Fluids, Electrolytes, & Acid/Base HL Exam 3

What is the IBW calculation for males?

50kg + (2.5kg/in x (inches - 60))

What is the IBW calculation for females?

45.5kg + (2.3kg/in x (inches - 60))

What is the cockcroft-gault equation for males?

[(140 - age) x IBW] / (72xSCr)

What is the cockcroft-gault equation for females?

[(140 - age) x IBW] / (72xSCr) x 0.85

What is total body water (TBW)?

directly related to body weight, but most just use 60% of lean body weight in adults regardless of gender

What are components of TBW?

intracellular fluid (ICF), extracellular fluid (ECF), and transcellular fluid

What is intracellular fluid (ICF)?

Represents water contained within cells and is rich in electrolytes (i.e., K, Mg, P) and proteins

How much of TBW is ICF?

Approximately ⅔ regardless of gender (~40%)

What is extracellular fluid (ECF)?

Fluid outside of the cell and is rich in Na, Cl, and Bicarbonate

made up of interstitial fluid & intravascular fluid (plasma)

How much of TBW is ECF?

Approximately ⅓ (~20% clinically) and is further subdivided into 2 compartments (ISF, IVF)

What is transcellular fluid?

Includes viscous components of peritoneum, pleural space, pericardium, cerebrospinal fluid, joint space fluid, GI digestive juices

How much of TBW is transcellular fluid?

approximately 1%

Can increase significantly during various illnesses favoring fluid collection (i.e., pleural effusions, ascites in peritoneum) → AKA third spacing

Which electrolytes are found in intracellular fluid (ICF)?

Potassium

Magnesium

Potassium

And proteins

Which electrolytes are found in extracellular fluid (ECF)?

Sodium

Chloride

Bicarbonate

How is fluid balance assessed?

passive measurement, BP, physical/bedside clinical exams, dynamic assessments of volume status

Done by several means, all having limitations

What are passive measurements of fluid?

Arterial catheter

Central venous catheter

Pulmonary arterial catheter

How can BP measure fluid?

estimate fluid status relative to the amount of blood volume pumped by the heart, BUT measurements are affected by cardiac function and vascular pliability

Who may appear hypotensive?

Significant volume deficiency, but is a late finding that may require 20% of TBW to be lost

Who may appear edematous?

Significant volume excess, but third-spacing may hide this finding until late in the course

How can a physical exam measure fluids?

indicate the presence of fluid deficits (i.e., dry mucous membranes) + fluid excess (i.e., peripheral edema, coarse breath sounds).

How can dynamic assessment of volume status measure fluids?

more accurate than either bedside clinical exams or passive measurements of volume status (i.e., arterial catheter, central venous catheter, pulmonary artery catheter)

What are examples of dynamic assessment of volume status?

Pulse pressure variability

Ultrasound derived vena cava diameter variations

Passive leg raising

What is the typical input?

Total amount of fluid gained throughout the day

Easily Measurable: ingested fluids (~1400mL/day)

Not Directly Measurable: ingested foods and water by-product of oxidation

What is the typical output?

Total amount of fluid lost

Easily Measurable: urinary and stool losses (AKA sensible losses)

Not Directly Measurable: evaporation of fluid via skin/lungs (AKA insensible losses)

What are I&Os for hospitalized patients?

routinely measured in hospitalized patients and are used to estimate total fluid balance for each 24hour period

What are other forms of fluid loss?

Enteric suctioning (most commonly, nasogastric [NG] tubes)

Surgical drains (eg, chest tubes, nephrostomy tubes, and pancreatic drains)

Fistulous tracts

Enhanced evaporative losses (burns and fever).

What is another name for TBW depletion

dehydration

What is the onset of dehydration?

gradual and chronic

True or False: dehydration is the loss of hypotonic fluid (more water is lost than Na) from all body compartments and is primarily a disturbance in osmolality.

True

What are S/S of dehydration?

CNS disturbances (mental status changes, seizures, coma)

Excessive thirst

Dry mucous membranes

Decreased skin turgor

Elevated serum sodium

Increased plasma osmolality

Concentrated urine

Acute weight loss

What are common causes of dehydration?

Insufficient oral intake

Excessive insensible losses

Diabetes insipidus

Excessive osmotic diuresis

Impaired renal concentrating mechanisms

Who is at risk for dehydration?

elderly long-term care residents (frequently admitted secondary to lack of adequate oral intake, often with concurrent excessive insensible losses)

Estimation of Patient Maintenance Fluid Requirements for Adults:

1500mL + 20mL for each kg above 20

Replacement Fluids Calculations (for losses of TBW):

Maintenance fluid requirements + ongoing exceptional losses + fluid deficit

What is the onset of ECF depletion?

acute

What are causes of ECF depletion?

Loss of isotonic fluid (proportional losses of Na and water)

External fluid losses (i.e., burns, hemorrhage, diuresis, GI losses, adrenal insufficiency)

Third spacing of fluids (i.e., septic shock, anaphylactic shock, abdominal ascites)

Major disturbances of plasma osmolality is NOT common

What are S/S of ECF depletion?

