2-4. THE ANESTHETIC AGENT
a. The preoperative patient is usually interested in and concerned about the anesthesia that he will receive. He has probably heard a lot of negative talk from family, friends, and the news media about anesthesia and has usually formed an opinion as to the good or bad points of various methods in use. It is strongly advised that the anesthesiologist/anesthetist and the operating room nurse make a preoperative visit to the patient. This visit will help to allay many of the fears that exist in the patient's mind, will help in building confidence, and will enable the patient to recognize familiar faces in the operating room.
b. Before surgery, the anesthesiologist/anesthetist reviews the patient's chart, evaluates the laboratory data and diagnostic studies, verifies the surgical procedure, examines the patient, and discusses the option for anesthesia and the attendant risks. The following factors are important in selecting an anesthetic agent:
(1) Type of surgery.
(2) Depth and extent of anesthesia required.
(3) Anticipated length of the procedure.
(4) Patient's condition.
(5) Patient's previous experiences with anesthesia.
(6) Preferences of the anesthesiologist/anesthetist and the patient.
(7) Available equipment.
(8) Skill of the anesthesiologist/anesthetist.
(9) Age of the patient.
FACTORS CONSIDERED WHEN SELECTING AN ANESTHETIC AGENT
The anesthesiologist/anesthetist must consider the following factors when selecting an anesthetic agent.
a. Smoking and drinking habits of the patient.
b. Presence of diseases that effect the:
(1) Pulmonary function/exercise tolerance.
(2) Hepatic function (the liver is involved in removal of most agents).
(3) Renal function.
(4) Cardiovascular function.
c. Medication history (medications that the patient is currently taking).
CLASSIFICATION OF ANESTHETIC AGENTS
As mentioned in Lesson 1, anesthesia is a partial or complete loss of sensation, with or without loss of consciousness, as a result of a disease, an injury, or administration of a drug. Inhalation anesthesia has been classified as the most popular because of its controllability. The intake and elimination of the agent is, in large measure, affected by pulmonary ventilation. The three classifications of anesthetic agents are general, regional or block, and local.
a. General Anesthetic.
(1) Definition. Produces loss of consciousness and thus affects the total person.
(2) Routes of administration.
(b) Intravenous injection.
(c) Rectal (not used very much in today's practice).
(3) Characteristics of the ideal general anesthetic.
(a) Produces analgesia.
(b) Produces complete loss of consciousness.
(c) Provides a degree of muscle relaxation.
(d) Obtunds reflexes.
(e) Is safe and has minimal side effects.
| NOTE: No single anesthetic meets all these criteria. A combination of several agents is usually used to obtain the optimal effects of each and decrease likelihood of toxicity. |
(4) Uses of general anesthesia.
(a) Major head and neck surgery.
(b) Intracranial surgery.
(c) Thoracic surgery.
(d) Upper abdominal surgery.
(e) Upper and lower extremity surgery.
b. Regional or Block Anesthetic.
(1) Definition. Anesthetizes large regions of the body.
(a) Spinal/subarachnoid. Anesthetic is injected into the cerebral spinal fluid (CSF) in the subarachnoid space; anesthetics from the umbilicus downward.
(b) Epidural block. Anesthetic is injected into the epidural space; anesthetizes from the umbilicus downward.
| NOTE: The choice of using a spinal/subarachnoid anesthetic versus an epidural block is based on the factors stated in paragraph 2-5. |
(c) Axillary block. Used to anesthetize an upper extremity.
c. Local Anesthetic.
(1) Definition. Administration of anesthetic directly into the tissues.
(2) How used. Local anesthetic can be injected intradermally or applied topically to the mucous membranes in the nasopharynx, mouth, vagina, and/or rectum.