Pare◦ shock caused by circulating toxins◦ treatment with phlebotomyBlalock◦ shock caused by hypovolemia◦ treatment with plasma replacementShires◦ deficit in functional extracellular volume◦ treatment with crystalloid fluids

Does total body water,as a percentage of body weight vary with:

◦ Age?

◦ Gender?

A decrease in the percent of body weight that is water is noted with increasing age.

Men have a slightly higher percentage of body weight as water than women.

Why?

Young - More percent muscleOld - Less percent muscle

Males - Less percent fatFemales - More percent fat

◦ What percentage of total body weight is water?

Males◦ 60% of total body weight is water

Females◦ 50% of total body weight is water

How much volume is Total Body Water in a typical 70-kg man?

70 kg x 1 L/kg x 60% = 42 L

What are the compartments?

What fractions of total body water?

2/3 Intracellular

1/3 Extracellular

◦ 3/4 Interstitial◦ 1/4 Intravascular

What are 3 clinical conditions where the ratio of interstital/intravascular volume is increased?

Congestive heart failureHypoalbuminemiaInflammation

The total osmotic activity in a solution is the sum of the individual osmotic activities of all the solute particles in the solution.

What is the osmolarity of◦ 0.9% NaCl?

0.9% NaCl = 154 mEq/L Na + 154 mEq/L Cl= 154 mOsm/L Na + 154 mOsm/L Cl= 308 mOsm/L

What is normal plasma osmolarity?

Normal plasma osmolarity = 280 - 290 mOsm/L

What is the difference between osmolarity and osmolality?

Osmolarity = osmotic activity per volume of solution

Osmolality = osmotic activity per volume of H2O

How can you estimate plasma osmolarity?

(2 x [Na]) + [Glucose]/18 + [BUN]/2.8

What are the primary electrolytes?

◦ Extracellular

◦ Intracellular

Extracellular◦ Cation - Sodium◦ Anion - Chloride

Intracellular◦ Cation - Potassium◦ Anion - Bicarbonate

Where is water lost normally?

How much water is lost normally?

What is the ideal maintenance fluid?

70 kg man average losses◦ Urine 1500 mL◦ Insensible 1000 mL◦ Stool negligibleTotal 2500 mL

What conditions exacerbate water loss?

DiureticsDiarrheaFeverOpen woundArtificial airway

In the nonstressed, fasting state, 150 g/day dextrose provides enough calories to limit proteolysis.

This protein-sparing effect is not sufficient in the stressed, catabolic patient.

What are the daily requirements for sodium and potassium?

70 kg man average needs

◦ Sodium 140 meq/day◦ Potassium 50 meq/day

What is the ideal maintenance fluid for the nonstressed, fasting, 70 kg man?

D5 + 1/2NS + 20meq/L KCl100 mL/hour

Provides total◦ 2.4 L water◦ 120 g dextrose◦ 185 meq sodium◦ 48 meq potassium

What is the estimated volume of fluid requirement for each degree of fever?

An extra 500 mL of fluid a day is required for every degree of fever above 37C.

What is “Third Space?”

Fluid compartments that are not freely mobilized by normal homeostatic mechanisms.

Body Spaces:◦ 1.Intracellular Space◦ 2.Extracellular Space

InterstitialIntravascular

◦ 3.Third SpaceGI tractPeritoneal cavityPleural cavityPathologic interstitial

Na+ K+ Cl- HCO3-Stomach Pancreas Bile S. Bowel L. Bowel

Na+ K+ Cl- HCO3-Stomach 70 15 100 0 Pancreas Bile S. Bowel L. Bowel

Na+ K+ Cl- HCO3-Stomach 70 15 100 0 Pancreas 140 10 70 70 Bile S. Bowel L. Bowel

Na+ K+ Cl- HCO3-Stomach 70 15 100 0 Pancreas 140 10 70 70 Bile 140 10 100 40 S. Bowel L. Bowel

Na+ K+ Cl- HCO3-Stomach 70 15 100 0 Pancreas 140 10 70 70 Bile 140 10 100 40 S. Bowel 70 10 50 20 L. Bowel

Na+ K+ Cl- HCO3-Stomach 70 15 100 0 Pancreas 140 10 70 70 Bile 140 10 100 40 S. Bowel 70 10 50 20 L. Bowel 30 10 10 0

What is the homeostatic response to volume deficit?

