Fluid, electrolyte and acide-base disturbances
in surgery (not only)

L.Dadak
Dept. of Anesthesia and
Intensive Care
St. Ann's University
Hospital

Homeostasis
●

●
●
●

●

tendency to keep stable
isovolemia
H+ = pH, pCO2,
Glc, ions
isohydria, isoionia, isoosmia

Laboratory
●

●

Never completely trust the laboratory
● errors with blood sample
Will result change my decision?

Never completely trust the laboratory
Quick
<0.10
( 0.70 - 1.34 ) <-( ) repeated
aPTT
>150
s ( 20.0 - 40.0 ) <=( ) repeated
Fibrinogen 4.50
g/l ( 1.80 - 4.00 )
( )->
Antitrombin III 32
% ( 80 - 120 ) <-( )
- - - - - - - - - - - same patient, 30 min later - - - - - - - - - - - - Quick
0.55
( 0.70 - 1.34 ) <-( )
aPTT
44.7
s ( 20.0 - 40.0 )
( )->
Aptt ratio
1.49
Fibrinogen 5.40
g/l ( 1.80 - 4.00 )
( )->
INR
1.59
( 0.85 - 1.38 )
( )->
Antitrombin III 61
% ( 80 - 120 ) <-( )

Blood for analysis
●
●
●

arterial
capillary
venous
●
●
●

peripheral
central
mixed venous (v.cava, a.pulmonalis)

Body Fluid Compartments
Total Body Water (TBW): 50-70% of total body
wt.
●
●

Avg. is greater for males.
Decreases with age. Highest in newborn, 7580%. By first year of life TBW ~ 65%.

●

Most in muscle, less in fat.

●

TBW= ECF + ICF

●

ICF ~ 2/3 & ECF ~ 1/3

●

ECF = Intravascular (1/3) + Interstitial (2/3)

Water - compartments:
ECF = IVF + ISF

ICF

5%

15%

40%

Na

Na + -

Na

K

K

P

P

++-

K

ICF (mEq/L)

ECF (mEq/L)

Cations
K+ (150-154)
Na+ (6-10)
Mg+2 (40)

Anions
Organic PO4-3 (100-106)
protein (40-60)
SO4-2 (17)
HCO3- (10-13)
organic acids (4)

Na+(142)
Ca+2 (5)
K+ (4-5)
Mg+2 (3)
Cl-(103-105)
HCO3- (24-27)
protein (15)
PO4-3 (3-5), SO4-2 (4)
Organic acids (2-5)

Electrolyte Physiology
●

●

●

●

Primary intravascular/ECF cation is Na+. Very
small contribution of K+, Ca2+, and Mg2+.
Primary intravascular/ECF anion is Cl-.
Smaller contribution from HCO3-, SO42- &
PO43-, organic acids, and protein.
Primary ICF cation is K+. Smaller contribution
from Mg2+ & Na+.
Number of intravasc anions not routinely
detected.

Intra Vascular Fluid
●

Treatable volume

Provides:
● Nutrition
● Oxygenation
● Waste removal
● Temperature
● Alkalinity

Priorities
1. fluid volume and perfusion deficits
2.
3.
4.

correction of pH
K, Ca, Mg
Na, Cl

IV Fluid/Electrolyte Therapy
Three key concepts in consideration of fluid and
electrolyte management:
●

cell membrane permeability

●

osmolarity

●

electroneutrality

Cell membrane permeability refers to the ability
of a cell membrane to allow certain
substances such as water and urea to pass
freely, while charged ions such as sodium
cannot cross the membrane and are trapped

Osmolarity
●

Osmolarity is a property of particles in
solution. If a substance can dissociate in
solution, it may contribute more than one
equivalent to the osmolarity of the solution.
For instance, NaCl will dissociate into two
osmotically active ions: Na and Cl. One
millimolar NaCl yields a 2 milliosmolar
solution.

