Fluid and Electrolyte
Balance
Word and Vocabulary
electrolyte电解质
dehydration脱水
sodium钠
potassium钾
urea 尿素
creatinine肌酐
chloride氯
bicarbonate碳酸氢
over-hydration水肿
anion阴离子
hyponatraemia低钠血症
constituent成分，组份 aldosterone醛固酮
acidosis酸中毒
alkalosis碱中毒
hyperkalaemia高钾血症
lethargy无生气的
mucous粘液
intracellular细胞内的
Cumulative累积的
extracellular细胞外的 interstitial细胞间的
schematic示意的
inlet入口
outlet 出口
visualise可视的
hydration水合作用
accumulate累积
cation阳离子
predominate主要的
ion离子
consequence结果 glomerular filtration rate
肾小球滤过率 variable变量
solute 溶质
solvent溶剂
semipermeable半透膜的 osmotic渗透的
shrink收缩
expand扩张
isotonic等渗的
formula公式，规则
flux 流动，变化 homeostatic稳态
deprive丧失
collapse崩溃
oxygen氧
nutrient营养
imbibe喝
overriding首要的
fluctuation波动 vulnerable易受攻击的
AVP(antidiuretic hormone,ADH)抗利尿激素
Perspiration出汗
respiration呼吸
hypothalamus下丘脑
posterior后的
pituitary
approximately大约地
infantile婴儿
diarrhoea腹泻
The importance to exam the fluid and
electrolyte balance
• Fluid and electrolyte balance is central to the
management of any patient who is seriously ill.
• The most commonly requested biochemistry
profile is the measurement of fluid and
electrolyte
Body Fluid Compartment
The intracellular fluid compartment (ICF) : is the volume
of fluid inside the cells.
The extracellular fluid compartment (ECF) : is the volume
which lies outside cells.
• plasma
•Interstitial
fluid
It is important to understand the difference between the ECF
and the effective circulating volume (ECV). The ECV is the
portion of the ECF that is actively perfusing tissues. In some
pathologic states (such as patients with heart failure, ascites,
or edema), the ECV may be decreased despite an increase in
the total ECF.
Water tank model of body fluid
compartments
Fluids
taken orally
or by
intravenous
infusion
Urinary
tract and
insensible
loss as
surface
evaporation
Dehydration and Over-hydration
Dehydration simply means that fluid loss has
occurred from body fluid compartments.
Over-hydration occurs when fluid accumulates in
body compartment
The effect of volume depletion and volume expansion on
the water tank model of body compartment
(a) Dehydration: loss of
fluid in ICF and
ECF due to
increased urinary
losses
(b) Over-hydration:
increased fluid in
ICF and ECF due
to increased intake
ELECTROLYTES
Na\Cl\
HCO3
K+
• Sodium(Na+) is the principal extracellular
cation
• Chloride(Cl-) and bicarbonate(HCO3-) are
predominate anion in ECF
• Potassium(K+) is the principal intracellular
cation
• Inside cells the main anions are the protein and
phosphate
OSMOLALITY
• Osmolality of a solution is decided by the
overall number of solute particles in a
specific compartment.
• Although body fluids vary greatly in their
composition, and the concentration of
substances differs in the different body
fluids, the osmolality is identical.
Sodium ion is present at the highest concentration
and hence make the largest contribution to the total
plasma osmolality.
And potassium ion’s concentration in ECF is less
comparing with that in ICF, but the changes in the
concentration in ECF are very important and may
have life threatening consequences.
Osmolality changes and water movement in
body fluid compartment
The osmolality in different body compartments must be equal.
This is achieved by the movement of water across
semipermeable membranes in response to concentration
changes.
Plasma osmolality
Plasma osmolality (Posm) is defined as the total amount of
solute particles, including anions, cations and other
solute, in 1 L water. Posm can be measured directly by
osmometry or estimated by the following formula:
plasma osmolality(mmol/kg)
=1.86 plasma[sodium＋glucose＋urea](mmol/l)+9
The unit of all [Na+], [glucose] and [urea] is mmol/L. Because Na+ is
the major cation and plasma is approximately 93% (0.93) water,
the sum of the anions and cations can be approximated by
multiplying the Na+ concentration by 1.86. The 9 mOsm/kg added
represents the contribution of other osmotically active substance
in plasma such as K+, Ca2+ and proteins. Thus, only Na+, urea,
and glucose need to be measured. Posm normally is 275~300
mOsm/kg.
