RENAL & URINARY FUNCTION

ANATOMIC & PHYSIOLOGIC OVERVIEW The primary function of the renal and urinary systems is to maintain the body's state of homeostasis by carefully regulating fluid and electrolytes, removing wastes, and providing hormones that are involved in red blood cell (RBC) production, bone metabolism, and blood pressure

ANATOMY OF THE RENAL AND URINARY SYSTEM: kidneys ureters bladder urethra Urine is formed by the kidney and flows through the other structures to be eliminated from the body.

GERONTOLOGIC CONSIDERATIONS Whether estrogen replacement improves incontinence remains controversial. The nurse must become familiar with resources addressing the medical, social, and functional needs of the older adult, such as rehabilitative services, Medicare/Medicaid reimbursement in both in- and outpatient settings, home care services, assisted care facilities, day programs, and long-term care facilities. Also it is necessary to address other lifestyle changes: proper exercise (at least 150 minutes of brisk walking or other moderate forms of exercise per week), proper nutrition (increased consumption of fruits and vegetables), adequate fluid intake of at least 1,000 mL/day, consumption of fat-free and low-fat dairy products, decreased intake of sugar and sodium, moderate alcohol intake (1 drink per day), and increased dietary fiber

ASSESSMENT Obtaining a comprehensive health history is the first step in assessing a patient with upper or lower urinary tract dysfunction. Health History Obtaining a urologic health history requires excellent communication skills because many patients are embarrassed or uncomfortable discussing genitourinary function or symptoms. - use language the patient can understand and to avoid medical jargon while reviewing risk factors, particularly for those patients who are at high risk. -

INSPECTION & PALPATION OF THE FEMALE GENITALIA The urethra is palpated for diverticula, and the vagina is assessed for adequate estrogen effect and any evidence of herniation. A urethrocele is the bulging of the anterior vaginal wall into the urethra. When the pelvic floor muscles, fascia, or supporting ligaments fail, pelvic organs may fall through the vagina. A cystocele is the herniation of the bladder wall into the anterior vaginal vault. Urinary stasis with a cystocele is a risk factor for the development of UTIs. A rectocele is herniation of the terminal rectum into the posterior vagina

ASSESSMENT FOR EDEMA AND BODY WEIGHT The patient is assessed for edema and changes in body weight. Edema may be observed, particularly in the face and dependent parts of the body, such as the ankles and sacral areas, and suggests fluid retention. An increase in body weight commonly accompanies edema. A weight gain of 1 kg equals approximately 1,000 mL of fluid (1 lb ≈ 500 mL).

REGULATION OF ACID- BASE BALANCE Two important chemical buffers are phosphate ions and ammonia (NH3). Through the buffering process, the kidney is able to excrete large quantities of acid in a bound form, without further lowering the pH of the urine. AUTO REGULATION OF BLOOD PRESSURE Regulation of blood pressure is also a function of the kidney. Specialized vessels of the kidney, called the vasa recta, constantly monitor blood pressure as blood begins its passage into the kidney. When the vasa recta detect a decrease in blood pressure, specialized juxtaglomerular cells near the afferent arteriole, distal tubule, and efferent arteriole secrete the hormone renin. Renin does not affect blood pressure directly. It converts a circulating plasma protein named angiotensinogen to angiotensin I, which is converted to angiotensin II and causes the blood pressure to increase by its vasoconstrictor properties and secretion of aldosterone

AUTO REGULATION OF BLOOD PRESSURE Aldosterone causes renal reabsorption of sodium and water by the distal tubules and collecting ducts, thus volume is returned to systemic circulation. Any etiology that results in poor perfusion or increasing serum osmolality, such as hemorrhage or diarrhea, will cause activation of renin, which leads to activation of angiotensin II and aldosterone secretion. The result is an increase in blood pressure. When the vasa recta recognize the increase in blood pressure, renin secretion stops. Failure of this feedback mechanism is one of the primary causes of hypertension.

BLADDER EMPTYING Micturition normally occurs approximately eight times in a 24-hour period. It is activated via the micturition reflex arc within the sympathetic and parasympathetic nervous system, which causes a coordinated sequence of events. Initiation of voiding occurs when the efferent pelvic nerve, which originates at S1 to S4, stimulates the bladder to contract, resulting in complete relaxation of the striated urethral sphincter. This is followed by a decrease in urethral pressure, contraction of the detrusor muscle, opening of the vesicle neck and proximal urethra, and flow of urine.

BLADDER EMPTYING The pressure generated in the bladder during micturition is about 20 to 40 cm H2O in females. It is somewhat higher and more variable in males 45 years of age and older due to the normal hyperplasia of the lobes of the prostate gland, which surround the proximal urethra. Any obstruction of the bladder outlet, such as in advanced benign prostatic hyperplasia (BPH), results in a high voiding pressure. High voiding pressures make it more difficult to start urine flow and maintain it. If the spinal pathways from the brain to the urinary system are destroyed (e.g., after a spinal cord injury), reflex contraction of the bladder is maintained, but voluntary control over the process is lost.

