Anesthesia evaluation refers to the series of interviews, physical examinations, and laboratory tests that are generally used in North America and western Europe to assess the general fitness of patients scheduled for surgery and to determine the need for special precautions or additional testing. There is no universally accepted definition of anesthesia evaluation as of 2003; however, the Task Force on Preanesthesia Evaluation of the American Society of Anesthesiologists (ASA) has tentatively defined it as "....the process of clinical assessment that precedes the delivery of anesthesia care for surgery and for non-surgical procedures." Anesthesia evaluation is usually discussed in the context of elective or scheduled surgical procedures rather than emergency surgery .
Anesthesia evaluation is a relatively recent development in preoperative patient care. Prior to the 1970s, anesthesiologists were often given only brief notes or outlines of the patient's history and physical examination written by the operating surgeon or the patient's internist. This approach became increasingly unsatisfactory as the practice of anesthesiology became more complex. In the last four decades, the introduction of new anesthetics and other medications, laser-assisted surgical procedures, increasingly sophisticated monitoring equipment, and new discoveries in molecular biochemistry and genetics have made the anesthesiologist's role more demanding. During the 1980s and 1990s, some departments of anesthesiology in large urban medical centers and major university teaching hospitals began to set up separate clinics for anesthesia evaluation in order to improve the assessment of patients before surgery.
Anesthesia evaluation has several different purposes. The information that is obtained during the evaluation may be used to:
There are several parts or stages in a typical anesthesia evaluation. The evaluation itself may be done in the hospital where the operation is scheduled, or in a separate facility attached to the hospital. The timing of the evaluation is affected by two major variables: the invasiveness of the operation to be performed and the patient's overall physical condition. An invasive operation or procedure is one that requires the surgeon to insert a needle, catheter, or instrument into the body or a part of the body. Surgical procedures are classified as high, medium, or low in invasiveness. Procedures that involve opening the chest, abdomen, or skull are usually considered highly invasive. Examples of less invasive procedures would include tooth extraction , most forms of cosmetic surgery, and operations on the hands and feet.
The patient's physical condition is classified according to the ASA's six-point system as follows:
As of 2003, the ASA recommends that patients with severe disease be interviewed and have their physical examination before the day of surgery. Patients in good health or with mild systemic disease who are scheduled for a highly invasive procedure should also be interviewed and examined before the day of surgery. Patients in categories P1 and P2 who are scheduled for low- or medium-invasive procedures may be evaluated on the day of surgery or before it.
The first part of an anesthesia evaluation is the anesthesiologist's review of the patient's medical history and records. This review allows the anesthesiologist to evaluate the patient for risk factors that may increase the patient's sensitivity to the sedatives or other medications given before and during the operation; increase the danger of complications related to heart function and breathing; and increase the difficulty of treating such complications.
These risk factors may include:
The anesthesiologist is responsible for interviewing the patient during the anesthesia evaluation. The interview serves in part as additional verification of the patient's identity; cases have been reported in which patients have been scheduled for the wrong procedure because of administrative errors. The anesthesiologist will check the patient's name, date of birth, medical record number, and type or location of scheduled surgery for any inconsistencies. Although the anesthesiologist will ask for some of the same information that is included in the patient's written medical records, he or she may have additional questions. Moreover, it is not unusual for patients to recall significant events or details during the interview that were left out of the written records. The anesthesiologist will explain what will happen during the operation and give instructions about fasting, discontinuing medications, and other precautions that the patient should take before the procedure. The patient will have an opportunity to ask questions about choice of anesthetic and other concerns during the interview.
The physical examination will focus on three primary areas of concern: the heart and circulatory system; the respiratory system; and the patient's airway. Heart and lung function are evaluated because surgery under general anesthesia puts these organ systems under considerable stress. The usual tests performed to evaluate heart and lung fitness are an electrocardiogram (ECG) and chest x-ray (CXR). These tests may be omitted if the patient was tested within the previous six months and the results were normal. If the patient has an ECG and CXR as part of the anesthesia evaluation and the findings are abnormal, the doctor may order additional tests of heart and lung function. These may include stress or exercise tests; echocardiography ; angiography ; pulmonary function tests (PFTs); and a computed tomography (CT) scan of the lungs.
Assessment of the airway includes an examination of the patient's teeth, nasal passages, mouth, and throat to check for any signs of disease or structural abnormalities. Certain physical features, such as an abnormally shaped windpipe, prominent upper incisor teeth, an abnormally small mouth opening, a short or inflexible neck, a throat infection, large or swollen tonsils, and a protruding or receding chin can all increase the risk of airway problems during the operation. A commonly used classification scheme rates patients on a four-point scale, with Class I being the least likely to have airway problems under anesthesia and Class IV the most likely.
Laboratory tests are categorized as either routine, meaning that they are given to all patients as part of the anesthesia evaluation, or indicated, which means that the test is ordered for a specific reason for a particular patient. Routine preoperative laboratory tests include blood tests and urine tests. Blood samples are taken for white and red blood cell counts and coagulation studies; tests of kidney function, most commonly measurements of blood urea nitrogen (BUN) and creatinine; and measurements of blood glucose and electrolyte levels. Urine samples are taken to evaluate the patient's nutritional status, to test for diabetes or the presence of a urinary tract infection, and to determine whether the patient is dehydrated. Some hospitals will accept blood and urine tests performed within six weeks of the operation if the results were within normal ranges. Some facilities also routinely test urine samples from women of childbearing age for pregnancy.
Indicated laboratory tests include platelet counts, certain blood chemistry measurements, and measurements of blood hemoglobin levels. These tests are usually performed for patients with blood or endocrine disorders; persons taking blood-thinning medications; persons who have been treated with some types of alternative therapy; and persons who are known to have kidney or liver disorders.
The anesthesiologist may consult other doctors as part of the anesthesia evaluation in order to obtain additional information about the patient's condition. Consultations are often necessary if the patient is very young or very old; is being treated for cancer; or has a rare disease or disorder.
Patients can prepare for an anesthesia evaluation by gathering information beforehand to give the hospital or clinic staff. This information includes such matters as insurance cards and documentation; a list of medications presently taken and their dosages; a list of previous operations or hospitalizations, if any; the names and telephone numbers of other physicians who have been consulted within the past two years; information about allergies to medications, if any; the name and telephone number of a designated family member or primary contact; and similar matters.
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Rebecca Frey, Ph.D.