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Anesthetic Management: Right Inguinal Herniotomy in a 2-Year-Old with Unrepaired TOF

Quick Framework

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PART 1: PATHOPHYSIOLOGY OF TOF (Exam Cornerstone)

1. Right ventricular outflow tract obstruction (RVOTO) - primarily infundibular/subpulmonic stenosis (dynamic component)
2. Non-restrictive VSD with right-to-left shunting
3. Overriding aorta
4. Right ventricular hypertrophy

Source: Morgan & Mikhail's Clinical Anesthesiology, 7e, pp. 787-788

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PART 2: PREOPERATIVE ASSESSMENT

History

• Duration and severity of cyanosis (baseline SpO2 - often 75-85% in unrepaired TOF)
• History of tet spells - frequency, triggers, posture adopted (squatting/knee-chest)
• Exercise tolerance / feeding history (proxy for functional status)
• Current medications: propranolol (beta-blocker for RVOTO), aspirin (if B-T shunt)
• Prior cardiac interventions (B-T shunt, RVOTO balloon dilatation)
• Chromosomal associations: 22q11.2 deletion (DiGeorge), trisomy 21

Examination

• Vital signs: baseline resting SpO2, HR, BP (bilateral arms if B-T shunt)
• Cyanosis assessment: clubbing, degree of central cyanosis
• Murmur: harsh ejection systolic murmur (RVOTO) - decreases during tet spell
• Airway: Mallampati, mouth opening (for challenging pediatric airway)
• Weight (for drug dosing): assume ~12-14 kg for a 2-year-old

Investigations

Cardiology Liaison (MANDATORY)

• This is elective surgery - formal written cardiology clearance should be obtained
• Risk stratification: unrepaired TOF is high-risk for non-cardiac anesthesia
• Discuss if cardiac correction/palliation should be done first (unless hernia is incarcerated)
• Consider deferring herniotomy if RVOT gradient is critical or tet spells are frequent

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PART 3: ANESTHETIC GOALS (The Exam Mantra for TOF)

"Maintain SVR. Avoid PVR rise. Avoid hypovolemia. Avoid sympathetic stimulation."

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PART 4: ANESTHETIC MANAGEMENT (Step-by-Step)

Preoperative Preparation

• NBM status: Standard pediatric guidelines (6h solids, 4h breast milk, 2h clear fluids) - avoid prolonged fasting (hypovolemia = tet spell risk)
• IV hydration if at risk: Begin maintenance IV fluids if any risk of dehydration
• Warm environment: Children lose heat rapidly; warm the OR in advance
• Equipment check: Age-appropriate ETT (cuffed 4.5-5.0 mm ID for 2-year-old), laryngoscope, resuscitation drugs drawn up and labeled, defibrillator

Premedication

• Oral midazolam: 0.5 mg/kg orally 30-45 min pre-op (max 15 mg) - widely used
• Oral/intranasal ketamine: Alternative or combination (IM ketamine 4-10 mg/kg if child is uncooperative)
• Atropine with IM ketamine to reduce secretions (20 mcg/kg IM)
• Avoid agents causing tachycardia alone (pure anticholinergics may not be ideal)

Monitors

• Pulse oximetry (pre-ductal and post-ductal if B-T shunt present)
• ECG (3-lead minimum; 5-lead preferred)
• Non-invasive blood pressure (cycle every 2-3 min minimum)
• EtCO2 (capnography - mandatory after intubation)
• Temperature
• Invasive arterial line (radial artery) - strongly recommended given high-risk cardiac status and need for real-time BP monitoring
• Precordial stethoscope (useful in children)

IV Access

• Two large-bore IV lines (ideally before induction if child is cooperative, or after inhalation induction)
• Strict air-bubble precautions: All lines must be bubble-free; right-to-left shunt allows paradoxical air embolism through VSD
• Aspirate before every injection

Induction

• Sevoflurane in O2/air mixture (avoid high FiO2 with N2O)
• Titrate cautiously - excessive depth causes SVR drop
• Right-to-left shunt slows uptake of inhalation agents (less pulmonary circulation)
• Establish IV access once asleep
• Note: Halothane theoretically better for TOF (less vasodilation than sevoflurane, maintains HR) but largely unavailable now

• Ketamine 1-2 mg/kg IV (agent of choice): maintains/increases SVR, maintains HR, does not increase PVR in children, safe in cyanotic CHD - well established per Morgan & Mikhail
• Supplement with fentanyl 2-3 mcg/kg IV for analgesia (reduces sympathetic response to intubation)
• Atropine 20 mcg/kg IV before induction (prevents vagal bradycardia)

• Ketamine 4-10 mg/kg IM + atropine 20 mcg/kg IM
• Onset within 5 minutes
• This is the safest approach for an agitated, crying child with TOF

