Hypoxic episodes are mainly seen in pulmonary cyanosis congenital heart disease with reduced pulmonary blood flow, especially in tetralogy of Fallot, which can be associated with hypoxic episodes in 20-70% of cases and is one of the main causes of death. Hypoxic attacks are also seen in right ventricular double outlet with pulmonary stenosis, tricuspid valve atresia with pulmonary stenosis, and single ventricle with pulmonary stenosis.
I. The pathogenesis of hypoxic episodes is generally considered to be related to the following.
1, right ventricular outflow tract muscle spasm: actions such as waking up from sleep, crying and defecation increase sympathetic excitability and promote myocardial release of catecholamines, which act on the funnel part of the right ventricular outflow tract to cause muscle spasm there, resulting in a sudden decrease or termination of pulmonary blood flow, leading to cerebral hypoxia and the appearance of syncope.
2, respiratory central reactivity abnormalities: feeding, crying and other actions can increase cardiac output, heart rate and venous return blood volume. Pulmonary blood flow in cyanotic congenital heart disease with reduced pulmonary blood flow is relatively fixed, so the increase in cardiac output and venous return blood volume with the result of spasm of right ventricular outflow tract will certainly increase the right-to-left fractional flow, causing arterial blood pH and PaO2 to fall and PaCO2 to rise, which together stimulate the respiratory center, further accelerating respiration and lowering peripheral vascular impedance, forming a vicious circle and leading to hypoxic attacks.
Clinical manifestations are: often triggered by certain factors, such as after sleep, crying, breastfeeding and defecation, infection and iron deficiency anemia can be caused.
The attack is characterized by shortness of breath, irritability, increased cyanosis, loss of consciousness or convulsions, and in severe cases, sudden death. Seizures last for several minutes or hours and are usually followed by general weakness and sleep. The ejective systolic murmur on cardiac auscultation between the 2nd and 3rd ribs at the left border of the sternum may temporarily decrease or disappear during the attack. Hypoxic attacks usually start from 2-6 months after birth and have a tendency to remit spontaneously between 1.5-2 years of age and decrease after 2 years of age.
III. Seizure prevention.
1. β-blockers: propranolol 1-4 mg/kg.d, divided into 3-4 oral doses.
2. Eliminate precipitating factors: limit daily activity and take in enough water daily to avoid blood concentration or dehydration. Iron can be added for those with anemia. Pay attention to the prevention of infection.
3.Prohibit the use of vasodilators, digitalis preparations and catecholamines.
4.Radical surgery or palliative surgery should be used according to the type of pulmonary cyanosis congenital heart disease with reduced pulmonary blood flow.
IV. Treatment.
1.Treatment during the attack period.
(1) Position: flex the lower limbs of the sick child to adopt the knee-chest position. This position can increase peripheral vascular impedance, reduce venous return, reduce right-to-left shunt flow, and reduce hypoxic attacks.
(2) Giving oxygen: general oxygenation is less effective, because the blood flow is reduced during the attack, and it is not suitable to achieve the effect of intrapulmonary oxygen exchange.
(3) Drug therapy.
(1) Morphine: has a sedative effect and can inhibit the respiratory center to reduce hypoxic episodes. Morphine hydrochloride 0.1-0.2mg/kg per dose, subcutaneous, intramuscular injection or sedation.
②β-blocker: Its effect can reduce the muscle spasm of the right ventricular outflow tract, prevent the peripheral vascular resistance from falling, slow down the heart rate and improve the right ventricular filling. Propranolol is commonly used, 0.05-0.1mg/kg each time, diluted with 10% glucose and injected slowly.
(4) Correction of metabolic acidosis: hypoxic attack accompanied by metabolic acidosis, especially if the attack is severe or lasts for a long time, it is easy to aggravate the acidosis and further stimulate the right ventricular outflow tract spasm, forming a vicious circle. Sodium bicarbonate can be given at a dose of 2-4 mmol/kg, slowly injected by sedation.
(5) Severe impairment of consciousness and unstable blood pressure: tracheal intubation and artificial ventilation should be actively performed, and emergency surgery if necessary.