Unilateral Subarachnoid Block for Ankle Arthrodesis in Patient on Long Term Amiodarone Therapy

Dear Sir,

Amiodarone, a class III antiarrhythmic agent, acts by prolongation of action potential and effective refractory period of the heart. Chronic usage of drug has been reported to cause pulmonary toxicity in 5-28% patients.¹ Fulminant life-threatening or fatal adult respiratory distress syndrome has been reported after general anesthesia in patients receiving long term amiodarone therapy, even in the absence of apparent preoperative pulmonary damage.²

A 67 year old male goldmine worker, a known case of COPD with pneumoconiosis was scheduled for left ankle arthrodesis at our hospital. Patient was receiving steroid and ipratropium bromide multidose inhalers for eight years. He was also on oral Amiodarone 100mg and anticoagulant Warfarin 2mg once a day for paroxysmal atrial fibrillation for five years. Tab.Verapamil 40mg was prescribed eight hourly for the recent episode of palpitation. Preoperative physical examination revealed BMI of 26 kg/m2 with a heart rate of 67 min-1 in sinus rhythm, blood pressure of 110/ 70 mmHg. Chest auscultation revealed loud P2 in the pulmonary area and a functional murmur in the tricuspid area. Bilateral basal crepitations were present. Chest roentgenogram revealed cardiomegaly and interstitial infiltrates. Electrocardiogram showed sinus rhythm with right ventricular hypertrophy and right axis deviation. Echocardiogram findings were normal left ventricle systolic function with ejection fraction of 40% with moderate pulmonary hypertension and tricuspid regurgitation. Pulmonary function studies showed FEV1=1.56 (61.5% predicted), and FVC=2.53 (74.9% predicted). CT thorax revealed multiple calcified mediastinal nodes and lung nodules.

Tab. Warfarin was stopped a week before surgery and the patient was heparinised during perioperative period. Preoperative INR was 1.2. Amiodarone (100mg) and Verapamil (40mg) was continued until the morning of surgery. Patient was fasted and premedicated. Baseline monitors (SpO2 / NIBP / ECG) were established. Central line was sited to follow the trend of central venous pressure. Patient was positioned in left lateral position and subarachnoid block was performed under aseptic precautions with 5mg of bupivacaine heavy and fentanyl 25μg after 12 hours of subcutaneous heparin. Patient was maintained in same position for 10 minutes and the measured sensory block was L1 on left side while he could ambulate his right leg. Central venous pressure, heart rate, blood pressure were closely monitored and maintained around baseline by administering crystalloids. The surgery lasted for 60 min and the patient did not need any anesthetic supplementation. The perioperative course was uneventful and the patient was shifted to high dependence unit for monitoring. He was discharged after 2 days and advised regular follow up.

The use of regional anaesthesia and avoidance of general anaesthesia is beneficial in patients with pneumoconiosis and pulmonary hypertension. Graded epidural, combined femoral and sciatic nerve blocks are attractive choices for lower limb procedures but they warrant larger volume of local anaesthetics.³ Several pharmacodynamic interactions have been described between amiodarone and class I antiarrythmic agent, lidocaine. Additive prolongation of QT interval, development of torsades de pointes, and a 30-50% increase in serum antiarrythmic concentration has been reported.⁴ Several cases of intraoperative sinus arrest, severe atropine-resistant bradycardia, and complete heart block have been reported in patients receiving amiodarone during anaesthesia.⁵ Single shot subarachnoid block with local anaesthetic has its pronounced effect on haemodynamics by decreasing SVR which may not be tolerated especially by cardiac patients on amiodarone and calaptin. Patients taking amiodarone have a state of non-competitive alpha and beta blockade. They, therefore have difficulty compensating for vasodilatation.⁶ Hence we decided to use a single shot unilateral subarachnoid block with 5mg of bupivacaine heavy with fentanyl 25μg. This maintained stable haemodynamics. A dose of bupivacaine above 8 mg is unlikely to maintain unilaterality. The effect of fentanyl is additive and so allows a small dose of bupivacaine combining the advantage of neuraxial block without the disadvantage of pronounced sympathetic block normally seen with spinal analgesia.