Nephro- Electrolytes & IVF

Cations or anions?

• Na+, K+, Ca++, Mg++, H+

Cations

Cations or anions?

• Cl-, HCO3-, proteins, lipids

Anions

What is the number of particles or osmoses dissolved in a solution?

Osmolality

What are the major cellular osmoles?

Na+ >> glucose > urea

What are exogenous osmoles?

Mannitol, ethylene glycol

What is the osmolality gap?

Measured osm - calc osm

What is the formula for osmolality gap?

2 x serum Na + (BUN/2.8) + (glucose/18)

What is the normal range for osmolal gap (OG)?

+10 to -10

What OG value is considered critical or cutoff?

> 15

What does the presence of low blood pH, elevated anion gap, & greatly elevated OG indicate?

Medical emergency requires prompt treatment

What is the major cation of extracellular fluid that has a role in water distribution, osmotic pressure, osmolality, & is a cofactor for nerves and muscle contractions?

Na

What regulates Na?

Kidneys → ADH & aldosterone

How does aldosterone affect Na?

Na retaining; increases Na & water with K loss

How does Na affect blood pressure?

Increases

What serum Na level indicates hyponatremia?

< 135 mEq/L

At what serum Na level are moderate to severe symptoms seen (N, generalized weakness, confusion, seizures)?

< 120 mEq/L

What type of hyponatremic state is characterized by:

• Decreased total body water (TBW)

• Decreased total body Na to a greater extent

• Decreased ECF volume

Hypovolemic hyponatremia

What type of hyponatremic state is characterized by:

• Increased TBW

• Normal total body Na

• Minimally-moderately increased ECF volume w/o edema

Euvolemic hyponatremia

What type of hyponatremic state is characterized by:

• Increased TBW to a greater extent

• Increased total body Na

• Markedly increased ECF volume with edema

Hypervolemic hyponatremia

What type of hyponatremic state is characterized by:

• Water shifts form intracellular to extracellular compartment → dilution of Na

• TBW & total body Na unchanged

• occurs with hyperglycemia or mannitol administration

Redistributive hyponatremia

What type of hyponatremic state is characterized by:

• Aqueous phase is diluted by excessive sugars, proteins, or lipids

• TBW & total body Na are unchanged

• seen with hypertriglyceridemia & MM

Pseudohyponatremia

What causes euvolemic or normovolemic hyponatremia?

Early SIADH, polydipsia, diuretics, hypothyroidism, severe hyperglycemia (polyuria)

How should pseudohyponatremia be corrected for hyperglycemia to get the true value of sodium?

Add 1.6 to the Na for every 100 mg/dL increment the glucose is over 100

**sweet 16 rule

What clinical syndrome of non-osmotic release or enhancement of ADH action leads to pathological H2O retention & hyponatremia?

Syndrome of inappropriate ADH (SIADH)

What are non osmotic releasers or enhancers of ADH that cause hyponatremia?

N +/- V, pain, lymphomas, leukemias, cancers, cirrhosis

What drugs can cause SIADH?

Lithium, SSRIs, ecstasy, cytotoxin, narcotics

What kind of hyponatremia is dehydration with both sodium and water losses cause?

Hypovolemic hyponatremia

What causes hypovolemic hyponatremia?

Loss of fluid (GI, burns), hypotonic fluid replacement, thiazide diuretics (Na & K loss), K depletion in cells (Na move into cells), aldosterone deficiency (inc Na & H2O loss)

What causes hypervolemic hyponatremia?

CHF (fluid from blood to interstitium), hepatic cirrhosis, over hydration, nephrotic syndrome, renal failure (inability to excrete water)

What serum Na level is defined as hypernatremia?

> 145 mEq/l

What is the major defense against the development of hypernatremia?

Thirst

What symptoms are associated with hypernatremia?

Tremors, irritability, ataxia, confusion, coma

What is the MCC of hypernatremia?

