14 - Treatment of Fluid/Electrolytes

What are the terms for:

• Intake > output of fluid

• Output → intake of fluid

• Positive fluid balance

• Negative fluid balance

What does ascites do to fluid in the body?

The fluid remains, yet values in the blood seem lower because all the fluid is in the peritoneal cavity

Simply, what do these represent?

• Plasma Na+

• Plasma K+

• HCO3-

• BUN, Cr

• Water balance

• Extracellular K+

• Acid-base balance

• Renal function

Signs of hypovolemia, euvolemia, hypervolemia in intracellular compartment

None, hard to measure

Signs of hypovolemia, euvolemia, hypervolemia in interstitial compartment

Hypovolemia: Dry lips, dry tongue, poor skin turgor(Doesn’t bounce back within 2 seconds)

Hypervolemia: Pitting edema

Signs of hypovolemia, euvolemia, hypervolemia in intravascular compartment

Hypovolemia: Flat JVP

Hypervolemia: Elevated JVP(Over 4cm above sternal angle), crepitations

How much of our body weight is water, and how is our total body water divided?

60% of our body weight is water, so a 70kg man would be 42L water

• Intracellular fluid(ICF) is 2/3 of our total body WATER, so here it would be 28L

• Extracellular fluid(ECF) is 1/3, so 14L, and there is the interstitial fluid which is ¾ of the ECF, so around 10.5, and intravascular fluid which is ¼ of the ECF, which is around 3.5 in this case

An easier way to think about it is that total body weight is 60% water, and so ICF is 40% of our total body weight while ISF is 15% of our total body weight, and intravascular fluid is 5% of our total body weight

CVP =

CVP = JVP + 5 cmH2O

MAP =

MAP = (SBP + 2DBP)/3

• MAP = PP/3/

Shock diagnostic criteria

Hypotension + Signs of poor tissue perfusion

• Hypotension = MAP < 65 or SBP < 90

• Signs of poor tissue perfusion: Alteration of consciousness, syncope, bowel ileus, cold clammy skin, oliguria

What type of shock do we avoid giving fluid in?

Cardiogenic

Crystalloids vs colloids

• Crystalloids are solutions of water containing small molecules like electrolytes, so they can cross capillary walls freely: Only ¼ stays in the blood while ¾ goes out to the ISF

• Colloids are solutions containing large molecules which stay in the intravascular space

Crystalloid and colloid groups

Crystalloids: Hypertonic, isotonic, and hypotonic solutions

Colloids: Blood products, semisynthetic colloids

Purpose of adding dextrose to solutions

1. Making free water safe to infuse by preventing hemolysis(Bc water would rush into red cells and cause hemolysis)

2. Provides calories and prevents hypoglycemia

Plasma osmolality equation and normal value

2Na + (Glucose/18) + (BUN/2.8)

Normal value: 280-295

Effective serum osmolarity

• What is it

• What does it measure?

• 2Na + (Glucose/18)

• It measures the tonicity of the plasma, aka the part that shifts water compartment to compartment

Isotonic crystalloids

• Isotonic saline(0.9% NaCl)

• Balanced salt solutions: Ringer’s lactate, Acetar

Isotonic saline

• Other names

• Concentration of solutes vs plasma

• Acidic or basic, and why?

• 1L distribution in the body

• Main indication

• 0.9% NaCl, Normal saline, NSS

• Na+ 154, Cl- 154mmol/L vs Na+ 135-145 and Cl- 98-106

• Acidic because we add Cl- without adding HCO3-

• ¼ into IVF(250mL), ¾ into ISF(750mL) and 0 into ICF because the similar tonicity means that there’s no net shift

• Shock with previous metabolic alkalosis

Why do we also give NSS in:

• Hypovolemia without shock:

• DKA

• HyperCa2+

• Traumatic brain injury

• Hypovolemia without shock(like vomiting) because we need to refill the vessels for cardiac output and vomiting also causes alkalosis

• DKA: Glucose spills into urine and pulls water out with it, so we have to restore volume

• HyperCa2+: High Ca2+ makes the CaSR’s insensitive to calcium, so we can’t express AQP2+ and pull water back → hypovolemia

• Traumatic brain injury: we want to give fluid to make sure brain stays perfused while also making sure that the blood isn’t hypotonic because that would cause brain edema

NSS side effects

1. Volume overload → interstitial edema

2. Hypernatremia

3. Hyperchloremic metabolic acidosis(normal gap)

4. AKI association

Ringer’s lactate(RLS)

• Concentration of solutes vs plasma

• Acidic or basic, and why?

• 1L distribution in the body

• Main indication

• Na+ 130 vs Plasma 135-145, K+ 4 vs plasma K+ 3.5-5, Ca2+ 3 vs plasma 4.5-5, Cl- 109 vs plasma 98-106, lactate buffer 28 vs plasma HCO3- 24, osmolality 273 vs plasma osmolality 280-295

• Basic due to the buffer(Utilizes cori cycle)

• ¼ into IVF(250mL), ¾ into ISF(750mL) and 0 into ICF because the similar tonicity means that there’s no net shift

• Shock with previous metabolic acidosis

Acetar

• Concentration of solutes vs plasma

• Acidic or basic, and why?

