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Clinical Nursing Skills

19.2 Nursing Assessment for Fluid and Electrolytes

Clinical Nursing Skills19.2 Nursing Assessment for Fluid and Electrolytes

Learning Objectives

By the end of this section, you will be able to:

  • Analyze the physical data used in assessment of fluid and electrolyte balances
  • Explain the nurse’s role in assessment of fluid intake and output
  • Recall different laboratory studies used in the assessment of fluid and electrolytes

The nurse is an essential part of the healthcare team. The nurse is the frontline caregiver who is often the first to recognize alterations in a patient’s fluid volume status. A thorough assessment provides valuable information about a patient’s current fluid, electrolyte, and acid-base balance, as well as risk factors for developing imbalances. Performing a chart review or focused health history is a good place to start collecting data, with any identified gaps or discrepancies verified during the physical assessment. It is also important to consider pertinent life span or cultural considerations that affect a patient’s fluid and electrolyte status.

Subjective Assessment

Subjective assessment data comprise information obtained from the patient as a primary source or family members or friends as a secondary source. This information must be obtained by interviewing the patient or someone accompanying the patient. Some of this information can be obtained through a chart review, but it should be verified with the patient or family member for accuracy.

Subjective data to obtain include age; history of chronic disease, surgeries, or traumas; dietary intake; activity level; prescribed medications and compliance with taking medications; pain; and bowel and bladder functioning. Subjective assessment data are helpful to determine normal pattern identification and risk identification. For example, a history of kidney disease or heart failure places the patient at risk for FVE, whereas diuretic use places the patient at risk for FVD and electrolyte and acid-base imbalances. A history of diabetes mellitus also places a patient at risk for fluid, electrolyte, and acid-base imbalances. Recognizing these risks helps nurses be prepared for complications that may arise and allows the nurse to recognize subtle cues as problems develop.

Objective Assessment

The physical assessment experience can elicit anxiety and fear in some patients. Having your body exposed and people touching you may be frightening and unpleasant for many people. The nurse should approach physical assessment with empathy. Introducing yourself and providing privacy are two simple steps to help your patient feel more comfortable. Only exposing one body part at a time and ensuring the patient is warm enough are important as well. The nurse should ask permission before touching the patient and provide an explanation about why this is necessary, making certain to speak to the patient using language that is appropriate for the individual. However, the nurse must be able to complete a thorough assessment and a level of cooperation by the patient is expected.

The following section describes how fluid status and electrolyte status influence the assessment of the skin, mucus membranes, vital signs, neurological function, and weight. Included in the section is information necessary to accurately record a patient’s intake and output (I & O) data.

Skin

Because the skin surface is easily accessible, the nurse can use the skin as one assessment indicator of fluid status. To assess the skin, the nurse should touch the patient’s skin on the head, torso, and extremities to assess texture and temperature. Ideally, skin should have an even, soft texture and consistent temperature in all areas. The speed with which the skin and its underlying subcutaneous tissue return to their starting position after being lifted is called skin turgor. You can assess skin turgor by gently pinching the skin, creating a “tent” shape, then releasing pressure and observing how quickly and completely the skin returns to its normal state. The best place to assess skin turgor on older adult patients is the sternum or antecubital fossa. Skin turgor can be described as any of the following:

  • brisk
  • elastic
  • good
  • nonelastic
  • poor
  • sluggish

Skin texture that feels dry could be an indication of an FVD. However, the nurse should consider other factors that can cause dry skin. Frequently bathing with hot water and soap can diminish the lipid layer of the skin and cause a dry texture. As a person ages, skin can normally lose some softness due to an increase in superficial dead-cell accumulation. In these cases, dryness may not be an indicator of volume deficiency. Additionally, the lips should be smooth and supple, without dryness, chapping, or cracking. Skin temperature should be consistent and warm. Generalized coolness can suggest hypovolemia; however, localized coolness is more likely related to arterial health.

Life-Stage Context

Skin Turgor Assessment in Older Adults and in Children

When turgor is assessed in older adult patients, the skin should be assessed on the anterior chest just under the clavicle—not the back of the hand. Because of degenerative age-related changes, including the loss of subcutaneous tissue and a reduction in the epidermal thickness of skin, skin turgor of the hand does not provide an accurate assessment of the older adult patient. In fact, some sources suggest even the chest wall skin turgor assessment may not accurately reflect fluid volume status in older patients (Jour et al., 2019). Also, it is recommended that when assessing skin turgor in children, skin on the abdomen, specifically the lateral abdominal wall near the umbilicus, be used instead of the back of the hand (Scott, 2024).

