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BD glenn surgery for TGA As a cardiac Anaesthesia What's the implications of this disease How to manage What are the steps in BD glenn How this surgery helps patient

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bidirectional Glenn procedure anesthesia management congenital heart disease authoritative review

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BD Glenn for TGA: first clarify the anatomy

A bidirectional Glenn (BDG) is a superior cavopulmonary connection: the SVC is disconnected from the right atrium and anastomosed end-to-side to the right pulmonary artery. Thus, venous blood from the head and upper body flows passively to both pulmonary arteries without passing through the ventricle.
In simple d-TGA with two adequate ventricles, BD Glenn is not the usual operation. The preferred repair is an arterial switch operation in the neonatal period. In d-TGA, aorta arises from the morphologic RV and PA from the morphologic LV, producing parallel circulations that require mixing to sustain life. - Miller's Anesthesia, p. 10881.
In a patient described as “TGA for BD Glenn,” assume there is a more complex substrate, such as:
  • TGA with unbalanced AV septal defect or hypoplastic ventricle
  • TGA with VSD plus severe pulmonary/subpulmonary stenosis or pulmonary atresia
  • Double-inlet LV / functionally single ventricle with transposed great arteries
  • Straddling AV valve, severe ventricular dysfunction, or anatomy unsuitable for a safe biventricular repair
  • A staged pathway to Fontan completion
This must be confirmed from echo, CT/cath, and the operative plan. The key question is: which ventricle is systemic, what is the source of pulmonary blood flow, and is there unobstructed systemic outflow?

How BD Glenn helps

BDG is usually the second stage of single-ventricle palliation.

Physiologic effect

Before GlennAfter Glenn
Systemic ventricle receives both SVC and IVC venous returnSVC blood bypasses the heart and reaches PA directly
Ventricular volume overload from pulmonary flowReduced ventricular preload and volume work
Pulmonary blood flow may depend on shunt, antegrade flow, or excessive mixingUpper-body venous return supplies pulmonary blood flow passively
Oxygen saturation may be low, but varies by pulmonary flowTypical saturation often about 75%-85%, not normal
Full Fontan physiology not yet presentIVC and hepatic venous blood still returns to the heart and mixes with pulmonary venous blood
The systemic ventricle is volume-unloaded, but its output is maintained because IVC return still enters the heart. The staged reduction in volume load permits ventricular remodeling before Fontan completion. Typical saturations after Glenn are about 80%. - Sabiston Textbook of Surgery, p. 2588.
It is a bridge to Fontan, not a complete separation of systemic and pulmonary circulations. Later, Fontan directs IVC and hepatic venous blood to the PAs as well.

Anaesthetic implications

1. Glenn circulation is dependent on low PVR and adequate SVC pressure

After completion, pulmonary blood flow is passive:
[ Q_p \approx \frac{\text{SVC pressure} - \text{LA pressure}}{\text{PVR}} ]
There is no subpulmonary ventricle to overcome increased PVR. Therefore, pulmonary blood flow, saturation, and cardiac output fall with:
  • Hypoxaemia
  • Acidosis
  • Marked hypercapnia
  • High mean airway pressure
  • Excessive PEEP
  • Atelectasis
  • Pulmonary infection / secretions
  • Pulmonary artery distortion, stenosis, or high PA pressure
  • Elevated LA pressure from ventricular dysfunction or AV valve regurgitation
  • Hypovolaemia or impaired venous return
Anaesthetic objective: preserve low PVR, good pulmonary venous drainage, sinus rhythm, contractility, systemic perfusion, and sufficient preload without producing venous congestion.
A practical caveat: in established Glenn physiology, a small rise in PaCO₂ can increase cerebral blood flow and hence SVC flow, potentially improving oxygen delivery. This is not a reason to accept respiratory acidosis. Usually target normocapnia or very mild, controlled hypercapnia, tailored to saturation, cerebral oximetry, SVC pressure, PA pressure, lactate, and surgical conditions. Recent paediatric CHD anaesthesia review discusses this stage-specific physiology.

2. Preoperative assessment

Define the anatomy and circulation

Review personally with cardiology and surgeon:
  • Exact diagnosis: d-TGA vs congenitally corrected TGA, VSD, pulmonary stenosis/atresia, AV valve anatomy, ventricular dominance
  • Planned pathway: Glenn only, Glenn with PA reconstruction, shunt takedown, PA band adjustment, DKS, atrial septectomy, arch work, etc.
  • Systemic ventricular function and end-diastolic pressure
  • Common AV valve / tricuspid regurgitation
  • Atrial-level mixing and adequacy of atrial septum
  • Systemic outflow obstruction, including bulboventricular foramen or subaortic obstruction in single-ventricle TGA
  • Branch PA size, confluence, distortion, stenosis, prior shunt-related PA distortion
  • Pulmonary venous obstruction
  • Bilateral SVC or persistent left SVC
  • Presence and magnitude of antegrade pulmonary blood flow
  • Aortopulmonary collaterals
  • Preoperative saturations, Hb/haematocrit, coagulation, renal/hepatic function, lactate

