The St.Emlyn’s Podcast

Understanding Relative Risk, Absolute Risk, and Number Needed to Treat: A Guide for Emergency Medicine

Welcome back to the St. Emlyn’s podcast. I’m Iain Beardsell and joining me is Simon Carley. Today, we’re delving into the complex yet critical concepts of relative risk, absolute risk, and the number needed to treat (NNT) in the context of emergency medicine. These metrics are essential for understanding the effectiveness of treatments and making informed decisions in clinical practice.

The Importance of Understanding Risk Metrics

In emergency medicine, it’s vital to comprehend how different treatments impact patient outcomes. This understanding not only helps in communicating with patients but also aids in making better clinical decisions. Two key terms frequently encountered are relative risk reduction and absolute risk reduction.

Relative Risk Reduction vs. Absolute Risk Reduction

Imagine we are conducting a trial on a new drug for myocardial infarction (AMI) patients. Typically, 10% of AMI patients die within a month. If our new treatment claims a 50% relative risk reduction, it sounds impressive. However, understanding what this actually means is crucial. A 50% relative risk reduction translates to reducing the death rate from 10% to 5%. While this is significant, it's essential to recognize the difference between relative and absolute risk reduction.

Calculating the Number Needed to Treat (NNT)

The NNT is a valuable metric for understanding how many patients need to receive a particular treatment to prevent one additional adverse outcome. It’s derived from the absolute risk reduction. For instance, if a treatment reduces mortality from 10% to 5%, the absolute risk reduction is 5%. To calculate the NNT, divide 100 by the absolute risk reduction percentage. In this case, 100 divided by 5 equals an NNT of 20. This means we need to treat 20 patients to save one life.

Examples of NNT in Practice

Let’s consider some real-world examples. Tranexamic acid in trauma has an NNT of around 50, meaning we need to treat 50 patients to save one life. For aspirin in treating myocardial infarction, the NNT is also around 50. These figures highlight the effectiveness of these treatments in clinical practice.

Balancing Benefits and Harms

Understanding NNT is crucial, but it’s equally important to consider the number needed to harm (NNH). This metric indicates how many patients need to receive a treatment before one adverse effect occurs. For example, in trials involving starch solutions for sepsis, the NNH was found to be around 10-16. This means for every 10 to 16 patients treated, one additional death occurred. Balancing the benefits and harms is essential for making informed clinical decisions.

Example: Stroke Thrombolysis

In stroke thrombolysis, the NNT is around 8, meaning one in eight patients benefits from the treatment. However, the NNH is about 16, indicating one in 16 patients might experience a harmful outcome, such as intracerebral hemorrhage. Communicating these risks and benefits to patients is crucial for informed consent and shared decision-making.

The Role of Natural Frequencies

Using natural frequencies, such as “one in 100 people” or “one in 50 people,” helps in explaining risks and benefits in a more understandable way. For instance, saying “one in 100 people in your neighborhood” or “one person in a packed football stadium” can make the statistics more relatable.

Misdiagnosis and Its Impact

A key takeaway is that not every missed diagnosis leads to adverse outcomes. Often, treatments may have minimal benefit, and in some cases, they could cause harm. For example, the rush to administer clopidogrel in acute myocardial infarction might not always be necessary, given its relatively high NNT.

Applying These Concepts in Clinical Practice

Understanding and applying these concepts can change how we approach patient care. It allows us to prioritize interventions that provide the most significant benefit while minimizing potential harm. It also highlights the importance of taking time to ensure the right diagnosis and treatment, rather than rushing into potentially harmful decisions.

The Number Needed to Educate (NNE)

A fun and thought-provoking concept introduced in our discussion is the Number Needed to Educate (NNE). How many blogs or articles do you need to read before it changes your clinical practice? This metric emphasizes the importance of continuous learning and staying updated with the latest evidence-based practices.

