BASIC FLUIDS AND
ELECTROLYTES
Douglas P. Slakey
Why ?
 Essential for surgeons (and all physicians)
 Based upon physiology
 Disturbances understood as pathophysiology
To Encourage Thought Not Mechanical
Reaction
Most abnormalities are
relatively simple, and many
iatrogenic
It's better to keep your mouth shut and let
people THINK you're a fool than to open it
and remove all doubt.
Mark Twain
It’s All About Balance
 Gains and Losses
 Losses
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Sensible and Insensible
Typical adult, typical day
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Skin
Lungs
Kidneys
Feces
600 ml
400 ml
1500 ml
100 ml
 Balance can be dramatically impacted by
illness and medical care
Fluid Compartments
 Total Body Water
 Relatively constant
 Depends upon fat content and varies with age
 Men 60% (neonate 80%, 70 year old 45%)
 Women 50%
TOTAL BODY WATER
60% BODY WEIGHT
ECF
ICF
2/3
H2O
1/3
Predominant solute
Predominant solute
K+
Na+
I Love Salt Water!
Electrolytes
(mEq/L)
Na 140
K
Ca 5
Mg 2
Cl
103
HCO3
Protein
Plasma
Intracellular
12
4
24
16
150
0.0000001
7
3
10
40
Fluid Movement
 Is a continuous process
 Diffusion
 Solutes move from high to low concentration
 Osmosis
 Fluid moves from low to high solute concentration.
 Active Transport
 Solutes kept in high concentration compartment
 Requires ATP
Movement of Water
 Osmotic activity
 Most important factor
 Determined by concentration of solutes
Plasma (mOsm/L)
2 X Na + Glc + BUN
18
2.8
Third Space
 Abnormal shifts of fluid into tissues
 Not readily exchangeable
 Etiologies
 Tissue trauma
 Burns
 Sepsis
Fluid Status
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Blood pressure
Check for orthostatic changes
Physical exam
Invasive monitoring
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Arterial line
CVP
PA catheter
Foley
Remember JVD?
Dx of Fluid Imbalances
 Must assess organ function
 Renal failure
 Heart failure
 Respiratory failure
•
•
•
Excessive GI fluid losses
Burns
Labs: electrolytes, osmolality, fractional
excretion of Na, pH,
Disorders to be able to diagnose
AND Treat
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Volume deficit
Volume excess
Hyper/hypo –natremia
Hyper/hypo –kalemia
Hyper/hypo -calcemia
Volume Deficit
 Most common surgical disorder
 Signs and symptoms
 CNS: sleepiness, apathy,
reflexes, coma
 GI: anorexia, N/V, ileus
 CV: orthostatic hypotension, tachycardia with
peripheral pulses
 Skin: turgor
 Metabolic: temperature
Dehydration
Chronic Volume Depletion
Affects all fluid components
Solutes become concentrated
Increased osmolarity
Hct can increase 6-8 pts for 1 L deficit
Patients at risk:
Cannot respond to thirst stimuli
Diabetes insipidus
Treatment: typically low Na fluids
Hypovolemia
Acute Volume Depletion
Isotonic fluid loss, from extracellular compartment
Determine etiology
Hemorrhage, NG, fistulas, aggressive diuretic
therapy
Third space shifting, burns, crush injuries,
ascites
Replace with blood/isotonic fluid
» Appropriate monitoring
»
Physical Exam
»
»
Foley (u/o > 0.5 ml/kg/min)
Hemodynamic monitoring
Fluid Replacement
 Isotonic/physiologic
 NS (154 meq, 9 grams NaCl/L)
 LR (130 Na, 109 Cl, 28 lactate, 4 K, 3 Ca)
 Less concentrated
 0.45NS, 0.2NS
 Maintenance
 Hypertonic Na
Fluid Replacement
 Plasma Expanders
 For special situations
 Will increase oncotic pressure
 If abnormal microvasculature, will extravasate
into “third space”
Then may take a long time to return to circulation
Fluid Replacement
 Maintenance
 4,2,1 “rule”
 Other losses (fistulas, NG, etc)
 Can measure volume and composition!!!
