Tet Spell in the OR: Physiologic Stabilization and Rapid Cardiopulmonary Bypass Initiation

1. Clinical Significance

A hypercyanotic spell in tetralogy of Fallot is an abrupt reduction in effective pulmonary blood flow with increased right-to-left shunting across the ventricular septal defect. In the operating room, it may develop during anesthetic induction, positive-pressure ventilation, sternotomy, cardiac manipulation, blood loss, or the interval before cardiopulmonary bypass. Deterioration can be rapid because hypoxemia and acidosis intensify sympathetic activation, which may further increase dynamic infundibular obstruction.

Tetralogy of Fallot consists of a large ventricular septal defect, overriding of the aortic root, right ventricular outflow tract obstruction, and secondary right ventricular hypertrophy. Cyanosis is determined predominantly by the severity and dynamic behavior of the right ventricular outflow tract obstruction and by the relative resistances of the pulmonary and systemic circulations [1]. A spell is therefore a hemodynamic crisis rather than simply an oxygenation problem.

The immediate objectives are to restore right ventricular filling, increase systemic vascular resistance, reduce infundibular hypercontractility, suppress adrenergic stimulation, optimize ventilation and oxygen delivery, and proceed rapidly to cardiopulmonary bypass when native pulmonary blood flow cannot be restored.

2. Hemodynamic Mechanism

The ventricular septal defect is usually large and nonrestrictive. Right and left ventricular systolic pressures are therefore nearly equal, and flow distribution is governed primarily by the relative impedance of the two ventricular outlets. Blood is preferentially directed toward the pulmonary artery when the pulmonary outflow pathway is favorable and toward the overriding aorta when right ventricular outflow resistance rises or systemic vascular resistance falls.

The characteristic sequence is:

Dynamic infundibular obstruction and/or reduced preload and/or reduced systemic vascular resistance→ reduced antegrade pulmonary blood flow→ increased right-to-left shunting→ reduced pulmonary venous return and left ventricular preload→ systemic desaturation and hypotension→ hypoxia, acidosis, and catecholamine release→ further infundibular contraction and circulatory deterioration

Intraoperative echocardiographic observations have demonstrated that a decrease in systemic vascular resistance or an increase in dynamic right ventricular outflow tract obstruction can increase right-to-left shunting and reduce arterial oxygen saturation [2]. Although the direct intraoperative evidence is limited, the observed physiology explains why treatment must address both the pulmonary outflow tract and the systemic circulation.

3. Why Anesthesia Can Trigger a Spell

Anesthetic induction alters several determinants of shunt direction simultaneously. Venodilation, fasting, positive-pressure ventilation, and excessive mean airway pressure may reduce venous return. Vasodilatory anesthetic agents may lower systemic vascular resistance. Airway stimulation, inadequate anesthetic depth, incision, sternotomy, or cardiac manipulation may provoke tachycardia and a catecholamine surge.

Reduced preload decreases right ventricular cavity size and may narrow the infundibular lumen. Reduced systemic vascular resistance makes the aorta a lower-resistance outlet, favoring right-to-left shunting. Increased contractility intensifies systolic infundibular narrowing. These effects commonly coexist.

In a retrospective series of 40 children undergoing tetralogy of Fallot surgery, hypercyanotic spells occurred during induction in six patients. Three postoperative deaths occurred in the cohort, although a causal relationship between the spells and mortality was not established [3]. The induction period should therefore be approached with volume, vasoactive drugs, emergency cannulas, and a primed bypass circuit immediately available in high-risk patients.

4. Recognition and Rapid Differential Diagnosis

A spell should be suspected when systemic saturation falls abruptly with evidence of reduced pulmonary blood flow. Findings may include:

• Sudden arterial desaturation or darkening of blood in the operative field
• Falling end-tidal carbon dioxide despite unchanged ventilation
• Tachycardia, followed by bradycardia in advanced deterioration
• Systemic hypotension or a narrowing pulse pressure
• Decreasing cerebral or somatic near-infrared spectroscopy values
• Hyperdynamic contraction of an underfilled ventricle
• Increased right-to-left shunting or dynamic outflow obstruction on echocardiography
• Progressive metabolic and lactic acidosis

Airway obstruction, endotracheal tube displacement, pneumothorax, inadequate ventilation, major blood loss, venous air embolism, arrhythmia, coronary ischemia, pulmonary hypertensive crisis, and mechanical caval compression must be assessed rapidly. Evaluation should occur in parallel with physiologic rescue.

5. Immediate Physiologic Rescue

5.1 Stop the Trigger and Coordinate the Team

Noxious stimulation and nonessential cardiac manipulation should stop. The surgeon should release excessive retraction or caval compression and return an elevated heart toward its normal position when feasible. The anesthesiologist should confirm the airway, ventilation, anesthetic depth, and neuromuscular blockade. The perfusionist should prepare for immediate bypass while stabilization proceeds.

