Merck Manual

Please confirm that you are a health care professional


Preoperative Evaluation


Paul K. Mohabir

, MD, Stanford University School of Medicine

Last full review/revision Apr 2018| Content last modified Apr 2018
Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Topic Resources

Before elective surgical procedures, a thorough preoperative medical evaluation by nonsurgical consultants (eg, internists, cardiologists, pulmonologists) may be necessary to help assess surgical risk. Such consultants may also help manage preexisting disease (eg, diabetes) and help prevent and treat perioperative and postoperative complications (eg, cardiac, pulmonary, infectious). Psychiatric consultation is occasionally needed to assess capacity or help deal with underlying psychiatric problems that can interfere with recovery.

Elderly patients may benefit from involvement of an interdisciplinary geriatric team, which may need to involve social workers, therapists, ethicists, and other practitioners.

If an emergency procedure is required (eg, for intra-abdominal hemorrhage, perforated viscus, necrotizing fasciitis), there is usually no time for a full preoperative evaluation. However, the patient's history should be reviewed as expeditiously as possible, particularly for allergies and to help identify factors that increase risk of emergency surgery (eg, history of bleeding problems or adverse anesthetic reactions).

Before elective surgery, the surgical team may consult an internist for a formal preoperative evaluation to minimize risk by identifying correctable abnormalities and by determining whether additional perioperative monitoring and treatment are needed. Additionally, elective procedures should be delayed when possible so that certain underlying disorders (eg, hypertension, diabetes, hematologic abnormalities) can be optimally controlled.

Routine preoperative evaluation varies substantially from patient to patient because surgical risk varies depending on the patient’s risk factors and risks of the procedure.


A relevant preoperative history includes information about all of the following:

  • Current symptoms suggesting an active cardiopulmonary disorder (eg, cough, chest pain, dyspnea during exertion, ankle swelling) or infection (eg, fever, dysuria)

  • Risk factors for excessive bleeding (eg, known bleeding disorder, history of bleeding excessively with dental procedures, elective surgeries, or childbirth)

  • Risk factors for thromboembolism (see Deep Venous Thrombosis (DVT))

  • Risk factors for infection

  • Known disorders that increase risk of complications, particularly hypertension, heart disease, kidney disease, liver disease, diabetes, asthma, and COPD

  • Previous surgery, anesthesia, or both, particularly their complications

  • Allergies

  • Tobacco, alcohol, and illicit drug use

  • Current prescription and nonprescription drug and supplement use

  • History of obstructive sleep apnea or excessive snoring

If an indwelling bladder catheter may be needed, patients should be asked about prior urinary retention and prostate surgery.

Physical examination

Physical examination should address not only areas affected by the surgical procedure but also the cardiopulmonary system, as well as a search for any signs of ongoing infection (eg, upper respiratory tract, skin).

When spinal anesthesia is likely to be used, patients should be evaluated for scoliosis and other anatomic abnormalities that may complicate lumbar puncture.

Any cognitive dysfunction, especially in elderly patients who will be given a general anesthetic, should be noted. Preexisting dysfunction may become more apparent postoperatively and, if undetected beforehand, may be misinterpreted as a surgical complication.


No preoperative tests are required in healthy patients undergoing operations with very low risk of bleeding or other complications; abnormal results are more likely to be false positives than in patients with symptoms or risk factors.

In symptomatic patients or in patients undergoing operations with a higher risk of significant bleeding or other complications, laboratory evaluation may include the following tests:

  • CBC and urinalysis (glucose, protein, and cells) usually are done.

  • Serum electrolytes and creatinine and plasma glucose are measured unless patients are extremely healthy and <50 yr of age, the procedure is considered very low risk, and use of nephrotoxic drugs is not expected.

  • Liver enzymes are measured if abnormalities are suspected based on the patient’s history or examination.

  • Coagulation studies and bleeding time are needed only if patients have a personal or family history of bleeding diathesis or a disorder associated with bleeding.

  • ECG is done for patients at risk of coronary artery disease (CAD), including all men > 45 and women > 50.

  • If a general anesthetic is to be used, a chest x-ray typically is done (or a recent x-ray is reviewed), but its usefulness is limited, particularly in younger patients and in patients without suspicion of heart or lung disease.

  • Pulmonary function testing may be done if patients have a known chronic pulmonary disorder or symptoms or signs of pulmonary disease.

Patients with symptomatic CAD need additional tests (eg, stress testing, coronary angiography) before surgery.

Procedural Risk Factors

Procedural risk is highest with the following:

  • Heart or lung surgery

  • Hepatic resection

  • Intra-abdominal surgeries that are estimated to require a prolonged operative time or that have a risk of large-volume hemorrhage (eg, Whipple procedure, aortic surgery, retroperitoneal surgery)

  • Open prostatectomy

  • Major orthopedic procedures (eg, hip replacement)

Patients undergoing elective surgery that has a significant risk of hemorrhage should consider banking blood for autologous transfusion should it be needed. Autologous transfusion decreases the risks of infection and transfusion reactions.

Emergency surgery has a higher risk of morbidity and mortality than the same surgery done electively.

Patient Risk Factors

Patient risk factors are stratified by some clinicians using published criteria. Older age is associated with decreased physiologic reserve and greater morbidity if a complication occurs. However, chronic disorders are more closely associated with increased postoperative morbidity and mortality than is age alone. Older age is not an absolute contraindication to surgery.