Dizziness

Orthostasis

Tachycardia

Decreased urine output

Increased hematocrit

Decreased central venous pressure

Hypovolemic shock

What are the types of tonicity for crystalloids?

isotonic, hypotonic, hypertonic

What are types of isotonic solutions?

0.9% NaCl (NS) & Lactated Ringers (LR)

What are indications of isotonic solutions?

Any TBW depletion:

Perioperative fluids

Shock

Sepsis hemorrhage

Burns

Fluid challenges in hypotensive or oliguric patients

Hyponatremia

Metabolic contraction alkalosis

How does LR work?

as a buffer to increase pH (should not be used in liver disease)

True or False: large volume of NS can cause metabolic acidosis

True

What are examples of hypotonic solutions?

0.45% NaCl (1/2 NS) and D5 1/2 NS

What is the use of 1/2 NS?

hypertonic patients bc of primary deplection of ECF

What should you monitor when using 1/2 NS or D5 1/2 NS?

serum Na

What is an example of hypertonic solution?

3% NaCl

When is D5 1/2 NS used?

maintenance therapy when fluid deficits have been corrected with NS or LR

When is 3% NaCl used?

Severe hyponatremia + S/S of low serum Na

When is 23.4% of NaCl used?

have been used to acutely lower intracranial pressure in brain injury or stroke

What do you monitor when using 3%NaCl?

serum na and neurologic checks

What are examples of colloids?

albumin, HES, dextran

What are indications of albumin?

Acute volume expansion (NOT as protein caloric supplement):

Pasmapheresis/apheresis

Large volume paracentesis (> 4 L removed)

Hypotension in hemodialysis

Spontaneous bacterial peritonitis

Most used

What are limitations of albumin?

limited availability and don't use for pancreatitis, alteration of drug PK, or acute normovolemic demodilution in surgery

What are characteristics of HES?

Have no oxygen carrying capacity and are administered IV as plasma expanders

What are limitations of HES?

$$$

Hypersensitivity

Bleeding

BBW: increased risk of mortality and renal injury -- Do NOT use in critically ill patients (i.e., sepsis, ICU)

What is dextran?

polysaccharide plasma expander

What are limitations of dextran?

anaphylactic rxns and prolonged bleeding times

What is osmolality?

measure of the number of osmotically active particles per unit of solution

What is the calculation for osmolality?

2 * (Na) + (glucose / 18) + (BUN / 2.8) + (ethanol/4.6)

What is the serum osmolality range?

280-300mOsm/kg

What is an osmolar gap?

difference between the measured serum osmolality and the calculated serum osmolality

= measured osmolality - calculated osmolality

What does an osmolar gap greater than 10 mOsm/kg suggest?

Suggests that there is presence of small osmotically active agent (usually a toxin) and is most commonly seen with alcohols (ethanol, methanol, ethylene glycol, isopropyl alcohol), mannitol, or lorazepam ingestion

What are S/S of hyponatremia < 120mEq/L (mmol/L)?

Irritability

Mental slowing

Unstable gait/falls fatigue

HA

NA

What are S/S of hyponatremia < 110mEq/L?

Confusion

Seizures

Stupor/coma

Respiratory arrest

What level is profound hyponatremia?

< 110mEq/L

What level is hyponatremia?

< 135mEq/L

What is the mechanism of hypertonic hyponatremia?

EC sodium is "decreased" (other osmotically active molecules in large quantities "dilute" the sodium- usually glucose)

Glucose is an osmotically active agent that leads to an increase in TBW with little change in total body sodium

What are common causes of hypertonic hyponatremia?

hyperglycemia >>> and hypertonic sodium-free solutions (i.e., mannitol)

How to manage hypertonic hyponatremia?

treat hyperglycemia to return serum Na to normal levels

What is dilutional hyponatremia?

hypotonic (hypervolemic) hyponatremia with increased ECF

What is the mechanism of dilutional hyponatremia?

Excess of total body Na and TBW (excess in TBW is greater than Na)

What are common causes of dilutional hyponatremia?

CHF, hepatic cirrhosis, nephrotic syndrome

How to treat dilutional hyponatremia?

Na and fluid restriction + treatment of underlying disorder

Example: Na/H20 restrictions, loop diuretics, ACEi, and spironolactone treat CHF

What is hypotonic hyponatremia with normal ECF?

hypotonic (euvolemic/isovolemic) hyponatremia

What is the mechanism of hypotonic (euvolemic/ isovolemic) hyponatremia?

Excess of TBW with normal Na levels (excess "free" water)

Some meds release ADH from pituitary gland resulting in water retention and dilution of body's Na stores

What are common causes of hypotonic (euvolemic/ isovolemic) hyponatremia?