Under normal circumstances, water intake is regulated by thirst.

Receptors in the hypothalamus are stimulated by changes in plasma osmolarity or circulating volume.

Actions◦ Maintenance of serum osmolarity◦ Regulation of extracellular volume◦ Sodium / Potassium ATPase

Regulation◦ ADH◦ Aldosterone

Etiology

◦ Normoosmolar◦ Hyperosmolar◦ Hypoosmolar

HypovolemiaEuvolemiaHypervolemia

Etiology

◦ Normoosmolar?

◦ What is pseudohyponatremia?

Extreme elevations in plasma lipids or proteins increase the plasma volume and can reduce the measured plasma sodium concentration.

Extracellular sodium relative to extracellular water is not decreased.

Normoosmolar

◦ Pseudohyponatremiahyperlipidemiahyperproteinemia

Etiology

◦ Hyperosmolar?

Hyperosmolar

◦ HyperglycemiaNa decreases 1.6 mEq/L per glucose increase of 100 mg/dL

◦ Mannitol

Etiology

◦ HypoosmolarHypovolemia?Euvolemia?Hypervolemia?

Hypoosmolar◦ Hypovolemia

RenalDiuretics, aldosterone deficiency, renal dysfuntion

NonrenalVomiting, diarrhea, third spacing, burns, salt wasting

◦ EuvolemiaSIADH, psychogenic polydipsia

◦ HypervolemiaCHF, liver failure

What is the etiology of cerebral salt wasting?

The cause is not clearly understood

◦ Excessive sympathetic stimulationRenovascular hypertensionDopamine release

◦ Circulating natriuretic factors

How do you distinguish between SIADH and psychogenic polydipsia?

SIADH◦ Una > 20 mEq/L◦ Uosm > Posm

Psychogenic polydipsia◦ Una < 10 mEq/L◦ Uosm < 100 mOsm/L H20

Why do patients with CHF and liver failure develop hyponatremia?

Activation of compensatory mechanisms◦ Sympathetic stimulation◦ Redistribution of blood flow

Shunting from visceral organs to brain and heart

Renal vasoconstriction / hypoperfusion◦ Sodium and water retention◦ Decreased sodium and water excretion

Manifestations?

Manifestations◦ CNS

DisorientationIrritabilitySeizuresLethargyComa

◦ ConstitutionalNauseaVomitingWeakness

Normoosmolar◦ Treatment?

Hyperosmolar◦ Treatment?

Normoosmolar◦ Treat underlying disease (hyperlipidemia)

Hyperosmolar◦ Treat underlying disease (hyperglycemia)

Hypoosmolar◦ Hypovolemic

Treatment?

Hypoosmolar◦ Hypovolemic

Treat underlying disease (bowel obstruction)Stop drug (diuretic)Replace with isotonic saline

How is aldosterone deficiency treated?

Mineralicorticoid effect◦ Fludrocortisone 50-100 mcg/d oral

Excess mineralicorticoid replacement◦ CHF, alkalosis, hypokalemia, Htn

Hypoosmolar◦ Hypervolemic

Treatment?

Hypoosmolar◦ Hypervolemic

Treat underlying cause (CHF)Give diureticDon’t give sodium supplements

Euvolemic◦ Treatment?

Euvolemic◦ Asymptomatic

Water restrictionLoop diuretic if necessary

◦ SymptomaticNormal saline or hypertonic salineGoal of > 130 mEq/LLoop diureticNa should not be increased > 12 mEq/L/day

Etiology?

Etiology

◦ Water deficit?

◦ Sodium excess?

Water deficit◦ Reduced intake◦ GI loss (diarrhea, vomiting)◦ Cutaneous loss (sweating, fever)◦ Renal loss (DI, diuretics)

Sodium excess◦ sodium administration

What is the difference between central and nephrogenic diabetes insipidus?

