Fluid and Electrolyte Balance

Acid/Base Balance

Week 45

Objectives• Identify the 2 major fluid compartments• Relate the thirst mechanism to the maintenance

of fluid balance• Describe the work of the kidney in maintaining

fluid balance and mechanisms that increase or decrease the amount of urine produced

• Explain the meaning of isotonic, hypertonic and hypotonic solutions and how they influence the transfer of fluids between compartments

• List the signs and symptoms of edema and dehydration

Objectives• Describe nursing actions to protect the patient who is

either dehydrated or has fluid overload• Relate dehydration and edema to the principles of fluid,

electrolyte and acid-base balance• Explain the relationship between fluid and sodium in the

body• List four routes of fluid loss from the body• Explain the Ph scale and the normal Ph of various body

fluids• Describe the importance of water to the functioning of

the human body.• Explain how a buffer system limits great changes in Ph.

Objectives• State the normal

range of each of the electrolytes

• List the major intracellular electrolytes

• List the major extracellular electrolytes

Balance: a set, desired level

Homeostasis

Electrolytes

• Chemicals that can carry an electrical charge

• Dissolved in body fluids• Concentration dependant on fluid balance

Sodium• Na+ 134- 142 mEq/L• Most abundant electrolyte in the body• Major extracellular electrolyte• Major source: diet• Primary route of excretion: kidneys• Functions

– Regulation of water balance– Increases cell membrane permeability– Stimulates conduction of nerve impulses– Maintain neuromuscular irritability– Controls muscle contractility, esp. cardiac

Na+ Replacement

• Common is IV therapy– 0.9% Solution AKA Normal Saline– 0.45% AKA half normal

• Adverse reactions: none

Potassium• K+ 3.5- 5 mEq• Dominant intracellular • Source: diet• Excretion: kidneys• Function:

– regulation of intracellular water and electrolytes– Promotes transmission of nerve impulses and skeletal

muscle function– Cellular metabolism of CHO– Control hydrogen ion concentration/ regulation of acid

base balance

Potassium Replacement

• Oral: give with food• IV

– may cause phlebitis– Tissue necrosis if extravasates

• Probably needed with diuretic therapy

Chloride• Cl- 96- 105 mEq/L• Extracellular• Chief anion in interstitial and intravascular fluid• Most often linked with Na+• Excreted via kidneys• Function

– Formation of hydrochloric acid– Regulates osmotic pressure between compartments– Regulation of acid/base balance

Calcium• Ca+ 4.5• 99% in bound in bones and teeth• 1% in soft tissue and extracellular fluid• Sources: Primarily milk and cheese, also nuts, beans,

egg yolk• Function

– Bone matrix– Blood clotting– Promotes normal transmission of nerve impulses– Regulates normal muscle contraction and relaxation– Holds body cells together by establishing the thickness and

strength of cell membranes– Enzyme activator for chemical reactions in the body

Calcium Replacement• PO

– GI upset– Concurrent ingestion with spinach or cereal

may decrease absorption.– Vitamin D required for absorption of Ca+– Decreases the effectiveness of atenolol,

verapamil• IV

– Vein irritation, tingling, metallic, chalky taste

Phosphorus• HPO4- 4mEq• Intracellular• Inverse relationship with calcium• 70% - 80% bound with Ca+ in bone• Sources: in many foods, particularly beef, dairy,

legumes. Seldom find deficiency.• Function:

– Maintain teeth and bones– Buffer to regulate acid/base balance– Promotes effectiveness of B vitamins– Normal nerve and muscle activity– CHO metabolism

Magnesium• Mg++ 1.5- 2.4• Second most abundant intracellular cation• Sources: widely distributed in foods• Excretion: kidneys• Function:

– Cofactor in the activation of enzymes– Promotes regulation of Ca+, Phosphate, K+– Essential for integrity of nervous tissue,

skeletal muscle and cardiac functioning

Magnesium Replacement• Used to control and prevent seizures of

eclampsia/ pre-eclampsia• May help reduce symptoms of RLS• Adverse reactions: related to overdose

– Flushing, sweating, HOTN, depressed reflexes, muscle weakness, respiratory failure, circulatory collapse

• Concurrent use with ACE inhibitors may result in hyperkalemia

Bicarbonate

• HCO3- 22-24 mEq• Major extracellular anion• Major function: acid/base balance

– Buffers acids. Maintains the 20:1 bicarbonate/ carbonic acid ratio

• Excretion: selectively by kidneys

Water

• Average adult male: 63% water• Average adult female: 52%• Infants: 77%• Elderly: 45%

What does water do?