NUCLEAR SCANS A nuclear scan requires injection of a radioisotope into the circulatory system; then the isotope is monitored as it moves through the blood vessels of the kidneys. The test provides information about kidney perfusion and function. It is used to evaluate acute and chronic kidney failure, renal masses, and blood flow before and after kidney transplantation. RENAL ANGIOGRAPHY In renal angiography, a catheter is threaded up through the femoral and iliac arteries into the aorta or renal artery. A contrast agent is injected to opacify the renal arterial supply. Angiography is used to evaluate renal blood flow, to differentiate renal cysts from tumors, to evaluate hypertension, and preoperatively, for renal transplantation. BLADDER SCAN A portable ultrasound device provides a 3D image of the bladder and measures bladder volume noninvasively, providing immediate details on the volume of urine retained within the bladder.

BLADDER ULTRASONOGRAPHY Ultrasonography is a noninvasive procedure that uses sound waves passed into the body through a transducer to detect abnormalities of internal tissues and organs. A bladder ultrasonography is a noninvasive method of measuring urine volume in the bladder; it automatically calculates and displays urine volume. The test requires a full bladder; therefore, fluid intake should be encouraged before the procedure. This test also can be used to determine if a patient is emptying the bladder after urination. URLOGIC ENDOSCOPIC PROCEDURES Endourology, or urologic endoscopic procedures, can be performed in one of two ways: using a cystoscope (Fig. 26-9) inserted into the urethra, or percutaneously, through a small incision

COMMON COMPLAINTS Fatigue, pain, changes in voiding, and GI symptoms are particularly suggestive of urinary tract disease. Dysfunction of the kidney can produce a complex array of symptoms throughout the body. Fatigue Gradual kidney dysfunction can be insidious in its presentation, although fatigue is a common symptom. Fatigue, shortness of breath, and exercise intolerance all result from the condition known as anemia of chronic disease. Although historically hematocrit has been the blood test of choice when assessing a patient for anemia, currently the use of the hemoglobin level rather than hematocrit is recommended because that measurement is a better assessment of the oxygen transport ability of the blood.

COMMON COMPLAINTS Pain Usually genitourinary pain is caused by distention of some portion of the urinary tract as a result of obstructed urine flow or inflammation and swelling of tissues. Severity of pain is related to the sudden onset rather than the extent of distention. Table 26-3 lists the various types of genitourinary pain, characteristics of the pain, associated signs and symptoms, and possible causes. Initially a gradual decline in kidney functioning may be asymptomatic and only noted when the patient presents for routine examination; an elevation in serum creatinine or abnormal urinalysis may be the first clue to kidney disease. However, some patients present with flank pain or extrarenal symptoms, such as edema, hypertension, hematuria, and signs of uremia (Rosenberg, 2015), leading the nurse to further explore kidney function.

ASSESSMENT When obtaining the health history specific to the renal and urinary systems, the nurse should inquire about the following: The patient's chief concern or reason for seeking health care, the onset of the problem, and its effect on the patient's quality of life The location, character, and duration of pain, if present, and its relationship to voiding; factors that precipitate pain and those that relieve it History of UTIs, including past treatment or hospitalization for UTI Presence of fever or chills Previous renal or urinary diagnostic tests Use of indwelling urinary catheters, suprapubic tubes, condom catheters, or intermittent catheterization Dysuria or painful urination which may occur at initiation or termination of voiding Hesitancy, straining, or pain during or after urination

CONTINUED Urinary incontinence (stress incontinence, urge incontinence, overflow incontinence, or functional incontinence) Hematuria (blood in urine) or change in color or volume of urine The presence of nocturia and number of episodes nightly Renal calculi (kidney stones), passage of stones or gravel in urine Female patients: Number and type (vaginal or cesarean) of deliveries; use of forceps; vaginal infection, discharge, or irritation; contraceptive practices History of anuria (less than 50 cc of urine a day) or other renal problem Presence or history of genital lesions or sexually transmitted diseases Use of tobacco, alcohol, or recreational drugs Any prescription and over-the-counter medications (including those prescribed for renal or urinary problems)

ASSESSMENT OF LOWER EXTREMITIES The deep tendon reflexes of the knee are assessed for quality and symmetry. This is an important part of testing for neurologic causes of bladder dysfunction because the sacral area, which innervates the lower extremities, is the same peripheral nerve area responsible for urinary continence. The gait pattern of the person with bladder dysfunction is also noted, as well as the patient's ability to walk heel to toe. These tests evaluate possible supraspinal causes for urinary incontinence.

DIAGNOSTIC Patients frequently feel discomfort and embarrassment about such a private and personal function as voiding. Voiding in the presence of others frequently can cause guarding, a natural reflex that inhibits voiding due to situational anxiety. Because the outcomes of these studies determine the plan of care, the nurse must help the patient relax by providing as much privacy and explanation about the procedure as possible. The following sections review some of the tests that might be used.

RISK FACTORS the nurse needs to be aware that multiparous women delivering their children vaginally have a high risk for stress urinary incontinence. Elderly women and people with neurologic disorders, such as diabetic neuropathy, multiple sclerosis (MS), or Parkinson disease, often have incomplete emptying of the bladder and urinary stasis, which may result in UTI or increasing bladder pressure, leading to overflow incontinence, hydronephrosis, pyelonephritis, or renal insufficiency People with diabetes who have consistent hypertension and those with primary hypertension are at risk for renal dysfunction as are those who suffer from autoimmune diseases, such as systemic lupus erythematosus (SLE). Older men are at risk for prostatic enlargement, which causes urethral obstruction and can result in UTIs and renal failure.

