T&P: Fluid Therapy

What is the average total body water content in animals?

60%

What is the average total body water content in neonates?

80%

Which fluid compartment contributes the most to total body water?

Intracellular fluid

How does increased body fat affect total body water percentage?

It decreases total body water percentage.

What are examples of sensible (measurable) fluid losses?

Urination, emesis (vomiting), and diarrhea.

What are examples of insensible (not measurable) fluid losses?

Sweating and fluid loss during respiration.

In which species is sweating a significant source of fluid loss?

Horses

Hypovolemia

Loss of intravascular fluids.

Dehydration

Other forms of fluid loss.

Skin Turgor Note

For horses and some dogs, check at the point of the shoulder, not the neck.

Objective Checks for Hydration Status

Packed Cell Volume (PCV), Plasma Protein, and Urine Specific Gravity. (All three usually elevated in dehydration.)

Anemia Note

Anemic patients may appear hydrated if PCV is low and body water is low. Always check PCV with total protein.

Subjective Checks for Hydration Status

Skin turgor, MM (mucous membrane) status, Sunken eyes, Approximate water intake and urine output (PUPD) & urine color, Tachycardia

What are the three primary components used to calculate total fluid requirements?

Maintenance fluid rate, fluid deficit, and ongoing losses.

What is the formula for the maintenance fluid rate in dogs?

132 x bodyweight(kg)^0.75 or 60 ml/kg/day.

What is the formula for the maintenance fluid rate in cats?

80 x bodyweight(kg)^0.75 or 40 mL/kg/day.

What is the simplified rule of thumb for maintenance fluid rates in dogs?

2-6 ml/kg/h.

What is the simplified rule of thumb for maintenance fluid rates in cats?

2-3 ml/kg/h.

How do you calculate the volume of a fluid deficit?

Weight (kg) x percent dehydration (as a decimal) = weight loss (kg); then multiply weight loss (kg) by 1000 ml/kg.

Provide two examples of ongoing fluid losses that should be accounted for.

Excessive urine volume, fluid-soaked bandages (can be measured)

Vomiting, diarrhea, wounds (can be estimated)

Over what time period is the total fluid volume (maintenance + deficit + ongoing) typically administered?

A 24-hour period.

What is the shock fluid rate for dogs?

80-90 ml/kg.

What is the shock fluid rate for cats?

50-55 ml/kg.

What is the recommended procedure for administering a shock bolus?

Administer a 25% bolus rapidly, evaluate the patient, then provide subsequent 25% boluses as needed.

At what point in shock fluid administration should you consider adding a colloid?

If there is no favorable response after 50% of the shock dose has been administered.

What is the traditional timeframe for administering a shock fluid bolus?

Over one hour.

What does parenteral fluid administration mean?

Administration by injection.

When is parenteral fluid administration useful?

For low dehydration rates.

What are the advantages of SQ (subcutaneous) fluids compared to drinking?

They are more effective than drinking, though they are slower than IV fluids.

What are the primary benefits of IV (intravenous) fluids?

They are quicker and more precise than other methods.

Osmolality

Ability of a fluid to 'pull in' water (oncotic pressure).

Two Kinds of Solutions

Colloids and Crystalloids.

Crystalloids

Most commonly used fluids classified as hypotonic, isotonic, and hypertonic.

Isotonic Crystalloids

Sodium content and osmolality close to ECF (approx. 300mOsm/L in dogs/cats).

Examples of Isotonic Crystalloids

0.9% saline, lactated ringers.

Administration of Isotonic Crystalloids

Can be given rapidly in large volumes; about 80% moves into interstitial compartment within 1 hour.

Uses of Isotonic Crystalloids

Works well with V/D, pancreatitis, shock, IBD.

Caution with Isotonic Crystalloids

Renal and cardiac disease (sodium can compromise function).

Hypotonic Crystalloids

Na and osmolality less than ECF, pulls fluid out of vasculature strongly.

Uses of Hypotonic Crystalloids

Used when sodium retention is a problem, or in DKA.

Examples of Hypotonic Crystalloids

0.45% saline, 2.5% dextrose.

Hypertonic Crystalloids

Osmolality greater than ECF, pulls fluid into intravascular space from ECF and intracellular space.

Caution with Hypertonic Crystalloids

Very cautious use, as they are dehydrating.

Uses of Hypertonic Crystalloids

Used for hypovolemia, sometimes for intracranial edema (though colloids are typical).

Examples of Hypertonic Crystalloids

7.5% NaCl.

