Causes \200 Reduced motility of the bowel : drugs (eg opiates, iron, anticholinergics, an tidepressants, antipsychotics, calcium channel blockers, calcium preparations), immobility, constitutional illness, electrolyte disturbances, dehydration, hypothyroidism, lack of die tary \201 bre, hypercalcaemia Failure to evacuate the bowels fully : any painful condition of the rectum or anus, dif \201 culty in access to the toilet, lack of privacy, altered daily routine Neuromuscular : Parkinson \200\231s disease, diabetic neuropathy pseudo- obstruction Mechanical obstruction of the bowel: carcinoma of the colon, diverticular disease CONSTIPATION 371 Prevention and treatment Precipitating causes such as dehydration, hypothyroidism, hypercal caemia, and drugs should be identi \201 ed and reversed. Non-pharmacological measures including regular exercise, improving access to the toilet, ad equate dietary \201 bre, and adequate hydration are effective. Laxatives should be used in combination with non-pharmacological measures. Unless there are reversible factors, always prescribe regular laxatives. Waiting for constipation to occur, then using \200\230prn \200\231 doses is far less effective. You will need to titrate the laxative dose with time and changing patient circumstances. There is little good evidence to guide the choice of laxative, and prescription varies with geography and personal choice. Here are some guiding principles: \200 Stimulant laxative s such as senna (1 \200\2234 tablets/day) or bisacodyl (5 \200\22320mg/day), or stimulant suppositories, may be appropriate for those with bulky, soft fecal overloading Avoid stimulant laxatives in patients with hard rocks of feces as this may produce abdomina l pain. Use a stool softening (osmotic) laxative instead such as lactulose (10 \200\22340mL /day) or a macrogol Long-term use of stimulant laxatives has been said to cause \200\230bowel tolerance \200 \231/neuronal damage leading to a dilated, atonic colon that required even more laxatives. There is very little evidence to support this, and stimulant laxatives are now considered s afe, in moderate doses, for long-term use 1 Sometimes stimulant and osmotic laxatives are used in combination, typically in severe cons tipation (eg opiate-induced) that has been unresponsive to a single drug Stool bulking agents such as methylcellulose or ispaghula are useful in prophylaxis, but ar e less effective in treating established constipation; both \201 bre and other bulking ag ents will increase stool volume and may increase problems Costs of laxatives vary enormously, and there is no correlation between cost and patient acceptability. Try cheaper preparations \201 rst ( \201 bre, se nna) Fecal retention severe enough to cause incontinence nearly always needs a determined effort to clear the colon (see b \200\230HOW TO Treat \200\234over- \202 ow \200\235 fe cal incontinence \200\231, p.545). 1 Muller-Lissuer SA, Kamm MA, Scarpignato C et al . (2005). Myths and misconceptions about chronic constipation. Am J Gastroenterol 100: 232 \200\22342. 372 CHAPTER 12 Gastroenterology Diverticular disease Narrow-necked pockets of colonic mucosa which occur adjacent to blood vessel penetrations of the muscle bands, like \200\230blow outs \200\231 on a tire. Occur anywhere in large bowel but most commonly in the sigmoid. \200 Rare in <40 years, increa sing frequency with age and almost universal > 85 years Cause : thought to be raised intraluminal pressure due to low \201 bre Western diet Investigation : colonoscopy/ \202 exible sigmoidoscopy and barium enema are usually diagno stic and rule out other pathology. CT colography (abdominal CT with oral contrast) is incre asingly used as a better tolerated test in the frail elderly 2The majority of cases are asymptomatic the majority of the time. On other occasions innoce nt diverticulae are blamed for symptoms that arise from other pathology, eg constipation, i rritable bowel disease, or gastro- enteritis. The previous diagnosis of diverticular diseas e should not stop the careful evaluation of new bowel symptoms to exclude important diag- n oses such as colitis or cancer. Pain may occur, and especially if associated with constipation, can be improved by a high \201 bre diet with or without extra stool bulking drugs (eg ispaghula 1 sachet/day). Complications Diverticulitis Should be thought of as \200\230left-sided appendicitis \200 \231. Infection occurs within a pocket and may be due to a faecolith blocking the neck so a voiding con- stipation is key to prevention. Abdominal pain and tenderness, diarrhea, and v omiting occur with fever and raised in \202 ammatory markers. Treat with antibiotics (incl ude anaerobic cover) \200\224 mild cases oral antibiotics at home, severe cases may need a dmission for iv rehydration, antibiotics, and liaison with surgical services. Hemorrhage Selective angiography