Fluid and electrolyte balance:
concepts and vocabulary
• The body has two main fluid compartments, the intracellular
fluid and extracellular fluid.
• The ICF is twice as large as the ECF.
• Water retention (over-hydration)will cause an increase in the
volume of both ECF and ICF.
• Water loss(dehydration) will result in a decreased volume of both
ECF and ICF.
• Sodium ions are the main ECF cations.
• Potassium ions are the main ICF cations.
• The volumes of the ECF and ICF are estimated from knowledge
of the patient’s history and by clinical examination.
• Serum osmolality can be measured directly or calculated from the
serum sodium, urea and glucose concentration.
WATER AND SODIUM BALANCE
Body water and the electrolytes it contains are in a state of the
constant flux.
It is important to maintain a steady state.
Failure to maintain ECF volume, with the consequence of impaired
blood circulation, rapidly leads to tissue death due to lack of
oxygen and nutrients, and failure to remove waste product
Normal water balance
Faece
s(粪
便)
The regulation of water balance by AVP
and osmolality
+
_
Normal sodium balance
The regulation of sodium
balance by aldosterone
Arterial
natriuretic
peptide
心钠素
adrenal gland;
adrenal organ
Regulation of volume
The amount of sodium in the ECF determines what the volume
of the compartment will be.
Aldosterone and AVP interact to maintain normal volume and
concentration of the ECF.
• When the ECF volume is low, aldosterone secretion is high.
•Thus as the patient begins to take fluids orally, any salt
ingested is maximally retained.
•As this raised the ECF osmolality, AVP action then ensures
that water is retained too.
Water and sodium balance
Water is lost from the body as urine and as obligatory “insensible”
losses from the skin and lungs.
Sodium may be lost from the body in prolonged vomiting,
diarrhoea and intestinal fistulae.
Arginine vasopressin(AVP) regulates renal water loss and thus
causes changes in the osmolality of body fluid compartments.
Aldosterone regulates renal sodium loss and controls the sodium
content of the ECF.
Changes in sodium content of the ECF cause changes in volume of
this compartment because of the combined actions of AVP and
aldosterone.
Case history 4
A man is trapped in a collapsed building
after an earthquake. He has sustained no
serious injuries or food or water until he is
rescued after 72 hrs.
What will have happened to his body fluid
compartments?
Word and Vocabulary(1)
diuresis 多尿
Hypernatraemia
Nephrogenic 肾源的
deficit 不足，短缺
cortisol 皮质醇
Hyperaldosteronism
pulmonary 肺的
carcinoma 癌肿
v.使不能
extremity （肢体） 末端，极点，困境
recumbent 横躺着的 ，休息的
Normotensive 血压正常的（人）
comatose 昏睡的
ambulant 可走动的，可起床的
saline 盐的，盐井
convulsion 震动，痉挛
fistula
ketoacidosis 酮症酸中毒
synonymous 同义的
incapacitate
Sacral 神圣的 ,骶骨的
vomit
compulsive
mineralocorticoid 矿物（盐）皮质激素
oedema 水肿
permeate 弥漫，渗透
shrivel v.皱缩
tubular 管状的
pneumonia 肺炎
Word and vocabulary(2)
abscess 脓肿
malignancy 恶毒，恶性肿瘤
nausea 恶心，极度厌恶
protract 延长，拖延
tachycardia
心动过速
Hypoglycaemia 高血糖
arginine 精氨酸
vasopressin 血管加压素
postural 体位的，姿势的
Anorexia 厌食
anaemia 贫血
venous
stimuli 刺激物，激励
disturbance 扰乱，失调
hypoalbuminaemia 低蛋白血症
sunken 凹陷的
pleural 胸膜的
Pseudohyponatraemia 假性低钠血症
sachet 香袋，袋子
gastrointestinal 胃肠道的
peritoneal 腹膜的
Detention 延迟，阻止
artefact 人工制品
1.Hypernatraemia is an increase in serum sodium
concentration above the reference range of
150mmol/L.
