Total Body Water (TBW) & Isotonic Fluids

Total Body Water (TBW)

• Males have approximately 60% TBW, while females have around 50% due to more fat
• Elderly individuals tend to have less water content because of decreased muscle mass and increased fat, making them more susceptible to dehydration
• Extracellular fluid (ECF) constitutes 1/3 of TBW and is further divided into plasma volume (1/4) and interstitial fluid (3/4)
• Intracellular fluid (ICF) makes up 2/3 of TBW and is the majority of the total body water

Isotonic Fluids

• Isotonic fluids have the same tonicity as blood
• 0.9% NaCl is a common isotonic solution
• Administering an isotonic fluid results in the fluid distributing into the extracellular space, with only 25% (250ml) entering the intravascular space (vessels) and 75% (750ml) going into the interstitial space
• Isotonic fluids may cause fluid overload in the interstitial space, requiring diuretics like Lasix to remove excess fluid
• Isotonic solutions should be administered even with dehydration to increase vascular space.
• Hypotonic solutions go into the cells.

Hypotonic Fluids

• Hypotonic fluids, such as 0.45% NaCl, are used to treat cellular dehydration
• 333ml of 0.45% NaCl administered, 83ml goes into IV space
• 0.45% NaCl (333ml) goes into majority of extracellular fluid (ECF)

Fluid Intake

• Average fluid intake
• 1300 mL from ingested fluids
• 1000 mL from water in foods
• 300 mL from oxidation

Fluid Loss

• Sensible fluid loss: fluid loss that can be seen, such as urine and feces
• Insensible fluid loss: fluid loss that is not easily seen, such as respirations and sweat
• Abnormal fluid loss: loss from fever, burns, hemorrhage, rapid breathing, emesis, fistulas, secretions, paracentesis, and thoracentesis

IV Fluids (Crystalloids)

• Isotonic fluids: increase intravascular volume and blood pressure
• Examples include 0.9% Saline (normal saline) and Lactated Ringers (contains K, Na, and other electrolytes)
• Hypotonic fluids: cause fluid to shift into the cells
• 0.45% Saline increases intravascular volume and correct free water deficit
• Best IVF for patient with dehydration unless hemodynamically unstable
• D5W is rapidly taken up by cells leaving only free water, therefore, it replaces free water deficit or hypoglycemia

Hypertonic fluid

• 3.0% Saline treats severe symptomatic hyponatremia and cerebral edema

Osmotically Active Substances

• Plasma proteins, especially albumin, help hold fluid in the vascular space
• In conditions like burns, malnutrition, or liver disease, inadequate albumin can cause fluid to leak into tissues, leading to shock
• Fluid accumulates in the interstitial space rather than the intravascular space
• Fluid volume in excess because they are so swollen from fluid accumulation in the tissues
• In the INTERSTITIAL SPACE not the INTRAVASCULAR SPACE
• Glucose is osmotically active and draws water out of the ICF into the ECF
• High blood sugar increases glucose particles compared to water in the vascular space
• Particle-induced diuresis (PID), hypergylcemia sometimes called osmotic diuresis occurs, leading to fluid loss
• The kidneys continue to filter the blood to decrease glucose, resulting in hypovolemia and shock.

Hormones Role on Electrolytes

• Insulin moves potassium from the blood to the inside of the cell, thereby decreasing serum potassium levels
• Always check potassium levels before administering insulin
• Parathyroid hormone (PTH) decreases calcium levels, increases phosphate excretion in urine.
• PTH increases calcium from the bone while decreasing calcium excretion
• When there is hypocalcemia, the parathyroid recognizes it and increases PTH from the bone
• Calcitonin increases calcium levels, thus, decreases calcium from the bone
• When the thyroid hormone recognizes increase calcium, calcitonin is secreted for increase calcium
• Aldosterone increases sodium retention and increases so kidneys hold onto sodium
• Block aldosterone with ACE inhibitors and ARBs causes a decrease in sodium and increase in potassium.
• ADH (antidiuretic hormone) relates directly to water.
• ↑ Osmolarity or↓ Blood Volume activates hypothalamus and↑ ADH from the Posterior Pituitary = ↑ Free water Reabsorption in collecting tubules = ↑ Circulating volume & ↓ Na Concentration.