Water DistributionIn a 70 kg male

Tissue % of water % of body weight Litres of water / 70 kg

Skin 72.0 18.0 9.07

Muscle 75.6 41.7 22.1

Skeleton 22.0 15.9 2.45

Brain 74.8 2.0 1.05

Liver 68.3 2.3 1.03

Heart 79.2 0.5 0.28

Lungs 79.0 0.7 0.39

Kidneys 82.7 0.4 0.25

Spleen 75.8 0.2 0.10

Blood 83.0 8.0 4.65

Intestine 74.5 1.8 0.94

Adipose tissue 10.0 Approximately 10.0 0.70

Where water is lost from the body in the healthy adult

GASTRO-INTESTINAL TRACT

(FECES) 6%

LUNGS (WATER VAPOR) 13%

SKIN (DIFFUSION & SWEAT) 19%

KIDNEYS (URINE) 62%

 

Water Balance

How water moves

Filtration

Oncotic Pressure

• The osmotic pressure attributed to proteins and other macromolecules

• Balances hydrostatic pressure• The overall osmotic effect of colloids like

plasma proteins• Also called colloid osmotic pressure

Osmolality• The concentration of a solution• Determined by number of particles dissolved in a

kilogram of water• Higher osmolality= more particles• Controls water movement and distribution• Intracellular maintained by K+• Extracellular maintained by Na+• Normal 280- 294• Osmolarity same idea, but is measured by

number of particles dissolved in a liter of water

Regulatory Mechanisms• Kidneys

– Filtration– Tubular reabsorption

• Hormones– Aldosterone– ADH– Atrial natriuretic factor– Renin

• Thirst

 

Age Related Changes

• Kidneys• Reduced sense of thirst• Total body water decline• Skin turgor less reliable indicator of fluid

balance• Drugs influence balance

Assessment of Balance

• Vital signs• I & O• Body weight• Skin characteristics• Mucous Membranes• Veins

Diagnostic Tests• Urine pH: 4.5- 8.0• Urine specific gravity: 1.010- 1.025• Urine osmolality: 250- 900 mOsm/kg H2O• Serum Hematocrit: 40-54 men 38- 47 women• Creatinine: 0.6- 1.5• BUN: 8- 20• Serum Osmolality: 280- 294• Serum Albumin: 3.5- 5.5• Serum electrolytes

Acid Base Balance• pH is the measure of

hydrogen ion concentration

• Water is neutral—it has a pH of 7

• Normal blood: 7.35- 7.45• pH < 6.8 or> 7.8 is usually

fatal• 20:1 Bicarbonate:

carbonic acid ratio

pH…What is normal?

• Blood 7.35 to 7.45• Intracellular fluid 6.8-7.0• Urine 4.5- 7.8• Gastric juice 1.0- 2.0• Saliva 5.8-6.2• Intestinal secretions 7.9- 8.4

Acid Base Balance• The Bird's Eye-View, Two Components: • Respiratory: When breathing is inadequate carbon dioxide

(respiratory acid) accumulates. The extra CO2 molecules combine with water to form carbonic acid which contributes to an acid pH. The treatment, if all else fails, is to lower the PCO2 by breathing for the patient using a ventilator.

• Metabolic: When normal metabolism is impaired – acid forms, e.g., poor blood supply stops oxidative metabolism and lactic acid forms. This acid is not respiratory so, by definition, it is “metabolic acid." If severe, the patient may be in shock and require treatment, possibly by neutralizing this excess acid with bicarbonate, possibly by allowing time for excretion/metabolism.

