Introduction
Cardiovascular disorders are common in critically ill children, accounting for around 30% of the UK annual total of 20,000 paediatric critical care unit admissions. Of these children, over 60% were under 1 year of age and 83% under 5 years of age on admission.
Assessment of the Circulation in Children
Assessment of the circulation in children must include both a rapid ‘ABC’ safety assessment (Is the airway clear? Is the child breathing adequately? Is there a pulse?), and then a more detailed examination. A child’s appearance is a good guide to their overall state of wellness. Are they moving normally for their age? Are they lethargic or lacking interest in parents or staff? Are they restless or inconsolable (cerebral hypoxia)? What do the parents think? Assessing work of breathing (WOB) is another important part of cardiorespiratory assessment, as it will be increased in the presence of pulmonary oedema which reduces lung compliance. The respiratory rate, the presence of grunting (indicating attempts to maintain lung recruitment), and the presence of intercostal and subcostal retractions, tracheal tug and head bobbing, which all indicate a child has significantly increased WOB, should be observed. Skin perfusion should be assessed by determining capillary refill time (<3 seconds after 5 seconds of pressure). Blood pressure, heart rate, respiratory rate and SpO2 should always be measured as part of the child’s initial admission assessment and at appropriate intervals thereafter, taking into account age related normal values (see Table 50.1) and in the case of SpO2, the expected saturation values for the child’s pathology. Understanding the physiology of congenital heart disease is key to its successful management in critical care.
Table 50.1 Normal values for heart rate and blood pressure in children
| Age of child (years) | |||||
|---|---|---|---|---|---|
| <1 | 1–2 | 2–5 | 5–12 | >12 | |
| Respiratory rate | 30–40 | 25–35 | 25–30 | 20–25 | 15–20 |
| Heart rate | 110–160 | 100–150 | 95–140 | 80–120 | 60–100 |
| Systolic blood pressure | 80–90 | 85–95 | 85–100 | 90–110 | 100–120 |
For neonates, as a rule of thumb, mean arterial blood pressure for term (40 weeks’ gestation) is 40 mmHg, and proportionately lower with increased prematurity.
Congenital Heart Disease
The incidence of congenital heart disease (CHD) is widely stated to be 8 per 1000 live births. Although rates vary, from region to region, up to 60% of babies with a congenital heart problem are identified antenatally. This is important as an appropriate plan for the care of the newborn infant can be established before birth. In the absence of antenatal detection, many babies with CHD present either immediately after birth or within the first weeks of life. The mode of presentation depends greatly on the nature and severity of the heart defect, and a structured approach to the neonate with CHD is required.
Approach to the Neonate with Suspected CHD
Common Presentations
Cyanosis
Persisting cyanosis after initial resuscitation at birth must be rapidly assessed and managed. The evaluation should assess the infant for airway, pulmonary and circulatory causes of cyanosis, using a logical ABC algorithm (see Table 50.2).
Table 50.2 Common causes of severe cyanosis in the neonate
| Airway | Breathing | Circulation |
|---|---|---|
| Pneumonia |
|
|
|
|
| Vocal cord paralysis | Phrenic nerve palsy |
|
| Central hypoventilation |
In the absence of major airway or breathing problems, neonatal cyanosis is most likely to be due to CHD or persistent pulmonary hypertension of the newborn (PPHN), which may occur with or without clear triggers.
At birth, important changes in cardiovascular and respiratory systems must occur for infants to adapt adequately to extrauterine life. In the foetus pulmonary blood flow remains low due to a high pulmonary vascular resistance. At birth as the lungs fill with air, pulmonary vascular resistance should fall rapidly with an 8- to 10-fold rise in pulmonary blood flow ensuring adaption to pulmonary oxygenation of blood. If factors such as meconium aspiration are present, pulmonary vascular resistance may not fall normally, a physiological state described as PPHN. Right to left shunting of blood then continues through foetal channels (the foramen ovale and arterial duct) resulting in systemic cyanosis.
Cyanosis due to congenital heart disease occurs in broad groups of anomalies: firstly those anomalies in which there is obstruction to blood flow to the lungs such as pulmonary atresia and critical pulmonary stenosis, and secondly conditions in which oxygenated blood does not reach the systemic circulation.
