3 - Respiratory Devo Flashcards
What are the precursor tissues of hte lower respiratory tract?
Endoderm: creates the pharynx (cranial foregut) > respiratory diverticulum > forms the epithelial lining of: larynx, trachea, bronchi, and lunga.
Mesoderm > lateral mesoderm > splanchnic mesoderm > forms the cartilage, smooth muscle, elastic tissue and fibrous CT of the trachea, bronchi, and lungs.
What part of respiratory development occurs in the embryonic phase (weeks 4-7)?
Lung primordium appears and the initial airway branching occurs.
A diverticulum comes off the developing foregut and begins to branch. The foregut becomes the esophagus and the diverticulum becomes the trachea.
What two anomalies can occur during the embryonic phase?
Inadequate partitioning, perhaps due to abnormal or insufficient development of tracheoesophageal septum.
Anatomic anomalies such as the absence of lungs, extra lobes, ectopic lobes, or absence of lobes, abnormal or insufficient branching, an accessory lungs, bronchogenic cysts, and pulmonary vascular anomalies.
A 32 week old male is 3.2 kg (small), has a normal prenatal US, but has excess secretions and RDS 30 minutes after birth. We are unable to pass an NG tube. What do you suspect is happening
Esophageal atresia/transesophageal fistula - this is a failure of the separation between the esophagus and the trachea.
Most common is distal fistula, resulting in reflux of gastric contents into lungs.
What are symptoms of esophageal atresia/transesophageal fistula and how would you diagnose it?
Air in bowel on xray confirms distal tracheoesophageal fistula. You can often tell because the NG tube can’t be placed.
Bronchoscopy identifies the fistula.
How often does Esophageal atresia/transesophageal fistula have associated anomalies? What is the significance of having an amomaly?
50% of patients have anomalies. Most common with isolated esophageal atresia and least common with isolated tracheoesophageal fistula.
Smaller infants have more associated anomalies.
Anomalies are the main determinants of survival.
What are some common associated anomolies that occur with Esophageal atresia/transesophageal fistula?
Cardiac (30%): VSD, PDA, ASD, tetrology, right-sided aortic arch
GI (12%): imperforate anus (opening missing), duadenal atresia, malrotation, etc.
GU: renal agenesis or dysplasia, polycystic kidneys.
MSK: hemivertabrae, radial dysplasia or amelia, polydactyly.
What are the most important indications of survival in kids with Esophageal atresia/transesophageal fistula?
The presence of other anomalies and birth weight.
What is the preoperative management of Esophageal atresia/transesophageal fistula?
- Position patient with head at least 30 degrees (to prevent reflux)
- Place NG tube in proximal pouch to handle secretions.
- Search for associated anomalies (with PE, cardiac echo, renal U/S)
- Identify position of the aortic arch (if it’s in the wrong location, you can’t open up the chest on that side for the surgery).
What makes a child a candidate for primary repair? In what instances would their repair be delayed?
Primary repair: healthy, near term, no major cards anomalies, no significant pulmonary disease.
Delayed repair: significant pulmonary compromise, significant cardiac anomalies, long-gap atresias. Venting gastrostomy, proximal pouch decompression.
How would you do pre-op managed isolated esophageal atresia?
- Gastrostomy for feeding
- Drain upper pouch
- Wait 6-12 weeks for pouch growth
- May utilize dilation methods to “stretch” pouch
- Re-evaluate the pouch prior OR
How do you operatively approach esophageal atresia with distal tracheoesophageal fistula? What is the landmark for the fistula?
Lateral thoracotomy.
The azygous vein is the gateway to finding the fistula because it’s right on top of it. It gets tied off.
What occurs during the pseudoglandular phase of pulmonary development (6-16 weeks)?
Airway branching continues.
Most of the bronchial tree is completed by the end of 16 weeks.
What occurs during the canalicular phase of pulmonary development (weeks 16-26)? What is the significance of the end of this time period?
