Section I. Characteristics of kidney and renal diseases in the elderly As in other parts of the world, our population is aging rapidly. The third census of China and the United Nations population projections show that in 1982, 7.63% of our population was over 60 years old, and by 2025, this proportion will rise to about 20%. At present, people over 65 years old in western countries have reached 12% and are increasing rapidly. It is expected that by 2040, people over 65 years old in the United States will account for 21% of the total population, and by 2050, one out of every 20 people in the United States will be over 85 years old. With increasing age, the kidney undergoes great changes in morphology, structure and function, and familiarity with the characteristics of these changes is important for the diagnosis and treatment of various geriatric kidney diseases. I. Physiological changes of kidneys in the elderly (a) anatomical and histomorphological changes The kidneys of newborns weigh only about 50 g. With growth and development, the weight of kidneys gradually increases to 250-270 g on average in young people, accounting for 0.4%-0.5% of body weight. With increasing age, the kidney volume also gradually decreases, with the volume of the two kidneys in young people being about 110 mm × 60 mm × 25 mm, and the volume of the kidneys in the 80-year-old population decreasing by 20%-40% compared to that of the 20-year-old. The loss of kidney tissue is mainly in the cortex, while the medulla is relatively little changed. With increasing age, renal histomorphology mainly shows the following changes: ① Vascular changes: all renal arteries in the elderly have varying degrees of atherosclerosis, intimal thickening and mild glassy changes. Renal microangiography shows that the small renal arteries and arch arteries are often shortened or spirally bent, with the most significant changes in the arch arteries. The vessel wall is degenerative, with mesangial fibrous tissue proliferation, inner elastic plate delamination, and luminal narrowing due to intimal thickening and hyaline degeneration. The decrease in glomerular capillary loops and the opening of micro-arterial short-circuit between the inlet and outlet small arteries resulted in a shunt of blood from the cortex to the medulla and a decrease in renal cortical blood flow, which may be an important reason for the loss of renal tissue mainly in the cortex. Glomerular capillary basement membrane wrinkling and thickening, capillary lumen narrowing and occlusion, which leads to glomerular atrophy and eventually glomerulosclerosis. Glomerulosclerosis occurs at the age of 30, but the number of glomerulosclerosis does not exceed 3% in healthy people over 40 years old, and exceeds 10% in people over 60 years old, and at the age of 80, the number of glomeruli with functional keys gradually decreases to 20%-30% of that of young people, or even up to 50%. When glomerulosclerosis is less than 5%, the distribution of sclerotic glomeruli in the cortex and medulla is basically the same; when glomerulosclerosis exceeds 5%, sclerotic glomeruli are mainly found in the renal cortex. Glomerular sclerosis is directly related to the aging changes of renal blood vessels and capillaries in the elderly. (③) Renal tubules: shortened tubules, marked thickening of the basement membrane, reduced number of tubular cells, epithelial cell atrophy and fatty degeneration. Ultrastructural observation showed a decrease in the number of mitochondria in the renal tubular epithelial cells, irregular morphology, formation of giant mitochondria, disorganized mitochondrial arrangement, longitudinal rows of mitochondrial cristae, fracture or lysis, and other degenerative changes, as well as a decrease in enzyme and adenosine triphosphate concentration. The above changes are most obvious in the proximal tubule, while the main changes in the distal tubule are luminal dilatation and common diverticula or cyst formation. (2) Functional changes are mainly manifested in the following aspects: ① Decrease in renal blood flow: In normal people, about 1000-1200 ml of blood flows through the kidneys every minute at rest, which is equivalent to 20%-25% of cardiac output. The blood flow per unit of renal tissue decreases progressively in the elderly, with the most pronounced decrease in blood flow in the outer cortical layer and a partial shunt of blood to the deeper renal tissue. This redistribution of renal blood flow from the outer cortical layer to the inner layer and medulla allows the elderly to maintain relatively stable water and electrolyte regulation, and also allows the elderly to have a slightly higher total