Clinical Chemistry

With so many tests available and increasingly fast laboratory processors, there is a growing temptation to request large numbers of blood tests on each and every patient. What we should remember is that they should be used as an adjunct to the history and clinical examination. Test results should reinforce the likely diagnosis and rule out our differentials, rather than be used to try and make the diagnosis per se. What makes things easier is to know how serum biochemistry and homeostasis are regulated and then to consider a number of questions: ● Which hormones are involved in the control of this electrolyte? ● What happens when these are increased or decreased? ● Does the patient have any renal or hepatic impairment? ● Are they taking any drugs that might be affecting serum electrolyte levels? ● Have they taken an overdose? ● Is the patient dehydrated/ hypovolaemic/ hypoxic? It can seem daunting at first when results come back unexpectedly out of range. They must be considered in combination with the patient’s clinical status; if the numbers just do not fit, then repeat the test— they may not be right. However, there are a few ‘unmissable’ electrolyte derangements that need to be dealt with immediately. Once detected, they should trigger the thoughts shown in Table 12.1. Interpreting serum values is important, but to prevent iatrogenic derangement, careful use and prescription of intravenous fluids are also needed. Does a patient who looks hypovolaemic, has a low blood pres­sure, and is tachycardic need crystalloids or blood? Colloids, such as ‘Gelofusine®’ or ‘Volplex®’, are now largely out of date, with evidence not supporting their use. Are they frail or do they have cardiac failure and therefore require cautious replacement? Do they have liver failure? Is their fluid balance so critical that close fluid monitoring in a level 2 crit­ical care setting required? Gone are the days when central venous lines are used on the wards for fluid balance. This chapter will help consider­ation of the whole picture before putting pen to paper and (potentially) wrongly prescribing 4 L of fluids a day for a frail older man with left ventricular failure.

Infectious Diseases

Infectious diseases are global and local. They impact health and dis­ease in every country, but protean factors— cultural, geographical, and political— determine their particular local distribution. Every single patient is globally colonized by microorganisms, but singular behaviours, genetics and co- morbidities significantly determine what organisms cause disease in any individual. The practice of infectious diseases medi­cine necessarily demands an understanding of the person and the world in which they live. This chapter will emphasize the importance of context in assessing patients for infectious diseases. In terms of global mortality, communicable diseases remain the leading causes of mortality. Despite the evocative epithet of ‘infectious diseases’, these are not all caused by creatures that creep and crawl. Cosmopolitan diseases (i.e. universally distributed infections such as influenza or bac­terial pneumonia) represent a huge burden wherever medicine is prac­tised. However, it is important to note that in high- resource settings, infection imported by travel and migration is increasing. In particular, the international traffic of emerging infections, such as Zika virus, and anti-microbial resistance (AMR) are already major healthcare problems. As the world shrinks and the climate changes, the distribution of infectious diseases will continue to change. The threat of AMR no longer looms— it is a present and real danger. In the time it will take for disciples of this text to reach the end of their specialty training, AMR will account annually for more deaths than cancer. The delivery of almost all interventional, surgical, and immunomodulatory therapies depends on our ability to provide effective anti- microbial prophylaxis and rescue. The ability of organisms to adapt rapidly to novel iatrogenic selection pressures means that the treatment of human immunodeficiency virus (HIV), tuberculosis (TB), malaria, and manifold other pathogens will be compromised, not simply anti- bacterial agents. The future of modern medicine depends on the global healthcare community sharing both concern and responsibility. This chapter will include cases pertaining to the management of AMR.

Eponymous Syndromes

Medicine has long been riddled with diseases and tests named after things, places, and people. Whilst this can be fun to learn and remember for pub quiz answers, this can become increasingly difficult and does not lend itself well to medical education assessment theory which would class recall of these names as rote learning. In this chapter, which looks at such syndromes, we have aimed to cover some of these eponymous syndromes but using their generic fea­tures, rather than focusing on their specific historical names.

Neurology

The face of neurology in clinical practice is changing. Neurology is no longer primarily a diagnostic specialty. As more therapeutic treatments become available in all fields from epilepsy to multiple sclerosis, early and accurate diagnosis is increasingly required so that patients can benefit from early treatment aiming to reduce the lifelong burden of neuro­logical disease. Diagnosis of neurological disorders is often considered by junior doc­tors to be highly complex and, as such, is responsible for a great deal of anxiety. One of the most difficult challenges can be determining the loca­tion of the lesion. A helpful approach to this is by analysis of the patterns that each lesion produces. Table 8.1 describes some of the common patterns seen in clinical practice, and the questions in this chapter will attempt to highlight some of the other specific presentations needed in assessing the neurology patient.