Intubation

• Maintain oxygenation throughout
• Rocuronium 0.6-1 mg/kg IV for muscle relaxation (avoid histamine-releasing agents like atracurium)
• Avoid mivacurium (histamine release)
• ETT size: (age/4) + 4 = 4.5 mm, or use cuffed ETT 0.5 size smaller
• Confirm with capnography

Maintenance

• Sevoflurane or isoflurane in O2/air
• Avoid nitrous oxide: may raise PVR, displaces O2, causes bowel distension (worsens surgical field)
• Fentanyl infusion or intermittent boluses (1-2 mcg/kg) for analgesia
• Goal: normocapnia (EtCO2 35-40 mmHg) - avoid hypercarbia
• Ventilation: low airway pressures, adequate tidal volumes (6-8 mL/kg), avoid air-trapping
• Maintain adequate preload with IV fluids (normal saline or Hartmann's, 5-10 mL/kg/h maintenance)
• Keep warm (forced-air warmer, warm IV fluids)

Regional Analgesia

• Ilioinguinal/iliohypogastric nerve block (ultrasound-guided): 0.2-0.3 mL/kg of 0.25% bupivacaine or 0.2% ropivacaine - excellent for inguinal herniotomy
• Alternatively: Single-shot caudal block (0.75-1 mL/kg of 0.25% bupivacaine) - effective but causes sympathectomy
• Caution with caudal/spinal: Classic teaching avoids regional techniques in unrepaired TOF due to SVR reduction from sympathetic block, but caudal at low doses has been used. Ilioinguinal block preferred as it avoids systemic hemodynamic effects.
• Benefits: Reduces intraoperative opioid requirements, allows lighter general anesthesia

Muscle Relaxant Reversal

• Neostigmine 50 mcg/kg + glycopyrrolate 10 mcg/kg (preferred over atropine - more stable HR)
• Ensure full reversal before extubation

Emergence and Extubation

• Awake extubation preferred in most cases (protect airway)
• Ensure child is warm, comfortable, and pain-free before awakening (prevent crying/agitation)
• Keep child positioned (knee-chest if needed) if desaturation occurs

Postoperative

• HDU or ICU monitoring for minimum 12-24 hours
• Continuous SpO2 monitoring
• Analgesia: paracetamol + NSAIDs (ketorolac/ibuprofen) + regional block
• Avoid dehydration - maintain IV fluids until oral intake is adequate
• Cardiology review in recovery

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PART 5: MANAGEMENT OF INTRAOPERATIVE TET SPELL

This is a critical exam question - know the algorithm cold.

Pathophysiology of Tet Spell

Recognition During Anesthesia

• Sudden fall in SpO2
• Hypotension
• Decrease in EtCO2 (less pulmonary blood flow)
• Murmur disappears or softens (less flow through RVOT)
• Bradycardia or metabolic acidosis (late sign)

Treatment Algorithm

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PART 6: DRUGS TO AVOID IN TOF

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PART 7: SPECIAL CONCERNS FOR THIS CASE

Polycythemia and Coagulation

• Hematocrit often >55-60% in chronic unrepaired TOF
• Increased blood viscosity → risk of thrombosis
• Mild coagulopathy possible (factor deficiency, thrombocytopenia)
• Do not over-transfuse - worsen viscosity

Air Embolism Prevention

• All IV tubing must be primed and bubble-free
• Aspirate all stopcocks before injection
• Use air-eliminating filters if available

Antibiotic Prophylaxis

• Standard surgical prophylaxis (cefazolin 30 mg/kg)
• Endocarditis prophylaxis: Not routinely required for herniotomy, but per local guidelines

Glucose Management

• Small child with prolonged NPO risk
• Check glucose pre-op and intraoperatively
• Include dextrose in maintenance fluids if at risk

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PART 8: TABLE VIVA - LIKELY MD EXAM QUESTIONS

Table 1: TOF Hemodynamics vs. Anesthetic Goals

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Table 2: Induction Agent Comparison in TOF

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Table 3: Tet Spell - Trigger vs. Prevention vs. Treatment

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Table 4: Why Regional Anesthesia is Controversial in TOF

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Table 5: Key Differences - Repaired vs. Unrepaired TOF for Non-Cardiac Surgery

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Table 6: Emergency Drug Doses (for 12-14 kg child, 2 years)

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PART 9: POTENTIAL VIVA QUESTIONS AND MODEL ANSWERS

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Summary Mnemonic for TOF Anesthesia: "KAFE - MAPS"

• Ketamine for induction
• Avoid SVR drop
• FiO2 high / Fluids adequate
• Exclude air bubbles from lines
• Monitor SpO2 + EtCO2 + arterial line
• Avoid PVR increase (normocapnia)
• Premedication (keep child calm)
• Spell management ready (phenylephrine + position + fluid)

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