FAMILY HISTORY People with a family history of urinary tract problems are at increased risk for renal disorders, such as autosomal dominant polycystic kidney disease (which occurs in 1 of 400 to 1,000 people) (Torres & Bennett, 2015), heredity nephritis, or urolithiasis SOCIAL HISTORY It is especially important to obtain a thorough medication history when assessing elderly patients, for whom the increased occurrence of chronic illness often leads to polypharmacy (concurrent use of multiple medications). Aging affects the way the body absorbs, metabolizes, and excretes drugs, placing the elderly patient at risk for adverse reactions. Aging also affects the genitourinary system, leading to compromise and dysfunction in the renal and urinary systems.

GERONTOLOGIC CONSIDERATIONS Also nocturia is common in older adults, resulting in disturbed sleep that impacts daytime fatigue. Because the individual must awaken at night to void, the risk of falls increases and may results in fractures . Other urologic disorders affected by aging are prostate and bladder cancers, BPH, and urinary incontinence, which is the most prevalent urologic disorder in the older adult As individuals age, the density of smooth muscle to connective tissue in the bladder decreases, increasing the likelihood of detrusor fibrosis. Because bladder capacity is reduced, patients may experience a decrease in the force of urinary stream, increased hesitancy, inability to empty the bladder fully, and urinary dribbling; although it may be unclear which symptoms are caused by comorbidities or are a result of aging (Griebling, 2014).

GERONTOLOGIC CONSIDERATIONS Hypertension increases in the geriatric population, contributing to kidney disease and erectile dysfunction Polypharmacy is another factor impacting urologic health, resulting in drug-induced urgency, frequency, retention, and urinary incontinence (Griebling, 2014). Urinary incontinence is common in the older adult, particularly in females, negatively impacting quality of life; frailty is a major risk factor. The nurse should teach bladder-training exercises, such as Kegel maneuvers (refer to Chapter 33, Box 33-9). Incontinence caused by urinary or vaginal prolapse should be referred to a specialist. UTIs always should be considered as a cause of incontinence along with the use of medications, such as diuretics, antidepressant medications, sedative hypnotics, adrenergic agonists, anticholinergics, and calcium channel blockers.

`GERONTOLOGIC CONSIDERATIONS As one ages, there is a decline in organ functioning but, in particular, in those organs that are paired, such as the lungs and the kidneys Examples include sclerosis of the glomerulus and renal vasculature, decreased blood flow, decreased GFR, altered tubular function, and acid-base imbalance. In addition, nephrons lose their ability to compensate as one becomes older

GERONTOLOGIC CONSIDERATIONS This steady decrease in glomerular filtration, combined with the use of multiple medications in which metabolites are cleared by the kidneys, puts the older person at higher risk for adverse drug effects and drug-drug interactions The elderly are more prone to develop hypernatremia and fluid volume deficit because increasing age also is associated with diminished osmotic stimulation of thirst (Greibling, 2014). The elderly, because of both decreased thirst and/or diminished access to fluids and/or impaired urinary concentrating ability, are at the highest risk of developing hypernatremia (an increase in the plasma Na+ concentration to at least 145 mEq/L).

GERONTOLOGIC CONSIDERATIONS Likewise, many older adults may be placed on diuretics, such as furosemide, to control congestive heart failure (CHF) meaning excess sodium may be lost in the urine. This sodium loss results in hyponatremia and a decrease in both central venous pressure (CVP) and arterial blood pressure, causing prerenal failure (Greibling, 2014). In addition, hypervolemic hyponatremia commonly occurs when patients have excess free water relative to serum sodium levels (e.g., kidney failure, cardiac failure, liver failure). Therefore the nurse is alert to sodium levels (hypernatremia or hyponatremia) and is aware of common causes and clinical presentation in order to alert practitioners to reverse this potentially life-threatening condition. Structural or functional abnormalities that occur with aging also may prevent complete emptying of the bladder. This may be due to decreased bladder wall contractility, secondary to myogenic or neurogenic factors, or it may be related to bladder outlet obstruction, such as in BPH (Grossman & Porth, 2014).

GERONTOLOGIC CONSIDERATIONS Vaginal and urethral tissues atrophy (become thinner) in aging women due to decreased estrogen levels, resulting in decreased blood supply to the urogenital tissues, with subsequent urethral and vaginal irritation and possible urinary incontinence. UTIs are common in individuals aged 65 years and over. Risk factors include patients residing in convalescent facilities as well as patients with chronic catheterizations and increasing antibiotic resistance. Symptoms present differently and more subtly than in younger adults and may include increasing confusion, falls, and a loss of appetite. In addition, older adults with impaired cognitive functioning may have difficulty communicating symptoms

CHANGES IN VOIDING Micturition is normally a painless function that occurs approximately eight times in a 24-hour period. The average person voids approximately 1,500 mL of urine in 24 hours, although this amount varies depending on fluid intake, sweating, environmental temperature, vomiting, or diarrhea. Common problems associated with voiding include frequency, urgency, dysuria, hesitancy, incontinence, enuresis (bed wetting), polyuria (more than 3 L/day of urine), oliguria (less than 400 mL/day), and hematuria (two to five RBCs per high-powered field or a positive dipstick) (Table 26-4). Pain that may be associated with an overdistended bladder, difficulty starting the stream of urine or decrease in amount of urine, or straining to void all may be symptoms of urinary retention (Bickley, 2013) and should be evaluated.

