fluid therapy in wildlife rehabilitation

Fluid therapy in wildlife rehabilitationSarah Reich, DVM

Willowbrook Wildlife Center

Glen Ellyn, IL

Overview

• Brief physiology overview

• Types of fluids

• Assessing hydration/dehydration

• Calculating fluid requirements

• Dilutions

• Administration 3

Physiology• Water is pretty damn important - ~60-70% of

mammal weight

• Total body water =

• ~2/3 TBW = intracellular fluid (ICF)

• ~1/3 TBW = extracellular (ECF)

• Extracellular compartment = intravascular fluid (plasma) and interstitial fluid

• Electrolytes (sodium, chloride, potassium etc) and non-electrolytes (protein, glucose, oxygen, etc) are all dissolved in these fluids

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Physiology• Fluid volume is highly dependent on osmotically active

molecules (mainly Na)

• Cell membranes separate the ICF and ECF compartments

• Membranes allow water to flow through freely but are selectively permeable to other molecules

• Osmolarity = number of osmoles of solute per liter of solvent

• Osmolality = number of osmoles of solute per kg of solvent

• Tonicity = osmotic pressure between two compartments

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Physiology

• Within the intravascular space, proteins limit the movement of water between the vessel and interstitial space

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Physiology

• A body will always try to maintain homeostasis

• Normal fluid loss – urine, feces, sweat, breathing

• Normal fluid gain – food, water, metabolic products

• A normal body can maintain balance with general fluid intake (drinking, eating, absorption through mucous membranes, etc)

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Causes of fluid loss • Reduced intake

• Mentally inappropriate

• Stress

• Malabsorption

• Increased loss

• Hemorrhage (including during surgery)

• Vomiting or diarrhea

• Burns and large wounds

• Fever

• Decreased production of intravascular contents

• Starvation 10

Fluid TypesCrystalloids

Colloids

Crystalloids• Can be hyo-, iso-, or hypertonic

• Isotonic solution: electrolyte composition and pH closely mirror those of plasma in mammals and birds (~280 – 300 mOsm/L)

• Generally, only isotonic and hypertonic fluids are given in wildlife medicine

• Only one-third to one-quarter of the volume administered remains in the intravascular space after 1 hour because of redistribution thru the entire extravascular space.

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Isotonic fluids

LRS

Osmolality: 273

Includes: Na, Cl, K, lactate

Normosol-R*

Osmolality: 295

Includes: Na, Cl, K, Mg,

acetate, gluconate

Plasmalyte

Osmolality: 295

Includes: Na, Cl, K, Mg,

acetate, gluconate

NaCl 0.9%

Osmolality: 310

Includes: Na, Cl

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Crystalloids

• The lactate in LRS is metabolized by the liver (and converted to bicarbonate)

• Suboptimal for patients hepatic dysfunction

• Neonates are able to use lactate as a fuel source, making LRS the preferred fluid choice for young patients

• Hypothesized that since aquatic turtles can utilize anaerobic metabolism (helpful during extended anoxia), providing lactate would be unadvisable

• However, clinically, not the case (and likely not enough lactate to make a difference)

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Crystalloids

• It is recognized that reptiles have a relatively higher intracellular fluid volume when compared to mammals and a lower blood osmolarity.

• For this reason, it is suggested to use fluids that are mildly hypotonic to facilitate their intracellular transfusion.

• HOWEVER, reptiles also tolerate a huge swing in osmolarity of blood, especially when dehydrated (250-400)

• 0.9% Na Cl + lactated Ringer's solutions 1:1 ratio

• Reptile Ringers solution

• Jarchow’s modification which consists of two parts 2.5% dextrose in 0.45% saline and one part lactated Ringer’s solution - 278 mOsm/L

• 1:1 mixture of 5% dextrose solution and isotonic crystalloid solution

• We just use regular ol’ LRS or 0.9% NaCl ☺

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Crystalloids

• Hypertonic solutions

• Hypertonic saline (3, 7.2%, etc)

• Mannitol (concentrated sugar)

• Precipitates when not kept warmed

• Can cause renal injury

• Help draw fluid from the interstitial space into the intravascular space (similar to colloids)

• Ideal for traumatic brain injuries (TBI)

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Crystalloids

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Colloids

• Solutions with larger molecules that cannot pass through the vascular membrane, so they stay within the intravascular space longer (2-8 hours)

• Biologic – whole blood, plasma

• Synthetic – hetastach, vetstarch, oxyglobin

• Can only be given IV or IO (never SQ)

• Inherently requires catheterization

• Can be ideal for TBI and severe fluid loss

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Fluid AdditivesCommon to add medications to crystalloids to improve patient outcome!

Fluid Additives

• Vitamin B Complex

• Improves metabolism, RBC production, neurological function, etc

• Appetite stimulant

• Light sensitive (cover with paper bag)

• Add enough to turn “urine color”

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Fluid Additives

• Dextrose

• Usually comes in bottles of 50% or bags of 5%

• Can give up to 5% IV/IO and up to 2.5% SQ

• Giving higher concentrations SQ can lead to tissue necrosis and sloughing*

• Life-saving for many neonates, especially ‘cataract squirrels’

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Dilutions

• It is extremely common to need to dilute medications in wildlife medicine (our patients are anywhere from 10 g to 10 kg!)

