By S. Elber. Massachusetts College of Art. 2019.
Incremental gain Incremental gain is the expected increase in diagnostic certainty after the appli- cation of a diagnostic test effective 400mg indinavir. The difference simply tells how much the test will increase the probability of disease or how much “bang for your buck” occurs when using a particular diagnostic test order indinavir uk. By convention use absolute values so that all the incremental gains are positive numbers purchase indinavir 400 mg mastercard. For a given range of pretest probability indinavir 400 mg mastercard, what is the diagnostic gain from doing the test? Using the example of strep throat in a child and beginning with a pretest probability of 50%, after doing the test the new probability of disease was 90%. For a negative test the incre- mental gain would also be 40% since the initial probability of no disease was 50% and the post-test probability of no disease was 90% (50 – 90). Doing the same calculations for a patient with a higher pretest probability of disease, but in whom there is still some uncertainty of strep on clinical grounds, say that the pretest probability was estimated to be between a coin toss (50%) and certainty (100%) so put it at about 75%. In order to avoid the false negatives it would probably be best to choose not to do the test if one was this certain and gave a high pretest Incremental gain and the threshold approach to diagnostic testing 287 Table 26. In general, the greatest incremental gain occurs when the pretest probability is in an intermediate range, usually between 20% and 70%. Notice also that as the pretest probability increased the number of false negatives also increased and the number of false positives decreased. The opposite happens when the pretest probability is very low and there will be an increased number of false positives and lower number of false negatives. The question that must then be asked is at what level of clinical certainty or pretest probability should a given test be done? Threshold values Incremental gain tells how much a diagnostic test increases the value of the pretest probability assigned based upon the history and physical and modiﬁed by the characteristics of the test and the prevalence of disease in the popula- tion from which the patient is drawn. One can decide not to do the test if the incremental gain is very small since very little is gained clinically. The midrange of pretest proba- bility yields the highest incremental gain, which is lost at the extremes of pretest probability range. Another way to look at the process of deciding whether to do a test is using the method of threshold values. In this process ﬁnd the probability of disease above which one should treat no matter what, and conversely the level below which one would never treat, and therefore shouldn’t even do the test. These are determined using the test characteristics and incremental gain to decide if it will be worthwhile to do a particular diagnostic test. At each step ask if one still wanted to treat based upon a positive result or would be willing to rule out based on a negative test result. Decision trees can also be used to determine the threshold values and these will be covered in Chapter 30. An alternative method uses a simple balance sheet to approximate the threshold values. In practice, clinicians use their clinical judgment to determine the threshold values for each clinical situation. Clinicians ask themselves “will I gain any additional useful clinical information by doing this test? They already know enough about the patient and should either treat or not treat regardless of the test result, since no useful additional information is gained by performing the test. The treatment threshold is the value at which the clinician asks “do I know enough about the patient to begin treatment and would treat regardless of the results of the test? If a test is done, it ought to be one with high speciﬁcity, which can be used to rule in disease. But if a negative test result is obtained a conﬁrmatory test or the gold-standard test must be done to avoid missing a person with a false negative test. If a test with high speciﬁcity only is chosen, a positive test will rule in disease, but there are too many false negatives, which must be conﬁrmed with a second or gold standard test. The testing threshold is the value at which the clinician asks “is the likelihood of disease so low that even if I got a positive test I would still not treat the patient? If a test is done it ought to be one with high sensitiv- ity, which can be used to rule out disease. But, if a positive test result is obtained a conﬁrmatory test or the gold-standard test must be done to avoid over-treating a person with a false positive test. If a test with high sensitivity only is chosen, a negative test will rule out disease, but there are too many false positives, which must be conﬁrmed with a second or gold standard test. Both of these threshold levels depend not only on the test characteristic, the sensitivity and speciﬁcity, and prevalence of disease, but also on the risks and beneﬁts associated with treatment or non-treatment. The values of probability of disease for the treatment and testing thresholds should be