can be used to demonstrate bleeding point. Diverticular abscess Ultrasound or CT for diagnosis and radiographically guided drainage un der local anesthesia. Perforation/peritonitis See b \200\230The \200\234acute surgical abdomen \200\235 \200 \231, p.380. Fistula Most commonly to bladder causing urinary infection and bubbles in urin e (pneumaturia). Cystoscopy or CT scan for diagnosis. Surgery is required but simple defunc tioning colostomy is often suf \201 cient. DIVERTICULAR DISEASE 373 HOW TO Image the older colon This requires careful consideration of the risk and discomfort of a test, balanced against the quality of the information obtained. Discussing the pros and cons of each investigation with the patients and/or relatives will often help. It is useful to clarify that a patient is \201 t for bowel preparation on the request form if relevant. \200 Flexible sigmoid oscopy is safe and generally well tolerated, requiring only an enema in preparation, allowing direct visualization and biopsy of rectal and lower colonic pathology. Sedation is usually not needed Colonoscopy allows direct imaging and biopsy of more of the colon, and is the preferred met hod for general population investigation, but carries an increased risk of bowel perforatio n in the over 75s. Full bowel clearance and sedation are required CT colonography involves using a CT scanner to produce two- and three-dimensional images of the colon, which are interpreted by a radiologist. This requires full bowel clearance and air insuf \202 ation during the procedure, both of which can be dif \201 cult for frailer old people. It is less invasive than colonoscopy and equivalent for detection of lesions o f a reasonable size. The technique is improving all the time, and is the investigation of c hoice for patients > 75 who are able to tolerate full bowel clearance Minimal preparation CT colon involves ingestion of a contrast agent 48 \200\22372hr before the scan, which then tags the fecal matter, and removes the need for bowel clearance. It is therefore a better investigation for frailer patients, although it misses smaller lesions Plain CT abdomen has reasonable sensitivity for large colonic lesions, may reveal other pat hologies, and requires no bowel preparation. It is therefore useful in emergency assessment , or where the pathology is not clearly colonic Barium enema requires bowel clearance and is less sensitive than CT colonography, so is becoming less frequently used Further reading Fenlon HM , Nunes DP , Schroy III PC , et al . ( 1999 ). A comparison of vi rtual and conventional colonoscopy for the detection of colorectal polyps . N Engl J Med 341 : 1496 \200\223 503 . Ganeshan A , Upponi S , Uberoi R , et al . ( 2007 ). Minimal-preparation CT colon in detect ion of colonic cancer, the Oxford experience . Age Ageing . 36 : 48 \200\223 52 . NICE . Computed tomographic colonography (virtual colonoscopy) ( 2005 ) online: M www.nice. org.uk/ipg129 . 374 CHAPTER 12 Gastroenterology In \202 ammatory bowel disease Ulcerative colitis and Crohn \200\231s disease are chronic, relapsing conditions caused by in \202 ammation of the bowel wall. In \202 ammatory bowe l disease is idiopathic and has an increasing incidence in the population as a whole. Initi al presentation is usually in adolescence but there is a second peak of incidence in older patients. Diarrhea and urgency in this age group can be particularly disabling and may resu lt in incontinence and social isolation. Features \200 Diarrhea (often with blood), malaise, weight loss, and abdominal pain. Delayed presentation may result from embarrassment or fear of cancer. Delayed diagnos is more common in elderly because symptoms are ascribed to one of the common differential d iagnoses such as diverticular disease, CDAD, colonic carcinoma, and ischaemic colitis Associated conditions include arthritis, iritis, sclerosing cholangitis, ankylosing spondyl itis, and skin disorders (pyoderma gangrenosum, erythema nodosum) Complications include thromboembolism, malabsorption and malnutrition, perforation, stenosis with obstruction, \201 stula formation, and colonic a nd biliary malignancy Investigations \200 Exclude infection with stool culture and examination for ova, cysts, and parasites and Clostridium toxin (if in hospital or recent antibiotics) \200 ESR and CRP a re usually elevated but may be normal in localized disease A normochromic normocytic anemia is common, but if there is excessive bleeding iron de \201 ciency can develop Plain X-rays are usually normal but contrast studies are often diagnostic \200 Sigmoidosc opy/colonoscopy and biopsy have high diagnostic yield Treatment Con \201 rmed cases are best managed by gastroenterologists who have specialist nurses and dieticians working with them. Treatment in older patients is not greatly differe nt and is aimed at obtaining and then main- taining