Central◦ Inhibition of ADH release from the posterior

pituitary.

Nephrogenic◦ Defective end-organ responsiveness to ADH.

Causes?

Central◦ Traumatic brain injury◦ Anoxic encephalopathy◦ MeningitisNephrogenic◦ Hypokalemia◦ Aminoglycosides◦ Amphotericin◦ Radiocontrast dyes◦ Polyuric phase of ATN

Manifestations?

Manifestations◦ CNS

LethargyComaSeizures

◦ ConstitutionalWeaknessPolyuriaPolydipsia

Treatment?

Water and sodium deficit◦ Give 1/2NS IVWater deficit◦ Give D5W◦ Give water enteralSodium excess◦ Diuresis and give water or D5WNa should not change > 20 mEq/L/day

TBW deficit = Normal TBW - Current TBW= Normal TBW - (Normal TBW x 140/[Na])= 0.5 x weight - (0.5 x weight x 140/[Na])

70kg man with [Na] = 150TBW deficit = 0.5 x 70 - (0.5 x 70 x 140/150)

= 35 - (35 x 0.93)= 35 -32.6= 2.4 L

Changes in sodium concentrations are usually caused by water excess or deficit, not sodium.

Alterations in sodium concentration primarily affect CNS function.

Actions◦ Maintenance of membrane potential◦ Sodium / Potassium ATPase

Regulation◦ Renal excretion◦ Insulin◦ Aldosterone

Etiology?

Etiology

◦ Decreased intake◦ Renal loss◦ Extrarenal loss◦ Transcellular shift

Decreased intake◦ Malnutrition, anorexia, alcoholism, TPNRenal loss◦ Diuretics, amphotericin, hypomagnesemiaExtrarenal loss◦ Sweating, GI lossTranscellular shift◦ Alkalosis, insulin

Manifestations?

Manifestations◦ Cardiac

ArrhythmiasST depressionT wave inversionQT prolongation

◦ ConstitutionalWeaknessIleus

Treatment?

Treat underlying disease (bowel obstruciton)

Stop drug, if possible (diuretic)

Treat hypomagnesemia (cofactor for K transport)

Correct alkalosis

Administer potassium◦ Enteral replacement, if possible◦ IV replacement

Maximum concentrationPeripheral 20 mEq/100 mLCentral 20 mEq/50 mL

Maximum rateUnmonitored 10 mEq/hMonitored 20 mEq/hSymptomatic 40 mEq/h

Etiology?

What is Pseudohypokalemia?

WBC > 50 or Platelets > 1K

Potassium release from cells during clot formation

Etiology◦ Hemolysis of sample◦ Pseudohyperkalemia◦ Massive blood transfusion◦ Excess supplements◦ TPN◦ Renal failure◦ Acidemia◦ Crush injury, rhabdomyolysis, burns◦ Adrenal insufficiency, hypoaldosteronism

Manifestations◦ Cardiac

ArrhythmiasProlonged PRWide QRSPeaked T wavesSine waves

◦ ConstitutionalWeaknessParesthesias

Treatment?

Treat underlying diseaseStop K intakeStop TPNTreat acidemiaStabilize myocardial cell membrane effects◦ Calcium chloride 1g IV◦ Effect lasts 30 min◦ May be repeated

List 3 mechanisms for potassium redistribution.

NaHCO3 50-100 mEq IV

D50W 50 g IV + Regular insulin 10 U IV

High-dose inhaled beta-agonists◦ Albuterol 10-20 mg

Eliminate K from body

◦ Renal excretion with loop diuretic

◦ GI elimination with K resinSodium polystyrene sulfonate (Kayexalate)

50 g in sorbitol 30 mL oral or enema

◦ Hemodialysis

Extreme elevations in potassium concentration reflect laboratory sample hemolysis or renal failure.

Alterations in potassium concentrations primarily affect cell membrane function and the cardiac effects may be life-threatening.