Showing posts with label Fluid and Electrolytes. Show all posts

Saturday, March 7, 2015

Fluid, Electrolytes, and Acid-Base Balance....

I. Fluid and Electrolytes

A. Water is the largest single component of the body
B. 60% of the average adult’s body is fluid
C. Homeostasis is the ability to maintain internal balance in the presence of external stressors

II. The Purpose of Body Fluids

A. Medium for transportation

1. Nutrients to cells
2. Wastes from cells
3. Hormones, enzymes, blood platelets, RBCs & WBCs

B. Cellular metabolism/chemical functioning

C. Normal body temperature

D. Facilitates digestion & elimination

E. Tissue lubricant

F. Solvent for electrolytes & nonelectrolytes

III. Body Fluids Overview

A. Intracellular ICF within the cells 40% body wt

B. Extracellular ECF (20% body wt)

1. Intravascular IVF contained within blood vessels
a. 5% body wt
2. Interstitial ISF surrounds cells, includes lymph
a. 15% body wt

C. Transcellular TCF includes cerebrospinal, pericardial, pleural, synovial and intraocular fluids, sweat, + digestive secretions <1% body wt

IV. Composition of Body Fluids

A. Electrolytes

1. Ions
a. Cations
1. Positively charged: sodium, potassium, calcium
b. Anions
1. Negatively charged: chloride, bicarbonate, sulfate

V. Variations in Fluid Content

A. Age

1. Infant 77% water
2. Adult 60% water
3. Elderly 45% water

B. Gender

C. Body Mass

VI. Movement of Body Fluids

A. Osmosis

1. movement of a pure solvent through semipermeable membrane from area of low concentration to area of greater concentration
B. Diffusion
1. movement of a solute in solution across a semipermeable membrane from area of high concentration to area of low concentration

C. Filtration

1. Process by which water & diffusible substances move together in response to fluid pressure; movement is from higher to lower pressure

D. Active Transport

1. Requires metabolic activity & expenditure of energy to move materials across cell membranes

VII. Osmosis

A. A shift of fluid from an area of low concentration to an area of higher concentration until the solutions are of equal concentration.

B. Membrane is permeable to the solvent, not the solute

C. Tonicity is the ability of solutes to cause osmotic driving forces

D. Moses moved water

VIII. Osmotic Pressure

A. Tonicity is the ability of solutes to cause osmotic driving forces

B. Exerted on permeable membranes by high molecular weight substances

C. To pull fluid across membranes

IX. Osmotic Pressure

A. A fluid with a high solute concentration has a high osmotic pressure

B. Of two solutions, higher osmotic pressure will draw fluid until equilibrium is reached

C. Osmotic pressure of a solution is called osmolarity

D. Osmolarity is measure used to evaluate serum and urine in clinical practice

E. Expressed in osmols, or milliosmols per kilogram (mOsm/kg)

F. Normal serum osmolarity is 280-295 mOsm/kg

X. Types of Solutions

A. Isotonic – .9%/Normal Saline

1. Same concentration of solute as blood
2. Expands body’s fluids without causing fluid shift

B. Hypertonic (hyperosmolar) – D5NS, LR

1. Greater concentration of solutes than blood
2. Pulls fluids from cells causing them to shrink

C. Hypotonic (hypo-osmolar) – .45% NS

1. lesser concentration of solutes than blood
2. Moves fluid into the cells, causing enlargement

XI. Colloidal Osmotic/Oncotic Pressure

A. Affected by naturally produced serum proteins

B. Albumin exerts colloid pressure to keep fluid in the intravascular compartment by pulling water from the interstitial space back into the capillaries

XII. Diffusion

A. Is the natural tendency of a substance (or gas) to move from an area of higher concentration to one of lower concentration

B. This achieves balance

C. The difference between the two concentrations is called the concentration gradient

XIII. Facilitated Diffusion

A. Diffusion is facilitated by a carrier substance.

B. Facilitated diffusion requires a concentration gradient and sufficient carriers

C. Example: O2 & CO2 exchange

XIV. Filtration

A. Process of water and diffusible substances move together in response to fluid pressure

1. Called hydrostatic pressure
2. Determines the movement of water

B. Examples

1. Increased hydrostatic pressure on the venous side (congestive heart failure) water and electrolytes from the arterial capillary bed move to the interstitial fluid
2. Results in edema

XV. Active Transport

A. Is necessary in the absence of concentration gradient or electrochemical gradient

B. Requires metabolic activity, expenditure of energy and, carrier substances to move materials across cell membranes

C. Allows cells to move molecules otherwise immovable – “uphill”

D. Examples

1. Na+ & K+ movement against the gradient
2. Mechanism that allows cells to absorb glucose & other substances to facilitate metabolic activities

XVI. Body Fluid Regulation

A. Homeostasis – physiological balance

B. Allows body to respond to disturbances in fluid & electrolyte levels to prevent & repair damage

C. Fluid intake

D. Hormonal regulation

E. Fluid output regulation

XVII. Cardiovascular System

A. Maintains:

1. Blood pressure
2. Cardiac output
3. Hydrostatic pressure
4. Adequate glomerular filtration rate

XVIII. Definitions

A. Osmolality

1. The concentration of osmotically active particles in solution expressed in terms of osmoles of solute per kilogram of solvent

