Fluid Therapy

Fluid Therapy:

It is administration of fluids as treatment or preventive measure. Fluid replacement is to replenish body fluids lost by sweating, bleeding, fluid shifts by pathological processes.

It can be administered by 1.Intravenous, intraperitoneal, subcutaneous, intraoseous, and oral routes.

Concept of body components:

Total body water is 60 % of total body weight. Extracellular fluid is 20 % and Intracellular fluid is 40%. In extracellular fluid plasma volume is 5 % and interstitial or tissur fluid is 15 %. Fluid therapy is indicated when fluid is lost or when there is risk of loss of fluid. It also depends on severity of fluid loss, compartment from which fluid is lost, choice of fluid and speed with which it is administered.

Indications of fluid therapy:

1.Hypotension

2. Hypovolemia

3.Electrolyte metabolic and acid-base disorders

4.Decreased oxygen delivery

5.In old patients at risk of organ failure.

Some definitions:

Osmosis: It is the movement of water across semi permeable membrane from its high concentration to its lower concentration.

Osmotic Pressure: Pressure caused by presence of solutes in the solution.

Oncotic Pressure : Pressure caused by Plasma proteins in blood.

Hypotonic Solution : Solution with OP lesser than plasma.

Isotonic Solution: Solution with OP equal to Plasma.

Hypertonic Solution: Solution with OP greater than plasma.

Normal fluid balance in the body by equalizing input and output of water.

Input of water	Output of water
Food	Urine
Free water(45-60ml/Kg/Day)	Feacal(Small)
Metabolism (4-6 ml/Kg/day) CHO+O2---CO2+H2O	Insensible (Respiration and Skin by sweating)

Abnormal fluid balance by imbalance of input and output.

Movement of fluid by

1.      Hydrostatic pressure-pressure exerted by fluid itself, favouring the water into interstitium.

2.      Osmotic pressure- To transfer the water between ECF and ICF.

3.       Oncotic Pressure- Colloidal oncotic pressure is OP exerted by protein with in blood stream.

Fluid deficit is either acute or chronic. Acute is caused by hypovolemia and chronic by dehydration.

Hypovolemic	Dehydration
Acute	Chronic
Reduction in intravascular volume	Loss of pure water often isotonic/hypotonic fluid.
Physical symptoms depend on volume lost and chronicity of that loss.	Estimated by mm colour and dryness, skin tenting and CRT.PCV and Total solids and urine specific gravity estimation will show the level of dehydration.
Symptoms—Tachycardia,Abnornmal pulse, Dry and cyanotic mucous membranes, Inc of CRT, altered mental status, cold extremities and tachypnea.

Level of dehydration	Clinical Signs
< 5 %	No symptoms
5-6 %	Some loss of skin elasticity
6-10 %	Sunken eyes, dry mm, delayed return of skin tent.
10-12 %	Tented skin in place, more sunken eyes, dry mm
12-15%	Like 10-12%, ans signs of shock like tachycardia, cold extremities, rapid and weak pulse, prolonged CRT.

Factors	Dehydration	Hypovolemia
Intravascular volume	Low	V.Low
Interstitial volume	Low	Low
Intracellular volume	Low	Nochange
Heart rate	No change	Increased
CRT	No change	Increased then increased
Skin turgor	Increased	No Change
Total solids/PCV	Increased	No Change or decreased
Urine out put	Decreased	Decreased
Pulse quality	No Change	Hyperdynamic pulse to hypodynamic.
		Prompt rapid fluid replacement, less urgent, replace over 24-36 hrs.

Types of fluids

Crystalloids (Enter all body components)			Colloids (Large molecules cannot pass out of vessels, restricted to plasma)
Isotonic	Hypotonic	Hypertonic	Eg: Dextran, Plasma,Albumin.
1.With bicarbonate like anions lactate and acetate. Eg: RL, Plasmate,Normosol R. 2. Without Bicarbonate like anions Eg: Ringers,NormalSaline.	ICF( Low Na and More H2O) Eg: Plasmalyte 56, 2.5,5,7.5 Detrose, Normosol M.	More Na than ECF draw water into vessels. Eg: 7.5 % saline solution.

Purpose of fluid therapy: It has two phases.

I Phase: Restore blood volume with crystalloids/colloids and renal perfusion.

II Phase: Correct acid-base and electrolyte imbalance and restore whole body fluid balance and patient maintenance.

During surgery, when animal is under anaesthesia, to maintain I/V route for emergency medication.

Choice of fluid is based on 3 factors

1.      Disease process

2.      Lab data

3.      Purpose as a) Emergency, b) Replacement, and c) Maintenance.

Two approaches for fluid therapy:

1.      Adopt a standard protocol to meet deficits or likely deficits.

2.      To acquire clinical and lab data on a patient and to administer the appropriate fluids to meet patients specific requirements.

