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BIO 169
FLUID, ELECTROLYTE,
AND ACID-BASE
BALANCE
Chapter 27
created by Dr. C. Morgan
1
TOPICS
Introduction
Fluid and Electrolyte Balance
Acid-Base Balance
Disturbances in Acid-Base Balance
Age Related Considerations
Resource: IPCD
Fluid, Electrolyte, and
Acid/Base Balance
2
Introduction Objectives
Review the importance of water to cellular life.
Distinguish between extracellular and intracellular fluids.
Discuss the meaning of fluid balance.
Discuss the meaning of electrolyte balance.
Discuss the meaning of acid-base balance.
3
Introduction
Cellular life consists of an unending chain of chemical
reactions we collectively call metabolism.
These chemical reactions occur in an aqueous medium.
If cells are to survive, the volume and composition of the
fluids within and outside cells must be maintained within
tolerable limits.
Extracellular fluids (ECF) are those present outside
cells (blood, lymph, interstitial fluid, kidney filtrate, etc).
Intracellular fluids (cytosol, mitochondrial matrix,
nucleoplasm, etc) are those present within cells.
Exchanges of water and solutes regularly occur between
the two fluid compartments.
4
Introduction (cont)
Homeostasis of all systems depends upon the daily
maintenance of fluid, electrolyte, and acid-base balance.
Fluid balance is achieved when water gain = water loss
along with the proper allocation to ECF and ICF.
Electrolyte balance is achieved when ion gain = ion loss
which is mostly influenced by activities of the digestive
and renal systems.
Acid-base balance refers to the maintenance of H+
concentration in body fluids within normal limits.
Proteins will denature if there is an extensive acid-base
imbalance.
Without functional proteins (enzymes), our cells will not
survive.
5
TOPICS
Introduction
Fluid and Electrolyte Balance
Acid-Base Balance
Disturbances in Acid-Base Balance
Age Related Considerations
6
Fluid and Electrolyte Balance Objectives
Discuss the composition of the human body with
respect to water and other components.
Describe the distribution of fluids in the ECF and ICF.
Show the main cations and anions in body fluids.
Present four principles that apply to fluid and
electrolyte balance.
Discuss the main regulatory hormones.
Discuss fluid balance.
Discuss electrolyte regulation of Na+, K+, Ca2+, and Cl–.
7
Fluid and Electrolyte Balance
Our body consists of liquids and solids.
Water comprises about 50% (females) to 60% (males)
of the total body weight with the gender differences
attributed to variations in adipose tissue versus muscle
mass.
Proteins comprise most of the solids with lipids second.
About ⅔ of the body H2O is present in the ICF.
Most of the ECF is interstitial fluid with plasma second.
Fluid exchanges between the ICF and ECF occur by
both passive and active transport processes.
Osmotic concentrations of the ICF and ECF are equal.
8
Fluid and Electrolyte Balance (cont)
Solid components of the body.
solids = 31.5 kg
Fig. 1 a
9
Fluid and Electrolyte Balance (cont)
Fluid components of the body (H2O + ions)
water = 38.5 l
Fig. 1 b
10
Fluid and Electrolyte Balance (cont)
ICF and ECF
contain similar ions
but they differ in
concentrations.
Among the cations,
Na+ is high in ECF
and K+ is high in the
ICF compartment.
Fig. 2 a
11
11
Fluid and Electrolyte Balance (cont)
Among the anions,
Cl– is the most
important in the
ECF while
phosphate ions
predominate in the
ICF.
Proteins are
abundant in the ICF
and many are
present in ECF.
Fig. 2 b
12
12
Fluid and Electrolyte Balance (cont)
Important principles:
*Homeostatic mechanisms respond to conditions in the
ECF (not the ICF).
*Receptors monitor plasma volume and osmotic
concentration which reflect fluid and electrolyte balance
in the entire body.
*Water moves by osmosis between the ECF and ICF.
*Water content and / or electrolytes will vary with intake
and the effects of circulating hormones – especially
antidiuretic hormone (ADH), aldosterone, and atrial
natriuretic peptide (ANP).
13