B. Osmolarity

1. The concentration of osmotically active particles in solution expressed in terms of osmoles of solute per liter of solution

XIX. Fluid Intake

A. Regulated through the thirst mechanism located in the hypothalamus

B. Conscious desire for water

C. One of the major factors in fluid intake

D. Osmoreceptors monitor serum osmotic pressure; osmolality increases; hypothalamus is stimulated; thirst results

1. Increased osmolality – can occur with inability to take in fluids or administration of hypertonic fluids
2. Vomiting or hemorrhage: Hypovolemia; dehydration

XX. Hormonal Regulation (Endocrine)

A. Antidiuretic hormone (ADH)

1. Stored in posterior pituitary gland
2. Released in response to changes in blood osmolarity

B. Aldosterone

1. Released by adrenal cortex in response to increased plasma K+ levels or part of renin-angiotensin-aldosterone mechanism in hypovolemia

C. Renin

1. Proteolytic enzyme secreted by kidneys, responds to decreased renal perfusion 2^nd to decrease extracellular volume
2. Triggers angiotensin I production converting to angiotensin II which causes massive selective vasoconstriction ultimately directing blood to perfuse kidneys

XXI. Fluid Output Regulation

A. Occurs through four organs of water loss

1. Kidneys
a. Major regulatory organs of fluid balance; receive 180 L of plasma to filter & produce 1200 to 1500 ml of urine/day
2. Skin
a. Regulated by the sympathetic nervous system; activates sweat glands
b. Sensible – excess perspiration; can be observed
c. Insensible – continuous; not perceived by the person; can increase significantly with fever or burns
3. Lungs
a. Expire about 400 ml of water daily
4. Gastrointestinal tract (GI)
a. 3 to 6 L of isotonic fluid moved into GI tract & returned to extracellular fluid daily

XXII. Regulation of Electrolytes

A. Cations

1. Sodium
2. Potassium
3. Calcium
4. Magnesium

B. Anions

1. Chloride
2. Bicarbonate
3. Phosphorus-phosphate

XXIII. Fluid Shifts

A. First Spacing

1. Normal fluid compartments

B. Second Spacing

1. Interstitial

C. Third Spacing

1. When fluid is trapped in a body space as a result of injury or disease,
2. Represents a fluid loss
3. Includes pericardial, pleural, peritoneal, joints

XXIV. Plasma to Interstitial

A. Pathology

1. + hydrostatic pressure
2. Decreased capillary osmotic pressure
3. + cap permeability
4. Obstructed lymph drainage

B. Manifestation

1. Edema, hypovolemia

C. Interventions

1. Fluid replacement
2. Monitor for overload

XXV. Interstitial to Plasma

A. Pathology

1. Decreased capillary permeability
2. Increased capillary osmotic pressure

B. Manifestations

1. Hypervolemia

C. Interventions

1. If normal, patient excretes fluid
2. With disease, must diurese

XXVI. Fluid Volume Deficit (FVD)

A. Thirst with 2% loss

B. Dry mucus membranes with 6% loss

C. Leads to cellular dehydration

D. Weight is best indicator

XXVII. FVD Causes

A. Anything causing loss of blood volume:

1. Blood loss
2. Polyuria
3. GI losses
4. Profuse diaphoresis
5. Third spacing
6. Decreased intake

XXVIII. FVD Manifestations

A. Hypotension

B. Increased pulse, respirations

C. Decreased urinary output, temperature

D. Poor skin turgor

E. Dry mucus membranes

F. Constipation

G. Increased hematocrit, plasma proteins, BUN, urine specific gravity

XXIX. FVD Interventions

A. Correct the underlying cause

B. Replace fluid depending on type lost

XXX. Fluid Volume Excess (FVE)

A. Caused by fluid overload

B. Renal failure

C. CHF

D. Cirrhosis

E. Corticosteroids

F. Cushing’s syndrome

XXXI. FVE Manifestations

A. BP up, bounding pulse

B. Distended neck veins

C. Rapid wt gain

D. Peripheral edema

E. Pulmonary edema

F. CVP elevated

G. BUN decreased, hematocrit decreased

H. Plasma proteins decreased

XXXII. FVE Interventions

A. Treat the underlying cause

B. Fluid and or sodium restriction

C. Diuretics

D. Dialysis, paracentesis

XXXIII. Regulation of Acid-Base Balance

A. Metabolic processes maintain a steady balance between acids & bases

B. Arterial pH inversely proportioned to the hydrogen ion concentration

C. The greater the concentration, the more acidic the solution, the lower the pH & vice versa

D. The lower the concentration, the more alkaline the solution, the higher the pH

XXXIV. Chemical Regulation

A. Largest chemical buffer is carbonic acid & bicarbonate buffer system

B. Carbonic acid – carbon dioxide

C. Bicarbonate – excretion by the kidneys

XXXV. Biological Regulation

A. Occurs when hydrogen ions are absorbed or released by cells

B. Occurs after chemical buffering & takes 2 to 4 hours

C. Hydrogen must exchange with another positively charged ion

1. Chloride shift
2. Hemoglobin-oxyhemoglobin system

XXXVI. Physiological Regulation

A. Act as buffers (compensation) to return the pH to normal

B. Lungs

1. When the respiratory system is the problem agent – resp. acidosis; resp. alkalosis
2. Acts as the buffer when renal system is the problem