Renal Medicine

The kidney causes problems for medical students and junior doctors alike— the convoluted journey from plasma to urine, the conundrum of what is reabsorbed and excreted where, and the tangled web of the glomerulonephritides are traditionally learnt, rather than actually understood. As in all clinical medicine, a good place to start is with the fundamen­tals of the organ in question. Passage from plasma to urine follows the pathway: ● Blood ● Glomerulus ● Tubules ● Collecting duct ● Ureter ● Bladder ● Urethra. The primary functions of the kidney are: ● Removal of toxins ● Electrolyte homeostasis ● Maintenance of acid– base balance ● Activation of vitamin D ● Stimulation of erythropoiesis ● Maintenance of blood volume. The challenge then is to implement these basics by being sensitive to deviations from normal physiology: recognizing the accumulation of any potential toxins (hyperkalaemia, uraemia, and acidosis) or the lack of any synthetic products (hypocalcaemia and anaemia), suggesting triggers for such deviations, and pinpointing the specific parts of the anatomy that may be malfunctioning in some way so as to cause impairment. Despite its bad reputation, the kidney reveals more about itself than any other organ and, in theory, should be the easiest to monitor. It achieves this through its raison d’être: urine. Its presence, absence, con­tents, smell, and colour offer a running commentary on the activity of the renal tract at any given point in time— it is the internal, intangible work­ings of specialized cells made physical, measurable, and dippable. So, far from being those much- feared Objective Structured Clinical Examination (OSCE) stations, the dipstick and the catheter are our friends. Or they should be, for it is our ability to harness the information that they pro­vide, allied to the series of numbers on the oft- requested ‘U&Es’ (urea and electrolytes), against a background of wide- ranging symptoms that will make us sensitive to the running of the kidney. This— not just our ability to regurgitate the three types of renal tubular acidosis— is what is at stake in this chapter.

Gastroenterology

Gastroenterology and hepatology encompass a vast array of organs that have diverse structure and function and are affected by a multitude of disease processes. Diseases of the digestive tract are a major cause of morbidity and mortality in the United Kingdom (UK) and worldwide. There have been great advances in our understanding, diagnosis, and management of gastrointestinal (GI) disease, and knowledge continues to develop at a great pace. Understanding the physiology and cellular and molecular events that drive pathological processes, as well as the devel­opment of sophisticated endoscopic and radiological tests, have trans­formed diagnostic capability. Therapeutic endoscopy has progressed to replace surgical management of common GI emergencies such as upper GI tract bleeding and decompressing biliary tract obstruction. However, as ever, there is still much work to be done. For example, the advances in biologic immunotherapy in inflammatory bowel disease has greatly im­proved patients’ quality of life and a reduction in the need for surgery, though the overall impact of these medications on the natural history of the disease is debatable at present. Hepatology is a greatly misunderstood specialty. The physiological changes that occur as cirrhosis and portal hypertension develop are the key to understanding all manifestations of a decompensating liver. Recently, there has been a significant increase in the prevalence of chronic liver disease in the UK, and as a result, hospital admissions have increased. Liver disease is the only major cause of death still increasing year on year, and twice as many people now die from liver disease than in 1991. The 2013 National Confidential Enquiry into Patient Outcome and Death (NCEPOD) of patients with alcohol- related liver disease (ARLD) found that less than half the number of patients who died from ARLD received ‘good care’, and avoidable deaths were identified. Allied to this, the enquiry shed light on a cultural pessimism regarding outcomes and prognosis of chronic liver disease and, in particular, ARLD from both the public and the medical profession as a whole. There is now a concerted drive towards improving awareness of chronic liver disease, and initial simple supportive treatments can greatly improve sur­vival, more so than previously thought.

Geriatric Medicine

Geriatric medicine is the largest ‘medical’ specialty in the United Kingdom, with the number of geriatricians expanding at a huge rate with significant demand. Pragmatic specialists in frailty and complex co- morbidity, the work of geriatricians reaches across geriatric medicine wards, the acute medical unit, emergency departments and acute frailty units, surgical wards, and tertiary medical wards and in the community from inner city London to rural Scotland. They can be found in residential and nursing care homes, rehabilitation teams, and hospital at home teams. Frailty, falls, delirium, dementia, continence, immobility, rehabilitation, polypharmacy, nutrition, end- of- life care, advanced care planning, com­munity medicine, and legal and ethical medicine are all core features of a geriatrician’s day. In this chapter, the questions give a taste of some of these concepts and will also demonstrate how geriatric medicine crosses almost every specialty.