Hypovolemic hypernatremia (caused by dehydration, V, or D)

What causes normovolemic hypernatremia?

Insensible losses (skin/stool/lung; ≥500 cc/day), polyuria (DI)

Will DI or DM have hypernatremia?

DI

Will DI or DM have pseudohyponatremia?

DM

What causes hypervolemic hypernatremia?

Hypertonic saline, sodium bicarb, hyperaldosteronism, cushing’s syndrome

What condition is characterized by increased thirst, hypernatremia, and loos of large volumes of urine (low specific gravity)?

Diabetes insipidus (DI)

What is the pathogenesis of DI?

Loss of ADH (vasopressin) production or function

What are ssx of DI?

Polydipsia & polyuria

How is DI diagnosed?

Measure ADH level & vasopressin challenge test

What is the treatment for DI?

Replete ADH or HCTZ, & indocin

What condition?

• absence or deficiency of ADH from the posterior pituitary

• Serum vasopressin levels low → no production of ADH

• excess renal H20 loss and hypernatremia

• caused by diseases, tumors, or trauma that affects hypothalamus & pituitary stalk (sarcoidosis, anoxia,, hemorrhage)

Central DI

What is the treatment for central DI?

Replete ADH- desmopressin acetate

What condition?

• medullary collecting tubule unresponsiveness to ADH

• adequate or high levels of circulating ADH

• excess renal H20 loss and hypernatremia

• causes: any dz that harms kidney

Nephrogenic DI

What is the treatment for nephrogenic DI?

HCTZ, indomethacin

What is the major intracellular cation that has a role in neuromuscular excitability, contraction of the heart, intracellular fluid volume, & H+ ion exchange?

K

What regulates potassium?

Kidneys → proximal tubule reabsorption

Aldosterone→ Na/K exchange at cortical collecting duct

What serum K+ level indicates hypokalemia and suggests low total body potassium?

< 3.5 mEq/L

What causes hypokalemia?

Dec dietary intake, diuretics (MC), insulin/DM, alkalosis, hypomagnesemia, hyperaldosteronism

How do loop and thiazide diuretics affect potassium?

Inc Na delivery to distal segment of distal tubule → stimulates aldosterone sensitive Na pump to increase Na reabsorption in exchange for K and H+ which are lost in urine (increases K loss)

What serum K levels indicate hyperkalemia?

> 5.5 mEq/L

What causes hyperkalemia?

Excess dietary intake, metabolic acidosis, insulin def, heparin, digoxin, cyclosporine, ACEis, K sparing diuretics, dec excretion from renal failure or hypoaldosteronism

What are symptoms of hyperkalemia?

Muscle weakness, cardiac arrhythmias/arrest, often fatal if not corrected

What is the major extracellular anion that always follows Na+, is excreted in sweat and urine, and has a role in osmolality, blood volume, & electric neutrality?

Cl

How does excess sweating affect Na & Cl?

Conserves it by stimulating aldosterone

What parallels hypernatremia and is caused by dehydration and hypertonic NaCl soln?

Hyperchloremia

What parallels hyponatremia and is caused by prolonged vomiting (HCl loss), metabolic alkalosis, and pylonephritis?

Hypochloremia

What results from increased loss of serum HCO3 and Na?

Acidosis

What results from loss of H+ and Cl, and excess HCO3?

Alkalosis

Where is HCOs reabsorbed?

PCT in kidneys, mainly as CO3

What does the GI loss of HCO3 (diarrhea) lead to?

Metabolic acidosis

How does renal tubular acidosis affect bicarbonate?

Failure to reclaim HCO3

What is the difference between cations, anions & negatively charged plasma proteins?

*K not included

Anion gap

What is the formula for calculating the anion gap (AG)?

Na⁺ - (Cl^- + HCO₃^-)

What is a normal AG?

10 (12 +/- 2)

What would cause a low AG (rare)?

MM or lab error

What is the MUDPILES mnemonic for high AG metabolic acidosis?

