Respiratory adaptation and pathologies Flashcards
What are the 3 common transition disorders that cause respiratory distress?
Transient tachypnea of the newborn (TTN)
Respiratory Distress Syndrome (RDS) / hyaline membrane disease
Persistent pulmonary hypertension of the newborn (as a result of meconium aspiration, lung hypoplasia, hyaline membrane disease, TTN, pneumonia)
What are the risk factors for respiratory distress at term?
- Infants born to diabetic mothers
- Congenital anomlaies
- IUGR
- Fetal distress
- Meconium liquor
- Elective LSCS
- PROM
- Untreated GBS
- Maternal fever
- Maternal chorioamnionitis
List clinical findings of neonatal respiratory distress.
• Nasal flaring • Mild intercostal and subcostal retractions • Expiratory grunting • Audible wheeze • Stridor • Cyanosis • Poor feeding • Lethargy • Tachypnoea (RR>60) <br>• Tachycardia (HR >160) <br>• Rales or rhonchi on auscultation <br>• Cardiac murmur<p></p>
What are the differential causes of neonatal respiratory distress at term?
• Common:
- transient tachypnoea of the newborn
• Less common:
- pneumonia/sepsis
- mec aspiration (Causes mechanical obstruction, chemical pneumonitis and reduced surfactant)
- pneumothorax (spont or mechanical vent/CPAP),
- congenital heart disease.
- Persistant pulmonary HTN,
- HIE
• Rare e.g. ;lung obstruction, severe anaemia
What is the pathogenesis of meconium aspiration syndrome?
Pathogenesis:
1) Passage of meconium into amniotic fluid; may be caused by
- increased vagal outflow associated with umbilical cord compression
- increased sympathetic inflow during hypoxia
- infection (e.g. listeriosis)
2)Aspirated during fetal gasping or in the initial breaths after delivery (more likely to occur in depressed infant)
- Causes mechanical obstruction and air trapping
- Causes a chemical pneumonitis
- Rarely causes infection, unless already infected neonate
What is Transient tachypnea of the newborn (TTN)
- A lung disorder presenting in the first few hours after birth, with marked tachypnoea and respiratory distress
- Results in decreased pulmonary compliance and increased airway resistance
- It is a self-limited condition (usually resolves in 48-72 hours), management is supportive
Caused by:
- pulmonary oedema due to delayed resorption of lung fluid
- Delivery by CS is a risk factor as it contributes to pathophysiology - passage through the birth canal exerts ‘squeeze’ which increases intrathroacic pressure and aids reabsorption of fluid through alveoli walls and pushes fluid out of the upper airways and pharynx. If elective then lack of catecholamines can also reduce resorption of fluid.
What is Respiratory Distress Syndrome (RDS)
AKA hyaline membrane disease
- Largely a disease of prematurity - Incidence and severity of RDS decreases with increasing gestational age
- Caused by reduced number and function of type II pneumocytes, causing a deficiency of pulmonary surfactant leading to decreased lung compliance
- Hypoxemia results primarily from V/Q mismatching due to collapse of large portions of the lung
- Administration of surfactant to infants with RDS improves survival
What is the pathophysiology and causes of Persistent pulmonary hypertension of the newborn?
• PPHN occurs primarily in term or late preterm infants ≥34 weeks gestation
Pathogenesis:
- Pulmonary vasoconstriction is exacerbated by hypoxia and acidosis.
- leads to right-to-left shunting through the foramen ovale and the ductus arteriosus
- Exacerbating hypoxemia and presenting with cyanosis
Causes:
- underdevelopment, maldevelopment, or maladaptation of pulmonary vasculature
- Meconium may trigger a vasoactive process to exacerbate this.
- Structural lung abnormalities (e.g. Congenital Diaphragmatic Hernia, Congenital Pulmonary Airway Malformations, Alveolar Capillary Dysplasia) are frequently associated with PPHN.
- Group B streptococcal sepsis via Strep polysaccharide toxins.
- Polycythaemia, hyaline membrane disease, hypocalcaemia and hypoglycaemia may contribute similarly.
- Some maternal medications e.g. NSAIDs, SSRIs²- persistently elevated pulmonary vascular resistance
Meconium aspiration syndrome:
- Incidence
- Which babies are most at risk?
- Incidence from 0.1-0.4% of all deliveries
- MAS occurs in 5-10% of newborns delivered with mec liquor
- Most at risk: infants who are post-mature, SGA, acute hypoxic event/fetal distress
Cause, Sx and Rx of RDS:
Due to a deficiency of surfactant leading to atelectasis, VQ mismatch and hypoventilation
Sx: tachypnoea, desaturation, respiratory distress, apnoea
Treatment: antenatal steroids, CPAP, surfactant, good neonatal care
What is the presentation and management of persistent pulmonary hypertension of the neonate (PPHN)?
Features:
- severe cyanosis and tachypnoea
Treatment:
- strategies for PPHN are directed at reducing pulmonary vascular resistance, reverse right-to-left shunting, minimise barotrauma as result of ventilation, treating acidemia and improving hypoxia and maintaining stable blood pressure
- Mechanical ventilation typically is needed early in the course
- 100% oxygen
- Pulmonary vasodilators: inhaled nitric oxide, MgSO4 if refractory
- Fluids +/- inotropes
- Alkalosis: hyperventilation +/- bicarbonate
- ECMO for severe and refractory cases
How do steroids reduce the risk of pulmonary morbidity in preterm babies?
- Promote lung maturation - alveoli growth, differentiation and thinning of the alveoli walls to promote gas exchange
- Promotes development of type II pneumocytes and thus surfactant production, to reduce the surface tension of alveoli and reduce the negative pressure required to take inspiratory breaths
- Increases nitric oxide in the pulmonary vasculature to increase pulmonary blood flow for gas exchange
- Increased sodium channels in the epithelium of lung, to increase sodium and water transport out of the alveolar space
What is bronchopulmonary dysplasia?
A chronic lung disease of newborns. Typically a complication of prematurity and those requiring oxygen supplementation after birth.
Characterised by irreversible damage to fragile airways and alveoli resulting in dysplasia.
Diagnosed if ongoing oxygen requirement at 36/40 gestation or >28 days from birth.
What is apnoea of prematurity?
cessation of breathing that lasts for more than 15 seconds and is accompanied by desaturation (SpO₂≤80%) or bradycardia (HR ≤2/3 of baseline HR) lasting ≥ 4 seconds in infants born under 37 weeks’ gestation
Causes:
- Immaturity of central respiratory drive
- Decreased peripheral reflex pathways (e.g. inactivity of carotid body or laryngeal chemoreceptor reflex)
- Increased bradycardia to hypoxia
Treat with caffeine and ventilatory support
What were the outcomes of the Cochrane 2020 review of antenatal steroids?
Looked at steroids for suspected delivery prior to 37 weeks
Outcomes:
Perinatal mortality RR 0.85
RDS RR 0.71
IVH RR 0.58
Childhood developmental delay RR 0.51
Little to no effect on birthweight (-14g, wide CIs),
Maternal outcomes, chorioamnionitis, endometritis - no effect
Subgroup analyses key points:
No difference in outcomes between the 2 overlapping subgroups 1) gestation <35+0, and 2) gestation 34-36+6
No difference in outcome when single course antenatal steroids vs weekly steroids as long as perceived risk of preterm birth continues