Mucous Membranes

Like a skin assessment, a mucous membrane assessment may elicit information about the fluid volume status of a patient. Mucous membranes are located throughout the body, generally where the body interacts with the outside environment. A mucous membrane is a thin layer of cells that covers a surface and secretes mucous. The surfaces that are easily accessible for a nurse to assess include the nares, gums, and tongue.

The nurse should assess the nares using a flashlight. The nares should be intact without evidence of cracks or bleeding. The nurse assesses the mouth by asking the patient to open their mouth. A penlight can assist the nurse to examine the structures of the mouth. The gums, regardless of the general skin tone of a patient should appear pink or light pink. Pale mucous membranes may be a sign of decreased perfusion, which can be a complication of decreased vascular volume. In individuals with dark skin, decreased mucous membrane perfusion may result in an ash-gray color (Pusey-Reid et al., 2022). The gums should be moist. The tongue, regardless of the skin tone of the patient, should be red or pink and moist. Saliva plays a crucial role in the health of the mouth and its components. If saliva is decreased due to an FVD, the patient may have bad breath, sticky or dry gums or tongue, and fissures may be present.

Vital Signs

Vital signs are an objective assessment of fluid volume status. Vital signs, specifically blood pressure and heart rate, reflect the degree of FVD or FVE. Hypervolemia manifests as high blood pressure (hypertension), the addition of a third heart sound (S3), bounding peripheral pulses, and visible jugular veins when the patient is sitting at a 45° angle or greater. See Chapter 24 Assessment of the Cardiovascular and Peripheral Vascular System for more about components of cardiac output when considering the fluid volume status of a patient.

As fluid volume increases, blood pressure may increase. However, the body space that excess fluid occupies determines whether the excess fluid remains in the vascular space, causing an elevated blood pressure, or is housed in the interstitial spaces, causing edema.

Blood pressure may or may not be altered with fluid balance alterations. The degree to which the body can compensate by increasing heart rate and by altering the degree of vasoconstriction or dilation will determine how blood pressure or heart rate are affected.

Clinical Judgment Measurement Model

Take Action: Determining the Cause of Tachycardia

The nurse is assessing the patient’s fluid volume status. The nurse assesses the patient’s vital signs and obtains the following results:

Blood pressure 142/82 mm Hg
Apical heart rate 112 bpm
Respiratory rate 20 bpm
Oral temperature 99.0°F
Oxygen saturation (Spo2) on room air 99 percent

The nurse recognizes the patient’s heart rate and blood pressure are elevated. The nurse first gathers more data by reviewing the patient’s chart to assess blood pressure and heart rate trends over the past several days. The nurse notes that the patient’s heart rate was in the 70 to 80 bpm range since admission and only recently elevated.

The nurse considers why a patient’s heart rate may be elevated. Possibilities include anxiety, pain, infection, or volume deficit. The nurse continues to gather more data. The nurse interviews the patient, who states they are feeling fine, is calm, and is not in any pain. The nurse reviews recent laboratory test values, including a complete blood cell count, and finds a normal white blood cell count of 6,700/µL but an increased hematocrit level of 50 percent. The nurse recognizes the clues are suggesting a fluid balance deficit. The nurse reviews the past several days’ I & O records and determines the patient had been NPO yesterday for an endoscopy and the fluid balance is −1,200 mL. The nurse encourages the patient to drink extra fluid, thereby averting a greater FVD well before blood pressure and organ perfusion are affected.

A subset of vital signs useful in the assessment of fluid status is termed postural vital signs, commonly also referred to as orthostatic vital signs. To measure orthostatic vital signs, the nurse will assess a patient’s blood pressure and heart rate when lying supine, and then immediately upon sitting upright or standing. Ideally, the patient will be supine for at least 5 minutes, then sit or stand. A blood pressure difference of −20 mm Hg systolic or −10 mm Hg diastolic between the supine and sitting/standing reading is considered orthostatic hypotension. Observe for symptoms: Ask the patient if they feel dizzy, lightheaded, or have any other symptoms upon standing. Monitor them closely for signs of orthostatic intolerance, such as pallor, sweating, nausea, or changes in level of consciousness.