Electrolytes and Insulin

• When administering insulin, especially IV insulin, watch the serum potassium level. It can drop, thus leading to life threatening arrhythmias.
• The only kind of insulin that can be given IV is regular insulin.
• Anytime serum calcium increases the phosphorus level decreases, and vice versa.

Sodium

• The amount of total body sodium is proportional to volume status
• Chief electrolyte in ECF
• Assists with nerve impulse generation and transmission
• Excess sodium is excreted by the kidneys
• Normal adult sodium level is 135 to 145 mEq/L

Hyponatremia

• Defined as serum sodium less than 135 mEq/L
• Commonly due to excess free water, but can also be due to decreased total body sodium
• Multiple causes, and the first step is to determine the cause
• Evaluation should include urine sodium, serum osmolality, and clinical status

Isotonic Hyponatremia

• Lab artifact

Hypotonic Hyponatremia (serum osmo < 280mOsm/kg)

• Hyponatremia and hypotonicity
• Low sodium and low osmolality, most common
• State of body water excess diluting all body fluids: clinical signs arise from water excess)
• Must assess if patient is hypovolemic or hypervolemic
• Hypovolemic with urine Na+ < 10 mEq/L results in Dehydration, Diarrhea, Vomiting
• Hypovolemic kidneys cant conserve Na with Urine Na+ > 20 mEq/L causes most common diuretics such as decreased aldosterone
• Decreased aldosterone causes Sodium and water are excreted while potassium is retained

Hypervolemic, hypotonic hyponatremia

• Excessive administration of D5W dilutes the sodium level
• Psychogenic polydipsia is excessive, rapid oral intake of fluids
• CHF causes the kidneys to keep water
• Liver Disease and Advanced Renal Failure causes
• Syndrome of inappropriate ADH ↑ ADH → ↑ Free water → ↓ Na concentration

Hypertonic Hyponatremia (serum osmolality > 290 mOsm/kg)

• Low sodium high osmo
• Hyperglycemia
• Usually form HHNK

Signs and Symptoms of Hyponatremia

• Lethargy and confusion due to cerebral edema
• It can lead to seizures, coma and death
• Muscle weakness due to decreased excitability of cell membranes
• Decreased deep tendon reflexes (DTRs) (Decreased excitability of cell membranes)
• Diarrhea due to increased GI tract motility
• Respiratory problems, late symptoms
• Muscle weakness leads to Respiratory Failure

Treatment of Hyponatremia

• Determine the cause: low sodium intake/extreme loss of sodium, or excess water diluting the serum sodium
• Acute hyponatremia must be corrected acutely (24-48 hours)
• Chronic hyponatremia must be corrected slowly
• Overly rapid correction can lead to serious brain injury (osmotic demyelination syndrome)
• Excess free water cause: fluid restriction (1L a day)
• Sodium wasting cause: 0.9% or 3.0% Saline
• Neuro symptoms and resp arrest cause aggressive treatment w/ aggressive treatment with 3% NaCal

Sodium Correction

• Avoid rapid correction of sodium.
• Want to increase NA in 24 houurs by about 5-8 points in a 24 hour period.
• 5-8 only!!!! will get osmotic demyelination
• <200 ml of urine output in 2 hours

Higher Sodium Concentrations

• End stage renal disease will get fluid restriction and dialysis
• Cirrhosis will get albumin because liver makes albumin and pt doesn’t have ability to make albumin so synthetic albumin

Hypernatremia

• Serum sodium greater than 145 mEq/L
• Usually a lack of free water
• Signs and Symptoms: Tachycardia, Dry mucus membranes, Altered mental status, Increased thirst, Muscle hyperactivity or hypoactivity; Can lead to seizures, coma, death
• Causes
• Profuse sweating without water replacement (heat stroke, lost desert)
• Diarrhea and vomiting; NPO
• Diabetes Insipidus & SIADH water dumps. Know your labs. High sodium!!!

Treatment of Hypernatremia

• Lack of free water: treat with hypotonic fluids (0.45%) or free water
• Excess sodium: stop giving Na products
• Think BRAIN first
• Fatal effects when administering rapid sodium increase or decrease.

