Tetralogy of fallot

Tetralogy of fallot

Table of Contents

Introduction

Prevalence

Tetralogy of Fallot (TOF) occurs in 5% to 10% of all CHDs.
This is the most common cyanotic heart defect.
The classic description of TOF includes the following four abnormalities: VSD, pulmonary stenosis (PS), right ventricular hypertrophy (RVH), and overriding of the aorta.
From a physiologic point of view, TOF requires only two abnormalities—a VSD large enough to equalise systolic pressures in both ventricles and a stenosis of the right ventricular outflow tract (RVOT) in the form of infundibular stenosis, valvular stenosis, or both.
RVH is secondary to PS, and the degree of overriding of the aorta varies widely and it is not always present.
The severity of the RVOT obstruction determines the direction and the magnitude of the shunt through the VSD.
With mild stenosis, the shunt is left to right, and the clinical picture resembles that of a VSD.
This is called acyanotic or pink TOF.
With a more severe stenosis, the shunt is right to left, resulting in “cyanotic” TOF.
In the extreme form of TOF, the pulmonary valve is atretic, with right-to-left shunting of the entire systemic venous return through the VSD.
In this case, the pulmonary blood flow (PBF) is provided through a patent ductus arteriosus (PDA) or multiple collateral arteries arising from the aorta.
In TOF, regardless of the direction of the ventricular shunt, the systolic pressure in the RV equals that of the LV and the aorta.
The combination of a small VSD and a PS is not TOF; the size of the VSD must be nearly as large as the annulus of the aortic valve to equalize the pressure in the RV and LV.
In acyanotic TOF, a small to moderate left-to-right ventricular shunt is present, and the systolic pressures are equal in the RV, LV, and aorta.
There is a mild to moderate pressure gradient between the RV and PA, and the PA pressure may be slightly elevated (because of a less severe stenosis of the RVOT).
Because the presence of the PS minimizes the magnitude of the left-to-right shunt, the heart size and the pulmonary vascularity increase only slightly to moderately.
These increases are indistinguishable from those of a small to moderate VSD.
However, unlike VSDs, the ECG always shows RVH because the RV pressure is always high.
Occasionally, LVH is also present.
The heart murmurs are caused by the PS and the VSD.
Therefore, the murmur is a superimposition of an ejection systolic murmur of PS and a regurgitant systolic murmur of a VSD.
The murmur is best audible along the lower left and mid-left sternal borders.
Therefore, in a child who has physical and radiographic findings similar to those of a small VSD, the presence of RVH or BVH on the ECG should raise the possibility of acyanotic TOF.
(A small VSD is associated with LVH or a normal ECG rather than with RVH or BVH.)
Infants with acyanotic TOF become cyanotic over time, usually by 1 or 2 years of age, and have clinical pictures of cyanotic TOF, including exertional dyspnea and squatting.
In infants with classic cyanotic TOF, the presence of severe PS produces a right-to-left shunt at the ventricular level (i.e.cyanosis) with decreased PBF.
The PAs are small, and the LA and LV may be slightly smaller than normal because of a reduction in the pulmonary venous return to the left side of the heart.
Therefore, chest radiograph films show a normal heart size with decreased pulmonary vascularity.
The systolic pressures are identical in the RV, LV, and aorta.
The ECG demonstrates RVH because of the high pressure in the RV.
The right-to-left ventricular shunt is silent, and the heart murmur audible in this condition originates in the PS (ejection-type murmur).
The ejection systolic murmur is best audible at the mid-left sternal border (over the infundibular stenosis) or occasionally at the upper left sternal border (in patients with pulmonary valve stenosis).
The intensity and the duration of the heart murmur are proportional to the amount of blood flow through the stenotic valve.
When the PS is mild, a relatively large amount of blood goes through the stenotic valve(with a relatively small right-to-left ventricular shunt), thereby producing a loud, long systolic murmur.
However, with severe PS, there is a relatively large right-to-left ventricular shunt that is silent, and only a small amount of blood goes through the PS, thereby producing a short, faint systolic murmur.
In other words, the intensity and duration of the systolic murmur are inversely related to the severity of the PS.
The extreme form of TOF is that associated with pulmonary atresia, in which the only source of PBF is through a constricting PDA or through multiple collateral arteries(MAPCAs).
All systemic venous return is shunted right to left at the ventricular level, resulting in a marked systemic arterial desaturation.
Probably the more important reason for such severe cyanosis is the markedly reduced PBF, with resulting reduction of pulmonary venous return to the left side of the heart.
Unless the patency of the ductus is maintained, the infant may die.
Infusion of prostaglandin E1 has been successful for a limited time period in keeping the ductus open in this and other forms of cyanotic CHDs that rely on the patency of the ductus arteriosus for PBF.
Heart murmur is absent, or a faint murmur of PDA is present.
RVH is present on the ECG as in other forms of TOF.
Chest radiographs show a small heart and a markedly reduced PBF, as well as absence of main pulmonary trunk (boot-shaped heart).

