Evidence-Based Emergency Care E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Evidence-Based Medicine
• Sprache: Englisch

Seitenzahl: 753

Veröffentlichungsjahr: 2012

Beschreibung

This book for emergency physicians and fellows training in emergency medicine provides evidence-based information on what diagnostic tests to ask for and when and how to use particular decision rules. The new edition builds on the success of the current book by modifying the presentation of the evidence, increasing the coverage, and updating the current information throughout.

Leseprobe

Table of Contents

Website: Evidence-Based Medicine Series

Title Page

Copyright

Dedication

About the Authors

Foreword

Preface

Acknowledgments

Section 1: The Science of Diagnostic Testing and Clinical Decision Rules

Chapter 1: Diagnostic Testing in Emergency Care

References

Additional Reading

Chapter 2: Evidence-Based Medicine: The Process

References

Additional Reading

Chapter 3: The Epidemiology and Statistics of Diagnostic Testing

The 2 × 2 table

Sensitivity and specificity

Incidence and prevalence

Predictive values

Integrating concepts

Using 2 × 2 tables: an example

Odds, probability, and the odds ratio

Likelihood ratios and interval likelihood ratios

Using odds, probabilities, and likelihood ratios: an example

Bayes theorem

Confidence intervals

Receiver operator characteristic (ROC) curves

References

Additional Reading

Chapter 4: Clinical Decision Rules

The clinical decision rule development process

References

Additional Reading

Chapter 5: Appropriate Testing in an Era of Limited Resources: Practice and Policy Considerations

Impact of diagnostic testing on healthcare expenditures

Downstream costs of diagnostic testing

Variation in testing and inappropriate testing

Causes of inappropriate testing

Improving appropriateness in diagnostic testing: practice considerations

Health policy considerations

References

Further Reading

Chapter 6: Understanding Bias in Diagnostic Research

Types of bias

Moving Beyond Bias to Effectiveness

References

Section 2: Trauma

Chapter 7: Cervical Spine Fractures

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 8: Cervical Spine Fractures in Children

Background

Clinical question

Clinical question

Comment

References

Chapter 9: Cervical Spine Fractures in Older Adults

Background

Clinical question

Comments

References

Chapter 10: Blunt Abdominal Trauma

Background

Clinical questions

Clinical question

Comment

References

Chapter 11: Acute Knee Injuries

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 12: Acute Ankle and Foot Injuries

Background

Clinical question

Clinical question

Comment

References

Chapter 13: Blunt Head Injury in Children

Background

Clinical question

Comments

References

Chapter 14: Blunt Head Injury

Background

Clinical question

Comments

References

Chapter 15: Blunt Chest Trauma

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 16: Occult Hip Fracture

Background

Clinical question

Clinical question

Comment

References

Chapter 17: Blunt Soft Tissue Neck Trauma

Background

Clinical question

Clinical question

Comments

References

Chapter 18: Occult Scaphoid Fractures

Background

Clinical question

Clinical question

Comments

References

Chapter 19: Penetrating Abdominal Trauma

Background

Clinical question

Comment

References

Chapter 20: Penetrating Trauma to the Extremities and Vascular Injuries

Background

Clinical question

Clinical question

Clinical question

Comments

References

Section 3: Cardiology

Chapter 21: Heart Failure

Background

Clinical question

Comment

References

Chapter 22: Syncope

Background

Clinical question

Comment

References

Chapter 23: Acute Coronary Syndrome

Background

Clinical question

Clinical question

Clinical question

Clinical question

Comments

References

Chapter 24: Palpitations

Background

Clinical question

Clinical question

Comment

References

Section 4: Infectious Disease

Chapter 25: Bacterial Meningitis in Children

Background

Clinical question

Comment

References

Chapter 26: Serious Bacterial Infections in Children Aged 1–3 Months

Background

Clinical question

Clinical question

Comment

References

Chapter 27: Necrotizing Fasciitis

Background

Clinical question

Clinical question

Comment

References

Chapter 28: Infective Endocarditis

Background

Clinical question

Comment

References

Chapter 29: Pharyngitis

Background

Clinical question

Clinical question

Comment

References

Chapter 30: Rhinosinusitis

Background

Clinical question

Comment

References

Chapter 31: Pneumonia

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 32: Urinary Tract Infection

Background

Clinical question

Clinical question

Comment

References

Chapter 33: Sepsis

Background

Clinical question

Clinical question

Comment

References

Chapter 34: Septic Arthritis

Background

Clinical question

Clinical question

Comment

References

Chapter 35: Osteomyelitis

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 36: Sexually Transmitted Diseases (STDs)

