Discuss the options for induction of anesthesia in a primary hip arthroplasty.
General anesthesia or neuraxial anesthesia can be per-formed for total hip arthroplasty. Neuraxial anesthesia includes spinal, epidural, or combined spinal/epidural anesthesia. When deciding on an anesthetic technique, the advantages and disadvantages need to be considered for each patient.
For general anesthesia, some of the advantages include a secured airway, excellent muscle relaxation, and the ability to extend the anesthetic for as long as the surgery takes. Disadvantages include a high incidence of postoperative nausea and vomiting, hemodynamic changes, and poor postoperative pain control. The advantages of neuraxial anesthesia include good postoperative pain control, decreased incidence of deep vein thrombosis, less nausea and vomiting, and decreased blood loss. Disadvantages include hemodynamic changes, possibility of postdural puncture headache, and possible airway management diffi-culty if excessive sedation is used or if there is a need to convert to general anesthesia in the middle of the procedure.
When planning any general anesthetic, options for securing the airway must be carefully considered. If there is no history of cervical arthritis, routine endotracheal intu-bation may be performed. However, it may be prudent to use a depolarizing muscle relaxant because of the possibil-ity of an unrecognized difficult intubation secondary to cricoarytenoid arthritis. If there is a history of cervical arthritis, endotracheal intubation with in-line cervical sta-bilization may be warranted. Fiberoptic intubation, either with the patient awake or after induction of anesthesia, may be the wisest option in selected patients. As in all potential difficult airway situations, it is imperative that the anesthesiologist be prepared with alternative methods of securing the airway should the initial plan fail.
Neuraxial anesthesia can also be performed safely but there are several considerations that need to be addressed:
· Duration of block: Spinal anesthesia, though quick and easy to perform, has a finite duration of action deter-mined by the local anesthetic used. Since there is no indwelling catheter, the duration of the block cannot be extended once the effects begin to wear off. An epidural in this setting has the advantage of the ability to prolong the effect of the block by the presence of a catheter that enables subsequent dosing. Though a combined spinal/epidural anesthetic is commonly used, it has the disadvantage that the epidural catheter’s efficacy will not be tested until the spinal anesthetic has begun to wear off during the procedure. If the catheter is not functioning, the anesthesiologist will be faced with a patient in the lat-eral decubitus position requiring conversion to a general anesthetic. In the patient with a difficult airway, it is probably prudent to perform an epidural (without a spinal) from the onset to ensure its efficacy. This is not completely fail-safe because despite initial success, epidurals occasionally become non-functional.
· Patient comfort: The lateral decubitus position is uncom-fortable for most patients and it is usually necessary to provide sedation. As the procedure progresses, patients tend to become restless despite sedation and it may be necessary to increase the sedation to the point where air-way obstruction may occur.
· Thromboembolism prophylaxis: The placement of neu-raxial anesthesia and removal of an epidural catheter needs to be coordinated with the surgeon’s plan for thromboembolism prophylaxis (see below).
· Length of procedure: Many anesthesiologists will have their own threshold for deciding whether to do general versus neuraxial anesthesia. A reasonable plan would be to do general anesthesia if the procedure is expected to last for more than 3–4 hours. This commonly occurs for revision hip arthroplasties as opposed to primary hip replacements. The length of the procedure will also depend on the surgeon.