Mini-Symposium: Pulmonary Complications of Paediatric Systemic Disorders
Pulmonary Complications of Congenital Heart Disease

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Summary

Cardiac and pulmonary pathophysiologies are closely interdependent, which makes the management of patients with congenital heart disease (CHD) all the more complex. Pulmonary complications of CHD can be structural due to compression causing airway malacia or atelectasis of the lung. Surgical repair of CHD can also result in structural trauma to the respiratory system, e.g., chylothorax, subglottic stenosis, or diaphragmatic paralysis. Disruption of the Starling forces in the pulmonary vascular system in certain types of CHD lead to alveolar-capillary membrane damage and pulmonary oedema. This in turn results in poorly compliant lungs with a restrictive lung function pattern that can deteriorate to cause hypoxemia. The circulation post single ventricle palliative surgery (the so called “Fontan circulation”) poses a unique spectrum of pulmonary pathophysiology with restrictive lung function and a low pulmonary blood flow state that predisposes to thromboembolic complications and plastic bronchitis. As the population of patients surviving post CHD repair increases, the incidence of pulmonary complications has also increased and presents a unique cohort in both the paediatric and adult clinics.

Introduction

In the healthy subject, there is a close relationship between the functions of the cardiovascular and respiratory systems such that changes in the metabolic requirements of the body are rapidly followed by changes in both cardiac output and minute ventilation. However, in the presence of congenital anomalies of the circulation this linkage is almost always broken. Under such circumstances, the ability of the heart to increase systemic and/or pulmonary blood flow is often limited, arterial PO2 may be decreased by shunt lesions, and O2 delivery cannot meet the needs of the tissues. Often the circulatory derangement also places stress on the respiratory system itself, causing signs and symptoms that mimic primary respiratory disease. Pathologies in both systems frequently coexist and impact each other, making patient diagnosis and management more challenging.1

Because congenital defects of the circulation are so common (approximately 7 infants per 1000 live births are affected) and the alterations in respiratory function are often so profound, it is essential that the physician interested in respiratory diseases be well acquainted with the spectrum of CHD and the ways in which it is manifested in infants and young children.

Direct pulmonary complications of CHD are either by structural impact on the airways, abnormal pathophysiological mechanisms leading to increased lung water and/or significant pulmonary disease. Many children with CHD are at greater risk of infection including respiratory tract infections, which can cause prolonged hospitalization and delay of definitive cardiac repair.

Section snippets

Anatomical Compression of the pAediatric airway

This is an often unrecognized complication of CHD. A high index of suspicion must be maintained in infants with wheezing, stridor, respiratory distress, apnoeic or cyanotic spells and atelectasis, which can all be due to underlying tracheobronchomalacia. The aetiology of airway obstruction can be divided into two groups:

Pathophysiology

Pulmonary oedema is caused by disturbance of the Starling forces (hydrostatic and oncotic pressures) that dictate the flow of water between capillaries and alveoli. Elevated hydrostatic forces within the pulmonary capillaries increase the driving pressure of fluid moving out of the capillary. This pressure disrupts the integrity of the alveolar-capillary membrane causing capillary stress fracture, which is visible on electron microscopy.7 As a result, water starts to accumulate in the

Palliative Single Ventricle Physiology

Palliative univentricular physiology (so-called “Fontan physiology”) is associated with passive, non-pulsatile drainage to the pulmonary arteries. Patients typically have congested, small lungs with a restrictive pattern of lung function (Section 9). The reason why lungs are smaller is unclear but may be related to previous pleurodesis in some cases. Alternatively, there may be an inherent degree of pulmonary hypoplasia due to the lack of pulsatile flow to potentially stimulate lung growth.