Electroneutrality
●
●

in every solution
sum of [mval/l] cations
is equal to sum of
anions

●
●

Na+, K+, Mg++, Ca++ ...
Cl-, HCO3-, PO4--,
proteins-

Osmolarity, osmolality
Each particle present in the water binds number
molecules of water.
Serum osmolarity is measured directly by determining the
freezing point of serum.
normal 275 .. 295 mOsm/l
Calculated osmolarity = 2 * Na + Glc + Urea [mOsm/l]
●

2* 140 + 5 + 3

Gap > 10 mOsm/l ... another solute (lactate, ethanol)
Gap > 50 mOsm/l ... often fatal
Osmolality [mmol/kg of water]

Water
●

55% - 60%, new born 80% of body weight

Basic Needs (Adult)
●
●

Basic need
Current losses
●
●
●

2 ml/kg/h

1°C fever = 500ml/d
sweating
diarrhea ... water with ions [mmol/l]

Types of IV Fluid
●

Crystalloid

●

Colloid

Crystalloid:
●

●

●

Balanced salt/electrolyte solution; forms a true
solution and is capable of passing through
semipermeable membranes. May be isotonic,
hypertonic, or hypotonic.
Normal Saline (0.9% NaCl), Lactated
Ringer’s, Hypertonic saline (3, 5, & 7.5%),
Ringer’s solution.
However, hypertonic solutions are considered
plasma expanders as they act to increase the
circulatory volume via movement of
intracellular and interstitial water into the

Colloid:
●

Colloid: High-molecular-weight solutions, draw
fluid into intravascular compartment via
oncotic pressure (pressure exerted by plasma
proteins not capable of passing through
membranes on capillary walls). Plasma
expanders, as they are composed of
macromolecules, and are retained in the
intravascular space.

●

HAES, Gelatina (Dextran);

●

Albumin, Plasma

"Free H2O solutions:"
●

●

Free H2O solutions: provide water that is not
bound by macromolecules or organelles, free
to pass through.
D5W (5% dextrose in water), D10W, D20W,
D50W, and Dextrose/crystalloid mixes.

IVF can supply 3 things
●

fluid,

●

electrolytes,

●

calories (150 ml/h D5W)

The most common uses for IVF:
●

Acutely expand intravascular volume in
hypovolemic states

●

Correct electrolyte imbalances

●

Maintain basal hydration

infusion:
●

Ringer's lactate solution

●

NS = Normal Saline = NaCl 0,9%

Normal Saline (0.9% NaCl):
●

●
●

●

●

Isotonic salt water.
154 mEq/L Na+; 154 mEq/L Cl-; 308mOsm/L.
(Cheapest), commonly used crystalloid.
High [Cl-] above the normal serum 103 mEq/L
imposes on the kidneys an appreciable load
of excess Cl- that cannot be rapidly excreted.
A dilutional acidosis may develop by
reducing base bicarb relative to carbonic acid.
Thus exist the risk of hyperchloremic acidosis.
Only solution that may be administered with
blood products.

Lactated Ringer's solution
●

isotonic, beginning of volume resuscitation

Ingredients:
* 130 mEq of sodium ion.
* 109 mEq of chloride ion.
* 28 mEq of lactate.
* 4 mEq of potassium ion.
* 3 mEq of calcium ion.
Lactate is converted readily to bicarb by the
liver. Has minimal effects on normal body fluid
composition and pH. More closely resembles

Volume
Volume deficits are best estimated by acute
changes in weight. Less than 5% loss is very
difficult to detect clinically and loss of 15+%
will be associated with severe circulatory
compromise.
●

Mild deficit represents a loss of ~ 4% body wt.

●

Moderate deficit --- a loss of ~ 6-8% body wt.

●

Severe deficit --- a loss of ~ >10% body wt.

Volume deficit may be a pure water deficit or
combined water and electrolyte deficit.

Resuscitative IV Fluids
Principle of trauma & surgery: Crystalloids;
isotonic balanced salt solutions (RingerLactate).
Amount given based upon body wt, clinical
picture, and vital signs = shock.
Generally a bolus of 500-2000cc is given
depending on the above, then rates are run at
1.5-2x maintenance or 10-20cc/kg/d on top of
maintenance. Continuous clinical
reassessment of vitals and response to fluids
already given is required for ongoing IVF

Monitoring endpoints for IVF
therapy
Endpoint should be maintenance or
reestablishment of homeostasis.
●

In order to reestablish homeostasis in a pt,
IVF therapy must not only provide a balance
of water and

electrolytes, but must ensure adequate
oxygen delivery to all organs and renal
perfusion as evidenced by urine output.
●

Endpoints: normalization of VS,
UO>0.5ml/kg/hr (1ml/kg/hr for a child) and
restoration of normal mental status and lack of

Hypovolemia
●
●

deficit of water
estimated from
●
●
●

weight loss
thirst
physical signs (soft eyes, tachycardia, hypotension, oliguria,
organ dysfunction – brain )