renal filtration fraction. The main reason for the decrease in renal blood flow is due to age-related sclerosis of the small renal arteries and reduction of the renal vascular bed. The decrease in cardiac output is also partly responsible for the decrease in renal blood flow. ②Decrease in glomerular filtration function: Glomerular filtration rate (GFR) decreases year by year with increasing age, and decreases by about 1 ml/min per year after the age of 40. muscle atrophy in the elderly, endogenous creatinine production decreases, and 24-hour urinary creatinine excretion decreases accordingly. when creatinine clearance (Ccr) decreases to 35% of normal, Scr in the elderly still remains in the normal range, therefore, the Scr does not sensitively reflect the changes in their GFR. (③) Decreased renal tubular function: In elderly people with decreased proximal tubular function, the maximum glucose reabsorption rate is reduced, but glomerular filtration of glucose is also reduced, so there is generally no significant increase in urinary sugar. The response of the renal tubules to changes in water intake is significantly reduced in the elderly. Rowe et al. reported that urine osmolality increased to an average of 1109 mmol/kg.H2O in young people after 12 hours of water restriction, compared to 882 mmol/kg.H2O in older adults. Linderman et al. reported that after a 20 ml/kg water load, the maximum free water clearance (CH2O) was 16.2 ml/min in young people, compared with 5.9 ml/min in older adults. Crowe et al. found that urine output occurred in young people at 1 – 2 hours after an oral water load of 20 ml/kg, whereas in the elderly it occurred only after 3 hours. Decreased dilutional function is mainly associated with decreased GFR and poor inhibition of antidiuretic hormone release. Urinary acid excretion is reduced in the elderly. 19% of acid is excreted in the elderly within 8 hours after chloramine loading, whereas 35% of acid is excreted in the young; urinary pH minimum and net acid excretion time are both defective, and prolonged acid loading can lead to acidosis. Defective acid excretion in the elderly is mainly due to reduced total normal renal tubular volume and reduced ammonia production, with reduced titratable acid production also playing a role. The reduced sodium retention capacity of the kidney in the elderly predisposes to hyponatremia when sodium uptake is insufficient or sodium loss is excessive. Therefore, for non-dialysis elderly patients with chronic renal insufficiency, it is not advisable to restrict salt intake too strictly. Plasma renin, angiotensin II and aldosterone levels are lower in the elderly than in the young, and medullary blood flow is relatively increased, resulting in an increase in plasma atrial peptide levels and a decrease in the ability of the distal tubules to reabsorb sodium. Total body potassium and exchangeable potassium decrease with age, which may be related to a decrease in total muscle mass in the elderly. In a study of the potassium response to intravenous potassium chloride in aged rats, the potassium response was the same in aged and young rats, but after a period of high potassium diet, the potassium response to intravenous potassium chloride was worse in aged rats, and the blood potassium was significantly higher than in young rats. If a high potassium diet is consumed after bilateral nephrectomy, the increase in blood potassium is also more pronounced in aged rats, indicating that the adaptation ability of renal and extrarenal potassium homeostasis is reduced in aged rats. Calcium metabolism was significantly altered in the elderly, with reduced 1α hydroxylase activity in renal tissue, reduced 1,25(OH)2D3 production, reduced intestinal calcium absorption, but no significant impairment in renal tubular calcium reabsorption, and almost all of the filtered calcium was reabsorbed by the renal tubules during the low calcium diet, and both intestinal phosphorus absorption and renal tubular phosphorus reabsorption were reduced. Changes in renal endocrine function: The kidney is one of the important endocrine organs in the body. It is known that the kidney can produce and secrete renin, angiotensin, erythropoietin, 1,25 dihydroxycholecalciferol, as well as prostaglandins, kinin release enzyme and other hormones and bioactive substances. The lower plasma renin and angiotensin II levels in the elderly compared to the young may be related to the aging-related changes in glomerular parietal organ morphology and function, decreased renal sympathetic nerve activity, and decreased secretion of related hormones (e.g., adrenocorticotropic hormones, sex hormones, etc.) Tsumoda et