Conclusion

In emergency medicine, understanding relative risk, absolute risk, and NNT is vital for making informed treatment decisions. These metrics help in balancing the benefits and harms of treatments, leading to better patient outcomes. By effectively communicating these risks and benefits to patients, we can ensure shared decision-making and improve overall patient care.

Read more at St Emlyns and on the accompanying blogpost

Exploring Diagnostic Testing in Emergency Medicine: A St Emlyn’s Perspective

Welcome back to the St Emlyn’s podcast! Today, we're diving deep into the world of diagnostic testing in emergency medicine, inspired by a recent discussion featuring our esteemed colleague Rick Boddie. This episode sheds light on the complexities of diagnosis, the probabilities involved, and the importance of shared decision-making with patients.

Understanding Diagnostic Probabilities

One of the critical points raised by Rick is the significance of understanding diagnostic probabilities. For instance, if a population has a 10% prevalence of a condition and we use a test with 90% sensitivity and 70% specificity, the post-test probability can be less than 2%. This scenario prompts the question: should we discharge a patient based on this probability or admit them for further testing?

In emergency medicine, our goal is to identify patients with serious conditions efficiently. Consider a thousand patients with chest pain; if the prevalence is 10%, around 100 of them will have the disease. With a 98% sensitivity test, we'll identify 98 patients but potentially miss two. However, this translates to missing only one in 500 patients overall, which is relatively low but still significant when considering the potential consequences of a missed diagnosis.

Consequences of Missed Diagnoses

The consequences of a missed diagnosis can vary. For some conditions, missing a diagnosis might not lead to severe outcomes. For instance, a small subarachnoid bleed might never recur, or an early-stage appendicitis could resolve on its own. In such cases, there might be no adverse consequences, and the patient could even benefit by avoiding unnecessary treatments.

However, for conditions like myocardial infarction (MI), the stakes are higher. Missing an MI can lead to severe complications, including cardiac arrest. Yet, it’s crucial to recognize that not every missed MI will result in a catastrophic outcome. Often, patients with missed diagnoses will experience further symptoms, allowing them another opportunity to seek medical attention.

Balancing Diagnostic Accuracy and Over-Investigation

In emergency medicine, we constantly balance the need for diagnostic accuracy with the risks of over-investigation. Over-investigating can lead to false positives, unnecessary treatments, and additional harm to patients. Therefore, it’s essential to adopt evidence-based guidelines and principles that help us make informed decisions without overburdening the diagnostic process.

One approach to achieving this balance is through shared decision-making with patients. Engaging patients in discussions about the risks, benefits, and potential harms of diagnostic tests can lead to better outcomes and increased patient satisfaction.

Shared Decision-Making in Practice

Shared decision-making is particularly valuable in complex cases, such as evaluating pregnant women for pulmonary embolism (PE). In these situations, the standard diagnostic pathway might involve tests that expose the patient and fetus to ionizing radiation. By discussing alternative diagnostic interventions, such as leg ultrasounds or modified VQ scans, we can involve patients in the decision-making process and tailor the diagnostic approach to their specific needs and concerns.

The Legal and Institutional Perspective

From a legal and institutional perspective, adhering to established guidelines and evidence-based practices provides protection for clinicians. If a missed diagnosis occurs despite following these principles, it is considered an acceptable risk within the diagnostic process. This understanding helps mitigate the fear of legal repercussions and allows clinicians to focus on delivering the best possible care based on current evidence.

Communicating with Patients

Effective communication with patients is a cornerstone of good medical practice. Instead of giving definitive statements like "you do not have this condition," it's more helpful to say, "we haven't found anything serious this time, but if you have any further symptoms or concerns, please come back." This approach not only sets realistic expectations but also encourages patients to seek further care if needed without feeling dismissed.

The Role of Technology in Diagnostics

Looking to the future, advancements in diagnostic technology could revolutionize emergency medicine. Imagine having a tool that could predict a patient's 30-day outcome or a "painometer" to measure pain levels accurately. Such innovations would enhance our ability to make precise diagnoses and provide targeted treatments, ultimately improving patient care.