remission. There are many new treatment s (eg ciclosporin, inf- liximab) which are beyond the scope of this text. Some principles f or treating elderly include: \200 Exacerbations of distal colitis are usually treated wit h topical mesalazine and steroids given as enemas \200\224 this may be impractical in older patients unless a carer can help and oral steroids can be a better option Budesonide is a steroid with high topical potency (poor absorption and rapid \201 rst pass metabolism) so equivalent doses cause fewer side effects Side effects, drug interactions, and polypharmacy may be more problematic in older patients, eg always consider bisphosphonates with oral steroids therap y Look for and treat proximal constipation which can impair the ef \201 cacy of treatment of a distal colitis INFLAMMATORY BOWEL DISEASE 375 Oral 5-aminosalicylic acid preparations (eg slow-release mesalazine) are often successful ( for exacerbations and maintenance) and well tolerated The risk of malignancy is higher the longer the patient has active disease so theoretically many older patients should be under surveillance by a gastroenterologist. Unfortunately th e risk of colonic perforation during colonoscopic screening is higher in the elderly popula tion so many screening programs stop at age 75 For failure of medical management elective colectomy is well tolerated and may give the bes t quality of life. In contrast emergency surgery in older patients has high mortality 376 CHAPTER 12 Gastroenterology Diarrhea in older patients Acute Short-lived bouts of diarrhea are commonly due to viral ga stroenteritis. Supportive management (rehydration, light diet) is usually suf \201 cient f or this self-limiting condition. It can spread rapidly in institutions (especially if due t o norovirus \200\224 responsible for much of the so-called \200\230winter vom- iting \200 \231) and appropriate infection control measures should be put in place. In frail, hospital ized patients, especially with recent antibiotic exposure, consider CDAD earlier rather tha n later. If diarrhea persists, always send samples for culture, ova, cysts, and parasites, and C. di f \201 cile toxin (see b \200\230 Clostridium dif \201 cile -associated diarrhea \200 \231, p.614). Chronic There is a group of elderly people who have chronic or recurring epi- sodes of diar rhea that merit active investigation \200\224 untreated they suffer high morbidity (especi ally if diarrhea induces fecal incontinence) and many causes are treatable. See b \200\230 HOW TO Investigate and manage chronic diarrhea \200\231, p.377 for a suggested plan o f investigation. Malabsorption Patients do not always have diarrhea. Look for low BMI and falling weight des pite reasonable oral calorie intake. Biochemical markers of malnutri- tion eg hypoalbuminae mia may be present. Anemia is caused by malab- sorption of iron, B12, or folate and is ther efore microcytic, macrocytic, or normocytic. The common causes of malabsorption in older patients often coexist and include: \200 Coeliac disease/gluten sensitive enteropathy Peak incidence age 50 but can manifest for the \201 rst time in old age with weight loss, bone pain (osteoporosis), fatigue (anemia), and mouth ulcers Duodenal biopsy should be performed in all who present with iron de \201 ciency undergoing endoscopy Anti-endomysial or tissue transglutaminase antibodies have very high speci \201 city (100 % ) and reasonable sensitivity (around 85 % ). False negatives can occur with low IgA so al ways check serum immunoglobulins at the same time Pancreatic insuf \201 ciency can occur without history of pancreatitis, alcoholism, or gal lstones. Request a fecal elastase \200\224 a low level supports pancreatic insuf \201 cie ncy Bile salt malabsorption . Ileal resection or disease allows bile salts to reach colon which causes diarrhea Bacterial overgrowth is particularly common in any person with anatomical abnormality of gut (eg post-gastrectomy, small bowel diverticula) but can also o ccur with normal gut architecture diarrhea IN OLDER PATIENTS 377 HOW TO Investigate and manage chronic diarrhea Diagnoses to consider in the elderly population include: \200 In \202 ammatory bowel dis ease \200 Malabsorption \200 Colonic tumor \200 Diverticular disease \200 Chronic i nfections \200 Constipation with over \202 ow diarrhea \200 Drugs \200\224 many drugs can cause diarrhea; review the list and stop any that may be implicated. Common culprits i nclude laxatives, antibiotics, bisphosphonates, NSAIDs, and PPIs History Ask about foreign travel, antibiotic exposure, full drug history, previous gut surg ery/pancreatitis, family history of in \202 ammatory bowel disease. Ask patient or carer t o make a record of stool frequency/texture. Examination Abdominal and digital rectal examination. If rectum is loaded be highly suspici ous of over \202 ow diarrhea. Investigations \200 