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It has to be one of the most common questions you will hear uttered in the NICU. What were the cord gases? You have a sick infant in front of you and because we are human and like everything to fit into a nicely packaged box we feel a sense of relief when we are told the cord gases are indeed poor. The congruence fits with our expectation and that makes us feel as if we understand how this baby in front of us looks the way they do. Take the following case though and think about how you feel after reading it. A term infant is born after fetal distress (late deceleration to as low as 50 BPM) is noted on the fetal monitor. The infant is born flat with no heart rate and after five minutes one is detected. By this point the infant has received chest compressions and epinephrine twice via the endotracheal tube. The cord gases are run as the baby is heading off to the NICU for admission and low and behold you get the following results back; pH 7.21, pCO2 61, HCO3 23, lactate 3.5. You find yourself looking at the infant and scratching your head wondering how the baby in front of you that has left you moist with perspiration looks as bad as they do when the tried and true cord gas seems to be betraying you. To make matters worse at one hour of age you get the following result back; pH 6.99, pCO2 55, HCO3 5, lactate 15. Which do you believe? Is there something wrong with the blood gas analyzer? How Common Is This Situation You seem to have an asphyxiated infant but the cord gas isn’t following what you expect as shouldn’t it be low due to the fetal distress that was clearly present? It turns out, a normal or mildly abnormal cord gas may be found in asphyxiated infants just as commonly as what you might expect. In 2012 Yeh P et al looked at this issue in their paper The relationship between umbilical cord arterial pH and serious adverse neonatal outcome: analysis of 51,519 consecutive validated samples. The authors sampled a very large number of babies over a near 20 year period to come up with a sample of 51519 babies and sought to pair the results with what they knew of the outcome for each baby. This is where things get interesting. When looking at the outcome of encephalopathy with seizures and/or death you will note that only 21.71% of the babies with this outcome had a gas under 7.00. If you include those under 7.10 as still being significantly distressed then this percentage rises to 34.21%. In other words almost 66% of babies who have HIE with seizures and/or death have a arterial cord pH above 7.1! The authors did not look at encephalopathy without seizures but these are the worst infants and almost 2/3 have a cord gas that you wouldn’t much as glance at and say “looks fine” How do we reconcile this? The answer lies in the fetal circulation. When an fetus is severely stressed, anaerobic metabolism takes over and produces lactic acid and the metabolic acidosis that we come to expect. For the metabolites to get to the umbilcal artery they must leave the fetal tissues and enter the circulation. If the flow of blood through these tissues is quite poor in the setting of compromised myocardial contractility the acids sit in the tissues. The blood that is therefore sitting in the cord at the time of sampling actually represents blood that was sent to the placenta “when times were good”. When the baby is delivered and we do our job of resuscitating the circulation that is restored then drives the lactic acid into the blood stream and consumes the buffering HCO3 leading to the more typical gases we are accustomed to seeing and reestablishing the congruence our brains so desire. This in fact forms the basis for most HIE protocols which includes a requirement of a cord gas OR arterial blood gas in the first hour of life with a pH < 7.00. Acidosis May Be Good For the Fetus To bend your mind just a little further, animal evidence suggests that those fetuses who develop acidosis may benefit from the same and be at an advantage over those infants who don’t get acidemia. Laptook AR et al published Effects of lactic acid infusions and pH on cerebral blood flow and metabolism. In this study of piglets, infusion of lactic acid improved cerebral blood flow. I would suggest improvement in cerebral blood flow of the stressed fetus would be a good thing. Additionally we know that lactate may be used by the fetus as additional metabolic fuel for the brain which under stress would be another benefit. Finally the acidemic fetus is able to offload O2 to the tissues via the Bohr effect. In case you have forgotten this phenomenon, it is the tendency for oxygen to more readily sever its tie to hemoglobin and move into the tissues. I hope you have found this as interesting as I have in writing it. The next time you see a good cord gas in a depressed infant, pause for a few seconds and ask yourself is this really a good or a bad thing?