Conclusion

Diagnostic testing in emergency medicine is a complex, nuanced process that requires balancing probabilities, understanding the consequences of missed diagnoses, and engaging in shared decision-making with patients. By adhering to evidence-based guidelines and maintaining open communication with patients, we can navigate these challenges effectively and deliver high-quality care.

At St Emlyn’s, we continuously strive to improve our diagnostic approaches and encourage open discussions about these critical topics. We invite you to share your thoughts and experiences with us on our website or via Twitter. Together, we can enhance our understanding and practices in emergency medicine.

Stay tuned for more insights and discussions in our next podcast episode. Until then, keep exploring, learning, and advancing the field of emergency medicine.

More listening about diagnosis

Podcast – Diagnosis in Emergency Medicine Part 1 – SpIN and SnOUT

Podcast – Diagnosis in Emergency Medicine Part 2 – Beyond a simple yes or no

Podcast – Diagnosis in Emergency Medicine Part 3 – The importance of prevalence

What is a Diagnosis?

A diagnosis is essentially a label that we put on a patient to indicate what they have, which then guides our treatment decisions. In the ED, our primary focus is on identifying life-threatening conditions. This approach often involves working backwards by first ruling out serious conditions before considering what a patient might actually have.

Initial Diagnostic Approach

As emergency physicians, our initial approach is to use tests with high sensitivity. These tests are designed to pick up anyone who might have the disease. Once we rule out the serious conditions, we look at tests with high specificity to confirm the diagnosis, as treatments often carry risks. For example, therapies such as thrombolysis come with significant risks, so we need to be fairly certain before proceeding, unlike less consequential treatments like wrist splints.

Understanding Probabilities in Diagnoses

When we say a patient has a diagnosis, we’re essentially saying it’s likely enough to treat. Conversely, when we say a patient doesn’t have a diagnosis, we mean it’s unlikely enough to withhold treatment. This probabilistic approach is vital in the ED and can be surprising to many people.

Case Study: Cardiac Chest Pain

Let’s apply this to a patient with cardiac-sounding chest pain. Our goal is to either rule out or confirm the disease and start appropriate treatment. We start with specific tests to rule in a diagnosis, such as an ECG. A positive ECG with significant ST segment changes indicates a high likelihood of disease, warranting immediate treatment. This approach quickly sorts out high-risk patients.

For patients with normal or near-normal ECGs but still concerning symptoms, we need sensitive tests to ensure we don't miss anyone with myocardial disease. About 10% of these patients might have underlying issues, so we need to ensure our tests are sensitive enough to catch these cases.

Using Prevalence and Pre-test Probability

To decide if a patient has the disease, we must consider the prevalence or pre-test probability in our population. For example, in patients with normal ECGs and no alarming history, the pre-test probability might be around 10%. This isn’t low enough to rule out the disease but also not high enough to justify treatment without further testing.

Diagnostic Processes in the ED

We use a step-by-step diagnostic process. Starting with the most specific tests to rule in a diagnosis, we then use sensitive tests like high-sensitivity troponin to rule out diseases. High-sensitivity troponin tests are great for ruling out diseases due to their sensitivity. If the test is negative, we can be confident the patient doesn’t have myocardial damage. If the test is positive but not dramatically high, we may need additional tests to confirm the diagnosis.

Each diagnostic step adjusts our patient’s probability of having the disease. Our goal is to reach a probability low enough to safely rule out the disease or high enough to justify treatment. This process is continuous, and we apply it to every patient, whether they have chest pain or another symptom like a headache.

Understanding Likelihood Ratios

We often use likelihood ratios to interpret diagnostic tests. A positive likelihood ratio increases the probability of the disease, while a negative likelihood ratio decreases it. For example, a high-sensitivity troponin test is excellent at ruling out myocardial infarction because of its high sensitivity, though it’s not as good at ruling in due to lower specificity.

