Preoperative Basics



Preoperative Basics





2.1 Preoperative Testing

David L. Hepner


INTRODUCTION

Routine preoperative testing lacks clinical utility and may lead to patient harm because of further testing to evaluate abnormal results. Routine testing may lead to unnecessary interventions, delay of surgery, patient anxiety, and inappropriate therapies. Tests done in low-risk populations are more likely to show falsely positive abnormal results than true pathologic abnormalities. These often mildly abnormal results are unlikely to affect anesthetic or surgical management, but can lead to further testing, consults, and procedures that incur additional costs and potential complications. In an era of value-based medicine, the only justification of preoperative screening is that the health benefits outweigh the risks and are worth the financial costs. Laboratory tests are not good screening mechanisms for disease. It is unlikely that, when done without an indication, abnormal laboratory findings will discover a new diagnosis, improve perioperative care, or affect length of hospital stay or patient outcomes.

A sound preoperative process ensures patient selection, maximizes economic efficiency, and optimizes the patient’s medical conditions. Preoperative testing is based on patients’ comorbidities, operative risk and findings from the history and physical examination. It is important to avoid testing in healthy patients having minimally invasive procedures and to avoid repetition of prior testing if there is no change in the patient’s condition. Routine testing does not increase safety for minimally invasive procedures regardless of the patient population. Routine screening is unlikely to impact risk stratification for low-risk procedures. A history and physical examination is mandatory prior to ordering laboratory testing, and is the most effective way to screen for disease. Clinical diagnosis rather than laboratory testing is more likely to lead to changes in operative plans. The majority of laboratory tests are superfluous to patient management.

It is essential to take into account the patient’s comorbidities and the risk of surgery in order to appropriately develop guidelines for preoperative testing. A test is indicated if it can identify abnormalities and change the diagnosis and management plan, or the patient’s outcome (1). A test should satisfy the following criteria to be useful:



  • Diagnostic efficacy; Does the test correctly identify abnormalities?


  • Diagnostic effectiveness; Does the test change your diagnosis?



  • Therapeutic efficacy; Does the test change your management?


  • Therapeutic effectiveness; Does the test change the patient’s outcome?


DANGERS OF ROUTINE TESTING

The detection of abnormalities does not justify testing because most abnormalities in asymptomatic patients do not reflect the presence of significant disease. The distribution of results in a population of patients is Gaussian for tests reported as continuous results. The values defining “abnormal” are set arbitrarily, so that test results above the 97.5 percentile or below the 2.5 percentile of values obtained from healthy individuals are deemed abnormal. Test results between these two extremes are within the reference range. Therefore, 5% of test results from patients without disease are outside the hospital reference range. Ordering multiple preoperative tests increases the chances of at least one abnormal result.

Testing not warranted by findings on a medical history does not provide protection against liability. Many unexpected abnormalities found on preoperative laboratory tests are not addressed in the medical record before surgery. The failure to pursue an abnormal laboratory finding poses a far greater risk of medicolegal liability than not discovering the abnormality. Additional unnecessary testing increases rather than decreases medicolegal risk to physicians. If you order a test, you must own the result and pursue it if it is abnormal.


CHEST RADIOGRAPHS

A chest radiograph is unlikely to detect lung disease requiring a change in anesthetic technique if the history and physical examination does not suggest concern. Chest radiographs have not been shown to predict postoperative pulmonary complications, and clinically significant abnormalities are unusual in asymptomatic patients. Chest radiographs are not indicated for asymptomatic patients who are free of risk factors for lung disease. Chest radiographs are indicated only in patients with cardiovascular or pulmonary signs or symptoms of undetermined cause or severity.


HEMOGLOBIN

A targeted history and physical examination determines the need for preoperative hemoglobin. Highly invasive surgeries with the potential for significant blood loss may be an indication for preoperative hemoglobin. The Anesthesia Task Force on Preanesthesia Evaluation recommends that type and invasiveness of procedure, extremes of age, and history of liver disease, anemia, bleeding, and other hematologic disorders are considered in determining the need for preprocedure hemoglobin (2). Preoperative hemoglobin should be obtained based on the likelihood of anemia, polycythemia and the likelihood of significant intraoperative blood loss. A preoperative hemoglobin should also be considered in patients with malabsorption or malnutrition, and in those who received recent chemotherapy.



