Lecture 3: Electrolytes and Fluid Balance II

Question 1

What organ maintains sodium intake and output?

Answer 1

Kidneys

Question 2

Where do we gain sodium?

Answer 2

Diet

Question 3

How do we loose sodium?

Answer 3

Kidneys, sweat, faeces, urine

Question 4

What controls urinary output of sodium?

Answer 4

Aldosterone

Vasopressin

Atrial natriuretic peptide

Question 5

What secretes aldosterone? Why?

Answer 5

Adrenal cortex (glands on top of kidneys)

In response to changes in the volume of the ECF compartment

Question 6

What does aldosterone do?

Answer 6

stimulates the reabsorption of sodium ions in the kidneys in exchange for potassium and hydrogen ions, which are excreted in the urine

Question 7

What secretes atrial natriuretic peptide? What does ANP do?

Answer 7

secreted by cells in the right atrium of the heart

increases urinary sodium excretion.

Question 8

Regulation of electrolytes and fluid in the kidneys

Answer 8

(see figure)

Question 9

What is Hyponatraemia?

Answer 9

Sodium concentration less than 135 - 145 mM

Caused either because of sodium loss or water retention

Patients don’t usually show peripheral edema

Question 10

What diseases cause loss of sodium?

Answer 10

Renal tubular necrosis

Gastrointestinal loss due to diarrhea, vomiting, and intestinal fistulae.

Aldosterone deficiency

Drugs that affect aldosterone action/secretion

Question 11

What causes water retention?

Answer 11

Deficiency in water excretion (drug induced, over secretion of vasopressin, trauma, surgery)

Infusion of intravenous hypotonic solution

Compulsive water intake (very rare occurs when there is dehydration followed by increased intake of water)

Question 12

What is hypernatraemia?

Answer 12

Sodium above 145 mM

Question 13

Causes of hypernatraemia

Answer 13

Water loss from decrease intake or excessive loss (comatose, elderly patients not eating well)

Deficiency in vasopressin secretion or action

Sodium gain or salt poisoning (high intake of sodium feed, sodium bicarbonate to correct for acidosis or drowning in salt water)

Hyperaldosteronism (Conn’s syndrome; over secretion of aldosterone)

Parenteral infusion of hypertonic sodium solution

Excessive sweating, vomiting, and diarrhea where more water is lost than salt (rarely this happens!)

Question 14

What does sodium depletion cause?

Answer 14

loss of osmotic pressure of the ECF, and hence loss of water.

This results in low blood volume (hypovolaemia) and blood pressure

Question 15

What is tachycardia usually accompanied by?

Answer 15

Low blood volume and low blood pressure

Question 16

Clinical symptoms of sodium depletion

Answer 16

Weakness, dizziness, and general tiredness

Renal failure can result due to low glomeruli pressure due to hypotension in the kidneys, oliguria (low urine output usually less than 400 mL/24 h), and tachycardia ( the heart beats faster to correct for the low
blood pressure).

Question 17

Symptoms of excess sodium

Answer 17

Related to increase in osmotic pressure in ECF, leading to expansion of ECF

Peripheral edema

decrease in ICF (water moves from ICF to ECF)

Hypertension

Venous congestion

Weight gain

Difficulty breathing (edema creates pressure)

Question 18

How is ingested potassium excreted?

Answer 18

Mostly by the kidneys

Some through the faeces

Small amount through sweat

Question 19

Normal concentration of serum potassium

Answer 19

4.5 mM (even small variation of water amount can change concentration significantly)

Question 20

What is cellular uptake of potassium stimulated by?

Answer 20

Insulin

**MAKE SURE TO ALSO GIVE PATIENT GLUCOSE OR ELSE THEY WILL BECOME HYPOGLYCEMIC

Question 21

Relationship between K+ and H+

Answer 21

Reciprocal relationship to maintain electrical neutrality

Question 22

Hyperkalemia

Answer 22

is associated with acidosis

hydrogen ions is taken up into the cells (ICF) and potassium is displaced from the cells into the ECF (it increases in concentration in the ECF)

Question 23

Hypokalaemia

Answer 23

is associated with alkalosis;

hydrogen is displaced from the ICF into the ECF; in contrast potassium is taken up into the ICF from the ECF (concentration of potassium decreases in the ECF).

Question 24

K+ conc. for hypokalemia

Answer 24

below 4 mM

Question 25

Why does hypokalemia arise?

Answer 25

1. Gastrointestinal losses (vomiting, diarrhea, fistulae) 2. Renal tubular disease 3. Administration of hypotonic solutions 4. Increased aldosterone (more sodium reabsorption means more K+ and H+ excretion) 5. Drug 6. Alkalosis (can result in movement of K+ frrom ECF to ICF

Question 26

K+ concentration for hyperkalemia

Answer 26

K+ exceeds 5 mM

Question 27

Reasons for hyperkalemia

Answer 27

1. Renal failure (glomerular filtration is low) 2. Deficiency in aldosterone secretion or action or aldosterone agonists (sodium reabsorption and K+ excretion are reciprocal) 3. Acidosis (movement of K+ from ICF to ECF to maintain electrical neutrality) 4. Potassium release from damaged cells (bone damage and fractures, muscle crush injuries)

Question 28

What does potassium depletion cause?

Answer 28

Hyperpolarization of excitable membranes, which causes: Decreased excitability of membranes Irritability Shallow respiration Confusion and Drowsiness Disturbances in neuromuscular activities: muscle weakness, lethargy, and irregular heart rate (arrhythmias), tachycardia (fast heart rate). Decrease bowel movements, resulting in constipation; decrease in nausea and vomiting in contrast to hyperkalemia. Alkalosis

Question 29

Why is hyperkalemia so dangerous?

Answer 29

Increases RMP, which is very dangerous for the heart

Question 30

Other signs of hyperkalemia

Answer 30

Decrease cardiac contractility Dysrhythmias (irregular rhythm of heart rate) Irritability & anxiety Muscle twitches and cramps Diarrhea, abdominal cramping, nausea and vomiting Low blood pressure  Acidosis

Question 31

Management of Hyperkalemia

Answer 31

IV insulin (promotes uptake of K+) IV glucose (so that patient doesn't become hypoglycaemic due to insulin) Bicarbonate solutions for acidotic patients (to neutralize acid) Renal dialysis (gets rid of potassium)

Question 32

Causes of electrolyte and fluid imbalance

Answer 32

1. Hormonal imbalance 2. Adverse drug effects 3. Cancer 4. Disease of the Kidneys 5. Water retention 6. Water loss 7. IV hypertonic/hypotonic solutions

Question 33

Guidelines for IV fluid therapy to correct imbalances

Answer 33

1. Clinically assess the primary cause for the imbalance 2. Assess the biochemical reason for this imbalance. 3. Pay particular attention to cardiac, renal, and liver functions.

Question 34

What are patients with hyponatraemia and edema likely to show in chronic state?

Answer 34

Water and sodium overload

Question 35

What is the usual cause of hypernatraemia?

Answer 35

Water loss because patients are unable to drink as well as insensitive loss of water through breathing and the skin

Question 36

Best treatment for hypokalemia

Answer 36

IV of potassium solution, take care not to cause hyperkalemia