VETN 227B: Fluid Therapy

What is TBW?

Total body water

How much is TBW of body weight? (In normal animals)

~60%

How much blood volume is in a dog?

80-90 ml/kg

How much blood volume is in a cat?

40-60 ml/kg

How much blood volume is in a horse?

80 ml/kg

Where do animals get most of their TBW?

Mostly from drinking

• Some from diet

• 10-15% from metabolism

What are the types of water losses?

1. Sensible

2. Insensible

What is sensible water loss?

You can physically see it

What are examples of sensible water loss?

• Urination - obligatory amt. of water in urine

  • Free water loss

What is insensible water loss?

You can’t really tell that water is being lost

What are examples of insensible water loss?

1. Fecal - obligatory loss → removes solutes in body

2. Respiration - panting

3. Cutaneous - sweat

4. Salivary - saliva (self-explanatory)

What does the body do to deal with water loss? (maintenance)

Maintain zero balance - keep water in when dehydrated, let water out when overhydrated

What are factors that help maintain that zero balance?

1. Determined from loss - sensible vs. insensible

2. Environment - hot areas vs. cool, watery areas

3. Activity - higher the activity, the more water

4. Disease - like polyuria, polydipsia

5. Diet - solutes produced from diet

How much water is lost from sensible water loss?

~67%

How much water is lost from insensible water loss?

~33%

What is daily water requirements for adult dogs?

~60 ml/kg/24hrs (1d)

What is the daily water requirement for adult cats?

~45-50 ml/kg/24hrs (1d)

What is the daily water requirements for neonates?

~70 ml/kg/24hrs (1d)

What are the TBW fluid compartments?

1. Barrier - cell membranes → keeps everything separate

2. Intracellular (ICF)

3. Extracellular (ECF)

About how much of BW (body weight) does ICF make up?

30-40% of BW

About how much of BW does ECF make up?

16-20% of BW

What are the compartments of ECF?

1. Barrier → vascular endothelium (which has blood)

2. Interstitial (ISF) - b/w the cells (~14% BW)

3. Plasma (IVF) - intervascular fluids (~5% BW)

4. Transcellular - moves across cells (~1% BW)

5. Blood (RBC, WBC) - 2% BW

Which substance can pass through cell membranes and how do they do it?

Water via concentration gradients and osmotic pull

What CAN’T pass through cell membranes and what do they do instead?

1. Electrolytes → active transport like Na+/K+ pumps

2. Colloids

How do colloids stay inside fluids?

Plasma expanders - synthesized by albumin in liver which keeps fluids in

If albumin is missing, what will happen to fluids?

No osmotic pull → liquid leaves/leaks out of compartments → dehydration (something like that?)

Which compartment is affected first when introducing fluids?

ECF plasma (extracellular fluid) - b/c of blood vessels (plasma) → doesn’t last too long

Which direction does water go across a semipermeable membrane?

It goes towards the side that has more solutes

• Follows a concentration gradient

• Does this in order to balance tonicity - solutes vs. water

If a cell was in an isotonic solution, where would water go?

It would be even and there wouldn’t be any water movement

If a cell was in a hypertonic solution (meaning more solutes in the solution), where would water go?

It would exit the cell into the solution, which would shrivel up the cell

If a cell was in a hypotonic solution (meaning less solutes in the solution), where would water go?

It would enter the cell because there are more solutes in the cell than the outside solution, causing water to rush in and expand the cell

What are the ECF electrolytes?

Na+ (sodium), Cl- (Chloride), HCO3- (bicarbonate ion)

What are the ICF electrolytes?

K+ (potassium), Mg2+

What can Na+ and K+ pass through the cell membrane with?

Sodium-potassium pump (Na+-K+- ATPase pump)

Does Na+ and K+ pass through equally?

No → 3 Na+ out, 2 K+ in

What does Na+ and K+ passing through the cell membrane do?

It creates an electrical difference (more negative outside, positive inside) → Maintains electrical potential at -70 mV (which contributes to muscle contraction)

What systems regulate water levels?

1. Endocrine - pituitary gland

2. Kidneys (Renal)

How does the pituitary gland regulate/maintain water balance?

Releases ADH (antidiuretic hormone) if osmolality changes

If osmolality increases… (meaning more solutes, and less water in body)

ADH is increased → leads to less urination → water is retained in the body → [urine] is increased (bc of solutes)

If osmolality is decreased… (which means less solutes, and more water in body)

ADH is decreased → leads to more urination → water is not retained and they can urinate more → [urine] is decreased (b/c less solutes)

What does ADH mean and do?

Antidiuretic hormone - keeps water in the body, less urination

What do the kidneys do to maintain water balance in the body?

Releases renin (hormones)

If low blood flow is detected, what does the kidney do?

Releases renin → releases more hormones and eventually aldosterone (adrenal gland) → keeps Na+ in the body → H2O is conserved in the body → increases thirst so you can drink water and increase blood volume (blood flow)

If an animal is dehydrated and lost 12-15% of water, they are considered…

In shock - lack of perfusion

What are the types of loss?

1. Primary H2O

2. H2O and electrolyte*

3. Blood loss - blood is 5% of BW

What is primary H2O loss?

Increased excretion of urine/water

What are some causes of primary H2O loss?

1. DI - diabetes insipidus (either affects CNS or renal)

2. Renal failure

3. Lack of intake - not drinking enough water

What is the most common type of loss?

H2O and electrolyte loss

What are some clinical conditions of water and electrolyte loss?

• Vomiting

• Diarrhea

• Wounds

• Burns

• Ascites - fluid in abdomen

• Peritonitis - peritoneal surfaces are inflammed

What electrolytes are lost in some clinical conditions of water/electrolyte loss?

