by-DR RAJESH KUMAR SINGH, JAMSHEDPUR, JHARKHAND
9431309542,rajeshsinghvet@gmail.com
What is Fluid Therapy?—-
Fluid Therapy is the administration of fluids to a patient as a treatment or preventative measure. It can be administered via an intravenous, intraperitoneal, intraosseous, subcutaneous and oral routes. 60% of total bodyweight is accounted for by the total body water. This can further be divided into intracellular or extracellular as shown below.
Fluid therapy is indicated either when there is a loss of fluid to any part of these compartments or there is a risk of loss of fluid. The severity of the fluid loss, and the compartment from which it has been lost, influence the choice of fluid and the speed at which it needs to be administered. If fluid therapy is performed as a treatment then it is necessary to diagnose and treat the underlying condition.
Basics of Body Fluid: —–
• An adult animal contains about 60% fluid of its body weight. • Intracellular fluid (ICF) consists of about two-thirds of total body fluids. • The extracellular fluid (ECF) which constitutes about one-third of the total body fluids. It is divided into three sub compartments— interstitial, intravascular, and trans cellular. The interstitial contains three-quarters of all the fluid in the extracellular space. • The intravascular contains the fluid, mostly plasma, that is within the blood vessels. Total blood volume is roughly 8% of bodyweight and plasma roughly 5% of bodyweight • The fluid in the trans cellular compartment is produced by specialized cells responsible for cerebrospinal fluid, gastrointestinal fluid, bile, glandular secretions, respiratory sections, and synovial fluids. • Daily water intake is about 10% of the body weight (can vary from animal to animal with respect of their age, environment, feed intake etc. ). • Daily water loss equals daily intake and this loss occurs through the skin, lung, kidney and gastrointestinal tract. • Body water contains solutes (substances that dissolve in solvent; particles). • Electrolytes are substances that split into ions when placed in water. • Primary ions in the body are sodium, potassium, chloride, phosphate, and bicarbonate. • Cations are positively charged ions. • Anions are negatively charged ions. • Body water is the solvent in biological systems • To establish equilibrium, body water moves along its concentration gradient
Composition of fluid. —–
• ICF—- Ca,Mg,K,PO4,protien.
• ECF—— Na,Cl,HCO3. Ca 2+ Mg 2+ K+ Na+ Cl- PO4 3- Organic anion HCO3 – Protein 0 50 50 100 150 100 150 Cations Anions ECFICF
Fluid therapy Types:——-
• Replacement therapy: Therapy in which we infuse same type of fluid which is lost from body .
• Adjunctive Therapy: One type of fluid is given to remove other type of fluid e.g. mannitol 25% is given in case of ascites and edema. • Supportive Therapy: Fluid is given to animal just to support him to cure quickly i.e. amino acids, minerals, multivitamins and carbohydrates etc.
Indications—–
Fluid therapy is indicated for any of the following reasons:
1. Replacement of fluid loss caused by dehydration, disease, hemorrhage, etc.
2. Correction of acid-base imbalances
3. Correction of electrolyte disturbances
4. Prevention of fluid loss during anesthesia, maintaining venous access, ensuring renal perfusion and adequate blood pressure, and counteracting vasomotor effects of anesthetic drugs
5. Maintenance of body fluid and electrolyte balance during on-going losses until the animal can compensate appropriately by eating and drinking
6. Administration of pharmaceuticals and parenteral nutrition
Fluids are administered to patients not only to replace fluid loss but also to correct electrolyte abnormalities, promote kidney diuresis, and maintain the tissue or organ perfusion
. • During shock.
• Dehydration.
• Diuresis (Toxicities , renal diseases).
• After surgical procedure i.e. to prevent hypotension as hypotension may be due to vasodilation, decreased cardiovascular function etc.
• Acid base abnormalities.
• Electrolyte abnormalities.
Definitions——-
• Osmosis is the net movement of water across a semi permeable membrane. The movement is caused by a concentration gradient due to different solute concentrations on each side of the membrane.
• Osmotic Pressure is the pressure caused by the solutes within the solution. The solute concentration prevents water movement across the membrane.