Catheterization data if available

Important parameters:
  • Mean PA pressure: ideally low, commonly less than about 15 mmHg in a favorable candidate
  • PVR index: low
  • Ventricular EDP / LA pressure: preferably low
  • PA anatomy and gradients
  • Saturation run and collateral burden

Correct before theatre where possible

  • Dehydration
  • Anaemia or excessive polycythaemia
  • Acidosis
  • Respiratory infection / atelectasis
  • Electrolyte abnormalities
  • Coagulopathy
  • Sepsis
Avoid unnecessary venesection in cyanotic children. Treat the cause of hyperviscosity symptoms rather than a number alone.

Intraoperative management

Monitoring and access

  • Standard ASA monitoring plus temperature
  • Pre-induction arterial line when feasible, usually radial
  • Large-bore peripheral access
  • Central venous access only after reviewing SVC anatomy and planned surgical field
  • Do not compromise the SVC with an internal jugular line in a small child unless there is a clear reason and surgical agreement
  • Femoral venous access is often more useful if central access is necessary
  • NIRS cerebral and somatic monitoring if available
  • TEE or epicardial echo, depending on patient size and institutional practice
  • Serial ABG, Hb, ionized calcium, glucose, lactate, coagulation
  • Ensure blood products are immediately available

Important line-related point

After Glenn, an upper-body central line measures Glenn/SVC pressure, not ordinary right atrial preload. A high SVC pressure can reflect high PVR, PA obstruction, high LA pressure, excess pulmonary blood flow, or obstruction at the anastomosis.

Induction and maintenance

The induction should be slow and titrated, particularly if there is ventricular dysfunction, systemic outflow obstruction, or marginal pulmonary blood flow.
Common approach:
  • Opioid-based technique: fentanyl or remifentanil
  • Low-dose volatile anaesthetic, carefully titrated
  • Ketamine can be useful where preservation of BP/SVR is desirable
  • Midazolam or dexmedetomidine as adjuncts, with caution for bradycardia
  • Neuromuscular blockade to prevent coughing, straining, and oxygen consumption
  • Treat hypotension promptly, usually with volume if genuinely preload-responsive and a vasopressor if low SVR
Avoid abrupt falls in SVR and myocardial depression. Propofol bolus is often poorly tolerated in marginal single-ventricle physiology.

Ventilation

Before Glenn completion, ventilation depends on the pre-Glenn balance of systemic versus pulmonary blood flow. After Glenn:
  • Use the lowest effective mean airway pressure
  • Avoid excessive PEEP
  • Prevent atelectasis
  • Use modest tidal volumes and avoid overdistension
  • Aim for normoxia and normocapnia, individualized to the child’s physiology
  • Avoid significant acidosis and hypothermia
  • Consider early transition to spontaneous breathing when safe and clinically appropriate
Positive-pressure ventilation raises intrathoracic pressure and PVR, impeding passive Glenn flow. Early extubation can be beneficial in an uncomplicated patient, but it is not mandatory. Do not extubate a child with poor cardiac output, high Glenn pressure, substantial bleeding, pulmonary dysfunction, significant acidosis, or residual surgical obstruction.

Key surgical steps in BD Glenn

The exact sequence varies by surgeon, anatomy, prior operations, and whether CPB is used.
  1. Median sternotomy / re-entry
    Adhesiolysis if prior shunt, Norwood, or other neonatal palliation.
  2. Assess anatomy
    Inspect SVC, innominate vein, branch PAs, prior shunt, PA size, and bilateral SVC if present.
  3. Establish CPB or temporary venous decompression strategy
    BD Glenn may be done:
    • On CPB, commonly in smaller or complex patients
    • Off-pump with a temporary SVC-to-RA shunt or venoatrial bypass in selected cases
    The central anaesthetic concern during SVC clamping is prevention of cerebral venous hypertension and impaired cerebral perfusion.
  4. Control existing pulmonary blood flow
    A prior systemic-to-pulmonary shunt may be taken down. Antegrade pulmonary flow from the ventricle may be reduced, banded, or retained selectively.
    This is a deliberate balance:
    • Too much antegrade flow: excessive PA pressure, venous congestion, pleural effusions, ventricular volume load
    • Too little flow: worse saturation and poor PA growth
  5. Divide the SVC near its atrial junction
    The cardiac end is oversewn or otherwise closed.
  6. Create the cavopulmonary anastomosis
    The cephalad SVC is anastomosed end-to-side to the superior aspect of the RPA, usually near the PA confluence. This allows SVC blood to flow to both the right and left PAs, hence “bidirectional.” - Sabiston Textbook of Surgery, p. 2588.
  7. Address associated lesions
    May include PA plasty, relief of pulmonary artery stenosis, atrial septectomy, shunt takedown, or management of systemic outflow obstruction.
  8. Wean from CPB and assess
    Check:
    • Glenn/SVC pressure
    • Systemic arterial pressure
    • Saturation
    • TEE/epicardial echo for ventricular function, AV valve regurgitation, PA flow, residual obstruction, and atrial-level mixing
    • Lactate, ABG, Hb, coagulation

Anaesthesia during SVC clamping

This is a high-risk moment.