5.2 Restore Preload

Volume administration increases systemic venous return, expands the right ventricular cavity, and may reduce dynamic infundibular narrowing. Crystalloid, albumin, or blood products may be used according to blood loss, hemoglobin concentration, and ventricular filling.

The goal is adequate preload rather than indiscriminate volume loading. Administration should be titrated against arterial pressure, atrial filling, echocardiographic appearance, surgical assessment, and near-infrared spectroscopy. Excessive positive end-expiratory pressure and unnecessarily high mean airway pressure should be avoided because both reduce venous return.

5.3 Increase Systemic Vascular Resistance

Phenylephrine is a logical first-line vasoconstrictor because it increases systemic vascular resistance without directly increasing myocardial contractility. Raising systemic arterial pressure reduces the relative advantage of the aortic pathway, thereby decreasing right-to-left shunting, supporting pulmonary blood flow, and improving coronary and cerebral perfusion.

Small boluses may be followed by a titrated infusion when vasodilation persists. Improvement in pressure and saturation supports the diagnosis of unfavorable shunt physiology. Failure to respond suggests severe pulmonary outflow obstruction, inadequate preload, or another cause of instability.

5.4 Reduce Infundibular Hypercontractility

Beta-adrenergic blockade reduces heart rate and contractility, prolongs diastolic filling, and limits dynamic systolic narrowing of the hypertrophied infundibulum. Classic physiologic studies showed that beta-sympathetic blockade attenuates dynamic right ventricular outflow tract obstruction and reduces the fall in arterial oxygen saturation during sympathetic stimulation [4].

Esmolol is useful intraoperatively because of its rapid onset and short duration. It should be given after or together with restoration of preload and systemic pressure. In a profoundly underfilled or hypotensive patient, isolated beta-blockade may reduce cardiac output.

The clinical evidence is derived mainly from observational case series. A structured review found that four of six included series reported a reduction in recurrent spells in at least 66% of patients after beta-blocker therapy, but the studies did not establish an optimal drug, dose, or route [5]. Beta-blockade should therefore be integrated with correction of loading conditions rather than used as an isolated intervention.

5.5 Deepen Anesthesia Without Producing Vasoplegia

Adequate anesthesia and analgesia blunt the catecholamine surge caused by airway stimulation, incision, sternotomy, and cardiac manipulation. Because deeper anesthesia can worsen systemic vasodilation, preload and systemic vascular resistance must be supported simultaneously. Ketamine may preserve arterial pressure in selected patients, but no anesthetic agent substitutes for direct correction of the shunt physiology.

5.6 Optimize Oxygenation, Ventilation, and Acid–Base Status

The inspired oxygen concentration should be increased. Oxygen maximizes saturation of the limited blood reaching the lungs and may reduce pulmonary vascular resistance, but it cannot overcome critical right ventricular outflow tract obstruction.

Hypoventilation, severe hypercarbia, hypoxemia, and acidosis should be corrected. Aggressive hyperventilation and excessive airway pressure should be avoided because impaired venous return may outweigh any reduction in pulmonary vascular resistance.

6. Manual Ascending Aortic Compression

When the heart is exposed and conventional measures are failing, gentle partial compression of the ascending aorta may be considered as a brief surgical rescue maneuver. The intended mechanism is an immediate increase in effective systemic afterload, analogous to pharmacologic elevation of systemic vascular resistance. This may transiently reduce right-to-left shunting and redirect output toward the pulmonary circulation.

Direct clinical evidence evaluating manual aortic compression for tet spells is lacking. It should therefore be regarded as an empiric bridge rather than a standardized treatment. Compression must be applied progressively under direct visualization and limited to the shortest possible interval while cannulation proceeds. Excessive compression may impair coronary perfusion, injure the aorta, increase ventricular wall stress, or provoke arrhythmia.

The maneuver should never delay cardiopulmonary bypass.

7. Criteria for Immediate Cardiopulmonary Bypass

Medical treatment should be judged by its effect over minutes. Immediate bypass is indicated when there is:

• Persistent or worsening severe desaturation
• Hypotension despite volume and vasoconstrictor support
• Progressive acidosis or rising lactate
• Bradycardia, ventricular arrhythmia, or impending arrest
• Declining cerebral or somatic near-infrared spectroscopy
• Recurrent spells with minimal manipulation
• Failure of preload restoration, phenylephrine, and beta-blockade to restore stable pulmonary blood flow

The objective is not to normalize every variable before cannulation, but to preserve coronary and cerebral perfusion while extracorporeal support is established.

8. Rapid Cardiopulmonary Bypass Initiation

8.1 Emergency Team Sequence

Once refractory physiology is recognized, heparin should be administered and the shortest safe cannulation plan announced. The surgeon, anesthesiologist, perfusionist, and nursing team should communicate continuously regarding pressure, saturation, rhythm, venous return, and cerebral perfusion.