GI SYMPTOMS GI symptoms may occur with urologic conditions because of shared autonomic and sensory innervation and renointestinal reflexes (Tortora & Derrickson, 2014). For example, afferent stimulation from the renal pelvis may cause spasms of the pylorus of the stomach; thus the patient may experience symptoms similar to peptic ulcer disease (Tanagho & McAninch, 2012). The most common signs and symptoms are nausea, vomiting, diarrhea, abdominal discomfort, and abdominal distention.

URINE FORMATION Protein molecules also are not usually found in the urine; however, low-molecular-weight proteins (globulins and albumin) may be excreted periodically in small amounts. Recall that the glomerulus filters the blood, similar to a strainer. Therefore, when significant proteinuria is found, glomerular disease is suspected. Levels of greater than 3.5 g/day are indicative of as well as a variety of glomerular disorders

GLOMERULAR FILTRATION normal blood flow through the kidneys is about 1,200 mL/min. Many factors can alter this blood flow and pressure, including hypotension, decreased oncotic pressure in the blood, and increased pressure in the renal tubules from an obstruction. TUBULAR REABSORPTION& TUBULAR SECRETION In tubular reabsorption, a substance moves from the filtrate back into the peritubular capillaries or vasa recta. In tubular secretion, a substance moves from the peritubular capillaries or vasa recta into tubular filtrate

PALPITATION OF THE KIDNEYS A normal right kidney may be palpable especially in very thin patients with relaxed abdominal muscles; however, a left kidney is not usually palpated. Palpation of the kidneys may detect an enlargement that could prove to be very important. The correct technique for palpation is illustrated in Figure 26-5. Renal dysfunction may produce tenderness over the costovertebral angle, which is the angle formed by the lower border of the 12th rib and the spine (Fig. 26-6).

Inspection, Palpation, Percussion, and Auscultation of the Abdomen The abdomen (just slightly to the right and left of midline in both upper quadrants) is auscultated to assess for bruits (low-pitched murmurs that indicate renal artery stenosis or an aortic aneurysm) (Fig. 26-7). The abdomen also is assessed for the presence of ascites (accumulation of fluid in the peritoneal cavity), which may occur with dysfunction of the kidney as well as the liver. On inspection, with the patient lying down, a distended abdomen is noted with bulging flanks (sides) due to the weight of fluid accumulation pressing against the flanks. On percussion, dullness is noted on the flank area (where the water is), whereas tympanic sounds are heard on the upper abdomen as the gas-filled intestines rise above the ascites fluid (refer to Chapter 21 for further details and techniques).

KIDNEYS retroperitoneally (behind and outside the peritoneal cavity) on the posterior wall of the abdomen—from the 12th thoracic vertebra to the 3rd lumbar vertebra in the adult weighs approximately 113 to 170 g (about 4.5 oz) The right kidney is slightly lower than the left due to the location of the liver. well protected by the ribs and by the muscles of the abdomen and back. fat deposits surround each kidney, providing protection against jarring An adrenal gland lies on top of each kidney. The renal parenchyma (organ tissue) is divided into two parts: the cortex and the medulla.

KIDNEYS The medulla is the inner portion of the kidney. It contains the loops of Henle, the vasa recta, and the collecting ducts of the juxtamedullary nephrons. Each kidney contains approximately 8 to 18 pyramids. The pyramids drain into 4 to 13 minor calices, which drain into 2 to 3 major calices that open directly into the renal pelvis. The renal pelvis is the beginning of the collecting system and is composed of structures that are designed to collect and transport urine. Once the urine leaves the renal pelvis, the composition or amount of urine does not change.

Blood SUPPY TO THE KIDNEYS The hilum, or pelvis, is the concave portion of the kidney through which the renal artery enters and the ureters and renal vein exit. kidneys receive 20% to 25% of the total cardiac output; all of the body's blood circulates through the kidneys approximately 12 times per hour. There are two kinds of nephrons. The cortical nephrons, making up 80% to 85% of the total number, are located in the outermost part of the cortex. The juxtamedullary nephrons, distinguished by long loops of Henle, make up the remaining 15% to 20%, are located deeper in the cortex, and are surrounded by long capillary loops called vasa recta that dip into the medulla of the kidney.

NURSING ALERT The nurse auscultates for renal artery bruits, which indicate turbulent blood flow and are associated with a narrowing of the blood vessel or increased flow. Any patient with hypertension should be evaluated for bruits. Typically they are noted with renal artery stenosis just above (2 cm) and to the right or left of the umbilicus. A whooshing sound is indicative of a bruit.

PERCUSSION OF THE BLADDER To check for residual urine, the bladder may be percussed after the patient voids. Percussion of the bladder begins at the midline just above the umbilicus and proceeds downward. The sound changes from tympanic to dull when percussing over the bladder. If dullness is noted, the bladder volume is typically 400 to 500 mL (Bickley, 2013). The bladder, which can be palpated only if it is moderately distended, feels like a smooth, firm, round mass rising out of the abdomen, usually at midline (Fig. 26-8). Dullness to percussion of the bladder after voiding indicates incomplete bladder emptying. A bladder scan can be performed to assess volume of urine retained after voiding.