Background

Clinical question

Clinical question

Comment

References

Chapter 37: Influenza

Background

Clinical question

Clinical question

Comment

References

Chapter 38: Pediatric Fever in Children Aged 3–36 Months

Background

Clinical question

Clinical question

Comment

References

Section 5: Surgical and Abdominal Complaints

Chapter 39: Acute, Nonspecific, Nontraumatic Abdominal Pain

Background

Clinical question

Comment

References

Chapter 40: Small Bowel Obstruction

Background

Clinical question

Comment

References

Chapter 41: Acute Pancreatitis

Background

Clinical question

Clinical question

Comments

References

Chapter 42: Acute Appendicitis

Background

Clinical question

Clinical question

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 43: Acute Cholecystitis

Background

Clinical question

Clinical question

Comments

References

Chapter 44: Aortic Emergencies

Background

Clinical question

Clinical question

Comment

References

Chapter 45: Ovarian Torsion

Background

Clinical question

Clinical question

Comment

References

Section 6: Urology

Chapter 46: Nephrolithiasis

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 47: Testicular Torsion

Background

Clinical question

Clinical question

Comment

References

Section 7: Neurology

Chapter 48: Nontraumatic Subarachnoid Hemorrhage

Background

Clinical question

Comment

References

Chapter 49: Acute Stroke

Background

Clinical question

Comment

References

Chapter 50: Transient Ischemic Attack

Background

Clinical question

Comment

References

Chapter 51: Seizure

Background

Clinical question

Clinical question

Comment

References

Section 8: Miscellaneous: Hematology, Ophthalmology, Pulmonology, Rheumatology, and Geriatrics

Chapter 52: Venous Thromboembolism

Background

Clinical question

Clinical question

Clinical question

Clinical question

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 53: Temporal Arteritis

Background

Clinical question

Clinical question

Comments

References

Chapter 54: Intraocular Pressure

Background

Clinical question

Comments

References

Chapter 55: Asthma

Background

Clinical question

Comments

References

Chapter 56: Nontraumatic Back Pain

Background

Clinical question

Clinical question

Comment

References

Chapter 57: Intravascular Volume Status

Background

Clinical question

Clinical question

Clinical question

Comment

References

Chapter 58: Geriatric Syndromes

Background

Clinical question

Clinical question

Clinical question

Comment

References

Index

Website: Evidence-Based Medicine Series

The Evidence-Based Medicine Series has a website at:

www.evidencebasedseries.com

Where you can find:

Links to companion websites with additional resources and updates for books in the series

Details of all new and forthcoming titles

Links to more Evidence-Based products: including the Cochrane Library, Essential Evidence Plus, and EBM Guidelines.

How to access the companion sites with additional resources and updates:

Go to the Evidence-Based Series site:

www.evidencebasedseries.com

Select your book from the list of titles shown on the site

If your book has a website with supplementary material, it will show an icon next to the title

Click on the icon to access the website

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Library of Congress Cataloging-in-Publication Data

Evidence-based emergency care : diagnostic testing and clinical decision rules / Jesse M. Pines … [et al.]. – 2nd ed.

p. ; cm.

Includes bibliographical references and index.

ISBN 978-0-470-65783-6 (pbk.)

I. Pines, Jesse M.

[DNLM: 1. Evidence-Based Emergency Medicine—methods. 2. Diagnostic Techniques and Procedures. WB 105]

616.02'5–dc23

2012025774

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

To my wife, Lori Uscher-Pines, and to my children, Asher and Molly Pines, for all their support and encouragement.

J.M.P.

To Danielle, for putting up with everything and keeping me despite it all.

A.S.R.

To my wife, Lauraine, and our kids, Henry and Maggie, for their love and support.

J.D.S.

About the Authors

Jesse M. Pines, MD, MBA, MSCE, is the Director of the Center for Healthcare Quality and an Associate Professor of Emergency Medicine and Health Policy at George Washington University. He is also a board-certified emergency physician. Dr. Pines has served as a Senior Advisor to the Center for Medicare and Medicaid Innovation at the U.S. government's Center for Medicare and Medicaid Services. Dr. Pines holds a bachelor of arts degree and a master's of science degree in clinical epidemiology from the University of Pennsylvania as well as a medical degree and a master's of business administration degree from Georgetown University. He completed a residency in emergency medicine at the University of Virginia and a fellowship in research at the Center for Clinical Epidemiology and Biostatistics at the University of Pennsylvania. He has received grant funding from several government agencies and private foundations to conduct research, and is author of over 120 peer-reviewed academic publications. He lives in Fairfax, Virginia, with his wife, Lori, and two children, Asher and Molly.