Capillary density increases
Alveolar cells (pneumocytes) begin to differentiate.
Weeks 22-24 is the limit of extrauterine viability (usually with assistance).
What occurs during the terminal sac phase of pulmonary development (week 26-birth)?
Distal airways dilate, forming terminal sacs (primitive alveoli).
What is congenital cystic adenomatoid malformation (CCAM)? How is it thought that this occurs?
Mass of pulmonary tissue in which there’s proliferation of bronchial structures at the expense of alveolar development.
Embryonic speculation: asynchronous maturation of the developing lung bud and surrounding mesenchyme between the 16th and 20th weeks, resulting in the overgrowth of the terminal airway structures.
Adenomatoid: refers to the histological pattern given by the proliferation of the bronchial glandular elements.
What is the histopathology of congenital cystic adenomatoid malformation (CCAM)? What are the different types?
Alveolar spaces lined by a combination of both respiratory and mucus-secreting epithelium, forming glandular (“adenomatoid”) architecture.
Type 1: large macroscopic cysts
Type 2: small macroscopic cysts
Type 3: microscopic cysts
What are common clinical characteristics of a baby with congenital cystic adenomatoid malformation (CCAM)?
- Respiratory distress (rare)
- Recurrent pulmonary infections
- Asymptomatic but detected radiographically (prenatal US or other chest radiography).
Usually affects a single lobe. Progressive airway trapping leads to distension.
What occurs with respiratory distress from congenital cystic adenomatoid malformation (CCAM)?
Occurs usually within the first days of life.
See tachypnea and hypoxia, requiring intubation.
Infant needs emergent surgery; the procedure of choice is an anatomic lobectomy.
What affect does congenital cystic adenomatoid malformation (CCAM) have on the rest of the organs within the chest cavity during development? What is the worst case scenario?
- Pulmonary hypoplasia
- Pulmonary HTN
- Distortion of mediastinum and impaired venous return
Can result in hydrops (this is the worst case - fetal heart failure), severe respiratory failure, pulmonary infection, or no symptoms.
Have been reports of cancers developing in CCAMs, at as young as 1 yo.
How would you treat nonemergent congenital cystic adenomatoid malformation (CCAM)?
Plain film chest xray in neonatal period.
Follow up CT scan within 1-2 months.
Elective resection within first 3-6 mo of life (if you wait until 6 months there’s a higher risk of infection).
What occurs in the alveolar phase of lung development (32 weeks to 8yrs)? What occurs during postnatal development?
Alveolar phase: alveoli formation begins by subdivision of terminal sacs (septation); alveolar septum (walls) become thinner
Postnatal: most alveoli form after birth and formation is proportional to body growth
Formation of the airways in the lung proceeds in what direction?
In the proximal to distal direction.
What do the prenatal lungs contain? What happens when this isn’t present?
Fluid
Insufficient fluid production by the lung leads to hypoplastic lung.
Describe the movements of the lungs of the fetus?
Respiratory movements are shallow and episodic.
Pulmonary vascular resistance is very high due to the fluid in it.
What are the pulmonary, circulatory, and neural changes that occur after birth?
Pulmonary: fluid replaced by air
Circulatory changes: cardiac shunts close, pulmonary vessels fill
Neural: breathing, sympathetic activation
What can happen if a baby has problems removing fluid from the lungs?
Wet lung (transient tachypnea) - usually a transient conditon
What are characteritics of new air/liquid interface within the alveoli once the baby is born? What is required?
- Thin compliant wall
- Subjecting to surface tension (require surfatant made by type II pneumocytes)
- Production begins toward end of canalicular period; significant increase in production of surfactant at 35 weeks
- Prior to 35 weeks there’s usually insufficient surfactant to support extrauterine life (but now we can give them artificial surfactant).
What are three functions of pulmonary surfactant? What are its components?
- Decrease surface tension
- Stabilize alveolar surface
- Decrease fluid transfer
Made of: phospholipids, proteins, and antioxidants
What are clinical signs of RDS?