Hypoxic Spell

Hypoxic spell is an urgent clinical situation that can occur in infants with uncorrected TOF or some other forms of cyanotic CHDs.
To handle the situation correctly, physicians should have full understanding of mechanism of the spell, clinical manifestation, and correct management of the situation.

Mechanism of Hypoxic Spell

A sudden increase in right-to-left shunt appears to be the prime event of hypoxic spell,considering the clinical manifestation of the spell.
The question is what causes the sudden increase in the right-to-left shunt?
Is it a RVOT spasm, as proposed previously by some investigators, or something else?
Because the VSD of TOF is large enough to equalise systolic pressures in both ventricles, the RV and LV may be viewed as a single chamber that ejects blood to the systemic and pulmonary circuits.
The ratio of flows to the pulmonary and systemic circuits (Qp/Qs) is related to the ratio of resistance offered by the RV outflow obstruction and the systemic vascular resistance (SVR).
Either an increase in the pulmonary resistance or a decrease in the SVR will increase the degree of the right-to-left shunt, producing a more severe arterial desaturation.
Although controversies exist over the role of the spasm of the RVOT as an initiating event for the hypoxic spell, there is no evidence that the spasm actually occurs as a primary event.
Pulmonary valve stenosis has a fixed resistance and does not produce spasm.
The infundibular stenosis, which consists of disorganised muscle fibers intermingled with fibrous tissue, is almost nonreactive to sympathetic stimulation or catecholamines.
Hypoxic spell also occurs in patients with TOF with pulmonary atresia in which the presence or absence of spasm would have no role in the spell.
Therefore, the likelihood of the RVOT spasm initiating the right-to-left shunt is remote.
It is more likely that changes in the SVR play a primary role in controlling the degree of the right-to-left shunt and the amount of PBF.
A decrease in the SVR increases the right- to-left shunt and decreases the PBF with a resulting increase in cyanosis.
In this case, the RVOT dimension may decrease, but it is likely secondary to the decreased amount of blood Flowing through it rather than primary spasm.
Conversely, an increase in SVR decreases the right-to-left shunt and forces more blood through the stenotic RVOT.
In addition to decreased SVR, other causes, such as excessive tachycardia or hypovolemia, can increase the right-to-left shunt through the VSD, resulting in a fall in the systemic arterial oxygen saturation.
Tachycardia or hypovolemia may narrow down the RVOT, as a secondary effect.
Slowing of the heart rate by β-adrenergic blockers, volume expansion, or interventions that increase the SVR or decrease the PVR (i.e., oxygen) have all been used to terminate the hypoxic spell.

Clinical Features of Hypoxic Spell

The hypoxic spell, also called the cyanotic spell, tet spell, or hypercyanotic spell, occurs in young infants with uncorrected TOF.
It is characterized by hyperpnea (i.e., rapid and deep respiration), worsening cyanosis, and disappearance of the heart murmur (secondary to the increased right-to-left ventricular shunt and decreased blood flow through the stenotic RVOT).
This occasionally results in complications of the central nervous system and even death.
Any event such as crying, defecation, or increased physical activity that suddenly lowers the SVR or produces a large right-to-left ventricular shunt may initiate the spell and, if not corrected, establishes a vicious circle of hypoxic spells.
The sudden onset of tachycardia or hypovolemia can also cause the spell.
The resulting fall in arterial Po2, in addition to an increase in Pco2 and a fall in pH, stimulates the respiratory centre and produces hyperpnea.
The hyperpnea, in turn, makes the negative thoracic pump more efficient and results in an increase in the systemic venous return to the RV.
In the presence of fixed resistance at the RVOT (i.e., pulmonary resistance [PR]) or decreased SVR, the increased systemic venous return to the RV must go out the aorta.
This leads to a further decrease in the arterial oxygen saturation, which establishes a vicious circle of hypoxic spells.