PALPATION OF THE PROSTATE & INGUINAL AREA In older men, BPH or prostatitis can cause difficulty with urination. The prostate gland is palpated by digital rectal examination (DRE) as part of the yearly physical examination in men 50 years of age and older A blood specimen to test the prostate-specific antigen (PSA) level is recommended for younger men (40 to 45 years of age) if they are at high risk for prostate cancer; namely, African American men and men who have a first-degree relative (father, brother, or son) diagnosed with prostate cancer at an early age (under 65 years of age); then the results of the DRE and PSA are correlated. If a PSA is to be drawn, the sample should be obtained before the DRE because manipulation of the prostate can cause the PSA level to increase temporarily. The inguinal area is examined for enlarged nodes or an inguinal or femoral hernia.

SOCIAL HISTORY Other key information to obtain includes an assessment of the patient's psychosocial status, level of anxiety, perceived threats to body image, available support systems, and sociocultural patterns. Obtaining this information during the initial and subsequent nursing assessments enables the nurse to uncover special needs, misunderstandings, lack of knowledge, and need for patient teaching.

PHYSICAL EXAMINATION Areas of emphasis include the abdomen, suprapubic region, genitalia, lower back, and lower extremities. FIGURE 26-5 Technique for palpating the right kidney (top). Place one hand under the patient's back with the fingers under the lower rib. Place the palm of the other hand anterior to the kidney with fingers above the umbilicus. Push the hand on top forward as the patient inhales deeply. The left kidney (bottom) is palpated similarly by reaching over to the patient's left side and placing the right hand beneath the patient's lower left rib.

SODIUM Activation of this system (by dehydration, e.g., shock or hypotension) will increase NaCl reclamation and, pari passu, water retention culminating in an expansion of the intravascular fluid volume. The net result is the maintenance of pressure within the glomerulus to ensure adequate glomerular filtration pressure and renal function. Nursing Alert The nurse recognizes that a mean arterial pressure (MAP) should be at least 65 mm Hg or higher in order to maintain renal perfusion.

POTASSIUM Nursing Alert When the level of potassium is above 6.5 mEq/L, it represents a medical emergency, primarily due to its effect on the heart. Renal perfusion is essential for excretion of potassium; when the MAP decreases to less than 70 mm Hg, urine volumes begin to decrease, resulting in impaired potassium excretion. Therefore, the nurse is alert to minimal urinary output hourly (0.5 to 1.0 mL/kg/hr) and its effect on K+. The nurse is aware that EKG changes include a progression from peaked T waves to a prolonged PR interval, and then to a widened QRS and heart block; a K+ level above 7 mEq/L is associated with serious arrhythmias.

REGULATION OF ACID- BASE BALANCE The kidney reabsorbs and returns bicarbonate from the urinary filtrate to the body's circulation. It also excretes acid in the urine. Because bicarbonate is a small ion, it is filtered freely at the glomerulus and reabsorbed in the urinary filtrate. To replace any lost bicarbonate, new bicarbonate is generated by the renal tubular cells and then reabsorbed by the tubules and returned to the body. The body's acid production is the result of the breakdown of proteins, which produces acid compounds. The normal daily diet also includes a certain amount of acid materials.

REGULATION OF ACID- BASE BALANCE Unlike carbon dioxide (CO2), the phosphoric and sulfuric acids produced are nonvolatile (solid) and cannot be eliminated by the lungs. If these acids were not excreted in the urine, accumulation of these acids in the blood would lower its pH and inhibit cell function. A person with normal kidney function excretes about 70 mEq of acid each day. The kidney is able to excrete some of this acid directly into the urine until the urine pH reaches 4.5, which is 1,000 times more acidic than blood.

REGUlATION OF WATER EXCRETION Regulation of the amount of water excreted is an important function of the kidney. Antidiuretic hormone (ADH), also known as vasopressin, plays a key role in the regulation of extracellular fluid by excreting or retaining water. ADH is secreted by the posterior portion of the pituitary gland and acts on the kidney in response to changes in osmolality of the blood; that is, ADH is secreted or suppressed depending on blood concentration or dilution, respectively.

REGUlATION OF WATER EXCRETION An increase in blood osmolality is seen with decrease water intake or increased water loss, stimulating ADH release. Consequently, a small volume of concentrated urine is excreted. ADH increases reabsorption of water and returns the osmolality of the blood to normal. With excess water intake or increased retention of water, as occurs in many disease states such as kidney failure, the blood becomes dilute, resulting in suppression of ADH secretion, causing less water to be reabsorbed by the kidney tubule. Assuming maintenance of kidney function, this would result in increased urine volume (diuresis)

REGUlATION OF WATER EXCRETION In general, individuals require about 100 mL of water per 100 calories metabolized in order to rid the body of metabolic waste products. Fevers increase the metabolic and respiratory rate; therefore, the patient will lose additional water via the lungs and perspiration The greatest source of body water is through liquid (1,000 mL) and solid (700 mL) oral intake with an additional 200 mL gained through oxidation. Of the fluid ingested, the main source of loss is through the urine (1,500 mL); approximately 800 mL is lost through the skin and lungs (called insensible loss), and 200 mL through feces (Grossman & Porth, 2014)

