Perioperative risk assessment should also seek to determine the patient’s functional capacity. An assessment of an individual’s capacity to perform a spectrum of common daily tasks has been shown to correlate well with maximum oxygen uptake by treadmill testing, i.e., ergometric exercising.18 A patient classified as high risk because of known CAD but who is asymptomatic and runs 30 minutes daily, clearly has good functional capacity. In contrast, a patient without a history of cardiovascular disease but poor functional capacity may present a perioperative risk. Functional capacity is expressed in metabolic equivalents (METs).
One MET is defined as baseline oxygen demand by a 40-year-old, 70-kg, man in a resting state (i.e., 3.5 ml of oxygen per kg per minute) without experiencing shortness of breath, diaphoresis, pallor, and tightness in the chest. A person who can climb two flight of stairs has a functional capacity of ≈4 METs, a person who can participate in moderately strenuous recreational activities, e.g., golf, bowling, dancing, or doubles tennis, has a functional capacity of ≈8 METs, while a person who can participate in strenuous recreational activities, e.g., swimming, singles tennis, skiing, football, has a functional capacity >10 METs.
Investigators, starting with the proven premise that functional capacity is a simple and reliable index to estimate cardiac function, evaluated the cardiovascular effects of infiltration anesthesia compared with those produced by ergometric exercising.40,41 The hemodynamic effects of infiltration anesthesia with 0.045 mg of epinephrine were found to be less than those produced by ergometric-stress testing at 25 watts in young patients and at 15 watts in older subjects. The workload of ergometric-stress testing at these levels is less than 4 METs.
Based on this report, 4.5 cc of a local dental anesthetic agent with epinephrine 1:100,000 can be administered safely to patients whose functional capacity is equal to or greater than 4 METs. In this study, there were no differences in hemodynamic responses (evaluated by echocardiography) between normotensive and hypertensive patients. This observation is useful because HTN is a reliable marker for CAD and structural coronary arterial abnormalities and their consequences and hypertension-induced hypertrophic cardiomyopathy are the cause of 90-95 percent of arrhythmias, which lead to sudden death.
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