Optimising Diagnostic Tests

Diagnostic tests like troponin can be optimized by adjusting the threshold levels. For instance, a higher threshold might improve specificity and thus be better at ruling in the disease, while a lower threshold improves sensitivity, making it better at ruling out the disease. This principle applies to various tests, including white cell counts and amylase levels.

Continuous Assessment and Reassessment

In the ED, we continuously assess and reassess patients. Each diagnostic step, whether it’s asking a question about symptoms or ordering a lab test, adjusts our understanding of the patient’s condition. This iterative process helps us make informed decisions about treatment and ensures that we don’t miss critical diagnoses.

Applying the Approach to Different Symptoms

This diagnostic approach isn’t limited to chest pain. Whether a patient presents with a headache, abdominal pain, or any other symptom, we apply the same principles of sensitivity, specificity, and likelihood ratios. Each question we ask and each test we perform helps refine our assessment and move closer to a definitive diagnosis.

Conclusion

Mastering diagnostic skills in the ED involves understanding and applying probabilities, using specific and sensitive tests effectively, and continuously reassessing the patient’s condition. By focusing on these principles, we can make more accurate diagnoses, provide appropriate treatments, and ultimately improve patient outcomes.

More listening about diagnosis

Podcast – Diagnosis in Emergency Medicine Part 1 – SpIN and SnOUT

Podcast – Diagnosis in Emergency Medicine Part 2 – Beyond a simple yes or no

Podcast – Diagnosis in Emergency Medicine Part 3 – The importance of prevalence

Patients often come to us with the fundamental question: "Doctor, what's wrong with me?" Our goal is to provide an answer through history, examination, and tests. Let's explore what it means to make a diagnosis in emergency medicine.

The Role of Diagnosis in Emergency Medicine

In day-to-day practice, making a diagnosis often means applying a label to a patient. This label helps us decide on the next steps, whether to treat or reassure and send them home. In emergency medicine, we frequently focus on ruling out serious conditions rather than confirming them. This approach allows us to prioritize immediate life-threatening issues and manage resources effectively.

Working Backwards: Ruling Out Serious Conditions

Our primary concern in emergency medicine is to identify conditions that can kill quickly, often within hours. Therefore, we start by ruling out the most serious conditions first. Diagnostic tests, including history and physical examination, play a crucial role in this process. Every question we ask and every examination we perform are part of our diagnostic strategy, aiming to rule out or confirm serious illnesses.

Sensitivity and Specificity in Diagnostic Testing

Understanding diagnostic tests involves two key concepts: sensitivity and specificity.

• Sensitivity refers to a test's ability to correctly identify those with the disease (true positives). High sensitivity means that a negative test result is reliable for ruling out the disease.
• Specificity measures a test's ability to correctly identify those without the disease (true negatives). High specificity means that a positive test result is reliable for confirming the disease.

For example, a D-Dimer test for thrombotic disease is highly sensitive. It picks up most cases of the disease but also includes some false positives. Conversely, a highly specific test like jaw claudication for temporal arteritis has very few false positives but isn't useful as a broad screening tool because only a small percentage of patients with the disease exhibit this symptom.

The Importance of Probability and Risk

In emergency medicine, we rarely achieve 100% certainty in diagnosis. Tests with 98% sensitivity, for instance, still miss 2% of cases. This level of uncertainty is part of our practice, and we must communicate it effectively to patients. Explaining the probabilistic nature of diagnosis helps patients understand the limitations of medical testing and the importance of follow-up if symptoms persist or worsen.

Balancing Diagnosis and Treatment

The consequences of diagnosing and treating a condition vary. For life-threatening conditions like myocardial infarction (MI), the treatment involves significant interventions such as thrombolysis or PCI, which carry their own risks. Therefore, we need a high degree of certainty before initiating such treatments. In contrast, diagnosing a viral sore throat, which requires minimal intervention, demands less certainty.