REGUlATION OF WATER EXCRETION Normal urine output is approximately 1.5 L in 24 hours (Grossman & Porth, 2014) and intake is roughly equivalent to output in a healthy person (see Table 26-1). It is important to consider all fluid gained and lost when evaluating total fluid status. Daily weight measurements are a reliable means of determining overall fluid status. One pound equals approximately 500 mL so a weight change of as little as 1 lb could suggest an overall fluid gain or loss of 500 mL. The nurse is aware that edema is not present until 2.5 to 3 L of interstitial fluid has been retained (Sterns, 2015). Nursing Alert It is important to maintain consistency when assessing daily weight: the nurse uses the same scale, with the patient wearing the same clothes at the same time daily.

RENAL CLEARANCE Renal clearance refers to the ability of the kidneys to clear solutes from the plasma. A 24-hour collection of urine is the primary test of renal clearance. Renal clearance depends on several factors: how quickly the substance is filtered across the glomerulus, how much of the substance is reabsorbed along the tubules, and how much of the substance is secreted into the tubules. It is possible to measure the renal clearance of any substance, but the one measure that is particularly useful is the creatinine clearance: as renal function declines, creatinine clearance decreases; that is, the patient's serum creatinine rises.

RENAL CLEARANCE Creatinine is an endogenous waste product of skeletal muscle that is filtered at the glomerulus, passed through the tubules with minimal change, and excreted in the urine, making creatinine clearance a good measure of the glomerular filtration rate (GFR). To calculate creatinine clearance, a 24-hour urine specimen is collected. Midway through the collection, the serum creatinine level is measured. The GFR in a young, healthy individual is 120 to 130 mL/min/1.73 m2 (Grossman & Porth, 2014).

URINALYSIS AND URINE CULTURE The urinalysis provides important clinical information about kidney function and helps diagnose other diseases, such as diabetes. The urine culture determines whether bacteria are present in the urine, as well as their strains and concentration. Urine culture and sensitivity (C&S) also identify the antimicrobial therapy that is best suited for the particular strains identified, taking into consideration the antibiotics that have the best rate of resolution in that particular geographic region. Appropriate evaluation of any abnormality can assist in detecting serious underlying diseases. Refer to Table 26-6 for the details regarding urinalysis components and potential significance.

RENAL FUNCTION TEST Renal function tests are used to evaluate the severity of kidney disease and to assess the status of the patient's kidney function. These tests also provide information about the effectiveness of the kidney in carrying out its excretory function. Renal function test results may be within normal limits until the GFR is reduced to less than 50% of normal. Common tests of renal function include renal concentration tests, creatinine clearance, and serum creatinine and blood urea nitrogen (BUN) levels. Table 26-7 describes the purpose and gives the normal range for each test. Other tests for evaluating kidney function that may be helpful include serum electrolyte levels (see Chapter 4).

CT & MRI Computed tomography (CT) scans and magnetic resonance imaging (MRI) are noninvasive techniques that provide excellent cross-sectional views of the kidney and urinary tract. They are used to evaluate genitourinary masses, nephrolithiasis, chronic kidney infections, renal or urinary tract trauma, metastatic disease, and soft tissue abnormalities. Occasionally, an oral or IV radiopaque contrast agent is used in CT scanning to enhance visualization, although the use of a CT scan should take into account the patient's previous exposures to radiation via imaging studies. In addition, the risks associated with contrast agents should be considered. Contrast-induced nephropathy is associated with a pre-existing renal insufficiency, history of diabetes, and reduced intravascular volume (Reekers, 2015). Preprocedure hydration, along with recognition of the lowest dose of contrast as possible for the study, is recommended. Nursing Alert The presence of urethral injury should be ruled out prior to Foley catheter placement in patients with blood at the urethra and suspicion of injury to the lower urinary tract. Catheter placement may potentially convert a partial urethral tear to a complete urethral disruption (Tibbles, 2015, p. 232).

RETROGRADE PYELOGRAPHY If an IV urography provides inadequate visualization of the collecting systems, a retrograde pyelography may be performed. It involves advancing catheters through the ureters into the renal pelvis by means of cystoscopy, followed by injection of a contrast agent. CYSTOGRAPHY In cystography, a catheter is inserted into the bladder, and a contrast agent is instilled to outline the bladder wall. This study aids in evaluating vesicoureteral reflux (backflow of urine from the bladder into one or both ureters) and in assessing for bladder injury. VOIDING CYSTOURETHROGRAPHY In a voiding cystourethrography, a urethral catheter is inserted, and a contrast agent is instilled into the bladder. When the bladder is full and the patient feels the urge to void, the catheter is removed, and the patient voids. This study uses fluoroscopy to visualize the lower urinary tract and assess urine storage in the bladder. It is used as a diagnostic tool to identify vesicoureteral reflux. Retrograde urethrography, in which a contrast agent is injected retrograde into the urethra, is always performed before urethral catheterization if urethral trauma is suspected.