Goals

  • Maintain cerebral perfusion
  • Avoid excessive rise in SVC pressure
  • Avoid hypotension
  • Ensure adequate venous decompression or CPB support
  • Watch NIRS closely
  • Communicate continuously with surgeon and perfusionist

Concerning findings

  • Abrupt NIRS decrease
  • Facial/upper-body venous congestion
  • Rising SVC pressure
  • Hypotension
  • New acidosis/lactate rise
  • Poor cerebral venous drainage
If clamping cannot be tolerated, temporary SVC decompression, CPB, or revision of strategy may be needed.

Postoperative management

Expected findings

  • Saturation often 75%-85%
  • Glenn/SVC pressure commonly in the low-to-mid teens, interpreted in context
  • Mild cyanosis remains expected
  • Chest drainage can be significant

ICU priorities

  1. Optimize passive pulmonary blood flow
    • Good lung expansion
    • Low PEEP / low mean airway pressure
    • Adequate analgesia and sedation without hypoventilation
    • Suction gently and only as needed
    • Treat atelectasis, infection, bronchospasm, and pleural effusions rapidly
  2. Maintain systemic perfusion
    • Monitor urine output, lactate, NIRS, arterial pressure, peripheral perfusion
    • Avoid both hypovolaemia and indiscriminate fluid loading
    • Use vasoactive support according to ventricular function and SVR
  3. Protect rhythm and ventricular function
    • Sinus rhythm is preferred
    • Correct potassium, magnesium, calcium, acidosis, hypothermia
    • Treat AV valve regurgitation / ventricular dysfunction aggressively
  4. Look for Glenn failure or obstruction
    • Persistently high SVC pressure
    • Low saturation out of proportion to baseline
    • Worsening lactate / low output
    • Facial edema or marked upper-body venous congestion
    • NIRS decline
    • Pleural effusions / chylothorax
    • Neurologic concern or seizures
  5. Thrombosis prophylaxis Institutional practice varies. Aspirin is commonly used when indicated, while anticoagulation depends on anatomy, thrombosis risk, shunt material, prior thrombosis, and surgeon/cardiology protocol.

Common post-Glenn complications and anaesthetic response

ProblemLikely causesImmediate priorities
Low saturationHigh PVR, PA stenosis, Glenn obstruction, low SVC flow, pulmonary venous issue, low cardiac outputABG, lung recruitment without high pressures, echo, assess PA/Glenn gradients, correct acidosis
High SVC/Glenn pressureHigh PVR, obstruction, high LA pressure, excess flow, PA hypoplasiaOptimize ventilation, assess echo, consider pulmonary vasodilator if appropriate, exclude mechanical obstruction
Low cardiac outputVentricular dysfunction, AVVR, preload deficit, systemic outflow obstruction, arrhythmiaTEE, targeted volume, inotrope/vasoactive therapy, rhythm correction
Pleural effusion/chylothoraxElevated venous pressure, lymphatic injuryDrainage, investigate Glenn pressure/obstruction, nutritional strategy
Neurologic injurySVC hypertension, low cerebral perfusion, thromboembolismNIRS, neuroassessment, imaging and multidisciplinary management
ThrombosisLow-flow state, technical narrowing, hypercoagulabilityUrgent echo/angiography, anticoagulation or intervention as indicated

Practical cardiac anaesthesia summary

For a TGA patient undergoing BD Glenn, think:
  1. This is usually complex TGA with functionally single-ventricle physiology, not simple d-TGA.
  2. Know the exact anatomy and the source of pulmonary blood flow.
  3. BD Glenn unloads the systemic ventricle by diverting SVC flow directly to both PAs.
  4. After completion, pulmonary flow is passive. Avoid raised PVR and raised intrathoracic pressure.
  5. SVC clamping is a cerebral-perfusion event. Plan venous decompression/CPB and monitor NIRS.
  6. A saturation around 80% can be appropriate. Treat the patient and perfusion markers, not saturation alone.
  7. High Glenn pressure plus low saturation or low output is an emergency until obstruction, high PVR, and high LA pressure are excluded.
For broader background, the NCBI Glenn overview describes BDG as the second-stage superior cavopulmonary connection, and the paediatric CHD anaesthesia review summarizes the ventilation and PVR principles relevant to single-ventricle palliation.

