PHRM 802: Lec 4, 5, 6 - Fluids and Electrolytes

body fluid basics

-adults are ~60% water by body weight

-ICF: ~⅔ of total body water = ~40% body weight

-ECF: ~⅓ = ~20% body weight

¾ interstitial (surrounds cell)

¼ intravascular (plasma)

-body water % decr with age

IBW equations

IBW = LBW

male = 50 kg + (2.3 * inches over 60")

female = 45.5 kg + (2.3 * inches over 60")

DBW (dosing body weight)

-used for dosing certain drugs when ABW is >130% IBW

-DBW = IBW + 0.4(weight - IBW)

NBW (nutrition body weight)

-used if ABW >130% of IBW for fluid, electrolyte, and nutrition parameters

-NBW = IBW + 0.25(weight - IBW)

fluid balance

-major organs: skin, lungs, kidneys

-fluid loss can be sensible and insensible

-goal: fluid intake = fluid loss

average fluid losses

1. sensible: urination (#1!), defecation, wounds = 1-1.5 L/day

2. insensible: skin, lungs = 1 L/day

-additional losses: vomiting, diarrhea, NG output, burns, drains, bleeding, wounds which may or may not be measurable but WILL affect fluid balance

***gastric, intestinal, pancreatic, and biliary secretions and reabsorbed and not counted in daily balance

volume regulation

1. kidneys

2. thirst

3. hormonal changes: ADH, RAAs, ANP

tonicity of fluids

1. isotonic: 275-290 mOsm/L. same conc as ECF = stay in place, prevents fluid shift

2. hypotonic:

Osmolarity

-measure of solute concentration

-ex: water has no solutes, 0 mOsm/L, so it is very hypotonic

-important to know because solutions that are hypotonic or hypertonic can result in hemolysis of RBCs, renal failure, and even death

Calculating Osmolarity of IVs

-total osmolarity = osmolarity of IV solution + osmolarity fo added electrolytes

-ex: calculate the osmolarity of 1L of 0.45% NaCl with 20 mEq KCl

Calculating MIVF requirements

-clinical estimate (adults): 30-40 mL/kg/day

-ex: KD is a 34 yom, ht 70", wt 91 kg

types of fluids: crystalloids

-provide water and/or sodium and maintain osmotic gradients btwn intravascular and extravascular compartments

-fast-acting

-low-cost

-move freely through cell membranes

-can be isotonic, hypotonic, or hypertonic

-ex: NS, 1/2 NS, LR, D5W, balanced salt solutions

***1st line

types of fluids: colloids

-increase plasma oncotic pressure and pull fluid from interstitial into the intravascular space

-contain large molecules which stay inside blood vessels longer to pull in fluid

-hypertonic

-ex: albumin (5% or 25%), hetastarch, tetrastarch, blood, plasmanate

***2nd line

types of IV fluids: NS

-normal saline: 0.9% NaCl

-not a maintenance fluid

-used for resuscitation

-Na+ or Cl- replacement

types of IV fluids: 1/2 NS

-half normal saline: 0.45% NaCl

-used for maintenance fluids

types of IV fluids: LR

-lactated ringers

-used for resuscitation (blood loss, trauma, burns)

types of IV fluids: D5W

-dextrose 5% water

-NOT resuscitative

-NOT a MIVF by itself

-used for free water replacement

balanced salt solutions

crystalloid solutions containing physiologic levels of: chloride and buffer solutions. (IV fluid with salt and acid close to normal human blood)

ex: LR, Normosol-R, Plasma-lyte

NS complications

-incr mortality

-incr hyperchloremic metabolic acidosis

-incr renal injury

**in comparison to a balanced crystalloid solution

colloids place in therapy

-"plasma expanders", used selectively for volume expansion and intravascular repletion

-2nd line for hypovolemic shock

albumin

-human-derived blood

-indications: volume expansion, shock, burn, ARDS, cardiopulmonary bypass, intraoperative fluid repletion

-adverse effects: hypervolemia, azotemia, anaphylaxis

-treatment is supportive and symptomatic unless hypoproteinemia

5% vs 25% albumin

-5%: 250 mL or 500 mL vial. for hypovolemia or intravascular depletion...VOLUME

-25%: 50 mL or 100 mL vial. fluid and/or sodium restricted pts....PROTEIN

synthetic colloids

-larger MW

-higher substition ratio

-ex: hetastarch (hespan), tatrastarch (voluven)

-safety concerns: incr risk of death, incr risk of renal replacement, incr bleeding risk

-BBW: severe sepsis

blood

-packed RBCs

-1 unit = 230-350 mL

-place in therapy: acute blood loss, inadequate resuscitation from fluids, pre-op, low hemoglobin ≤ 7-8 g/dL (1 unit incr hemoglobin by ~1 g/dL)

What is the most common MIVF?

D5w + 1/2 NS + 20 mEq KCL / L

-used to incr plasma oncotic pressure

-similar composition to urine

Monitoring Fluid Status

-weight daily

-I/O daily

-volume status: overload? euvolemic? dehydration?