al. concluded that the age-related decrease in renin activity is not due to a decrease in plasma concentrations, but mainly to They hypothesized that this may be due to a decrease in the conversion of inactive renin to active renin in the kidneys of the elderly, but the exact in vivo mechanism is not well understood. The ability of the aged kidney to produce 1,25-(OH)2-D3 is significantly reduced, which predisposes the elderly to a range of abnormalities in calcium metabolism, osteoporosis, metabolic bone disease, and pathological fractures. Changes in renal erythropoietin, prostaglandins and other bioactive substances in the elderly have not been reported. Some characteristics of renal diseases in the elderly Chronic renal diseases in the elderly have complex etiology, many influencing factors, atypical performance and heavy disease, rapid development and slow recovery, etc. Due to aging of various organs and renal function in the elderly, the incidence and clinical manifestations of renal diseases are different from those of young people: ① Chronic renal diseases are easily missed and misdiagnosed in the elderly, who often have hypertension, atherosclerosis, diabetes mellitus They may have different degrees of abnormalities in urine examination and kidney function, and when various chronic kidney diseases occur, they are easily considered to be caused by the development of these diseases. ②Predisposition to acute kidney damage In the elderly, the incidence of diseases that can lead to acute renal failure increases significantly, such as acute myocardial infarction, heart failure, serious infections, gastrointestinal blood loss, urinary tract obstruction caused by prostate hypertrophy or tumors, renal artery atherosclerosis, severe vomiting and diarrhea, etc. Diuretics causing water loss, contrast agents, and the application of nephrotoxic drugs are common predisposing factors. When also affected by certain diseases or stress factors, elderly people are more likely to have acute renal failure than young people, and the condition is serious, and renal function is not easily recovered or recovered slowly. For example, many elderly people have good renal function before surgery, and there is no hemorrhage, cardiac arrest, or application of nephrotoxic drugs during surgery, but acute renal failure often occurs after surgery. The incidence of atherosclerotic renal artery stenosis is high: atherosclerotic renal artery stenosis is one of the main causes of hypertension and renal failure in the elderly, and its incidence in the whole population is not clear. Schwartz’s non-selective autopsy study showed a 5% incidence of severe atherosclerotic renal artery stenosis in people younger than 64 years of age, and up to 18% in people aged 65-74 years. The Japanese scholar Uzn performed 1788 autopsies and found that 10.4% of those aged ≥40 years with a history of stroke had at least one renal artery stenosis of more than 75%; of the 297 cases of pathologically diagnosed heart attacks over 40 years of age, 35 cases (12%) had atherosclerotic renal artery stenosis (stenosis ≥75%), and the incidence of renal artery stenosis increased significantly with the increase in the number of stenotic coronary branches. Both domestic and international data show that among those with significant coronary artery stenosis, 12%-20% had significant renal artery stenosis (stenosis >50%). The high incidence of poor urinary flow or obstruction in the elderly makes it difficult for bacteria to be removed by flushing, and they multiply in the urethral sludge. The bladder response to urine pressure is reduced in the elderly, the incidence of neurogenic or weak bladder is higher, and the increased residual urine or urinary retention causes increased pressure in the bladder, which reduces capillary blood flow in its mucosa and decreases local antimicrobial power, combined with low immune function of the urinary tract, rising pH of vaginal secretions after menopause, fecal incontinence in elderly women, and perineal infection can spill over to the urethra, so the elderly are prone to urinary tract infections. The clinical manifestations of urinary tract infection in the elderly are atypical, with no obvious symptoms of urinary tract irritation, and asymptomatic bacteriuria is more common than extrarenal non-specific symptoms, such as fever, lower abdominal discomfort and downward sensation, and lumbosacral ache. Therefore, unexplained fever in the elderly needs to be considered a urinary tract infection, and blood cultures should be performed at the same time in addition to a midstream urine culture. Urinary tract infections in the elderly are mostly