I think you are still making the answers for theory exam I passed my theory exam So now i want you to explain in depth from basic to most advanced concepts about this I want to know the pathophysiology of TGA,in detail,why the patient has low saturation,what are the effects of it Then how its different from TOF How to manage the desaturations in both of them Does the management of hypoxia is different in them Do both have cynotic spells Then come toh the surgery,how it helps Nd now how to manage in the post op period

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transposition great arteries AND tetralogy Fallot

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TGA versus tetralogy of Fallot cyanosis hypercyanotic spell management bidirectional Glenn postoperative care

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https://pmc.ncbi.nlm.nih.gov/articles/PMC10285149

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https://pmc.ncbi.nlm.nih.gov/articles/PMC11589288

You are right. Let’s approach this as cardiac anaesthesia and ICU physiology, not an exam answer.
The most important starting point:
“TGA undergoing BD Glenn” is not usually simple neonatal d-TGA.
Simple d-TGA with two usable ventricles usually receives an arterial switch operation. A Glenn implies either complex TGA with single-ventricle-type physiology, an inadequate ventricle, unbalanced AV canal, straddling AV valve, complex DORV/TGA anatomy, or occasionally a 1.5-ventricle strategy.
So before managing desaturation, establish the patient-specific circulation from echo and the surgeon:
  1. What is the morphology and function of the systemic ventricle?
  2. Is there a VSD, and is it restrictive?
  3. Is pulmonary blood flow excessive, restricted, duct-dependent, or dependent on a shunt?
  4. Is there pulmonary stenosis or atresia?
  5. Is systemic outflow obstructed?
  6. Is the planned Glenn part of a Fontan pathway or a 1.5-ventricle repair?

1. Normal circulation: the reference point

Normally the circulation is in series:
[ \text{Body} \rightarrow RA \rightarrow RV \rightarrow PA \rightarrow lungs \rightarrow LA \rightarrow LV \rightarrow aorta \rightarrow \text{body} ]
  • All systemic venous blood reaches lungs before returning to the body.
  • Arterial saturation is therefore near 100%, subject to normal pulmonary gas exchange.
  • Oxygen delivery is:
[ DO_2 = CO \times CaO_2 ]
And arterial oxygen content is approximately:
[ CaO_2 = (1.36 \times Hb \times SaO_2) + (0.003 \times PaO_2) ]
In cyanotic congenital heart disease, PaO₂ may increase a little with oxygen, but if blood bypasses the lungs or mixing is inadequate, SaO₂ and hence CaO₂ remain low. This is why oxygen alone can be a weak treatment for cardiac cyanosis.

2. d-TGA: what is wrong?

Anatomy

In d-transposition of the great arteries:
  • Aorta arises from the morphologic RV
  • Pulmonary artery arises from the morphologic LV
  • Atrioventricular connections remain normal
So:
[ RA \rightarrow RV \rightarrow Ao ]
[ LA \rightarrow LV \rightarrow PA ]
The pulmonary and systemic circuits are no longer in series. They are in parallel.

The two loops in d-TGA

Systemic venous loop

[ \text{Body} \rightarrow RA \rightarrow RV \rightarrow Ao \rightarrow \text{Body} ]
Deoxygenated blood keeps returning to the body.

Pulmonary venous loop

[ \text{Lungs} \rightarrow LA \rightarrow LV \rightarrow PA \rightarrow \text{Lungs} ]
Oxygenated blood keeps circulating back to the lungs.
Without communication between these two loops, the newborn cannot survive.
This is the central idea:
In uncomplicated d-TGA, cyanosis is primarily a mixing problem, not primarily a pulmonary blood-flow problem.
Miller's Anesthesia, p. 10881; Sabiston Textbook of Surgery, p. 2576.

Why saturation is low in d-TGA

The arterial blood is coming from the RV into the aorta. That RV receives systemic venous blood from the RA, so it is poorly oxygenated.
Systemic saturation depends on the amount of blood that can mix between the two circuits through:
  • Patent foramen ovale / ASD
  • VSD
  • PDA
  • A combination of all three
If there is poor atrial mixing, the baby may be profoundly cyanotic despite lungs that are structurally normal and well ventilated.

Why atrial mixing matters so much

In d-TGA with intact ventricular septum, the atrial septum is often the key “mixing site.”
Pulmonary venous blood enters LA. Unless it can cross to RA, it continues LV → PA → lungs and never reaches systemic circulation.
A restrictive PFO means severely restricted mixing. The baby becomes cyanotic, acidotic, poorly perfused, and can deteriorate very quickly as the ductus closes.
Balloon atrial septostomy creates a nonrestrictive ASD, allowing bidirectional atrial mixing. It commonly improves saturation into roughly the 70%-80% range, rather than normalizing it. - Sabiston Textbook of Surgery, p. 2576.

