TWO PATIENTS IN ONE
PRIMER ON PREMATURITY Terry Cohen , MD , FAAP
Although few would admit it at the time , the 1 in 160 physicians 1 who ultimately became neonatologists knew by the end of their first NICU rotation , even if it was during medical school , that their career path would take them into this uniquely different world .
While some saw the “ baby laboratory ” as a pariah to be avoided , they saw it as a lonely medical orphan in need of adoption . It is a place where the rules of pathophysiology are not always consistent , and rarely play fair . The chance to see patients with a myriad of unusual diagnoses - congenital birth defects , genetic oddities and atypical infections - brings doctors in , but usually it is prematurity , especially at the extremes of viability , that keeps us coming back .
Premature infants can be divided roughly into three major categories which describe a sigmoid function , or “ S-curve ” centered at approximately 29 weeks of gestation . Infants born before 27 weeks will usually have a long and complex initial phase of care with a significant risk of mortality and long-term morbidities . 2 Those born after 32 weeks of gestation may experience a few days of transitional respiratory problems but have long-term risks only slightly greater than that of a term infant . The five weeks in between , from 27 through 31 weeks of gestation are often viewed a golden period , with sharply declining complexity and risks with each advancing week , let alone every day the fetus remains in utero , and when antenatal glucocorticoids given to the mother seem to have the greatest effect . 3 For those who do not know , especially in the case of optimistic parents , when it comes to gestational age , by convention , there is no rounding up . 4
The best general explanation for the relative flatness of this curve during early periods of viability , which has persisted despite decades of medical advancement , corresponds to the overall incompleteness of organ structural integrity and biologic systems . The lungs , brain and immune system of the micro-preemie ( less than 750g ) are especially important as the origin of the three major causes of mortality in this population : pulmonary failure , intracranial hemorrhage and sepsis .
8 LOUISVILLE MEDICINE
Survivors who experience early pulmonary damage in the form of alveolar overdistension , pneumothorax and / or pulmonary interstitial emphysema often develop severe bronchopulmonary dysplasia . 5 Likewise , those that experience early brain damage in the form of advanced intraventricular or cortical hemorrhage , or periventricular leukomalacia , have the greatest risk of neurodevelopmental impairment and cerebral palsy . 6
Further contributing to the difficulty in management are the size limitations of medical equipment , especially the increased resistance and difficulty clearing small caliber lumens , whether an endotracheal tube with a 2.5mm inner diameter , ventilator tubing that is asked to reliably deliver tidal volumes less than 5mL , or an IV pump that is asked to push total parenteral nutrition ( TPN ) and medications through a multi-ported 1mm PICC line .
Advancements in neonatology have been made in parallel , although seemingly paradoxically countered , by advancements in its companion specialty , maternal-fetal medicine . Early identification and improved care for mothers at risk for delivery at extremely early gestation have shifted many of those cases into later , lower risk gestational ages . Although perhaps anecdotal , these same improvements seem to have not only brought many formerly previable infants into the high-risk period , but there is a general feeling amongst neonatologists that the micro-preemies of our current generation are
Survival at 5 1 / 2 years , survival without severe / moderate neurodevelopmental disabilities , and survival without any neurodevelopmental disabilities by week of gestational age at birth , among preterm born children in the EPIPAGE-2 study .