Stool: culture, C. dif \201 cile toxin, ova, cysts, and parasites \200 Blood tests: FBC (anemia) haematinics (iron, B12, folate de \201 ciency) endomysial antibodies and/or tissue transglutaminase antibodies (and IgA levels), CRP, and ESR Radiology: plain AXR is rarely diagnostic (except unexpected, left sided fecal loading) Sigmoidoscopy: biopsy in several places even if mucosa looks normal to exclude microscopic colitis (see b \200\230Other colonic conditions \200\231, p.378) More extensive colonic imaging may be needed (see b \200\230HOW TO Image the older colon \200\231, p.373) Treatment Obviously depends on cause but in patients in whom diagnosis is not clear and the y are not \201 t for, or refuse, more complex investigations there is a place for a trial of empirical treatment. One such strategy is at least 2 week trials of: \200 Metronidazo le (for overgrowth/diverticular disease) \200 Pancreatin, eg Creon (pancreatic disease ) \200 Bile acid sequestrants, eg colestyramine (bile salt malabsorption) \200 Steroids (for colitis) Pick the most likely or try each in turn for a few weeks. 378 CHAPTER 12 Gastroenterology Other colonic conditions Irritable bowel syndrome A chronic, non-in \202 ammatory conditio n characterized by abdominal pain, altered bowel habit (diarrhea or constipation), and abdo minal bloating, but with no identi \201 able structural or biochemical disorder. \200 Ne w onset is rare in older age and this diagnosis should not be made \200\230de novo \200 \231 in older patients without very careful exclusion of structural disease (particularly c olonic tumors and diverticulitis) Lifelong sufferers may continue with symptoms in later life but if the symptoms change the patient should also undergo investigations \200 Pain or diarrhea that wakes a patient at night, blood in stool, weight loss, or fever are NEVER features of irritable bowel syndrome \200 Some drugs used to tre at irritable bowel syndrome (eg tricyclic antidepressants) are less well tolerated in older patients. Mebeverine might be better tole rated for spasm Dietary advice should be given (low \201 bre for bloating or wind, high \201 bre for di arrhea or constipation, exclude exacerbating foods) Stool bulking drugs can be useful for constipation \200 Loperamide or codeine can be used for disabling diarrhea Angiodysplasia Tiny capillary malformations (like spider naevi) that can occur anywhere in the gut are important only because they bleed. \200 Slow blood loss leads to unexplained recurrent iron de \201 ciency anemia, brisk loss may produce life-threatening hemorrhage Unless they are inherited in a syndrome (eg hereditary haemorrhagic telangiectasia) they are acquired and therefore have increased prevalence with age (most ca ses aged over 70) Asymptomatic angiodysplasia in older patients is common. Diagnosis is often by exclusion of other causes of iron de \201 ciency anemia. Many patients are reinvestigated for recurren t anemia, and the absence of sinister features over a period of time with no demonstrated p athology on standard tests may suggest angiodysplasia is the cause Sometimes colonoscopy can visualize lesions (which can then be treated by diathermy) but CT does not reveal this pathology Selective mesenteric angiography can demonstrate lesions that are actively and rapidly bleeding Tranexamic acid and oestrogens are sometimes successful in controlling chronic blood loss Microscopic colitis Also known as collagenous or lymphocytic colitis. An idiopathic condi- tion causing chronic or episodic watery, non-bloody diarrhea but with no gross structural c hanges seen at colonoscopy. \200 Biopsy changes are diagnostic with collagenous thickenin g of the subepithelial layer and in \201 ltration with lymphocytes Peak incidence in 50s \200 There is no increased risk of cancer \200 Keep treatment as simple as possible \200\224 start with diet and anti- diarrhoeal drugs, mesalazine then steroids OTHER COLONIC CONDITIONS 379 Intestinal ischaemia There is a variety of presentations. Pain out of proportion to the abd ominal examination \201 ndings is common in these syndromes, and should always make you c onsider them. An elevated lactate acidosis should alert you to the possibility of dead b owel. \200 Intestinal angina results from chronic arterial obstruction of the coeliac axis or superior mesenteric artery. Epigastric pain occurs after eating. Diagnosis is tricky as the pain is similar to peptic ulcer pain but angiography is diagnostic. Treat with antiplatelet agents. Vascular reconstruction or stenting may be useful Small bowel ischaemia results from mesenteric artery occlusion, often by an embolus (more c ommon in AF). There is acute colic with rectal bleeding, followed by circulatory collapse. Laparotomy is required, but outcome is poor Ischaemic colitis is an underdiagnosed cause of acute diarrhea blood in dehydrated, hypo tensive