Effect of PDA in d-TGA

A PDA allows another site of mixing.
But its effect is not just “more pulmonary blood flow.” Its benefit depends on the pressure relationship and direction of ductal shunting.
Prostaglandin E1 maintains ductal patency and can improve oxygenation, especially while awaiting septostomy or surgery. In TGA with pulmonary atresia, it is essential for pulmonary blood flow. In TGA with coarctation/arch hypoplasia, it may also be important for systemic perfusion. - Sabiston Textbook of Surgery, p. 2576.

Effects of chronic or severe hypoxaemia in TGA

Acute severe cyanosis leads to:
  • Anaerobic metabolism and rising lactate
  • Metabolic acidosis
  • Pulmonary vasoconstriction, which worsens the situation
  • Myocardial dysfunction
  • Reduced cerebral oxygen delivery
  • Reduced coronary oxygen content
  • Shock, bradycardia, arrest
In a neonate, low saturation can be deceptively tolerated for a while because fetal Hb and high Hb concentration preserve oxygen content. But that compensation has limits. A fall in saturation plus low cardiac output, acidosis, rising lactate, oliguria, or impaired NIRS is dangerous regardless of the displayed SpO₂.

3. TOF: why it is different

Anatomy

Tetralogy of Fallot consists of:
  1. Large malalignment VSD
  2. Overriding aorta
  3. RV outflow tract obstruction, which may be dynamic and/or fixed
  4. RV hypertrophy secondary to outflow obstruction
The primary embryologic lesion is anterior deviation of the infundibular septum, producing both the VSD and variable RVOTO. - Sabiston Textbook of Surgery, p. 2573.

The physiology is different from d-TGA

In TOF, the circuits are still arranged in series. The aorta receives blood from both ventricles because it overrides the VSD.
The problem is that the RV has two available exits:
  • Through a narrowed RVOT to PA
  • Across the large VSD to the overriding aorta
If resistance through the RVOT is high, blood takes the easier path across the VSD into the aorta.
[ RV \rightarrow VSD \rightarrow Ao ]
This produces a right-to-left shunt and reduced pulmonary blood flow.
In TOF, cyanosis is primarily a pulmonary oligemia / RVOT obstruction problem.
The more severe the RVOTO, the more right-to-left shunting and the lower the saturation. - Sabiston Textbook of Surgery, p. 2573.

4. TGA versus TOF: the useful bedside comparison

Featured-TGATOF
Main defectVentriculoarterial discordanceVSD plus RVOTO and overriding aorta
CircuitsParallelIn series, but with intracardiac right-to-left shunt
Main cause of cyanosisInadequate mixing between parallel circuitsReduced pulmonary blood flow due to RVOTO
Role of ASD/PFOOften lifesaving for mixingUsually not central to baseline physiology
Role of VSDImproves mixing but may cause pulmonary overcirculationThe route for right-to-left shunting
PGE1Often used to improve mixing; essential if duct-dependentUsed in severe neonatal RVOTO / pulmonary atresia to maintain pulmonary flow
Balloon atrial septostomyCommon urgent intervention in restrictive atrial mixingNot standard treatment
Typical “Tet spell”NoYes, classic
Definitive surgeryArterial switch in simple d-TGAVSD closure plus relief of RVOTO
GlennOnly for selected complex TGA/single ventricle pathwaysUncommon, but may be used in selected complex or 1.5-ventricle settings

5. Do both have cyanotic spells?

TOF: yes, classic hypercyanotic or Tet spells

A Tet spell is an acute, often dramatic fall in pulmonary blood flow due to a vicious cycle:
  1. Agitation, crying, feeding, pain, fever, dehydration, or emergence causes catecholamine release.
  2. Dynamic infundibular muscle contracts and worsens RVOTO.
  3. More RV blood shunts across VSD to the aorta.
  4. Pulmonary blood flow falls.
  5. Saturation falls and metabolic acidosis develops.
  6. Acidosis, tachycardia, and catecholamine release further worsen dynamic RVOTO.
The child becomes deeply cyanosed and tachypnoeic. Severe spells can cause altered consciousness, seizures, stroke, or death. - Sabiston Textbook of Surgery, p. 2573.

Simple d-TGA: no, not in the same sense

d-TGA patients can deteriorate abruptly, but that is usually from:
  • Ductal constriction/closure
  • Inadequate atrial-level mixing
  • Restriction of an ASD/PFO
  • PVR changes that alter mixing
  • Pulmonary disease
  • Low cardiac output
  • Arrhythmia or myocardial dysfunction
This is not an infundibular spasm-mediated Tet spell.
A complex TGA patient with VSD plus severe pulmonary stenosis can behave more like a pulmonary-oligaemic lesion and may have episodic desaturation. Still, you must identify the mechanism rather than calling all acute cyanosis “spelling.”

6. Managing desaturation: TGA versus TOF

This is where the clinical distinction matters most.