• Tonicity is the term used to compare the osmotic pressure of different solutions
• A hypotonic solution is one that has an osmotic pressure lower than plasma.
• A isotonic solution is one that has an osmotic pressure the same as plasma.
• A hypertonic solution is one that has an osmotic pressure higher than plasma.
• Hypovolaemia is a reduction in normal blood volume which can be caused by:—–
• Excessive sweating
• Water deprivation
• Vomiting and diarrhoea
• Haemorrhage
• Pathological dilatation of capacity of the ciruclatory system, and therefore a relative reduction in circulating blood.
• Hypervolaemia’ is an increase in blood volume, which can be caused by congestive heart failure.
What Type of Fluid Should Be Given?——–
The composition of a balanced fluid (e.g., lactated Ringer’s solution) resembles that of extracellular fluid
(ECF) whereas that of an unbalanced solution (e.g., normal saline) does not. Fluid preparations may be further
classified as crystalloids or colloids. Crystalloids (e.g., 5% dextrose, 0.9% saline, lactated Ringer’s solution) are
solutions containing electrolyte and non-electrolyte solutes capable of entering all body fluid compartments.
Colloids are large-molecular-weight substances that normally are restricted to the plasma compartment and
include plasma, dextrans, and hydroxyethyl starch (hetastarch). Crystalloid solutions expand the plasma
compartment with equal effectiveness, but 2.5 to 3.0 times as much crystalloid solution must be given (compared
with a colloid solution) because the crystalloid is distributed to other sites (e.g., interstitial compartment,
intracellular compartment).
Crystalloid solutions also can be classified as replacement or maintenance solutions. The composition of
replacement solutions resembles that of ECF whereas maintenance solutions contain less sodium (40 to 60
mEq/L) and more potassium (15 to 30 mEq/L) than do replacement fluids. Most animals that require fluid therapy
can be managed with a limited number of crystalloid and additive solutions. The most useful crystalloid solutions
for routine use are a balanced replacement solution (e.g., lactated Ringer’s solution, Normosol-R, Plasma-Lyte
148), 0.9% saline, and 5% dextrose in water. Supplementation of crystalloid solutions with KCl may be necessary
when body fluid losses have included large amounts of potassium.
The choice of fluid to administer is dependent on the nature of the disease process and the composition of
the fluid lost. The patient’s acid-base and electrolyte disturbances should be considered when choosing a fluid,
and losses should be replaced with a fluid similar in volume and electrolyte composition to the fluid that has been
lost. If clinical assessment of the patient suggests a fluid-responsive type of shock, the resuscitation phase of fluid
therapy should be instituted. If clinical signs of hypovolemia are not present, the hydration deficit and maintenance needs may be combined and administered during the next 24 hours.
• Types of fluid:——-
• (a) Crystalloids.—–
• • Contain sodium as the main osmotically active particle. • Useful for volume expansion (mainly interstitial space). • For maintenance infusion. • Correction of electrolyte abnormality.
• • Types of crystalloids —-
• • Isotonic crystalloids Lactated Ringer’s, 0.9%NaCl(Normosol) • Only 25% remain intravascularly
• • Hypertonic saline solutions 3% NaCl 0.9% normal saline with 5% dextrose 10% dextrose in water
• • Hypotonic solutions D5W(dextrose 5 % in water) 0.45% NaCl 0.25% NaCl less than 10% remain intravascularly, inadequate for fluid resuscitation.
• Lactated Ringer’s Solution: —-• Composition closely resembles ECF • Contains physiological concentrations of: sodium, chloride, potassium, and calcium • Also contains lactate, which is metabolized by the liver alkaline- forming • Because small animals that are sick or under anesthesia tend towards acidosis
• Ringer’s Solution: —–• Same as LRS except no lactate added • Commonly used in Large animals • Large animals who are sick tend towards alkalosis instead of acidosis
• Normal Saline: ——• 0.9% Sodium chloride = ISOTONIC • Lacking in K+, Ca2+ • Used for hyperkalemia, hypercalcemia • Used as a carrier for some drugs • Used if don’t want lactate
• do not readily migrate across capillary walls • Preparations – Albumin: 5%, 25% – Dextran – Gelifundol – Haes-steril 10%
•
• (b) Colloids———
• • Contain high molecular weight substances
• Natural Colloids • Blood products: • Whole blood • Plasma • Platelet-rich plasma • Packed RBC’s
• Synthetic Colloids • Dextrans, Hetastarch • Used when quantity of a crystalloid is too great to be able to infuse quickly • Stays within the vasculature maintain blood pressure • Duration of effect is determined by molecular size: • bigger = longer • Small volumes produce immediate increases in blood pressure