REGULATION OF RED BLOOD CELL PRODUCTION When the kidneys sense a decrease in the oxygen tension in renal blood flow, they release erythropoietin. Erythropoietin stimulates the bone marrow to produce RBCs, thereby increasing the number of circulating RBCs, raising the O2 carrying capacity of the blood. Some conditions, such as chronic kidney disease, require that patients receive exogenous erythropoietin in order to maintain RBC production. VITAMIN D SYNTHESIS The kidneys also are responsible for the final conversion of inactive vitamin D to its active form, 1,25-dihydroxycholecalciferol. Vitamin D is necessary for maintaining normal calcium balance in the body.

SECRETION OF PROSTAGLANDINS The kidneys also produce prostaglandin E and prostacyclin, which have a vasodilatory effect and are important in maintaining renal blood flow. EXCRETION OF WASTE PRODUCTS The kidney functions as the body's main excretory organ, eliminating the body's metabolic waste products. The major waste product of protein metabolism is urea, of which about 25 to 30 g are produced and excreted daily. All of this urea must be excreted in the urine; otherwise it accumulates in body tissues. Other waste products of metabolism that must be excreted are creatinine, phosphates, and sulfates. Uric acid formed as a waste product of purine metabolism, also is eliminated in the urine. The kidneys serve as the primary mechanism for excreting drug metabolites.

SODIUM The regulation of sodium volume excreted depends on aldosterone, a hormone synthesized and released from the adrenal cortex. With increased aldosterone in the blood, less sodium is excreted in the urine, as aldosterone causes renal reabsorption of sodium. The release of aldosterone from the adrenal cortex is largely under the control of angiotensin II, the most effective physiologic vasoconstrictor known. Angiotensin II levels are controlled by renin, a proteolytic enzyme released from specialized juxtaglomerular cells in the renal afferent arteriole (see Fig. 26-4).

SODIUM Renin secretion is controlled by three distinct but overlapping regulatory systems: (1) renal afferent arteriolar pressure (if it decreases renin secretion increases); (2) cardiopulmonary baroreceptors that are capable of modulating sympathetic nervous system outflow (a fall in blood pressure increases renin secretion by increasing sympathetic tone); and (3) the delivery of NaCl to the macula densa, a group of modified distal tubular cells (a decrease in NaCl delivery to these cells increases renin secretion while an increase in NaCl delivery has the opposite effect).

URETERS, BLADDER, AND URETHRA The functional capacity of the adult bladder is about 300 to 500 mL. The bladder has two inlets (the ureters), which are angled to prevent retrograde flow of urine into the ureters and one outlet (the urethra). When the detrusor muscle contracts, urine is released from the bladder; thus, the detrusor is responsible for micturition (voiding). When the bladder is relaxed, the muscle fibers are closed and functions as a sphincter The sphincteric mechanism helps maintain continence. Another muscle involved in continence is the external urinary sphincter at the anterior urethra, the segment most distal from the bladder

URETERS, BLADDER, AND URETHRA During micturition, increased intravesical pressure keeps the ureterovesical junction closed and keeps urine within the ureters. As soon as micturition is completed, intravesical pressure returns to its normal low baseline value, allowing efflux of urine to resume. The only time that the bladder is completely empty is in the last seconds of micturition, before efflux of urine resumes.

NEPHRONS Nephrons (the functional units of the kidney)- responsible for the initial formation of urine. If the total number of functioning nephrons is less than 20% of normal, renal replacement therapy needs to be considered. The glomerulus is a unique network of capillaries suspended between the afferent and efferent blood vessels, which are enclosed in an epithelial structure called Bowman capsule. The distal tubular cells located in this area, known as the macula densa, function with the adjacent afferent arteriole and create what is known as the juxtaglomerular apparatus. This is the site of renin production. Renin is a hormone involved directly in the control of arterial blood pressure; it is essential for proper functioning of the glomerulus

URETERS, BLADDER, AND URETHRA The urine formed in the nephrons flows into the renal pelvis and then into the ureters, which are long fibromuscular tubes that connect each kidney to the bladder terminates in the trigone of the bladder wall. The movement of urine from each renal pelvis through the ureter into the bladder is facilitated by peristaltic contraction of the smooth muscles in the ureter wall. There are three narrowed areas of each ureter: the ureteropelvic junction, the ureteral segment near the sacroiliac junction, and the ureterovesical junction. These three areas of the ureters have a propensity for obstruction by renal calculi (kidney stones) or stricture (narrowing). Obstruction of the ureteropelvic junction is the most serious because of its close proximity to the kidney and the risk of associated kidney dysfunction.

URINE FORMATION Urine is formed in the nephrons through a complex three-step process: glomerular filtration tubular reabsorption Tubular secretion The various substances normally filtered by the glomerulus, reabsorbed by the tubules, and excreted in the urine include sodium, chloride, bicarbonate, potassium, glucose, urea, creatinine, and uric acid. Water, electrolytes, and other substances, such as glucose and creatinine, are filtered by the glomerulus;

URINE FORMATION Glycosuria occurs if the amount of glucose in the blood and glomerular filtrate exceeds the amount that the tubules are able to reabsorb. Renal glycosuria occurs in cases of diabetes and is the most common clinical expression of a blood glucose level exceeding the kidneys' reabsorption capacity. In general, the serum glucose level is greater than 180 to 200 mg/dL when glycosuria is seen.