chronic and persistent, with a high rate of recurrence and reinfection. Usually the causative agent of urinary tract infection is one, but in complicated cases there can be a mixture of two bacteria. Enlarged prostate is a common cause in men, while lesions above the ureteral opening of the bladder are predominant on one side. In women, cervical cancer or pelvic malignancy infiltrating or metastasizing to compress the ureter, urinary stones, detachment of necrotic tissue from the renal papilla, hyperplasia of fibrous tissue in the retroperitoneum, lymphoma or malignant tumor metastasizing to the retroperitoneal cavity are common causes of urinary tract obstruction. Primary hyperuricemia or hyperuricemia occurring as a result of cytotoxic drug therapy for leukemia can lead to intratubular obstruction due to increased uric acid concentration in the urine. (6) Prone to drug-related kidney damage The elderly have an increased chance of taking various drugs due to their increased chance of disease, and the variety of drugs taken is relatively large, so it is often difficult to quickly identify which drug is causing the kidney damage when it occurs. The kidneys and liver are the main sites for excretion of drugs or their metabolites, and kidney and liver function in the elderly gradually decreases with age. As organs age, cells are more susceptible to damage and often to a greater degree. Therefore, the elderly must be very careful with medication, especially those who have chronic kidney disease or are prone to chronic kidney disease. Section 2: Selection of dialysis modality for elderly patients with end-stage renal failure With the aging population and the increasing number of elderly patients with end-stage renal failure, the number of elderly patients on dialysis is rapidly increasing worldwide and has become the fastest growing segment of the dialysis population. It has been reported that elderly patients account for about 40% of the patients currently receiving maintenance dialysis in China. In the United States, 47% of dialysis patients are elderly, and this percentage will reach 60% by the end of the century. 35% of end-stage renal disease (ESRD) patients in Canada were older than 65 years in 1989, compared to 25% in 1981. 25% of patients over 65 years of age started dialysis in 1990 at a US abdominal dialysis center providing solo kidney disease services to a population of 1.2 million. The European Renal Association registry reported a similar trend: only 9% of patients older than 65 years who started renal replacement therapy in 1977, 11% in 1980, 30% in 1983, and nearly 37% by 1992. There has been a long-standing debate about which dialysis modality is appropriate for older patients with uremia. In many countries, hemodialysis is the primary treatment modality for elderly patients with ESRD. Chronic peritoneal dialysis, although widely used in Canada, the United Kingdom and some other countries, is less commonly used in some other countries such as the United States, where only 16% of elderly patients with kidney disease are treated with peritoneal dialysis. The vast majority (about 85%) of uremic patients in China are also treated with hemodialysis, but in Hong Kong, 80% of ESRD patients are treated with peritoneal dialysis. The preference of scholars in different countries and regions in the choice of dialysis modality is more due to factors other than medical treatment than to disparate differences in the perception of different dialysis modalities. I. Comparison of peritoneal dialysis and hemodialysis techniques 1. Advantages of peritoneal dialysis in the elderly Peritoneal dialysis is widely used in the treatment of ESRD worldwide, and it plays an important role in the treatment of ESRD in the elderly in particular. there are many advantages of CAPD in the treatment of elderly ESRD patients. Most elderly patients have a combination of other diseases such as diabetes mellitus, especially cardiovascular diseases such as hypertension, congestive heart failure, ischemic heart disease, arrhythmias and acute myocardial infarction. Compared to hemodialysis, peritoneal dialysis has less adverse hemodynamic effects, and CAPD generally does not induce or exacerbate arrhythmias, cause hypotension, or worsen cardiac ischemia, even in elderly cardiac patients. Therefore, peritoneal dialysis is relatively safe for elderly patients with renal failure who are less tolerant of hemodialysis and have more severe cardiovascular disease. patients with CAPD can obtain better blood pressure control with fewer antihypertensive drugs, and can maintain water-electrolyte and acid-base balance more safely and better; blood