8.2 Ascending Aortic Cannulation

The ascending aorta in tetralogy of Fallot is often relatively generous because of aortic override and chronic preferential systemic ejection. This frequently permits rapid arterial cannulation, although cannula size, insertion depth, jet direction, arch anatomy, and the planned cross-clamp site must be considered.

The cannula should be secured immediately. Malposition, posterior wall injury, dissection, or dislodgement during urgent manipulation can cause hemorrhage or malperfusion.

8.3 Rapid Right Atrial Venous Cannulation

In profound instability, single right atrial venous cannulation may be the fastest route to initial bypass. A cannula placed through the right atrial appendage or free wall can provide sufficient drainage to begin partial support and restore systemic oxygen delivery. Flow should be increased progressively according to venous return and arterial pressure.

Incomplete drainage, atrial collapse, cannula obstruction, and air entrainment are recognized limitations. These are temporarily acceptable when the immediate objective is rescue rather than definitive exposure.

8.4 Conversion to Bicaval Drainage

After oxygenation, perfusion pressure, and rhythm have stabilized, venous drainage should be converted for repair. The original cannula may be directed into one caval pathway while a second cannula is added, or dedicated superior and inferior vena caval cannulas may be placed. Caval snares then permit right atriotomy and ventricular septal defect closure.

Conversion should be controlled; hurried repositioning should not create air entrainment, caval injury, or loss of venous return.

9. Alternative Emergency Bridges

A recent single-case report described an emergency aorto-pulmonary shunt created with two intravenous cannulas during a refractory perioperative spell. Saturation reportedly increased from approximately 20% to 70% within seconds, providing time for controlled initiation of bypass [6]. The report demonstrates the physiologic value of rapidly restoring pulmonary blood flow, but the technique remains an isolated rescue and is not an established substitute for conventional cannulation.

In a center with a primed circuit and accessible ascending aorta and right atrium, rapid arterial and venous cannulation will usually be the most reproducible strategy.

10. Transition to Definitive Repair and Operative Principles

Cardiopulmonary bypass interrupts the self-amplifying spell by providing systemic oxygen delivery independent of native pulmonary blood flow. Definitive repair then addresses the anatomical substrate through ventricular septal defect closure, resection of obstructive infundibular muscle, pulmonary valvotomy when appropriate, and right ventricular outflow tract or annular enlargement when valve-sparing relief is inadequate.

The preceding hypoxemia, hypotension, acidosis, and catecholamine exposure should inform myocardial protection and postoperative planning because they may contribute to ventricular dysfunction, arrhythmia, vasoplegia, neurologic injury, and coagulopathy.

The practical sequence is:

• *Increase preload
• increase systemic vascular resistance
• reduce infundibular hypercontractility
• suppress adrenergic stimulation
• optimize oxygenation and ventilation

→ reduce right-to-left shunting and restore pulmonary blood flow**

If this sequence fails, manual aortic compression may provide only a brief bridge. Persistent instability requires immediate cardiopulmonary bypass. The safest management is anticipatory: identify high-risk physiology before induction, maintain preload, avoid abrupt reductions in systemic vascular resistance, have phenylephrine and esmolol immediately available, prime the bypass circuit, and agree on an emergency cannulation sequence before the operation begins.

References

[1] Bailliard F, Anderson RH. Tetralogy of Fallot. Orphanet J Rare Dis. 2009;4:2. doi:10.1186/1750-1172-4-2.

[2] Greeley WJ, Stanley TE, Ungerleider RM, Kisslo JA. Intraoperative hypoxemic spells in tetralogy of Fallot: an echocardiographic analysis of diagnosis and treatment. Anesth Analg. 1989;68(6):815-819. doi:10.1213/00000539-198906000-00026.

[3] Karacaer F. Experiences in anesthetic management of pediatric patients undergoing Fallot tetralogy correction operations. Journal of Cardio-Vascular-Thoracic Anaesthesia and Intensive Care Society. 2019. doi:10.5222/gkdad.2019.99810.

[4] Honey M, Chamberlain DA, Howard J. The effect of beta-sympathetic blockade on arterial oxygen saturation in Fallot’s tetralogy. Circulation. 1964;30:501-510. doi:10.1161/01.CIR.30.4.501.

[5] Fanous E, Mogyorósy G. Does the prophylactic and therapeutic use of beta-blockers in preoperative patients with tetralogy of Fallot significantly prevent and treat the occurrence of cyanotic spells? Interact Cardiovasc Thorac Surg. 2017;25(4):647-650. doi:10.1093/icvts/ivx135.

[6] Singh A, Sharma P, Malhotra V, Sharma V. Emergency aorto-pulmonary shunt using two IV cannulas technique: a rapid stabilization technique for cyanotic spells in tetralogy of Fallot before cardiopulmonary bypass. International Journal of Cardiovascular and Thoracic Surgery. 2025;11(2). doi:10.11648/j.ijcts.20251102.11.