Fetal - Neonatal Transition Physiology Flashcards
What are the 5 stages of fetal lung development?
- Embryonic
- Pseudoglandular
- Canalicular
- Saccular
- Alveolar
Embryonic stage: length and events.
- Implantation to 5 weeks
- trachea and bronchi formed
- evidence of 5 lobes
Psudoglandular phase: length and events
- 5-16 weeks
- airway branching up to 15 generations
- growth of cuboidal cell lining
Canalicular phase: length and events
- 16 - 24 weeks
- enlargement of the airways
- epithelium thins
- capillaries develop
Saccular phase: length and events
- 24-36 weeks
- basement membranes fuse to form the blood gas barrier
- type II pneumocytes start producing surfactant
Alveolar phase: length and events
- 36 weeks to 8-10 years
- capillaries bulge into terminal sacs
- formation of septae/crests
- increase in total SA
Compare and contrast between the histology of an immature and mature lung
Immature:
- thick blood gas barrier
- poorly vascularized
- small area for gas exchange
Mature
- thin blood-gas barrier
- highly vascularized
- large area for gas exchange
How is fetal lung fluid formed? How much is formed/day ?
Ultrafiltration of pulmonary capillary blood and active secretion of chloride ions.
About 250-300ml is formed per day but slows in later pregnancy
What mechanisms exist to deal with fetal lung fluid at birth?
- switch from Cl- secretion to Na+ absorption during labour
- Vaginal squeeze forces fluid out of lungs
- Clearance by capillaries and lymphatics as lungs distend and drive fluid into the interstitium
What are 4 radiological findings of an infant with TTN?
- increased central vascular markings
- Hyperaeration
- Evidence of interstitial and pleural fluid
- Prominent interlobar fissures
What is the rough % composition of surfactant ?
70-80% phospholipids
10% proteins
10% neutral lipids
What is RDS?
Respiratory Distress Syndrome.
- aka hyaline membrane disease
Surfactant deficiency (mainly in premies) results in poor lung compliance given the high alveolar surface tension.
Atelectasis then occurs and babies enter resp. distress due to inadequate ventilation, hypoxia and then acidosis.
What are fetal breathing movements?
Rhythmic contractions of the diaphragm lasting from 1-60 minutes.
- increase after maternal meals and at night
- related somewhat to melatonin concentration
What substances or situations can inhibit fetal breathing movements?
- acute/severe hypoxia
- sedatives
- alcohol
- PGE2
What 2 mechanisms allow for breathing to become regular at birth?
- Sensory stimuli (touch, temp, auditory, and visual)
2. loss of placental inhibitor peptide
Describe the reversal of cardiovascular shunts that occurs at the time of birth?
- First breath decreases PVR and increases blood flow to lungs
- This causes a shift from R–> L shunting to normal circulation which mechanically closes the foramen ovale
- Increasing PO2 stimulates closure of the DA along with decreases in PGE2
- Ductus venosus closes due to constriction of the sphincter following a drop in blood flow through the umbilical sinus.
What are 3 benefits and 1 downside to delayed cord clamping?
- higher Hb at 24-48 hours
- Reduced iron deficiency at 3-6 months
- Pre-term infant have lower rates of intraventricular hemorrhage
one downside is increased need for phototherapy for neonates with jaundice
What are the 5 criteria of the APGAR score?
- Appearance (colour)
- Pulse
- Grimace (response to stimulation)
- Activity (muscle tone)
- Respiration
What are the possible ratings given for colour in the APGAR?
0: blue or pale
1: acrocyanotic
2: all pink
What are the possible ratings given for pulse rate on the APGAR?
0: absent
1: <100 bmp
2: >100 bmp
What are the possible ratings given for response to stimulus in the APGAR?
0: none
1: grimace
2. sneeze or cough
What are the possible ratings given for activity on the APGAR?
0: limp
1: some flexion
2: active motion
What are the possible ratings given for respiratory effort on the APGAR?
0: absent
1: slow/irregular
2: regular/crying
What is a normal HR for a newborn?
120-180 bpm
What are the 4 mechanisms of heat loss that the newborn is susceptible to?
- Radiation
- Convection
- Conduction
- Evaporation
What is the role of brown fat? where is it located?
Brown fat is mitochondria rich fat located around the viscera of the infant and is crucial for thermogenesis for the newborn.
Sympathetic stimulation triggers hydrolysis of triglycerides, release of FA + glycerol and the production of heat
Describe the features of fetal metabolism
- Anabolism mainly
- glucose, lactate, and amino acids are main substrates
- Glucose is most important (70-80% of maternal levels)
Describe the metabolic changes that need to occur at the fetal - neonatal transition
- switch from anabolic to catabolic state
- fall in neonatal glucose levels once cord is cut.