Although there are several potential causes for this drop in blood pressure, hypovolemia is a common cause. The nurse, in collaboration with providers, would need to rule out other causes, such as fever, prolonged bed rest, medication reactions, or autonomic nervous system compromise, but should consider FVD as a possible cause. As the patient becomes upright, gravity shifts fluid to the trunk and lower extremities. If volume is not adequate, blood pressure decreases and heart rate elevates. The nurse must be certain to address patient safety during this evaluation because decreased cerebral perfusion can lead to dizziness and falls (Ringer & Lappin, 2023).

Clinical Judgment Measurement Model

Take Action: Preventing Patient Falls

The nurse is requested to assess for orthostatic blood pressure changes in a patient. The nurse understands that if orthostatic changes are present, blood may too quickly pool in the lower extremities and venous system of the GI tract and as a result, the patient is at risk for falls due to dizziness.

To decrease the risk of a patient falling while obtaining orthostatic vital signs, the nurse will make sure all equipment is in the room. The nurse will coordinate to have another healthcare provider in the room if the patient will be standing up. If the patient is standing up, nonslip socks are provided. The nurse makes certain the area is free from objects that could injure the patient if they were to fall.

The nurse will explain the procedure to the patient and stress that although this assessment requires the patient to change positions as requested, normally, the patient should change positions slowly.

Unfolding Case Study

Unfolding Case Study #3: Part 10

Refer back to Unfolding Case Study #3: Part 9 to review the patient data.

Flow Chart 2130:
Blood pressure: 152/85 mm Hg
Heart rate: 121 bpm
Respiratory rate: 28 breaths/minute
Temperature: 99.6 °F (37.5°C)
Oxygen saturation: 93 percent on 2 L nasal cannula
Pain: 3/10 with breathing
Provider’s Orders 2140:
Supplemental oxygen to maintain oxygen saturation >92 percent
Insert peripheral intravascular access
Furosemide 20 mg IV × 1 dose
Monitor and document accurate I & O information
3.
Prioritize hypotheses: On the basis of the patient’s vital signs, describe what is happening in the patient’s body related to cardiac output and preload.
4.
Generate solutions: What is the rationale for administering furosemide to the patient? How will this medication affect preload?

Neurologic Assessment

The neurological system is sensitive to fluid volume changes. If cardiac output is low due to a low stroke volume, the amount of blood delivered to the brain tissue will be decreased. Decreased brain tissue perfusion results in decreased oxygen delivery to brain tissue, and brain tissue, including neurons, will have decreased function. This decreased function may be witnessed during a nurse’s assessment as a decrease in cognitive and/or motor abilities. Additionally, when a volume deficit is present, brain tissue can shrink. Brain tissue shrinkage will affect cellular function but may also cause tissue to pull away from the sites of attachment to the skull, causing inflammation and bleeding.

Fluid volume excesses may be equally concerning to neurological function. As cerebral tissue expands due to cerebral edema from hydrostatic pressure increase, capillary permeability changes, or osmotic disturbances (refer to Fluid Volume Excess), brain cells and neurons are compacted, and cerebral perfusion is decreased due to compression of the cerebral vasculature. Neuronal and cellular ischemia results in dysfunction, which is manifested as cognitive and motor skill decline. The nurse should perform a full neurological assessment.

Patient Conversations

Completing an Assessment of Orientation

Scenario: Nurse walks into the patient’s room to perform an assessment of the patient’s level of orientation as part of a full neurological assessment, which is indicated whenever fluid volume or electrolyte level abnormalities exist or may potentially exist.

Nurse: Good morning. My name is Kameron and I am going to be your nurse today. Can you tell me your name and date of birth, please?

Patient: Yes, I sure can. [Patient says this jokingly.]

Nurse: [Laughs a little] I understand this may seem strange, but I need you to tell me to properly identify you.

Patient: Ted Richardson, April 8, 1943.

Nurse: Thank you, Mr. Richardson. I just have a few more questions. Do you know where you are?

Patient: I’m in the hospital.

Nurse: Can you tell me which hospital you are in?

Patient: I am at City General Hospital in Bay City, Rhode Island.

Nurse: I appreciate that, Mr. Richardson. Last question: Why are you here today?

