Pediatric and Neonatal Respiratory Care Embryologic Development

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Pediatric and NeonatalRespiratory
CareEmbryologic Development

• Mary P. Martinasek, BS, RRT

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Overview

• Introduction
• Development of the Pulmonary System
• Development of the Cardiovascular System
• Fetal Circulation
• Development of Other Intrauterine Structures

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Introduction

• General Fetal Development
• Ovum
• Embryo
• Fetus
• Cellular Development

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Germ Layers of the Embryo

• Endoderm
• Respiratory Tract
• Mesoderm
• Ectoderm

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General Development
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Development of the Pulmonary System

• Embryonic Period
• Pseudoglandular Period
• Canalicular Period
• Saccular and Alveolar Period

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Embryonic Period

• From Conception to 4-6 weeks gestation
• Development of proximal airways
• 0-24 days one central tube
• 24 days - primitive lung bud appears

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Embryonic Period (continued)

• 26-28 days form right and left lung buds
• Primitive airways progress in dividing
• Lobar bronchi - day 31
• diaphragm starts and is completely developed by
  8th week

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Pseudoglandular Period

• 7-16 week gestation
• development of conducting airways
• 7th week - epiglottis formation starts
• 7th week - choana disintegrates and palates
  development begins

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Pseudoglandular Period (cont.)

• 8th week - vocal cord development begins
• Lung resembles gland
• Dichotomy results
• 11th week - cartilage in airways appears
• 12th week - major lobes identifiable

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Pseudoglandular Period (cont.)

• 13th week - goblet cells form
• 13th-24th week bronchial glands develop
• 10 week - ciliated cells start to appear

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Canalicular Period

• 17-24 weeks gestation
• Development of acinus
• Tremendous amount of vasularization
• Outpouchings appear on wall of bronchioles

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Canalicular Period (continued)

• Two types of cells start to differentiate
• Capillaries present but too far away from
  alveolar cavity

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Saccular (Alveolar) Period

• 24th week - birth
• Development of gas exchange units
• 25th-26th week alveolar-capillary membrane able
  to sustain extrauterine life

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Saccular Period (continued)

• 28-29th week terminal sacs line with mature Type
  II cells - surfactant appears
• 34-36th week mature alveolar structure
  evident
• approximately 55 million alveoli (10 m2)

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Surfactant

• Composition
• Phospholipids and Protein
• Phosphoatidylcholine (Lecithin) Major
  surfactant appears at 18 weeks and peaks at 38
  weeks
• Sphingomyelin Surfactant found in the amniotic
  fluid (decreases after 30 weeks)
• Production
• Secreted by Type II Alveolar Cells

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Fetal Lung Fluid

• Composition
• Different than amniotic fluid
• Decreased levels of bicarbonate and protein
• Increased levels of Sodium and Chloride

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Fetal Lung Fluid cont.

• Function Maintain patency
• Term 20-30 ml/kg in lungs
• Production decreases days prior to clinical
  detection of labor

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Hazards of Retention

• TTN Transient tachypnea of the newborn
• May present as RDS
• Grunting, flaring and retracting (GFR)

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Determination of Lung Maturity

• Shake (Foam) Test
• LS ratio (Lecithin to sphingomyelin ratio)
• Lungs mature when 21 (35 weeks)
• PG detection (Phosphatidylglycerol)
• Lipid
• Absent until about 35 weeks gestation

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Lung Maturity Cont.

• FLM or FP Assay Fluorescence Polarization
• Surfactant to Albumin
• Quick and Reliable
• Lung Profile
• LS and PG detection

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Conditions that DelaysSurfactant Production

• Acidemia
• Hypoxia
• Shock
• Overinflation
• Underinflation
• Pulmonary Edema

• Mechanical Ventilation
• Hypercapnia
• Maternal Diabetes (A,B,C)
• Smaller of Twins

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Conditions that AccelerateSurfactant Production

• Maternal diabetes (D, F, and R)
• Maternal heroin addiction
• Premature rupture of membranes
• Maternal hypertension

• Maternal infection
• Placental insufficiency
• Betamethasone or thyroid hormone
• Abruptio placentae

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Development of theCardiovascular System
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Development of Cardiovascular System

• 3rd week - two tubes surrounded by myocardial
  tissue
• Tubes fuse form single chamber

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Development of Cardiovascular System(continued)

• 4th week - heart begins to beat
• Heart begins to twist and fold
• Eventually will form four chambers

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Development of Cardiovascular System(continued)

• Sinus venosus - horns at bottom of embryonic
  heart - will become vena cavas and portion of
  right atrium
• Truncus arteriosus - will form pulmonary artery
  and aorta

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Development of Cardiovascular System(continued)

• Bends in middle - S shape
• Rapid growth
• Development of chambers
• Blood flow begins - one way flow

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Development of Cardiovascular System(continued)

• 5th week - heart takes on shape of adult heart
• Developing veins and arteries couple the heart to
  circulatory system
• Separate blood paths created

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Development of Cardiovascular System(continued)

• Four chambers formed with openings between the
  atria and the ventricles
• Truncus arteriosus allows blood to exit right
  ventricle

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Fetal Circulation

• Pressure in the fetal vasculature
• Systemic Low resistance
• Placental Low resistance
• Pulmonary High resistance

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Characteristics of Fetal Circulation

• Normal shunts in the fetus
• Foramen ovale bypasses lung
• Ductus arteriosus bypasses lung
• Ductus venosus bypasses liver

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Fetal Circulation

• Flow chart of the most oxygenated fetal blood
• Bypasses liver - ductus venosus
• Bypasses lungs - foramen ovale

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Fetal Circulation (continued)

• Flowchart of least oxygenated fetal blood
• Small amount feed lungs (high resistance)
• Most bypasses lungs - ductus arteriosus

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Development of Intrauterine Structures

• Placenta
• Umbilical cord
• Amnion
• Amniotic fluid

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Placental Development

• Placenta organ of respiration for fetus
• Umbilical arteries carry unoxygenated blood from
  fetus
• Intervillous space acts as alveolar-capillary
  membrane
• Umbilical vein carries oxygenated blood to fetus

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Umbilical Cord

• Life line
• Whartons Jelly
• 2 arteries and 1 vein

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Amnion

• Sac surrounding fetus containing amniotic fluid
• Possible rupture can occur in utero

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Amniotic Fluid

• 1 liter at term
• Constantly recirculated and replenished through
  lung fluid and urination
• Amount of fluid depends on recirculation

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Function of Amniotic Fluid

• Thermoregulation
• Facilitation of movement

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Amniotic Fluid Abnormalities

• Polyhydramnios large amount of amniotic fluid (
  greater than 200ccs)
• Causes
• CNS malformation
• Orogastric malformation
• Esophageal atresia
• Pyloric stenosis

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Abnormalities Cont.

• Causes of polyhydramnios cont.
• Downs syndrome, CHD, IDM, and prematurity

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Amniotic Fluid Abnormalities Cont.

• Oligohydramnios decreased amount of amniotic
  fluid
• Usually defect in urinary system
• Renal agenesis (Potters syndrome)
• Urethral stenosis
• Risk of asphyxia due to cord compression
• Possible skeletal deformities

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