●

hypo, iso, hypertonic

●

Treatment: add water (crystaloid, coloid)

Hypervolemia
●
●
●

hypotonic – excess of water (no ions e.g. 5% Glc)
isotonic – anuria + intake crystaloids
hypertonic – intake of concentrated solutions, loss of
hypoosmolar fluid. / rare/

Ions in the body
●
●
●
●

●

Sodium Na+
Potassium K+
Calcium Ca++
Magnesium Mg++
Phosphorus PO4-

Chloride Cl---------● Glucose Glc
●

Sodium Na+
●
●

●
●

extracellular fluid
intracellular fluid
Hyponatremia
Hypernatremia

140 mmol/l
10 mmol/l

Hyponatremia
●
●

●

Na+ in serum < 120 mmol/l

usually due to hemodilution by too much water
sodium loss
● vomiting
● diarrhea
● sweating,
● renal / CNS disorders, diuretics
● third space sequestration (burns, pancreatitis,
peritonitis)
factitous (hyperglycemia, hyperlipidemia, manitol) osmolality normal / increased

Hyponatremia - symptoms
●
●
●
●
●

●

Fatique
Apathy, coma, change in mental status
Headache
Muscle cramps, weakness
Anorexia, nausea, vomiting,

Mild to moderate hyponatremia is usually asymptomatic.

Treatment of hyponatremia
●
●

●

●

stable pat. - water restriction (less 1l/d)
severe, acute hyponatremia (duration < 48 h) ,
symptomatic pt. with brain edema
3% NaCl i.v.
Rate of correction should not exceed 0.5-1 mEq/L/h, with
a total increase not to exceed 12 mEq/L/d
Risk of rapid treatment - demyelinisation

Hypernatremia
inadequate water intake
● excessive loss of water
● diarrhea
● vomiting
● hyperpyrexia
● excessive sweating
● diabetes insipidus (ADH) = loss of hypotonic urine
● increased intake of salt
● coma, no responce to thirst
Therapy: Glc 5% i.v.
●

Potassium K+
●
●
●
●

●

Major intracellular cation
serum (2% of total)
3.8 .. 5.6 mmol/l
electric potential on membrane (Na+/K+ ATPasa)
arytmias
extremly responsive to changes of pH!!
Acidosis in cell (H+) banish K+ out of cell.
delta pH 0,1 ..... 0,5..0,6 mmol/l (i.v.)

Hypokalemia K < 4 mmol/l
●
●
●
●
●

losses in urine
diurettics, diarrhea, vomiting
reduced intake
Alcalosis
CAVE severe muscle weakness, asystolia

Treatment:
●
●

KCl p.os; max KCl 40 mmol/h i.v.
ECG monitoring !!!!

Hyperkalemia
●
●
●
●

●

hemolysis
muscle damage
anuria, renal failure
Acidosis

CAVE intracardiac block
(diastolic arest) or fibrilation
muscle weakness – ventilatory failure
therapy:
●

●
●
●
●
●

stop intake
Glc + HMR i.v., loop diuretic (furosemide)
Calcium i.v., bicarbonate i.v
resonium p.os
dialysis

Calcium Ca++
●
●

most abundant mineral in the body 2kg
Parathormone PTH
●
●
●

●

Calcitonin
●

●

stimulate osteoklast
stimulate intestine
resorption in kidney
inhibites osteoklast

Vitamine D
●

potens saving Ca++

Ionised Ca = 1.1 mmol/l // efect of all Calcium
bound by proteins =ineffective to receptors

Calcium Ca++
●

Hypocalcemia
●
●
●

●

Respiratory Alcalosis, hypoPTH,
shock, sepsis, pancreatitis
together hypomagnesemia