Surgery

Starting a surgical job can feel like learning a completely new language. It may be the first time seeing patients in acute severe pain with a variety of lumps and bumps and a past history of previously unheard of complex operations. It can be easy to get hung up on whether the distended large bowel loop on the X- ray is a caecal or sigmoid volvulus or whether the strangulated hernia is femoral or inguinal. Ultimately, however, the most important point is that, as a junior doctor, it is being able to recognize that the patient is acutely unwell and may require an operation that will save lives. Ironically, a surgical rotation involves little time in the operating theatre— mostly, it will be spent dealing with problems during the peri-­operative period. This may start a week or two before the patient is even admitted, in the shape of a pre- assessment clinic, though these are increasingly nurse- led clinics with minimal input from junior doctors. Such clinics are, however, a good opportunity to see stable patients with interesting pathology and good clinical signs and to establish how well they look before the majority of their large bowel or their stomach is removed. The preoperative preparation of the patient goes beyond bloods and a cursory chat, and will require one to be on the lookout for previously undiagnosed cardiorespiratory or rheumatological conditions, among others, that might affect the patient getting to sleep or staying safely asleep under anaesthesia. Liaising with the anaesthetist about possible sources of difficulty well in advance of the planned procedure will ensure that operations do not get cancelled. The acute abdomen will take centre stage during general surgical takes. A thorough history and sound anatomical knowledge will help create a list of differential diagnoses. Accurate and careful palpation of the abdomen will reveal peritonism and the presence of any masses, and simple bedside observations and tests can greatly aid the diagnosis. Surgical specialties have a heavy reliance on imaging— erect chest X- ray, ultrasound, computed tomography (CT)/ magnetic resonance imaging (MRI) scan— each providing different information for the symp­toms displayed.

Haematology

Tackling haematology is never easy. Revision can be a struggle, as it may not always be obvious which topic areas will be directly relevant to clin­ical practice. We still, however, benefit from an understanding of these areas and an appreciation of how to do and interpret the basics and when more expertise is required. Sometimes the answers require a trip right back to the stem cell. A junior doctor’s most frequent contact with haematology is in interpreting a full blood count. In this task, the core skills of the chapter come to the fore— in response to an anaemia, we should be able to explore the possibilities of iron deficiency, vitamin deficiency, and haem­olysis. On seeing a thrombocytopenia or an abnormal clotting profile, we should be able to make a clinical assessment and perform further appropriate tests, with a view to suggesting differential diagnoses. The questions in this chapter aim to build confidence in these tasks. There is a lot more to haematology, however, than a blood count. As a junior doctor, there will be regular practical challenges such as pre­scribing and altering anticoagulation therapy, overseeing the safe delivery of a blood transfusion, and managing acute situations such as sickle- cell crises. The way forward is to be able to master these basics and start to see the bigger picture. This means developing a feel for the more subtle symptoms and signs of haematological disease and becoming proactive in the face of abnormal blood results. As with all of the chapters in this book, it is a way of thinking that is crucial— one that allows confident management of common situations and recognition of potentially catastrophic conditions, but also one that encourages creativity and initiative. When faced with a clinical conun­drum, we should have the knowledge and confidence to ask appropri­ately: ‘Is the answer in the blood?’

Emergencies

All doctors have to deal with emergencies— this can be a daunting pro­spect, particularly when first on the scene. The fear may be that one wrong decision could be crucial and that the recovery of the patient de­pends entirely on what is done at this moment. The truth is that doctors are rarely— if ever— alone for long and that senior help is, for the most part, just a few seconds away. It should also serve as some consolation that the approach to any clinical emergency should be much the same and depends heavily on the basic and advanced life support algorithms. This chapter is written in the spirit that any clinical encounter should be approached as if it is an emergency— this means resorting to the ABCDE (airway, breathing, circulation, disability, exposure) approach. Clearly, if the patient to whom we are called is sitting up in bed talking and drinking a cup of tea, then expectations can be tailored accordingly. As it is so hard to categorize what constitutes a clinical emergency, it is better that we go into every encounter expecting one. It is easier to taper down one’s level of urgency than it is to suddenly escalate treatment in the light of sudden surprising findings. In this way, the idiosyncratic situations— such as the call regarding the post- op thyroid patient— should be considered just as urgent as the seemingly clear car­diac arrest calls. Having performed the systematic ABCDE assessment of each situ­ation, the next stage is to develop the knowledge and confidence to go on and diagnose which specific emergency is unfolding and to apply appro­priate management plans. Questions in this chapter aim to reinforce the ability to perform this assessment, as well as outlining some of the spe­cific therapies that are required to manage individual emergencies.