Fluid and Electrolyte Balance (cont)
Osmoreceptors in the hypothalamus are sensitive to even
slight changes in the osmotic concentration of the ECF.
The rate of ADH release from hypothalamic neurons
varies directly with ECF osmotic concentration.
ADH results in increased reabsorption of water by the
kidneys and stimulates thirst to increase H2O volume.
Aldosterone is secreted when K+ rises, Na+ falls, or by
the RAA response.
Renin is secreted by the JGA when BP drops,  filtrate
osmotic concentration in the DCT, or the K+ / Na+
concentration changes as noted above.
Aldosterone results in enhanced Na+ reabsorption with
Cl– following along with water by osmosis.
14
Fluid and Electrolyte Balance (cont)
Fluid Balance
water constantly
moves between
cells, cavities and
compartments
pericardial
thoracic
peritoneal
synovial
blood / CSF
80% in interstitium+
compartments
20% in plasma
blood / interstitium
Fig. 3
1515
Fluid and Electrolyte Balance (cont)
Fluid Balance (cont)
Net filtration pressure determines fluid exchanges
between the blood and interstitium.
Inability to return adequate amounts of fluid from the
interstitium may result in edema (tissue swelling).
Fluids also exchange with the outside environment.
Ideally, water losses will be balanced by water gains.
You lose about 2500 ml / day of water in urine, feces,
insensible perspiration (lungs and skin), and sensible
perspiration (sweat gland activity).
Water is gained by intake (2200 ml / day) and during
metabolism (300 ml / day).
TABLE 1 summarizes fluid gains and losses.
16
Fluid and Electrolyte Balance (cont)
Fluid Balance (cont)
Body water varies with the amount of Na+ present in the
ECF which is ideally around 136 – 142 mEq / l.
When the Na+ level rises above 150 mEq / l, the body is
in a state of hypernatremia.
When the Na+ level falls below 130 mEq / l, the body is in
a state of hyponatremia.
The Na+ rise and fall in concentration is due the loss or
gain of water respectively.
Dehydration will cause Na+ concentration to rise while
overhydration will dilute the Na+ concentration
The interdependence of solute concentration and fluid
volume is evident.
17
Fluid and Electrolyte Balance (cont)
Fluid Balance (cont)
Fluid shifts between the ICF and ECF are due to
changes in the osmotic concentration of the ECF.
The ICF represents a water reserve.
When the ECF becomes hypertonic to the interior of
cells, water will move from the ICF to the ECF by
osmosis.
Conversely, when the ECF becomes hypotonic to the
interior of cells, water will move into cells from the ECF.
Within volume limits, homeostasis with regard to the
osmotic concentration of the ICF and ECF is constantly
maintained by fluid shifts.
18
Fluid and Electrolyte Balance (cont)
Electrolyte Balance
Electrolyte balance is important since electrolytes affect
water balance and cell functions depend on a balance of
electrolytes, especially Na+ and K+.
At 136 – 142 mEq / l, Na+ salts (NaCl and NaHCO3)
account for more than 90% of the ECF solutes.
ICF Na+ is only about 10 mEq / l.
At 160 mEq / l, K+ predominates in the ICF and in the
ECF it is present from 3.8 – 5 mEq / l.
*Most electrolyte imbalances involve Na+
*K+ problems do occur and are more dangerous than
Na+ balance problems.
19
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – Na+ issues
Total ECF Na+ is determined by absorption across the
intestinal villi epithelium (48 – 144 mEq / day) and kidney
function in reabsorption and excretion plus other losses
such as in sweat.
Osmosis and hormonal regulation of fluid shifts keep the
ECF concentration of Na+ within normal limits.
Kidney function in the presence of the regulatory
hormones ADH and aldosterone is the most important
homeostatic regulatory mechanism for sodium balance
and ECF fluid volume.
ANP inhibits mechanisms that elevate blood pressure.
The ECF Na+ concentration and fluid volume are closely
integrated.
20
Fluid and Electrolyte Balance (cont)
Response mechanisms to rising Na+ in the ECF.
Fig. 4
21
21
Fluid and Electrolyte Balance (cont)