Christopher Carpenter, MD, MSc, FACEP, FAAEM, is the Director of Evidence Based Medicine for the Division of Emergency Medicine at Barnes Jewish Hospital at Washington University, St. Louis, Missouri. Dr. Carpenter completed an internal medicine–emergency medicine residency at Allegheny General Hospital in Pittsburgh, Pennsylvania, and a master's degree in clinical investigations at Washington University. Dr. Carpenter's research focuses on improving geriatric adult emergency care using evidence-based medicine and implementation science, and has been funded by federal agencies and foundations. Dr. Carpenter is Chair-Elect of the American College of Emergency Physicians' Geriatrics Section, as well as faculty at the McMaster University Evidence Based Clinical Practice course. Dr. Carpenter is an Associate Editor for Academic Emergency Medicine and formerly Chief Clinical Editor of Emergency Physicians Monthly. Dr. Carpenter has published over 40 peer-reviewed papers and has led the development of the “Evidence Based Diagnostics” series in Academic Emergency Medicine. Dr. Carpenter lives in St. Louis, Missouri, with his wife, Panechanh, and two children, Cameron and Kayla.

Ali S. Raja, MD, MBA, MPH is the Director of Network Operations and Business Development for the Department of Emergency Medicine and the Associate Director of Trauma for Brigham and Women's Hospital, an Assistant Professor of Medicine (Emergency Medicine) at Harvard Medical School, and on the faculty of the Center for Evidence-Based Imaging at BWH. He is a board-certified emergency physician who completed a residency in emergency medicine at the University of Cincinnati and holds a master's of public health degree from the Harvard School of Public Health as well as a medical degree and a master's of business administration degree from Duke University. The author of over 40 peer-reviewed journal articles, his federally funded research focuses on improving the appropriateness of radiology utilization and the management of patients with trauma. Dr. Raja has received both the BWH Outstanding Attending award from the Harvard-Affiliated Emergency Medicine Residency and the Exemplary Emergency Medicine Attending award from the BWH Emergency Department nurses. He serves as a national faculty member of the Difficult Airway Course, is a major in the US Air Force Reserve, and is the tactical physician for the Boston FBI SWAT team. Dr. Raja lives in Sudbury, Massachusetts, with his wife, Danielle, and son, Chase.

Jeremiah (Jay) Schuur, MD, MHS, FACEP, is the Director of Quality, Patient Safety and Performance Improvement for the Department of Emergency Medicine at Brigham and Women's Hospital and an Assistant Professor of Medicine (Emergency Medicine) at Harvard Medical School. Dr. Schuur completed an emergency medicine residency at Brown University in Providence, Rhode Island, and a fellowship as a Robert Wood Johnson Clinical Scholar at Yale University. Dr. Schuur's research has been funded by federal agencies and foundations and focuses on developing, evaluating, and improving measures of quality of care and patient safety in emergency medicine. Dr. Schuur chairs the Quality and Performance Committee of the American College of Emergency Physicians, is the emergency medicine representative to the American Medical Association Physician Consortium for Performance Improvement, and is an appointed member of the Medicare Evidence Development and Coverage Advisory Committee (MEDCAC). Dr. Schuur has published over 40 peer-reviewed papers and has led the development of seven quality measures that have been approved by the National Quality Forum. Dr. Schuur lives in Cambridge, Massachusetts, with his wife, Lauraine, and two children, Henry and Maggie.

Foreword

Diagnosis correctly sorts truth and fiction into labeled bins. Diagnosis requires human intelligence, experience, and evidence. Intelligence may be inherited, and experience earned, but evidence must be acquired by reading. This second edition of Evidence-Based Emergency Care: Diagnostic Testing and Clinical Decision Rules provides a one-stop resource for the evidence of diagnosis in emergency care, continuing the tradition set by the first edition, except with greater depth and reach. To my knowledge, no other single resource offers a more comprehensive, contemporaneous, and parsimonious accumulation of the data to accelerate “clinical decisioning” at the bedside in emergency medicine. This book provides both an efficient pocket reference for daily practice and also expert interpretation to help us understand the context and rationale of key studies, as well as where the literature is lacking. The lean writing style respects its readers' time, but the scope of 58 chapters respects the breadth of emergency care. This textbook not only encompasses bread-and-butter topics, such as imaging patients with low-risk head injury, but also ventures into the unusual and provides useful data that I submit will surprise and inform veteran practitioners. What is the positive likelihood ratio for jaw claudication as a predictor of temporal arteritis? Should you care to know this datum, turn to chapter 53 and see the summary table that condenses each chapter for readers with limited time or attention spans.