C. Kidneys

1. When the renal system is the problem agent – metabolic acidosis; metabolic alkalosis
2. Acts as the buffer when respiratory system is the problem

XXXVII. Disturbances in Electrolyte, Fluid, & Acid-Base Balance

A. Seldom occur alone

B. Can disrupt normal body processes

C. Each disturbance can cascade into a disturbance of the other

XXXVIII. Electrolyte Imbalances

A. Sodium

B. Potassium

C. Calcium

D. Magnesium

E. Chloride

XXXIX. Sodium

A. Hyponatremia

1. Net sodium loss or excess water excess
2. Indicators & treatments depend on cause & ECF status

B. Hypernatremia

1. Excess water loss or sodium excess
2. Increases aldosterone secretion, sodium is retained, potassium is excreted
3. Body conserves fluid through renal reabsoption

XXL. Potassium

A. Normal amount is very small with little tolerance for fluctuation

B. Hypokalemia

1. One of most common electrolyte imbalances
2. Inadequate amount of potassium circulates in the ECF
3. Severe cases can affect cardiac conduction and function; most common cause is use of potassium-wasting diuretics

C. Hyperkalemia

1. Produces marked cardiac conduction abnormalities
2. Primary cause is renal failure; also seen in crushing injuries

Calcium

A. Hypocalcemia

1. Results from severe illnesses, especially ones that directly affect thyroid & parathyroid glands; renal insufficiency (inability to excrete phosphorous, as phosphorous rises, calcium declines)
2. S/S related to neuromuscular, cardiac, & renal systems

B. Hypercalcemia

1. Frequently a symptom of underlying disease resulting in excess bone reabsorption

Magnesium

A. Symptoms are a result of changes in neuromuscular excitability

B. Hypomagnasemia

1. Occurs with malnutrition, malabsorption disorders, & neuromuscular system disorders

C. Hypermagnasemia

1. Depresses skeletal muscles & nerve function
2. Depresses acetylcholine leads to sedative effect; leading to bradycardia, ECG changes, cardiac arrhythmias, decreased respiratory rate & depth

Chloride

A. Commonly associated with acid-base imbalance

B. Hypocloremia

1. Occurs with vomiting or prolonged NG tube or fistula drainage with loss of hydrochloric acid
2. Use of loop & thiazide diuretics
3. Can result in metabolic alkalosis

C. Hypercloremia

1. Occurs when serum bicarbonate falls or sodium level rises

Fluid Disturbances

A. Isotonic

1. Occur when water & electrolytes are gained or lost in equal proportions

B. Osmolar

1. Occur with losses or excesses of only water so that concentration of serum is affected

Acid-Base Balance

A. Arterial blood gases (ABG) are the best way to evaluate

B. Involves analysis of 6 components

1. pH
2. PaCO2
3. PaO2
4. Oxygen saturation
5. Base excess
6. Bicarbonate (HCO3)

C. Deviation from a normal value indicates imbalanc

PH

A. Measures hydrogen ion concentration in body fluids

B. Even slight changes can be potentially life threatening

C. Normal ranges 7.35 to 7.45

D. RULER OF THE BODY

PaCO2

A. Partial pressure of carbon dioxide

B. Reflects depth of pulmonary ventilation

C. Normal range 35 to 45 mm Hg

D. Indicates the concentration of CO2 in the blood

PaO2

A. Partial pressure of oxygen

B. No primary role in acid-base balance regulation if within normal limits

C. Lower levels < 60mm Hg can lead to anaerobic metabolism, resulting in lactic acid production & metabolic acidosis

D. Normal range is 80-100 mm Hg

Oxygen Saturation

A. Point at which hemoglobin is saturated by O2

B. Can be affected by changes in temparture, pH, & PaCO2

C. Normal range is 95% to 99%

Base Excess

A. Amount of blood buffer that exists

B. High value indicates alkalosis

1. Can result from sodium bicarbonate, citrate excess with blood transfusions, IV infusions of sodium bicarbonate to correct ketoacidosis

C. Low value indicates acidosis

1. Can result from elimination of too many bicarbonate ions, i.e. diarrhea

Bicarbonate (HCO3)

A. Major renal component of acid-base balance

B. Excreted & reproduced by the kidneys to maintain normal acid-base environment

C. Normal range is 22 to 26 mEq/L (this may vary slightly from lab to lab)

D. Indicator of metabolic cause of acidosis or alkalosis

E. Is buffer agent in respiratory acidosis or alkalosis

Types of Acid-Base Imbalances

A. Respiratory Acidosis

1. Excessive carbonic acid & increased hydrogen ion concentration (low pH)

B. Respiratory Alkalosis

1. Decreased carbonic acid & decreased hydrogen ion concentration (high pH)

C. Metabolic Acidosis

1. High acid content in blood causing loss of HCO3
2. Analysis of serum electrolytes to detect anoin gap (which reflects unmeasurable anoins)