Response mechanisms to falling Na+ in the ECF.
Fig. 4
22
22
Fluid and Electrolyte Balance (cont)
Fig. 5
23
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – Na+ issues
Other hormonal effects:
Estrogens have aldosterone-like effects.
Progesterones block aldosterone.
Glucocorticoids may mimic aldosterone.
24
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – K+ issues
98% of the potassium in the body is contained in the ICF.
The ECF K+ level is due to absorption across the digestive
epithelium (50 – 150 mEq / day) and urinary losses.
There are no other routes of appreciable K+ losses.
Renal tubular secretion varies
*directly with K+ ECF concentration,
*preferential H+ secretion for pH maintenance rather than
K+ secretion (meaning K+ is retained), and
*aldosterone levels which influence Na+ reabsorption and
K+ secretion.
25
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – K+ issues
K+ imbalances cause numerous physiological problems.
Hypokalemia, a plasma K+ level < 2 mEq / l, may result
from inadequate dietary intake, diuretic administration,
excessive aldosterone secretion, or the renal response
to  pH of the ECF.
Muscular weakness and paralysis may result.
Hyperkalemia, a plasma K+ level > 8 mEq / l, may result
from renal failure, diuretics that block Na+ reabsorption,
and a  in pH.
Cardiac arrhythmias accompany hyperkalemia.
26
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – other regulated ions
Calcium, the most abundant body mineral, is absorbed
across the intestinal mucosa, deposited and released
from bone, reabsorbed from the filtrate as it is
processed in the kidneys, and slightly lost in the bile.
The normal serum range is 4.5 – 5.3 mEq / l
(plasma range is 8.5 – 11 mEq/l) (why the difference?)
Parathyroid hormone and calcitriol stimulate absorption
across the intestinal mucosa and reabsorption from the
DCT.
Hypercalcemia exists when the ECF concentration
exceeds 11 mEq / l with hyperparathyroidism the most
common cause.
Severe cardiac arrhythmias may result.
27
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – other regulated ions
Hypocalcemia exists when the ECF serum concentration
is less than 4 mEq / l with hypoparathyroidism, vitamin D
deficiency, or renal failure the main causes.
The condition results in cardiac arrhythmias and
decreased contractility , osteoporosis, muscle spasm,
and possibly convulsions.
Magnesium, an enzymatic cofactor, is present in the ICF
at about 26 mEq / l and at 1.5 – 2.5 mEq / l in the ECF.
The skeleton contains 60% of the Mg2+ in the body.
28
Fluid and Electrolyte Balance (cont)
Electrolyte Balance (cont) – other regulated ions
Phosphate ions are used in bone mineralization, as
cofactors, in making ATP and other high energy
compounds, and for the synthesis of nucleic acids.
The serum concentration of PO4 3¯ is 1.8 – 2.6 mEq / l.
Calcitriol stimulates reabsorption along the PCT but
some is lost in urine and feces.
Chloride ion serum concentration is from 100 – 108
mEq / l and only 3 mEq / l in the ICF.
Cl– moves with Na+ and provides electrical balance.
You only need 48 – 146 mEq / day (1.7 – 5.1 g).
TABLE 2 lists normal ECF range of the ions discussed.
29
TOPICS
Introduction
Fluid and Electrolyte Balance
Acid-Base Balance
Disturbances in Acid-Base Balance
Age Related Considerations
30
Acid – Base Balance Objectives
Review some terms related to acid – base balance.
Discuss the importance of pH control in body fluids.
Describe the types of acids in the body.
Discuss the mechanisms of pH control by buffer
systems.
Discuss the maintenance of acid – base balance.
31
Acid – Base Balance
By definition, an acid releases H+ ions into solution and a
base removes H+ from solution usually by supplying
OH– which combines with the H+ to form H2O.
The strongest acids and bases dissociate completely;
weaker acids and bases do not have all molecules
dissociated.
Salts dissociate to release ions that are not H+ or OH– .
Buffers are substances that oppose pH changes by
supplying or removing H+ from body fluids (TABLE 3).