Methanol ingestion

Uremia- inc BUN

DKA

Paraldehyde or phosphates

Iron, ischemia, or isoniazid

Lactic acidosis

Ethanol & ethylene glycol

Salicylates & starvation

What is the HARDUP mnemonic for normal AG metabolic acidosis?

Hyperalimentation

Acetazolamide

RTA

Diarrhea

Ureteroenteric fistula

Pancreatic fistula

What should always be looked at when determining type of fluids to administer?

Water & volume status

What are indications for IV fluids?

Shock, hemorrhaging, burns, volume depletion

Which crystalloid IVF should be given for symptomatic hyponaturemia?

Hypertonic → 3% saline (513 mEq/L of sodium)

When would crystalloid IVFs be used?

Fluid deficit, third space losses, maintenance (not used for large replacements)

What IVFs are colloids?

Albumin (#1 IVV expander), dextran, packed RBCs, plasma protein products (FFP)

What crystalloid IVFs are sodium chloride (saline) solutions that have toxicities close to that of plasma?

Isotonic saline / LR solns (0.9% saline, ringer’s lactate)

When are isotonic saline / LR solns used?

To expand ECFV (stays mostly in ECFV, mainly IVV)

What delivers 50 g/L of glucose?

D5 0.9% saline & D5 ringer’s lactate

What IVF is appropriate for the following situations?

• ECFV depletion from any cause

  • *hypotonic IVF would produce hyponatremia*

• postop fluid mgmt

  • *hypotonic IVF would produce hyponatremia*

• shock from any cause

• hemorrhage, burns

• in conjunction with blood transfusions

  • *hypotonic IVF would cause RBC lysis*

0.9% saline

What are indications for 3% hypertonic saline?

Seizures, coma, focal findings

What danger is associated with 3% hypertonic saline?

Central pontine myelinolysis → rapid correction of hyponatremia results in rapid shift of water out of brain that is already swollen & causes osmotic demyelination, mostly in pons

What crystalloid IVFs are ½ normal (isotonic) saline (.45%) & ½ H2O?

Hypotonic saline solns

When are hypotonic saline solns used?

To both expand ECVF & deliver free H20 to the intertstitium in a hypertonic patient, hyperosmolar states d/t severe hyperglycemia, & hypernatremia w/ ECFV depletion

What delivers 1 liter of H2O & 50 g of glucose, and is used to provide free H2O?

D5W

When is D5W used?

Dehydrated patient with normal BP

Why can’t pure H2O be given IV?

Causes hemolysis

What might be used in the following situations?

• correct hypernatremia (carefully watch for hyperglycemia or glyuosuria)

• dehydration w/ normal BP

• delivery of meds in non diabetic pt

• as KVO (keep vein open)

• ECFV overload (will not further expand bc does not contain Na)

D5W (free H20)

What IVF is dangerous due to risk of acute hyperkalemia & is irritating to the veins?

Potassium IV

In what situations would potassium IV be given?

profound, life threatening hypokalemia & unable to tolerate K+ PO (max 20 meqv in 1 L)

How should patients on IVFs be monitored?

Weigh daily, strict I & Os (allow for sensible losses), and measure elytes, BUN & Cr

What is the daily requirement for H2?

2000-2500 cc/day

(500-1000 cc/day loss from lungs, skin, and stool

1500 cc/day for urine volume)

When would H2O requirements be significantly greater than 2000-2500 cc/day?

Mechanical vent, GI losses, & fever (~60-80 mL/24 hrs for each degree F)

How much Na should be supplied each day in IVFs?

50-100 meq/day as sodium chloride

*except pts w renal dz, CHF or cirrhosis → give as little as possible

What is the amount of K that should be supplied each daily in maintenance IV solns under normal circumstances?

20-60 meq/day

What can the administration of solns w/o K supplementation result in?

Inc distal delivery of Na & Na/K exchange → hypokalemia from inc K loss in urine

*monitor serum K closely!