Commonly seen in: Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

1. Carcinomas (lung, pancreas)

2. Pulmonary (pneumonias, Tb)

3. CNS (meningitis, stroke, tumor, trauma)

4. Meds (sulfonylureas, antineoplastics, barbiturates, morphine, antipsychotics, tricyclic antidepressants, NSAIDS, SSRIs, DA agonists, general anesthetics)

What is the short term treatment of hypotonic (euvolemic/ isovolemic) hyponatremia?

1. Remove or treat underlying cause

2. Restrict free water (remember IV fluids are source of additional water)

3. Severe sx (Na

What is the long term treatment of hypotonic (euvolemic/ isovolemic) hyponatremia?

fluid restriction, demeclocycline, loop diuretics, lithium, tolvaptan (do not need to know doses)

True or False: overly aggressive corrections of hyponatremia (>12 mEq/L/day) can cause central pontine myelinolysis (aka osmotic demyelination syndrome)

True

What is the mechanism of hypovolemic hyponatremia with decreased ECF?

Deficit of total body Na + TBW (Na deficit is greater than TBW)

What are common causes of hypovolemic hyponatremia with decreased ECF?

1. Diuretic use

2. Profuse sweating

3. Wound drainage

4. Burns

5. GI losses (D/V)

6. Hypoadrenalism (low cortisol, low aldosterone)

7. Renal tubular acidosis

How to treat hypovolemic hyponatremia with decreased ECF?

1. Correct underlying cause

2. Calculate Sodium deficit = TBW (desired Na — Current Na)

Administer Na to correct Na deficit + administer H2O to correct TBW deficit (0.9% NS is the safest way to replace sodium and water. Hypertonic saline is generally reserved for severe hyponatremia)

What level is hypernatremia?

> 145mEq/L

What level do S/S manifest in hypernatremia?

> 160mEq/L

What are S/S of hypernatremia?

thirst, mental slowing, dry mucous membranes

severe: confusion, hallucinations, acute weight loss, decreased skin turgor, intracranial bleeding, coma

What are common causes of hypernatremia?

1. Dehydration (from loss of hypotonic fluid from respiratory tract/skin)

2. Decreased water intake

3. Osmotic diuresis (i.e., mannitol)

4. Diabetes insipidus (i.e., decreased ADH, phenytoin, Li)

5. In hospitalized patients, it's secondary to inappropriate fluid management

6. Iatrogenic hypernatremia is caused by administration of excessive hypertonic saline

How to manage hypernatremia?

1. Calculate TBW deficit

2. Replace fluids with 0.9% NaCl until stable, then change to D5W or 0.45%NaCl over 24-48 hours

True or False: correction is okay to exceed 0.5 mEq/L/h in some cases

False

we would avoid this to prevent cerebral edema and death

What is clinical presentation of hypokalemia?

Asymptomatic

Cramps, muscle weakness, polyuria, ECG changes, cardiac arrhythmias

What are common causes of hypokalemia?

GI losses (N/D/NG tube)

renal losses (high ald, low Mg)

inadequate K intake

medications

What medications can cause hypokalemia?

B2 agonists (albuterol), Insulin,

loop diuretics (furosemide,lasix),

thiazide diuretics (HCTZ),

high dose antibiotics (Penicillin),

corticosteroids (Prednisone),

Amphotericin B,

Cisplatin,

Foscarnet

What agent is used to manage hypokalemia?

KCl & K acetate >>>

Alkalosis? KCl

Acidosis? K acetate

What route is used to treat moderate hypokalemia (K = 2.5-3.5)?

oral replacement of 40-120mEq QD

What route is used to treat severe hypokalemia (K < 2.5)?

IV

do NOT exceed 10 mEq/h without continuous cardiac monitoring

What is the clinical presentation of hyperkalemia?

Muscle weakness

Paresthesias

Hypotension

ECG changes (eg, peaked T waves, shortened QT intervals, and wide QRS complexes)

cardiac arrhythmias

decreased pH

What are common causes of hyperkalemia?

increased K intake (diet, fluids, meds)

dec K excretion (renal failure, addison's)

K release from intracellular space (tissue breakdown, transfusions, metabolic acidosis)

What meds can increase K intake?

K sparing diuretics, cyclosporine, ACEi, NSAIDS, pentamidine, UFH, LMWH

How to manage hyperkalemia?

"C A BIG K Drop"

Calcium gluconate if >7 or EKG changes

Albuterol nebulizer

Bicarb

Insulin &

Glucose

Kayexalate/sodium polystyrene sulfonate or sodium zirconium cyclosilicate (Lokelma)

Diuretics and dialysis

What is the clinical presentation of hypocalcemia (< 6.5mg/dL)?

Tetany, circumoral tingling, muscle spasms, hypoactive reflex, anxiety, hallucinations, hypotension, MI, seizures, lethargy, stupor, Trousseau sign or Chvostek sign

What are common causes of hypocalcemia?

Hypoparathyroidism,

hypomagnesemia,

Alcoholism,

Hyperphosphatemia,

blood product infusion (due to chelation by citrate buffers),

chronic renal failure,

Vitamin D deficiency,

acute pancreatitis,

Alkalosis,

hypoalbuminemia

Meds