The normal pH of ECF is 7.35 – 7.45.
Deviations from the normal pH range threaten life and
mechanisms constantly operate to maintain pH
homeostasis.
32
Acid – Base Balance (cont)
Acidemia is a plasma pH < 7.35 resulting in acidosis.
Alkalemia is a plasma pH > 7.45 resulting in alkalosis.
The CNS and cardiovascular system are very sensitive to
pH fluxuations.
Acidosis is a more prevalent deviation from normal.
There are three types of acids in the body.
*A volatile acid will leave the body as a gas.
Carbonic acid is our only volatile acid.
CO2 + H2O  H2CO3  H+ + HCO3–
The CO2 you exhale is the key component of the volatile
acid that may leave the body and enter the atmosphere.
33
Acid – Base Balance (cont)
The CO2 – pH balancing act
Fig. 6
3434
Acid – Base Balance (cont)
*Fixed acids do not leave solution and are eliminated by
the kidneys.
Sulfuric and phosphoric acid are the main fixed acids
which are generated during metabolism of amino acids
and compounds containing phosphate groups.
*Organic acids are those that participate in the TCA
cycle or evolve as byproducts of metabolism.
Lactic acid and ketone bodies are the main forms.
Lactic acid builds up as an end product of anaerobic
metabolism and excess ketone bodies are generated
during prolonged lipid and amino acid catabolism (as
in starvation).
35
Acid – Base Balance (cont)
Buffer systems exist to maintain acid–base balance.
Buffers are able to donate H+ to solution or remove H+
from solution.
H+ ions are absorbed across the intestinal villi and are
generated during metabolism.
H+ ions are eliminated by the kidneys and indirectly by
the lungs as CO2 is exhaled and water is formed.
There are three major buffer systems:
*the protein buffer system
*the carbonic acid–bicarbonate buffer system
*the phosphate buffer system
36
Acid – Base Balance (cont)
The three buffer
systems
Fig. 7
37
Acid – Base Balance (cont)
Protein Buffers
Amino acids are able to donate an H+ from their carboxyl
end or bind an H+ on their amino end.
Peptides have buffering ability only at the ends of their
amino acid chain or side groups of histidine and cysteine.
If pH
rises
If pH
falls
Fig. 8
In the ECF, plasma proteins and hemoglobin are buffers.
In the ICF, intracellular proteins are efficient buffers.
38
Acid – Base Balance (cont)
Protein Buffers (cont)
Proteins present in the plasma and interstitial fluids act
as buffers.
Intracellular functional and structural proteins serve to
buffer acids produced during metabolism.
Since ion exchanges occur between the ECF and ICF,
intracellular functional and structural proteins are able
to assist in buffering the ECF.
H+ ions may be pumped from an acidic ECF into cells
where intracellular proteins act as buffers.
ECF K+ ions may also exchange for intracellular H+ ions
when the ECF pH rises above normal.
These buffering processes are relatively slow.
39
Acid – Base Balance (cont)
Protein Buffers (cont)
Hemoglobin molecules have the ability to bind H+ on their
polypeptide chains and supply bicarbonate which
moves into the plasma where it may buffer H+.
The H+ evolves from the familiar equation:
CO2 + H20  H2CO3  H+ + HCO3–
Recall that in the lungs, the equation shifts to the left.
The hemoglobin buffering system helps to maintain
plasma pH homeostasis when there are fluxuations in
PCO2.
This is the only intracellular buffering system that is able
to immediately change the pH of the ECF.
40
Acid – Base Balance (cont)
Carbonic Acid – Bicarbonate Buffer System
The main role of this system is to buffer organic and fixed
acids that move into the ECF.
The supply of bicarbonate ions may be quickly consumed
so must be replaced from the bicarbonate reserve
(NaHCO3) present in body fluids.
Fig. 9 a
41
Acid – Base Balance (cont)
As the bicarbonate is consumed in buffering the H+ from
acids, more carbonic acid is formed driving the equation to
the left when the blood reaches the lungs.
The amount of available HCO3– ions is the limiting factor.
replacement required
lungs

