Cyanotic heart disease and tetralogy of Fallot spells

5.1 Cyanotic heart disease and tetralogy of Fallot spells

Robin Choong

Essentials

1 Cyanosis is dependent on haematocrit and oxygen saturation.
2 Cyanosis is caused by arterial oxygen desaturation or increased capillary oxygen extraction.
3 The hyperoxia test helps differentiate cardiac from other causes of cyanosis:
• Measure SpO2 in room air or low FiO2;
• Remeasure SpO2 in 100% O2;
• If SpO2 remains low consider a fixed intracardiac shunt (cyanotic congenital heart defect);
• If SpO2 increases consider other causes, e.g. lung disease.
4 If a cardiac cause is suspected check the pulses, blood pressure, ECG, and chest X-ray. Consult with a neonatologist, paediatrician or cardiologist early.
5 Cyanosis may be due to a duct-dependent lesion. A prostaglandin infusion may be advised following consultation.

Tetralogy spells

1 Cyanosis is variable and depends on the amount of pulmonary blood flow and right-to-left shunting.
2 Hypercyanotic spells treatment:
• ‘Knee-chest position’ or over parent’s shoulder with knees bent;
• Supplemental oxygen;
• Sedation: intravenous or subcutaneous morphine, 0.1 mg kg–1;
• Intravascular volume expansion.
3 In prolonged cyanosis consider a vasoconstrictor.
4 For prevention of spells, propranolol (0.5–1 mg kg–1 po qid).
5 A Blalock–Taussig shunt may be used for palliation before corrective surgery.

Introduction

Cyanosis is a bluish discolouration of skin and mucous membranes due to excessive concentration of reduced haemoglobin in the blood.1 Cyanosis is evident when deoxygenated haemoglobin in the cutaneous veins reaches approximately 5 g dL–1.2 Deoxygenated haemoglobin may occur either from arterial blood desaturation or increased oxygen extraction by peripheral tissue. Central cyanosis is produced as a result of arterial desaturation, i.e. aortic blood carrying deoxygenated haemoglobin. Isolated peripheral cyanosis may result from excessive deoxy-haemoglobin caused by extensive oxygen extraction.1 Haemoglobin level affects the presence of cyanosis. Cyanosis is detected at a higher oxygen saturation in children with polycythaemia and is more difficult to detect in children with severe anaemia. Causes of cyanosis are listed in Table 5.1.1.

Table 5.1.1 Causes of cyanosis2–7
Differential diagnosis
Arterial oxygen desaturation (central cyanosis [pO2 <50 mmHg])
1. Airway
• Airway obstruction
2. Breathing
• Lung disease
• Central nervous system depression (e.g. coma)
• Respiratory muscle weakness
• Reduced respiratory drive (e.g. morbid obesity)
3. Circulation
• Intracardiac right-to-left shunt (e.g. cyanotic congenital heart disease, pulmonary hypertension)
• Intrapulmonary shunt (e.g. pulmonary atrioventricular fistula)
Increased capillary oxygen extraction (peripheral cyanosis)
1. Circulatory shock, e.g. sepsis
2. Congestive heart failure
3. Environmental, e.g. cold
4. Acrocyanosis of the newborn (autonomic – may last 72 hours)
Abnormal haemoglobin (not related to level of oxygenation)
1. Methaemoglobinaemia (pO2 >50 mmHg but low O2 saturation)

Cyanotic congenital heart disease

Cyanotic congenital heart disease (CHD) generally presents in the neonatal period. In the newborn, mild cyanosis (mild hypoxia SaO2 >85%) may be difficult to detect clinically. Other confounding factors may be acrocyanosis (a normal finding, which may last 72 hours), polycythaemia (giving the appearance of cyanosis) and dark skin (cyanosis is more difficult to detect). Cyanosis is better appreciated in natural light than in artificial light.

Arterial oxygen saturation should always be assessed with pulse oximetry when considering cyanosis in the newborn. The hyperoxia test may help distinguish cyanosis caused by cyanotic heart defects from other defects.2–4,8

Hyperoxia test

• Measure SpO2 in room air or low FiO2.
• Remeasure SpO2 after 15 minutes in 100% O2.
• If SpO2 remains low, consider fixed intracardiac shunt (cyanotic congenital heart defect). Most cyanotic CHDs have a PaO2 <60 mmHg (8 kPa).
• If SpO2 increases, consider other causes, e.g. lung disease. PaO2 > 150 mmHg (20 kPa) almost completely excludes cyanotic CHD.

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Sep 7, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Cyanotic heart disease and tetralogy of Fallot spells

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