- Rapid breathing (>60 breaths/min)
- Flaring nostrils
- Restractions
- Expiratory grunt
- Often cyanotic
- Rapid HR
- Anxious expression
Respiratory distress is a medical emergency!!!!
What can cause RDS in a newborn?
Respiratory distress syndrome/hyaline membrane disease, is a clinical condiction where newborn babies have what?
- Experience respiratory distress
- Are usually premature
- Have immature lunds
- Often develop hyaline membrane in their lungs
Describe hyaline membrane formation seen in respiratory distress syndrome/hyaline membrane disease?
Type 1 alveolar cell injury > Breakdown of air/capillary barrier > serum leaks into alveolar lumen from the vascular system > hyaline membrane forms and surfactant function is disrupted.
This can lead to atalectisis > alveolar collapse.
What causes RDS?
An inability to keep alveoli filled with air.
A decrease in surfactant production results in:
- poor compliance of lung tissue
- atelectasis due to alveolar collapse
- engorgement of pulmonary capillaries
- formation of hyaline membrane
What is the most common cause of respiratory distress in preterm infants?
Respiratory distress syndrome (RDS) aka hyaline membrane disease.
Due to structural and functional immaturity of lungs: underdeveloped parenchyma and/or surfactant deficiency
Results in decreased lung compliance and unstable alveoli
What are risk factors for RDS?
<28 weeks of age (100%), 28-34 (33%).
Perinatal depression
Male predominant: males lungs develop slower than females
Maternal DB
C-section
Multiple births
What is seen on lab in RDS?
- Moderate hypoxia
- Respiratory acidosis
- Metabolic acidosis (delayed)
How would you treat RDS? What is the typical outcome?
Oxygen supplmentation, assisted ventilation, fluid restriction.
Outcome: peak severity, recovery coincides with diuresis beginning at 72 hours. Severe cases evolve into chronic lung disease.
How does transient tachypnea of the new born (TTN) compare to RDS? What will TTN show on the chest xray?
TTN happens IMMEDIATELY after birth or within 2 hours. Respiratory distress happens within DAYS.
TTN symptoms can last few hours to two days (ie transient!)
Chest Xray will show diffuse parenchymal infiltrates, a “wet silhouette” around the heart, or intralobar fluid accumulation.
What is meconium aspiration and what does it cause? How common is it?
- 1.5-3% in term or post-term infants.
- Meconium is a locally irritative, obstructive and medium for bacterial culture.
- Can significant respiratory distress. Hypoxia occurs because aspiration occurs in utero.
CXR shows patchy atalectasis or consolidation.
What can reduce the risk of respiratory distress when risk of preterm delivery is high?
Prenatal admin of corticosteroids between 24 and 34 weeks gestation.
Post natal steroids may decrease mortality but may increase risk of cerebral palsy.
If a baby is premature and has RDS, what do you suspect? If they are to term and has RDS what would you suspect?
Premature: hyaline mambrane respiratory distress syndrome
To term: transient tachypnea or meconium aspiration
What does the lecithin/sphingomyelin ratio tell us?
Lung maturity and changes of developing respiratory distress syndrome.
- If over 2.0 98% chance they are OK
- 1.5-1.9 there’s a 50% chance of RDS
- <1.5 there’s a 73% chance of RDS
What is a more accurate indicator of lung maturity than LS ratio?
Detecting the presence of phosphatidylglycerol (PG)
How would you enhance the fetal lung maturation?
Give glucocorticoids to the mother before delivery.
Administer artificial surfactant to the newborn.
The lower portion of the respiratory system develops from a ___________, surrounded by _________.
The lower portion of the respiratory system develops from a ventral foregut (endoderm), surrounded by splanchnic mesoderm.
Interaction between _____ and ______ results in airway branching which proceed sin the proximal to distal direction.
Endoderm and splanchnic mesoderm.