I believe this book will improve and streamline my thought process at least once on every shift. It is often said that knowledge is power. And while this text conveys plenty of knowledge, more importantly, it may reduce practitioner stress by facilitating access to data, thus helping transform knowledge into diagnostic knowhow. So, for the next patient you see with chest pain, you need not spend your precious human computing power trying to remember where to find the decision rules for acute coronary syndrome, or the components of the various published decision instruments, or their authors, or levels of validation. Instead, you can relax (at least a little) and apply your mind power toward the good and valuable goal of listening to the patient and thinking about what he or she is telling you. And this attention provides the knowhow to correctly sort clinical truth and fiction. In the second edition of Evidence-Based Emergency Care: Diagnostic Testing and Clinical Decision Rules, Pines, Carpenter, Raja, and Schuur have provided a truly useful tool for the practice of emergency medicine. Keep a copy nearby for your next shift.

Jeffrey Kline 2012

Preface

One of the most vital skills in emergency medicine is the ability to differentiate patients who need emergency treatment from those who do not. The primary means of doing so include a detailed history, a skilled physical examination, and well-informed clinical judgment. While the skilled clinician acquires the basic tenets of taking a history, doing a physical examination, and developing reasonable clinical judgment through medical school and residency training, this knowledge is constantly updated through the experience of evaluating and treating patients in emergency care settings.

The technologies available to evaluate patients with emergency medical conditions have blossomed over the past 50 years and continue to evolve rapidly with a greater availability of advanced radiography and novel laboratory tests. The methods of conducting and reporting diagnostic research have also evolved significantly. In addition, clinicians now recognize the myriad forms of bias that impede confident interpretation of diagnostic studies, and methods to assess the quality of individual studies in diagnostic meta-analyses have been developed.

Modern emergency medicine is a delicate balance of practicing an evidence-based approach to diagnostic testing. The term that is often used is “appropriate use.” Appropriate use means finding a balance between overuse (e.g., overtesting low-risk patients) and underuse (e.g., discharging people with undiagnosed, potentially life-threatening conditions). Appropriate testing should be patient centered, well reasoned, and evidence based. However, given the spiraling costs of healthcare, we need to also be cost conscious. This is one of the hardest parts of our jobs as emergency physicians.

Many disease processes can be safely and reliably excluded by clinical criteria alone. There has been a proliferation of research studies designed to guide test ordering; the best example of this is the use of radiography for ankle sprains, since only a small proportion of patients will have radiographs that demonstrate clinically significant fractures. These clinical decision rules for diagnostic testing can serve as guides for deciding which patients may or may not benefit from testing. Because this skill, the art and science of diagnostic testing, is so central to emergency medical practice, emergency physicians and other providers working in emergency care settings must be experts in this area.

The purpose of this book is to present relevant questions on diagnostic testing that arise in everyday emergency medicine practice and to comment on the best available evidence. The first part of the book serves as an overview of the science of diagnostic testing, reviewing the process behind the development of clinical decision rules and exploring the pressures that emergency practitioners will face in the coming years to increase the efficiency of diagnostic test utilization. Subsequent chapters focus on practical questions that have been addressed by original research studies. We provide a review of the current literature on a specific question, an interpretation of the clinical question in the context of the literature, and ?nally how we, as practicing clinicians, apply the evidence to the care of our patients. Importantly, we also try to provide the actual data, sample sizes, and statistics. As readers, you can come to your own conclusions about how to interpret the best available data by understanding not just the bottom-line study conclusions but also the limitations of various study designs. As a caveat, our comments section should not be interpreted as the standard of care. Not all emergency care settings have the same resources for testing or treatment, nor do all settings have the same availability of specialty consultation. Therefore, it is vital to evaluate our interpretation of the literature in the context of your local resources and practice patterns.

In this second edition of the book, we have expanded the book considerably, adding new evidence and many new chapters since the first edition was published in 2008. We hope that you enjoy and your patients benefit from this effort!

Jesse M. Pines Christopher R. Carpenter Ali S. Raja Jeremiah D. Schuur 2013

Acknowledgments

We would like to thank the following individuals for their contributions to the second edition of Evidence-Based Emergency Care: Diagnostic Testing and Clinical Decision Rules: Worth W. Everett, MD, for his authorship and help writing the first edition of the book; Lisa Hayes at Washington University at St. Louis for helping with the image permissions; and Dorothea B. Hempel, MD, for help obtaining images from the Brigham and Women's Hospital Department of Emergency Medicine image library.