2.The causes of the hypernatraemia may be:
1)water depletion (decreased intake, excessive loss)
2)water and sodium depletion
3)excessive sodium intake or retention in the ECF
4)very rarely renal failure with inability to excrete
sodium
Hypernatraemia is commonly associated with a
contracted ECF volume, and less commonly with
an expanded compartment
(a) Volumes of ECF and
ICF are reduced.
(b) ECF volumes is
shown here to be
slightly expanded;
ICF volume is
normal
Water depletion
• From a decreased intake
• From an excessive loss
• The most common reason is: the water
intake fails to match the insensible water
loss
Water and sodium depletion
• Hypernatraemia occurs only if more water
than sodium is lost.
• Loss of body fluids (vomiting, diarrhoea,
etc.) may result in hypernatraemia, but in
fact hyponatraemia is more often seen than
hypernatraemia.
Increase in sodium content
of the ECF
• In order to correct an acidosis ,sometimes high
concentrated sodium bicarbonate(8.4%) is
administrated to the patient.
• This may lead to hypernatraemia because
sodium bicarbonate(8.4%) contains much more
sodium than the physiological fluid.
• So, a less concentrated solution(1.26%) is
preferred to correct an acidosis.
Clinical features
• The clinical features associated with the
hypernatraemia are variable.
• If there has been fluid loss, then the features
of dehydration may be present.
• In the case of salt gain, there may be
indications of fluid overload (raised jugular
venous pressure , pulmonary oedema).
Decreased skin turgor(充实度)
This sign is
frequently unreliable
in the elderly, who
have reduced skin
elasticity(弹性). In
the young it is a sign
of severe
dehydration with
fluid loss from the
ECF.
Treatment of hypernatraemia
• The patient should be given water orally if
possible.
• If not, then 5% dextrose can be given
intravenously.
Hypernatraemia
•Hypernatraemia is most commonly due to water loss(e.g. because of
continuing insensible losses in the patient who is unable to drink)
•Failure to retain water as a result of impaired AVP secretion or action
may cause hypernatraemia
•Hypernatraemia may be the result of a loss of both sodium and water as
a consequence of an osmotic diuresis e.g., in diabetic ketoacidosis.
•Excessive sodium intake, particularly from the use of intravenous
solutions, may cause hypernatraemia. Rarely, primary
hyperaldosteronism(Conn’s syndrome) may be the cause.
•A high plasma osmolality may be due to the presence of glucose, urea or
ethanol, rather than sodium(in other osmolaity disorders)
Hyponatraemia
1.Hyponatraemia is significant fall in serum sodium
concentration below the reference range of 130 mmol/l.
2.Causes: retention of water.
Sodium loss
Water tank model of hyponatraemia
(a) Water retention throughout ECF and ICF
(b) Sodium loss
Clinical features
• For patients whose syndrome develops over
a long period, they may be asymptomatic.
• For acute patients, they will be shown with
neurological symptoms(confusion,
convulsions, coma, etc.)
• The principal causes of oedema are heart failure
and hypoalbuminaemia.
• Patients who have generalized oedema have an
increase in both total body sodium and water, but
have a reduced effective blood volume.
• The reduced effective blood volume stimulates
the secretion of aldosterone and the AVP. So
water is retained.
The development of hyponatraemia
in the oedematous patient
Clinical features
• Pitting oedema
For ambulant patients, look for pitting in
the lower extremities.
For recumbent patients, look for pitting
in the sacral area.
Pitting
oedema
After
depressing the
skin firmly for a
few seconds an
indentation or
pit is seen.
Treatment of oedematous
hyponatraemia
• The underlying condition should be treated.
• Excess sodium and water should be reduced by
means of a diuretic and by fluid restriction.
Hyponatraemia: water retention
•Hyponatraemia because of water retention is the commonest
biochemical disturbance encountered in clinical practice. In many
patients the non-osmotic regulation of AVP overrides the osmotic
regulatory mechanism and this results in water retention which is
a non-specific feature of illness.
•Hyponatraemic patients without oedema, who have normal
serum and creatinine and blood pressure, have water overloaded.
This may be treated by fluid restriction.
•Hyponatraemia patients with oedema are likely to have both
water and sodium overload. These patients may be treated with
diuretics and fluid restriction.
