CHAPTER 17 Preoperative Evaluation
The preoperative evaluation consists of gathering information about the patient and formulating an anesthetic plan. The overall objective is reduction of perioperative morbidity and mortality. Ideally the preoperative evaluation is performed by the person who will administer the anesthetic.
The anesthesiologist should review the surgical diagnosis, organ systems involved, and planned procedure. Important features include personal interview, physical examination, and review of medical records. Important questions involve medications, drug allergies, substance abuse (e.g., cigarettes, alcohol, illicit drugs), review of systems, and prior anesthetic experience (i.e., history of difficult intubation, delayed emergence, malignant hyperthermia, prolonged neuromuscular blockade, or postoperative nausea and vomiting). From this evaluation the anesthesiologist decides if any preoperative tests or consultations are indicated and then formulates an anesthetic care plan.
It has been found that care plans were altered in 20% of all patients (including 15% of American Society of Anesthesiologists [ASA] class 1 and 2 patients) because of conditions identified at the preoperative evaluation. The most common conditions resulting in changes were gastric reflux, insulin-dependent diabetes mellitus, asthma, and suspected difficult airway. These findings indicate that, whenever possible, it is preferable in all patients to do the preoperative evaluation before the day of surgery.
Informed consent involves the communication of the anesthetic plan in terms the patient understands and covers everything from premedication and preoperative procedures to intraoperative management and postprocedural care (e.g., management of pain, nausea, and vomiting). The alternatives, potential complications, and risks vs. benefits are discussed, and the patient’s questions are answered. Preoperative evaluation and informed consent establish a trusting doctor-patient relationship that significantly diminishes patient anxiety and measurably influences postoperative recovery and outcome.
The ASA classification was created in 1940 for the purposes of statistical studies and hospital records. It is useful both for outcome comparisons and as a convenient means of communicating the physical status of a patient. Unfortunately it is imprecise, and a patient often may be placed in different classes by different anesthesiologists. In addition, the higher ASA class only roughly predicts anesthetic risk. The six classes are:
|Ingested Material||Minimum Fasting Period (Hours)|
|Clear liquids (examples include water, fruit juices without pulp, carbonated beverages, clear tea and black coffee; clear liquids should not include alcohol)||2 hours|
|Breast milk||4 hours|
|Infant formula||6 hours|
|Nonhuman milk||6 hours|
|Light meal (a light meal typically consists of toast and clear liquids)||6 hours|
|Full, heavy, fatty meal||8 hours|
These guidelines should be modified according to the patient’s disease state and airway difficulty. Current fasting guidelines for pediatric patients are as follows: clear liquids up to 2 hours before surgery; breast milk up to 4 hours before surgery; and solid foods, including nonhuman milk and formula, up to 6 hours before surgery.
7 What are the appropriate preoperative laboratory tests? Which patients should have an electrocardiogram? Chest radiography?
No evidence supports the use of routine laboratory testing. Rather, there is support for the use of selected laboratory analysis based on the patient’s preoperative history, physical examination, and proposed surgical procedure (Table 17-2). Unless there has been an intervening change in status, electrocardiogram and chest radiograph obtained within 6 months of the procedure need not be repeated. Likewise, chemistries and hemoglobin/hematocrit values obtained within 1 month are acceptable in the stable situations. Coagulation studies should be no more than 1 week old.
|Electrocardiogram||Cardiac and circulatory disease, respiratory disease, advanced age|
|Chest radiograph||Chronic lung disease, history of congestive heart disease|
|Pulmonary function tests||Reactive airway disease, chronic lung disease, restrictive lung disease|
|Hemoglobin/hematocrit||Advanced age, anemia, bleeding disorders, other hematologic disorders|
|Coagulation studies||Bleeding disorders, liver dysfunction, anticoagulants|
|Serum chemistries||Endocrine disorders, medications, renal dysfunction|
|Pregnancy test||Uncertain pregnancy history, history suggestive of current pregnancy|
The definition of advanced age is vague and should be considered in the context of that patient’s overall health.
* At least 50% of the task force experts agreed that the listed tests were beneficial when used selectively. Because of a lack of solid evidence in the literature, these indications are somewhat broad and vague and limit the clinical use of the guidelines.
There is no specific minimum; it depends on the clinical setting. Screening baseline hemoglobins for surgeries without significant blood loss do not add any value to estimations of perioperative risk or adverse outcomes. The potential blood loss and oxygen demands associated with the proposed surgical procedure must be considered, as well as patients’ medical conditions that may place them at increased risk for ischemia, including coronary atherosclerosis, cerebral insufficiency, or renovascular disease. Patients with advanced pulmonary disease also tolerate anemia poorly. Elderly patients with anemia often have a poorer functional status, longer hospitalizations, and higher mortality at 1 year.