1. Crystalloids are able to enter all body compartments.
2. Colloids are restricted to the plasma compartment.
If there is an electrolyte imbalance present then it may be necessary to add the appropriate electrolyte solution.
Routes of Fluid administration ——-
Oral—–
•Safest route •Easy •Less rapid absorption •Possible aspiration •Cannot use for vomiting animals
Subcutaneous—-
•Relatively easy to administer •Absorption distributed over time •Possible infection •Must use isotonic fluids •Slower absorption
Intravenous——-
•Precise amount given is available rapidly •Various tonicities of fluid can be used •Possible fluid overload and vessel damage •Requires close monitoring •Must be sterile
Intraperitoneal———
•Relatively rapid absorption •Can be used when IV access is not available •Possible infection •Cannot use hypertonic solutions •Abdominal surgery hindered after administration
Intraosseous——-
•Useful for small animals, birds, and pocket pets
•Can be used when vein inaccessible
•Rapid absorption
•Lack of confidence in administering fluid via this route
•Possible infection Rectally
•Good absorption
•Not frequently used
Fluid Rate Calculations——-
When calculating the fluid requirements of a patient, there are 3 elements to consider –
1. Replacement
2. Maintainance
3. Ongoing Losses
Replacements are calculated based on the level of dehydration. Dehydration is based upon clinical assessment of each individual patient. Most commonly, skin tent is used for assessment. To calculate the amount required for replacement within a 24 hour period, the percentage dehydration is used in the following calculation.———
Replacement = % Dehydration x Bodyweight (kg) x 10
Maintainance is the basic rate which a patient requires during a 24 hour period. It is commonly calculated as 50ml/kg/24hr, or 2ml/kg/hr.
Ongoing losses are calculated based on a predicted fluid amount lost by a patient within a 24 hour period. Common losses include vomitting and diarrhoea. It is often helpful here if the owners are able to give a detailed history as this makes it easier to predict the pattern of losses. In some patients there may be no ongoing losses and so this step can be skipped.
To calculate the fluid requirement, the following calculation is used.—-
Ongoing losses = Amount per loss (ml/kg) x Bodyweight (kg) x No. of losses
These calculations are then added together to allow for the total fluid requirement in a 24 hour period. It is important to assess these requirements on a daily basis as losses may be increased/reduceed for example.
The calculated fluid requirement is multiplied by the bodyweight of the individual patient to give the total amount of fluid required for that patient as ml/24hr period. This is then further calculated depending on whether a drip pump is used or fluid rate is adjusted manually as shown below.
Requirement per hour (ml/hr) = Requirement per day (ml/24hr) ÷ 24
Requirement per minute (ml/min) = Requirement per hour (ml/hr) ÷ 60
Requirement per second (ml/s)= Requirement per minute(ml/min) ÷ 60
Drops per second = Requirement per second (ml/s)x Giving Set Factor
How Much to Give?——–
• Correct dehydration • Weight in kg times percent dehydration equals the amount in liters that the animal is dehydrated
• Example: 10 kg animal who is 8% dehydrated • 10kg X 0.08 = 0.8 liters
• Patient is lacking 0.8 liters, or 800 ml fluids
So How Is It Delivered?——-
• Infusion pump (easy) • IV drip set: drops per ml written on package • Regular Drip sets have 10, 15, or 20 drops per ml • Med – large dogs • Micro drip sets have 60 drops per ml • Small dogs – cats
Calculate Drops Per Hour ———
• Calculate ml/hr.
