Presentation of occult Chiari I malformation following spinal anesthesia
A 60 year old ASA III female patient (BMI: 40 kg/sq. m) was scheduled for left total knee replacement. Her past history was significant for morbid obesity, hypertension and on regular medications. She had past history of snoring but denied sleep studies. She had uneventful multiple General anaesthesia (GA) previously. She was evaluated for syncope while coughing 3 months back but her Holter monitoring and bilateral carotid Doppler studies were negative. Pan endoscopy done to evaluate her dysphagia revealed no abnormality. Her airway and physical examination were unremarkable. Her blood investigations were normal. Chest X-ray revealed cardiomegaly and electrocardiogram showed left ventricular enlargement. Moderate concentric left ventricular hypertrophy with inferior wall motion abnormality with ejection fraction of 56% was documented by transthoracic echocardiogram. Anaesthetic concerns were discussed and patient was consented for regional anaesthesia, subarachnoid block (SAB) along with left femoral nerve block.\nIn the operating room, baseline monitors (pulsoximetry, non-invasive blood pressure and electrocardiogram) were established. To avoid anxiety, 2 mg of i.v midazolam was administered. Under aseptic precautions, SAB was performed with 12.5 mg of bupivacaine and 100 mcg of morphine using 27G atraumatic spinal needle. She had an adequate surgical block with the sensory blockade to the level of T10 dermatome level. No further sedatives were given since she was drowsy with the initial dose of midazolam. However, she was responding to verbal commands with stable vital signs. The rest of the intraoperative period was unremarkable and transferred to post-anaesthetic care unit (PACU) subsequently.\nIn the PACU, she continued to be very drowsy, with worsening upper airway obstruction. There was an occasional drop in oxygen saturation below 90% despite oxygen supplementation. Arterial blood gas analysis done 2 hours later showed hypercapnic respiratory failure with pH of 7.28, PaCO2 65 mmHg and PaO2 84 mmHg. Patient's trachea was intubated and lungs were ventilated in view of gradual deterioration of consciousness, airway protection and to facilitate ventilatory support. Oxygenation and ventilation were maintained easily after intubation (pH 7.34, PaCO2 38 mmHg, PaO2 148 mmHg, inspired O2 40% and PEEP 5 cm H2O). She was transferred to ICU and gradually weaned over next 36 hours.\nFollowing extubation, she developed difficulty in swallowing which persisted beyond 48 hours. She also complained of visual disturbance in left eye and syncope while coughing. However, she could ambulate on the floor. Ophthalmologist, neurologist and otolaryngologist consultations were done and magnetic resonance imaging (MRI) of the brain was done.\nMRI brain showed CM-I with 17 mm cerebellar tonsillar herniation below the foramen magnum compressing lower medulla without hydrocephalus []. Neurosurgeons were consulted. They recommended conservative management followed by surgery at a later date. The symptoms improved with conservative management over a period of 2 weeks. The sleep study performed 2 months later was consistent with moderate-severe OSA and continuous positive airway pressure (CPAP) therapy was instituted. She had an uneventful posterior fossa decompression for CM-I after 3 months. She was symptomatically better and advised regular follow-up.