Basic Fluids and Electrolytes Douglas P. Slakey

Why Listen to This? Essential for surgeons Based upon physiology –Disturbances understood as pathophysiology Most abnormalities are relatively simple, and many iatrogenic

Purpose of this Talk To Encourage Thought Not Mechanical Reaction

You Have to Read!

It’s All About Balance Gains and Losses –Losses Sensible and Insensible Typical adult, typical day –Skin600 ml –Lungs400 ml –Kidneys1500 ml –Feces100 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 ICF 2/3 Predominant solute K + ECF 1/3 Predominant solute Na + H2OH2OH2OH2O

(mEq/L)Plasma Intracellular Na14012 K4150 Ca Mg27 Cl1033 HCO Protein1640 Electrolytes

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

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?

Fluid Imbalances Must assess organ function –Renal failure –Heart failure –Respiratory failure Excessive GI fluid losses Burns

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, LR 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

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

Maintenance Fluids To Replace Ongoing Losses, NOT Pre-existing Deficits

Maintenance Fluids D NS + 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

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

NaVolume Check Ur Na < 10 mmol/L Vomiting Diarrhea 3rd space Hepatorenal Adrenal Insufficiency Diuretics Salt-Wasting Syndrome SIADH > 20 mmol/L

SIADH Causes –Cancers (pancreas, oat cell) –CNS (trauma, stroke) –Pulmonary (tumors, asthma, COPD) –Surgical stress –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 GFR 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 (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

Paradoxical Aciduria Na Cl Na H K Loop of Henle Hypochloremic Hypovolemia

Hypernatremia Relatively too little H 2 O –Free water loss (burns, fever) –Diabetes insipidus (head trauma, surgery, infections, neoplasm) Dilute urine –Nephrogenic DI Kidney cannot respond to ADH

Hypernatremia Hypovolemic –GI loss, osmotic diuresis –Increased Na load (usually iatrogenic) [0.6 X wt (kg)] X [Serum Na/ ] Free water deficit:

Hypernatremia Volume Replacement Example: Na 153, 75 kg person (0.6 X 75) X [(153/140) - 1] 45X [ ] 45 X = 4.2 Liters

Potassium 98% intracellular 20 to 40 mEq/L of urine –Kidneys cannot retain K Dietary sources –Chocolate, dried fruits, nuts –Fruits: oranges, bananas, apricots –Meats –Potatoes, mushrooms, tomatoes, carrots

Potassium and Ph Acidosis –Extracellular H + increases, moves intracellular forcing K + extracellular Alkalosis –Intracellular H + decreases, to keep intracellular fluid neutral, K + moves into cells

Hyperkalemia Associated medications –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

Hyperkalemia Emergency (> 6 mEq/l) Treatment –Monitor ECG, VS –Calcium gluconate IV –Insulin and glucose IV –Kayexalate, Lasix + IVF, dialysis