Basic Fluids and Electrolytes
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Transcript of Basic Fluids and Electrolytes
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BASIC FLUIDS AND ELECTROLYTES
Douglas P. Slakey
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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
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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
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It’s All About Balance
Gains and Losses Losses
Sensible and Insensible Typical adult, typical day
Skin 600 ml Lungs 400 ml Kidneys 1500 ml Feces 100 ml
Balance can be dramatically impacted by illness and medical care
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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%
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TOTAL BODY WATER60% BODY WEIGHT
ICF
2/3Predominant solute
K+
ECF
1/3
Predominant solute
Na+
H2O
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I Love Salt Water!
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(mEq/L) Plasma IntracellularNa 140 12K 4 150Ca 5 0.0000001Mg 2 7Cl 103 3HCO3 24 10Protein 16 40
Electrolytes
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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
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Movement of Water
Osmotic activity Most important factor Determined by concentration of solutes
Plasma (mOsm/L)
2 X Na + Glc + BUN 18 2.8
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Third Space
Abnormal shifts of fluid into tissues Not readily exchangeable Etiologies
Tissue trauma Burns Sepsis
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Fluid Status
Blood pressure Check for orthostatic changes Physical exam Invasive monitoring
Arterial line CVP PA catheter Foley
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Remember JVD?
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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,
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Disorders to be able to diagnoseAND Treat
Volume deficit Volume excess Hyper/hypo –natremia Hyper/hypo –kalemia Hyper/hypo -calcemia
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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
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DehydrationChronic Volume Depletion
Affects all fluid componentsSolutes become concentrated
Increased osmolarityHct can increase 6-8 pts for 1 L deficit
Patients at risk:Cannot respond to thirst stimuliDiabetes insipidus
Treatment: typically low Na fluids
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HypovolemiaAcute Volume Depletion
Isotonic fluid loss, from extracellular compartmentDetermine etiology
Hemorrhage, NG, fistulas, aggressive diuretic therapyThird 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
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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
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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
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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)
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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 Pre-existing Deficits
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Maintenance FluidsD5 0.45NS + 20 mEq KCl/L at 125 ml/hr
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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)
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“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
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SIADH
Causes Surgical stress (physiologic) Cancers (pancreas, oat cell) CNS (trauma, stroke) Pulmonary (tumors, asthma, COPD) Medications
Anticonvulsants, antineoplastics, antipsychotics, sedatives (morphine)
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SIADHToo much ADH Affects renal tubule permeability
Increases water retention (ECF volume)
Increased plasma volume, dilutional hyponatremia, decreases aldosteroneIncreased Na excretion (Ur Na >40mEq/L)
Fluid shifts into cellsSymptoms: thirst, dyspnea, vomiting, abdominal
cramps, confusion, lethargy
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SIADH Treatment
Fluid restriction Will not responded to fluid challenge!
i.e. a “Bolus” will not work (distinguishes from pre-renal cause)
Possibly diuretics
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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
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Paradoxical Aciduria
Na
Cl
Na
H
K
Loop of Henle
HypochloremicHypovolemia
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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
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Hypernatremia
Hypovolemic GI loss, osmotic diuresis Increased Na load (usually iatrogenic)
[0.6 X wt (kg)] X [Serum Na/140 - 1]
Free water deficit:
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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
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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)
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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
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Hyperkalemia
Emergency (> 6 mEq/l) Treatment
Monitor ECG, VS Calcium gluconate IV (arrhythmias) Insulin and glucose IV Kayexalate, Lasix + IVF, dialysis
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The End
Makani U’i