Hyponatraemia
--- due to sodium loss:
Gastrointestinal loss (severe and prolonged
vomitting, diarrhoea, fistula)
Urinary loss (aldosterone deficiency,drugs
antagonizing aldosterone action)
loss from the skin
Fig The causes of hyponatraemia due to water
retention
Clinical features
• Patients with hyponatraemia due to sodium
loss, will be shown with clinical signs of
ECF depletion.
• Of the clinical signs of ECF depletion, the
most important are hypotension and
tachycardia (especially in the recumbent
state ).
The clinical features of ECF compartment
depletion
Treatment
Treatment is based upon two principles:
• Correction of the sodium loss(0.9%NaCl
iv,oral salt tablets)
• Treatment of the underlying disorder(steroid
therapy, surgical treatment)
ECF DEPLETION—A
NOTE OF CAUTION
(effective blood volume
reduced)
Water tank models show
that reduced ECF
volume may be
associated with reduced,
increased or normal
serum[Na]+
Pseudohyponatraemia
Hyponatraemia :sodium loss
• Hyponatraemia may occur in the patient with
gastrointestinal or renal fluid losses which have
caused sodium depletion. The low sodium
concentration in serum occurs because water retention
is stimulated by increased AVP secretion.
• Patients with hyponatraemia because of sodium
depletion show clinical signs of fluid loss such as
hypotension. They do not have oedema.
• Treatment of hyponatraemia, due to sodium depletion,
should be with sodium and water
replacement,preferably orally.
POTASSIUM
DISORDERS
The concentration of potassium in
serum is around 4mmol/l.
Word and Vocabulary
Ingest
cellular
reciprocal
相互的，交感神经的
Electroneutrality 电中性
hypokalaemia 低血钾
potential 电势，电位，潜在的
Excitable 易激的
hyperkalaemic 高血钾的
para esthesiae 感觉异常
Herald n.先锋 v.预报
redistribution 再分布
trauma n.外伤
Rhabdomyolysis n. 横纹肌溶解
artefactually 人为地
haemolysis 溶血
Arrhythmia 心律不齐
cardiac arrest 心脏停搏
asymptomatic 无征兆的
insulin 胰岛素
corticosteroid 皮质类固醇
antagonist 拮抗剂
digoxin
地高辛
Priority 优先
Potassium balance
Glomerular filtration
SERUM POTASSIUM
• Serum potassium is much less compared with that
in the ICF.
• Factors which cause a small or sudden shift of ICF
potassium will cause a big change in the ECF
content .
• Cellular uptake of potassium is stimulated by
insulin.
• Potassium and hydrogen ions can exchange freely
via cell membrane in order to maintain
eletroneutrality.
• Despite its low content in the ECF, the shift of
plasma potassium may be life-threatening.
Hyperkalemia is associated with
acidosis
The causes of hyperkalaemia
• Renal failure (reduced GFR)
• Mineralocorticoid deficiency (decreased
aldosterone secretion)
• Acidosis
• Potassium release from damaged cell
Clinical features
• The first manifestation is often cardiac arrest.
• The cardiac arrest is heralded(proclaimed) by the
obvious shift on the ECG.
• The shift on the ECG is not diagnostic.
• The patients can also be presented with muscle
weakness, preceded by paraesthesiae (tingling,
paralyzed, etc).
Typical ECG changes associated
with hyperkalaemia
(a) Normal ECG (lead II) (b) Patient with hyperkalaemia: note
peaked T-wave and widening of the QRS complex.
(b) cardiac arrest
Treatment
• Infusion of insulin and glucose to move
potassium ions into cells.
• Dialysis is necessary to treat severe
hyperkalaemia.
• Cation exchange resin
Hypokalaemia
• The main clinical effects of hypokalaemia
are severe weakness, hyporeflexia, cardiac
arrhythmias.
• A increased sensitivity to digoxin.
• May be asymptomatic if develops slowly.
• Typical ECG changes.
