#015 - Use of abdominal NIRS for NEC

Hello friends 👋

In this conversation, Dr. Samer Bou Karroum emphasizes the significance of early planning and preparation in shaping one's career and future. He discusses how contemplating future paths can provide clarity and direction, even if the future remains uncertain. The insights shared highlight the importance of laying a solid foundation to build upon for future success.

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Short Bio: Samer Bou-Karroum, MD, FAAP, is a Neonatal-Perinatal Fellow at Washington University in St. Louis. Originally from Lebanon, he completed pediatric residency in Texas before pursuing advanced training in neonatology. His clinical interests include neonatal transports and point-of-care ultrasound (POCUS) use. His research focuses on neonatal hemodynamics, including near-infrared spectroscopy (NIRS) and its role in diagnosing, predicting, and describing necrotizing enterocolitis (NEC). He is passionate about medical education and enjoys bringing complex topics to broader audience.

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The transcript of today's episode can be found below 👇

[00:00:00] Srirupa: Hello everyone, welcome to another fantastic episode of Fellows Friday. I am very excited to welcome Dr. Samer Bou Karroum from Washington University. He is a second-year neonatology fellow who has done some amazing work with abdominal near-infrared spectroscopy (NIRS) in predicting necrotizing enterocolitis (NEC). I am excited to learn more about his research. Interestingly, we are practically neighbors — as you all remember, I am also in St. Louis at Cardinal Glennon, and he is a fellow at Washington University. We have been joking that we probably should have done this in person. Anyhow, we are going to learn more about his amazing research. First of all, Samer, welcome to our show.

[00:00:42] Dr. Samer Bou Karroum: Thank you, I am so excited to be here.

[00:00:44] Srirupa: Wonderful. For all you listeners, Samer has had a fantastic journey in medicine so far. He completed his medical training in Lebanon, moved here for residency at Texas Tech Lubbock, and is currently a second-year neonatology fellow at Washington University. Share with us what got you interested in medicine and pediatrics, Samer.

[00:01:10] Dr. Samer Bou Karroum: The event that really changed my life was volunteering with the Lebanese Red Cross. Back home in Lebanon, our EMS sector is based on volunteering, which gave me experience dealing with patients across the full spectrum — gunshot wounds, seizures, motor vehicle accidents, and more. That experience made me realize I could make a difference in people's lives through medicine. During medical school, I realized pediatrics was the population I wanted to work with. And for the NICU, I think we all agree it is the best specialty out there.

[00:02:04] Srirupa: Obviously, that is the best.

[00:02:07] Dr. Samer Bou Karroum: It combines so much of what you see in medicine in general. It has the acuity of ICU patients, but also the continuity of clinic patients if you opt to do a high-risk follow-up clinic. It has procedures, it has the inpatient component — it really encompasses everything. That is how I chose the NICU.

[00:02:40] Srirupa: Absolutely. I still tell medical students that the NICU should be a separate residency in itself, given how amazing a field it is. I cannot imagine doing anything else, and I am pretty sure most of you listening can relate. But let us talk about the research you are currently doing at WashU. Share with us about your fellowship project.

[00:03:14] Dr. Samer Bou Karroum: We just finished collecting and analyzing data from our first project, which looks at abdominal NIRS in relation to NEC. For those unfamiliar with NIRS, it is essentially an additional vital sign — similar to a pulse oximeter in that it has a light sensor and detector that measures differences in hemoglobin light absorption, giving us a percentage of oxygenated versus deoxygenated blood. The key difference between NIRS and SpO2 is that NIRS is a marker of regional oxygenation, because it predominantly detects venous blood. Placing a NIRS sensor over the liver gives an estimate of hepatic oxygenation; placing it on the flank gives renal oxygenation.

When I was rotating through the NICU as a resident, I noticed we had all these NIRS monitors but were not making much sense of the data. We follow trends, which is helpful, but we do not have defined thresholds or specific values that would alert us and say: this patient is heading toward NEC, something is wrong.

[00:04:36] Dr. Samer Bou Karroum : I found that gap really interesting. Our project focuses specifically on abdominal NIRS — placing the sensor on the abdomen and correlating those values with NEC. Abdominal NIRS has been studied before, with prior papers attempting to establish normal values in premature infants and explore its relationship with NEC. However, those studies had limitations: smaller sample sizes, and the fact that NEC occurs in only about 10 to 20% of patients, making NEC-specific cohorts quite small. Additionally, NEC detection was often a secondary aim rather than the primary focus. These limitations prompted us to conduct a larger, more targeted study at our institution.

