LECTURE SIX
Digestive system disordersNeonatal necrotizing enterocolitis ( NEC ) : refers to a spectrum of varying degrees of acute intestinal necrosis usually following injury of the bowel with secondary invasion and devitalization of the bowel wall .
Incidence . this is a serious and common problem affecting 1-5% of all newborn admitted to the intensive care units . affected infants most commonly are premature near 90% , asphyxiated and suffering from other medical problems . necrotizing enterocolitis rarely observed in a healthy term infants and less common in infants fed human milk .
Etiology and pathogenesis :
Bowel ischemia secondary to preceding perinatal asphyxia generally is regarded as the cause of bowel wall injury . the introduction of formula or human milk then provides the substrate for bacterial overgrowth . bacterial invasion of the bowel wall often with gas production ( pneumatosis intestinalis ), leads to tissues necrosis and perforation .
Other predisposing factors includes :
Systemic hypotension .
Patent ductus arteriosus .
Placement of au umbilical artery catheter .
Exchange transfusion .
Previous treatment with systemic antibiotics .
Use of hyperosmolar formula .
Rapid advancement of the feeding volume .
Clinical features and diagnosis : signs and symptoms are usually are noted during the first 2 wks of life , shortly after enteric feeding has begun :
Gastric residuum which often is bile stain .
Abdominal distension .
Blood in stool .
Lethargy and apnea .
Poor perfusion with hypotension or shock .
Abdominal wall discoloration .
Unstable temperature and metabolic acidosis .
Laboratory findings :
Suggestive on blood film leukocytosis , neutropenia or thrombocytopenia.
Suggestive findings on abdominal radiography include :
Dilated thickened bowel loops .
Pneumatosis intestinalis which usually starts in the right lower part .
Perforation , with free abdominal air and portal vein air .
5--Clinical course :two distinct clinical patters are noted :
Most infants follow a course characterized by feeding intolerance , abdominal distension occult blood in the stool , and dilated bowel loops on radiography . these finding improve rapidly with therapy .
The other group of infants has severe progressive symptoms including gros s blood in the stool , extreme abdominal tenderness , hypotension disseminated intravascular coagulation and sepsis . peumatosis intestinalis and perforation frequently occur in this setting .
Therapy :
Treatment should begin with discontinuation of enteric feeding , gastric drainage and administration of intravenous fluid .
Once culture have been taken ,systemic antibiotics ( e.g. ampicillin ,gentamicin ) shloud be given .also any accompanying disorders (e.g. DIC) should be treated .
Surgical resection of the necrotic bowel segment is indicated for infants who have a progressive downhill course and for those in whom intestinal perforation has occurred .
Prognosis : the mortality rate associated with necrotizing enterocolitis which is highest in the most premature infants is approximately 30% .later complications may include intestinal strictures and short bowel syndrome ..
Anemia of the newborn
Neonatal hemoglobin concentration at birth about 16.5-18 g/dl. After birth hemoglobin decline to 11-12 g/dl at 3-6 months at term . premature infant has a lower hemoglobin concentration to achieves a nadir at 1-2 months after birth .fetal hemoglobin represent 60- 90 %of hemoglobin at term birth and the level decline to adult level by 4 months of age . for term infant blood volume is 70-90 ml/kg and a preterm infant ,blood volume is 90-100 ml/kg .The physiological anemia noted at 2-3 months of age in term infant and at 1-2 months of age in preterm infants , is a normal process that does not result in signs of illness and does not require any treatment . it is a physiological condition believed to be related to several factors including increased tissue oxygenation experience at birth , shortened RBC life span and low erythropoietin levels .
Etiology : symptomatic anemia in the newborn period may be caused by decreased RBC production ,increased RBC destruction or blood loss ..
Hemolytic disease of the newborn ( erythroblastosis fetalis ) .
Result from blood group incompatibility between the mother and the fetus . hemolysis occurs when maternal antibodies to a particular blood group antigen cross the placenta and bind to fetal red blood cells , which are then destroyed in the spleen .
ABO blood group incompatibility : with neonatal hemolysis develops only if the mother has IgG antibodies from a previous exposure to A or B antigens .these IgG antibodies cross the placenta by active transport and affect the fetus or newborn . sensitization of the mother to fetal antigens may have occurred by previous transfusion or by condition of pregnancy that result in transfer of fetal erythrocyte into maternal circulation such as first trimester abortion , ectobic pregnancy amniocentesis , or normal pregnancy .
