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BASIC FLUIDS AND ELECTROLYTES

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.

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BASIC FLUIDS AND ELECTROLYTES

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  1. BASIC FLUIDS AND ELECTROLYTES Douglas P. Slakey

  2. 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

  3. 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

  4. 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

  5. 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%

  6. TOTAL BODY WATER 60% BODY WEIGHT ECF 1/3 ICF 2/3 H2O Predominant solute K+ Predominant solute Na+

  7. I Love Salt Water!

  8. Electrolytes (mEq/L) Plasma Intracellular Na 140 12 K 4 150 Ca 5 0.0000001 Mg 2 7 Cl 103 3 HCO3 24 10 Protein 16 40

  9. 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

  10. Movement of Water • Osmotic activity • Most important factor • Determined by concentration of solutes Plasma (mOsm/L) 2 X Na + Glc + BUN 18 2.8

  11. Third Space • Abnormal shifts of fluid into tissues • Not readily exchangeable • Etiologies • Tissue trauma • Burns • Sepsis

  12. Fluid Status • Blood pressure • Check for orthostatic changes • Physical exam • Invasive monitoring • Arterial line • CVP • PA catheter • Foley

  13. Remember JVD?

  14. 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,

  15. Disorders to be able to diagnoseAND Treat • Volume deficit • Volume excess • Hyper/hypo –natremia • Hyper/hypo –kalemia • Hyper/hypo -calcemia

  16. 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

  17. 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

  18. HypovolemiaAcute 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

  19. 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

  20. 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

  21. 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)

  22. 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

  23. Maintenance Fluids D5 0.45NS + 20 mEq KCl/L at 125 ml/hr

  24. 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)

  25. “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

  26. SIADH • Causes • Surgical stress (physiologic) • Cancers (pancreas, oat cell) • CNS (trauma, stroke) • Pulmonary (tumors, asthma, COPD) • Medications • Anticonvulsants, antineoplastics, antipsychotics, sedatives (morphine)

  27. 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

  28. SIADH Treatment • Fluid restriction • Will not responded to fluid challenge! • i.e. a “Bolus” will not work • (distinguishes from pre-renal cause) • Possibly diuretics

  29. 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

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

  31. 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

  32. Hypernatremia • Hypovolemic • GI loss, osmotic diuresis • Increased Na load (usually iatrogenic) Free water deficit: [0.6 X wt (kg)] X [Serum Na/140 - 1]

  33. 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

  34. 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)

  35. 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

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

  37. The End Makani U’i

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