Patient: I was feeling dizzy a lot at home. Dr. Atkins wanted me to come to the hospital for some tests. We were both concerned I could fall at home.

Nurse: Thank you again, Mr. Richardson. I know patients can get tired of answering the same questions over and over, but it’s important that we continually ask them so we can tell if anything is changing. I appreciate your patience.

Fluid Intake and Output Assessment

The nurse must closely monitor a patient’s I & O to determine if a fluid balance alteration is developing, preferably before major manifestations occur. In most cases, the fluid balance is totaled at the end of each shift. In critical care areas, I & O may need to be monitored hourly. Follow individual facility protocols to determine how often a fluid balance should be recorded. The fluid balance is the difference between how much fluid is taken in and how much fluid is lost. A positive fluid balance means more fluid has been taken in than lost, whereas a negative fluid balance indicates more fluid is being eliminated than taken in.

Intake

Fluid intake includes oral fluid intake. Fluids included as intake are from any food item that is liquid at room temperature or of which fluid is the main ingredient. Examples include many dairy-based foods like custards, yogurts, ice cream, pudding, and gravy. Soups and broth are considered oral intake. Frozen water-based foods such as ice chips and popsicles are also considered intake but are counted as half their volume. High-water-content fruit like watermelon or cantaloupe are also considered fluid intake and count as half their volume.

Other sources of intake include enteral feedings of prepared nutrition as well as free-water supplementation delivered into an enteric tube such as a nasogastric tube or gastric tube. Intravenous (IV) fluids are also considered intake and include maintenance fluids, parenteral nutrition, and fluid associated with medication administration such as continuous IV drips and intermittent medications such as antibiotics and IV flushes. Lastly, it is important to consider any type of irrigation as input. For example, if the nurse completes an indwelling bladder catheter irrigation using 60 mL of sterile water, the nurse must include this as input because it will be returned as urine output.

Output

The nurse must closely monitor a patient’s total output. Output includes urine, either freely voided or from an indwelling urinary catheter (IUC), urinary diversion, or nephrostomy. Other sources of output may include liquid stool, gastric secretions, emesis, any type of drain a patient has (regardless of what type of fluid the drain contains), blood, serous fluid, biliary fluid, and so forth. Sweat is not measurable and is not recorded as output, although significant sweating should be reported to the provider for consideration. In the event a patient is incontinent of urine or liquid stool, the nurse should document each occurrence.

Patient Conversations

Discussing Sensitive Bodily Functions with Patients

Scenario: The nurse is caring for a patient experiencing frequent liquid diarrhea and needs to record an accurate I & O. The nurse gathers a urinal and a toilet hat for the patient.

Nurse: Hello, Mr. Williams, my name is Abena and I am going to be your nurse today. I have brought you a urinal and a collection hat. The urinal is to collect and measure your urine, and the hat will go into the commode so I can measure how much diarrhea you are having.

Patient: Oh, that must be an awful job. I am so sorry you must do that. Can’t I just tell you how much I have gone? I am embarrassed to have to save my stool.

Nurse: I understand you are uncomfortable saving your stool for me to measure. Using the bathroom is a private experience. Let me reassure you that the most important thing for me is to accurately measure how much liquid you are losing. I don’t want you to get dehydrated. I will do my best to empty your hat as soon as possible, so please let me know when you have used it.

It is essential that the nurse performs timely documentation of the patient’s I & O (Table 19.4). Often, accurate I & O recordings can predict an FVD or excess before manifestations appear, allowing providers to intervene early.

Time of Day Intake (mL) Output (mL)
Oral Enteral Parenteral Urine Drains/Tubes Other
0700–0800 500 75
0800–0900 75 400
0900–1000 75
1000–1100 75
1100–1200 75 350
1200–1300 240 125
1300–1400 75
1400–1500 75 425 75
8-hour total 740 0 650 1,175 75
8-hour intake 1,390
8-hour output 1,250
Balance of 8-hour intake and output: −140 mL
Table 19.4 Sample Intake and Output Documentation All sources of fluid intake and all sources of fluid output should be recorded. Totals should be calculated every 8 hours and for every 24 hours, or according to facility policy.

Clinical Safety and Procedures (QSEN)

QSEN Competency: Assisting with the Use of a Bedpan and a Urinal

See the competency checklists for Assisting with the Use of a Bedpan & Assisting with the Use of a Urinal. You can find the checklists on the Student resources tab of your book page on openstax.org.