Immediate management of the neonate with suspected cyanotic CHD and adequate breathing includes oxygen therapy and the administration of alprostadil (prostaglandin E1) or dinoprostone (prostaglandin E2) to re-establish patency of the arterial duct, which permits flow of blood from the aorta to the pulmonary artery. This will not cause harm even if the cause of the cyanosis is PPHN. Urgent evaluation will include chest X-ray, ECG, and echocardiogram and a hyperoxia test.
If CHD with obstructed pulmonary blood flow is confirmed, prostaglandin infusion should continue until a more definitive pulmonary blood supply is established through surgical or cardiological intervention. Care should be taken to ensure that prostaglandins E1 and E2 are infused at the lowest effective dose, as dose related apnoeas are common at doses >10 ng/kg/minute. Usual starting doses are 5–10 ng/kg/minute; maximum recommended dose for both drugs is 100 ng/kg/minute.
Cardiogenic Shock
Neonates may also present at birth or in the early neonatal period with shock. The differential diagnosis includes sepsis, metabolic disorders, arrhythmias and structural cardiovascular disease. Common structural heart conditions presenting as shock soon after birth include critical aortic stenosis, aortic coarctation and hypoplastic left heart syndrome (HLHS), all of which result in circulatory decompensation when the arterial duct closes. Decompensated babies with aortic coarctation or interrupted aortic arch classically present in shock due to minimal descending aortic blood flow, with raised plasma lactate, weak or absent femoral pulses and right upper limb hypertension. A standard ABC approach to evaluation and resuscitation should be adopted and, as with cyanotic lesions, a prostaglandin E1 or E2 infusion should be started even if the definitive diagnosis has not been established. Care should be taken to minimise FiO2 in babies with HLHS and other ‘single ventricle’ lesions, as inadvertent lowering of pulmonary vascular resistance by generous oxygen therapy risks diverting blood away from the systemic circulation (Qs) by increasing pulmonary blood flow (Qp).
Pulmonary Oedema
Neonates with obstructed total anomalous pulmonary venous drainage (TAPVD) may present with severe dyspnoea, hypoxia and circulatory collapse soon after birth. Chest X-ray will show severe pulmonary oedema. Non-cardiac causes of neonatal cardiorespiratory failure must be rapidly ruled out, and echocardiographic examination obtained urgently, although TAPVD can be challenging to diagnose, especially in critically ill ventilated babies.
Other congenital heart lesions also present with pulmonary oedema (see below), although the severity of pulmonary oedema is initially less, and the onset of milder symptoms is more gradual, starting at the age of several weeks or months, rather than at or within days of birth.
Heart Failure and Failure to Thrive
Infants with several common congenital heart lesions, such as ventriculoseptal defect (VSD), atrioventriculoseptal defect (AVSD), large atrial-septal defects (ASD) and rarer conditions such as truncus arteriosus and aortopulmonary window, gradually develop congestive cardiac failure as their pulmonary vascular resistance gradually falls over the first weeks of life. This often presents as tachypnoea, hepatomegaly and failure to thrive. The chest X-ray usually demonstrates cardiomegaly and signs of increased pulmonary blood flow. Echocardiographic examination is required to establish the definitive diagnosis.
Initial management of infants presenting with heart failure, following a rapid ‘ABC’ assessment, is to start diuretics (frusemide ± spironolactone) and possibly an ACE inhibitor (captopril). Oxygen therapy should be avoided unless the baby presents with cyanosis, as higher inspired oxygen fractions will further lower pulmonary vascular resistance and may worsen cardiac failure. Nasal or facial CPAP or BiPAP is effective in off-loading the left ventricle and is an effective adjunct to diuretics in the acutely decompensated babies with left or congestive heart failure.
Arrhythmia
Babies may develop arrhythmia in utero to the extent that they are compromised before, during and after birth. Congenital complete heart block may be relatively well tolerated, or may be associated with foetal hydrops, critically low cardiac output and multiorgan failure. Adrenaline or isoprenaline infusions may be used to increase heart rate temporarily until definitive cardiac pacing is established.