• Vomit - Cl-

• Diarrhea - combo of Na+, Cl-, K+

• Wounds - Na+ (anything in the ECF space)

• Burns

• Ascites

• Peritonitis

What are the parts of blood loss?

1. External - visible

2. Internal - fluid is not where its supposed to be

   1. Thoracic or Abdominal

3. Isotonic - has [concentration] similar

What problems lead to Na+ loss?

1. Vomit, diarrhea

2. Addison’s → hypoadrenocorticism → Na+ is decreased, K+ is increased

3. Renal disease

What problems lead to Cl- loss?

1. Vomit

What problems lead to K+ loss?* (pretty important)

• Anorexia, vomit

• Cushing’s → hyperadrenocorticism → low K+

• Diabetes mellitus (Type 2)

What problems lead to HCO3- loss? (bicarbonate ion)

• Diarrhea

What are some clinical problems when it comes to K+ abnormalities?

• Heart rhythm*

• Acid-base

• Muscle

• Kidney

How should you treat K+ problems? (clinical therapy)

1. Hyperkalemia - high K+ → avoid any K+

2. Hypokalemia - low K+ → add K+

What are some low K+ problems when it comes to muscles?

1. <3.0 mEq/L weakness (in muscles)

2. <2.0 mEq/L → rhabdomyolysis - skeletal muscle breakdown

What are some low K+ problems when it comes to the heart?

ECG anomalies

What are some low K+ problems when it comes to acid-base levels?

Acidosis - HCO3- levels changes (bicarbonate ions will decrease, thus pH will decrease)

What are some low K+ problems when it comes to kidneys?

Hypokalemic nephropathy - kidneys are bad

What are some high K+ problems when it comes to muscles?*

If >8.0, leads to weakness

What are some high K+ problems when it comes to the heart?*

Severe arrhythmia - heart gradually slows down and leads to death

How do you determine hydration status?

Rough estimate only

What are some things to consider when it comes to taking a history of hydration status?

1. Duration of the problem - acute vs. chronic

2. Anorexia - 0.1-0.3kg/24hr/1000kcal → typically less than fluid loss (anorexia contributes less to weight loss than fluid loss, meaning losing fluids will lead to more weight loss)

3. Vomit + Diarrhea - ~4ml/kg per ep of vomit/diarrhea

When figuring out how much fluids to give, what are the 3 main things you should know?**

1. Maintenance (#ml/kg/24hrs (1d))

2. Hydration deficit

3. Ongoing/contemporary losses - vomit/diarrhea

1L of water is equal to…

1kg

480 mL is equal to…

1lb

<5% of dehydration status is…

Undetectable

5-6% dehydration is…

Subtle loss of elasticity

6-8% dehydration is…

Mild skin tenting (mostly around eyes), sometimes increased CRT, sometimes sunken eyes

9-12% dehydration is…

Decreased* turgor with prolonged tenting, increased CRT, dry MM, sunken eyes, may have shock signs

12-15% dehydration is…

Shock/near death - emergency

When should you take lab examples when administrating fluid therapy?

Before therapy*

What happens to PCV when taking a lab example before administrating fluids?

1. Plasma loss → Increased PCV (which means more RBC)

2. Evaluate PCV with TP - check for albumin, immunoglobulins

What happens to TP when taking a lab example before administrating fluids?

Generally increases b/c of albumin

What happens to USG when taking a lab example before administrating fluids?

Usually increases → >1.040 b/c there are more solutes than water in urine

What is the normal urine output of an animal?

1-2 ml/kg/hr

• Usually decreased if dehydrated

What is CVP?

Central venous pressure

How is CVP measured and what is the normal amount?

Measured using a water manometer

Normal: 0-3 cm H2O

• If >3cm = overhydrated, should never be >10-12 cm H2O

What could help treat shock?

Hypertonic solutions - causes water to stay in the body

Colloids - keeps water in compartments (I think…)

What is pH?

Measurement of H+

What is considered neutral?

pH = 7

What is considered acidic?

pH < 7

What is considered alkaline?

pH > 7

What is the body’s normal range in pH?

7.35-7.45 - very miniscule difference

What is acidosis?

pH < 7.35

Can be life threatening*

What is alkalosis?

pH > 7.45

What causes acid production? (H+ production)

Metabolism of proteins, phospholipids, and CO2

What systems control pH?

1. Renal - Kidneys

2. Respiratory

3. Buffers (internal) - substances that give up/accept protons (H+)

What does the kidneys (renal system) do to maintain acid-base levels?

Regulates HCO3- (bicarbonate ions)

What does the respiratory system do to maintain acid-base levels?

Regulates CO2 levels by the H-H equation

If CO2 levels increases, it leads to…

Acidosis - high CO2 → high H+ → more acidic

If CO2 levels decreases, it leads to…

Alkalosis - low CO2 → low H+ → less acidic OR more alkaline

What are buffers?

They accept/donate H+

What are the types of buffers?

1. HCO3- (bicarbonate ions) - via kidneys

   1. Are the primary buffer in ECF

2. Proteins → Hemoglobins

3. Phosphates - urinary

What is metabolic acidosis?*

Where there is less HCO3 in the plasma → increase of H+ → decrease of pH (<7.35) → more acidic in the body

• Most common

What is metabolic alkalosis?

Increase of HCO3 in the plasma → decrease in H+ → increase in pH (b/c less acidic) (>7.45) → more alkaline in the body

What is respiratory acidosis?

Increase in CO2 → b/c animal is not breathing enough → increase in H+ → low pH → more acidic in the body

What is respiratory alkalosis?

Decrease in CO2 → b/c animal is breathing too much → decrease in H+ → high pH → more alkaline in the body