COAGULATION STUDIES

Activated partial thromboplastin time (aPTT) and prothrombin time (PT) are useful diagnostic tests in patients who have a history of bleeding. They have not been shown to have value as screening tests in asymptomatic patients. The partial thromboplastin time (PTT) and PT were developed to identify clotting factor deficiencies in vitro and are not predictive of clinical bleeding (3). Coagulation testing in patients with no risk factors for coagulopathy or no history of bleeding does not predict perioperative bleeding (3).

A thorough patient history looking for bleeding abnormalities is more important and includes a family history of coagulation issues, history of increased bleeding with previous surgical procedures, and use of anticoagulants. Clinical conditions that predispose patients to bleeding such as liver and renal dysfunction should also be noted. A study of neurosurgery patients compared an assessment of patient history with preoperative hemostasis screening and demonstrated that patient history had a higher sensitivity for the detection of bleeding (4).

It is important to note that the presence of lupus anticoagulant is the most likely reason for an elevated aPTT. This is associated with a hypercoagulable rather than an increased bleeding risk (5). Routine coagulation studies are not recommended unless the patient history suggests a coagulation disorder, liver disease, malnutrition, or the patient is taking anticoagulants. An aPTT is indicated with a personal or family history of a bleeding disorder, unfractionated heparin (UFH) use, and in patients with an undiagnosed hypercoagulable condition. A PT is indicated in patients with alcohol abuse, personal or family history of bleeding disorder, hepatic disease, malabsorption, malnutrition, and warfarin use. A PT is also indicated as a baseline prior to planned initiation of warfarin for the first time in the hospital.


ELECTROLYTES

Electrolytes should be done when one either suspects an undiagnosed or worsening condition or when no laboratory values are available and the results will affect perioperative management. Preoperative electrolytes can be considered in patients with a history of renal or hepatic disease, malnutrition, malabsorption, alcohol abuse, anasarca, gastric bypass procedures, body mass index (BMI) <16, severe or undiagnosed dyspnea, inflammatory bowel disease, syncope, heart failure, arrhythmias, or use of medications such as digoxin, steroids, and diuretics. Electrolytes are not necessary in healthy patients without significant systemic disease (6).


RENAL FUNCTION TESTING

Patients undergoing low-risk procedures or ambulatory surgery are unlikely to benefit from renal function testing. A creatinine is obtained in patients with known kidney disease or with risk factors for renal dysfunction (e.g., diabetes mellitus, vascular disease, systemic lupus erythematosus (SLE)), for patients using diuretics, or when there is planned use of radiographic dye. A creatinine can also be considered in patients with anasarca, anemia, recent chemotherapy, severe or undiagnosed dyspnea, heart failure, hepatic disease, malnutrition, or malabsorption. Serum creatinine level directly depends on muscle mass, gender, and age. Most laboratory
centers provide an estimated glomerular filtration rate (eGFR) together with a serum creatinine. eGFR estimates renal function by eliminating the influence of body mass, gender, and age (7).


SERUM GLUCOSE AND GLYCATED HEMOGLOBIN

A serum glucose is considered in patients with diabetes, obesity (BMI greater than 50), family history of diabetes, cerebrovascular or intracranial disease, or in those taking steroids. A glycosylated hemoglobin (HbA1c) is a measure of long-term (3 months) glucose control and is a much better assessment of adequacy of diabetic therapy than a fasting or random blood glucose measurement. One-half of the HbA1c determination is from the previous 30 days and the time period of 2 to 3 months before contributes the other half. An elevated HbA1c is associated with an increased risk of cardiovascular events, postoperative infections, and fasting gastric fluid volumes (8). It is reasonable to obtain an HbA1c for all diabetics before surgery, as an HbA1c level can guide glucose management to intensify therapy before a procedure.