D. Metabolic Alkalosis

1. Heavy loss of acid or increased HCO3 content in blood
2. Most common cause is gastric suction

Nursing Knowledge

A. Imbalances can occur at any age

B. Body’s adaptive compensatory mechanisms fail to maintain balance adequately

C. Health becomes compromised

D. Severity & long-term effects can influence client’s ability to return to optimal health

E. Prolonged compromise can lead to irreversible chronic health problems that affect the quality of life for client & family

Nursing Process – Assessment

A. Nursing history

1. Client’s history determines goals
2. Age of client is important factor

B. Prior medical history

1. Acute illnesses
a. Surgeries, burns, respiratory disorders, head injuries
2. Chronic illnesses
a. Cancer, cardiovascular disease, renal disease, GI disturbances
3. Environmental factors
a. Exercise, exposure to temperature extremes
4. Diet
a. Intake of fluids, changes in appetite, metabolic interference, physical problems
5. Lifestyle
a. Smoking, alcohol use/abuse, drugs
6. Medication
a. Prescription or OTC meds that perpetuate fluid imbalances

Physical Assessment

A. F&E/A-B imbalances can affect all systems

B. Thorough exam

C. Include client’s intake/output history, genitourinary patterns/changes

D. Lab study results

E. Client expectations

Nursing Process – Nursing Diagnoses

A. Actual

1. Ineffective breathing patterns
2. Decreased cardiac output
3. Deficient fluid volume
4. Excess fluid volume
5. Impaired gas exchange
6. Impaired mobility
7. Impaired tissue integrity/perfusion

B. Risks

1. Imbalanced body temperature
2. Deficient fluid volume
3. Impaired skin integrity/perfusion

Nursing Process – Planning

A. Goal & Outcomes

1. Client free of complication
2. Demonstrates fluid balance
3. Labs in range

B. Setting Priorities

1. Client’s condition sets priorities of ND

C. Continuity of Care

y1. Discharge planning should happen early

Nursing Process – Implementation

A. Health promotion

1. Teach client & family to recognize risk factors
a. Age, activities, specific chronic illness affects

B. Acute care

1. Daily weights
2. Enteral replacement of fluids
3. Fluid restrictions
4. Parenteral fluid & electrolyte replacement
5. IV therapy implications & risks

Complications of IV Fluid Administration

A. Systemic:

1. Fluid Overload
2. Air Embolism
3. Septicemia

B. Local:

1. Infiltration and Extravasation
2. Phlebitis
3. Thrombophlebitis
4. Hematoma
5. Clotting and obstructing

Fluid Overload

A. Fluid Overload: too much fluid in circulatory system: Rapid infusion, underlying cardiac, liver, or renal disease

B. S+S: moist crackles, edema, wt gain, dyspnea, shallow rapid resp

C. Treatment: Decrease flow rate, monitor VS + BS, position High Fowlers

D. Prevent: IV pumps, careful assessment

E. Complications: CHF, Pulmonary edema

Air Embolism

A. Occurs when air enters the bloodstream.

B. Is threatening when the air displaces blood to the cells

C. Most often associated with central veins

D. S+S; dyspnea, cyanosis, hypotension, weak, rapid pulse, loss of consciousness, chest shoulder, low back pain. Complication: death

E. Treatment

1. Clamp iv lines;
2. L trendelenberg position;

F. Prevention

1. Careful filling of IV tubes and syringes;
2. LuerLock adapters;
3. Air sensing pumps

Septicemia

A. Infection disseminated through the blood stream

B. Cause:

1. Contaminated IV products, break in technique

C. Risk: immunocompromised

D. S+S:

1. Elevated Temp, backache, headache, pulse and resp elev.

E. Treatment:

1. Symptomatic, local or systemic

F. Prevention:

1. Critical hygiene and technique

Infiltration

A. Infiltration:

1. Introduction of a non vesicant solution into surrounding tissues
2. Extravasation: Introduction of a vesicant or irritating solution into surrounding tissues.

B. S+S: edema, coolness, decreased flow, discomfort

C. Tx:

1. Discontinue, restart, compress with warm or cold to affected site, elevate

D. Prevention:

1. Careful securing of IV tubing, limit mobility of limb with IV, frequent observation of site

Phlebitis & Thrombophlebitis

A. Phlebitis:

1. inflammation of a vein from chemical or mechanical irritation.
2. S+S: red, warm at site or along vein, pain, tenderness, swelling.
3. Prevention: (frequency parallels length of insertion), use good aseptic technique, observe frequently.
4. Tx: discontinue IV, warm moist compress, elevate

B. Thrombophlebitis:

1. presence of a clot in addition to phlebitis.
2. S+S: same + more discomfort, elevated WBC, immobility
3. Tx: same: Prevent: avoid trauma at insert.