Cardiac risk factors

Cardiac risk factors dramatically increase surgical risk. Perioperative cardiac risk is typically assessed using the American College of Cardiology/American Heart Association's Revised Cardiac Risk Index (see Figure: Algorithm for risk stratification for noncardiac surgery). It considers the following independent predictors of cardiac risk:

  • History of CAD

  • History of heart failure

  • History of cerebrovascular disease

  • Diabetes requiring treatment with insulin

  • Serum creatinine (2.0 mg/dL)

Risk of cardiac complications increases with increasing risk factors:

  • No risk factors: 0.4% (95% confidence interval 0.1 to 0.8%)

  • 1 risk factor: 1.0% (95% confidence interval 0.5 to 1.4%)

  • 2 risk factors: 2.4% (95% confidence interval 1.3 to 3.5%)

  • ≥ 3 risk factors: 5.4% (95% confidence interval 2.8 to 7.9%)

A high-risk surgical procedure (eg, vascular surgery, open intrathoracic or intraperitoneal procedure) also independently predicts a high cardiac perioperative risk.

Patients with active cardiac symptoms (eg, of heart failure or unstable angina) have a particularly high perioperative risk. Patients with unstable angina have about a 28% risk of perioperative MI. In patients with stable angina, risk is proportional to their degree of exercise tolerance. Patients with active cardiac symptoms thus require thorough evaluation. For example, the cause of heart failure should be determined so that perioperative cardiac monitoring and treatment can be optimized before elective surgery. Other cardiac testing, such as stress echocardiography or even angiography, should be considered if there is evidence of reversible cardiac ischemia on preoperative evaluation.

Preoperative care should aim to control active disorders (eg, heart failure, diabetes) using standard treatments. Also, measures should be taken to minimize perioperative tachycardia, which can worsen heart failure and increase risk of MI; for example, pain control should be optimized and β-blocker therapy should be considered, especially if patients are already taking β-blockers. Coronary revascularization should be considered for patients with unstable angina. If a heart disorder cannot be corrected before surgery or if a patient is at high risk of cardiac complications, intraoperative and sometimes preoperative monitoring with pulmonary artery catheterization may be advised. Sometimes the cardiac risk outweighs the benefit of surgery.

Algorithm for risk stratification for noncardiac surgery

*Active clinical conditions include unstable coronary syndromes, decompensated heart failure, significant arrhythmias, and severe valvular disorders.

See the 2014 ACC/AHA guideline on perioperative cardiovascular evaluation and management of patients undergoing noncardiac surgery.

Clinical risk factors include coronary artery disease, history of heart failure, history of cerebrovascular disease, diabetes mellitus, and preoperative creatinine > 2.0 mg/dL.

ACC = American College of Cardiology; AHA = American Heart Association; HR = heart rate; MET = metabolic equivalent.

Adapted from Fleisher LA, Fleischmann KE, Auerbach AD, et al: ACC/AHA 2014 guideline on perioperative cardiovascular evaluation and management of patients undergoing noncardiac surgery (executive summary); a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation 130:2215-2245, 2014.

Algorithm for risk stratification for noncardiac surgery


Incidental bacterial infections discovered preoperatively should be treated with antibiotics. However, infections should not delay surgery unless prosthetic material is being implanted; in such cases, surgery should be postponed until the infection is controlled or eliminated.

Patients with respiratory infections should be treated and have evidence that the infection has resolved before receiving inhalational anesthesia.

Viral infections with or without fever should be resolved before elective surgery is done, especially if a general anesthetic is going to be used.

Fluid and electrolyte imbalances

Fluid and electrolyte imbalances should be corrected before surgery. Hypokalemia and hyperkalemia must be corrected before general anesthesia to decrease risk of potentially lethal arrhythmias. Dehydration and hypovolemia should be treated with IV fluids before general anesthesia to prevent severe hypotension on induction—BP tends to fall when general anesthesia is induced.

Nutritional disorders

Undernutrition increases risk of postoperative complications in adults. Nutritional status is assessed preoperatively using history, physical examination, and laboratory tests. Indicators of undernutrition include the following:

  • A history of weight loss > 10% of body weight over 6 mo or 5% over 1 mo

  • Suggestive physical examination findings (eg, muscle wasting, signs of specific nutritional deficiencies)

  • Low serum albumin levels

Serum albumin is an inexpensive, widely available, and reliable indicator of undernutrition; it should be measured preoperatively in patients who may be undernourished. Values < 2.8 g/dL predict increased morbidity and mortality. Because the half-life of serum albumin is 14 to 18 days, levels may not reflect acute undernutrition. If more acute undernutrition is suspected, a protein with a shorter half-life can be measured; for example transferrin (half-life 7 days) or transthyretin (half-life 3 to 5 days). Preoperative and perioperative nutritional support is most likely to improve outcomes in patients whose histories of weight loss and protein levels indicate severe undernutrition. In some cases, surgery can be delayed so patients can receive nutritional support, sometimes for several weeks.

Significant obesity (BMI > 40 kg/m2) increases perioperative mortality risk because such patients have increased risk of cardiac and pulmonary disorders (eg, hypertension, pulmonary hypertension, left ventricular hypertrophy, heart failure, CAD). Obesity is an independent risk factor for deep venous thrombosis and pulmonary embolism; preoperative venous thromboembolism prophylaxis is indicated in most obese patients. Obesity also increases risk of postoperative wound complications (eg, fat necrosis, infection, dehiscence).

More Information

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Also of Interest


View All
How to Fit and Use Crutches
How to Fit and Use Crutches
How to do Ultrasonography: Console and Controls
How to do Ultrasonography: Console and Controls