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 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

I Love Salt Water!

(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?

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 Pre- existing Deficits

Maintenance Fluids D NS + 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 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(Opposite of SIADH) 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 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