The respiratory system is able to compensate for the
metabolic generation of H+ ions.
Fig. 9 b
42
42
Acid – Base Balance (cont)
Kidney Function
Transport processes
along the DCT result
in the generation of
bicarbonate while
secreting H+ ions
into the tubular fluid.
This new bicarbonate
becomes part of
the plasma
bicarbonate reserve.
Fig. 26-14 c
43
43
Acid – Base Balance (cont)
Phosphate Buffer System
Dihydrogen phosphate (H2PO4– ) is a weak acid that will
dissociate to supply an anion that is able to buffer H+.
H2PO4–  H+ + HPO4 2–
As the monohydrogen phosphate is consumed during
buffering, more is released from a phosphate reserve.
Na2HPO4  2 Na+ + HPO4 2–
This system has greatest importance in the ICF.
This system is also employed as a buffer in the urine.
44
Acid – Base Balance (cont)
Buffering is only a short term solution to pH imbalances.
Long term maintenance of acid–base balance depends
on eliminating excess H+ ions from the ECF so buffers
are free to be used again.
Likewise, if H+ ions need to be supplied to correct an
alkalotic condition, the supply of H+ ions obtained from
buffers may be rapidly exhausted unless the H+ ions are
replaced.
The solution is to integrate activities of the respiratory and
urinary systems to eliminate or supply H+ ions to the ECF
while buffers solve immediate pH imbalances.
pH homeostasis is critically important in maintaining the
integrity of functional and structural proteins.
45
Acid – Base Balance (cont)
Respiratory compensatory mechanisms involve a change
in respiratory rate and depth of ventilation which results
in an alteration of the amount of CO2 leaving the body.
This mechanism manipulates the carbonic acid –
bicarbonate buffer system.
CO2 + H20  H2CO3  H+ + HCO3–
Recall that central and peripheral chemoreceptors send
information to the respiratory center in the medulla
oblongata which results in appropriate adjustments to
ventilation for pH maintenance of the ECF.
 pH   ventilation
 pH   ventilation
46
Acid – Base Balance (cont)
Renal compensatory mechanisms involve changing the
rates of secretion or reabsorption of H+ and newly
generated HCO3– ions.
Kidney tubular cells are able to secrete H+ until the pH
falls to about 4.0 to 4.5 after which buffering is required.
The kidneys eliminate H+ in the form of ammonium ions
(NH4+), dihydrogen phosphate (H2PO4– ), and utilizing the
carbonic acid – bicarbonate system.
When alkalosis develops, the kidneys decrease H+
secretion, reclaim fewer bicarbonates, and excrete
HCO3– while reabsorbing H+ and Cl–.
47
Acid – Base Balance (cont)
Acidosis response
PCT
Collecting duct
Fig. 10 a
Renal compensation using
buffer systems
1. bicarbonate
2. monohydrogen phosphate
3. ammonia
48
Acid – Base Balance (cont)
Acidosis response
renal tubule cell
of the PCT
The amino acid glutamine
supplies ammonia and
bicarbonate for buffering.
Fig. 10 b
The toxic NH3 is detoxified
to ammonium ion (NH4+)
during buffering.
49
Acid – Base Balance (cont)
Renal response to
alkalosis
Reclaim H+
Fig. 10 c
Secrete HCO3–
50
TOPICS
Introduction
Fluid and Electrolyte Balance
Acid-Base Balance
Disturbances in Acid-Base Balance
Age Related Considerations
51
Acid – Base Disturbances Objectives
Describe the most common causes of acid–base
disturbances.
Discuss respiratory acidosis.
Discuss respiratory alkalosis.
Discuss metabolic acidosis.
Discuss combined respiratory and metabolic acidosis.
Discuss metabolic alkalosis.
Describe methods to detect acidosis and alkalosis.
52
Acid – Base Disturbances
Balancing pH means controlling the gains and losses of H+.
Buffers and the respiratory ventilation and renal
mechanisms all have a role in maintaining pH balance.
The acid–base disorders include acidosis and alkalosis
from respiratory or metabolic causes.
These disorders arise when the pH cannot be controlled by
the various available mechanisms.
Factors that affect any one of the regulatory mechanisms
may lead to an acid–base disturbance.
In respiratory acid–base imbalances the CO2 level in the
ECF is abnormal.
In metabolic imbalances, the ECF HCO3– level is abnormal.
53
Acid – Base Disturbances
NORMAL BLOOD VALUES
pH = 7.35 – 7.45
PCO2 = 35 – 45 mmHg
HCO3– = 24 – 28 mEq / l (text)
HCO3– = 22 – 26 mEq / l (other sources)
acidosis = pH < 7.35
alkalosis = pH > 7.45
TABLE 4
54
Acid – Base Disturbances (cont)
Interactions in response to acidosis.
Fig. 11 a
55
55
Acid – Base Disturbances (cont)
Interactions in response to alkalosis.
Fig. 11 b
56
56
Acid – Base Disturbances (cont)
Respiratory acidosis, the most common acid–base
disturbance, develops when there is more CO2 produced
by the metabolism of cells than can be eliminated from
the body.
The plasma pH drops below 7.35 because of
hypercapnea which drives the carbonic acid equation to
the right.
Hypoventilation is the most common cause.
Acute respiratory acidosis is severe and develops
quickly.
Chronic respiratory acidosis persists with COPD,
paralysis, or any disorder that decreases ventilation .
The kidneys attempt to compensate for the H+ buildup.
57
Acid – Base Disturbances (cont)
Respiratory acidosis: characteristics and responses
Fig. Fig.
12 a12 a
58
58
Acid – Base Disturbances (cont)
Respiratory alkalosis, an infrequent disturbance, results
in a rise in pH above 7.45 due to hypocapnia caused by
hyperventilation.
Hyperventilation is usually associated with stress and
pain or infrequently with adaptation to high altitude,
brain stem injuries, or mechanical ventilation.
Hyperventilation does not usually result in acid–base
disturbances that require medical intervention.
Chemoreceptor responses will result in changes in
ventilation that correct for respiratory acidosis and
alkalosis in healthy individuals.
59
Acid – Base Disturbances (cont)
Respiratory alkalosis: characteristics and responses
Fig. 12 b
6060
Acid – Base Disturbances (cont)
Metabolic acidosis, the second most common acid–base
disturbance, may be due to
* a buildup of fixed and organic acids in the ECF
lactic acidosis due to strenuous exercise; hypoxia
ketoacidosis in uncontrolled diabetes mellitus or
starvation
* the loss of HCO3– (usually from chronic diarrhea)
* failure of the kidneys to secrete adequate H+
diuretic therapy
kidney disease
Compensation is by the respiratory and renal systems.
61
Acid – Base Disturbances (cont)