Hematoma

A. Blood leaking into tissue.

B. From perforation of vein during insertion or later.

C. S+S: ecchymosis, swelling, leak blood

D. Tx: remove, pressure, +/- ice, heat.

E. Prevent: careful technique during insertion

Clotting and Obstruction

A. Occur from kinked tubing, slow infusion rate, failure to flush line, empty IV bag

B. S+S: decreased flow, blood backing up,

C. Tx: if clotted, restarting at a new site is necessary

Nursing Process – Evaluation

A. Client care

1. Client teaching
2. Recognition of signs/symptoms of imbalance
3. Consult physician to enhance care in chronic conditions

B. Client expectations

1. Evaluate the client’s perception of care and goals
2. Use client input to understand needs and expectations

Thursday, June 9, 2011

Management of Hypernatremia...

The ED management of hypernatremia revolves around 2 tasks: restoration of normal serum tonicity, and diagnosis and treatment of the underlying etiology. When possible, providing free water to a patient orally is preferred.
Hypernatremia should not be corrected at a rate greater than 1 mEq/L per hour.
Carefully monitor all patients' inputs and outputs during treatment.
Consider CNS imaging to exclude a central cause or to identify CNS bleeding from stretching of veins.
Using isotonic sodium chloride solution, stabilize hypovolemic patients who have unstable vital signs before correcting free water deficits because hypotonic fluids quickly leave the intravascular space and do not help to correct hemodynamics. Once stabilization has occurred, free water deficits can be replaced either orally or intravenously.
Euvolemic patients can be treated with hypotonic fluids, either orally or intravenously (ie, dextrose 5% in water solution [D5W], quarter or half isotonic sodium chloride solution), to correct free fluid deficits.
Hypervolemic patients require removal of excess sodium, which can be accomplished by a combination of diuretics and D5W infusion. Patients with acute renal failure may require dialysis.
Traditionally, correction of hypernatremia begins with a calculation of the fluid deficit as shown below. Predicted insensible and other ongoing losses are added to this number and the total is administered over 48 hours. Recheck serum electrolyte levels frequently during therapy. To avoid cerebral edema and associated complications, the serum sodium level should be raised by no more than 1 mEq/L every hour. In patients with chronic hypernatremia, an even more gradual rate is preferred.
An alternative method to plan the correction of sodium imbalances has been proposed by Adrogue and Madias. They have devised a formula that can be used to calculate the change in serum sodium level after the administration of 1 L of a given infusate. This formula has the advantages of taking into consideration the tonicity of the infusate and encouraging reassessment of the treatment plan with each liter of solution or new set of electrolytes.
Free Water Deficit = Body Weight (kg) X Percentage of Total Body Water (TBW) X ([Serum Na / 140] - 1)
The percentage of TBW should be as follows:

Young men - 0.6%
Young women and elderly men - 0.5%
Elderly women - 0.4%

An example is as follows: A serum sodium level of 155 in a 60-kg young man represents a fluid deficit of 60 X 0.6 X ([155 / 140] - 1) or 3.9 L. With another 900 mL of insensible losses, the patient requires 4.8 L of fluid in the next 48 hours, resulting in an infusion rate of 100 mL/h.
The Adrogue and Madias formula is as follows: Change in Serum Sodium = ([Na] Infused - [Na] serum) / (TBW + 1)
The "1" in the denominator represents the extra liter of infusate added to TBW. When TBW is calculated as above, TBW = Body Weight (kg) X Percent Water
An example is as follows: For the patient above, the expected change can be calculated with D5W or D5 half isotonic sodium chloride solution.
For D5W, Change = (0 - 155) / ([60 X 0.6] + 1) = -4.18 mEq/L
For half isotonic sodium chloride solution, Change = (77 - 155) / ([60 X 0.6] + 1) = -2.1 mEq/L
If D5W is chosen to avoid fluid overload, an infusion rate of 250 mL/h results in a correction just over 1 mEq/h. (Note: This assumes the patient has no other losses during this time. Intrinsic losses make the correction slower [more conservative] than calculated.)

Thursday, May 19, 2011

I.V. Fluids...What nurses need to know

TYPE OF FLUID	DEFINITION	EXAMPLES
Isotonic	concentration of dissolved particles is similar to that of plasma infused solutions remain in the extracellular space and increase intravascular volume	0.9% sodium chloride lactated Ringer's solution 5% dextrose in water Ringer's solution
Hypotonic	lower tonicity or solute concentration fluids shift from the intravascular space to both the intracellular and interstitial spaces	0.45% sodium chloride 0.33% sodium chloride 0.2% sodium chloride 2.5% dextrose in water
Hypertonic	higher tonicity or solute concentration water is drawn out of the intracellular space, increasing extracellular fluid volume	3% sodium chloride 5% sodium chloride 5% dextrose and 0.45% sodium chloride 5% dextrose and 0.9% sodium chloride D₅LR D₁₀W D₂₀W D₅₀W

It surprised me to put D₅W in the list of examples for isotonic solutions.

CAN YOU IMAGINE A LIFE without water? Of course not, because water is essential to sustain life. Likewise, body fluids are vital to maintain normal body functioning.

Figure. No caption a... - Click to enlarge in new window

The body reacts to internal and environmental changes by adjusting vital functions to keep fluids and electrolytes in balance, maintaining homeostasis. This article will explore how fluid acts within the body and discuss when and why various I.V. fluids can be used to maintain homeostasis. Subsequent articles in this series will discuss specific electrolyte imbalances. Unless otherwise specified, information applies to adults, not pediatric patients.