Potassium

• Makes skeletal and cardiac muscle work correctly.
• Chief electrolyte in ICF
• Plays a vital role in the transmission of electrical impulses.
• Food sources: peaches, strawberries, bananas, figs, dates, apricots, oranges, melons, raisins, prunes, broccoli, potatoes, and tomatoes.
• Excreted by the kidneys
• Stomach contains large amount of potassium Vomiting contributes to hypokalemia
• Normal potassium level: 3.5 mEq/L to 5.3 mEq/L.1

Hypokalemia

• Serum Potassium less than 3.5 mEq/L.
• Causes:
• Diuretics K excreted
• Steroids retain sodium and water and excretes potassium
• GI suction, Vomiting, and Diahrea removes potassium
• NPO status Kidneys lose potassium with age and causes low potassium
• Cushing syndrome retains sodium and water, therefore lossing K
• Alkalosis causes K to move into the cells dropping serum potassium Alkolosis= A lo K Signs and Symptoms of Hypokalemia
• Paralytic ileus
• Muscle cramps, muscle weakness
• EKG shows PVCs, V tach, V fib, flattened T wave, ST depression, and a U-wave

Treatment of Hypokalemia

• High potassium diet
• IV or oral potassium chloride increasing serum K
• Check kidney function
• PO Can cause GI upset
• If acidosis is present, correct K first to show correct lab values
• The amount of expected K increase is 0.5 mil equivalent for every 100 meq

Hyperkalemia

• Serum Potassium above 5.3 mEq/L
• S/S: Diarrhea, Muscle Twitching, Cardiac arrhythmia
• Causes
• Renal Insufficiency, IV KCl Overload, Burns or Crush injuries causing K excretion to be impaired.
• Tight Tourniquets
• Hemolysis of CBC sample
• Salt Substitutes
• K Sparring diuretics
• Blood Transfusions
• ACE Inhibitor
• Acidosis
• Addison’s Disease = Adrenal Insufficiency Treatments:

1. STAT EKG and Hold K retaining medications
2. Remove Excess K with Kayexalate PO or Rectal

• Veltassa and it binds the K and they urinate the K out

3. STABILIZE the Cardiac membrane with Calcium Gluconate
4. SHIFT THE K Intracellular with: a. IV insulin (10U) with D50 b. Sodium Bicarbonate (Alkalosis)will correct acidosis c. Albuterol
5. Dialyze if refractory or severe

Calcium

• Acts like a sedative on muscles at high levels
• Most abundant electrolyte in the body.
• Has an inverse relationship to phosphorus. (low ca high phos. High ca low phos)
• Necessary for nerve impulse transmission, blood clotting, muscle contraction, and relaxation.
• Promotes strong bones and teeth.
• Must have vitamin D present to utilize calcium.
• If blood levels of calcium decrease, the body takes calcium from the bones and teeth.
• S/S: Muscle Cramps Tetany, Convulsions, Arrhythmias Positive Chvostek’s Hyperactive DTRs Cardiac Changes (↑QT intervals, decreased myocardial contractility)

Hypocalcemia and Hypercalcemia

• Normal calcium: 9.0 to 11.0 mg/dL.

Causes Why Decreased Ca intake Renal Failure ↓ Vit D and ↑ PO4 (phos) which drives Ca into cells ↓ Vit intake (common in Ohio) Vit D is required to absorb Ca from the GI tract Diarrhea Ca is excreted in the GI tract Pancreatitis Ca combines with fatty acids in the pancreas Hyperphosphatemia ↑ PO4 drives Ca into the tissue Thyroidectomy. hypoparathyroidism Parathyroid may be accidentally removed Low albumin Causes falsely lowered Ca concentration

Hypercalcemia

• Immobilization Calcium, Ca, and Vit D increases Serum Calcium
• S/S: Decreased DTRs, Muscle weakness,Kidney Stones, Pathological fractures & bone pain Depression fatigue Confusion, Early cardiac changes, ,Constipation N&V Increases urine.
• Tx: Normal Saline. Loop diuretics

Phosphorus

• Promotes the function of muscle, red blood cells (RBCs), and the nervous system
• Food sources: beef, pork, dried peas/beans, cheese, shellfish, fish, pumpkin seeds. o Kidney failure, needs to be managed
• failure patients kidneys cant clear phos out so avoid these foods
• Has an inverse relationship with calcium. Regulated by the parathyroid hormone. Normal phosphorus Hypophosphatemia: Serum Phosphate < 2.5 mg/dL and inverse relationship.

Magnesium

Normal magnesium: 1.5 to 2.5 mEq/L.

Hyperactive Cardiac changes Majority of magnesium comes from our dietary intake S/S Drowsiness, Weakness and decreased respiration. Eacts Renal failure Antacids Loop diuretics