• That's it! The whole of acid-base balance in six sentences.

• Why do we care?• Variations in pH or PCO2 used to be viewed

as though they were the causes of pathology. Experiments have shown, however, that very low pH and very high PCO2 may both be well tolerated when circulation and oxygenation are maintained. The implication is that abnormal levels of PCO2 or pH are best used as indicators of serious trouble, but not as causes themselves.

• Acid Production & Compensation.• Our Fuel makes CO2 As fire makes smoke, so

metabolism makes acid - CO2 and metabolic acids. The body's own regulators of acid-base balance are the lungs, liver and kidneys which are responsible for excreting and metabolizing these acids. In acid-base disturbances, there is an imbalance between the quantity of acids produced and the body's ability to respond.

• Acid Production• The body's metabolism produces acid - which is

released into the capillaries and makes the blood slightly more acidic. The blood arrives in the arterioles with a pH of 7.4 (equivalent to [H+] = 40 nMol/L) and leaves the venules with an average pH of 7.36 (equivalent to [H+] = 44 nMol/L).

• Hydrogen ions have been added to the blood from the interior of the cell which has an average pH around 7.0 (equivalent to [H+] = 100 nMol/L). It is as though hydrogen ions falls down the steep gradient from the higher concentration in the cell to the more alkaline plasma outside.

• The acids produced are: a) respiratory acids, in practice a single acid (CO2), and b) all other acids, non respiratory, which are by definition metabolic. The body's principle regulators of acid-base balance are the lungs and the kidneys which excrete the respiratory and metabolic acids respectively.

• Acid Elimination.• Respiratory Acid. The quantity of respiratory acid produced per

day is easily calculated. Two hundred milliliters of carbon dioxide per minute is (0.2 * 60 * 24 = ) 288 liters per day. Since each gram molecule of gas occupies 22.4 liters at STP, approximately 12 moles of carbon dioxide are produced daily. This enormous quantity is matched to an appropriately powerful means of elimination - our lungs.

• Metabolic Acid. By contrast very little metabolic acid is produced - normally only about 0.1 moles (100 mEq) of acid per day. This production is eliminated by the kidney or metabolized by the liver and, appropriately, their capacity is less than that of the lungs. Metabolic acids include lactic, pyruvic, and the keto-acids of diabetic acidosis.

•

Buffers

• Three buffering systems– Blood buffers– Respiratory system– Kidneys

Respiratory Buffering

• Acts quickly• Breathing slows to retain CO2, speeds to

eliminate it.

Renal buffering

• The Difference in Compensation

Rapid Respiratory Compensation. The power of the lungs to excrete large quantities of carbon dioxide enables them to compensate rapidly.

Unless the respiratory system is diseased or depressed, metabolic disturbances stimulate a prompt response, i.e., metabolic acidosis and

metabolic alkalosis normally elicit characteristic partial respiratory compensation almost immediately.

Slow Metabolic Compensation. The smaller capacity of the kidneys corresponds to a relatively slower rate of compensation; a patient can be ventilated at an abnormal PCO2 for a day or two before the characteristic,

partial compensation is achieved. In the operating room and in the emergency room, therefore, an abnormal PCO2 is not usually associated with a metabolic "compensation". It follows that when a metabolic acidosis

or alkalosis is detected, it usually reflects either a separate metabolic disturbance or compensation for a chronic respiratory problem.

What is the right solution?

• Which fluid isthe right fluid?

Tonicity……..

• Isotonic• Hypotonic• Hypertonic

Plasma

• Increase blood volume after severe hemorrhage while awaiting whole blood

• Replacement

Plasma Expanders

• Not a blood product• Hespan• Dextran• Expand blood volume when shock caused

by bleeding, surgery, trauma

Nutrition

• TPN---total parenteral nutrition• Lipids• PPN—peripheral parenteral nutrition

Nursing Assessment of the Patient Receiving IV Fluids

• Monitor IV site• Watch of signs of fluid overload• Monitor I & O• Change IV tubing per hospital protocol