Pulmonary Infection

Respiratory tract infection in children with CHD is an important cause of morbidity and mortality including respiratory failure, prolonged mechanical ventilation, and hospitalization.15 These patients often have many contributing factors that place them at increased risk for respiratory tract infection (Table 2). Respiratory viruses including respiratory syncytial virus (RSV), human metapneumovirus, and influenza are commonly seen. In a study of 2613 children under 24 months old with CHD,

Pathophysiology

Atelectasis in patients with CHD can be attributed to extrinsic compression from vascular malformation (section 1), restrictive defects from pulmonary oedema (section 2) or from underlying respiratory tract infection (section 4). There are many postoperative factors that place a patient at risk for the development of atelectasis.21 These include immobilization, splinting, cough suppression, mucus plugging and hypoventilation from pain and sedation. Neonates, who comprise a large population of

Pulmonary Haemorrhage

CHD leading to Eisenmenger's syndrome or PH is associated with a paradoxical state of coexisting thrombotic and bleeding diathesis. In the presence of severe PH, pulmonary hemorrhage is life-threatening. Haemoptysis has been reported as the cause of death in 11-30% of patients, though it can be self-limiting.22, 23 It should be noted that pulmonary haemorrhage clears on chest radiograph usually within 72 hours and may therefore be differentiated from infectious consolidation.

Pulmonary embolism

Thrombosis of the

Pulmonary hypertension

A broad spectrum of cardiac and pulmonary diseases can lead to the development of Pulmonary Hypertension (PH).1 Children with PH have pulmonary hypertensive crises precipitated by a rapid increase in pulmonary vascular resistance (PVR) in response to stimuli including: hypercarbia, acidosis, and hypoxia. If PVR increases to the point where pulmonary artery pressure exceeds systemic blood pressure, right ventricular diastolic and systolic function decrease acutely and can rapidly progress to

Surgical Trauma Impacting the Respiratory System

Despite advances in surgical interventions for CHD, complications from injury to surrounding structures remain a significant risk (Table 3). Congenital cardiac surgery has become the most common cause of chylous pleural effusion or chylothorax in tertiary pediatric hospitals with an incidence of 3.8%.29 The incidence of diaphragmatic paralysis due to phrenic nerve injury during CHD surgery is up to 10% in certain studies.30, 31, 32 Close monitoring with early detection and treatment of

Pulmonary Function Testing

Restrictive lung function appears to be a prominent finding in many types of CHD both pre and post surgical repair.33, 34, 35 In addition, both obstructive and diffusion defects can also be seen depending on the underlying pathophysiology (Table 4). A study of 52 patients post Fontan procedure at a median follow up of 10 years demonstrated restrictive lung function with reduced forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and FEV1/FVC in 58% of patients.34 These

Pathophysiology of Respiratory Manifestations

From a clinician's point of view, respiratory complications of cardiovascular anomalies are characterized by the physical findings. Frequently there is an increase in the amount of work the respiratory system must do to maintain adequate ventilation. The mechanisms responsible for the increase in the work of breathing vary depending on the mechanical alterations caused by each cardiovascular anomaly.

Most patients with a large-to-left right shunt or a left ventricular obstruction will develop

Practice Points

  • Anatomical compression of the paediatric airway due to cardiac disease or vascular malformation can be diagnosed early and in most cases is treatable.

  • Diuretics are important in the treatment of pulmonary oedema but overall focus should be on treating the primary cardiovascular problem with relief of pulmonary venous or lymphatic obstruction and eliminating shunts.

  • Patients with surgical single ventricle palliative physiology present a unique spectrum of pulmonary complications including

Research Directions

  • Approach to the management of atelectasis in the patient with congenital heart disease.

  • Effect of different types of congenital cardiac lesions (hypo versus hyperperfusion of the lungs) on lung function in both the pre and postoperative phase.

  • Guidelines on the management of postoperative pulmonary complications in paediatric patients with CHD including diaphragmatic paralysis and recurrent laryngeal nerve injury.

Conclusion

To completely assess the clinical impact of CHD one must consider the effect on pulmonary physiology. Disruption of the Starling forces within the vascular system will disturb pulmonary vascular physiology with resultant abnormalities in lung function. Earlier repair of CHD during the period of active postnatal lung growth in the first few years of life may have less of an impact on alveolar growth and function. As the number and age of patients surviving post CHD repair increases, the

Educational Aims

  • To discuss the variety of ways in which paediatric cardiac disease impacts the lung including anatomical and pathophysiological mechanisms.

  • To understand pulmonary oedema as it applies to the paediatric population, including the various pathophysiological mechanisms and resultant effects on lung function.

  • To emphasize the effects that cardiac surgery itself including cardiopulmonary bypass and direct trauma can have on pulmonary structure and function.

Conflict of interest statement

The authors of this manuscript have no relevant conflicts of interest to declare.

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