Treatment of Hypoxic Spells

Treatment of the spell is aimed at breaking this cycle by using one or more of the following maneuvers:
Picking up the infant in such a way that it assumes the knee–chest position and traps systemic venous blood in the legs, thereby temporarily decreasing systemic venous return and helping to calm the baby.
The knee–chest position may also increase SVR by reducing arterial blood flow to the lower extremities.
Morphine sulfate suppresses the respiratory center and abolishes hyperpnea.
Sodium bicarbonate (NaHCO3) corrects acidosis and eliminates the respiratory center–stimulating effect of acidosis.
Administration of oxygen may improve arterial oxygen saturation a little.
Vasoconstrictors such as phenylephrine raise SVR and improve arterial oxygen saturation.
Ketamine is a good drug to use because it simultaneously increases SVR and sedates the patient.
Both effects are known to help terminate the spell.
Propranolol has been used successfully in some cases of hypoxic spell, both acute and chronic.
Its mechanism of action is not entirely clear.
When administered for acute cases, propranolol may slow the heart rate and perhaps reduce the spasm of the RVOT (although not likely as discussed earlier).
More important, propranolol may also increase SVR by antagonising vasodilating effects of β-adrenergic stimulation.
The successful use of propranolol in the prevention of hypoxic spell is more likely the result of the drug’s peripheral action.
The drug may stabilise vascular reactivity of the systemic arteries, thereby preventing a sudden decrease in SVR.

Squatting

Infants and toddlers with uncorrected TOF often assume a squatting position after playing hard.
During the play, these children become tachypneic and dusky.
When they assume a squatting position and rest a little while, these symptoms disappear and then they resume playing.
What is the mechanism of recovery from these symptoms during squatting?
Squatting position is the same as knee–chest position (which is used to treat hypoxic spells in infants).
Squatting or knee chest position increases systemic arterial oxygen saturation.
Three mechanisms may be involved.
First, reduction of the systemic venous return by trapping venous blood in the lower extremities reduces right-to-left shunt.
Second, a reduced arterial blood flow to legs reduces venous washout from leg muscles.
Third, squatting might also increase SVR, a known mechanism to reduce right-to-left ventricular shunt.

Clinical Manifestations

History

A heart murmur is audible at birth.
Most patients are symptomatic with cyanosis at birth or shortly thereafter.
Dyspnea on exertion, squatting, or hypoxic spells develop later, even in mildly cynotic infant.
Occasional infants with acyanotic TOF may be asymptomatic or may show signs of CHF from a large left-to-right ventricular shunt.

Physical Examination

Varying degrees of cyanosis, tachypnea, and clubbing (in older infants and children) are present.
An RV tap along the left sternal border and a systolic thrill at the upper and mid-left sternal borders are commonly present (50%).
An ejection click that originates in the aorta may be audible.
S2 is usually single because the pulmonary component is too soft to be heard.
A long, loud (grade 3 to 5 of 6) ejection-type systolic murmur is heard at the mid and upper left sternal borders.
murmur originates from the PS but may be easily confused with the holosystolic regurgitant murmur of a VSD.
more severe the obstruction of the RVOT, the shorter and softer the systolic murmur.
In the acyanotic form, a long systolic murmur, resulting from VSD and infundibular stenosis, is audible along the entire left sternal border, and cyanosis is absent.
auscultatory findings resemble those of a small-shunt VSD(but, unlike VSD, the ECG shows RVH or BVH).