General emergency actions for either patient

For abrupt desaturation:
  1. Confirm it is real: waveform, probe, arterial blood gas.
  2. ABC assessment: airway, tube position, ventilation, pneumothorax, secretions, lung compliance.
  3. Check perfusion: arterial pressure, pulse quality, capillary refill, lactate, NIRS, urine output.
  4. Check rhythm and ECG.
  5. Establish whether this is:
    • Low pulmonary blood flow
    • Inadequate mixing
    • Increased PVR
    • Low cardiac output
    • New mechanical obstruction
    • Pulmonary pathology
  6. Call the congenital cardiologist/surgeon early and obtain focused echo promptly.
But after this common first response, management diverges.

A. Desaturation in d-TGA: improve mixing or restore ductal flow

Ask

  • Is the atrial septum restrictive?
  • Is the PDA closing or already closed?
  • Is there a VSD?
  • Is pulmonary blood flow adequate?
  • Is there pulmonary venous hypertension or lung disease?
  • Is there low output or severe acidosis?

Priorities

1. Start or increase PGE1 when ductal-dependent physiology or inadequate mixing is likely
This is a time-critical intervention in an unstable neonatal d-TGA patient.
2. Urgent balloon atrial septostomy if atrial mixing is inadequate
This is definitive acute physiology management for a restrictive atrial septum. Oxygen, fluid, and ventilation cannot substitute for an adequate mixing communication.
3. Correct factors that increase PVR
  • Oxygen if needed
  • Correct acidosis
  • Avoid severe hypercapnia
  • Ensure lung recruitment without excessive mean airway pressure
  • Treat pneumothorax, atelectasis, sepsis, or aspiration
4. Maintain cardiac output
  • Correct hypovolaemia if present
  • Avoid excessive vasodilation
  • Support ventricular function and coronary perfusion as necessary

Important practical point

A d-TGA saturation of 75% after satisfactory BAS can be acceptable if the child has good cardiac output, reasonable lactate, good systemic perfusion, and stable acid-base status.
Trying to force a saturation of 95% with aggressive hyperventilation or high pressures may worsen haemodynamics without correcting the central problem.

B. TOF hypercyanotic spell: increase pulmonary flow by changing the resistance balance and relieving dynamic RVOTO

The logic is:
  • Increase SVR
  • Reduce dynamic RVOT spasm
  • Reduce PVR
  • Restore preload
  • Reduce agitation and oxygen consumption

Immediate bedside sequence

1. Calm and position
  • Stop stimulation.
  • Knee-chest position in a spontaneously breathing child.
  • This raises SVR and improves venous return.
2. Oxygen
  • Give high-flow oxygen.
  • It may not fully correct saturation because the principal problem is low pulmonary flow, but it helps reduce hypoxic pulmonary vasoconstriction.
3. Analgesia/sedation
  • Morphine is traditional.
  • In ICU/OR, fentanyl or ketamine-based approaches may be appropriate depending on BP and ventilation.
  • The goal is to break catecholamine-driven infundibular spasm and reduce oxygen consumption.
4. Volume
  • Give a cautious crystalloid bolus if preload depletion is plausible.
  • Dehydration is a frequent contributor.
5. Raise SVR
  • Phenylephrine is a common first choice.
  • Noradrenaline or vasopressin can be used in selected refractory cases.
6. Reduce RVOT spasm
  • Beta blockade, commonly propranolol or esmolol, if BP and ventricular function allow.
7. Correct acidosis and PVR
  • Ensure adequate ventilation.
  • Treat metabolic acidosis, hypoxia, hypercarbia, and hypothermia.
  • Avoid excessive PEEP and high intrathoracic pressure.
8. Escalate
  • Intubation and controlled ventilation for refractory spells, exhaustion, severe acidosis, reduced consciousness, or haemodynamic instability.
  • Induction can lower SVR and worsen the spell, so have vasopressor ready before induction.
  • If refractory, proceed to surgical/catheter intervention or ECLS depending on anatomy and local capability.
A recent PICU review summarizes this same strategy: decrease PVR and dynamic RVOTO, increase SVR, treat agitation, restore preload, and escalate rapidly if refractory. TOF intensive-care review

The one-sentence difference

In d-TGA, fix the mixing or ductal communication. In TOF, increase pulmonary blood flow by relieving RVOT obstruction and shifting blood away from the VSD-to-aorta route.

7. How surgery helps

Simple d-TGA: arterial switch operation

The arterial switch restores the normal series circulation:
  • Aorta is connected to LV
  • PA is connected to RV
  • Coronary arteries are transferred to the neoaorta
  • LeCompte maneuver brings the PA anterior to the aorta in most repairs
This is anatomical and physiological correction. The LV becomes the systemic ventricle, as nature intended.
The critical perioperative issue is coronary transfer. Any coronary kinking, ostial distortion, compression, or inadequate perfusion may cause ischaemia, ventricular dysfunction, arrhythmias, failure to separate from bypass, or low cardiac output. - Sabiston Textbook of Surgery, pp. 2577-2578.