We analyzed data from 194 patients. Approximately 12% had NEC — around 24 patients — which is consistent with the literature and a solid number compared to prior studies. The results showed a clear pattern: non-NEC patients reach their lowest abdominal NIRS values at around 25 to 30 days of life, while NEC patients reach their lowest values earlier, around 15 days of life.

[00:07:02] Dr. Samer Bou Karroum : In other words, abdominal NIRS values begin declining earlier in NEC patients — around day 15 — compared to non-NEC patients, whose values drop around days 25 to 30. Furthermore, non-NEC patients recover after this nadir, with abdominal NIRS values rising back above 90%. In contrast, patients with both medical and surgical NEC take longer to recover and maintain values between 60 and 80% throughout their hospitalization.

Another distinction from prior studies is the duration of monitoring. Previous studies followed patients for anywhere from one day to two weeks. Our study followed patients for up to three months — 120 days — allowing us to capture the full longitudinal NIRS pattern, including the recovery phase. Non-NEC patients recover toward 100%, while those with medical or surgical NEC remain between 60 and 80%.

We also stratified patients by gestational age — extremely preterm, very preterm, and late preterm — and found differences across groups. In extremely preterm infants, as might be expected, we observed a longer dip and a longer recovery phase in abdominal NIRS values.

[00:09:36] Srirupa: Fantastic. With so much technology coming into newborn medicine, these tools are so helpful in improving outcomes for our little ones. Out of my own curiosity — how did you define NEC in your population, given how variable the definitions can be?

[00:10:03] Dr. Samer Bou Karroum: We stratified NEC into medical and surgical NEC, consistent with standard clinical practice, and used Bell's criteria — stage II for medical NEC, with the well-established surgical definition for surgical NEC.

[00:10:23] Srirupa: And from my own research interest — how many of these babies had a hemodynamically significant patent ductus arteriosus (PDA)? I ask because I think that could also play a role in abnormal abdominal NIRS values.

[00:10:42] Dr. Samer Bou Karroum: Great point. There are many factors that can influence abdominal NIRS values, which is actually part of what drives our future studies. The PDA is one of them. We did not systematically record PDA data in this cohort, though we did exclude patients with hemodynamically significant congenital heart disease and genetic conditions. Not recording PDA status is a limitation we will be adding to the paper.

[00:11:21] Srirupa: Definitions of hemodynamically significant PDA are all over the place — some use clinical criteria, some echocardiographic, some a combination. Always a challenge. Such a fascinating project. Share with our listeners — mostly fellows — how you developed this research interest and found your mentor.

[00:12:00] Dr. Samer Bou Karroum: It is genuinely hard as a resident to think about your future fellowship research, especially with limited NICU exposure during residency. I was fortunate to have three months of NICU training plus an additional elective. It was during that elective that I really started asking: what is NIRS, and how could I use it in research?

The lesson there is to look beyond your required rotations. During required rotations, I was focused on being a good resident. During my elective, I had space to think about what truly interested me. I did that elective at UT Southwestern and met Dr. Eric Ortigoza, who was doing fascinating research on non-invasive techniques to diagnose NEC — including NIRS, acoustic methods, and others. His work drew me toward NIRS, and I kept reading from there.

Around the same time, my wife became pregnant and started asking me breastfeeding questions I could not answer. That sparked an interest in feeding, gut development, and the relationship between nutrition and NEC. Together, those two threads put me on a path focused on the GI system and non-invasive monitoring.

[00:14:16] Dr. Samer Bou Karroum : For finding a mentor, I really appreciate our program directors, who on day two of fellowship sent us an email asking about our research interests. It felt stressful at the time, but I now appreciate how proactive that was. That early prompt gave me the opportunity to meet with many people — basic scientists, clinical researchers, attendings across different areas — to sharpen my interests and understand what was actually feasible within our program. Through those conversations, I learned not just what I wanted to do, but also what I did not want to do and what resources were realistically available to me. Starting early and doing those meetings was key to getting to where I am now.

[00:15:41] Srirupa: That is great. How do you see the next steps for your project and your future career?