Responses to
metabolic acidosis
Fig. 13

62
Acid – Base Disturbances (cont)
Respiratory and metabolic acidosis often occur
simultaneously since hypoventilation leads to tissue
hypoxia so cells must resort to anaerobic metabolism.
During anaerobic metabolism (glycolysis only), pyruvic
acid is converted into lactic acid.
Metabolic alkalosis is due to increased HCO3– which
remove H+.
The most common cause is vomiting resulting in losses
of HCl which is replaced while generating a prolonged
alkaline tide into the ECF.
Ingestion of alkaline drugs and gastric suctioning are
also causes.
Compensation is by the respiratory and renal systems.
63
Acid – Base Disturbances (cont)
Responses to
metabolic alkalosis


Fig. 14
64
Acid – Base Disturbances (cont)
A study of the blood chemistry will reveal information about
acid–base disturbances (see TABLE 4).
The usual test is to analyze a sample of arterial blood
(ABG = arterial blood gas) which reveals pH, blood gas
partial pressures, and the bicarbonate level.
Analysis of ABGs may be done in a series of steps.
• check pH for acidosis or alkalosis
• check to see of PCO2 or HCO3– is abnormal
• if the PCO2 is abnormal, the cause is respiratory
• if the HCO3– is abnormal, the cause is metabolic
• examine the value that does not correspond with the pH
change to determine if compensation is occurring.
65
Acid – Base Disturbances (cont)
ABG correlation guide
HCO3–
pH
PCO2
Normal plasma values
7.35 – 7.45
35 – 45 mm Hg
22 – 26 mEq/l
Respiratory acidosis
renal compensation


normal

Respiratory alkalosis
renal compensation


normal

Metabolic acidosis
respiratory compensation

normal



Metabolic alkalosis
respiratory compensation

normal


Hb saturation 95% or >
PO2 = 80 – 100 mm Hg
66
Acid – Base Disturbances (cont)
Fig. 15
anion gap= (Na+) – (HCO3¯ ) + (Cl¯ )
normal = 10-12 mEq/l
67
TOPICS
Introduction
Fluid and Electrolyte Balance
Acid-Base Balance
Disturbances in Acid-Base Balance
Age Related Considerations
68
Age Related Considerations Objectives
Describe considerations with fluid balance.
Describe considerations with renal function.
Discuss concerns with mineral content of the body.
Discuss concerns with respiratory function.
Describe some concerns with infants.
69
Age Related Considerations
More fluid, electrolyte, and acid–base balance problems
accompany aging than occur in infants and children.
*The total amount of body water decreases after age 60.
This decrease results in less ability to dilute toxins,
waste products of metabolism, and drugs.
*The total number of functional nephrons decreases which
reduces the GFR.
This decrease reduces renal compensatory mechanisms.
*There is a reduced sensitivity to ADH and aldosterone.
This reduces reabsorption of fluid and loss of body water.
*Total mineral content of the body declines.
This affects buffering ability.
70
Age Related Considerations
*Reduced vital capacity limits the ability of the respiratory
system to compensate for metabolic acidosis.
Infancy considerations:
The volume of the ECF is about equal to the ICF volume.
Changes in the ECF status will quickly alter the
intracellular conditions and intracellular buffering ability
may be quickly exhausted.
Infants have less minerals in reserve.
Metabolic rate of infants is twice that seen in adults.
Kidneys cannot produce a urine that exceeds 450 mOsm/l.
Because the functional residual capacity is small in infants,
they may quickly develop respiratory disturbances that
lead to acidosis and alkalosis.
71
TOPICS
Introduction
Fluid and Electrolyte Balance
Acid-Base Balance
Disturbances in Acid-Base Balance
Age Related Considerations
72