PREOPERATIVE URINE ANALYSES

Although abnormalities are commonly found on urinalysis, these abnormal results usually do not lead to beneficial changes in management. Furthermore, most findings that do lead to beneficial changes can be obtained by history. There is no evidence supporting routine urine analysis in asymptomatic patients without clinical suspicion. Unfortunately, urine cultures are often obtained before many procedures. At a Veterans Affairs medical facility urine cultures were obtained before one-quarter of orthopedic, cardiothoracic, and vascular procedures (9). Asymptomatic bacteriuria was detected in 11% of patients. Even though postoperative urinary tract infections were more frequent in patients with bacteriuria than in those without, surgical site infection was similar in both groups. Interestingly, bacteriuria was rarely treated, or there was no benefit when treated. Therefore, preoperative urinalysis and treatment of asymptomatic bacteriuria should be avoided in most patients. Preoperative urine analysis is only recommended when a urinary tract infection is suspected in patients.

The most common surgeries for which a urine analysis is requested are for joint replacements and urologic procedures. There is a lack of a clear association between bacteriuria and joint infections. Furthermore, there is a difference in the types of pathogens causing bacteriuria and surgical site infections (10). The Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults recommends to screen for asymptomatic bacteriuria before transurethral resection of the prostate (TURP) and to treat shortly before the procedure because of the high rate of postprocedure bacteremia and sepsis (11). Even though there is little data for other procedures, these guidelines also recommend to screen for and treat asymptomatic bacteriuria before other urologic procedures for which mucosal bleeding is anticipated because of the potential risk for bacteremia and sepsis. Antibiotic therapy can be initiated the night before or immediately before the procedure.



PREOPERATIVE PREGNANCY TESTING

The detection of a pregnancy in a woman scheduled to undergo a nonobstetric surgery will very likely alter management. The patient may decide to cancel the surgery, the surgeon may change the procedure, or the anesthesiologist may counsel the patient about the effects of anesthesia on an early pregnancy or modify the anesthetic plan. Even though the American Society of Anesthesiologists Task Force on Preanesthesia Evaluation states that the literature is inadequate to inform patients or physicians on whether anesthesia causes harmful effects in early pregnancy, it recommends that pregnancy testing be considered in female patients of childbearing age if the results will change the patient’s management (2).

Institutions vary in guidelines regarding preprocedure pregnancy testing. Obtaining an accurate menstrual history is mandatory as no test has 100% positive predictive value, and pregnancy testing should be offered where appropriate. The value of preoperative pregnancy testing may be greatest in pediatric patients who are having menses, in women who are poor historians, in women undergoing infertility treatment, or in women with histories of irregular periods. In women capable of childbearing with unreliable histories, pregnancy testing should be considered. The sensitivity and specificity of testing will depend on the type of testing used and the timing of the menstrual cycle. If the test is obtained very early after implantation, a urine pregnancy test may be negative, but a serum pregnancy test can be positive.


CURRENT RATES OF TESTING

Studies indicate that routine blood work, including a CBC and metabolic panels, are done before nearly 30% of low-risk, mainly ambulatory, surgeries (12). Comorbidities and age are associated with routine testing. It is important to point out that although studies demonstrate increased laboratory abnormalities with advancing age, these abnormalities are not predictive of postoperative complications. Preoperative medical consultation, but not preanesthesia evaluation, is associated with routine testing (12). Geographic location of surgery is the strongest predictor for preoperative laboratory testing, with significant variation within and among institutions. Similar results have been shown before extremely low-risk surgery such as cataract procedures (13). Preoperative testing before cataract surgery is more likely to be associated with the practice patterns of the ophthalmologist and a preoperative visit rather than with patient comorbidities. In one large study, 53% of patients had a preoperative test before cataract surgery, with no difference in the prevalence of testing compared to 20 years ago (13). A third of ophthalmologists ordered tests in 75% or more of their patients. Although there are significant evidence and national guidelines against the utility of routine preoperative testing, evidence-based guidelines alone do not change individuals’ behaviors (14,15). Providing institutions and individual providers feedback about rates of testing may have the potential to reduce low-value care and should be considered.