elderly patients with vascular disease. Often self-limiting if volume depletion cor rected and the bowel is rested. May result in colonic stricture Colonic gangrene occurs after profound hypotension typically in older ITU patients with heart failure and sepsis. Laparotomy and colectomy is required, but fatal ity is high 380 CHAPTER 12 Gastroenterology The \200\230acute surgical abdomen \200\231 2Peritonitis/perforation often presents in a n on-speci \201 c way. Patients often present to medicine rather than surgery. The diagnosis is easily missed so always have a high index of suspicion and examine the abdomen carefull y and repeatedly in sick elderly patients without a diagnosis. Common causes in older patients include: Complications of diverticular disease \200 First presentation of tumor (gut, pancreatic) \200 Ischaemic bowel (emboli in patients with AF) \200 Strangulated hernias (always rem ember groin examination) \200 Ruptured abdominal aortic aneurysm \200 Duodenal ulcer pe rforation (becoming less common) \200 Biliary stones/sepsis (stones) and pancreatitis \200 Appendicitis Signs Peritonitis/perforation may not have guarding or rigidity, particularly in the very o ld, those on steroids, or people with diabetes. Lack of bowel sounds can be helpful. Signs may develop with time, so repeated assessments are mandatory. Investigations Erect CXR can reveal air under the diaphragm (this is sometimes the only ind ication of a \200\230silent \200\231 perforation). Ultrasound or CT imaging will often rev eal the cause. Management Always involve the surgical team even where patient is unsuitable for operation as they can advise on conservative management and occa- sionally an \200\230interval \200 \231 procedure is appropriate (eg gallstone surgery once cholecystitis has settled). 2Ensur e that surgical decisions are made on the basis of frailty and co-morbidity, or occasionall y on an informed, competent patient deci- sion and not just age alone. Aim to achieve a sen ior medical, surgical and anesthetic consensus. Medical management involves: \200 Broad-spectrum iv antibiotics \200 Resting the bowel (nil by mouth, NG tube if vomiting) \200 Careful monitoring of \202 uid balance \200 \224 heart failure from \202 uid overload or renal failure from dehydration are often the mechanisms of death. A urinary catheter and central venous pressure monitoring are sometim es necessary. Consider prophylactic low molecular weight heparin It is surprising how often patients surv ive with conservative measures so continue to monitor the patient and adjust treatment care fully. Once the signs/symptoms recede try to get the patient eating, on oral antibiotics, a nd mobilizing as soon as possible to avoid the complications of malnutri- tion, pressure so res, VTE and C. dif \201 cile colitis which may be more lethal than the initial peritoniti s. OBSTRUCTED BOWEL IN OLDER PATIENTS 381 Obstructed bowel in older patients As with peritonitis this often presents in a non-speci \201 c or non-dramatic way. Common causes in older patients include: \200 Constipation \200 Colonic tumors \200 Sigmoid volvulus \200 Strangulated hernias (remember to exami ne groins) \200 Adhesions (look for old abdominal scars) \200 Complications of divertic ular disease (abscess, localized perforation, stricture) Signs Consider excluding obstruction (with plain X-ray) in any patient with persistent vomi ting and/or abdominal bloating (ask the patient if their tummy is a normal size for them). Pain/colic, absence of defaecation, tin- kling bowel sounds, and gastric splash are helpful when present (but often absent). Always examine the groins in both sexes for obstructed he rniae. Investigations Plain AXR shows dilated bowel \200\224 standing AXRs have \202 uid levels but are often impractical in older patients and rarely add diagnostic information to a sup ine \201 lm. Ultrasound or CT imaging may localize a cause. Contrast radiology and gastro scopy are sometimes useful. Management Always involve the surgical team who can advise on diagnosis and con- servative management, eg insertion of a \202 atus tube for sigmoid volvulus. General management usually involves: Resting the bowel (nil by mouth and wide-bore NG tube). \200 Careful monitoring of \202 uid balance \200\224 heart failure from \202 uid overload or renal failure from dehydra tion are often the mechanisms of death. Consider broad-spectrum antibiotics if there is fever or features of coexistent perforation. Consider prophylactic low molecular weight heparin Where conservative management fails and an operation is necessary, less invasive/palliative procedures are often more appropriate ( eg defunc- tioning colostomy rather than anterior resection). Pseudo-obstruction presents with vomiting and dilated bowel on X-ray but is due to an atoni c bowel so bowel sounds are absent or decreased rather than increased. Frail, older, immobi le, debilitated patients are more at risk. Can occur with electrolyte abnormality (especial ly low potassium), postsurgery, with drugs (eg opiates, anticholinergics), in neurological disease (eg Parkinson \200\231s or Alzheimer \200\231s) or any severe illness (eg septi- ca emia). Supportive care with hydration and bowel rest is needed, along with correction of th e underlying abnormality. Often resolves with this approach, but decompression or surgery a re occasionally needed. 