Cardiovascular problems

Question 1

Why is a PDA more common in premature infants?

Answer 1

Smooth muscle in the wall of ductus is less responsive to high PaO2, thus less likely to constrict

Question 2

Risk factors for PDA

Answer 2

• Prematurity
• Hypoxia
• Acidosis
• Increased pulmonary pressure/PVR
• Systemic hypotension
• Local release of prostaglandins

Question 3

Why can a PDA be problematic from a physiological perspective?

Answer 3

Haemodynamically-significant PDA causes “ductal steal” - left-right shunting causes increased pulmonary blood flow and reduced systemic perfusion (with complications resulting from both of these)

Question 4

Consequences of PDA

Answer 4

Effects of increased pulmonary blood flow:

• Pulmonary oedema
• Pulmonary haemorrhage
• Bronchopulmonary dysplasia (4-5x risk in VLBW infants)

Effects of reduced systemic perfusion:

• IVH (ischaemia-reperfusion injury)
• NEC
• Renal failure

Question 5

Clinical manifestations of PDA

Answer 5

• Hyperdyamic precordium, bounding pulses
• Wide pulse pressure
• Machine-like continuous or systolic murmur
• Hepatomegaly
• Increased O2 dependence and CO2 retention
• renal failure
• X-ray - cardiomegaly, incr pulmonary vascular markings

Question 6

Approach to management of PDA

Answer 6

Controversial:

1. Prophylactic treatment
2. Closure of asymptomatic PDA
3. Closure of only symptomatic PDA

Question 7

Treatment options for PDA

Answer 7

• Fluid restriction
• Pharmacologic - COX inhibitors
• Surgical ligation

Question 8

What are the options for pharmacological closure of a PDA and what are their pros and cons?

Answer 8

All are COX inhibitors - inhibit prostaglandin production. Efficacy inversely proportional to GA and postnatal age.

• Indomethacin 3/7 course - reduces risk of severe IVH, pulmonary haemorrhage, symptomatic PDA; no sig incr risk of NEC or spont perf
• Ibuprofen - as effective as indocid but lower rates of oliguria, reduces mechanical vent, reduced rate of NEC; BUT does not reduce risk of IVH
• Paracetamol - may be effective, less SEs

Question 9

Contraindications to pharmacological treatment of PDA (indomethacin)

Answer 9

• Thrombocytopenia <80
• Active haemorrhage (incl severe IVH)
• NEC
• Incr creatinine >150 or oliguria <1
• also avoid with concomitant use of hydrocortisone (incr risk of spont perf)

Question 10

Indications for surgical ligation of PDA

Answer 10

failed pharmacological treatment or contraindications to COX inhibitors

Question 11

Predisposing factors for PPHN

Answer 11

• Birth asphyxia
• MAS
• Sepsis
• RDS
• Hypoglycaemia
• Polycythaemia
• Maternal use of NSAIDs (in utero DA constriction)
• Maternal late trimester use of SSRIs
• Pulmonary hypoplasia
  BUT often idiopathic

Question 12

What is the pathophysiology of PPHN?

Answer 12

Increased neonatal PVR, due to:

• Maladaptive from an acute injury (not demonstrating normal vasodilation in response to incr PaO2 after birth)
• Result of incr pulmonary artery medial muscle thickness and extension of smooth muscle into normally non-muscular peripheral arterioles - result of chronic fetal hypoxia
• Consequence of pulmonary hypoplasia
• Obstructive - result of polycythaemia, TAPVR, or congenital diffuse developmental disorders of acing lung development