

I think we may have one here that has pervaded Neonatology across the globe. Imbedded in the fallacy is the notion that because the dark green aspirates look gross and we often see such coloured aspirates in patients with necrotizing enterocolitis or other bowel disease, all green aspirates must be bad for you. The second fallacy is that the darker the aspirate the more seriously you should consider discarding it. This may surprise you but on their own there isn’t much of anything that has been shown to be wrong with them. Looking for evidence to demonstrate increased rates of NEC or other abdominal issues in an otherwise well patient finds pretty much nothing to support discarding.

A challenge to discarding

Athalye-Jape G et al published Composition of Coloured Gastric Residuals in Extremely Preterm Infants-A Nested Prospective Observational Study. The study was a nested one in that questions about gastric residuals were taken from two studies on the use of probiotics. As with other studies on the use of probiotics there were some benefits seen as shown in Table 2 but that is not the main reason for sharing this study with you.

The main reason for the share of this paper is what is in Table 3.

Although not significantly different the mean estimates for concentration of bile acids in the pale and dark green aspirates came close to being different. Other nutritional content such as fat, protein and carbohydrate were no different. As the bile became darker though the bile acids tended to increase. It is this point that is worthy of discussion.

A Breakdown of the Aspirate

I’m with you. When you look at that murky dark green fluid in the syringe it just seems wrong to put that back into a belly. Would you want to eat that? Absolutely not but when you break it down into what is in there, suddenly it doesn’t seem so bad. We assume that we would not want to refeed such putrid looking material and that is where the logical fallacy exists. What evidence do we have that refeeding that fluid is bad? As I said above not much at all. Looking at the fact that there is actual nutritional calories in that fluid and bile acids as well you come to realize that throwing it away may truly not be in the best interest of the baby. Calories may wind up in the garbage and along with them, bile acids.

Bile acids are quite important in digestion as they help us digest fat and moreover as they enter the ileum they are reabsorbed in large quantities which go to further help digestion. In addition bile acid concentrations are what helps draw fluid into bile and promotes bile flow. By throwing these bile acids out we could see lower bile volumes and possible malabsorption from insufficient emulsification of fat.

The other unmeasured factors in this fluid are the local hormones produced in the bowel such as motilin which helps with small bowel contractility. Loss of this hormone might lead to impairment of peristalsis which can lead to other problems such as bacterial overgrowth and malabsorption.

Now all of this is speculative I will admit and to throw out one dark green aspirate is not going to lead to much harm I would think. What if this was systematic though over 24 or 48 hours that such aspirates were being found and discarded. Might be something there, What I do think the finding of such aspirates should trigger however is a thorough examination of the patient as dark green aspirates can be found in serious conditions such as NEC or bowel perforation. In the presence of a normal examination with or without laboratory investigations what I take from this study is that we should question are tendency to find and discard. Maybe the time has come to replace such fear with a practice of closing our eyes and putting that dark green aspirate right back where it came from.

Gastric or transpyloric feeding. Which is better for babies with BPD?

Gastric or transpyloric feeding. Which is better for babies with BPD?

First off I should let you know that we do not do transpyloric feeding for our infants with BPD. Having said that I am aware of some units that do. I suspect the approach is a bit polarizing. A recent survey I posted to twitter revealed the following findings:

I think the data from this small poll reveal that while there is a bias towards NG feeds, there is no universal approach (as with many things in NICU).

Conceptually, units that are using transpyloric feeds would do so based on a belief that bypassing the stomach would lead to less reflux and risk of aspiration. The question though is whether this really works or not.

New N of 1 Trial

I don’t think I have talked about N of 1 trials before on this site. The trials in essence allow one patient to serve as a study unto themselves by randomizing treatments over time for the single patient. By exposing the patient to alternating treatments such as nasogastric or nasoduodenal feedings one can look at an outcome and get a sense of causality if a negative or positive outcome occurs during one of the periods consistently. That is what was done in the study Individualising care in severe bronchopulmonary dysplasia: a series of N-of-1 trials comparing transpyloric and gastric feeding by Jensen E et al from the Children’s Hospital of Philadelphia. The authors in this study determined that using a primary outcome of frequency of daily intermittent hypoxaemic events (SpO2 ≤80% lasting 10–180 s) they would need 15 patients undergoing N of 1 trials between nasogastric and nasoduodenal feeding. Included infants were born at <32 weeks and were getting positive airway pressure and full enteral nutrition at 36 0/7 to 55 6/7 weeks PMA. Infants who were felt to be demonstrating signs of reflux or frank regurgitation were enrolled.

The findings

Thirteen of 15 enrolled patients completed the study. The two who did not complete did so as their oxygen requirements increased shortly after starting the trial and the clinical team removed them and chose their preferred route of feeding. Randomization looked like this:

Of the 13 though that completed and using an intention to treat analysis of the other two the findings were somewhat surprising. Contrary to what one might have thought that transpyloric would be a lung protective strategy, the findings were opposite.