Electrocardiography

Right axis deviation (RAD) (+120 to +150 degrees) is present in cyanotic TOF.
In the acyanotic form, the QRS axis is normal.
RVH is usually present, but the strain pattern is unusual(because RV pressure is not suprasystemic).
BVH may be seen in the acyanotic form.
RAH is occasionally present.

Radiography

Cyanotic Tetralogy of Fallot

heart size is normal or smaller than normal, and pulmonary vascular markings are decreased.
“Black” lung fields are seen in TOF with pulmonary atresia.
A concave main PA segment with an upturned apex (i.e.“boot-shaped” heart or coeur en sabot) is characteristic.
RA enlargement (25%) and right aortic arch (25%) may be Present.

Acyanotic Tetralogy of Fallot

Radiographic findings similar to that of mild to moderate size VSD (but patients with TOF have RVH rather than LVH on the ECG).

Echocardiography

Two-dimensional echo and Doppler studies usually make the diagnosis and quantitate the severity of TOF.
Careful echo study can delineate anomalous coronary arteries, which has important surgical consequences.
A large, perimembranous infundibular VSD and overriding of the aorta are readily imaged in the parasternal long-axis view.
Anatomy of the RVOT, the pulmonary valve, the pulmonary annulus, and the main PA and its branches is imaged.
Doppler studies estimate the pressure gradient across the RVOT obstruction.
Anomalous coronary artery distribution can be imaged in most cases by echo studies, major concern is to rule out any branch of the coronary artery crossing the RVOT.
preoperative cardiac catheterization solely for the diagnosis of coronary artery anatomy is most of the time no longer necessary; when in doubt, CT or MRI angiography could be used as an alternative, noninvasive imaging modality.
Associated anomalies such as ASD and persistence of the left SVC can be imaged.

Other Studies

Two-dimensional echo and Doppler studies are the primary method of evaluation before surgery.
CT and MRI angiography may clarify questions on the anomalous coronary arteries.
Cardiac catheterization is reserved only for patients with specific unanswered questions after the noninvasive studies.

Natural History

Infants with acyanotic TOF gradually become cyanotic.
Patients who are already cyanotic become more cyanotic as the infundibular stenosis worsens, and polycythemia develops.
Polycythemia develops secondary to cyanosis.
Physicians need to watch for the development of relative iron-deficiency state (i.e., hypochromia).
Hypoxic spells may develop in infants.
Growth retardation may be present if cyanosis is severe.
Brain abscess and cerebrovascular accident rarely occur.
Subacute bacterial endocarditis (SBE) is occasionally a complication.
Some patients, particularly those with severe TOF, develop aortic regurgitation (AR).
Coagulopathy is a late complication of a long-standing cyanosis.

Management

Medical

Physicians should recognize and treat hypoxic spells.
It is important to educate parents to recognize the spell and know what to do.
Oral propranolol therapy, 0.5 to 2mg/kg every 6 hours, is occasionally used to prevent hypoxic spells while waiting for an optimal time for corrective surgery in the regions where open-heart surgical procedures are not well established for small infants.
Balloon dilatation of the RVOT and pulmonary valve, although not widely practiced, has been attempted to delay repair for several months.
Relative iron-deficiency state should be detected and treated.
Iron-deficient children are more susceptible to cerebrovascular complications.
Normal hemoglobin or hematocrit values or decreased red blood cell indices indicate an iron-deficiency state in cyanotic patients.

Surgical

Palliative Shunt Procedures

Indications

Shunt procedures are performed to increase pulmonary blood flow.
Indications for shunt procedures vary from institution to institution.
Many institutions, however, prefer primary repair without a shunt operation regardless of the patient’s age.
However, when the following situations are present, a shunt operation may be chosen usually rather than primary repair.
Neonates with TOF and pulmonary atresia
Infants with hypoplastic pulmonary annulus, which requires a transannular patch for complete repair
Children with hypoplastic PAs
Unfavorable coronary artery anatomy
Infants younger than 3 to 4 months old who have medically unmanageable hypoxic spells
Infants weighing less than 2.5 kg

