Principles of anesthesia

40.1

Anesthesia: safety, comfort, and facilitation of the procedure

The anesthesiologist is a key member of the team conducting the intraoperative neurophysiology (ION), whether the monitoring is surgical in the operating room, or procedures such as neurovascular embolization, in the interventional radiology suite. The anesthesiologist works to insure the safety and comfort of the patient through management of the patient’s medical issues (e.g., heart disease and diabetes) and management of physiological variables to optimize organ safety (e.g., blood pressure and organ perfusion). In addition, the anesthesiologist participates in maintenance of a position that facilitates the procedure, while reducing the risk of iatrogenic injury. Finally, the anesthesiologist attempts to identify and maintain an anesthetic pharmacologic state that is compatible with ION . Each of these factors directly affects the ION such that their management is key to the health of the tissue at risk and the success of the monitoring. When monitoring signals change, the anesthesiologist should participate to help identify the etiology of the change . If adverse neurological conditions are suggested, the anesthesiologist should discuss with the surgeon or proceduralist and monitoring professionals to determine if altering management could reduce the neural risk [e.g., adjusting position, improving the physiological management, such as raising the blood pressure, or using pharmacologic management to reduce risk (e.g., steroids or barbiturates as appropriate)].

40.2

Medical and physiological management

As the “internist in the operating room,” the anesthesiologist needs to manage those patient issues that are key to the general health of the patient and subsequently the health of the neural tissues at risk. Physiological control is part of normal anesthetic management and, to some extent, is used to guide the pharmacologic administration. The physiological monitors that the anesthesiologist normally uses can be used to gauge the impact of physiological factors on the ION. Many of these variables directly impact the health of the organ tissues, and values of these parameters should be available to the ION team during the procedure.

A variety of reviews are available that discuss the impact of physiological changes on monitoring . A good example is blood pressure, which may be manipulated for the purposes of the procedure (e.g., deliberate hypotension or hypertension). Since tissue ischemia can lead to neural dysfunction and injury, it is common for the anesthesiologist to raise the blood pressure during presumed neural ischemia to reduce the risk of injury. Other physiological parameters may include localized and global temperature, vascular spasm, and oxygen carrying capacity.

40.3

Patient positioning

The anesthesiologist usually participates and assesses the positioning of the patient during the procedure. In preparation for the surgery the anesthesiologist cooperates to ensure good head, neck, and extremities positions (especially during sitting, lateral, or prone positions), in addition to inspecting the mouth to make sure of uncompromised tongue or lips. In some cases the ION changes may signal that an unfavorable position is occurring with undue stress on blood vessels or nerves that could lead to injury . A common example of this is a compromised arm placement leading to brachial plexus or peripheral nerve injury. Changes related to patient’s position may start in the early stages of the procedure such as extreme head positioning to the side or flexion of the neck, such as craniotomies or posterior cervical surgeries. Changes may also occur at later stages such as unintended changes in the positions of one or more extremity or due to sagging shoulders as a result to surgical decompressions during high-spine surgeries.

40.4