Typical ECG changes associated
with hypokalaemia
(a) Normal ECG (lead II) (c) Patient with hypokalaemia: note
flattened T-wave. U-waves are prominent in all leads. cardiac
arrhythmias
Causes of Hypokalaemia
•
•
•
•
Gastrointestinal losses(vomitting ,diarrhoea,fistula)
Renal loss(increased aldosterone production)
Drug-induced (thiazide diuretics, corticosteroids,etc)
Alkalosis(transportation of potassium into cell)
Treatment
• Orally intake in an enteric coating
• Severe potassium depletion ,by intravenous
potassium infusion, not faster than 20 mmol/h
usually.
Case history 8
AB, a 55-year-old man was trapped for 7 hours in a railway accident. He
sustained severe multiple injures including crush injuries to both thighs,
fractures of the pelvis and scalp laceration. On arrival at Accident &
Emergency he was still conscious and breathing spontaneously. His pulse
was 130/min and his BP was 60/40 mmHg. A set of U & Es showed the
following:
Na+
K+
Cl-
HCO3-
Urea
Creatinine
--------------------------------mmol/l------------------------------------- mol/l
141
8.1
108
9
What are the priorities in managing this patient?
6.9
107
Potassium disorder
•Potassium is the main intracellular cation, but the small amount in the
ECF is important in maintaining the membrane potential of muscle and
nerve cells.
•Changes in serum potassium concentration may reflect gains or losses in
whole body potassium content, or shifts of potassium in and out of cells.
•Hyperkalaemia is potentially life-threatening, and the death may occur
with no clinical warning signs. A high serum potassium is associated
with a decreased renal function.
•Hypokalaemia is usually caused by excessive gastrointestinal or renal
loss of potassium.
Case history 5
A 76-year-old man with depression and very severe incapacitating
disease was admitted as an acute emergency. He was clinically
dehydrated. His skin was lax and his lips and tongue were dry and
shrivelled looking. His pulse was 104/min, and his blood pressure was
95/65 mmHg. The following biochemical results were obtained on
admission:
Na+
K+
Cl-
HCO3-
Urea
Creatinine
--------------------------------mmol/l------------------------------------mol/l
162
•
3.6
132
18
Comment on these biochemical findings.
22.9
155
LABORATORY MEASUREMENT
•
The electrolytes tested usually in clinic are Na+, K+
and chloride ion (Cl-). Methods for Na+ and K+
determination include flame photometry, ionselective electrode method (ISE) and
spectrophotometry. The ISE, coulometry
• 电量计, spectrophotometry using a reagent
containing mercuric thiocyanate硫氰酸汞 and ferric
ion 高铁离子 are used to determine Cl- in the body
fluids. Presently, ISE is the most common method for
Na+, K+ and Cl- in clinical laboratory.
Specimens for Electrolyte Determinations
Serum or plasma, obtained from blood collected by venipuncture into an evacuated
tube, are the usual specimen used for assay of Na+, K+, Cl- and HCO3-. Capillary
blood is also commonly analyzed. Heparinized arterial specimens obtained for blood
gas and pH determination may also presented for analysis. Either serum or plasma is
appropriate for assay, and with direct ion selective electrodes(ISEs), whole blood may
be used. But there are differences for values of these analytes in different specimens,
only the differences between serum and plasma K+ can be considered clinically
significant. Furthermore, plasma or whole blood has a distinct advantage in
determining K+ concentrations, which are higher in serum in a manner that is
dependent on platelet count.
Specimen tubes should be centrifuged unopened, and the serum or plasma should
be separated. Hemolysis causes erroneously high results in K+ assay. In addition,
unhemolyzed specimens that are not promptly processed may have increased levels
because of intracellular K+ leakage, which is exaggerated when whole blood is stored
at 4°C.
Urine collection for Na+, K+, Cl- assay should be made with out addition of
preservatives.
Sodium Determination
Serum, heparinized plasma, whole blood, sweat, urine, feces, or
gastrointestinal fluids may be assayed for sodium. Serum, plasma, and
urine may be stored at 2-4°C or frozen for delayed analysis. Lipemic
samples should be ultracentrifuged unless Na+ is measured with a
direct ISE
Chloride
Chloride is most often measures in serum or plasma, urine, and
sweat. Cl- is quite stable in serum and plasma. Even gross hemolysis
does not significantly alter serum or plasma concentration because
the erythrocyte concentration of Cl- is approximately half of that in
plasma.
Thanks for your
attention!