Basic Fluids and Electrolytes Douglas P. Slakey. Why Listen to This? Essential for surgeons Based upon physiology –Disturbances understood as pathophysiology.

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– 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 WATERTOTAL BODY WATER60% BODY WEIGHT60% BODY WEIGHT

ICF

2/3

Predominant solute

K+

ECF

1/3

Predominant solute

Na+

HH22OO

(mEq/L) Plasma IntracellularNa 140 12K 4 150Ca 5 0.0000001Mg 2 7Cl 103 3

HCO3 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?

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

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

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

D5 0.45NS + 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

Na Volume

Check Ur Na

< 10 mmol/L

VomitingDiarrhea3rd spaceHepatorenal

Adrenal InsufficiencyDiureticsSalt-Wasting SyndromeSIADH

> 20 mmol/L

SIADH• Causes

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

• Anticonvulsants, antineoplastics, antipsychotics, sedatives (morphine)

SIADHToo 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 cellsSymptoms: 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

HypochloremicHypovolemia

Hypernatremia

Relatively too little H2O

– 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/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

• 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