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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
Patient Safety
Let’s add all sorts of layers of complexity and
make healthcare safer!
It’s All About Balance
• Gains and Losses
– Losses
• Sensible and Insensible
• Typical adult, typical day
–
–
–
–
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
K
Ca
Mg
Cl
HCO3
Protein
Plasma
140
4
5
2
103
24
16
Intracellular
12
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
•
•
•
•
Blood pressure
Check for orthostatic changes
Physical exam
Invasive monitoring
–
–
–
–
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
•
•
•
•
•
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
Gulf of Honduras
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/H
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)
Assessment of Disorders of
Volume and Electrolytes
• Effects are variable and complex
• Simplified treatment algorithms cannot
address the variable and complex nature of
these disorders
• Acid - Base balance is integral with these
disorders
“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
Na
Volume
Check Ur Na
< 10 mmol/L
Vomiting
Diarrhea
3rd space
Hepatorenal
> 20 mmol/L
Adrenal Insufficiency
Diuretics
Salt-Wasting Syndrome
SIADH
FeNa
Na urine x Cr serum
--------------------------------------------
Na serum x Cr urine
SIADH
• Causes
–
–
–
–
–
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
• 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
Do you want more?
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
Aldosterone
• Reduced (Addisons) Increased (Conns)
• Mineralocorticoid
• Increases Na and water reabsorption and K
excretion
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
–
–
–
–
Monitor ECG, VS
Calcium gluconate IV (arrhythmias)
Insulin and glucose IV
Kayexalate, Lasix + IVF, dialysis
The new boat
Makani u’i