Section 1

The Science of Diagnostic Testing and Clinical Decision Rules

Chapter 1

Diagnostic Testing in Emergency Care

As emergency department (ED) physicians, we spend a good deal of our time ordering, interpreting, and waiting for the results of diagnostic tests. When it comes to determining who needs a test to rule out potentially life-threatening conditions, ED physicians are the experts. There are several reasons for this expertise. First and foremost, we see a lot of patients. Especially for those working in busy hospitals, the expectation is to see everyone in a timely way, provide quality care, and ensure patients have a good experience. If we order time-consuming tests on everyone, ED crowding and efficiency will worsen, costs of care will go up, and patients will experience even longer waits than they already do. In addition, the way ED physicians in the United States are paid may be changing over the coming years through mechanisms such as accountable care organizations and payment bundling. There may be more pressure to carefully choose who needs and who does not need tests in an evidence-based manner.

Differentiating which patients will benefit from further testing in the ED is a complex process. Over the past 30 to 40 years, science and research in diagnostic testing and clinical decision rules in emergency care have advanced considerably. Now, there is a greater understanding of test performance regarding the reliability, sensitivity, specificity, and overall accuracy of tests. Validated clinical decision rules exist to provide objective criteria to help distinguish who does and does not need a test. Serious, potentially life-threatening conditions such as intracranial bleeding and cervical spine (C-spine) fractures can be ruled out based on clinical grounds alone. There are also good risk stratification tools to determine a probability of disease for conditions like pulmonary embolism before any tests are even ordered.

How do we decide who to test and who not to test? There are some patients who obviously need tests, such as the head-injured patient who has altered mental status and who may have a head bleed where the outcome may be dependent upon how quickly the bleeding can be detected with a computed tomography (CT) scan. There are also patients who obviously do not need tests, such as patients with a simple toothache or a mild upper respiratory tract infection. Finally, there is a large group of patients in the middle for whom testing decisions can sometimes be challenging. This group of patients may leave you feeling “on the fence” about testing. In this large middle category, it may not be clear whether to order a test or even how to interpret a test once you have the results. And when we receive unexpected test results, it may not be clear how best to use those results to guide the care of an individual patient.

Let's consider a different scenario. Consider a positive D-dimer assay in a 22-year-old male with atypical chest pain, no risk factors, and normal physical examination including a heart rate of 70 beats per minute and an oxygen saturation of 100% on room air. What do you do then? Should he be anticoagulated and admitted? Does he have a pulmonary embolism? Should you move forward with further confirmatory testing before initiating treatment? Or is he so low risk that he's probably fine anyway? Of course, you might wonder why, if he was so low risk, was the D-dimer ordered in the first place?

As a third example, you are evaluating a 77-year-old female who has fallen down, has acute hip pain, and is unable to ambulate. The hip radiograph is negative. Should you pursue it? Possibly get a CT or magnetic resonance imaging (MRI)? But even though the hip radiograph is negative, will she be able to go home?

These are examples of when test results do not confirm your clinical suspicion. What do you do in those cases? Should you believe the test result or believe your clinical judgment before ordering the test? Were these the optimal tests in the first place? Remember back to conversations with your teachers in emergency medicine on diagnostic testing. Didn't they always ask, “How will a test result change your management?” and “What will you do if it's positive, negative, or indeterminate?”

The purpose of diagnostic testing is to reach a state where we are adequately convinced of the presence or absence of a condition. Test results are interpreted in the context of the prevalence of the suspected disease state: your clinical suspicion of the presence or absence of disease in the individual patient. For example, coronary artery disease is common. However, if we look for coronary disease in 25 year olds, we are not likely to find it because it is very uncommon in that population. There are also times when your clinical suspicion is so high that you do not need objective testing. In certain patients, you can proceed with treatment. For example, some emergency physicians may choose to treat a dislocated shoulder based on the clinical examination rather than first obtaining a radiograph. However, testing is often needed to confirm a diagnosis or to rule out more severe, life-threatening diseases.

