KEY POINTS

1. Successful local anesthesia requires proper patient selection. Patients with chronic cough, shortness of breath while lying flat, parkinsonian head tremor, Alzheimer's disease, or claustrophobia may be very difficult to manage with regional anesthesia.
2. Disadvantages of peribulbar blocks versus retrobulbar blocks include larger injected volumes, slower onset, and vertical diplopia caused by myotoxicity of the inferior rectus muscle.
3. The practice of having the patient look upward and inward during a block brings the optic nerve and vascular structures closer to the needle and thereby increases the risk of retrobulbar hemorrhage, optic nerve injury, and central apnea from brainstem anesthesia. It is safer to have the patient look straight ahead.
4. The oculocardiac reflex is a trigeminal-vagal reflex response manifested by cardiac arrhythmias and hypotension. Pain, pressure, or manipulation of the eye may elicit it. If arrhythmias persist, treat with intravenous atropine and local injection of lidocaine.
5. Gas bubbles such as air, sulfur hexafluoride (SF₆ ) or carbon octofluorine (C₃ F₈ ) are used in vitreoretinal surgery. Nitrous oxide will enter gas bubbles and cause a dangerous increase in intraocular pressure. Nitrous oxide should be avoided when a gas bubble is to be placed and for 4 weeks afterward or until the bubble has been absorbed.
6. Bilateral recurrent laryngeal nerve injury is one mechanism of bilateral vocal cord paralysis. The recurrent laryngeal nerves are vulnerable to injury during surgery. They are especially likely to be injured during thyroid and cervical spine surgery. Such patients may require a tracheostomy.
7. Laryngospasm is reflex closure of the upper airway from spasm of the glottic musculature. Applying sustained positive pressure and increasing the depth of anesthesia can often disrupt the laryngospasm. Sometimes muscle relaxation is needed. Failure to treat laryngospasm in a timely manner can lead to negative-pressure pulmonary edema.

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8. Difficult airways can be classified into difficult intubations and compromised airways. Difficult intubations are usually caused by anatomic abnormalities such as micrognathia, limited jaw motion, congenital syndromes, obesity, acromegaly, or cervical spine problems. A compromised airway implies partial obstruction to airflow and the risk of total obstruction if the airway narrows further. All compromised airways are difficult intubations, but not all difficult intubations occur in patients with compromised airways.
9. Lasers can ignite materials used in anesthesia practice. The CO₂ laser can penetrate an endotracheal tube and ignite a fire, supported by oxygen and N₂ O. With the use of recommended equipment, techniques, and gas mixtures, airway fires should be rare. During laser surgery on the airway, not more than 30% oxygen in nitrogen or helium should be used. Protected endotracheal tubes reduce the risk of fire.
10. Changing a tracheotomy tube after a fresh tracheotomy can be dangerous but may be required. The new tube may enter a false passage. The resulting subcutaneous emphysema soon removes all possibility of easily reestablishing the airway.
11. For the first week or so, all tube changes should be carried out in the operating room by an experienced surgeon and anesthesiologist under good lighting with a full set of surgical instruments. A fiberoptic bronchoscope can confirm tracheal placement before attempting positive-pressure ventilation.