• 1L distribution in the body

• Main indication

• Na+ 130 vs Plasma 135-145, K+ 4 vs plasma K+ 3.5-5, Ca2+ 3 vs plasma 4.5-5, Cl- 109 vs plasma 98-106, acetate buffer 28 vs plasma HCO3- 24, osmolality 273 vs plasma osmolality 280-295

• Basic due to the buffer(Utilizes skeletal muscle)

• ¼ into IVF(250mL), ¾ into ISF(750mL) and 0 into ICF because the similar tonicity means that there’s no net shift

• Shock with previous metabolic acidosis

Side effects of RLS and acetar

• Volume overload → Interstitial edema

• Metabolic alkalosis

Difference of indication of balanced salt solutions vs NSS

Balanced salt solutions aren’t used in TBL because they are slightly hypotonic, and RLS isn’t used in acute/chronic liver disease

Hypotonic crystalloids

• What are they

• 0.45% NaCl

0.45% NaCl

• Other name

• Concentration of solutes

• Acidic or basic, and why?

• 1L distribution in the body

• Main indication

• NSS/2

• Na+ 77, Cl- 77, Osm. 154, pH about 5

• Mildly acidifying

• Think of it as 500 mL normal saline, 500 mL free water

  • 500 mL normal saline stays in the ECF, ¼ to IVF(125mL), ¾ to ISF(375mL)

  • 500 mL free water goes 2/3 ICF(333mL), ¼ x 1/3 goes to IVF(42mL), ¾ x 1/3 goes to ISF(125mL)

• Hypovolemic hypernatremia(Aka patients lost Na+ and water, but relatively more water), DKA/HHS, diuretic phase of ATN

Why can we replace IV sterile water with IV 0.45% NaCl?

Because it is also hypotonic but it doesn’t cause hemolysis

0.45% NaCl side effects

1. Hyponatremia → free water lowers serum sodium

2. Interstitial edema

Main types of dextrose solutions

Named with concentration of dextrose followed by the base fluid

• D5, 10, 25, 50 + NSS, NSS/2, W(water)

How much dextrose is considered high osmolarity?

• 25% and 50% dextrose

How would 1L of D5W be metabolized, and what about the other types?

• Firstly, the dextrose is immediately metabolized, so it leaves just free water, which moves by osmosis

• 2/3 will go to the cells → 667 mL ICF

• 1/3 will go to the ECF → 333 mL ECF

  • ¼ of 1/3 to IVF = 83mL

  • ¾ of 1/3 to ISF = 250mL

• The other types will just follow their bases, so NSS would go ¼ plasma, ¾ interstitium, none into cells

How much mOsm/L is too high, and what does that mean?

900-1,200 mOsm/L is too high, and here we shouldn’t give IV to peripheral veins and we should instead give it to central veins, inserting via IJV, subclavian vein, femoral vein, and basilic veins and released at the SVC/IVC(if femoral), and if it’s at the SVC, we make sure that the tip stays above the level of the lower border of right main bronchus

Cases where dextrose would be used

1. Hypoglycemia

2. Hyperkalemia treatment: with insulin to prevent hypoglycemia

3. Maintenance fluid in NPO patients and patients who need parenteral nutrition

4. Hypernatremia: We want to give free water, but that’s dangerous, so we give it with dextrose

Dextrose side effects

• Hyperglycemia

• Hypokalemia: insulin activates Na+K+ATPase

• Hyponatremia

• Polyuria

• Catheter related bloodstream infections

Calculating maintenance fluid requires what formula, and what does this formula tell us?

Holiday-Segar formula: How much fluid to give

Holiday-Segar formula

• Try it on a 60kg patient

0-10kg: 100 mL/kg

10-20kg: 1,000mL + 50mL/kg for each kg above 10 kg

20kg+: 1,500 mL + 20mL/kg for each kg above 20kg

Use the third version: 1,500 + 20 × 40 = 2,300mL

• He needs 2,300mL fluid per day, so /24 is 96mL per hour

What do we do after the holiday-segar formula, and how do we do it?

We need to calculate how much sodium the patient needs, and how we fit in the volume of fluid we’re giving

• We need 2-3mmol/kg/day, so a 60kg patient would need around 120-180 mmol/day

• However, we aren’t done, because we need to convert that to concentration, which is mmol/volume. We also have to make sure the units are the same, because mmol is measured per liter, but volume we got via mL, so we have to do 120 to 180/2,300, which gives us mmol per mL, but then x1000 to get in L, so we get 52mmol/L to 78 mmol/L, and in this case, it fits the Na+ concentration of NSS/2

Once we have the volume of fluid and type of fluid, what do we do next?