Nursing Alert The kidneys are responsible for excretion of waste products that account for a daily solute load of approximately 600 mOsm. It is approximated that 500 cc of urine is required daily to excrete that solute load. Without that excretion of 500 cc, toxins and waste products will rise in the serum or blood value. The term azotemia refers to the buildup of excessive nitrogenous wastes in the blood (refer to Chapter 27 for additional detail).

URINE STORAGE The bladder is a hollow, distensible, muscular organ whose size, shape, and position vary in relation to the amount of urine it contains. Both filling and emptying of the bladder are mediated by coordinated sympathetic and parasympathetic nervous system control mechanisms involving the detrusor muscle and the bladder sphincters. Conscious awareness of bladder filling occurs as a result of sympathetic neuronal pathways that travel via the spinal cord to the level of T10 through T12, where peripheral, hypogastric nerve innervation allows for continued bladder filling. As bladder filling continues, stretch receptors in the bladder wall are activated, coupled with the desire to void. This information from the detrusor muscle is relayed back to the cerebral cortex via the parasympathetic pelvic nerves at the level of S1 through S4. Overall bladder pressure remains low due to the bladder's compliance (ability to expand or collapse) as urine volume changes.

URINE STORAGE To maintain adequate kidney filtration rates, bladder pressure during filling must remain lower than 40 cm H2O. This low pressure allows the urine to leave the renal pelvis and enter the ureters freely. The bladder is capable of holding 1,500 to 2,000 mL of urine. This is referred to as the anatomic capacity of the bladder. sensation of bladder fullness is transmitted to the central nervous system when the bladder has reached about 150 to 250 mL in adults A marked sense of fullness and discomfort with a strong desire to void usually occurs when the bladder contains 350 mL or more of urine, referred to as the functional capacity. Neurologic changes to the bladder at the level of the supraspinal nerves, the spinal nerves, or the bladder wall itself can cause abnormally high volumes of urine to be stored due to a decreased or absent urge to void.

URINE STORAGE The bladder should be able to store urine for periods of 2 to 4 hours at a time during the day. At night, the release of vasopressin in response to decreased fluid intake causes a decrease in the production of urine and makes it more concentrated. It allows the bladder to continue filling for periods of 6 to 8 hours in adolescents and adults, making them able to sleep for longer periods before needing to void. This process, which is less pronounced in the elderly, coupled with decreasing bladder compliance and decreased vasopressin (ADH) levels, often causes nocturia.

NURSE ALERT The nurse understands that a normal BUN/creatinine (Cr) ratio is approximately 10:1. As kidney function declines, both the BUN and the Cr rise, thus although elevated the ratio remains within normal limits. If a BUN is elevated but the creatinine is normal (BUN/Cr greater than 20:1), the nurse must assess for causes excluding renal dysfunction. Reasons may include GI bleeding such as gastric ulcers, duodenal ulcers, and gastric cancer (digestion of RBCs elevates the protein level which is transported to the liver and metabolized to BUN), or dehydration (less water available in the intravascular space) where the BUN may increase in a higher proportion than the creatinine, thus indicators of intravascular depletion include an elevated hematocrit value, and a BUN/Cr ratio of greater than 20:1. In situations where the BUN/Cr ratio is less than 10:1, the nurse considers conditions where there is decreased urea synthesis such as severe liver disease or starvation, syndrome of inappropriate ADH (increased water in the intravascular space), and pregnancy (since the GFR increases 50% in pregnancy, there is a resultant decrease in serum creatinine).

X-RAY; KUB This x-ray delineates the size, shape, and position of the kidneys and reveals abnormalities, such as calculi in the kidneys or urinary tract, hydronephrosis, cysts, tumors, or kidney displacement by abnormalities in surrounding tissues. INTRAVENOUS UROGRAPHY This test shows the kidneys, ureters, and bladder via x-ray imaging as a radiopaque contrast agent that is administered intravenously moves through the upper and then the lower urinary system. It may be used as the initial assessment of many suspected urologic problems, especially lesions in the kidneys and ureters and provides an approximate estimate of kidney function.

BLADDER EMPTYING In both situations, the detrusor muscle can contract and expel urine, but generally the contractions are insufficient to empty the bladder completely so residual urine (urine left in the bladder after voiding) remains. Normally, residual urine amounts to no more than 50 mL in the middle-aged adult and less than 50 to 100 mL in the older adult. NURSING ALERT Any anatomical or functional disorder causing urinary obstruction or stasis places the individual at risk for urinary tract infections (UTIs) (Kasper et al., 2015). A post-void residual (PVR) of less than 50 cc is considered normal bladder emptying, whereas a PVR of over 200 cc is a risk factor for a UTI (Grossman & Porth, 2014).

`GERONTOLOGIC CONSIDERATIONS Upper and lower urinary tract function changes with age (Table 26-2). The GFR decreases, starting between 35 and 40 years of age, and a yearly decline of about 1 mL/min continues thereafter (Kasper et al., 2015). In patients 80 years of age and over, system function is about one half to two thirds less efficient than in young adults (Griebling, 2014). The elderly are more susceptible to acute and chronic kidney failure due to the structural and functional changes in the kidney.