- rapid glycogenolysis from FFA, ketones, and lactate occurs to raise blood glucose + feeding
What is the definition of neonatal hypoglycaemia?
glucose <2.6mmol/L
What would symptoms of hypoglycaemia look like in the newborn?
- Jitteriness, tremor, seizure, coma
- Irritability, lethargy, stupor
- hypotonia, limpness
- Apnea, cyanotic spells
- Poor feeding
- Hypothermia
What are 3 possible causes for neonatal hypoglycemia?
- decreased substrate - generally if premature or small for gestational age
- hyperinsulinemia - born to diabetic mother
- Increased utilization - from other medical cause
What is the most common cause of cardiorespiratory failure in newborns?
Hypoxemia
what are 4 signs and symptoms of respiratory distress in neonates and their etiology?
- nasal flaring
- compensatory reaction to decrease nasal airway resistance - Retractions
- if chest wall compliance is high and/or lung compliance is low, the negative intrapleural pressure will be decreased, causing indrawing during respiration - Grunting
- occurs when the vocal cords are partially closed a the end of respiration. This generates positive end expiratory pressure (PEEP) to stent open small areas and improve the V/Q ratio - Head bobbing
- contractions of sternoclenomastoids when accessories muscles are recruited
What is the ACoRN respiratory score used for?
Assessment tool used to grade the severity of distress in a newborn. Lower scores correlated with milder distress
What is the most common cause of neonatal respiratory distress?
TTN
- aka: wet lung disease, transient respiratory distress, neonatal retained fluid syndrome
What is the clinical course of TTN?
generally self limiting and transient (resolved in under 48-72 hours)
What are some risk factors for developing TTN?
- Delivery by c/s
- precipitous delivery
- Maternal diabetes
- maternal sedation
- Perinatal depression
What is the management protocol for a baby with TTN?
- Respiratory support and monitoring
- O2 supplementation
- +/- CPAP
What are the radiographic findings of a baby with respiratory distress syndrome (RDS)
- ground glass opacity
- prominent interstitial markings
- small lung volume
- loss of cardiac silhouette
- air bronchograms
- loss of diaphragmatic silhouette
What is the pathophysiology of RDS?
Lack of surfactant produced by type II pneumocytes, usually due to prematurity (<24 weeks) causes progressive collapse of the terminal bronchioles and alveoli (atelectasis)
This leads to hypoventillation and V/Q missmatch –> hypoxemia and hypercarbia –> acidosis (both resp and metabolic).
Pulmonary vasoconstriction can occur as a result of the acidosis, further exacerbating V/Q missmatch and hypoxemia. It can also cause production of a proteinaceous exudate which causes the classic “eosinophilic hyaline membranes”
What are 4 risk factors for developing RDS? 1
- Preterm
- Male
- Perinatal depression
- Maternal diabetes
What is the management protocol for RDS?
- artificial surfactant
- respiratory support and monitoring
- O2 supplementation
- Fluid and metabolic management
What can be done to prevent RDS?
- antenatal corticosteroids if premature labour is anticipated
- use of tocolytic agents to potentially arrest premature labour
What are 3 risk factors for babies to developing a pneumothorax?
- aspiration
- Underlying lung disease
- high ventilatory pressures
what is the management protocol for a pneumothorax?
if ventilated, lower pressures and increase rate
needle aspiration or chest tube for continuous air leak.
What are the radiographic findings of a baby with meconium aspiration syndrome?
- bilateral diffuse patchy opacities
- atelectasis and consolidation - Hyperinflation of lungs
- areas of emphysema
- spontaneous pneumothorax and pneumomediastinum
- small pleural effusions
What % of deliveries have evidence of MSAF?
10-15%
What % of MSAF births result in MAS?
only 5%
What is the mortality rate of MAS?
5%
What are 4 risk factors for developing MAS?
- full term or post-mature
- in utero hypoxia
- meconium stained amniotic fluid
- fetal distress
What is the pathophysiology of MAS?
aspiration causes mechanical obstruction, chemical inflammation and surfactant inactivation leading to V/Q missmatch, R–> L shunting, acidosis and eventually cardiopulmonary failure.
May also be accompanied by persistent pulmonary hypertension of the newborn.
What is the management of MAS?
- respiratory ventilator support
- Management of pulmonary hypertension
- Abx
- +/- surfactant
- monitor for pneumo
