3Medical Fitness and Anaesthesia for Surgery

FFitness for general anaesthesia

Candidacy assessment must include the patient's general health and ability to undergo a general anaesthetic for the necessary mastoid surgery; implantation under local anaesthetic is described but constrains the soft-tissue dissection and is generally not recommended. Perioperative antimicrobial prophylaxis is recommended to cover skin and middle-ear flora, most commonly with first- or second-generation cephalosporins. A full medical history, otologic history and appropriate laboratory studies are obtained; aetiology of deafness is rarely a contraindication but a meningitis history must prompt planning for an ossified cochlea. Microscopic ear examination screens for active external or middle-ear disease, which may need staged treatment such as canal closure before or with implantation.[2009][2012]

TThe cardiac trap: long-QT and metabolic syndromes

Jervell and Lange-Nielsen syndrome pairs congenital severe-to-profound deafness with a prolonged QT interval and syncope, affects about 0.25% of people with profound congenital hearing loss, and can cause sudden death if missed. Authorities recommend that all children with congenital or early-onset hearing loss have a 12-lead ECG to screen for JLNS, with beta-blockade started before anaesthetic induction and arrhythmias fully controlled. Patients with JLNS can be implanted safely provided special precautions are observed, including cardiac monitoring for 48 hours perioperatively and perioperative beta-blockade. Mitochondrial syndromes such as MELAS warrant preoperative ECG and intraoperative cardiac monitoring for cardiomyopathy and conduction defects, attention to oxygenation and glucose to avoid lactic acidosis, and avoidance of malignant-hyperthermia triggering drugs.[2009][2002]

FAnaesthetic technique and facial nerve monitoring

The standard is general endotracheal anaesthesia with an epinephrine-compatible agent in the otologic position, the table turned away from the anaesthesiologist and the head turned away from the surgeon. Long-acting muscle relaxants are strictly avoided because they abolish the electromyographic facial nerve monitoring used throughout the case; a short-acting relaxant for intubation only is acceptable. Facial nerve monitoring electrodes are placed in the orbicularis oris and orbicularis oculi before prep, and the anaesthesia team must know that paralytics are off so monitoring quality is preserved. Local infiltration of the incision with lidocaine and 1:100,000 epinephrine reduces bleeding and pain and lets the patient be kept relatively light during the case. Deep extubation is favoured to avoid straining and Valsalva, and intravenous antiemetics reduce postoperative nausea and vomiting.[2016][2009]

CThe small child and the syndromic child

Anaesthetic risk is higher in very young children, especially with coexisting illness, so an experienced paediatric anaesthesiologist is recommended, particularly for the youngest infants. Blood loss must be minimised given the small circulating volume of infants and the high marrow content of the immature mastoid; imaging in 7-to-12-month infants shows greater marrow but adequate pneumatisation for safe landmark identification. Because the mastoid tip is undeveloped, the tympanic ring narrow and subcutaneous tissue scant, the main trunk of the facial nerve lies just below the skin in the young child and can be injured by a poorly placed incision. Syndromic children carry stacked risks: CHARGE association brings airway and cardiac anomalies plus aberrant temporal-bone anatomy and a high jugular bulb, and inner-ear malformations raise the chance of a perilymph gusher. Around 2.5 cm of electrode-lead redundancy is left in the mastoid to accommodate head growth, since from age 1 to adulthood the mastoid lengthens about 2.6 cm in males and 2.0 cm in females.[2009][2007]