Figure. Two basic fluid compartments

Fluids and electrolytes move between compartments via passive and active transport. Passive transport occurs when no energy is required to cause a shift in fluid and electrolytes. Diffusion, osmosis, and filtration are examples of passive transport mechanisms that cause body fluid and electrolyte movement.2

Osmolality and osmolarity are two similar terms that are often confused. Osmolality, which is usually used to describe fluids inside the body, refers to the solute concentration in fluid by weight: the number of milliosmols (mOsm) in a kilogram (kg) of solution. Osmolarity refers to the solute concentration in fluid by number of mOsm per liter (L) of solution. Because 1 L of water weighs 1 kg, the normal ranges are the same and the terms are often used interchangeably.

Changes in the level of solute concentration influence the movement of water between the fluid compartments. The normal osmolality for plasma and other body fluids varies from 270 to 300 mOsm/L. Optimal body function occurs when the osmolality of fluids in all the body compartments is close to 300 mOsm/L. When body fluids are fairly equivalent in this particle concentration, they're said to be isotonic.

Fluids with osmolalities less than 270 mOsm/L are hypotonic in comparison with isotonic fluids, and fluids with osmolalities greater than 300 mOsm/L are hypertonic.2 Tonicity of I.V. fluids will be discussed in detail later in this article.

Through the use of mechanisms such as thirst, the renin-angiotensin-aldosterone system, antidiuretic hormone, and atrial natriuretic peptide, the body works to maintain appropriate fluid and electrolyte levels and to prevent imbalances within the body. When an imbalance occurs, you must be able to identify the cause of the problem and monitor the patient during treatment.

Crystalloids vs. colloids

One of the methods for treating fluid and electrolyte alterations is the infusion of I.V. solutions, which have distinctive differences in composition that affect how the body reacts to and utilizes them. When administering I.V. therapy, you need to understand the nature of the solution being initiated and how it will affect your patient's condition.

I.V. solutions for fluid replacement may be placed in two general categories: colloids and crystalloids. Colloids contain large molecules that don't pass through semipermeable membranes. When infused, they remain in the intravascular compartment and expand intravascular volume by drawing fluid from extravascular spaces via their higher oncotic pressure. We'll discuss colloids in detail later.

Crystalloids are solutes capable of crystallization that are easily mixed and dissolved in a solution. The solutes may be electrolytes or nonelectrolytes, such as dextrose.

Crystalloid solutions contain small molecules that flow easily across semipermeable membranes, allowing for transfer from the bloodstream into the cells and body tissues. This may increase fluid volume in both the interstitial and intravascular spaces.

Crystalloid solutions are distinguished by their relative tonicity (before infusion) in relation to plasma. Tonicity refers to the concentration of dissolved molecules held within the solution.5,6 The following sections discuss isotonic, hypotonic, and hypertonic crystalloid solutions in detail.

ISOTONIC FLUIDS

A solution is isotonic when the concentration of dissolved particles is similar to that of plasma. Isotonic solutions have an osmolality of 250 to 375 mOsm/L.7 With osmotic pressure constant both inside and outside the cells, the fluid in each compartment remains within its compartment (no shift occurs) and cells neither shrink nor swell. Because isotonic solutions have the same concentration of solutes as plasma, infused isotonic solution doesn't move into cells. Rather, it remains within the extracellular fluid compartment and is distributed between the intravascular and interstitial spaces, thus increasing intravascular volume.6 Types of isotonic solutions include 0.9% sodium chloride (0.9% NaCl), lactated Ringer's solution, 5% dextrose in water (D₅W), and Ringer's solution.

A solution of 0.9% sodium chloride is simply salt water, and contains only water, sodium (154 mEq/L), and chloride (154 mEq/L). It's often called "normal saline solution" because the percentage of sodium chloride dissolved in the solution is similar to the usual concentration of sodium and chloride in the intravascular space.

Because water goes where sodium goes, 0.9% sodium chloride increases fluid volume in extracellular spaces. It's administered to treat low extracellular fluid, as in fluid volume deficit from hemorrhage, severe vomiting or diarrhea, and heavy drainage from GI suction, fistulas, or wounds. Conditions commonly treated with 0.9% sodium chloride include shock, mild hyponatremia, metabolic acidosis (such as diabetic ketoacidosis), and hypercalcemia; patients requiring a fluid challenge may also benefit from 0.9% sodium chloride solution. It's the fluid of choice for resuscitation efforts.2,8 In addition, it's the only fluid used with administration of blood products.

Remember that because 0.9% sodium chloride replaces extracellular fluid, it should be used cautiously in certain patients, such as those with cardiac or renal disease, because of the potential for fluid volume overload.

