The prone position is used for spinal cord, occipital lobe, craniosynostosis, and posterior fossa procedures. The prone position has also been referred to, aptly, as the Concorde position because, for cervical spine and posterior fossa procedures, the final position usually entails neck flexion, reverse Trendelenburg positioning, and elevation of the legs, usually with pillows. This orientation serves to bring the surgical field to a horizontal position.
Before turning the patient to the prone position, the anesthesiologist should ensure that the intravenous catheter and endotracheal tube are secure and that appropriate personnel are available to prevent injury during the turn. The anesthesiologist should have a plan for detaching and reattaching monitors in an orderly manner to prevent an excessive monitoring “window.” Awake tracheal intubation and prone positioning can be employed in patients with an unstable cervical spine in whom an unchanged neurologic status should be confirmed before induction of anesthesia in the final surgical position. It is also occasionally performed in very obese patients.
The head can be positioned in a pin head holder (applied before the turn), a horseshoe headrest, or a disposable foam headrest. Complications of the prone position to which there must be constant attention are retinal ischemia and blindness from orbital compression. This problem may be compounded by low arterial pressure, low hematocrit level, and poor cerebral venous drainage. 56 It must be intermittently ascertained, such as every 15 minutes and after any surgery-related head/neck movement, that pressure has not come to bear on the eye. Various degrees of pressure necrosis of the forehead and maxillae can also occur, especially during prolonged spinal procedures. Other pressure points to be checked include the axillae, breasts, iliac crests, femoral canals, genitalia, knees, and heels. An antisialogogue, such as glycopyrrolate, may help to reduce loosening of tape used to secure the endotracheal tube.
An objective during prone positioning, especially for lumbar spine surgery, is the avoidance of inferior vena caval compression. Impairment of vena caval return diverts blood to the epidural plexus and increases the potential for bleeding during laminectomy. This avoidance is an objective of all the spinal surgery frames and is accomplished very effectively by both the Relton-Hall and the Andrews variants. This does, however, introduce a risk of air embolism, 57 although clinical occurrences have been very infrequent.
There should be attention to preventing injury to the patient‘s tongue in the prone position. With both cervical and posterior fossa procedures, it is frequently necessary to flex the patient‘s neck substantially to facilitate surgical access. This reduces the anteroposterior dimension of the hypopharynx, and compression ischemia of the base of the tongue (as well as the soft palate and posterior wall of the pharynx) can occur in the presence of foreign bodies (endotracheal tube, esophageal stethoscope, oral airway). The consequence is “macroglossia” and unexpected postextubation airway obstruction. Accordingly, unnecessary paraphernalia in the pharynx should be avoided. Omitting the oral airway entirely is unwise because the tongue may then protrude between and be trapped by the teeth as progressive swelling of facial structures occurs during a prolonged procedure with the patient in the prone position. A bite block akin to those used with laryngeal masks prevents this problem without adding bulk to the hypopharynx.
Factors contributing to spinal cord infarction occurring in surgery performed in the prone position 1).