• c1v1=c2v2 (C=concentration, V=volume)

• 3 out of 4 of these variables are “known”

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Pop quiz!

Presentation

0.1 kg Grey Squirrel w/

hypoglycemia

Therapy

5 ml LRS+2.5% dextrose

Supplies

LRS

50% dextrose

Solution

C1 = 50

V1 = X

C2 = 2.5

V2 = 5

50X=2.5 x 5

X = 0.25 ml

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Add 0.25 ml of 50% dextrose to 4.75 ml of LRS

BUT WAIT, THERE’S MORE!

1/10 of 50% = 5%

1/10 of 5 ml = 0.5 ml

½ of 5% = 2.5%

½ of 0.5 ml = 0.25 ml

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Assessing hydration/dehydration

Assessing hydration

•<5%--Normal–No clinical signs

–Skin turgor return time = 1 sec

– Pink, moist MM

•5-6%--Mild Dehydration–Tacky MM

–Signs of fluid loss

–Skin turgor return time = 2-5 sec

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•6-8%--Moderate Dehydration–Weak pulse, sunken eyes

–Depressed, lethargic

–Skin turgor return time = 2-5 sec

•10-12%--Severe Dehydration –General signs of shock (pale, cold extremities, mentation changes, tachycardia/bradycardia)

–Inelastic skin

–No return of skin turgor

Whoops, went overboard!

• Very uncommon in wildlife

• Challenging without vascular access

• Signs of overhydration

• Increased respiratory rate and effort

• Serous nasal discharge

• Excessive weight gain with little water output

• Edema

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Routes and Rates of Administration

Routes of Administration

• By mouth (per os, aka PO)

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• Subcutaneous (SQ, Sc)

• Intravenous (IV)

• Intraosseous (IO)

• Intracoelomic (ICoe, ICe)

• Intraperitoneal (IP)

Enteral

Paraenteral

Fluid Administration• Ideally, fluid needs are met via enteral route

• Water

• Food items (raptors)

• Cloacal sucking

• Self hydration limits:

• Stress

• Risk of fluid overload

• Risk of trauma due to injection

• However, a patient needs to be mentally appropriate for oral administration

• Also, a patient needs to be minimally dehydrated 33

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20-40 ml/kg

60-80 ml/kg

80-100 ml/kg

50-60 ml/kg

Fluid administration

• The amount of fluids needed to perform bodily functions at rest

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• Replacement of current and/or ongoing fluid loss

Maintenance Deficit

Fluid replacement

• Ideally, fluid deficit should be replaced over a few days

• Day 1 – 100% maintenance + 75% deficit

• Day 2 – 100% maintenance + 25% deficit

• Day 3 – 100% maintenance

Another…Pop Quiz!!• Clinical presentation

• 2 kg raccoon with estimated 8% dehydration

• Maintenance rate

• 2 kg x 60 ml/kg/day = 120 ml

• Deficit

• 2 kg = 2,000 g

• 2,000g x 0.08 = 160 ml

• Day 1 = 120 ml + 160 ml(0.75) = 240 ml

• Day 2 = 120 ml + 160 ml(0.25) = 160 ml

• Day 3 = 120 ml

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*You can give entire daily

maintenance amount in one

administration but if larger amount,

should be spread out to at least BID

Shock dosing

• Vascular access is necessary for ideal fluid resuscitation in cases of shock

• Isotonic Crystalloid

• Dog – 90 ml/kg/hr

• Cat – 60 ml/kg/hr

• Generally given as ¼ dose or 15-20 ml/kg every 15 min

• Colloid/Hypertonic Crystalloid

• Hypertonic saline – 3-5 ml/kg

• Hetastarch – 3-5 ml/kg (can repeat up to 40 ml/kg total)

• Given slowly, over 15-20 min

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Parenteral Administration

Avian

• SQ

• Inguinal leg flap/fold

• IV

• Jugular, cutaneous ulnar, or medial metatarsal veins (dependent on species)

• IO

• Distal ulna or proximal tibiotarsus

• Do not place in humerus or femur – pneumatic bones!

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Don’t do it!

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PRESENTATION TITLE 41

11/25/2021 46

Mammal

• SQ

• Dorsal midline, between scapula

• IV

• Cephalic, saphenous, or jugular veins

• Dependent on species

• IO

• Proximal tibia or proximal femur

• IP

• Not recommended 48

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Reptile

• SQ

• Turtles – prefemoral fossa

• Snakes/Lizard – lateral body wall

• IV

• Jugular, cephalic, or tail vein (may require cut down); heart (snakes)

• IO

• Proximal tibia, gular plastron (chelonians)

• ICoe

• Not recommended 52

Needle choice

• Small songbirds – 25-27 ga

• Small neonate mammals – 25 ga

• Small juvenile mammals – 23-22 ga

• Medium birds (ex: COHA) – 22 ga

• Adult rabbits/squirrels – 20 ga

• Large birds (ex: RTHA) – 20 ga

• X-Large birds/mammals (CAGO) – 18-20 ga

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Duration of fluids

• Try to discontinue parenteral fluids as soon as possible

• We usually stop when patient is self-feeding

• Some disease processes necessitate fluid admin for extended period of time (chelation therapy for lead toxicosis in mammals)

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[email protected]

Let’s give some fluids!!

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fluid therapy in wildlife rehabilitation

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