[00:15:58] Dr. Samer Bou Karroum: When I joined this program, I came in with the abdominal NIRS project and data already in place. But I also thought ahead: what if abdominal NIRS shows a connection to NEC, and what if it does not? Abdominal NIRS has known limitations — bowel contents, peristalsis, and abdominal distension in NEC all affect the values. So I started thinking about alternatives, and that is how renal NIRS came in.

We actually started the renal NIRS project in parallel with the abdominal NIRS project, before the latter was even complete. We are now actively recruiting patients for the renal NIRS study, looking for a similar correlation to what we found abdominally. The reasons for choosing renal NIRS are several: it has already been linked to acute kidney injury (AKI) and sepsis; the flank placement is anatomically well-defined and consistent across different practitioners, unlike abdominal placement, which can vary; and it remains non-invasive with no significant side effects — we saw no skin irritation in our cohort.

[00:18:17] Dr. Samer Bou Karroum : Long-term, I see NIRS as an additional vital sign — one more piece of the clinical puzzle. It will never be a standalone diagnosis. But I envision it contributing to a NEC probability calculator, similar in concept to the HeRO score, which analyzes heart rate variability to predict sepsis or mortality. I see a future where NIRS data — both abdominal and renal — feeds into a machine learning or AI model that generates a NEC probability for individual patients. Now that we have demonstrated a difference in abdominal NIRS patterns between NEC and non-NEC patients, and if renal NIRS provides a similarly reliable signal, combining both layers of data would substantially strengthen that predictive model.

[00:20:10] Srirupa: You clearly have a lot of great ideas and insight into where this field is heading. Any NIRS enthusiasts among our listeners, keep a close eye on Dr. Samer Bou Karroum. Now share with us the challenges you faced during your project — I ask this as a somewhat loaded question, because fellowship research can be challenging in many different ways.

[00:20:57] Dr. Samer Bou Karroum: That is a very important question. When you first envision a research project, you think: collect data, analyze it, done in three to six months. Once you actually start, you realize how many unexpected obstacles come up at every step.

One of the biggest challenges we face is recruitment — particularly recruiting the smallest infants, specifically those at 22 to 24 weeks gestation. Including extremely preterm infants is important for statistical power and clinical relevance, but these babies are extraordinarily fragile. Even minimal handling — including placing a NIRS sensor, which is comparable in size to a SpO2 probe — can trigger a desaturation event that alarms the nurses and distresses the parents. That makes consent very difficult.

[00:23:21] Dr. Samer Bou Karroum : What I have learned is that you have to be genuine with families. I recruit patients myself — this is my project — and speaking from the heart makes a real difference. You acknowledge their concerns, explain that we use NIRS clinically on our sickest babies already, and also make clear that this is a research study, not part of their baby's treatment. And you give them full grace if they decline. I do not have a formula. I just know that when I speak genuinely, families are more likely to say yes.

[00:24:08] Srirupa: Research in neonatology is always challenging, especially when consent is involved — families are at their most vulnerable, often facing an unexpected delivery or a critically ill newborn. Kudos to you for navigating that. One last question: what is the one piece of advice you would give an incoming neonatology fellow interested in your line of research?

[00:24:48] Dr. Samer Bou Karroum: Start early. There is no such thing as too early. We all get asked where we see ourselves in five years, and I used to dismiss that question. But thinking ahead is genuinely important — not because you are committing to a path, but because preparation gives you a foundation to build on.

For me, it all started with that elective as a resident. That is when the light went on. And then my program directors accelerated it by pushing us early to meet with researchers across disciplines. My advice is: start early, think ahead, and do not be shy about reaching out. I was fairly introverted about that at first, but the neonatology community is small and genuinely supportive. Email fellows, email attendings, ask questions, meet people. Everyone is willing to help. The earlier you start building those connections and clarifying your interests, the better positioned you will be when fellowship begins.

[00:26:52] Srirupa: Golden words. Starting early is so important. I can absolutely relate — "I don't know" used to be my answer to the five-year question. But taking the time before my job search to actually think it through was genuinely helpful. Thank you so much, Samer, for joining us today and sharing such significant and impactful research. We wish you all the best with everything you are doing at WashU.

[00:27:41] Dr. Samer Bou Karroum: Thank you very much.