Hypercalcemia
●
●

muscle damage
malignancy

Chloride Cl●
●

Major anion in Extracellular fluid
see ABR

Glucose
●
●

●

hyperglycemia
hypoglycemia / insulin overdose/

next week

Acide-base
arterial blood:

pH
pCO2
pO2
HCO3BE
SpO2

7,35-7,45
4,6-6 kPa
10-13 kPa
22-26mmol/L
-2 .. +2 mmol/L
95-98%

Steward's principle
160

Mg++,Ca++

CO3--

140

mEq/L

120
100
80
60
40
20
0

SIDa

HCO3A-

SIG

SIDe
laktát

Na++

Cl-

Kationty

Anionty

My 4 Steps to figure out the Patients ABGs

●

●

●

If I were to start on the top step going down, I would decide if my patient has
acidosis or alkalosis by looking at his pH level. If it is normal but the PCO2 or
HCO3- is off, I would keep looking knowing that compensation may have
happened.
If the PCO2 has an indirect relationship to the pH (if pH is high, but PCO2 is
low or if pH is low and PCO2 is high) then I will know the patients condition is
Respiratory. (involving the lungs) Either Respiratory Alkalosis or Respiratory
Acidosis depending on the pH.
If the HCO3- has a direct relationship or is normal (if pH is high, and HCO3- is
high, or if pH is low and HCO3- is low), then I know the problem is Metabolic
(involving the kidneys). Either Metabolic Acidosis or Alkalosis – dependent upon
the abnormal value of the pH.
Lastly I would use my bottom step to decide the compensation. Has there been
compensation? If the pH is normal, then the body has been working to get it’s pH
values back to normal. If it isn’t normal, I would look at the HCO3- for
Respiratory (we didn’t look at this one early on for Respiratory), or I would look at
PCO2 for Metabolic ( we didn’t look at this one for Metabolic). – Generally, if all
values are off: you have partial compensation (the body is still trying to
compensate).

CO2
Glc + O2 →

CO2 + H2O

CO2 + H2O → H2CO3 →

∆pH
0.1

Η+

+ Η CO3-

∆ p CO2
1,6 kPa = 12 mmHg

Genesis of Acid
●
●
●
●

= donor of H+

lactate - shock
strong acids intake (HCl, H2SO4)
acetylsalicilic acid (drug overdose)
...

∆pH
0.1

∆ BE
6mmol/l

Basic laws
pH = - log [H+]
[H+] ... mol/l
pH = pK + log (H+ acceptor /H+ donor)
[H+] = 24 x paCO2 / [HCO3-] Henderson equation
● acidosis
pH < 7.36
● alcalosis
pH > 7.44
Place of error:
● Respiratory (lung)
... pCO2
● Metabolic (kidney,...)
... BE
BE = number of acid needed to correct sample to pH 7.4

Easy equation

∆pH
0.1

BE
6mmol/l

∆ p CO2
1,6 kPa = 12 mmHg

Easy equation

∆pH
0.1

BE
6mmol/l

∆ p CO2
1,6 kPa = 12 mmHg

Kilopascals for PCO2.
●

●

●

Many texts and papers express the PCO2 in kilopascals (kPa). It is
useful to remember that this value is almost the same as the
percentage of atmospheric pressure. For example, the normal
arterial PCO2 of 40 mmHg is 5.33 kPa or 5.61 %.

To convert pressure in mmHg to kPa, it is necessary to divide
the value in mmHg by 7.5
[40mmHg /7,5 = 5,33kPa]

Respiratory Acidosis (RAc)
●

●

●

The decision to ventilate a patient to reduce the PCO2 is a clinical decision and
is based on exhaustion, prognosis, prospect of improvement from concurrent
therapy, and in part on the PCO2 level. Once the decision is made, the PCO 2
helps to calculate the appropriate correction.
The PCO2 reflects a balance between the carbon dioxide production and its
elimination. Unless the metabolic rate changes, the amount of carbon dioxide to
be eliminated remains constant. It directly determines the amount of ventilation
required and the level of PCO2. Where VT equals tidal volume and f equals
respiratory rate:
PCO2 x Ventilation = Constant, i.e.,
PCO2 x VT x f = k

MAc
•kidney unable to eliminate H+
•big production of acides.

= anuria

•The treatment for a metabolic acidosis is, again, judged largely on
clinical grounds. Bicarbonate therapy is justified when metabolic
acidosis accompanies difficulty in resuscitating an individual or in
maintaining cardiovascular stability.
•A typical dose of bicarbonate might be 1 mEq per kilogram of body
weight followed by repeat blood gas analysis.
•Calculation is based on BE and the size of the treatable space (0.3 x
weight, e.g., 21 liters):
Dose (mEq) = 0.3 x Wt (kg) x BE (mEq/L).