Procedures, Complications, and Mortality

Although several other procedures were performed in the past ,a modified BT (Gore-Tex interposition) shunt is the only procedure performed at this time.
Classic BT shunt (1945), anastomosed between the subclavian artery and the ipsilateral PA, is usually performed for infants older than 3 months because it is often thrombosed in young infants.
A right-sided shunt is performed in patients with left aortic arch; a left-sided shunt is per- formed for right aortic arch.
Potts operation (1946), anastomosed between the descending aorta and the left PA, is no longer performed either.
It may result in heart failure or pulmonary hypertension.
Waterston shunt (1962), anastomosed between the ascending aorta and the right PA, is no longer performed because of a high incidence of surgical complications.
Complications resulting from this procedure included too large a shunt, leading to CHF or pulmonary hypertension, and narrowing and kinking of the right PA at the site of the anastomosis.
Modified BT shunt.
A Gore-Tex interposition shunt is placed between the subclavian artery and the ipsilateral PA.
It is the most popular procedure for any age, especially for infants younger than 3 months of age.

Complete Repair Surgery

Timing of this operation varies from institution to institution, but early surgery is generally preferred.

Indications and Timing

Most centers prefer primary elective repair between 3 months and 12 months of age, even if they are asymptomatic, acyanotic (i.e., “pink tet”), or minimally cyanotic.
Advantages cited for early primary repair include not only avoiding risks associated with a shunt operation but also diminution of hypertrophy and fibrosis of the RV, normal growth of the PAs and alveolar units, and reduced incidence of postoperative ventricular arrhythmias and possible sudden death.
2.frequent occurrence of hypoxic spell is generally considered an indication for operation, even in conservative centers.
Mildly cyanotic infants who have had previous shunt surgery may have total repair 1 to 2 years after the shunt operation.
Patients with coronary artery anomalies may have an early surgery at the same time as those without anomalous coronary arteries.
In the past, surgery for these patients was delayed until after 1 year of age because a conduit placement may be required between the RV and the PA.

Anesthetic considerations

Initial assessment and planning

Hypoxemia becomes progressive over time as Pulmonary blood flow diminishes concordant to the increasing obstruction by the RVOT .
Some patients experience hypercyanotic episodes when the oxygen saturation acutely drop to 20–30% or less.
Since systolic pressure in the RV reflects the pressure in the LV and aorta, a decrease in systemic arterial pressure (as may occur with peripheral vasodilatation caused by anesthetic agents and sedative drugs, or prolonged fasting) results in decreased RV pressure and Pulmonary blood flow.
An increase in LV pressures, as induced by vasoactive agents and volume administration, can reverse shunting of blood from the RV into the LV and promote pulmonary blood flow.
Close monitoring of blood pressure changes from anesthetic interventions can provide early physiological guidance for optimising Pulmonary blood flow and preventing hypercyanotic episodes.
Preoperative assessment should include the history of hypercyanotic episodes in patients who are not palliated or repaired.
Patients with severe cyanosis present with failure to thrive and polycythemia unless they are anemic.
Polycythemia actually enhances the “blueness” during hypercyanotic episodes due to higher levels of deoxygenated hemoglobin.
Patients with stable and mild cyanosis often have had generous weight gain from frequent feedings given to prevent agitation and worsened cyanosis.
Anticipation, early recognition, and management of potential hypercyanotic episodes are essential for avoiding cardiovascular collapse.
Preoperatively, the following factors are considered for preventing hypercyanotic episodes:
Minimise patient agitation to reduce tachycardia, increased infundibular tone and increased oxygen consumption.
Keep the patient at ease by avoiding irritating events; use premedication in a monitored setting and comfort the infant as needed (e.g., judicious use of sugar drops or a pacifier may mitigate hunger).
Minimise dehydration by avoiding prolonged fasting.
Offer clear fluids up to 1–2 hours prior to anesthesia induction or administer IV fluids if IV access is present.
Beta blocker therapy should be continued as prescribed.
Even under anesthesia, increased stimulation can incite infundibular spasm that enhances right-to-left shunting, precipitating a hypercyanotic episode.
Anesthetic induction and times of surgical manipulation are especially vulnerable periods for occurrence of a hypercyanotic episode.
Infants with unrepaired TOF may present for anesthetic care for non‐cardiac interventions such as cardiac catheterizations, MRI, and CT , or for surgical procedures that cannot be delayed until cardiac palliation or repair.

