chapter 30 Fundamentals of General Anesthesia
General anesthesia has been defined as an irregular, reversible depression of the higher centers of the central nervous system (CNS) that makes the patient unconscious and insensible to pain.1 Pallasch2 described general anesthesia as “hypnosis (sleep or loss of consciousness) accompanied by the loss of protective laryngeal reflexes (cough). Ideally, general anesthesia represents the simultaneous presence of analgesia (loss of pain), amnesia (loss of memory) and hypnosis along with reflex inhibition and loss of skeletal muscle tone which allows for safe surgical procedures.” When the CNS is depressed to the extent that consciousness is lost, changes occur in the physiology of the patient that would be life threatening in the absence of a “guardian” trained in the management of the unconscious patient. These changes include partial or complete airway obstruction, hypoxia, hypercapnia, loss of the ability to clear the tracheobronchial tree, respiratory depression, blood gas and pH changes, cardiovascular depression, and depressed or absent protective reflexes.
Since the introduction of the techniques of minimal, moderate, and deep sedation into clinical practice, the requirement for general anesthesia has diminished. Minimal and moderate sedation possess a number of advantages, not the least of which is the retention of consciousness and the ability of the patient to maintain his or her airway and protective reflexes. One of the inherent dangers of general anesthesia is that these three factors are lost, making it the obligation of the anesthesiologist to provide a patent airway and to protect the patient during the period of unconsciousness.
Several types of general anesthesia are recognized. The most frequent use of general anesthesia in dentistry is within the specialty of oral and maxillofacial surgery. The oral and maxillofacial surgeon has been responsible, in large part, for the development of outpatient or ambulatory general anesthesia using intravenous (IV) drugs, originally barbiturates (termed ultralight general anesthesia, where the patient is maintained in Guedel stage II of anesthesia) or conventional general anesthetic agents (with the patient maintained in Guedel stage III of anesthesia) (Table 30-1). As hospital costs rise, ambulatory general anesthesia has gained popularity within the medical profession. The dentist anesthesiologist, a dentist trained in anesthesiology (minimum of 2 years), has made ambulatory general anesthesia available to patients requiring nonoral surgical dental care, such as periodontics, endodontics, implants, and restorative procedures.
|Four stages of anesthesia are described.|
|Guedel based his observations on the following parameters:|
A third type of general anesthesia available to the dental patient is traditional inpatient general anesthesia. Whether the anesthesiologist is a dentist or a physician, the patient is admitted into the hospital and brought to the operating theater, where general anesthesia is induced and the dental procedure completed. The dentist performing the dentistry need not be trained in general anesthesia for this type of anesthesia to be used because the anesthesiologist assumes responsibility for inducing and maintaining the appropriate depth of anesthesia. Each of these types of general anesthesia is described in Chapter 31.
During ultralight general anesthesia with IV barbiturates (e.g., methohexital or thiopental) or, more commonly today, propofol, the use of local anesthesia is more critical to success. In ultralight general anesthesia, the level of unconsciousness (e.g., the depth of CNS depression) is kept minimal to hasten the patient’s postoperative recovery. However, when this happens, the patient may respond to noxious stimulation during the dental or surgical procedure.
To prevent this response, two things may be done: The level of CNS-depression may be increased and/or local anesthesia administered. Increasing the depth of general anesthesia through administration of additional drugs will prolong the recovery period, which in outpatient settings is undesirable. Through the administration of local anesthesia, response to painful procedures is prevented both during the operative procedure and, equally important, into the postoperative period.
In addition to monitoring equipment, other equipment is required for the administration of general anesthesia, including a laryngoscope, endotracheal tubes, and oropharyngeal or nasopharyngeal airways. The absence of adequate equipment either for monitoring or the administration of general anesthesia represents an absolute contraindication to the use of this technique.