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Ductus Dependent Circulation

The event of birth is usually followed by closure of Ductus arteriosus. Failure to accomplish this transition (due to any cause) significantly compromises the heart and circulation of the newborn infant. However, the other side of spectrum points to the need to keep the Ductus open so as to maintain stable hemodynamics. Such a situation arises when the neonate has congenital heart disease which depends on a patent ductus to provide stability. Such cardiac lesions are called ductus dependent lesions.

Below is a list of cardiac lesions that require the Ductus to be kept open:

A) Ductus dependent systemic blood flow

These are commonly called left sided obstructive lesions. These include a spectrum of hypoplasia of the left sided structures of the heart. These may range from coarctation of the aorta to hypoplastic left heart syndrome.

These include

Aortic stenosis – Critical aortic stenosis.

Coarctation of aorta

Interrupted aortic arch

Hypoplastic left heart syndrome

Ductus Dependent Pulmonary Blood Flow

This group includes lesions associated with restriction to pulmonary blood flow from significant obstruction to no flow leading to varying degrees of cyanosis and hemodynamic compromise. These include:

1) Critical Pulmonary stenosis

There is Dysplastic pulmonary valve with obstruction with associated hypoxemia due to R – L shunt through patient foramen ovale.

2) Pulmonary atresia with intact ventricular septum (hypoplastic right heart syndrome)

3) Tricuspid atresia with severe PS.

4) TOF

5) Ebstein’s anomaly

C) Parallel circulation

TGA with IVS

EVALUATION

Usually neonates with congenital heart diseases associated with Ductus dependent lesions are quite sick and prior to detailed evaluation would require management of shock and cyanosis.

Management

The mainstay of management of neonates with Ductus dependent congenital heart disease is the early institution of Prostaglandin E1 to maintain ductal patency.

The following flow diagram sums it up:

HYPOPERFUSION STATE/ LOW OUTPUT STATE

It is one of the commonest modes of presentation of critical neonate in the NICU. The causes of this state can be multiple and not just cardiac. Hence a close scrutiny, detailed history and evaluation required. Usually it is due to inadequate ejection of blood by the left ventricle into systemic circulation which leads to hypotension and subsequently acidosis.

Heart Diseases associated with poor perfusion are:

A) Those where inflow to and outflow from LV is disrupted/ obstructed.

a) Inflow disrupted

- Cortriatriatum

- Mitral stenosis

- Supramitral ring

- Obstructed Total anomalous pulmonary venous connection.

b) Left ventricular Outflow Obstruction/disruption

- Coarctation

- Hypoplastic Left heart Syndrome

- Interrupted aortic Arch

- Critical/Severe AS

In inflow obstructed lesions the role of ProstaglandinE1 is controversial, though some authors do advocate its use. In outflow obstruction prostaglandin E1 is essential for systemic perfusion to prevent end organ damage.

Prostaglandins

These are derivatives of Arachidonic acid metabolism in the body and play a variety of roles in the maintenance of physiologic milieu inside the body. Of these the most important prostaglandin from cardiac point of view is Prostaglandin E1.

Prostaglandin E1 was shown by early studies by a number of researchers to be 1000 times more potent than other prostaglandins in relaxation of ductus muscle.(3).

Prostaglandin is usually given by intravenous infusion at a initial dose of 0.05-0.1mcg/k/min. Once the desired effect is attained then the dose is tapered to 0.01-0.025mcg/k/min.

To prepare prostaglandin infusion we use the same formula discussed in congestive cardiac failure,i.e,

1 ampule of PGE1 contains 500mcg of drug or 0.5 mg. So if we want to prepare infusion then we add 0.5mg to 50ml syringe prefilled with 50 ml normal saline.

Going by the formula: wt x dose(in mcg/kg/min desired) x 3 ( multiplying factor)/ amount of drug in 50 ml syringe.

= The rate of infusion.

So if we have a 3kg neonate with ductus dependent lesion in whom we want to start prostaglandin infusion then we calculate as follows

Wt (3kg) x Dose (0.05mcg/k/min) x 3/ 0.5mg=0.9ml/hour.

Hence if we add 1 ampule of PGE1 to 50ml syringe and run it at 0.9 ml/hr through an infusion pump then we deliver 0.05mcg/k/min of the drug.

Adverse Effects

Hypotension, apnea, fever, irritability, lethargy, and NEC. In view of risk of apnea, Neonates who are on PGE1 and need to be transferred from one hospital to another should be intubated and ventilated prior to transfer.

 

References

1) Carcillo J, What is new in Pediatric Intensive care, Critical Care Medicine2006,Vol 34,No.9(supplement) pps183-s190.

2) Burns S., Wernowsky G, Cardiac Disorders chapter 25 In: Cloherty J, Eichenwald E, Stark A(eds) Manual Of Neonatal Care,5th edition 2004, Lippincott Williams and Wilkins

3) Corbet A, Medical manipulation of the Ductus Arteriosus,Chapter113,In: GarsonA, Bricker J.,Fisher D., Neish S.,(eds), The Science and Practice of Pediatric Cardiology , 2nd Edition, Vol II,1999, Williams and Wilkins.

4) Brook M., Heymann M., Teitel D., The Heart, Chapter 14,In: Klaus and Fanaroff (eds), Care of the High Risk Neonate,5th Edition, 2001, W.B Saunders Company.

5) Park M., In: Park M Pediatric Cardiology for Practitioners 4th Edition 2002.Mosby.

6) Chang A., Hanley F., Wernowsky G., Wessel D., (Eds),), Pediatric Cardiac Intensive Care, 1998, Williams and Wilkins.