The human body truly is a wondrous thing. Molecules made from one organ, tissue or cell can have far reaching effects as the products take their journey throughout the body. As a medical student I remember well the many lectures on the kidney. How one organ could control elimination of waste, regulate salt and water metabolism, blood pressure and RBC counts was truly thought provoking. At the turn of the century (last one and not 1999 – 2000) Medical school was about a year in length and as the pool of knowledge grew was expanded into the three or four year program that now exists. Where will we be in another 100 years as new findings add to the ever growing volume of data that we need to process? A good example of the hidden duties of a molecule is erythropoetin (Epo) the same one responsible from stimulating red blood cell production. Double Duty Molecule In saying that I am simplifying it as there are likely many processes this one hormone influences in the body but I would like to focus on its potential role in neuroprotection. In 1999 Bernaudin Et al performed an animal study in mice to test this hypothesis. In this elegant study, strokes were induced in mice and the amount of Epo and Epo receptors measured in injured tissues. Levels of both increased in the following way “endothelial cells (1 day), microglia/macrophage-like cells (3 days), and reactive astrocytes (7 days after occlusion)”. To test the hypothesis that the tissues were trying to protect themselves the authors then administered recombinant human Epo (rhEpo) to mice prior to inducing stroke and the injury was clearly reduced. This established Epo as a potential neuroprotectant. Other animal studies then followed demonstrating similar findings. A Human Trial When you think about hypoxic ischemic encephalopathy (HIE) you can’t help but think of whole body cooling. The evidence is pretty clear at this point that cooling in this setting reduces the combined outcome of death or neurodevelopmental disability at 18 months with a number needed to treat of 7. The risk reduction is about 25% compared to not those not cooled so in other words there is room to improve. Roughly 30-40% of infants who are cooled with moderate to severe HIE will still have this outome which leaves room for improvement. This was the motivation behind a trial called High-Dose Erythropoietin and Hypothermia for Hypoxic-Ischemic Encephalopathy: A Phase II Trial. This was a small trial comparing 50 patients (24 treated with rhEpo and cooling to 26 given placebo) who were treated with 1000 U of rEpo on days 1,2,3,5 and 7. Primary outcome was neurodevelopment at 12 months assessed by the Alberta Infant Motor Scale (AIMS)and Warner Initial Developmental Evaluation. A significant improvement in a subset of mobility on the latter was found and a significant difference in the AIMS overall. An additional finding giving support for a difference was that blinded reviews of MRI scans demonstrated a singificant improvement in brain tissue in those who received rhEPO. One curious finding in this study was that the mean timing of administration of rhEPO was 16.5 hours of life. Knowing that the benefit of cooling is best when done before 6 hours of age one can only wonder what impact earlier administration of a neuroprotective agent might have. This suggests that the addition of rEPO to cooling has additional impact but of course being a small study further research is needed to corroborate these findings. The Next Step This past week Malla et al published an interesting paper to add to the pool of knowledge in this area; Erythropoietin monotherapy in perinatal asphyxia with moderate to severe encephalopathy: a randomized placebo-controlled trial. This study was done from the perspective of asking if rhEPO by itself in resource poor settings without access to cooling in and of itself could make a difference in outcome for patients with HIE. This was a larger study with 100 Hundred term neonates (37 weeks or greater) with moderate or severe HIE. Fifty were randomized by random permuted block algorithm to receive either rhEPO 500 U kg− 1 per dose IV on alternate days for a total of five doses with the first dose given by 6 h of age (treatment group) or 2 ml of normal saline (50 neonates) similarly for a total of five doses (placebo group) in a double-blind study. The primary outcome was combined end point of death or moderate or severe disability at mean age of 19 months and the results of this and other important outcomes are shown below. Outcome Treatment Placebo p Death/disability (mod/severe HIE) 40% 70% 0.003 Death/disability (mod HIE only) 21% 61% 0.004 Cerebral Palsy 23% 45% 0.04 MRI abnormalities 40% 60% 0.04 Seizures treatment at 19 months 19% 43% 0.03 To say that these results are impressive is an understatement. The results are on par with those of cooling’s effect on reduction of injury and improvement in outcome. When looking at the primary outcome alone the result in dramatic when put in perspective of looking at number needed to treat which is 4! This is significant and I can’t help but wonder if the impact of this medication is at least in part related to starting the dosing within the same window of effectiveness of therapeutic hypothermia. Importantly there were no adverse effects noted in the study and given that rhEpo has been used to treat anemia of prematurity in many studies and not found to be associated with any significant side effects I would say this is a fairly safe therapy to use in this setting. Next Steps I find this puts us in a challenging position. The academic purists out there will call for larger and well designed studies to test the combination of rhEPO and cooling both initiated within 6 hours of age. While it takes years to get these results might we be missing an opportunity to enhance our outcomes with this combination that is right in front of us. The medication in question other than raising your RBC count has little if any side effects especially when given for such a short duration and by itself and possibly with cooling increases the rate of neuroprotection already. I don’t know about you but I at least will be bringing this forward as a question for my team. The fundamental question is “can we afford to wait?”
Guest posted a topic in Congresses and coursesFew places left for this unique symposium. It is a collaboration between UCL, KCL and Imperial College London and brings together 3 active research centres in the field of Neonatal Neuroprotection. The course will cover current and future treatments, Insight in imaging modalities and discuss outcomes Will also offer the opportunity for practical small group workshops on imaging, EEG, aEEG, legal aspects To register please go to http://www.guysandstthomasevents.co.uk/paediatrics-training/london-neonatal-neuroprotection-symposium/ A4 flyer - Neuroprotection 2014 low res.pdf
KCL, UCL, Imperial, Guys and St Thomas and Evelina London are organising a 2 day symposium on neonatal neurprotection, 29 - 30 May 2014 Details: http://www.guysandstthomasevents.co.uk/paediatrics-training/london-neonatal-neuroprotection-symposium/