In addition to measuring the quantity of urine output, the nurse should also consider characteristics of the urine. As fluid volume decreases, urine becomes more concentrated and appears a darker yellow or brown. “Straw-colored’ urine is a common term to describe dark yellow urine, and “tea” colored urine is a common description of concentrated urine that is brown.

Daily Weight

An easy and inexpensive method to monitor a patient’s fluid volume status is by weighing the patient. Additionally, a patient’s weight may be used to determine the amount of medication to administer to a patient. Although weighing a patient is a simple task and often is delegated to an unlicensed assistant, the nurse must be certain that several factors are considered. Documenting how a patient is weighed upon initial assessment is crucial to using weight as an ongoing assessment indicator. The nurse should note on what scale the patient was weighed, what time of day the patient was weighed, and what clothing and footwear the patient was wearing at the time the weight was taken and documented. For consecutive weight comparison, the patient should be weighed at the same time, with the same scale, and wearing the same amount of clothing or bedding.

In hospitals and care facilities, often a sling-type scale or a bed scale is used. If a sling-type scale or a bed scale is used, it is essential that the nurse ensure the number of linens, including pillows, are consistent when the patient is weighed. In institutions, the sling-type scale or bed scale can be zeroed. “Zeroing” a scale is done before the patient is in the bed and is done by placing appropriate linens and pillows on the scale or bed, then electing this weight as zero. Typically, linens will include a bottom sheet, draw sheet, top sheet, comforter, pillow, pillowcase, and a pillow. Once the patient is placed in the sling or on the bed, the weight will not include the linens or pillows, and will be an accurate reflection of the patient’s weight. Any subsequent weights performed must have the same number of linens and pillows. Thus, any change in weight can be attributed to the patient, not to changes in the number of linens. Additionally, the nurse must be certain that drains and catheter bags are empty and held by a bystander so those are not included in the patient’s weight. If the drains are not held by a bystander and are hanging off the bed or held by the patient, their weight will be included in the patient’s weight and will result in an inaccurate measurement of the patient’s weight.

Significant unexplained weight changes may be the result of fluid loss or retention. One liter of water weighs approximately 1 kilogram (kg), or approximately 2.2 pounds. Therefore, accurate daily monitoring of weight can suggest changes in a patient’s fluid balance. Although this is a simple, inexpensive, and unobtrusive means to monitor fluid balance, the nurse is challenged to obtain an accurate patient weight. Detailed documentation and consistent replication of the how the baseline weight was measured is necessary.

Real RN Stories

Weight-Based Heparin

Nurse: Paula, RN
Clinical setting: Emergency department (ED)
Years in practice: 1
Facility location: Large teaching hospital in Denver, Colorado

I work in the ED of our level I trauma hospital. On the nightshift over Thanksgiving weekend, a father and son pair of duck hunters was reported missing and, after a nearly 16-hour search, they were located. The father had fallen down a steep embankment and his son was scared to leave him to try to find help. The father arrived by ambulance to our ED.

The father sustained multiple injuries and was already experiencing symptoms consistent with disseminated intravascular coagulation upon arrival to the ED. Once settled in the bed, I started gathering supplies to start a stat continuous heparin infusion. Almost immediately I realized I could not obtain a weight for the patient because the bed had not been zeroed. Unit policy dictates that all empty beds be ready with fresh linens and zeroed; however, in this case that did not occur.

Because heparin is a weight-based medication and an accurate weight is crucial to safely dosing this medication, I had no choice but to transfer the patient to another bed that had been properly zeroed. Not only did this additional move cause the patient pain, it also delayed the start of the heparin drip by nearly 30 minutes.

I felt frustrated about what happened and discussed it with my manager the next morning. My manager told me that I was correct in my understanding that whoever had made the bed should have zeroed it and that the patient shouldn’t have had to experience that additional pain and delay. However, she suggested that the best thing to do is to always double check. We are all human, and we all make mistakes. I will always double check my bed first thing.