 Should be thoughtfully assessed and
prescribed separately if pathologic
 (i.e. gastric: H, Na, Cl)
Maintenance Fluid
 Daily Na requirement: 1 to 2 mEq/kg/day
 Daily K requirement: 0.5 to 1 mEq/kg/day
 AHA Recommended Na intake: 4 to 6
grams per day
To Replace Ongoing Losses, NOT Preexisting Deficits
Maintenance Fluids
D5 0.45NS + 20 mEq KCl/L at 125 ml/hr
How much Sodium is Enough???
» NS
»
0.9% = 9 grams Na per liter
» 0.45 NS = 4.5 grams per liter
» 125 ml/hour = 3000 ml in 24 hours
» 3 liters X 4.5 grams Na = 13.5 GRAMS Na!
(If 0.2 NS: 3 liters X 2 grams Na = 6 grams Na)
“BTW Dr Slakey, the sodium is 120”
Hyponatremia
 Na loss
 True loss of Na
 Dilutional (water excess)
 Inadequate Na intake
 Classified by extracellular volume
 Hyovolemic (hyponatremia)
 Diuretics, renal, NG, burns
 Isotonic (hyponatremia)
 Liver failure, heart failure, excessive hypotonic
IVF
 Hypervolemic (hyponatremia)
 Glucocorticoid deficiency, hypothyroidism
SIADH
 Causes
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Surgical stress (physiologic)
Cancers (pancreas, oat cell)
CNS (trauma, stroke)
Pulmonary (tumors, asthma, COPD)
Medications
 Anticonvulsants, antineoplastics, antipsychotics,
sedatives (morphine)
SIADH
Too much ADH

Affects renal tubule permeability
 Increases water retention (ECF volume)
Increased plasma volume, dilutional
hyponatremia, decreases aldosterone
Increased Na excretion (Ur Na >40mEq/L)
Fluid shifts into cells
Symptoms: thirst, dyspnea, vomiting, abdominal
cramps, confusion, lethargy
SIADH Treatment
 Fluid restriction
 Will not responded to fluid challenge!
 i.e. a “Bolus” will not work
 (distinguishes from pre-renal cause)
 Possibly diuretics
Hypovolemia and Metabolic Abnormality
 Acidosis
 May result from decreased perfusion i.e
decreased intravascular volume
 Alkalosis
 Complex physiologic response to more chronic
volume depletion
 i.e. vomiting, NG suction, pyloric stenosis,
diuretics
Paradoxical Aciduria
Hypochloremic
Hypovolemia
Na
Na
H
Cl
K
Loop of Henle
Hypernatremia
Relatively too little H2O
 Free water loss (burns, fever)
 Diabetes insipidus (head trauma, surgery,
infections, neoplasm)
 Dilute urine (Opposite of SIADH)
 Nephrogenic DI
 Kidney cannot respond to ADH
Hypernatremia
 Hypovolemic
 GI loss, osmotic diuresis
 Increased Na load (usually iatrogenic)
Free water deficit:
[0.6 X wt (kg)] X [Serum Na/140 - 1]
Hypernatremia Volume Replacement
 Example:
 Na 153, 75 kg person
 (0.6 X 75) X [(153/140) - 1]
 45
X [1.093 -1]
 45 X 0.093 = 4.2 Liters
Potassium and Ph
 Normally 98% intracellular
 Acidosis
 Extracellular H+ increases, H+ moves
intracellular, forcing K+ extracellular
 Alkalosis
 Intracellular H+ decreases, K+ moves into cells
(to keep intracellular fluid neutral)
Hyperkalemia
 Associated medications
 Too much K+, ACE inhibitors, beta-blockers,
antibiotics, chemotherapy, NSAIDS,
spironolactone
 Treatment
 Mild: dietary restriction, assess medications
 Moderate: Kayexalate
 Do NOT use sorbitol enema in renal failure
patients
 Severe: dialysis
Hyperkalemia
 Emergency (> 6 mEq/l)
 Treatment
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Monitor ECG, VS
Calcium gluconate IV (arrhythmias)
Insulin and glucose IV
Kayexalate, Lasix + IVF, dialysis
The End
Makani U’i