The choice over whether to test or not test in the ED also depends upon the resources of the hospital and of the patient. Some hospitals allow easy access to radiographic testing and laboratory testing. In other hospitals, obtaining a diagnostic test may not be as easy. Some hospitals don't have CT scanners. Others do not have the staff available for certain types of tests at night or on weekends (like MRIs and ultrasounds). Sometimes patients may not need a test if you believe that they are reliable to return if symptoms worsen. For others, you may believe that a patient's emergency presentation may be the only time he or she will have access to diagnostic testing. For example, saying to a patient, “Follow up with your doctor this week for a stress test” may be impractical if the patient does not have a primary doctor or does not have good access to medical care. Many providers practice in environments where they cannot order a lot of tests (like developing countries). You also may practice in an office environment that simply does not have easy access to testing. However, regardless of the reason why we order tests in the ED or other acute settings, what is certain is that the use of diagnostic testing in many cases can change how you manage a patient's care.

Sometimes, you may question your choice of whether to test, to not test, or to involve a specialist early. Should you get a CT scan first or just call a surgeon in for a young male with right lower quadrant pain, fever, nausea, and possible appendicitis? How many cases have you seen where the CT scan has changed your management? What if the patient is a young, nonpregnant female? Does that change your plan?

How about using clinical decision rules in practice? By determining if patients meet specific clinical criteria, we can choose not to test some patients if they are low risk. Do all patients with ankle sprains need X-rays? Can you use the Ottawa ankle rules in children? What are the limits of clinical decision rules? Is it possible to apply the Canadian C-spine rules to a 70-year-old female? What is sufficiently “low risk”? These questions come up daily in the practice of emergency medicine. In fact, a major source of variability among physicians is whether or not they order tests. Remember back to your training when you were getting ready to present a patient to the attending physician. Weren't you trying to think to yourself, “What would she do in this case? What tests would she order?”

Access to test results helps us decide whether to treat a disease, initiate even more testing, or no longer worry about a condition. The cognitive psychology of clinical decision making has evolved rapidly over the last several decades. As ED physicians, we gain confidence in this process with experience. Much of the empirical science and mathematics behind testing that are described in this book become instinctive and intuitive the longer you practice emergency medicine. Sometimes we may think a patient does not need to be tested because the last hundred patients who had similar presentations all had negative tests. Maybe you or your colleagues were “burned” once when a subtle clinical presentation of a life-threatening condition was missed (like a subarachnoid hemorrhage). The next patient who presents with those symptoms is probably more likely to get a head CT followed by a lumbar puncture. Is this evidence based? Recognizing our individual diagnostic biases is one way to decrease the likelihood of erroneous decision making while increasing efficiency and effectiveness.

Step back for a moment and think about what we do when ordering a test. After evaluating a patient, we come away with a differential diagnosis of both the most common and the most life-threatening possibilities. The following approach to medical decision making was derived by Pauker and Kassirer in 1980.1 Imagine diagnostic testing as two separate thresholds, each denoted as “I” (for indeterminate). The scale at the bottom of Figure 1.1 denotes pretest probability, which is the probability of the disease in question before any testing is employed. In practice, it is often a challenge to come up with a pretest probability, and frequently opinions on pretest probability differ considerably between experienced physicians. However, for the moment, assume that pretest probability is a known quantity.

Figure 1.1 Pretest probability of disease. (Source: Data from Pauker and Kassirer (1980)).

In Figure 1.1, the threshold between “don't test” and “test” is known as the testing threshold. The threshold between “test” and “treat” is known as the test–treatment threshold. In this schema, treatment should be withheld if the pretest probability of disease is smaller than the testing threshold, and no testing should be performed. Treatment should be given without testing if the pretest probability of disease is above the test–treatment threshold. And, when our pretest probability lies between the testing and test–treatment thresholds, the test should be performed and the patients treated according to the test results. That is the theory. But now let's make this more clinically relevant.

Sometimes disease is clinically apparent and we do not need confirmatory testing before proceeding with treatment. If you are evaluating a patient with an obvious cellulitis, you may choose to give antibiotics before initiating any testing. How about a 50-year-old male with acute chest pain who on his electrocardiogram (ECG) has large inferior “tombstone” ST-segment elevations consistent with acute myocardial infarction (AMI)? Cardiac markers will not be very helpful in the acute management of this patient. This is an example of a situation in which it is important to treat the patient first: give the patient aspirin, anticoagulation, beta blockers, and oxygen, and send him off to the cardiac catheterization lab if your hospital has one or provide intravenous thrombolysis if cardiac catheterization is not readily available. Well, now imagine that the patient has a history of Marfan's syndrome and you think he is having an AMI, but you want to get a chest X-ray or even a CT scan to make sure he doesn't have an aortic dissection before you anticoagulate him. That might put you on the “test” side of the line.