We need to see if the patient is receiving enough energy. We need a range of 200-500 for protein sparing, so if we give D5/NSS/2, that would be 5g of dextrose per 100mL, and 1g of dextrose is 3.4kcal, which means that 100mL would be 17 kcal.

• We’re giving 2,300 mL, so it would be 17 × 23, which is 391, which fits 200-500.

What is something that should be assessed in a patient with hypoglycemia?

Their thiamine levels

What is the maintenance amount of glucose we should give after an IV bolus, and how much should a 60kg patient get, and what’s something we should consider?

2mg/kg/min, so a 60kg patient would have to get 2mg x 60, so 120mg per minute. In hours that would be 7200mg, but in grams that would be 7.2g/h and 173g a day.

• We need to consider that this has to get in via some fluid, and we want to make sure this fluid doesn’t exceed 3,000mL a day. If we give 5% dextrose, that would mean 5g per 100mL, aka 20mL per gram. To get 7.2 grams, we would do 7.2 × 20 and get 144 mL/h, and in a day that would be 3,456 mL, which is a dangerous amount (3000mL is dangerous).

• Instead we should give 10% dextrose, because that’s 10g per 100mL, aka 10mL of fluid per gram of glucose. To get 7.2 grams, we would only be giving 72mL fluid, and in a day, that would be 1.728k mL, a safe amount.

Hypertonic crystalloids

• What are they

• 3% NaCl

3% NaCl

• Concentration of solutes

• Acidic or basic

• Main indication

• Side effects

• 513 Na+, 513 Cl-, 1026 mOsm/L

• Acidic

• Symptomatic hyponatremia, raised intracranial pressure

• Hypernatremia, ODS(Brain adapts to hyponatremia and the resulting swelling by removing some of it’s solutes, so when we add too much hypertonic solution, we can’t bring in solutes in time, water rushes out of cells and this damages myelin)

ODS symptoms

1. Quadriparesis

2. Ophthalmoplegia

3. Altered consciousness

4. Numbness

Hyponatremia treatment

• Symptomatic: 3% NaCl

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What are some causes that cause euvolemic hyponatremia that aren’t SIADH?

1. Diuretics

2. Hypothyroidism

3. Adrenal insufficiency

Hypernatremia treatment

• Low ECF volume: Sodium and water lost, but water lost more than sodium → NSS/2 or D5W, isotonic saline if the pt. is in shock

• Normal ECF volume: Pt. lost just water, but because the water lost was from cells, it’s hard to tell.

  • If pt. is ADH responsive, they have central DI, so we give them DDAVP with NSS/2

  • If pt. isn’t ADH reponsive, they have nephrogenic DI, so we give NSS/2

• High ECF volume: Sodium was gained → remove sodium

HypoK+ treatment

• If pt. can eat: Elixir KCl or elixir M. potassium citrate(The latter for acidosis)

• If pt can’t eat: IV KCl

Things to watch out for during hypoK+ treatment

1. Shift cause: Rebound hyperK+

2. Low urine output: HyperK+ risk

Why do we not mix KCl with dextrose?

Because dextrose boosts insulin, activates Na+K+ATPase which pushes K+ into cells

DKA/HHS treatment

K+ levels are often overstated because no insulin causes K+ to leak out more(Less Na+K+ATPase activity), high plasma osmolality from glucose will pull water out of cells and K+ follows, and in DKA acidosis will swap out K+ for H+(to tuck H+ away into cells)

• If K > 5: Give insulin but not K+

• If K 3.5-5: Give insulin and K+ because potassium will be driven down from insulin

• If K >3.5: Give K+ but not insulin yet because we don’t want K+ to be too low

HyperK+ treatment

1. Calcium gluconate: To raise threshold potential and fix what high K+ did, given when ECG changes occur

2. Insulin with dextrose and Beta2 agonists: To boost Na+K+ATPase and push K+ into cells

3. Furosemide, dialysis, kalimate(Absorbs K+ into gut, but requires passing of stoll)

NaHCO3-

• Used in

• Side effects

• Metabolic acidosis

• Hypervolemia and hypernatremia(bc it’s very hyper tonic), metabolic alkalosis, hypocalcemia(More alkaline environment causes albumin to release H+, and Ca2+ binds albumin and we have less usable Ca2+), hypokalemia(H+ rushes out, K+ comes into cells), hypercapnia(More bicarb will turn into CO2 + H2O)

Acetazolamide

• Inhibits carbonic anhydrase → prevents bicarbonate reabsorption

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Why can we excrete bicarbonate better once volume and chloride is fixed?

Volume-depleted patient’s keep sodium because sodium holds volume. To keep sodium, the body boosts RAAS, which leads to more Na+ reabsorbed at the collecting duct, but this exchanges H+ out. And H+ out is reclaimed as bicarbonate. Not only that, Na+ is reabsorbed with Cl-(like with NKCC2 or NCC), so if there’s no Cl-, Na+ is reabsorbed with bicarbonate instead. And finally, the collecting duct usually get rid of bicarbonate by swapping bicarbonate for chloride, but we can’t do that if we have less Cl-.