Tachyarrhythmias commonly presenting at birth include atrial flutter and supraventricular tachycardia. Neonates may be severely shocked as a result of fast rhythms and require urgent treatments including cardioversion (atrial flutter), intravenous bolus adenosine (converts or permits diagnosis by transient slowing of heart rate in SVT) and intravenous amiodarone (slows/facilitates return to sinus rhythm in a variety of supraventricular and ventricular tachycardias).
Postoperative Care of the Child Following Cardiac Surgery
Cardiopulmonary bypass in neonates and young children frequently results in a clinically important systemic inflammatory response causing important organ assistant dysfunctions including myocardial depression, acute kidney injury and a loss of capillary integrity leading to generalised extravascular fluid accumulation.
Low cardiac output frequently occurs following cardiac surgery. Common causes include hypovolaemia, myocardial depression and the effects of residual cardiac defects and arrhythmias. A structured approach to the management of low cardiac output is shown in Figure 50.1. As well as clinical and haemodynamic assessment including ECG, careful echocardiograph examination should be undertaken to assess the integrity of the cardiac repair, detect the presenceof any residual lesions, provide information on ventricular contractility to guide therapy, and to identify pericardial effusion as a cause of the low output state.
Figure 50.1 Management of a child with low cardiac output state.
Assess Airway, Breathing and Circulation:
Consider underlying physiology – univentricular versus biventricular circulation
Correct hypoxia, acidosis, hyperthermia and electrolyte imbalance
Look for tamponade, residual or unsuspected anatomical or physiological abnormality – perform echocardiography
Consider need for respiratory support – non-invasive or invasive – beware of vasodilatation and myocardial depression of anaesthesia drugs.
Tamponade and Delayed Sternal Closure
In children as in adults, haemorrhagic pericardial tamponade can cause major haemodynamic instability following cardiac surgery. Haemorrhagic tamponade must be actively prevented by careful surgical haemostasis and normalisation of coagulation. Tamponade must be actively excluded in patients who continue to bleed or who develop unexplained cardiovascular instability following surgery. In neonates and young children, tissue oedema resulting from the systemic inflammatory response may result in swelling of the intrathoracic organs and consequent pressure on the heart with similar effects to haemorrhagic tamponade. For this reason, many surgeons choose to delay sternal closure thereby decompressing the thorax and preventing this complication. The sternum can then be formally closed a few days following surgery once haemodynamic stability is achieved and tissue oedema has subsided.
Pulmonary Circulation and Pulmonary Hypertension
Understanding of the physiology and pharmacology of the right ventricle and pulmonary circulation are crucial to the good management of children with congenital heart disease. A low pulmonary vascular resistance (PVR) is necessary when congenital heart lesions require cavopulmonary connections (see below). Children with uncontrolled pulmonary blood flow from large left-to-right shunts, and those with obstructed pulmonary venous drainage or very high systemic atrial pressures are at risk of developing muscularisation of pulmonary arterioles, raised PVR and high pulmonary artery pressures (PAP). The inflammatory response to CPB may cause temporary elevations in PVR or increased pulmonary vascular reactivity requiring interventions to lower PVR and PAP, as failure to do so will result in acute right ventricle failure with secondary left ventricular failure and cardiovascular collapse.
Simple measures to ensure low PVR include careful pulmonary management. Maintaining lung recruitment, avoiding alveolar hypoxia whilst avoiding lung over-distension all act to minimise PVR. Acidosis, both metabolic and respiratory, and pain also cause PVR to rise. Whilst induced alkalosis is not recommended for the prevention of PHT, brief periods of hyperventilation to lower pCO2 and raise pH, thereby lowering PVR, can be successful in controlling sudden dangerous rises in PAP/PVR. The aim should be to maintain normal pH and avoid acidosis and inadequate pain relief, which will act to raise PVR/PAP.
Inhaled nitric oxide (iNO) is a specific pulmonary vasodilator and can be extremely effective in lowering PAP/PVR in the postoperative period. Phosphodiesterase 5 inhibitors such as sildenafil may be used as an adjunct to iNO acutely, or for longer term pulmonary vasodilatation. Endothelin receptor blockers and prostacyclin are also effective pulmonary vasodilators most useful in longer term management.
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