TOF complete repair

The procedure aims to:
  • Close the VSD so the LV ejects only to the aorta
  • Relieve RVOTO by muscle resection, pulmonary valvotomy/valvuloplasty, transannular patch, RV-PA conduit, or a valve-sparing repair if possible
This eliminates the right-to-left VSD shunt and restores adequate pulmonary blood flow.
The tradeoff is that relief of RVOTO, especially with a transannular patch, may produce chronic pulmonary regurgitation, leading later to RV dilatation and arrhythmias. - Miller's Anesthesia, p. 10878.

8. Why a BD Glenn helps in complex TGA

For a complex TGA patient on a single-ventricle pathway, the problem is often not simply parallel circulation. It is that one ventricle cannot safely support both systemic output and the full pulmonary circulation.
Before Glenn, the systemic ventricle may receive:
[ \text{SVC return} + \text{IVC return} + \text{pulmonary venous return} ]
This creates substantial volume load.
In BD Glenn:
[ SVC \rightarrow PA ]
The SVC is divided from the right atrium and anastomosed to the RPA, ideally near the PA confluence, so SVC blood distributes to both lungs.
Now:
  • Upper-body venous return goes directly to lungs
  • The heart no longer handles the SVC volume
  • Ventricular volume loading falls
  • Pulmonary overcirculation from a shunt can be reduced
  • The ventricle has time to remodel before Fontan completion
  • IVC and hepatic venous return still enters the heart and mixes with pulmonary venous return
Thus, post-Glenn saturation remains subnormal, often around 75%-85%. The patient is intentionally still cyanotic because IVC blood bypasses the lungs and enters the systemic ventricle. - Sabiston Textbook of Surgery, p. 2588.

9. Glenn physiology: advanced but practical

After Glenn:
[ Q_p = \frac{P_{SVC} - P_{LA}}{PVR} ]
There is no subpulmonary ventricle. Pulmonary blood flow depends on the gradient between SVC pressure and left atrial pressure, divided by PVR.
Therefore, low saturation or low pulmonary flow after Glenn can result from:

Reduced driving pressure

  • Hypovolaemia causing low SVC flow
  • Low cerebral venous return
  • Excessive vasodilation or poor systemic perfusion
  • Obstruction of SVC, Glenn anastomosis, PA, or pulmonary veins

Increased downstream pressure

  • Raised LA pressure
  • Ventricular diastolic dysfunction
  • Significant AV valve regurgitation
  • Pulmonary venous obstruction

Increased PVR

  • Hypoxia
  • Acidosis
  • Major hypercapnia
  • Atelectasis
  • Pneumonia
  • Excess PEEP or high mean airway pressure
  • Pulmonary oedema
  • Distended lungs
  • High haematocrit/hyperviscosity
  • Pulmonary artery distortion or hypoplasia

10. Postoperative care after BD Glenn

This is the relevant postoperative framework for your original scenario.

What is expected?

  • Saturation frequently 75%-85%, depending on anatomy and retained antegrade pulmonary flow
  • SVC/Glenn pressure often in the low teens
  • Mild cyanosis
  • A degree of pleural drainage
Do not treat the monitor number alone. Evaluate oxygen delivery:
  • MAP and diastolic pressure
  • Lactate trend
  • NIRS trend
  • ABG and pH
  • Urine output
  • Peripheral perfusion
  • Ventricular function and AV valve regurgitation
  • Glenn pressure and its trend

A. Ventilation after Glenn

The central rule:
Passive pulmonary blood flow dislikes high intrathoracic pressure.

Aim for

  • Good lung expansion
  • Avoidance of atelectasis
  • Low-to-moderate PEEP, individualized
  • Lowest effective mean airway pressure
  • Avoidance of overdistension
  • Normoxia
  • Usually normocapnia or mild permissive hypercapnia depending on local strategy and observed physiology
  • Early extubation if haemodynamics, bleeding, ventilation, and neurologic status permit
Spontaneous breathing reduces mean intrathoracic pressure and can enhance venous return and Glenn pulmonary flow. But do not extubate solely to improve Glenn flow if the patient has ongoing low output, high lactate, major bleeding, lung disease, severe acidosis, or residual structural obstruction.
A nuance: modest hypercapnia may increase cerebral blood flow, which can increase SVC flow into the Glenn. However, excessive hypercapnia or acidosis raises PVR and depresses myocardial function. This is individualized physiology, not a routine target.

B. Fluids and vasoactive support

Both overfilling and underfilling are harmful.

