ALL NEW FOR 2005(6)! Fluids and Electrolytes Made Simple
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Transcript ALL NEW FOR 2005(6)! Fluids and Electrolytes Made Simple
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
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 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
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
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
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
Monitor ECG, VS
Calcium gluconate IV (arrhythmias)
Insulin and glucose IV
Kayexalate, Lasix + IVF, dialysis
The End
Makani U’i