Respiratory Problems Flashcards
Risk factors for RDS
- Male sex
- Maternal diabetes
- multiple birth (second twin esp)
- Elective caesarean
- Precipitous delivery
- Family history
- Sepsis
Protective factors for RDS
- Female sex
- PROM
- Antenatal steroids
- IUGR
- Chronic or gestational hypertension
- Maternal opiate or heroin use
What are the steps that occur in the normal transition to pulmonary respiration?
- Before birth - increased levels of catecholamines, vasopressin, prolactin and glucocorticoid enhance lung fluid resorption
- First breath triggered by decline in PaO2, acidosis and hypercapnia from interruption of placental circulation
- Air entry into lungs displaces fluid to establish FRC
- Increased pulmonary blood flow further enhances fluid resorption
Why do preterm infants have more difficulty in transition to pulmonary respiration?
- Surfactant deficiency increases surface tension and impairs ability to establish FRC
- Compliant chest wall means more energy required to generate sufficient negative pressure for first breath
3 types of apnoea and how do they differ?
- Obstructive apnoea - absence of airflow but persistent chest wall motion
- Central apnoea - no airflow or chest wall motion
- Mixed apnoea - most common in apnoea of prematurity - usually obstructive apnoea precedes central apnoea
What is the mechanism behind apnoea of prematurity?
Immature brainstem respiratory centres - attenuated response to CO2 and paradoxical response to hypoxia (causes apnoea rather than hyperventilation)
What is the mechanism of action of methylxanthines for apnoea of prematurity?
Increase respiratory drive by lowering threshold of response to hypercapnia, enhance contractility of diaphragm, prevent diaphragmatic fatigue
What are 5 types of lung injury that can be seen in RDS? (largely ventilator-induced)
- Atelectrauma - injury resulting from repeated alveolar collapse and expansion (recruitment/derecruitment injury)
- Volutrauma - overdistension of alveoli resulting from mechanical ventilation
- Barotrauma - pressure injury from ventilation
- Oxygen toxicity - caused by oxygen free radicals
- Ischaemic injury
What is the primary pathological change seen in respiratory distress syndrome?
Hyaline membranes in alveolar spaces.- formed from effusion of proteinaceous material from damaged cells and cellular debris
What cell type produces surfactant?
Type 2 pneumocytes
What is the composition of surfactant (and what component contributes to reduction in surface tension)?
- Phospholipids - lower surface tension
- Other lipids e.g. surfactant proteins A-D - facilitate adsorption and spreading of surfactant and have immunoregulatory properties
- Platelet activating factor
Typical radiological findings in RDS
Low lung volumes, ground glass appearance, air bronchograms
Below what gestation is routine antenatal corticosteroid administration recommended to reduce risk of RDS?
<37/40 (+consider before elective CS up to 38+6)
In relation to mechanical ventilation, what are the factors that affect oxygenation?
- FiO2
- Mean airway pressure (which depends on PIP, i-time, PEEP, RR [and thus e-time])
In relation to mechanical ventilation, what are the factors that affect ventilation/CO2 elimination?
Determined by minute ventilation - tidal volume (determined by PIP and i-time) and RR
Why is volume-targeted ventilation particularly important in RDS?
Rapid changes in lung compliance occur with surfactant treatment - high risk of volutrauma and air leak with pressure-limited ventilation. With VTV, PIP varies depending on respiratory compliance to achieve a set tidal volume