Anesthesia for pituitary surgery follows the same principles as those for general neuroanesthesia and includes maintenance of cerebral perfusion and oxygenation while providing suitable surgical conditions and rapid emergence to allow early neurologic assessment. This review concentrates on the specific issues regarding pituitary surgery.
Sedative premedication is often withheld in patients undergoing neurosurgi-cal procedures. However, if anxiolysis is deemed necessary, a small dose of benzodiazepine is appropriate. It must be remembered that all sedative drugs exacerbate obstructive sleep apnea and should be avoided in those patients suspected of having the condition. It is common practice to administer hydrocortisone (100 mg) on induction of anesthesia, although the need for this is being increasingly questioned.
Maintenance of the airway and ventilation with a bag and mask is generally straightforward in patients with acromegaly although large face pieces and oral airways are necessary. Similarly, tracheal intubation, in our experience, is usually uneventful if long-bladed laryngoscopes are used. However, severe involvement of laryngeal mucosa and vocal cords may make tracheal intubation impossible with conventional laryngoscopes. In such cases, fiber-optic tracheal intubation is a safe alternative. Some authorities suggest tracheostomy for such patients, and equipment for this procedure should be available should the need arise. After intubation, the tracheal tube must be securely fixed in a suitable position and the mouth and pharynx packed to prevent passage of blood into the glottis and stomach.
Adequate vasoconstriction of the nasal mucosa is essential for providing reasonable conditions for transsphenoidal surgery. This need becomes even more important if an endoscopic technique is being used. Traditionally, mixtures of cocaine and epinephrine have been used, but the high incidence of subsequent arrhythmias has resulted in the search for safer alternatives; a mixture of the sympathomimetic xylometazoline and lidocaine produces effects equivalent to those of cocaine.
A subarachnoid lumbar drain may be inserted in patients with macroadenomas with significant suprasellar extension. This has two purposes. Introduction of 10 mL aliquots of 0.9% saline during surgery increases pressure within the lateral ventricles and produces prolapse of the suprasellar portion of the tumor into the operative field. In addition, should the dura be breached during the procedure, CSF can be drained postoperatively through the catheter.
The choice of anesthetic technique used falls outside the remit of this chapter but follows that used for other neurosurgical procedures. There are periods of intense surgical stimulation while the surgeon gains access to the pituitary fossa, and these are accompanied by episodes of hypertension. The short-acting opioid drug remifentanil is ideally suited to offset the blood pressure changes and its short context-sensitive half-life ensures rapid recovery. However, if this agent is used, it is vital to administer a long-acting analgesic (such as morphine) before the end of surgery to provide adequate analgesia on emergence. Patients should be monitored as for all neurosurgical procedures.
After surgery, extubation of the trachea is carried out after return of spontaneous ventilation, removal of the throat pack, and careful suctioning of the pharynx.
Patients undergoing uncomplicated transsphenoidal surgery generally return to the general ward after a period in the recovery room; those who have undergone cranial surgery are nursed in the intensive care unit for 24 h.
Postoperative management consists of careful airway management, provision of adequate postoperative analgesia, appropriate fluid and hormone replacement, and careful monitoring for postoperative complications. The latter include the development of diabetes insipidus, (DI) and hyponatremia and are discussed in Chapter 11 and 12.
Maintenance of a clear airway in those patients undergoing transsphenoidal surgery may be difficult in the immediate postoperative period. The presence of blood within the pharynx, the distorted upper airway anatomy of the patient with acromegaly patient and the use of nasal packs all contribute to compromise airway patency. Acute pulmonary edema after extubation has been reported in this group of patients. It is therefore vital that patients with compromised airways are nursed in a high-dependency area where close monitoring of ventilation can be carried out.
Although traditionally codeine phosphate has been the drug of choice to produce postoperative analgesia after neurosurgery, recent work has shown that morphine produces more effective and longer lasting analgesia; in addition,morphine is not associated with an increased rate of side effects. It is rapidly replacing codeine as the first-line drug postoperatively.
Most centers continue to prescribe regular hydrocortisone during the postoperative period, although this may be unnecessary for some patients. Most units performing several hypophysectomies have their own protocols (drawn up with their endocrinology colleagues) for hormone replacement.
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