Perioperative anaesthetic consideration for surgical palliation

Most neonates or infants needing surgical palliation are critically ill and dependent on PGE1 infusion to maintain ductal patency for augmenting pulmonary blood flow and managing hypoxemia.
Some other infants become symptomatic shortly after discharge from the hospital as they develop cyanosis and failure to thrive.
Anesthetic goals are to maintain pulmonary blood flow by limiting right‐to‐left intracardiac shunting and preserving adequate SVR.
Induction of anesthesia can be successful with ketamine and/or fentanyl with an inhaled agent for maintenance.
General anesthesia and potent inhaled agents have been demonstrated to depress ventricular function.
IV fluids and phenylephrine are useful to increase SVR.
Inotropic drugs can increase heart rate and contractility and worsen infundibular spasms.
In the absence of reliable IV access, inhalational induction with sevoflurane, and intramuscular ketamine and rocuronium as needed can provide adequate conditions for IV access and tracheal intubation.
Central venous access is obtained for the infusion of fluids and vasoactive agents.
An arterial line is placed for close hemodynamic monitoring and blood gas sampling.
If placing a radial arterial line, it is recommended on the contralateral side of the anticipated modified BT shunt(mBTS), so that blood pressure assessment is unbiased by the run‐off from the ipsilateral innominate artery or by possible stenosis at the anastomotic site.
Although mBTS was traditionally done via a thoracotomy, the mBTS is now often performed via median sternotomy.
Median sternotomy permits exposure for conversion to a central shunt, institution of CPB in the event of severe hemodynamic instability or need to patch augment the BPAs, inspection of the coronary anatomy, division of the PDA while confirming adequacy of the shunt flow, and avoidance of a separate incision site after full repair.
Median sternotomy also avoids the lung retraction required for exposure with thoracotomy.
Heparin at 100 units/kg is given prior to shunt placement.
Hypoxemia and hemodynamic instability can occur during the partial clamping for the graft anastomosis and is managed with vasoactive support, fluids, and ventilatory adjustment.
Once the shunt is open, oxygen saturation acutely improves while blood pressure decreases.
A widened pulse pressure gradient results due to low diastolic pressure secondary to blood run‐off to the lungs; insufficient diastolic blood pressure can compromise coronary perfusion.
Management with normoventilation, low FiO2, volume, and vasopressors can temporize this problem.
If a mBTS was done via a right thoracotomy and a PDA was present, the excessive diastolic run‐off may continue until the PDA closes.
PGE1 infusion is discontinued when alternative pulmonary blood flow (PBF) is established.
A shunt flow approaching Qp:Qs of 1:1 under normal physiological conditions of normocarbia while breathing spontaneously in room air is ideal, resulting in an SpO2 of 80–85% in the absence of parenchymal lung disease.
Intraoperatively, simulating normal physiological conditions as closely as possible is important for accurate clinical assessment of Qp:Qs.
If the ductus is still open, the additional PBF must be considered in Qp:Qs.
Otherwise, saturations too high or too low would indicate an imbalanced Qp:Qs.
Lower than expected saturations, after ruling out reversible ventilatory impairments such as atelectasis or endobronchial intubation, may indicate that the shunt is inadequate.
Some surgeons prefer the larger diameter shunts if physiologically tolerated to accommodate patient growth and associated increased PBF needs prior to the full repair.
Platelet transfusions are avoided whenever possible due to an increased risk of shunt thrombosis.

Postoperative care for surgical palliation

In the ICU, the patient is supported with mechanical ventilation for the next 12–24 hours for stabilization, monitoring and management of ongoing physiologic changes.
Potential complications include unilateral or bilateral pulmonary edema or hemorrhage from increased PBF.
Also, low systemic diastolic blood pressure can compromise coronary artery flow during diastole, causing myocardial ischemia.
Shunt thrombosis is always a potential risk, and heparin infusion at 6–10 units/kg/hour is commenced to maintain shunt patency after the risk of surgical bleeding subsides.
A shunt murmur, reflecting presence of shunt blood flow, can be easily auscultated by pausing ventilation and placing the stethoscope at the end of the endotracheal tube; the murmur is transmitted via the endotracheal tube because the shunt is near the bronchus.
Antiplatelet therapy is initiated with aspirin when enteral intake is started and continued until the time of complete repair.
Other perioperative complications include recurrent laryngeal nerve and phrenic nerve damage and development of chylothorax from thoracic duct injury.