-Urine output (OUP) in mL/kg/hr

-vitals

Possible signs of dehydration

-decr skin turgor

-dry mucus membranes

-delayed capillary refill

-tachycardic

-hypotension

-decr urine output: < 0.5 mL/kg/hr

-BUN/SCr ratio > 20

electrolyte concentrations in body fluids

-ECF: sodium

-ICF: potassium

goals of electrolyte therapy

-prevent and tx complications

-normalize serum conc

-identify and correct underlying causes

-avoid overcorrection

normal physiological serum sodium levels

135-145 mEq/L

-necessary to maintain cellular integrity

-maintain osmolar gradient: regulate fluid homeostasis

*primary* extracellular cation

hyponatremia

-Na+

what is osmolality?

-# of particles per liter of water (mOsm/L)

-equation: Osm = (2 * Na+) + (BUN/2.8) + (glucose/18)

-normal: 275-290 mOsm/L

isotonic hyponatremia, aka "pseudo" hyponatremia

-275-290 mOsm

-normal mOsm serum with Na+

hypertonic hyponatremia

->290 mOsm

-high Osm serum

-low Na+, high amounts of solutes

-common example if elevated BG

-know how to find calculated Osm and corrected serum sodium

hypotonic hyponatremia

-

hypovolemic hypotonic hyponatremia

-decr TBW

-decr sodium

-RENAL causes (urine Na+ > 20 mEq/L): diuretics, adrenal insufficiency, salt-losing nephropathy

-NON-RENAL causes (urine Na+ < 20 mEq/L): blood loss, burns, sweat, vomiting, diarrhea

isovolumic hypotonic hyponatremia

-incr TBW

-normal/slightly incr Na+

-causes: SIADH, hypothyroidism, adrenal insufficiency, psychogenic polydipsia

hypervolemic hypotonic hyponatremia

-highly incr TBW

-incr Na+

-causes: CHF, cirrhosis, kidney failure, nephrotic syndrome

What is SIADH and its Tx?

-sydrome of inappropriate antidiuretic hormone release

-most common cause of isovolemic hypotonic hyponatremia

-water intake exceeds capacity of kidneys to excrete

-main cause: DRUGS like NSAIDs, antipsychotics, carbamazepine

-Tx: remove drug is possible. restrict free H2O. vaptans can be used is water restriction fails.

clinical presentation of hypotonic hyponatremia

-mostly asymptomatic

-hypovolemia: dehydration...decr skin rugor, hypotension, techycardic, dry mucous membranes

-isovolemic: malaise, psychosis, seizures, coma

-hypervolemic: fluid overload...edema and weight gain

-acute hyponatremia: over 12 hrs or less. nausea, malaise, weakness, HA, disoriented, coma, seizures, respiratory arrest

acute vs chronic hyponatremia

-acute: <48 hrs, death more common, brain damage (cerebral edema), altered mental status, seizures

-chronic: >48 hrs, death not common, brain damage less common

Tx of acute symptomatic hyponatremia

-incr Na+ by 1-2 mEq/L/hr until sx resolve

-Max incr: 8-12 mEq/L in the first 24 hrs

-usually sufficient: 4-6 mEq/L

-correction that occurs too fast causes central pontine myelinolysis (demyelination)

-risk vs benefit: risk of cerebral edema outweights risk of demyelination from quick correction

demyelination risk factors

hypokalemia, alcohol use disorder, malnutrition, advanced liver disease

goals of hypotonic hyponatremia Tx

-hypovolemic: restore volume deficit

-isovolemi/hypervolemic: underlying cause? pt symptomatic?

-avoid rise in serum Na+ > 0.5 mEq/L/hr no more than 8-12 mEq/L/day

hyponatremia Tx: hypovolemic

-symptomatic: 3% NaCl

-asymptomatic: 0.9% NaCl

hyponatremia Tx: isovolemic

-symptomatic: furosemide + 3% NaCl

-asymptomatic: 0.9% NaCl if asymptomatic and water restriction

hyponatremia Tx: hypervolemic

-symptomatic: furosemide + judicious 3% NaCl

-asymptomatic: furosemide

Pt case: EA is a 36 yof multiple trauma pt who has been receiving D5W for her MIVF for the past two days at 150 mL/hr. Today her serum sodium was found to be 110 mEq/L and she is 55 kg. She has no neurologic signs of acute hyponatremia

at this time. What is her sodium deficit? How should it be corrected?

