Obstetrical anesthesia: placenta previa
1. A patient who is near term arrives in the operating room urgently with very heavy bleeding. What is your differential diagnosis?
2. You are almost certain that she will need a cesarean section. How will you proceed immediately?
Drug interactions: halothane and epinephrine: Your colleague never uses halothane when epinephrine is to be injected intraoperatively.
1. Is this reasonable?
2. How great is the hazard?
3. What are some alternatives to the use of epinephrine?
4. What are some alternatives to the use of halothane?
Complications of endotracheal intubation
Three weeks following surgery with endotracheal intubation, a patient is still hoarse.
1. How do you determine whether or not it is related to the endotracheal tube?
2. Discuss the potential hazards of endotracheal tube intubation to the larynx and the trachea.
3. How does one minimize this risk?
4. What is the anatomy of the larynx?
The larynx is located at about level C5. It has three unpaired cartilages, the thyroid, cricoid, and epiglottis. There are three paired cartilages, the arytenoid, corniculate, and cuneiform. The arytenoids may be the only visible structures in an "anterior" airway, as they are the posterior attachment of the vocal cords.
The innervation consists of two nerves, the superior laryngeal nerve and the recurrent laryngeal nerve. Sensory innervation above the cords is from the internal branch of the superior laryngeal nerve, and the external branches are motor to the cricothyroid muscle. Below the cords, the recurrent laryngeal nerve is sensory, and is motor to all of the other muscles. The glossopharyngeal nerve is sensory to the tongue base and to the vallecula, where the curved laryngoscope contacts.
Arterial supply to the larynx is from the superior laryngeal branch of the superior thyroid artery, and also from the inferior laryngeal arteries that are from the inferior thyroid arteries.
5. What are intubation criteria?
A respiratory rate over 35 bpm, a vital capacity of less than 15 ml/kg in adults and less than 10 ml/kg in children, the inability to generate a negative inspiratory force of at least 20 mmHg, a paO2 less than 70 mmHg on an FIO2 of 40%, an alveolar/arterial gradient greater than 350 mmHg on an FIO2 of 100%, a paCO2 greater than 55 mmHg, and a dead space over 0.6 are all indications for endotracheal intubation.