Overall the combined results from these 15 patients demonstrated that nasogastric feedings were protective from having intermittent hypoxic events.

How can this be explained?

To be honest I don’t really know but it is always fun to speculate. I can’t help but wonder if the lack of milk in the stomach led to an inability to neutralize the stomach pH. Perhaps distension has nothing to do with reflux and those with BPD who have respiratory distress with some degree of hyperinflation simply are prone to refluxing acid contents due to a change in the relationship of the diaphragmatic cura? It could simply be that while the volume in the stomach is less, what is being refluxed is of a higher acidity and leads to more bronchospasm and hypoxemic events.

What seems to be clear even with this small study is that there really is no evidence from this prospective trial that transpyloric feeding is better than nasogastric. Given the size of the study it is always worth having some degree of caution before embracing wholeheartedly these findings. No doubt someone will argue that a larger study is needed to confirm these findings. In the meantime for those who are routinely using the transpyloric route I believe what this study does at the very least is give reason to pause and consider what evidence you have to really support the practice of using that route.

It’s time to approach nutrition in extreme preemies as if it were a drug

It’s time to approach nutrition in extreme preemies as if it were a drug

One of the benefits of operating this site is that I often learn from the people reading these posts as they share their perspectives.  On a recent trip I was reunited with Boubou Halberg a Neonatologist from Sweden whom I hadn’t seen in many years.  I missed him on my last trip to Stockholm as I couldn’t make it to Karolinska  University but we managed to meet each other in the end.  As we caught up and he learned that I operated this site he passed along a paper of his that left an impact on me and I thought I would share with you.

When we think about treating an infant with a medicinal product, we often think about getting the right drug, right dose and right administration (IV, IM or oral) for maximum benefit to the patient.  When it comes to nutrition we have certainly come a long way and have come to rely on registered dietitians where I work to handle a lot of the planning when it comes to getting the right prescription for our patients.  We seem comfortable though making some assumptions when it comes to nutrition that we would never make with respect to their drug counterparts.  More on that later…

A Swedish Journey to Ponder

Westin R and colleagues (one of whom is my above acquaintance) published a seven year retrospective nutritional journey in 2017 from Stockholm entitled Improved nutrition for extremely preterm infants: A population based observational study.  After recognizing that over this seven year period they had made some significant changes to the way they approached nutrition, they chose to see what effect this had on growth of their infants from 22 0/7 to 26 6/7 weeks over this time by examining four epochs (2004-5, 2006-7, 2008-9 and 2010-11.  What were these changes?  They are summarized beautifully in the following figure.

Not included in the figure was a progressive change as well to a more aggressive position of early nutrition in the first few days of life using higher protein, fat and calories as well as changes to the type of lipid provided being initially soy based and then changing to one primarily derived from olive oil.  Protein targets in the first days to weeks climbed from the low 2s to the mid 3s in gram/kg/d while provision of lipid as an example doubled from the first epoch to the last ending with a median lipid provision in the first three days of just over 2 g/kg/d.

While figure 3 from the paper demonstrates that regardless of time period there were declines in growth across all three measurements compared to expected growth patterns, when one compares the first epoch in 2004-2005 with the last 2010-11 there were significant protective effects of the nutritional strategy in place.  The anticipated growth used as a standard was based on the Fenton growth curves.

What this tells us of course is that we have improved but still have work to do.  Some of the nutritional sources as well were donor breast milk and based on comments coming back from this years Pediatric Academic Society meeting we may need to improve how that is prepared as growth failure is being noted in babies who are receiving donated rather than fresh mother’s own milk.  I suspect there will be more on that as time goes by.

Knowing where you started is likely critical!

One advantage they have in Sweden is that they know what is actually in the breast milk they provide.  Since 1998 the babies represented in this paper have had their nutritional support directed by analyzing what is in the milk provided by an analyzer.  Knowing the caloric density and content of protein, carbohydrates and fats goes a long way to providing a nutritional prescription for individual infants.  This is very much personalized medicine and it would appear the Swedes are ahead of the curve when it comes to this.  in our units we have long assumed a caloric density of about 68 cal/100mL.  What if a mother is producing milk akin to “skim milk” while another is producing a “milkshake”.  This likely explains why some babies despite us being told they should be getting enough calories just seem to fail to thrive.  I can only speculate what the growth curves shown above would look like if we did the same study in units that actually take a best guess as to the nutritional content of the milk they provide.

This paper gives me hope that when it comes to nutrition we are indeed moving in the right direction as most units become more aggressive with time.  What we need to do though is think about nutrition no different than writing prescriptions for the drugs we use and use as much information as we can to get the dosing right for the individual patient!