Lactated Ringer's (LR), also known as Ringer's lactate or Hartmann solution, is the most physiologically adaptable fluid because its electrolyte content is most closely related to the composition of the body's blood serum and plasma. Because of this, LR is another choice for first-line fluid resuscitation for certain patients, such as those with burn injuries. It contains 130 mEq/L of sodium, 4 mEq/L of potassium, 3 mEq/L of calcium, and 109 mEq/L of chloride. LR doesn't provide calories or magnesium, and has limited potassium replacement.2

LR is used to replace GI tract fluid losses, fistula drainage, and fluid losses due to burns and trauma. It's also given to patients experiencing acute blood loss or hypovolemia due to third-space fluid shifts.6 Both 0.9% sodium chloride and LR may be used in many clinical situations, but patients requiring electrolyte replacement (such as surgical or burn patients) will benefit more from an infusion of LR.6

LR is metabolized in the liver, which converts the lactate to bicarbonate. As an alkalinizing solution, LR is often administered to patients who have metabolic acidosis. Don't give LR to patients who can't metabolize lactate for some reason, such as those with liver disease or those experiencing lactic acidosis.

Because a normal liver will convert it to bicarbonate, LR shouldn't be given to a patient whose pH is greater than 7.5. Because it does contain some potassium, use caution in patients with renal failure.3

Ringer's solution, like LR, contains sodium, potassium, calcium, and chloride in similar concentrations (147 mEq/L of sodium, 4 mEq/L of potassium, 4 mEq/L of calcium, and 156 mEq/L of chloride). But it doesn't contain lactate. Ringer's solution is used in a similar fashion as LR, but doesn't have the contraindications related to lactate. However, because it's not an alkalizing agent, it may not be indicated for patients with metabolic acidosis.3,6

D5W is unique in that it may be categorized as both an isotonic and a hypotonic solution. The amount of dextrose in this solution makes its initial tonicity similar to that of intravascular fluid, making it an isotonic solution. But dextrose (in this concentration) is rapidly metabolized by the body, leaving no osmotically active particles in the plasma.6

D₅W provides free water: free, unbound water molecules small enough to pass through membrane pores to the intracellular and extracellular spaces. This smaller size allows the molecules to pass more freely between compartments, thus expanding both compartments simultaneously.6 The free water initially dilutes the osmolality of the extracellular fluid; once the cell has used the dextrose, the remaining saline and electrolytes are dispersed as an isotonic electrolyte solution, providing additional hydration for the extracellular fluid compartment. Dextrose solutions also provide free water for the kidneys, aiding renal excretion of solutes. Because it provides free water following metabolism, D₅W is also considered a hypotonic solution.6

D₅W is basically a sugar water solution that provides 170 calories per liter, but it doesn't replace electrolytes. However, it's appropriate to treat hypernatremia because it dilutes the extra sodium in extracellular fluid.

D₅W shouldn't be used in isolation to treat fluid volume deficit because it dilutes plasma electrolyte concentrations. It's also contraindicated in these clinical circumstances:

* for resuscitation, because the solution won't remain in the intravascular space.

* in the early postoperative period, because the body's reaction to the surgical stress may cause an increase in antidiuretic hormone secretion.2

* in patients with known or suspected increased intracranial pressure (ICP) due to its hypotonic properties following metabolism.

Although it supplies some calories, D₅W doesn't provide enough nutrition for prolonged use.

Nursing considerations for isotonic solutions

Be aware that patients being treated for hypovolemia can quickly develop hypervolemia (fluid volume overload) following rapid or overinfusion of isotonic fluids. Document baseline vital signs, edema status, lung sounds, and heart sounds before beginning the infusion, and continue monitoring during and after the infusion.

Frequently assess the patient's response to I.V. therapy, monitoring for signs and symptoms of hypervolemia, such as hypertension, bounding pulse, pulmonary crackles, dyspnea/shortness of breath, peripheral edema, jugular venous distention (JVD), and extra heart sounds, such as S₃. Monitor intake and output, hematocrit, and hemoglobin. Elevate the head of bed at 35 to 45 degrees, unless contraindicated. If edema is present, elevate the patient's legs. Note if the edema is pitting or nonpitting and grade pitting edema. For an example, see Checking for pitting edema.

Also monitor for signs and symptoms of continued hypovolemia, including urine output of less than 0.5 mL/kg/hour, poor skin turgor, tachycardia, weak, thready pulse, and hypotension.2

Educate patients and their families about signs and symptoms of volume overload and dehydration, and instruct patients to notify their nurse if they have trouble breathing or notice any swelling. Instruct patients and families to keep the head of the bed elevated (unless contraindicated).

HYPOTONIC FLUIDS

Compared with intracellular fluid (as well as compared with isotonic solutions), hypotonic solutions have a lower concentration, or tonicity, of solutes (electrolytes). Hypotonic I.V. solutions have an osmolality less than 250 mOsm/L.6

Infusing a hypotonic solution into the vascular system causes an unequal solute concentration among the fluid compartments. The infusion of hypotonic crystalloid solutions lowers the serum osmolality within the vascular space, causing fluid to shift from the intravascular space to both the intracellular and interstitial spaces. These solutions will hydrate cells, although their use may deplete fluid within the circulatory system.6

Types of hypotonic fluids include 0.45% sodium chloride (0.45% NaCl), 0.33% sodium chloride, 0.2% sodium chloride, and 2.5% dextrose in water. Hypotonic solutions assist with maintaining daily body fluid requirements, but don't contain any electrolytes (except for sodium and chloride) or calories (except for D₅W, which is also considered a hypotonic solution after metabolism).3 Administering hypotonic saline solutions also helps the kidneys excrete excess fluids and electrolytes.