382 CHAPTER 12 Gastroenterology Obesity in older people In developed countries, there is a general increase in body weight and BMI until about 60 years of age, after which both tend to decline. The body composition also changes, with an increasing proportion of intra- abdominal fat. Weight gain in older people usually relates to a reduction in activity and falling basal me tabolic rate rather than an alteration in calorie intake (which actually tends to get lower with age). The ideal body mass for an elderly person has not been established, although it is probably higher than that for a younger person. Impact of obesity The relationship between mortality and obesity in older people has not be en established. The following should be considered: \200 Weight loss has been reported to increase, not alter, or decrease mortality \200\224 but all the studies have methodologic al problems, and weight loss is a marker of underlying disease which may be occult \200 T hose with chronic disabilities and diseases will reduce activity more than \201 t older people, and so may gain weight more easily In care home residents, only morbid obesity is clearly associated with an increase in morta lity. In addition care homes may need special equipment (eg wider frames, wheelchairs) to a llow for their care \200 Obesity will increase morbidity from conditions such as arthriti s and diabetes and increase cardiovascular risk Obese older people are more likely to have mobility problems and their quadriceps strength to weight ratio is key to standing ability \200 Frailty is certainly associated with incr eased mortality, but this relates to much more than just weight Treatment The goal of treating obesity in older people is to reduce weight without losing l ean mass or contributing to frailty \200\224 excessive weight loss in elderly people is as sociated with an increase in mortality. In the very old, there is little to be gained from altering a lifelong dietary and exercise habit where there are few complications from obesity, but younger patients (60s and 70s) w ith diabetes or vascular disease may bene \201 t greatly from healthier eating habits. \200 Increased physical activity is the mainstay of treatment. This may increase energy expenditure and promote weight loss, improve muscle strength and stamina, r educe intra-abdominal fat and promote a feeling of well-being Calorie restriction should be undertaken with caution, and include at least 800kcal/day with good \202 uid intake Remember to stop supplements in patients who have a high BMI \200 Drugs to enhance weight loss are rarely useful (risk > bene \201 t), although inhibitors of fat absorption (eg orlistat) may be useful in people with diabetes Gastric surgery is higher risk in older obese people, and not frequently undertaken 383 Chapter 13 Renal medicine The ageing kidney 384 Acute kidney injury 386 Acute kidney injury: management 388 HOW TO Perform a \202 uid challenge in AKI/anuria 389 Chronic kidney disease 392 HOW TO Estimate the glomerular \201 ltration rate 393 Chronic kidney disease: complications 394 Renal replacement therapy: dialysis 396 Renal rep lacement therapy: transplantation 398 Nephrotic syndrome 399 Glomerulonephritis 400 Renal a rtery stenosis 401 384 CHAPTER 13 Renal medicine The ageing kidney Kidney function tends to decline with age, but unless there is additional disease, function is usually suf \201 cient to remove waste and to regulate volume and el ectrolyte balance; it is only when stressed that lack of renal reserve becomes apparent. Th e relative contribution of cumulative expo- sure to risk factors (extrinsic ageing), diseas e acquisition (often occult) and intrinsic ageing is unknown, but not all the changes descr ibed are universal in an older population. Falling renal reserve Glomerular \201 ltration rate (GFR) falls steadily after the age of 40 in most healthy older people, possibly due to the following age-related changes: \200 Rise in blood pressure within the normal range \200 Numbers of glomeruli fall (750 % few er age 70 than age 30) \200 Increase in sclerotic glomeruli Renal blood \202 ow decreas es by around 10 % per decade (cortex more than medulla, leading to patchy cortical defects on renal scans). Lower GFR and renal blood \202 ow are the major causes of reduced renal reserve, with the following clinical implications: \200 Renally excreted substances are l ikely to be retained longer (especially drugs) making prescription amendments necessary (see b \200\230Pharmacology in older patients \200\231, p.126) Reduced threshold for damage with ischaemia or nephrotoxins The normal range for plasma ure a and creatinine does not change with age. However, as production of urea and creatinine de creases with falling body muscle mass, renal function is often substantially diminished in an older person, even with apparently normal blood chemistry. 