Now imagine the scenario of the potential use for tissue plasminogen activator (tPA) in stroke, a situation frequently encountered in the ED. When a patient comes to the ED within the first few hours of the onset of her stroke symptoms, you rush to get her to the CT scanner. Why? The primary reason is to differentiate between ischemic and hemorrhagic stroke, which will make a major difference in whether or not the patient is even eligible to receive tPA.

Now imagine cases that fall below the testing threshold. You have a 32-year-old male with what sounds like musculoskeletal chest pain. Many would argue that the patient doesn't need any emergency tests at all if he is otherwise healthy and the physical examination is normal. Others might get a chest X-ray and an ECG to rule out occult things like pneumothorax and heart disease, while some others may even get a D-dimer to rule out pulmonary embolism. What is the right way to manage the patient? Is there any evidence behind that decision, or is it just the physician's preference? In some patients, at the end of the ED evaluation, you may not have a definitive answer. Imagine a 45-year-old female with atypical chest pain, a normal ECG, and normal cardiac markers, who you are evaluating at a hospital that does not perform stress testing from the ED. Does she need a hospital admission to rule out acute myocardial infarction and a stress test?

The way that Pauker and Kassirer designed the test–treatment thresholds more than 30 years ago did not account for the proliferation of “confirmatory” diagnostic testing in hospitals. While the lower bound testing threshold is certainly lower than it has ever been, the upper bound threshold has also increased to the point where we are sometimes loath to treat before testing, even when the diagnosis seems apparent. The reason for this is that Occam's razor often does not hold true in emergency medicine. What is Occam's razor? Fourteenth-century philosopher William of Occam stated, “Plurality must not be posited without necessity,” which has been interpreted to mean, “Among competing hypotheses, favor the simplest one.”2 When applied to test–treatment thresholds, what we find is that a patient with objective findings for what might seem like pneumonia (e.g., hypoxia, infiltrates, and a history of cough) likely does have pneumonia, and should be treated empirically, but may also have a pulmonary embolism. While finding that parsimony of diagnosis is important, often the principle of test–treatment thresholds means that if you're above the test–treatment threshold, then you should certainly treat the patient but also consider testing more, particularly in patients with objective signs of additional disease.

Think about how trauma surgeons practice. In the multi-injured trauma patient, isn't their approach to test, test, test? In a seriously injured patient trauma surgeons often default to scanning everything (aka the pan-scan). Some surgeons order CT scans of areas in which the patient has no complaints. They argue that this approach is not illogical. When a patient has been in a major car accident and has a broken left femur, a broken left radius, and mild abdominal tenderness, do they need more CT scans to rule out intra-abdominal injuries and intracranial injuries? Where Occam's razor dulls is that while the most parsimonious diagnosis (just radial and femoral fractures) is possible, patients with multiple traumatic injuries tend to have not only the obvious ones, but also occult injuries. This may necessitate a diagnostic search for the occult intra-abdominal, intrathoracic, and intracranial injuries in a patient with an obviously broken arm and leg.

Risk tolerance refers to the posttest probability at which we are comfortable with excluding or confirming a disease. That is, risk tolerance is where we are comfortable setting our own testing and test–treatment thresholds; it guides where we draw these thresholds and how much we do or do not search for the occult. When deciding on care plans, we develop our own risk tolerance based on our training, clinical expertise, and experiences, as well as local standard practice and the attitudes of the patient, family, or other physicians caring for the patient.

For example, consider possible acute coronary syndrome. After your ED evaluation with cardiac markers, an ECG, and a chest X-ray, you estimate that your patient has a 2% risk of having an unexpected cardiac event within 30 days if he is sent home without additional testing. Is it OK to send him home with this level of risk? Isn't 2% the published rate for missed AMI? What if the risk is 1%, or 0.5%, or 0.1%?

How do you make the decision about when to order a test or just treat? How do you assign a pretest probability? How do you apply test results to an individual patient? This is where research and the practice of evidence-based medicine (EBM) can influence practice by taking the best evidence in the literature about diagnostic testing or clinical decision rules and using that information to make an informed decision about how to care for patients. Chapters 2 and 3 provide an updated overview of the process of EBM as well as examples of the application of EBM to individual patients in the ED, levels of evidence, and how to evaluate a body of literature on diagnostic testing. Chapter 4 is a revised discussion of how we derive, validate, and study the impact of clinical decision rules in practice. Chapter 5, a new chapter in the second edition of this book, reviews recent trends in health policy that may force us to reduce test ordering and use clinical decision rules. Chapter 6 describes various forms of bias that can skew estimates of diagnostic accuracy in research settings.