All these solutions provide free water, sodium, and chloride, and replace natural fluid losses. In addition, the solution containing dextrose offers a low level of caloric intake.

Figure. Checking for... - Click to enlarge in new window

Figure. Checking for pitting edema

Nursing considerations for hypotonic solutions

Hypotonic fluids are used to treat patients with conditions causing intracellular dehydration, such as diabetic ketoacidosis, and hyperosmolar hyperglycemic state, when fluid needs to be shifted into the cell. Be aware of how the fluid shift will affect various body systems. The lower concentration of solute within the vascular bed will shift the fluid into the cells and also into the interstitial spaces.

Use caution when infusing hypotonic solutions; the decrease in vascular bed volume can worsen existing hypovolemia and hypotension and cause cardiovascular collapse.6

Monitor patients for signs and symptoms of fluid volume deficit as fluid is "pulled back" into the cells and out of the vascular bed. In older adult patients, confusion may also be an indicator of a fluid volume deficit. Instruct patients to inform a nurse if they feel dizzy or just "don't feel right."

Never give hypotonic solutions to patients who are at risk for increased ICP because of a potential fluid shift to the brain tissue, which can cause or exacerbate cerebral edema. In addition, don't use hypotonic solutions in patients with liver disease, trauma, or burns due to the potential for depletion of intravascular fluid volume.2

HYPERTONIC SOLUTIONS

Compared with intracellular fluid (as well as with isotonic solutions), hypertonic solutions have a higher tonicity or solute concentration, causing an unequal pressure gradient between the inside and outside of the cells. Hypertonic fluids have an osmolarity of 375 mOsm/L or higher. The osmotic pressure gradient draws water out of the intracellular space, increasing extracellular fluid volume. Because of this property, hypertonic solutions are used as volume expanders. Hypertonic solutions may be prescribed for patients with severe hyponatremia. Patients with cerebral edema may also benefit from an infusion of hypertonic sodium chloride.6

Hypertonic sodium chloride solutions contain a higher concentration of sodium and chloride than that normally contained in plasma. Examples include 3% sodium chloride (3% NaCl), with 513 mEq/L of sodium and chloride, and 5% sodium chloride (5% NaCl), with 855 mEq/L of sodium and chloride. As the infusion of these hypertonic solutions raise the sodium level in the bloodstream, osmosis comes into play, removing fluid from the intracellular space, and shifting it into the intravascular and interstitial spaces. These solutions are highly hypertonic and should be used only in critical situations to treat hyponatremia. Give them slowly and cautiously to avoid intravascular fluid volume overload and pulmonary edema.3

When dextrose is added to isotonic or hypotonic solutions, the net result can be a slightly hypertonic solution due to the higher solute concentration. Thus, adding D₅W to sodium chloride solutions (such as 5% dextrose and 0.45% sodium chloride, and 5% dextrose and 0.9% sodium chloride) or to lactated Ringer's solutions such as D₅LR will provide the same electrolytes already discussed for each of those solutions, with the addition of calories. Plain glucose solutions with a concentration higher than 5%, such as 10% dextrose in water (D₁₀W), are also considered hypertonic. D₁₀W provides free water and calories (340 per liter), but not electrolytes.

Twenty percent dextrose in water (D₂₀W) is an osmotic diuretic, meaning the fluid shift it causes between various compartments promotes diuresis.

Fifty percent dextrose in water (D₅₀W) is a highly concentrated sugar solution. It's administered rapidly via I.V. bolus to treat patients with severe hypoglycemia.3

Nursing considerations for hypertonic solutions

Maintain vigilance when administering hypertonic saline solutions because of their potential for causing intravascular fluid volume overload and pulmonary edema.2 Hypertonic sodium chloride solutions should be administered only in high acuity areas with constant nursing surveillance for potential complications. Hypertonic sodium chloride shouldn't be given for an indefinite period of time. Prescriptions for their use should state the specific hypertonic fluid to be infused, the total volume to be infused and infusion rate, or the length of time to continue the infusion. As an additional precaution, many institutions store hypertonic sodium chloride solutions apart from regular floor stock I.V. fluids, so they must be ordered separately from the pharmacy.

Monitor serum electrolytes and assess for signs and symptoms of hypervolemia. Because hypertonic solutions can cause irritation, damage, and thrombosis of the blood vessel, some of these solutions shouldn't be administered peripherally. The Infusion Nurses Society states that "[p]arenteral nutrition solutions containing final concentrations exceeding 10% dextrose should be administered through a central vascular access device with the tip located in the central vasculature, preferably the subclavian/right atrium junction for adults."9

Instruct patients to notify a nurse if they develop breathing difficulties or if they feel their heart is beating very fast.

Hypertonic solutions shouldn't be given to patients with cardiac or renal conditions who are dehydrated. These solutions affect renal filtration mechanisms and can cause hypervolemia. Patients with conditions causing cellular dehydration, such as diabetic ketoacidosis shouldn't be given hypertonic solutions, because it will exacerbate the condition.