2GFR is a better estimate of renal function than plasma urea and cre- atinine ( see b \200\230HOW TO Estimate the glomerular \201 ltration rate \200\231, p.393) Blunted \202 uid and electrolyte homeostasis The following changes occur with age: \200 A blunted response to sodium loading and depletion, so equilibrium is achieved more slowly Reduced ability to dilute and concentrate urine (falls 5 % every decade) \200 Lower renin and aldosterone levels (30 \200\22350 % less than young people) \200 Loss of the sensati on of thirst, even when plasma tonicity is high (reasons unclear \200\224 may relate to altered baroreceptor function, dry mouths or alter ed mental capacity) Reduced response to vasopressin \200 In addition, many commonly prescribed drugs interfer e with renal function (diuretics, NSAIDs, ACE inhibitors, lithium, sedatives, etc.) Hyponatraemia is therefore common (low sodium intake combined with renal sodium wasting), b ut in times of acute illness (increased \202 uid demand and decreased intake) the slower adaptive mechanisms make hypernat- raemic dehydration more common. THE AGEING KIDNEY 385 Hypokalaemia is common because of poor intake and frequent diuretic use, but lower GFR and hypoaldosteronism lead to a vulnerability to hyperkalaemia especially when exacerbating dru gs (NSAIDs, spironolactone, ACE inhibitors) are used. Structural changes \200 Renal mass falls by 20 \200\22330 % between 30 and 90 years, maki ng kidneys appear smaller on ultrasound scanning, without necessarily implying disease Distal nephrons develop diverticulae (3 per tubule by age 90) that may become retention cysts (benign \201 nding in older people) Other changes \200 Renal 1-hydroxylase activity decreases with age leading to decreased v itamin D production. Combined with low phosphate intake, this can mildly elevate parathyroi d hormone levels There is a loss of the circadian rhythm, owing to altered sodium handling and patterns of aldosterone secretion, so that over the age of 60 the proportion o f water, sodium, and potassium excretion occurring at night increases, causing nocturia 386 CHAPTER 13 Renal medicine Acute kidney injury Previous called acute renal failure. This is more common in older peopl e, but with a similar prognosis if occurring de novo and treated correctly. 2Do not deny tr eatment based on age alone \200\224 even anuric patients can make a full recovery Causes 80 % of cases of acute kidney injury (AKI) are caused by pre-renal failure and ATN ( acute tubular necrosis). Pre-renal causes Due to poor renal perfusion. May be caused by: \200 Dehydration (commonl y associated with sepsis) \200 Volume loss (eg bleeding, over-diuresis) \200 Volume red istribution (eg with low serum albumin) \200 Poor cardiac output (eg post-MI) \200 Aggr avated by many drugs (eg diuretics, ACE inhibitors, NSAIDs) Older patients are prone to sep sis, have less capacity to maintain circu- lating volume in the face of stress and are more likely to be on aggra- vating medications, making this a very common problem (eg urinary s epsis in a patient taking diuretics and NSAIDs can often cause pre-renal renal impairment, and responds well to antibiotics, \202 uids, and drug cessation). 2All unwell elderly pat ients should have renal function checked routinely and repeatedly. Consider stopping diuret ics and ACE inhibitors during an acute illness. Renal causes Due to direct damage to the kidney. Commonly ATN, which may be: \200 Ischaem ic (occurs when pre-renal failure is not corrected quickly, eg with sepsis, surgical proced ures, prolonged hypotension, etc.) \200 Nephrotoxic (usually medication such as aminoglyc oside antibiotics, eg gentamicin) Due to pigment deposition (eg myoglobin in rhabdomyolysis, See b \200\230Rhabdomyolysis \200\231, p.505) Not all renal failure is ATN. Other (rarer) causes include: \200 Glomerulonephritis \200 \224 diffuse in \202 ammatory change to glomeruli with resulting haematuria and red cell casts Acute interstitial nephritis \200\224 consider drug induced nephritis. May have \202 ank pain, rash, fever, eosinophilia, and urine white blood cells/casts but consider if new dru g recently even in absence of these features These less common causes are important because they are often respon- sive to speci \201 c treatment (usually steroids). The patient should be assessed by a renal physician promptly and often need a