ABO incompatibility with sensitization usually does not cause fetal disease other than mild anemia . it may produce hemolytic disease of newborn , however which is manifested as significant anemia and jaundice . because many mother who have blood group O have antibodies to A and B before pregnancy , the first born infant of A or B type may be affected . in contrast to RH disease , ABO hemolytic disease does not become more severe with subsequent pregnancies .hemolysis with ABO incompatibility is a less severe than hemolysis in RH-sensitized pregnancy , either because the anti A or anti B antibody may bind to non erythrocytic cells that contain A or B antigen or because fetal erythrocyte have a fewer A or B antigenic determinants than they have RH sites . with declining incidence of RH hemolytic disease , ABO incompatibility has become the most common cause of neonatal jaundice requiring therapy .
Erythroblastosis fetalis :
Erythroblastosis fetalis classically is caused by Rh blood group incompatibility . most RH negative mother have no anti-Rh antibodies at the time of their first pregnancy . in most Rh-sensitized cases ,the D antigen of the fetus sensitized the Rh negative mother resulting in IgG antibody production during the first pregnancy . because most mothers are not sensitized to Rh antigen at the start of pregnancy . Rh erythroblastosis fetalis is uaually a disease of second and subsequent pregnancies .the first affected pregnancy results in an antibody response in the mother which may be detected during antenatal screening with coombs test and determined to be ant-D antibody .
The first affected newborn may show no serious fetal disease and may manifest hemolytic disease of the newborn only by development of anemia and jaundice . subsequent pregnancies result in an increasing severity of response because of an earlier onset of hemolysis in utero . fetal anemia , heart failure elevated venous pressure , portal vein obstruction and hypoalbuminemia result in fetal hydrops, which is characterized by ascites , pleural and pericardial effusion and anasarca .the risk of fetal death is high .
If the fetus near term can be delivered and treated in neonatal intensive care unit . if the fetus less than 33 wks and immature lung intrauterine transfusion O-negative blood into the umbilical vein is indicated and may have to be repeated until pulmonary maturity is reached
Prevention : of sensitization of the mother carrying an Rh –positive fetus is possible by treating the mother during gestation ( more than 28 wks gestational age and within 72 hrs after birth with anti-Rh-positive immune globulin . the dose (300ug) is base on the ability of this amount to antiRh- positive antibody to bind all the possible fetal Rh positive erythrocytes entering the maternal circulation during the fetal –to-maternal transfusion at birth ( approximately 30 ml).
Diagnosis and management :
Hemolysis in utero result in hydrops with ( ansarca ,heart failure,and pulmonary odema that result in asphyxia , hepatosplenomegaly ,pallor and become jaundice within 24 hrs after birth . patients with ABO incompatibility often are asymptomatic and show no physical signs at birth , mild anemia with jaundice develops during the first 24-72 hrs of life .
Newborn with acute blood loss due to( feto-maternal hemorrhage , placenta previa ,or internal hemorrhage ) is characterized by pallor , diminished peripheral pulses ,and shock but no hepatosplenomegaly .
Newborn with chronic blood loss caused by ( chronic fetal-maternal hemorrhage , twin to twin transfusion ) present with marked pallor , heart failure hepatosplenomegaly with or without hydrops with low Hb at birth and decreased serum iron store . shock is more typical in patient with internal hemorrhage whereas in hemolytic diseases heart failure may be seen with severe anemia .
Laboratory evaluation :
A complete blood count , blood smear , reticulocyte count , blood type and direct coombs test (to determined the presence of antibody coated RBCs) should be performed in the initial evaluation of all infants with hemolysis .
RBC enzymes , hemoglobin electrophoresis and RBC membrane tests .
The diagnosis of fetal- maternal hemorrhage is confirmed by the Kleihauer –Betke acid elusion test .
Internal hemorrhage or when nonimmune hemolysis is suspected ,ultrasound of liver brain spleen or adrenal gland may be indicated .
The treatment of symptomatic neonatal anemia is transfusion of cross matched packed RBCs .if immune hemolysis is present ,the cells to be transfused must be cross matched against maternal and neonatal plasma .
Acute volume loss may need non blood products such as saline if blood not available .
To correct anemia 10-15 ml/kg of packed RBCs can be given