established before doing the test. The clinician selects a pretest probability of disease, and deter- mines whether performing the test will result in placing the patient above the treatment threshold or below the testing threshold. Some patients Incremental gain and the threshold approach to diagnostic testing 289 testing treatment Fig. The pretest probabil- ity of disease is so great that treatment should proceed regardless of the results of the test. This is because if the test results are negative they are more likely to be a false negative and could miss someone with the disease. In that set- ting one must be ready to do a conﬁrmatory test, possibly the gold standard test. In other words, one should be more willing to treat someone who does not have the disease and has a false positive test result, than to miss treating some- one who is a false negative. This may not be true if treatment involves a lot of risk and suffering such as needing a major operation or taking potentially toxic medication. Patients would be unnec- essarily exposed to the side effects of further testing or treatment with very little beneﬁt. The likelihood of disease in someone with a positive test is so small that treatment should not be done even if the test is positive since it is too likely that a positive test will be a false positive. For the child in our example with a sore throat, this testing threshold is a pretest probability of strep throat below 10%. Below this level, applying the rapid strep antigen test and getting a positive result would still not increase the prob- ability of disease enough to treat the patient and one can be certain enough that disease is not present that the beneﬁt of treating is extremely small. Similarly, the treatment threshold is a pretest probability of strep throat above 50%. Above this level, applying the rapid strep antigen test and getting a negative result would still not decrease the probability of disease enough to refrain from treating the patient and one can be certain enough that disease is present so that the ben- eﬁt of treatment is reasonably great. Between these values of pretest probabil- ity (from 10–50%) do the test ﬁrst and treat only if the test is positive, since the post-test probability then increases above the treatment threshold. If the test is negative, the post-test probability is now below the testing threshold. In this example of the child with a sore throat, almost all clinicians agree that if the pretest probability is 90% as would be present in a child with a severe sore 290 Essential Evidence-Based Medicine throat, large lymph nodes, pus on the tonsils, bright red tonsils, fever, and no signs of a cold, the child ought to be treated without doing a test. There would still be a likelihood of incorrectly diagnosing about 10% of viral sore throats as strep throats with this estimate of disease. In general, as the probability of dis- ease increases, the absolute number of missed strep throats will increase. In fact, most clinicians agree that if the post-test probability is greater than 50%, the child ought to be treated. Similarly, if the probability of strep throat was 10% or less in a child with mild sore throat, slight redness, minimal enlargement of the tonsils, no pus, minimally swollen and non-tender lymph nodes, no fever, and signs of a cold, half of all pos- itives will be false positives and too many children would be overtreated. There won’t be much gain from a negative test, since almost all children are negative before we do the test. The addition of the test is not going to help in differentiating the diagnosis of strep throat from that of viral pharyngitis. Therefore one should not do the test if this is the pretest probability of disease. If the pretest probability is between 10% and 50%, choose to do a test, probably the rapid strep antigen test that can be done quickly in the ofﬁce and will give an immediate result. The options here are not to treat or to do the gold-standard test on all those children with a negative rapid strep test and with a moderately high pretest probability of about 50%. It is about ﬁve times more expensive and takes 2 days as opposed to 10 minutes for the rapid strep antigen test. However, there will still be a savings by having to do the gold-standard test on less than half of the patients, including all those with low pretest probability and negative tests and those with high pretest probability who have been treated without any testing.