Continuous Learning and Improvement

Reflecting on our diagnostic processes is crucial for improvement. Recognizing that we work in a probabilistic environment helps us balance the need for thorough investigation with the risk of over-testing. By continuously learning and refining our approach, we can enhance patient care and outcomes.

Favourite Diagnostic Tools

To conclude, let's talk about our favorite diagnostic tools. Personally, I appreciate the value of ultrasound in the resuscitation room, especially for diagnosing pneumothorax in trauma patients. It's a quick, effective tool that guides immediate intervention. Simon, on the other hand, highlights the D-Dimer test. Despite its controversial reputation, it serves as a prime example of a test that, when understood and used correctly, can be incredibly valuable.

We hope this podcast has provided some insight into the complexities and nuances of diagnosis in emergency medicine. Stay tuned for our next episode, where we'll delve deeper into the probabilistic nature of diagnosis and how we make informed decisions in the emergency department. Until then, take care and continue to enjoy your practice in emergency medicine.

More listening about diagnosis

Podcast – Diagnosis in Emergency Medicine Part 1 – SpIN and SnOUT

Podcast – Diagnosis in Emergency Medicine Part 2 – Beyond a simple yes or no

Podcast – Diagnosis in Emergency Medicine Part 3 – The importance of prevalence

Welcome to the St Emlyn's Podcast: A New Chapter in FOAMed

We're thrilled to announce the launch of the St Emlyn's podcast, bringing fresh perspectives and insights from the world of emergency medicine. I'm Iain Beardsell, and alongside Simon Carley, we're excited to extend our reach from the St Emlyn's blog to your favourite podcast platforms.

Why a Podcast?

The landscape of medical education is evolving, and while there's a plethora of excellent podcasts out there, there's a notable gap in UK-centric content. Our aim is to fill that void, offering a unique blend of clinical discussions, evidence-based medicine, and practical management tips tailored for emergency physicians in the UK and beyond.

What is FOAMed?

For those new to the term, FOAMed stands for Free Open Access Medical Education. It's a philosophy we deeply believe in: sharing knowledge, experiences, and lessons to improve patient care globally. FOAMed isn't just about free resources; it's about fostering a community where we can all learn from each other.

What Makes St Emlyn's Podcast Unique?

While we draw inspiration from giants like EMCrit and Scott Weingart, our podcast will provide a distinct UK perspective. Here's what you can expect:

1. Evidence-Based Medicine: We'll dive deep into journal appraisals and discuss the latest research, making it relevant to our everyday clinical practice.
2. Practical Clinical Tips: As practising clinicians, we bring real-world experience from our busy emergency departments, tackling the challenges we all face.
3. Management Insights: Working in high-intensity, high-risk environments, we’ll share strategies on managing departmental flow, dealing with access block, and improving patient outcomes.

Upcoming Episodes

Our first few episodes will focus on diagnosis—a cornerstone of emergency medicine. We'll explore what makes diagnostic tests effective, how to interpret them, and why sometimes we just get lucky. Understanding these elements is crucial for any emergency physician aiming to excel in their field.

Join Our Journey

We’re not just podcasters; we're part of a broader community of emergency medicine professionals. We'll be featuring guests who are experts in their fields, sharing their insights and experiences. These aren't just any guests; they're some of the smartest and most renowned clinicians, who, unbeknownst to them, will soon be part of our podcasting journey.

A Regular Dose of Education

We plan to release episodes regularly, ensuring you have a steady stream of content to enhance your practice. Whether you're commuting, walking the dog, or just relaxing, our podcast will be a valuable addition to your routine.

Stay Tuned

Subscribe to our podcast on iTunes or your preferred platform, and keep an eye on the St Emlyn's blog for more updates. We look forward to embarking on this new journey with you, bringing the best of emergency medicine education to your ears.

Thank you for joining us, and let's make this an engaging and enlightening experience for all.