Matthew Kuestner, M.D., attending anesthesiologist at Kosair Children’s Hopsital, overviews hematopoiesis, fetal hemoglobin and physiologic anemia in pediatrics. Dr Kuestner is a board certified pediatric anesthesiologist and a Diplomate of the American Board of Anesthesiology.
Hematopoiesis, Fetal Hemoglobin & Physiologic Anemia in Pediatrics by Dr. Kuestner
- Liver will produce fetal erythropoietin in the first 24 weeks of life.
- In the last trimester of pregnancy the erythropenia will be coming from the kidney.
- At 10-12 weeks 80% of hemoglobin is fetal hemoglobin or hemoglobin-F which decline to 0% by six months of age.
- So a term baby has 20% of Adult or hemoglobin-A.
- Hemoglobin-A is made up of 2 Alpha and 2 beta polypeptide chains.
- Fetal hemoglobin behaves differently than adult hemoglobin. Fetal hemoglobin shifts from a P-50 of 19.4 on the first day of life to 30.3 at eleven months of age.
- Normal adult P-50 is 27.
- P-50 is the conventional measure of Hemoglobin’s affinity for oxygen.
- Fetal oxygen hemoglobin dissociation curve will shifted to the Left of moms curve.
- Fetal hemoglobin must have a greater affinity for oxygen than maternal hemoglobin to be accepted in the uterine villi and supply oxygen to the fetus.
- Fetal hemoglobin’s greater affinity for oxygen is due to its low capacity to interact with (2,3 DPG).
- The binding site for (2,3 DPG) is on the Beta chain. Which is absent in fetal hemoglobin.
- Oxygen will still transfer from mother to fetus when hemoglobin-A is transfused in utero. So if you have to give a fetus a transfusion with adult hemoglobin the fetus will still get the oxygen they need.
Normal Physiologic Shift in Hemoglobin Values
- Normal Neonate hemoglobin is 17, mostly hemoglobin-F.
- At 3-4months of age, in a full term newborn hemoglobin will drop to 10-11. Termed the normal physiologic anemia of infancy.
- At age 2 hemoglobin should be around 12.
- Slow increases to 13-14 by the age of 10.
The normal physiologic anemia occurs because hemoglobin-F is transitioning to hemoglobin-A. The drop in hemoglobin stimulates the erythropoietin to be produced by the kidney.
Premature babies do things differently. They drop further and faster and the take longer to transition to adult hemoglobin.
Difference in premature and healthy full term babies.
- The anemia in healthy full term babies are symptomatic.
- In premature babies it occurs earlier, persist longer and it causes them to be symptomatic.
- In premature babies hemoglobin may drop to as low as 8 by the 4th week of age.
- The anemic infant could have bradycardia, apnea, delayed growth, and poor weight gain.
- The bradycardia, apnea, and hemodynamic changes are big concerns in anesthesia.
In infants weighing less than 1kg often blood sampling and lab work exceeds or equals half of their blood volume. So then they get transfused with adult hemoglobin-A. Therefore, there is no stimulation of for the kidneys to produce erythropoietin. So the red cells don’t last very long and they become anemic again.
For a NICU baby make sure blood is available for these kids before going back for surgery.
New information says it’s better to start transfusing on the earlier side of things, so you don’t have to give the blood so quickly and at the same time you’re decreasing their risk of hyperkalemia.
You do not want to wait until the baby has become tachycardia or bradycardia to start your intervention.