Perioperative anesthetic management for surgical repair

The pre‐CPB goal is the promotion of PBF, and post‐CPB goals are preservation of ventricular function and Cardiac output optimization.
Monitors include central venous pressure and invasive arterial blood pressure.
Cerebral oximetry is helpful.
TEE is recommended post‐CPB to assess the surgical repair, but epicardial echocardiography can be used if TEE is not feasible.
Induction of anesthesia for complete repair can be similarly accomplished as for the palliative shunt placement.
For patients at a low risk of hypercyanotic episodes, inhalational induction of anesthesia is generally safe.
There are several described techniques for maintenance of anesthesia.
If immediate extubation in the operating room or early extubation in the ICU (within 6 hours after surgery) is anticipated, then a multimodal low‐dose opioid technique is recommended.

Considerations for separation from CPB include:

RV dysfunction can occur especially if a ventriculotomy was performed.
Pre‐ existing RV hypertrophy and diastolic dysfunction may require high filling pressures to maintain Cardiac output.
Management should target increasing preload, decreasing RV afterload, and adding inotropic support such as milrinone (0.375–0.75 μg/kg/min) and perhaps low dose epinephrine (0.02–0.04 μg/kg/min).
Tachydysrhythmias occur frequently after complete TOF repairs.
Surgical repair frequently disrupts the conduction system located in close proximity of the VSD.
JET is a narrow complex tachydysrhythmia originating from the AV node and His bundle area; it often develops within 24 hours after repair and has been associated with increased length of stay.
JET is characterized by heart rates above 170/min and AV dissociation leading to significant hemodynamic instability.
Risk factors include young age, long CPB and aortic cross clamp times, preoperative tachycardia, high inotropic requirements, and surgical intervention near the AV node.
Treatment consists of sedation, electrolyte correction, cooling to 34–35 °C, and IV amiodarone.
Heart block is common after separation of CPB.
The heart block may be transient due to inflammation around conduction fibers.
A temporary pacemaker is helpful while awaiting recovery of normal cardiac conduction.
In some patients, recovery is not seen until for 7–10 days; afterward, a permanent pacemaker is considered.
Many patients demonstrate right bundle branch block on postoperative ECG, particularly those who underwent ventriculotomy.
Coagulopathy and bleeding after separation of CPB is common after TOF repair.
Hemodilution of coagulation factors and platelets, pronounced inflammatory effects of CPB and immature coagulation systems increase the risks for bleeding in small, young patients undergoing early TOF repair.
Transfusion of multiple component blood products is almost always required for this patient group.
The use of antifibrinolytics such as epsilon‐aminocaproic acid or tranexamic acid have been shown to reduce post‐CPB bleeding and minimize the use of blood products.
Residual VSDs appear to be common.
Small VSDs are usually hemodynamically insignificant and are likely to close spontaneously.
If greater than 2–3 mm, excessive PBF will be poorly tolerated and it may be necessary to resume CPB for further VSD closures after quantification of the shunt magnitude by echocardiography and hemodynamic evaluation.
Also, some VSDs that were undetected preoperatively due to equalisation of ventricular pressures may be now visualized after relief of the RVOT obstruction.
The degree of additional shunting and hemodynamic significance may indicate a return to CPB.
Indications for returning to CPB include coronary compromise by excessive traction or injury, residual VSDs, residual RVOT obstruction.
patient selection and the implementation of strong strategies for managing postextubation pain, sedation, RV dysfunction, and pulmonary status are essential for successful early extubation and good outcomes.
Reintubation after extubation failure is associated with increased morbidity, hospital stay.

Reference

1 Andropolous 23rd edition

2 Park paediatric cardiology seventh edition