A recent Internet survey asking about medical risk assessments in a major disaster came up with the following results: “What do you see as the most likely common source of medical problems? Battlefield injuries 5 % Lack of surgical care 36 % Environmental related 8 % Infectious disease (naturally occurring) 64 % Infectious disease (biological warfare) 20 % Nuclear conflict (radiation buy indinavir 400 mg cheap, blast cheap indinavir 400 mg otc, burns) 4 % ” (Frugal’s forum 1/04 with permission order indinavir 400mg. However cheap indinavir 400mg otc, regardless of whatever the initial triggering event after the initial wave of injuries or illness associated with it the majority of medical problems that happen will be common, and mundane, and not nearly as interesting as the above survey results suggests. The record keeping was a bit unreliable at times, but the following summary is reasonably accurate. Abdominal pain (2 confirmed acute appendix + 1 gangrenous gall bladder; no cause found. Morphine The above gives you a variety of insights into what medical problems might occur and what medications are likely to be required. You should - 11 - Survival and Austere Medicine: An Introduction focus on dealing with the common problems, and doing common procedures well, and you will save lives, and improve the quality of people’s lives. While major trauma and surgical emergencies occur – they are reassuringly not that common. To deal with these will require additional knowledge and resources over and above what is require to safely manage 95% of common medical problems. Perhaps the single most important piece of advice in this book: While the focus of this book is on practicing medicine in an austere environment it does not address one key area which must be considered as part of your preparations: That is optimising your health prior to any disaster; losing weight, keeping fit, maintaining a healthy diet, and managing any chronic health problem aggressively. This is well covered in 100s of books about getting fit and staying healthy, but if you do not take some action in this regard all of your other preparations may be in vain when you drop dead of a heart attack from the stress of it all. Then try and learn as much anatomy and physiology as possible –A & P are the building blocks of medicine. Once you understand how the body is put together and how it works you are in a much better position to understand disease and injury and apply appropriate treatments. Then you should try and obtain some more advanced medical education and practical experience. There is no syllabus that we can list that will tell you what you need to know to cover every eventuality. Ultimately what you need to be able to do is: “Know how to perform a basic assessment, established a rough working diagnosis, and know where to look to find further information about what to do next. Anyone with a bit of intelligence, a good A&P book, and a good basic medical text can easily learn the basics. The ideal is a trained health care professional and anything else is taking risks, but in a survival situation any informed medical care is better than no medical care. Formal training Professional medical training: The ideal option is undertaking college study in a medical area e. This clearly isn’t an option for many, but it is still the best option and should be clearly identified as such. While we have heard positive things about the commercial courses mentioned we do not offer any endorsement of any - 13 - Survival and Austere Medicine: An Introduction Table 2. While in theory the content is the same, there is wide variation in quality of teaching over different sites. This is probably the minimum standard to aim for – it provides an overview of anatomy and physiology, and an introduction to the basics of looking after sick and injured patients. It is based around delivering the patient to a hospital as an end result so is of limited value in remote and austere medicine – but it provides a solid introduction. Covering similar material in much less detail it is a good start but not overly in-depth. The usual course length is 40-80 hours – most quality schools offer a 60+ hour course. Various community education groups offer the course and the Red Cross also offers a variation. These courses give a basic background in anatomy and physiology, medical terminology, and the essentials of emergency medicine. Another highly recommended course is the Operational and Emergency Medical Skills course. This course is unfortunately only available to medical staff attached to the Department of Defence and other federal agencies. Some other providers of these types of courses include: Insight training http://www. These courses are unique in catering specifically for survival situations and are highly endorsed. There are probably a number of other more advanced courses available but we have had difficulty obtaining information on them. They offer the basic Immediate Care course and the more advanced Pre-hospital Emergency Care course. They are also affiliated with the Faculty of Pre-Hospital of the Royal College of Surgeons of Edinburgh. Basic surgical skills for remote medics: An intensive three-day course aimed at teaching the basics of surgical practise and to challenge the students with different problems using their newfound skills. Not delivered at a particularly advanced level, but goes well beyond a standard first aid course and is focused on remote work. Many Emergency Departments regularly have a variety of people coming through for practical experience from army medics, to off-shore, island, forest service staff, to fishing boat medics. However, if you are not actually going to touch a patient and are just going to be there to observe then if you ask the right people it should be easy to arrange. While not the same as “hands on” experience, simply experiencing the sights and sounds of illness and injury will help prepare you for if you have to do it yourself. Arrange some teaching: Another option is