Skip to Main Content

++

I. Intensive care

++

  1. Definition

    1. Jaundice

      1. Jaundice (as distinct from hyperbilirubinemia) relates to the yellow color produced in the sclera, skin, and subcutaneous tissues by deposition of bilirubin in those sites.

      2. Not all jaundiced newborns are necessarily hyperbiliru-binemic.

      3. Visual assessment of jaundice is an inaccurate way of determining whether a baby is actually hyperbilirubinemic, especially in a premature infant.

    2. Hyperbilirubinemia

      1. In term infants, hyperbilirubinemia is frequently defined as a serum total bilirubin (STB) concentration >95th percentile on the hour-specific bilirubin nomogram.

      2. In preterm infants, in contrast, there are no clear definitions of normal or physiologic bilirubin levels and hence of hyperbilirubinemia. The reasons for this are multifold.

        • Almost all preterm infants develop some degree of jaundice during the first postnatal days.

        • There are dynamic changes in STB levels during this period.

        • The significance of the jaundice with regard to bilirubin neurotoxicity may increase with decreasing gestational age.

        • Phototherapy is used frequently in these infants, thereby moderating STB values and preventing these from reaching natural peaks.

    3. Practical definitions

      1. For practical purposes in the preterm infant in the intensive care setting, we suggest the following, based on the indications for phototherapy and exchange transfusion:

        • Moderate hyperbilirubinemia: Includes any STB level meeting accepted criteria for phototherapy

        • Severe hyperbilirubinemia: Regarded as any STB meeting or exceeding the indications for exchange transfusion

  2. Incidence

    1. Almost all premature infants develop some degree of increased STB concentration that may cause jaundice and, in some instances, hyperbilirubinemia.

      1. In the absence of specific criteria for hyperbilirubinemia, the incidence of the condition is difficult to determine.

      2. The majority of premature infants <1.5 kg birthweight will meet phototherapy requirements during the first postnatal week.

  3. Pathophysiology

    1. Physiology of bilirubin metabolism

      The physiology of bilirubin is similar in the premature and term infant.

      1. Bilirubin formation

        Red blood cells are continually being broken down in the reticuloendothelial system and replaced. This process releases heme, which is catabolized by the enzyme heme oxygenase 1 to biliverdin and thence to bilirubin. This form of bilirubin is called unconjugated or indirect bilirubin. Bound to serum albumin the bilirubin is transported to the liver.

      2. Bilirubin conjugation and elimination

        After uptake into the hepatocyte, unconjugated bilirubin is glucuronated to form water soluble mono- and diglucuronides, known as conjugated or direct bilirubin. The enzyme controlling the conjugation process is UDP-glucuronosyltransferase 1A1 (UGT). Direct bilirubin is excreted via bile to the bowel from which it is excreted from the body.

      3. Genetic control of bilirubin conjugation

        The enzyme UGT1A1 is encoded by the gene UGT1A1. This gene contains a noncoding promoter region and a coding region. Polymorphisms of the promoter region, such as the (TA)n polymorphism, result in diminished expression of a normally formed enzyme and are associated with Gilbert syndrome. Coding area mutations result in an abnormally structured enzyme with no or little conjugating ability, such as is seen in Crigler-Najjar syndrome.

      4. Enterohepatic circulation

        In the newborn bowel, conjugated bilirubin may be unconjugated by the enzyme ?-glucuronidase and reabsorbed into the bloodstream, thereby adding to the bilirubin pool and straining the already deficient bilirubin ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessPediatrics Full Site: One-Year Subscription

Connect to the full suite of AccessPediatrics content and resources including 20+ textbooks such as Rudolph’s Pediatrics and The Pediatric Practice series, high-quality procedural videos, images, and animations, interactive board review, an integrated pediatric drug database, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPediatrics

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.