....

hypernatremia

-Na+ > 145 mEq/L

-associated with hypertonicity

-causes: water loss, impaired thirst, inadequate access to water

-must assess volume status (ECF)

hypovolemic hypernatremia

-loss of water

-loss of Na+

-causes: renal, GI, adrenal, lung, skin

-Tx: restore free water deficit

isovolemic hypernatremia

-loss of water

-causes: diabetes insipidus, skin loss, latrogenic, osmotic diuresis, primary polydipsia

hypervolemic hypernatremia

-gain of water

-gain of Na+

-causes: Na+ overload, mineralcorticoid excess, hypertonic saline resuscitation

-Tx: diuretic if needed, try to match I/O

calculating free water deficit for hypovolemic hypernatremia

free H2o deficit = NL TBW x [(serum Na+/140) -1]

replacing free H2O deficit

-provide free water: D5W continuous infusion, enteral free water feeding tube

-match I/O if possible

-replace 1/2 deficit in first 24 hr

-remaining 1/2 over next 24-48 hr

-goal: 0.5 mEq/L/hr

Pt case: RS is a 52 yom admitted with 47% TBSA full thickness burns after throwing gasoline on a brushfire. [Wt = 124 kg, Ht = 68"]. He is PBD #4 and his serum sodium today is 153 mEq/L. He has been receiving concentrated enteral feeds with no additional MIVF. What is his free water deficit? How should it be corrected?

...

estimating change in sodium

change in serum Na+ = (Na+ fluid - Na+ serum)/[TBW + 1L]

-use to double check

-estimates change in Na+ per one L of any fluid

normal potassium

3.5-5 mEq/L

-primary intracellular cation

-critical for cardiac and neuromuscular function

-hypo and hyperkalemia are associated with fatal arrhythmias

-causes: K+-wasting diuretics, β-agonists, NG drainage, metabolic alkalosis, diarrhea, Mg2+ depletion (co-factor for Na/K ATPase)

-Sx: weakness, cramping, N/V, muscle weakness, arrhythmias

Tx of hypokalemia

1. 3.5-4 mEq/L: usually no Tx, ICU goal may be ≥ 4 mEq/L

2. 3-3.4: Tx debatable, PO may be used for pt with cardiac problems

3. <3: always Tx. PO for asymptomatic. IV for symptomatic.

***always try to correct Mg2+ deficit

Intravenous K+

-severe hypokalemia: < 2.5-3

-symptomatic

-arrhythmias/cardiac arrest if given too quickly

-burning @ infusion site

-infusion rate w/o monitoring: 10 mEq/hr

-infusion rate w/ monitoring: 20 mEq/hr, 40-60 if severe (cardiac arrest)

hyperkalemia

≥ 5.5 mEq/L

-mild: 5.5-6

-mod: 6.1-6.9

-severe: ≥7

-major concern: arrhythmias

-Tx goals: protect heart, shift K+ into cells, remove K+ from the body

C A BIG K DROP

1. antagonist membrane actions: Calcium

2. decrease extracellular K+: Albuterol, Bicarb, Insulin + Glucose

3. remove K+ from the body: Kayexalate/Lokelma, Diuretics (furosemide), Renal unit for dialysis Of Patient

acute hyperkalemia Tx options

1. calcium chlrodie

2. regular insulin OR D50W OR NaHCO3 OR Albuterol

3. furosemide OR hemodialysis OR Lokelma OR Kayexalate

chronic hyperkalemia Tx options

1. patiromer

-moa: binds K+ on GI tract to decr absorption

-dose: 8.4 gm PO QD

-onset: 7 hrs

-ADR: hypomagnesemia, constipation, diarrhea, nausea, abdominal discomfort, flatulence

magnesium

1.5-2.5 md/dL

-neuromuscular function

-co-factor for enzymes

hypomagnesemia

-drugs: mainly diuretics like thiazides or loops

-GI or kidney disorders

-diarrhea

-usually associated with other electrolye disturbances which MUST also be treated

Tx of hypomagnesemia

1. PO: preferred. for aymptomatic pts with Mg > 1 mg/dL.

-milk of mag

-Mag-Ox

2. IV: symptomatic prs.

-Mg 1-2 md/dL: 0.5 mEq/kg

-Mg < 1 md/dL: 1 mEq/kg

Calcium

8.5-10.5 md/dL

-bone and neuromuscular

-bone, kidneys, intestine

hypocalcemia

-Mg deficiency

-large volumes of blood products

-hypoalbuminemia

calcium correction

measured Ca2+ + [(4 - measured albumin) x 0.8]

acute hypocalcemia tx

100-300 mg elemental Ca2+ IV over 5-10 min.

-1 g Ca chloride = 3 g Ca gluconate

-administration rate: 1 gm/hr

-correct hypomagnesemia!

chronic hypocalcemia tx

-PO calcium: 1-3 g/day of elemental Ca2+

-vit D supplementation

phosphorus

2.5-4.5 mg/dL

-source of high energy bonds of ATP

-regulated by intake, vit D, parathyroid hormone, renal function

hypophosphatemia

1. mild-mod: PO4 conc 1-2 mg.dL

2. severe: Po4 < 1 mg/dL

-sx: cardiomyopathy, decr contractility, arrhythmias, ATN (renal)

hypophosphatemia Tx

1. mild-mod: PO PO4

2. severe: IV PO4

KPhos if K⁺

phosphate replacement

1 mMol NaPhos = 1.33 mEq Na+ and 1.33 mEq phos

1 mMol KPhos = 1.47 mEq K+ and 1.47 mEq phos

-Infuse no faster than 7 mmol/hr