biopsy. ACUTE KIDNEY INJURY 387 Post-renal causes \200 Obstruction of the renal tract at some point, eg prostatic enlarge ment, renal stones, urethral strictures, pelvic tumors \200 Ultrasound scan shows a dilated col lecting system \200 These conditions are all more common in older people, and are very responsive to treatment if found early, often with full recovery of renal function 388 CHAPTER 13 Renal medicine Acute kidney injury: management Is this acute kidney injury? Older people are more likely t o have underlying chronic kidney disease (CKD), and this confers a worse prognosis. Check o ld notes, ask the patient, family, and GP about history, and look back at blood test result s. Generally, management does not differ signi \201 cantly from younger patients. Investigations \200 See Table 13.1 \200 Treat cause Older people respond as well to most treatments Monitor meticulously \200 Pulse and blood pressure, cardiac monitor, input (iv and oral) and output (urine, fecal matter, vomit, drains, sweat) May be best done on HDU \200 Aim for euvolaemia (assessed clinically may need to correct de \201 cit) then maintain by matching input to output on an hourly basis initially Fluid balance is likely to be harder in older people because of comorbidity (especially heart failure) 2The presence of peripheral oedema does not necessarily indicate \202 uid overload. Circu lating volume is best assessed by blood pressure, pulse, JVP, and skin turgor (see b \200 \230Challenges to volume status assessment in elderly patients \200\231, p.405) \200 May need central venous catheter and urinary catheter initially, but remove as soon as possible because of infection risk \200 Document daily weight and total \202 uid balance summary \200 Be prepared for polyuria in the recovery phase, and ensu re that the patient does not become \202 uid depleted Treat complications Importantly hyperkalaemia, acidosis, and pulmonary oedema. Refer early for further renal support ( \201 ltration or dialysis) a patient can remain ol iguric for some time while renal recovery is occurring, but it is sensible to make the rele vant teams aware of a potential patient. The indications for renal replacement therapy are as follows: \200 Refractory pulmonary oedema (older people are particularly prone to this after over enthusiastic initial \202 uid replacement) Persistent hyperkalaemia (K > 7 mmol/L) that cannot be controlled by insulin/glucose infusions and iv calcium Worsening acidosis (pH <7.2) \200 Uraemic pericarditis \200 Uraemic encephalopathy ACUTE KIDNEY INJURY: MANAGEMENT 389 HOW TO Perform a \202 uid challenge in AKI/anuria Many older patients are clearly dehydrated with mildly impaired renal function tests and th ese patients can be simply rehydrated orally or parenterally. If the patient presents with established AKI or is found to be anuric despite simple rehydr ation then a \202 uid challenge should be contemplated. This is an important clinical ski ll to develop and requires advanced clinical acumen and an investment of time. The key is a n accurate assessment of \202 uid status with the aim of rendering the patient euvolaemic . A urinary catheter is needed and a central venous pressure monitoring device is helpful if facilities exist. \200 Start by assessing and clearly documenting ba seline \202 uid status as this will inform your management and will be helpful when the p atient is reassessed If the patient is already \202 uid overloaded then a single bolus of iv loop diuretic and early contact with the renal specialist team is need \200 If the patient app ears to be hypovolaemic, give 500mL of normal saline (sodium bicarbonate may be considered if they are profoundly acidotic) over 30 \200 \22360min and review If the patient appears to be euvolaemic then the \202 uid challenge should be more cautious. Give 100mL bolus intravenously and review after about 15min For the review repeat and document the \202 uid status and urine output. Repeat this cycle of \202 uid prescription and do a careful review as the clinica l progression becomes clear 3 9 0 Table 13.1 Acute renal failure \200\224 investigations C H A P T E R Investigation Rationale Special points in older people Urea and creatinine Elevated in renal failure Elderly people with very little muscle mass will have lower baseline levels, so a urea of 1 0 in a small elderly woman will represent signi \201 cant renal impairment 1 3 R e n a l Urea: creatinine ratio can be useful \200\224 elevated in pre-renal and post- renal failur e, acting as a marker of dehydration or obstruction m e d i c i n e Electrolytes Potassium rises dangerously in ARF More prone to cardiac complications of electrolyte disturbance \200\224 monitor carefully Arterial blood gasses Monitor pH which falls in ARF pH can also be checked on a venous sample Check for infection Common precipitant of ARF in older people (may be occult)