Metabolic Acidosis
●
●
●

Unmeasured Anions {organic acids - lactate, …}
Clloss of HCO3, Na,K,Cl
{diarrheal fluid, wrong ratio}

RAl
●
●

hyperventilation
lost of ionized Calcium / hypocalcemia / tetania

MAl
●
●
●

increased loss of NH4 to urine
saving HCO3- by kidney
loss of Cl- (vomiting)

●
●
●
●
●

BE > O
pH > 7.44
Th: i.v. FR (NaCl)

How to
1. what is wrong
2. what the body do
3. what to do

OR / AAA, 5 000ml lost, haemorh. shock, NA i.v.,
general anesthesia, VCV
pH akt.
)
pCO2
)->
pO2
)=>
BE
)
BB
)
HCO3 akt.
)

7.083
6.36 kPa
30.78 kPa

( 7.350 - 7.450 ) <-(
( 4.80 - 5.90 )

(

( 10.66 - 13.30 )

(

-15.8 mmol/l

( -2.6 - 2.6 )

<=(

32.1 mmol/l

( 40.0 - 44.0 )

<=(

13.9 mmol/l

( 22.0 - 26.0 )

<=(

OR / AAA, 6 500ml loost, haemorh. shock, NA i.v.
pH akt.
pCO2
* )

7.1
( 7.350 - 7.450 ) <=(
5.0 kPa
( 4.80 - 5.90 )

BE
)

-18

lactate
=>

mmol/l

13 mmol/l

( -2.6 - 2.6 )

( 1 – 2.5 )

)
(

<=(

(

)=

Try it yourself
pH = 7,2
pCO2 = 14 kPa
BE = 20 mmol/l

pH 7,35-7,45
pCO2
4,6-6 kPa
pO2 10-13 kPa
HCO3
22-26mmol/L
BE -2 .. +2 mmol/L
SpO2 95-98%

• polytrauma + sepsis + ARDS

Measured

Calculated

Na

131

↓

HCO3-

21

↓

K

4,2

=

BE

-4

↓

Mg

3,6

↑

Ca

2,2

=

Cl

86

↓

Pi

2,3

↑

Alb

8

pH

7,31

PaCO2

5,4

↓
↓
↓
=

• polytrauma + sepsis + ARDS

Measured

Calculated

Na

↓

HCO3-

21

↓

K
Henderson-Hasselbach:
• metabolic acidosis

131
4,2

=

BE

-4

↓

Mg

3,6

↑

Ca

2,2

=

Cl

86

↓

Pi

2,3

↑

Alb

8

pH

7,31

↓

PaCO2

5,4

=

↓
↓

• polytrauma, sepse s ARDS

Measured

Calculated

Na

• hypoalbuminemic alkalisis

HCO3-

21

↓

4,2

=

BE

-4

↓

Mg

• dilution acidosis
• hypochloremic alkalosis

↓

K

Stewart-Fencl:
• lactic acidosis

131

3,6

↑

Ca

2,2

=

Cl

86

↓

Pi

2,3

↑

Alb

8

pH

7,31

↓

PaCO2

5,4

=

↓
↓

SUMARY
●

●

●

Biologic system react primary to rate of change
and not to absolute concentrations.
Abnormalities should be treated at proximately
the rate at which they developed.
DO NOT rapid correction of a chronic
asymptomatic abnormality.

When order electrolytes exam:
●
●
●
●
●
●
●
●
●

poor oral intake
vomiting
chronic hypertension
diuretic use
recent seizure
muscle weakness
age over 65
alcoholism
history of electrolyte abnormality

When order blood gasses:
●
●
●

acid-base problems
artificial ventilation

acute CNS change
immediately look for
● hypoxemia
● hypoglycemia
● hyponatremia
● sepsis

Priorities
1. fluid volume and perfusion deficits
2.
3.
4.

correction of pH
K, Ca, Mg
Na, Cl

Bleeding – transfusion strategy
Indication:
Transfuse to Maintain:
● Transfuse any symptomatic patient
● Until no longer
(e.g., tachycardia, hypotension, CHF,
symptomatic
angina)
● Asymptomatic, presurgical, stable
● Hb 7-8 g/dl
patient
● Hemodynamically stable postsurgical
● Hb 8 g/dl
stable patient
● Hb 10 g/dl
● Postsurgical patient at risk for ischemic
disease (e.g., cardiac, bowel)
● Hemodynamically stable, nonpregnant, ● Transfuse at 7 g/dl
to maintain Hb at 7ICU patients >age 16 without ongoing
9 g/dl
blood loss