Since medical problems are common in surgical patients, optimal perioperative management is a part of clinical practice. Practices are often based on inconclusive evidence or extrapolated from understanding of physiology. Cheng reviewed guidelines and practices for four perioperative situations: (1) endocarditis prophylaxis; (2) perioperative anticoagulation in patients with mechanical heart valves; (3) perioperative glucose control in diabetic patients; and (4) the use of beta-adrenergic blocking agents to prevent postoperative cardiac complications.
Since many invasive procedures cause transient bacteremia, patients with cardiac abnormalities may be more likely to develop bacterial endocarditis. Rates of bacteremia seem highest following dental work and other procedures involving the oropharynx (often associated with alpha-hemolytic Streptococcus species, particularly Streptococcus viridans), and procedures of the genitourinary and gastrointestinal tracts (often associated with Enterococcus species). The American Heart Association 1997 guidelines for endocarditis prophylaxis recommend prophylaxis only in patients with a moderate- or high-risk cardiac abnormality (see the accompanying table) who are undergoing a high-risk procedure. Examples of high-risk procedures include dental extraction, dental work in which bleeding is anticipated, tonsillectomy and adenoidectomy, surgery involving the biliary tract or intestinal mucosa, prostate surgery and cystoscopy. The standard regimen for dental, esophageal and upper respiratory tract procedures is amoxicillin, in a dosage of 2 g orally one hour before the procedure and, before gastrointestinal or genitourinary procedures, 2 g of ampicillin administered intravenously or intramuscularly, plus gentamicin, in a dosage of 1.5 mg per kg (up to 120 mg), within 30 minutes of the procedure and followed in six hours by ampicillin, in a dosage of 1 g intravenously or intramuscularly, or amoxicillin, in a dosage of 1 g orally.
Concerning perioperative anticoagulation in patients with mechanical valve prostheses, more recent valve designs are less thrombogenic. Routine perioperative heparinization in patients with aortic valve prostheses seems unjustified. Since a mechanical mitral valve incurs a greater risk of thromboembolism, heparinization should be considered in these patients, especially those who have older valve designs. The role of low-molecular-weight heparin is uncertain.
Diabetic patients have an increased risk of surgical wound complications, especially infections. Data are insufficient to advocate tight perioperative control, although a reasonable goal would be to keep glucose levels below 250 mg per dL (13.87 mmol per L). The method of insulin delivery depends on patient-specific criteria even though intravenous administration of insulin allows tighter glucose control than subcutaneous administration.
Based on the concept of surgical stress causing increased sympathetic tone with tachycardia and hypertension, beta-adrenergic blocking medications have been used to decrease perioperative cardiac risk in patients undergoing noncardiac surgery. Although parameters for usage are less clear in patients who have only risk factors for coronary artery disease, evidence confirms the value of pre-surgical beta-blocking agents in patients with known coronary artery disease or uncontrolled hypertension.