glucose control is made more desirable and convenient by intraperitoneal insulin placement. The effect of peritoneal dialysis on residual renal function is less than that of hemodialysis. In elderly ESRD patients with residual renal function, urine output often decreases rapidly soon after receiving hemodialysis or even becomes absent soon afterwards, whereas in those who use peritoneal dialysis, urine output can be maintained at pre-dialysis levels for a long time if the dialysis is properly dehydrated. Therefore, many scholars advocate that peritoneal dialysis should be the first choice for patients who still have more residual kidney function. Patients with chronic renal failure on CAPD often have less anemia than those on hemodialysis because of less blood loss, greater removal of erythropoietin inhibitors from the blood, and less hemolysis. CAPD is more effective at removing β2-microglobulin and other intermediate molecules (e.g., parathyroid hormone). Peritoneal dialysis is performed at home and is more convenient than hemodialysis for patients who live far from dialysis centers and in nursing homes. 2, the shortcomings of peritoneal dialysis in the elderly peritoneal vascular sclerosis in the elderly, the amount of ultrafiltration is unpredictable, solute clearance may be poor, easy to induce heart failure as a result. On the contrary, if there is too much ultrafiltration and at the same time insufficient water and sodium intake, CAPD patients with chronic hypotension may show symptoms of insufficient vascular blood supply, especially in the lower extremities. The high glucose concentration in the abdominal dialysis fluid may cause hyperglycemia. Considerable amounts of protein and amino acids are lost daily from the peritoneal dialysis fluid, more so when complicated by peritonitis, and most elderly people already have protein-energy malnutrition before starting dialysis and often have combined gastrointestinal diseases, which may cause or worsen malnutrition because of the added possibility of further loss of appetite after starting dialysis. Treatment of ESRD in the elderly requires changes in the lifestyle of patients and their families. Elderly people with comorbid dementia, mental illness, blindness, hemiplegia and other physical disabilities that prevent dialysis operations are dependent on family members for peritoneal dialysis operations, which adds considerable stress to family members. Older adults have a higher incidence of hernia, peripheral vascular disease, s-compartment disease and lower back pain, and may have to discontinue peritoneal dialysis treatment if these comorbidities develop during the course of abdominal dialysis treatment. There is a high incidence of previous abdominal surgery in the elderly, which may result in peritoneal adhesions that reduce the peritoneal surface area and significantly reduce the efficacy of peritoneal dialysis. Comparison of peritoneal dialysis and hemodialysis in elderly patients 1. Comparison of morbidity and mortality rates Hemodialysis and peritoneal dialysis are considered equally valuable renal replacement therapies for elderly ESRD patients, and most studies have shown no difference in morbidity and mortality rates between those treated with CAPD and HD. The effect of age and co-morbidities on patient survival was statistically significant, whereas the mode of dialysis had no such effect. It has been suggested that older patients with diabetes who undergo CAPD in the United States have a higher relative risk of death than HD patients with diabetes, but more recent cohort studies have shown no significant difference. In contrast, in Canada, patient survival in maintenance dialysis patients – at least in the first two years – was better with abdominal dialysis than with hemodialysis in all age groups in their 10-year (1983-1993) In the study, Marcelli et al. reported that the survival of 895 diabetic patients was similar in both dialysis modalities. In a multivariate analysis, the authors analyzed the effects of gender, age, pretreatment risk factors such as severe cardiac disease, severe vascular disease, cirrhosis, cachexia and other risk factors such as malignancy on the survival of patients on maintenance dialysis and found that age, type of diabetes, severe pretreatment vascular disease and cachexia were independent risk factors significantly associated with survival, while dialysis modality was not. Gentil et al. reported that older diabetic patients who underwent hemodialysis had a higher likelihood of switching to CAPD, while those treated with CAPD tended to remain on their original dialysis modality. 1997 USRDS report showed that in younger