The Elderly:
Physiological changes associated with aging as well as altered drug sensitivity and metabolism place elderly patients at an increased risk of perioperative morbidity and mortality.33 Bag-mask ventilation may be more difficult in the edentulous patient, and limitations in cervical spine range of motion may make direct laryngoscopy and tracheal intubation more difficult. Elderly patients have an increased incidence of age-related co-morbid conditions as well as diminished organ function and reserve. Common comorbidities include CAD, hypertension, diabetes, CHF, and renal failure. Elderly patients are more sensitive to CNS depressants and are at risk of postoperative cognitive dysfunction and delirium.
Obesity:
The perioperative risk of complications is related to the degree of obesity, which is defined by the body mass index (BMI). Comorbidities commonly associated with morbidly obese patients include CAD, hypertension, OSA, and insulin resistant diabetes mellitus.34 The World Health Organization (WHO) obesity classification is listed in Table 3.5.
Morbidly obese patients may be difficult to ventilate using positive pressure with bag-mask ventilation (BMV). They are prone to rapid desaturation following induction of general anesthesia (see Fig. 9.1). The rapid desaturation is due to an increase in oxygen consumption as well as a restrictive lung disorder and is accompanied by a reduction in total lung capacity, functional residual capacity (FRC), and expiratory reserve volume. As a result, the FRC can fall below the closing capacity, resulting in small airway collapse even during normal ventilation in an awake obese patient. The onset of general anesthesia results in a further fall in the FRC.
In a small percent of patients with severe obesity, respiratory failure may result from central hypoventilation causing Pickwickian Syndrome. The clinical features of this syndrome include somnolence, hypoxia, hypercapnia, pulmonary hypertension, cor pulmonale, and polycythemia. The risk of aspiration is increased due to low gastric pH, increased abdominal pressures, and increased gastric volume. The obese patient may also face issues with difficult intravenous access, altered drug metabolism, and difficulty with mobilization. Anesthetic techniques, such as epidural analgesia, may be technically challenging to perform. The risk of epidural failure in the postoperative period is increased in obese patients secondary to catheter movement and dislodgement resulting from abundantly mobile and lax soft tissues.
Patients with Cancer:
Oncology patients commonly present for surgical procedures that may or may not be related to their cancer. In addition to the usual medical history, it is important to discern the type of cancer, staging and presence of metastases, and/or paraneoplastic syndromes. The patient should be asked about treatments received, including chemotherapy and radiation. Certain chemotherapy drugs (anthracyclines, herceptin) can affect cardiac contractility; hence, a review of the patient’s functional capacity and available cardiac investigations would be appropriate. If radiation is administered to the patient’s neck or chest, be sure to conduct a thorough airway examination as radiation fibrosis of the airway tissues is associated with an unanticipated difficult tracheal intubation (see Chapter 7).
OTHER KEY INFORMATION TO ELICIT
In addition to the review of systems, there are several other basic elements of the patient’s medical history that should be addressed.
Investigations:
Laboratory investigations should not be ordered routinely as part of the preoperative evaluation. Laboratory and diagnostic investigations should be ordered only when indicated by the patient’s medical comorbidities, drug therapy, or nature of the proposed procedure. The 2011 Canadian Anesthesiologists’ Society (CAS) Guidelines to the Practice of Anesthesia offers suggestions to guide preoperative testing (Table 3.6).
In 2007, the American College of Cardiology and the American Heart Association (ACC/AHA) revised their guidelines on perioperative cardiovascular evaluation and care for patients undergoing noncardiac surgery.1 Fig. 3.1 illustrates the ACC/AHA algorithm that can be used to guide investigation and management of patients with cardiovascular disease undergoing noncardiac surgery.
Fig. 3.1 Cardiac evaluation and care algorithm for non cardiac surgery based on active clinical conditions, known cardiovascular disease, or cardiac risk factors for patients 50 years of age or greater. Clinical risk factors* include ischemic heart disease, compensated or prior heart failure, diabetes mellitus, renal insufficiency and cerebrovascular disease. Consider perioperative beta blockade for populations in which this has been shown to reduce cardiac morbidity/mortality. ACC/AHA indicates American College of Cardiology / American Heart Association. HR = heart rate; LOE = level of evidence; MET = metabolic equivalent. Adapted from the ACC/AHA.
Summative Risk and The Risk of Anesthesia:
Understanding the extent of a patient’s disease is of paramount importance as many organ systems are directly affected by the delivery of anesthesia. Evaluation of a patient’s overall perioperative risk must consider the patient’s preoperative medical condition, the nature of the proposed surgical procedure, and the risks associated with anesthesia. Fortunately, anesthesia-related morbidity and mortality are rare.
It is difficult to make generalized statements about risk due to the wide variety of surgical procedures and anesthetic techniques combined with the diversity of a patient’s comorbid conditions. It is rare for patients to receive an anesthetic without undergoing a surgical procedure, which makes it a challenge to separate the relative contributions of anesthesia and surgery from the adverse outcomes. Generalized estimates of all-cause perioperative morbidity of 1:500 and anesthesia-related mortality of 1:13,000 have been relatively consistent over the past forty years.35
The question that needs to be answered is “What is the risk of this particular procedure in this particular patient who has these medical conditions and is receiving this specific anesthetic technique?” Numerous investigators have attempted to address this very complex question. Most of the work, however, addresses the operative risk according to the patient’s preoperative medical status.
Perioperative Risk Assessment:
Perhaps the oldest and simplest method of risk assessment is the American Society of Anesthesiologists (ASA) physical status classification system (Table 3.7).
ASA Physical Status Classification:
The ASA physical status classification originally proposed in 1941 and revised by Dripps in 196136 provides a simple clinical assessment of a patient’s preoperative physical