• Calculate drops/hr by: ml/hr X drops/ml (from the package)
• Gives you drops needed in an hour
• Example: 100 ml X 10 drops per ml = 1000 drops in the first hour
Calculate Drops Per Minute——-
• Divide drops per hour by 60 min/hr to get drops per minute
• Ex: 1000 drops/ hr divided by 60 minutes per hour = 16.7 drops per minute
• 16.7 drops/min divided by 60 sec per min = 0.28 drops/sec
Principles of Rehydration:——–
• Correct dehydration, electrolyte, and acid-base abnormalities prior to surgery
• . Do not attempt to replace chronic fluid losses all at once
• Severe dilution of plasma proteins, blood cells and electrolytes may result
• Aim for 80% rehydration within 24 hours
• Monitor pulmonary, renal and cardiac function closely
For example. —–
• An adult 18kg cat with 6% dehydration comes into the clinic. It is estimated that the cat vomited 150 ml of fluid overnight
• Maintenance fluids can be dosed at 50 ml/kg/day in adults and 110 ml/kg/day in young animals
• Calculate maintenance volume 18kg x 50 ml/kg/day = 900ml per day
• Rehydration fluid is based on the estimated percent of dehydration % dehydration x weight in kg = deficit in liters
• Calculate replacement for dehydration 6% = 0.06 0.06 x 18 kg = 1.08 l 1.08 l x 1,000 ml/l = 1080 ml 1080ml x 0.8 (80% of dehydration value replaced in 24 hours) =840 ml to replace on first day
• Take estimated volume lost in fluid and add to the other volumes
• Final step: Take all values and add together 900ml + 840 ml + 150 ml = 1890ml
When should fluid therapy be discontinued?——–
Repeated assessment of the patient by observation of clinical signs and determinations of body weight,
urine output, PCV, TPP, and USG is necessary to make appropriate adjustments in fluid therapy. The animal’s
urine output should be observed carefully after fluid therapy has begun. Measurement of central venous pressure
(CVP; normal, 0-3 cm H2O) with a jugular catheter positioned at the level of the right atrium allows the
cardiovascular response to fluid administration to be monitored. CVP increases from below normal into the
normal range when fluids are administered to a dehydrated animal. A progressive increase in CVP above normal
during fluid therapy is an indication to decrease the rate of fluid administration or to stop fluid therapy
temporarily. Ideally, fluid therapy is discontinued when hydration is restored and the animal can maintain fluid
balance on its own by eating and drinking. As the animal recovers, fluid therapy usually is tapered by decreasing
the volume of fluid administered by 25% to 50% per day
Fluid overload:——–
• Serous nasal discharge
• Increased respiratory rate (Dyspnea)
• Crackles or muffled lung sounds on pulmonary auscultation
• Late stage consequence = pulmonary edema (or pleural effusion in cats)
• Decreased PCV
• Increased BP
Dehydration: ——-
• Dehydration or the loss of fluid from the interstitial space in the form of increased fluid loss from vomiting, diarrhea, or polyuria is one of the main cause of water reduction in body.
• Signs include decreased skin tenting, sunken eyes, depressed mentation, and tacky/dry mucous membranes, CRT 2-3 sec in mild cases and >3 sec in severe cases, Slight depression of eyes into sockets.
Diagnosing Dehydration: ——-
• Physical exam
• Weight loss
• PCV (HCT) increased
• Albumin or total protein increased
• BUN, creatinine
• Prerenal azotemia
Clinical examination of Degree of Dehydration ———-
Degree of Dehydration(%)– Clinical signs <5 Not clinically detectable.
5-6 Subtle-loss of skin elasticity
6-8 Obvious delay in return of tented skin. Slightly ↑ CRT Eye possible sunken & dry mucous membrane.
10-12 Skin remain tented. Very prolonged CRT. Sunken eyes & dry mucous membranes. Possibly signs of shock (tachycardia, cool extremities, rapid & weak pulse)
12-15 Obvious signs of shock. Death imminent
Monitoring Fluid Therapy——–
Fluid therapy can be monitored by observing urine output, Packed Cell Volume (PVC), Total Protein (TP, or Total Solids, TS), mucous membrane colour, and blood pressure among others. It is important to also observe for signs of oedema, such as pulmonary oedema or ascites. It should not be stopped until hydration of the patient has returned to normal and the patient is able to maintain a normal hydration status independently.