Laboratory Studies Assessment

Diagnostic tests and laboratory tests provide important information about fluid status, electrolyte status, and acid-base balance and should be used in conjunction with a thorough subjective and objective assessment to form a complete picture of the patient’s overall status. This will help ensure correct information is reported to the provider as necessary. There are several laboratory test results that are useful for identifying fluid volume changes in patients. Hematocrit, serum osmolarity, and BUN and creatinine levels can contribute to the interpretation of a patient’s fluid volume status.

Hematocrit

Hematocrit (HCT) is a blood test that measures how much of your blood is made up of red blood cells compared with the liquid component of blood, called plasma. The HCT is often part of a complete blood cell count (CBC), a routine test that measures different components of your blood. The normal HCT for men is 42 percent to 52 percent; for women, it is 37 percent to 47 percent, however, these ranges may vary slightly across laboratories.

In addition to measuring red blood cells, HCT levels can also be used to evaluate fluid balance. When there is a FVD, the plasma component of the blood also decreases, causing an elevated concentration of red blood cells (and an elevated HCT). In this case, drinking more fluid or receiving IVFs will bring the HCT level back to normal range. Conversely, if a patient is experiencing FVE, the plasma component of the blood is increased, causing dilution of the red blood cells and a decreased HCT level (Figure 19.12).

Graphic showing the differences between a normal HCT, decreased HCT, and an increased HCT.
Figure 19.12 A normal HCT, decreased HCT, and an increased HCT contain variations in plasma levels. (credit: modification of work from Anatomy and Physiology. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Blood Urea Nitrogen and Creatinine

Blood urea nitrogen measures the amount of urea nitrogen in your blood. Blood urea nitrogen and serum creatinine levels are used to evaluate kidney function, with increased levels indicating worsening kidney function. In general, the normal BUN range is 10 to 20 mg/dL, but normal ranges vary depending on the reference range used by the laboratory and the patient’s age. Patients with deficient fluid volume can also have elevated BUN levels for the same reason that HCT is affected: as plasma levels decrease, the blood becomes more concentrated.

These two laboratory values are used together to determine how well a patient’s kidneys are working, but in some cases can also be used as an indicator of blood water volume. This comparison is called a BUN to creatinine ratio. A normal BUN to creatinine ratio is around 20:1. Since creatinine is supposed to be mostly eliminated, creatinine is a good indicator of how well the kidneys are working to eliminate waste. If creatinine is increased, and BUN is increased, it is usually because the kidneys are not working optimally. However, because the majority of BUN is not eliminated but is instead reabsorbed into the blood, when it is increased and creatinine is normal, it often means the fluid volume in the vascular space is decreased (Table 19.5).

Laboratory Test Normal Serum Level Example of a High Level Example of a Consistent or Low Level
BUN, mg/dL 10–20 30 8
Creatinine, mg/dL 0.7–1.2 2.0 0.5
BUN to creatinine ratio 20:1 30:1 15:1
Possible cause Low water volume Poor kidney function
Table 19.5 Using BUN and Creatinine to Interpret Fluid Volume Status

Serum Osmolarity

Serum osmolarity (often interchanged with the term serum osmolality) measures the concentration of particles in the blood with a normal range of 275 to 295 mmol/kg. Normal value ranges may vary slightly among different laboratories. In healthy people, when serum osmolality in the blood becomes high, the body releases ADH. This hormone causes the kidneys to reabsorb water, resulting in dilution of the blood and the return of serum osmolarity to normal range. An elevated serum osmolarity level means the blood is more concentrated than normal and often indicates deficient FVD. A decreased serum osmolarity means the blood is more dilute than normal and may indicate an FVE.

Urine Laboratory Data

Urine osmolarity measures the concentration of particles in the urine. An increased urine osmolarity result means the urine is concentrated and can indicate FVD. A decreased urine osmolarity result means the urine is dilute and can indicate excess fluid intake. A type of urine test for urine specific gravity measures hydration status by measuring the concentration of particles in urine. Normal urine specific gravity levels are between 1.010 and 1.020. A urine specific gravity above 1.020 indicates concentrated urine and can indicate an FVD, similar to an elevated urine osmolarity. A urine specific gravity below 1.010 indicates dilute urine, which can occur with excessive fluid intake.

When excessive fluid volume occurs, altered physiological mechanisms affect the kidney’s ability to increase urine output to eliminate excessive fluid volume, causing urine output to decrease. As a result, the serum osmolarity decreases as fluid is retained, but the urine specific gravity is elevated because urine is concentrated.

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