Administration of Hypertonic Crystalloids

Can be used in very large dogs when isotonic fluids are insufficient for severe hypovolemia.

Use of Colloids

Mostly for hypovolemia not from dehydration, hypoalbuminemia, septic shock.

Colloids for Edema

Great for edema and head trauma (hypertonic saline, 23.4%, reduces intracranial pressure and improves cerebral blood flow).

Caution with Colloids

Very dehydrating.

Examples of Colloids

• Synthetic (Hetastarch, Vetstarch, Turbo starch),

• Natural (Blood Products)

Synthetic Colloids

Vetstarch, hetastarch, turbo starch (colloid + 23.4% saline in 2:1 ratio).

Hetastarch

Hydroxyethyl starch

Vetstarch

Smaller molecular weight, higher rate, can reduce vascular inflammation. (Now commonly used)

Plasma Volume Expansion

Vetstarch expands plasma volume for 12-36 hours (preferable to Dextrans, which last 4-8 hours and are expensive).

Natural Colloids

Blood Products: FFP (Fresh Frozen Plasma), PRBC (packed red blood cells), whole blood, Albumin.

Hetastarch Issues

Volume overload, coagulopathy, hypersensitivity reactions (Type III), AKI and Hetastarch

Coagulopathy

Hetastarch prolongs PT, PTT, bleeding times; lowers fibrinogen, clotting factor VIII.

Hypersensitivity Reactions

Type III reactions associated with Hetastarch.

AKI and Hetastarch

Conflicting studies; best to use in critically ill animals without underlying renal insufficiency.

Albumin

Primary natural colloid.

Fresh Frozen Plasma (FFP)

Contains all blood clotting factors.

Frozen Plasma (FP)

FFP becomes FP when refrozen. Does not contain factor V or VIII.

Whole Blood

• Indicated for rapid decrease in hematocrit or signs of anemia (blood loss anemia).

• PRBCS

• Stored blood contains anticoagulant that precipitates calcium

• Contains factors 2, 7, 9, 10

PRBCs

Used for pure red cell loss.

Stored Blood Complications

Hypocalcemia can be a complication with multiple transfusions.

The Pain Pathway

1. Transduction

2. Transmission

3. Modulation

4. Perception

Transduction

Stimulus of sensory nerve endings (nociceptors) translates physical stimulus into excitation. Local anesthetics can block this.

Transmission

From stimulated receptor to sensory nerve, carrying it to the spinal cord. Nerve blocks can interrupt.

Modulation

Transmission up spinal cord to the brain. Body produces neurotransmitters to dampen (or amplify) signal. Epidural blocks this.

Perception

Pain impulse reaches conscious level in the brain. Recognition.

How can pain progress?

Pain can progress from acute focal to diffuse throbbing.

How does the inflammatory process start?

Inflammatory process starts after trauma, making adjacent pain receptors more sensitive.

Hyperalgesia

Increased sensitivity to potentially painful stimuli.

Hyperesthesia

Increased sensitivity to any stimuli.

Allodynia

Pain due to a stimulus that does not normally provoke pain.

What reduces receptor sensitivity post-trauma?

Decreasing inflammation post-trauma can reduce receptor sensitivity.

Wind-Up

• Process of increasing success in transmitting pain up spinal cord, leading to increased pain intensity over time.

• Combination of hyperalgesia and allodynia

Hyperalgesia

Increased sensitivity to pain.

Allodynia

Pain due to a stimulus that does not normally provoke pain.

Spinal Cord Modulation

The spinal cord effectively transmits pain, initially dampening occurs, but over time this dampening reduces.

Importance in Surgery (Wind-Up Phenomenon)

Unconscious animal still experiences spinal cord modulation via wind-up, leading to higher pain perception upon waking.

What medications prevent wind-up, improving post-operative recovery?

Analgesics/Anti-Inflammatories

What is most potent pain relieving drugs in veterinary medicine?

Opioids

Opioids

Most potent pain-relieving drugs in veterinary medicine.

Analgesics (Opioids)

Relieve pain sensation.

Opiates

Derived from poppy seeds.

Narcotics (Opioids)

Can be used with anesthetics (reducing anesthetic amount needed) or alone.

Controlled Substances

Schedule I-V, depending on medical use, misuse risk, and dependence likelihood.

Types of Opioids

endogenous and exogenous

Endogenous

Produced by the body (e.g., Endorphins = Endogenous Morphine).

Exogenous

Introduced to the body.