Understanding the evidence behind diagnostic testing and using clinical decision rules to decide when not to test is at the core of emergency medicine practice. Think back to your last shift in the ED: how many tests did you order?

The purpose of this book is to demystify the evidence behind diagnostic testing and clinical decision rules in emergency care by carefully evaluating the evidence behind our everyday decision making in the ED. This book is written to provide objective information on the evidence behind these questions and our opinion on how we manage our patients with specific clinical problems given the best available evidence. It should be noted that we are writing this from the perspective of academic emergency physicians. We all work in academic EDs with abundant (although not always quick) access to consultants, state-of-the-art laboratories, and high-resolution imaging tests. As you read this, realize that not all emergency medicine practice is the same and you should interpret the literature yourself in the context of your own clinical practice environment.

We have designed each chapter around clinical questions that come up in everyday emergency medicine practice. In the second edition of the book, we have added more chapters and updated all of the old chapters to include new and relevant studies or insights that have emerged in the literature since the first edition was published in 2008. For each question, we present the objective data from published studies and then provide our “expert” comments on how we use these tests in our practice. While we try to provide insight into how we interpret the literature for each testing approach, again, our comments should not be interpreted as the standard of care in emergency medicine. Standard of care is based on practice guidelines and local practice patterns. Instead, these chapters should serve as a forum or basis for discussion. If you are a researcher, you can also think of this book as a roadmap to what is really “known” or “not known” with regard to diagnostic testing in emergency medicine and what needs further study. Finally, rigorous and sound research often takes months to years to accomplish, and sometimes longer to publish. Therefore the discussions we present are likely to change as newer, larger, more comprehensive studies are published, as new prediction or decision rules are validated and replicated, and as newer diagnostic technology is introduced.

References

1. Pauker SG, Kassirer JP. The threshold approach to clinical decision making. New England Journal of Medicine. 1980; 302: 1109–17.

2. Drachman DA. Occam's razor, geriatric syndromes, and the dizzy patient. Annals of Internal Medicine. 2000; 132: 403–4.

Additional Reading

1. Bossuyt PMM, Reitsma JB, Bruns DE, Gatsonis CA, Glasziou PP, Irwig L et al. The STARD statement for reporting studies of diagnostic accuracy: Explanation and elaboration. Annals of Internal Medicine. 2003; 138: W1–W12.

2. Brownlee S. Overtreated: Why too much medicine is making us sicker and poorer. New York: Bloomsbury; 2007.

3. Empey M, Carpenter C, Jain P, Atzema C. What constitutes the standard of care? Annals of Emergency Medicine. 2004; 44: 527–31.

4. Kovacs G, Croskerry P. Clinical decision making: An emergency perspective. Academic Emergency Medicine. 1999; 6: 947–52.

5. Schünemann AHJ, Oxman AD, Brozek J, Glasziou P, Jaeschke R, Vist GE et al. GRADE: Grading quality of evidence and strength of recommendations for diagnostic tests and strategies. British Medical Journal. 2008; 336(7653): 0.3. Available from: http://www.bmj.com/content/336/7654/0.3

6. Whiting P, Rutjes AWS, Westwood ME, Mallett S, Deeks JJ, Reitsma JB et al. QUADAS-2: A revised tool for the quality assessment of diagnostic accuracy studies. Annals ofInternal Medicine. 2011; 155: 529–36.

Chapter 2

Evidence-Based Medicine: The Process

The process we use in this book has been termed evidence-based medicine (EBM). The first question is “What is EBM?” EBM has been defined as “the conscientious, explicit and judicious use of current best evidence in making decisions about the care of patients.”1 However, evidence alone does not define EBM. Instead, EBM occurs within the context of our clinical expertise and incorporates each patient's unique circumstances and preferences. The best way to describe EBM in the emergency department (ED) is as a process by which we (i) ask relevant, focused clinical questions to answer a (ii) search for literature to answer this question, (iii) critically appraise the literature and make conclusions with an understanding of the strength of evidence behind a particular recommendation, and (iv) apply the evidence to the way that individual patients in the ED are managed. For this book, we use the process of EBM to answer important and relevant clinical questions regarding the use of diagnostic testing and clinical decision rules in the ED. Most of the questions we ask and attempt to answer in this book have to do with how to use, when to use, and how much to trust diagnostic testing and clinical decision rules, followed by how to apply published knowledge to individual patients. In this book, we will focus on diagnostic testing and clinical decision rules, however EBM can also be used for other applications in emergency medicine outside of diagnostic testing, such as the determination of which treatment is best for an individual patient.