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 600 ml Lungs 400 ml Kidneys 1500 ml Feces 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 WATER60% BODY WEIGHT

ICF

2/3Predominant solute

K+

ECF

1/3

Predominant solute

Na+

H2O

I Love Salt Water!

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

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 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 diagnoseAND 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

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

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

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 FluidsD5 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)

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

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

HypochloremicHypovolemia

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)

[0.6 X wt (kg)] X [Serum Na/140 - 1]

Free water deficit:

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