befriending (or recruiting) a health care professional and arranging classes through them. It is common for doctors to be asked to talk to various groups on different topics so an invitation to talk to a "tramping club" about pain relief or treating a fracture in the bush would not be seen as unusual. Volunteering: Many ambulances and fire services have volunteer sections or are completely run by volunteers. Organisations such as the Red Cross, Search and Rescue units, or Ski patrols also offer basic first aid training, as well as training in disaster relief and outdoor skills. It is also often possible to arrange "ride alongs" with ambulance and paramedic units as the 3rd person on the crew and observe patient care even if you are not able to be involved. However, the larger the group the more formalised and structured your medical care should be. Someone within the group ideally with a medical background should be appointed medic. Their role is to build up their skill and knowledge base to be able to provide medical care to the group. There should also be a certain amount of cross training to ensure that if the medic is the sick or injured one there is someone else with some advanced knowledge. The medic should also be responsible for the development and rotation of the medical stores, and for issues relating to sanitation and hygiene. In regard to medical matters and hygiene their decisions should be absolute, and their advice should only be ignored in the face of a strong tactical imperative. Small groups don’t require a formal “sick-call” or clinic time; you provide care if and when required and fit it in around other jobs. For a larger group dedicated time is required for running clinics and other related medical tasks e. Risk Assessment/Needs Assessment: As alluded to in the introduction what you plan for depends on what you are worried about. As part of your medical preparations you should undertake a detailed needs assessment. Have I considered how I will deal with difficult issues relating to practicing medicine: Confidentiality, death and dying, sexuality, scarcity of resources, etc. What they complained of, the history and examination, what you diagnosed, and how you managed them, a very clear note of any drugs you administer, and a description of any surgical procedure you perform should all be recorded. Anyone with an ongoing problem should have a chronological record of their condition and treatment over time recorded. First is that for the ongoing care of the patient often it is only possible to make a diagnosis by looking over a course of events within retrospect and it is also important to have a record of objective findings to compare to recognise any changes over time in the patient condition.
The headache is more severe on the left side order cheap indinavir on-line, in the area above and in front of her ear purchase indinavir 400mg with visa. A 65-year-old man comes to the physician because of a 6-week history of fatigue and difficulty swallowing buy discount indinavir 400 mg on-line; he also has had a 6 purchase 400mg indinavir overnight delivery. Ten years ago, he underwent operative resection of squamous cell carcinoma of the floor of the mouth. He has smoked 2 packs of cigarettes daily for 40 years and drinks 60 oz of alcohol weekly. A 35-year-old woman comes to the physician because of abdominal pain for 6 months. Physical examination shows ecchymoses in various stages of healing over the upper and lower extremities. It is most appropriate for the physician to ask which of the following questions to begin a discussion with this patient about the possibility of physical abuse? A 22-year-old football player is brought to the emergency department 1 hour after he sustained a left leg injury during a tackle. Physical examination shows mild tenderness and anterior instability of the tibia with the knee in 90 degrees of flexion (positive drawer sign). A postmenopausal 60-year-old woman comes to the physician because of a 2-year history of vaginal dryness, intermittent vaginal pain, and decreased pleasure with sexual intercourse. A 73-year-old woman is brought to the emergency department because of severe back pain for 1 day. Which of the following is the most likely underlying cause of this patient’s condition? An 18-year-old man comes to the physician because of nausea, headache, blood in his urine, and malaise for 2 days. Three weeks ago, he had severe pharyngitis that resolved spontaneously after several days without antibiotic therapy. A 60-year-old woman comes to the physician because of a 3-month history of abdominal fullness and increasing abdominal girth with vague lower quadrant pain. Which of the following is the most appropriate statement by the physician at this time? A 26-year-old woman comes to the emergency department because of a 12-hour history of lower abdominal pain and vaginal bleeding. Measurement of which of the following is the most appropriate next step in management of this patient? A 25-year-old woman with stable cystic fibrosis meets inclusion criteria for a placebo-controlled industry-sponsored research study on a new treatment. The primary care physician is not part of the research team, but he is familiar with the research and considers it to be