Preoperatively focus on discovery of precipitating factors for hypercyanotic tet spells and what relieves the symptoms. Fasting should be avoided for long periods of time as dehydration will contribute to decreased SVR and increased right-to-left shunting. Beta blockers, if prescribed, should be taken the same day as surgery.

Induction – there is not an established best method for induction. However, recommendations are to use methods that favor pulmonary blood flow and guarantee hemodynamic stability. For this reason, ketamine is sometimes recommended as one of the drugs of choice.

Increase SVR – A reduction in SVR will make the right-to-left shunt worse. Be especially mindful of this during induction. Increases in SVR, whether pharmaceutically or physically induced (squatting), will reduce right-to-left shunt. Reducing SVR will make the shunt worse.

Avoid any hypercyanotic “tet” spells – these can be precipitated by crying, feeding, metabolic acidosis, increased circulating catecholamines (avoid any kind of stress), surgical stimulation, and increased PaCO2. Tet spells may or may not have an obvious precipitating factor.

Debubble – Bubbles in the IV may result in a paradoxical embolism.

Treatment for hypercyanotic “tet” spells – elmination of the activity/stressor, administration of a systemic vasoconstrictor (eg. phenylephrine), 100% oxygen, sodium bicarbonate, IV fluid bolus, positioning (bending the patient at the hip and/or light pressure on the abdomen), sedation and analgesia (if the patient is light or in pain).

Tetralogy of Fallot is the most common cyanotic congenital heart defect (CHD). This defect accounts for 4-11% of CHDs in general.

Four common features are found with this defect: a ventricular septal defect (VSD), an aorta that overrides the VSD, right ventricular outflow obstruction (RVOTO), and right ventricular hypertrophy. RVOTO and the VSD varies widely from mild to severe. The degree of RVOTO and size of the VSD determines the severity of cyanotic symptoms.

RVOTO may present as a murmur at the left sternal border, the intensity of which has an inverse relationship with the degree of cyanosis. As cyanosis increases, the murmur will decrease in intensity or even disappear.

The body compensates to chronic cyanosis by producing more red blood cells. This increases viscosity and coagulation, which can result in a paradoxical emboli (common, especially in patients with a hematocrit greater than 60).

Infants 2-3 months of age appear to be the most susceptible to acute hypercyanosis or “tet” spells. Most spells will occur within the first year of life, but may occur at any stage of life.

Classic symptoms of a “tet spell” or hypercyanotic episode include: profound/acute cyanosis, increases in rate and depth of breathing (hyperpnea), stroke, seizure, possible loss of consciousness, and potentially death. The patient will physically squat to increase SVR.

Definitive diagnosis is made by echocardiography.

Surgical repair involves closure of the VSD and widening of the RVOTO