CHOOSING WISELY

Primary care and specialty physician groups joined forces to create the “Choosing Wisely” campaign, aimed directly at decreasing unnecessary health care (16). The
participating professional societies, including the American Society of Anesthesiologists, developed lists of five practices that are over used. The messages were targeted at both physicians and patients. The Choosing Wisely Campaign encourages ongoing dialogue among patients and physicians to eliminate unnecessary tests and procedures (17). Common low-value, overutilized tests in anesthesiology include baseline laboratory studies in healthy patients without significant systemic disease when blood loss is expected to be minimal (6). Examples of these low-value tests include a CBC, basic and comprehensive metabolic panels, and coagulation studies.




REFERENCES

1. Hepner DL. The role of testing in the preoperative evaluation. Clev Clin J Med. 2009; 76(Suppl 4):S22-S27.

2. Pasternak LR, Arens JF, Caplan RA, et al. Practice advisory for preanesthesia evaluation: an updated report by the American Society of Anesthesiologists Task Force on Preanesthesia Evaluation. Anesthesiology. 2012;116:522-538.

3. Chee YL, Crawford JC, Watson HG, et al. Guidelines on the assessment of bleeding risk prior to surgery or invasive procedures. British J Haematol. 2008;140:496-504.

4. Seicean A, Schiltz NK, Seicean S, et al. Use and utility of preoperative hemostatic screening and patient history in adult neurosurgical patients. J Neurosurg. 2012;116:1097-1105.


6. Onuoha OC, Arkoosh VA, Fleisher LA. Choosing wisely in anesthesiology: the gap between evidence and practice. JAMA Intern Med. 2014;174:1391-1395.

7. Levey AS, Bosch JP, Lewis JB, et al. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Ann Intern Med. 1999;130:461-470.

8. Bock M, Johansson T, Fritsch G, et al. The impact of preoperative testing for blood glucose concentration and haemoglobin A1c on mortality, changes in management and complications in noncardiac elective surgery. Eur J Anaesthesiol. 2015;32:152-159.

9. Drekonja DM, Zarmbinski B, Johnson JR. Preoperative urine cultures at a veterans affairs medical center. JAMA Intern Med. 2013;173:71-72.

10. Sousa R, Munoz-Mahamud E, Quayle J, et al. Is asymptomatic bacteriuria a risk factor for prosthetic joint infection? Clin Infect Dis. 2014;59:41-47.

11. Nicolle LE, Bradley S, Colgan R, et al. Infectious Diseases Society of America; American Society of Nephrology; American Geriatric Society. Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis. 2005;40:643-654.

12. Kirkham KR, Wijeysundera DN, Pendrith C, et al. Preoperative laboratory investigations: Rates and variability prior to low-risk surgical procedures. Anesthesiology. 2016;124: 804-814.


13. Chen CL, Lin GA, Bardach NS, et al. Preoperative medical testing in Medicare patients undergoing cataract surgery. N Engl J Med. 2015;372:1530-1538.

14. Keay L, Lindsley K, Tielsch J, et al. Routine preoperative medical testing for cataract surgery. Cochrane Database Syst Rev. 2012;3:CD007293.


16. Cassel CK, Guest JA. Choosing wisely: helping physicians and patients make smart decisions about their care. JAMA. 2012;307:1801-1802.



