Brain Abscess Drainage in a Case of Uncorrected Tetralogy of Fallot Under Scalp Block and Dexmedetomidine

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To JNA Readers:
Tetralogy of Fallot (TOF) consists of ventricular septal defect, right ventricular outflow obstruction, right ventricular hypertrophy, and an overriding aorta. It contributes to 13% to 70% of all brain abscess cases.1 We present a case of excision of parietal abscess in a 15-year-old male patient with uncorrected TOF under scalp block and dexmedetomidine.
A 15-year-old male patient with a diagnosis of TOF since 10 years had fever, vomiting, headache, and left-sided hemiparesis for 15 days, with dyspnea on exertion grade II since 5 years, without a history of cyanotic spells. He was febrile, had clubbing grade III, central cyanosis, and grade III ejection systolic murmur at the pulmonary area. GCS was 15/15.
His investigations revealed a hemoglobin level of 21.7 g/dL, and a hematocrit level of 76% with INR 1.5. All other investigations were normal. ABG revealed compensated respiratory alkalosis with PaO2 of 50 mm Hg and SpO2 on air of 78%. Electrocardiography showed right ventricular hypertrophy with right axis deviation. Echocardiography revealed TOF, severe pulmonary stenosis with a gradient of 60 mm Hg, and large 12-mm malaligned bidirectional VSD. CT scan of the brain showed large 54×44×30 mm abscess in the right parietal region with mass effect and minimal midline shift.
The patient was scheduled for craniotomy for excision of brain abscess. He underwent phlebotomy a day prior. All intravenous lines were deaired. He was hydrated with Ringer’s lactate at a dose of 2 mL/kg/h, and ceftriaxone 500 mg IV was administered for infective endocarditis prophylaxis. Standard monitors were attached. Preinduction vitals were as follows: blood pressure 118/70 mm Hg and pulse 72/minute. SpO2 was 78% on air, which improved to 85% with oxygen supplementation (FiO2 0.5). Midazolam 0.03 mg/kg and fentanyl 2 μg/kg IV were administered as premedication. A 16/18 G peripherally inserted central line and left radial arterial line were secured under local anesthesia for invasive monitoring. Dexmedetomidine infusion at 0.5 μg/kg/h was started without a loading dose. Scalp block was administered with 20 mL of 0.75% ropivacaine without epinephrine. Spontaneous respiration with 50% oxygen and stable hemodynamics with CVP 6 to 8 cm H2O were maintained throughout the procedure. Intraoperative course was uneventful.
Polycythemia-induced cerebral infarcts, bypass of pulmonary phagocytosis, compromised immunity, and paradoxical air emboli contribute to brain abscess in these cases. Perioperative dehydration because of vomiting, fever, starvation, and diuretics should be avoided to prevent hyperviscosity and thromboembolism. Hematocrit level was >65% and hemoglobin level was >20 g/dL, with symptoms of hyperviscosity, which is an indication for phlebotomy.2 Correction of deranged coagulation, maintenance of fluid and acid-base balance, prevention of paradoxical air embolism by deairing intravenous lines, and infective endocarditis prophylaxis3 are recommended.
Our anesthetic goals were to prevent right to left shunt and cyanotic spells by maintaining systemic vascular resistance (SVR), decreasing pulmonary vascular resistance (PVR), and providing mild myocardial depression. We preferred administering a scalp block with dexmedetomidine infusion and spontaneous ventilation over general anesthesia to avoid a sudden fall in SVR because of anesthetic drugs, increase in PVR because of positive pressure ventilation, hemodynamic changes because of polypharmacy, and sympathetic stimulation during laryngoscopy, as well as extubation. This technique provided excellent analgesia and decreased the chances of postoperative hypoxia. Ropivacaine, being less cardiotoxic, was preferred for scalp block, without epinephrine to prevent tachycardia and arrhythmia. Dexmedetomidine provides sedation, analgesia, stable hemodynamics, with minimal respiratory depression and minimal effect on intracranial dynamics. Its loading dose was avoided to prevent a fall in SVR. Senzaki et al4 reported dexmedetomidine use for management of hypercyanotic spells as a 0.2 μg/kg/h infusion without a loading dose. Dexmedetomidine with ketamine use for patients of uncorrected TOF is reported.

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