Too little volume

  • Low SVC return
  • Poor Glenn flow
  • Low cardiac output
  • Worsening saturation and lactate

Too much volume

  • Pleural effusions
  • Pulmonary oedema
  • Increased venous pressure
  • Ventricular diastolic impairment
  • Prolonged ventilation
Use small, reassessed boluses when there is evidence of preload responsiveness. Track response with arterial pressure, NIRS, saturation, echo, Glenn pressure, urine output, and lactate.
Vasoactive selection depends on the dominant problem:
  • Low SVR with adequate ventricular function: vasopressor support may restore systemic and coronary perfusion.
  • Ventricular dysfunction: inodilator/inotrope strategy may be needed, balanced against undesired SVR reduction.
  • High PVR with poor Glenn flow: correct ventilation/lung pathology first; consider selective pulmonary vasodilator therapy only when indicated and in conjunction with the cardiac ICU team.
  • High LA pressure due to AVVR or diastolic dysfunction: vasoactive manipulation alone will not fix the problem. Echo and surgical discussion are essential.

C. A structured response to low saturation after Glenn

Step 1: Is this true and is it urgent?

  • Check waveform and ABG.
  • Compare with expected baseline.
  • Assess lactate, pH, NIRS, BP, cardiac output, and mental status.

Step 2: Is pulmonary blood flow inadequate?

Think:
  • High PVR
  • Atelectasis
  • High PEEP
  • Pneumothorax
  • Pulmonary infection
  • Airway obstruction
  • Pleural effusion
  • Glenn or branch PA obstruction
  • Thrombosis

Step 3: Is the gradient across the Glenn inadequate?

Think:
  • Hypovolaemia
  • Low SVC return
  • Low systemic output
  • High LA/ventricular EDP
  • Significant AV valve regurgitation
  • Pulmonary venous obstruction

Step 4: Is there excessive venous pressure?

High Glenn/SVC pressure plus poor saturation is concerning for:
  • High PVR
  • Mechanical Glenn narrowing
  • Branch PA stenosis
  • Pulmonary venous obstruction
  • Elevated LA pressure
  • Excessive antegrade pulmonary blood flow in selected patients

Step 5: Obtain echo early

Focused assessment should include:
  • Glenn flow pattern and anastomotic gradient
  • Branch PA flow
  • Ventricular function
  • AV valve regurgitation
  • Atrial septal patency/mixing if relevant
  • Pulmonary venous return
  • Pericardial effusion/tamponade
  • Residual systemic outflow obstruction

D. Post-Glenn complications

1. Elevated SVC pressure and facial/upper-body edema

Consider:
  • Glenn pathway obstruction
  • High PVR
  • PA hypoplasia/stenosis
  • High LA pressure
  • SVC thrombosis
This has cerebral consequences. Elevated SVC pressure impairs cerebral venous drainage and lowers cerebral perfusion pressure:
[ CPP = MAP - CVP ]
After Glenn, upper-body CVP is effectively Glenn/SVC pressure. A high SVC pressure can compromise cerebral perfusion even when MAP looks “acceptable.”

2. Pleural effusions or chylothorax

Common causes:
  • Elevated systemic venous pressure
  • Lymphatic injury
  • Elevated PVR
  • Obstruction in the Glenn/PA circuit
Treat drainage, nutritional consequences, and especially the haemodynamic driver.

3. Low cardiac output

Look for:
  • Ventricular dysfunction
  • AV valve regurgitation
  • Myocardial ischaemia
  • Arrhythmia
  • Excessive afterload
  • Hypovolaemia
  • Tamponade
  • Systemic outflow obstruction

4. Neurologic issues

Potential mechanisms:
  • SVC hypertension
  • Low cerebral perfusion
  • Hypoxaemia
  • Thromboembolism
  • Seizures
NIRS is helpful as a trend monitor, but it does not replace clinical examination, ABG, haemodynamic interpretation, or imaging where indicated.

5. Thrombosis

A low-flow or obstructed Glenn can thrombose. Consider this with sudden desaturation, rising SVC pressure, facial edema, or new neurologic concern. Antiplatelet versus anticoagulation strategy is anatomy- and center-specific.

Practical mental model

When you see cyanosis, ask this first:

In TGA:

“Are the two parallel circulations mixing adequately?”
Management:
  • PGE1 if ductal patency/mixing support is needed
  • BAS for restrictive atrial mixing
  • Correct PVR, acidosis, low output
  • Urgent surgical repair when indicated

In TOF:

“Is RVOT obstruction diverting blood across the VSD to the aorta?”
Management:
  • Calm, sedate, oxygenate
  • Restore preload
  • Increase SVR
  • Reduce dynamic infundibular spasm
  • Lower PVR
  • Escalate to intubation, palliation, repair, or ECLS if refractory

After BD Glenn:

“Is passive SVC-to-PA flow adequate, and what is raising PVR, LA pressure, or Glenn resistance?”
Management:
  • Optimize lung volume without high intrathoracic pressure
  • Maintain suitable preload and systemic perfusion
  • Identify and correct high PVR
  • Exclude Glenn/PA/pulmonary venous obstruction and ventricular/AV valve problems early with echo
The TOF PICU review is a useful bedside reference for hypercyanotic spell physiology and escalation.
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