2.2 Preoperative Electrocardiograms

Obianuju Okocha

Christina Chae

An electrocardiogram (ECG) is one of the most frequently ordered preoperative tests, but its usefulness is not clearly established. Abnormal tracings are common and in the majority of cases do not change anesthetic management (1). Meanwhile a normal ECG adds little to the preoperative evaluation. Abnormal ECG findings in asymptomatic patients are reported to range anywhere from 4.6% to 44.9% of patients, and abnormalities led to cancellations of surgery or changes in management in only 0.46% to 2.6% of case (2). A normal ECG cannot exclude cardiac disease. The specificity of an ECG abnormality for predicting postoperative cardiac complications is low. In an observational single center cohort study of 2,232 patients undergoing noncardiac surgery, troponin I elevation was seen in 315 cases. However, only about 30 patients with elevated troponin I had accompanying ischemic changes that were seen on ECG (3). A single center retrospective study looked at postoperative troponin I levels and 12-lead ECGs in 337 patients undergoing vascular surgery. Troponin levels were drawn within 48 hours of surgery and daily ECGs completed for 3 postoperative days. Forty percent of patients were noted to have elevated troponin levels, however only 6% of patients had ischemic changes noted on ECG. Death at 1 year was associated with elevations in troponin but not with ECG changes (3). Multiple large scale surgical trials have shown that troponin is superior to ECG in diagnosing type 1 and 2 MI. Even in the setting of critical illness, ECGs are only moderately reliable for predicting major cardiac complications (3). The current use of ECGs may have developed as a method to screen for MI when little else was readily available. The routine addition of ECGs to postoperative care has not been examined in any prospective randomized trials (3). Therefore, a recommendation for the routine use of ECGs as a screening tool for predicting postoperative cardiac complications cannot be made.

ECG abnormalities are not included in the Revised Cardiac Risk Index (RCRI) or the National Surgery Quality Improvement Program (NSQIP) due to low prognostic value. A retrospective study investigating 23,036 patients scheduled for 28,457 surgical procedures found patients with abnormal ECG findings preoperatively had a greater incidence of cardiovascular death than those with normal ECG (1.8% vs. 0.3%). The absolute difference in the incidence of cardiovascular death between those with and without ECG abnormalities was only 0.5% in patients having low- or intermediate-risk surgery (4). Although it is widely accepted that pre-existing heart
disease increases perioperative risk, a resting ECG is not a reliable screen for CAD and is a poor predictor of heart disease. Advanced age is likely the most common reason prompting a preoperative ECG. One study found that in patients 70 years and older (highest risk population), the incidence of abnormal ECG was 75.2% but the presence of ECG abnormalities was not associated with an increased risk of postoperative cardiac complications (5). In addition to clinical risk factors noted in patient history, the relative risk of the surgical procedure determines the need for a preoperative ECG. It has been demonstrated that cardiovascular morbidity and mortality is associated with the type and urgency of surgery, with an increased rate of adverse event with intermediate- to high-risk procedures (6).

History and physical examination are likely to predict cardiac complications and should be the primary basis for obtaining preoperative ECGs. Cardiac examination findings such as irregular rhythms, abnormal heart rates, ectopy or when patient history suggests ongoing ischemia, history of near syncope/syncope, warrant obtaining an ECG. A preoperative ECG is reviewed for signs of myocardial ischemia such as Q waves or ST segment changes. Other abnormalities of importance are left ventricular hypertrophy (LVH), QTc prolongation, bundle branch block (BBB), and arrhythmias. ECG abnormalities, such as new Q waves and arrhythmias, are important predictors of cardiac complications (4). It is important to consider, however, that although Q waves are characteristic findings in myocardial infarction, they are not always associated with prior infarction. Other causes for Q waves other than MI may include physiologic and positional effects, ventricular enlargement, or altered ventricular conduction (7). Numerous medical organizations have issued practice guidelines for preoperative ECG testing. The two most notable are the 2014 American College of Cardiology Foundation/American Heart Association (ACC/AHA) shown in Table 2.1 and the American Society of Anesthesiologists (ASA).








TABLE 2.1 Summary of Recommendations for Supplemental Preoperative Evaluation

























Recommendations


COR


LOE


The 12-lead ECG




Preoperative resting 12-lead is reasonable for patients with known coronary heart disease or other significant structural heart disease, except for low-risk surgery


IIa


B


Preoperative resting 12-lead ECG may be considered for asymptomatic patients, except for low-risk surgery


IIb


B


Routine preoperative resting 12-lead ECG is not useful for asymptomatic patients undergoing low-risk surgical procedures


III: No Benefit


B


COR, Class of recommendation; LOE, level of evidence


From Fleischer LA, Fleischmann KE, Auerbach AD, et al. ACC/AHA Guideline on perioperative cardiovascular evaluation and management of patients undergoing noncardiac surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2014;64:e77.

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Nov 14, 2018 | Posted by in ANESTHESIA | Comments Off on Preoperative Basics
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