scientifically sound. The research protocol provides medication and medical care limited to assessing medication effects and adverse effects for 6 months. Which of the following is the most appropriate initial response by the primary care physician? The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. Department of Health and Human Services Office of Disease Prevention and Health Promotion, Contract No. Food and Drug Administration; the National Institutes of Health; the Centers for Disease Control and Prevention; the U. Department of Agriculture; the Department of Defense; the Institute of Medicine; the Dietary Reference Intakes Private Foundation Fund, including the Dannon Institute and the International Life Sciences Institute, North America; and the Dietary Reference Intakes Corporate Donors’ Fund. Contributors to the Fund in- clude Roche Vitamins Inc, Mead Johnson Nutrition Group, and M&M Mars. The views pre- sented in this report are those of the Institute of Medicine Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its panels and subcommittes and are not necessarily those of the funding agencies. Library of Congress Cataloging-in-Publication Data Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids / Panel on Macronutrients, Panel on the Definition of Dietary Fiber, Subcommittee on Upper Reference Levels of Nutrients, Subcommittee on Interpretation and Uses of Dietary Reference Intakes, and the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board. The serpent has been a symbol of long life, healing, and knowledge among almost all cul- tures and religions since the beginning of recorded history. The serpent adopted as a logo- type by the Institute of Medicine is a relief carving from ancient Greece, now held by the Staatliche Museen in Berlin. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its mem- bers, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engi- neering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. His expertise in protein and amino acid metabolism was a special asset to the panel’s work, as well as a contribution to the understanding of protein and amino acid requirements. Close attention was given throughout the report to the evidence relating macronutrient intakes to risk reduction of chronic disease and to amounts needed to maintain health. Thus, the report includes guidelines for partitioning energy sources (Acceptable Macronutrient Distribution Ranges) compatible with decreasing risks of various chronic diseases. Thus, although governed by scientific rationales, informed judgments were often required in setting reference values. The quality and quantity of information on overt deficiency diseases for protein, amino acids, and essential fatty acids available to the com- mittee were substantial. Unfortunately, information regarding other nutri- ents for which their primary dietary importance relates to their roles as energy sources was limited most often to alterations in chronic disease biomarkers that follow dietary manipulations of energy sources. Also, for most of the nutrients in this report (with a notable exception of protein and some amino acids), there is no direct information that permits estimating the amounts required by children, adolescents, the elderly, or pregnant and lactating women. Dose–response studies were either not available or were suggestive of very low intake levels that could result in inadequate intakes of other nutrients. These information gaps and inconsistencies often precluded setting reli- able estimates of upper intake levels that can be ingested safely. The report’s attention to energy would be incomplete without its substantial review of the role of daily physical activity in achieving and sustaining fitness and optimal health (Chapter 12). The report provides recommended levels of energy expenditure that are considered most com- patible with minimizing risks of several chronic diseases and provides guid- ance for achieving recommended levels of energy expenditure. Inclusion of these recommendations avoids the tacit false assumption that light sedentary activity is the expected norm in the United States and Canada. With more experience, the proposed models for establishing reference intakes of nutrients and other food components that play significant roles in pro- moting and sustaining health and optimal functioning will be refined. Also, as new information or new methods of analysis are adopted, these reference values undoubtedly will be reassessed. Many of the questions that were raised about requirements and recommended intakes could not be answered satisfactorily for the reasons given above. Thus, among the panel’s major tasks was to outline a research agenda addressing information gaps uncovered in its review (Chapter 14). The research agenda is anticipated to help future policy decisions related to these and future recommendations. This agenda and the critical, com- prehensive analyses of available information are intended to assist the private sector, foundations, universities, governmental and international agencies and laboratories, and other institutions in the development of their respective research priorities for the next decade. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process.