Degree of dehydration or fluid volume deficit by clinical signs like

1.      Skin elasticity-Skin tenting test- Normal 1-2 seconds, >6-8 sec shows severe dehydration.

2.      Pulse rate-weak irregular pulse.

3.      Mucous membrane-Moist and warm to cold, dry, cyanotic.

4.      Temperature of extremities-cold.

5.      Nature and position of eyes-slightly sunken to deeply sunken and dry cornea.

6.      Capillary refill time->3 seconds.

Quantity of fluid is based on response to therapy

Diagnosis of fluid volume deficits by

a)      Accurate assessment of patients fluid volume.

b)     Acid-Base balance.

c)      Electrolyte status.

a)      Accurate assessment of patients fluid volume.

For mild dehydration-4-6% body weight.

For severe dehydration-10% BW.

Degree of hypovolemia is estimated by PCV and TPP(Total plasma protein).

If  TPP and PCV are decreasing, it shows that volume replacement is proceeding normally.

If TPP and PCV both are increasing despite intensive fluid therapy, it is poor sign as the intravascular volume is decreasing and pooling of fluid is taking place peripherally by vascular dialatation.

If TPP is decreasing and PCV is increasing, it shows that intravascular volume is not increasing and protein is being lost from vascular system by increased vascular permeability.

Serum creatinine and urea concentration elevated in dehydration.

b)      Diagnosis of Acid-Base imbalance

Acid-Base imbalances are noted by

a)      Clinical signs

b)      Serum biochemical profile

c)      Blood gas analysis(PH,Pco2,Po2)

PH shows net effect of respiratory and metabolic acidosis.

PCO2, if >45mm Hg—Respiratory Acidosis, but if <35 mm Hg—Respiratory Alkalosis.

Treatment of respiratory acidosis by proper ventilation and treatment of metabolic acidosis by soda bicarb.

If blood gas machine is not available, total CO2 level estimated by Harleco CO2 apparatus, to know excess/deficit of bicarbonate.

c)       Diagnosis of electrolyte abnormalities

Principally sodium, potassium and chloride ions are estimated.

Sodium level—Indicates the fluid level in body, In isotonic loss sodium and water both are lost. Hypernatremia is a clinical problem with soda bicarb and intensive fluid therapy.

Potassium level—Hyperkalemia in metabolic acidosis by redistribution of K+ ions.

In acidosis due to diarrhoea, intracellular K+ moves out of cell and excess H+ into cell. When renal threshold of K+ ions is reached, K+ is lost leading to hypokalemia.

In abomasal torsion there is decrease in Cl2 ions and dramatic change towards increase in Chloride ions after surgery.

Fluid therapy in elective surgery:

Four essential principles of fluid therapy

1.      Replacement of existing deficits.

2.      Fulfillment of maintenance requirement.

3.      Replacement of anticipated additional losses.

4.      Monitoring  patient response to therapy.

A polyionic, isotonic solution with alkalizing effect should be given in anaesthesia, like lactated ringers solution, 4-6ml/Kg/hr is sufficient in elective surgery.

Fluid therapy in compromised patient:

1.      For volume deficits.

2.      Acid-Base imbalance.

3.      Electrolyte change.

Decrease in TPP without volume deficit indicates protein loss, TPP less than 4gm/dl, plasma expanders indicated, costly and adverse reactions are seen.

In past any decrease in PH was treated with soda bicarb, but in large animals metabolic acidosis develops as secondary to hypovolemia and inadequate peripheral tissue perfusion.

Lactate will get converted to bicarbonate , but it depends on liver functioning and adequate oxygen perfusion, but contraindicated in septicaemia, endotoxemia and liver disorders, for them specific bicarbonate directly.

In metabolic acidosis created by hyponatremia or hypocholeremia, bicarbonate is administered. In metabolic acidosis in cattle by abomasal disorder, saline is given to replace volume and chloride ions which causes alkalosis.

In renal compromised patients, hypernatremia is a problem.

Fluids in patient without data:

If volume replacement is continued, if PCV and TPP is elevated. If acid-base data is not available then 50-100 gms of soda bicarb empirically is administered for increased CO2 in hypoventilation in anaesthesia.

Surgery in cattle results generally in metabolic alkalosis. 12-20 lts/hr/horse in shock, after urination infusion rate is decreased with 3-5 lts/hr for maintenance. For 450 kg horse, 27 lts of water per day is required.

Disorder	Fluid used
Severe Vomition	NS
Diarrhoea	RL
Primary water depletion	NS/5%DNS-Maintenance fluid in surgery
Bowel obstruction	Colloid+RL
Urethral Obstruction	NS/5%DNS
Severe haemorrhage	Colloid/RL , Whole blood, if PCV less than 25% after Colloid/RL.
Severe liver disorder	NS/5 % DNS
Neonatal animals	Half strength solution(dilute with sterile water)
Anorexia	<3days—5 % DNS
	>4days—30ml/kg of lipid emulsion+30ml/kg of 5%DNS/5% aminoacid/day.

Fluid rate calculations:

Three elements are considered

1.      Replacement 2. Maintenance 3. Ongoing losses

1.Replacement—Calculated based on the level of dehydration by skin tenting test.

Replacement for 24hr period = % dehydrated X Body W(Kg)X10

2.Maintenance—Basic rate for 24hrs period = 2ml/Kg/hr or 50ml/kg/24hr.

3.Ongoing losses—Calculated based on predicted fluid lost by the patient with 24hr period, common losses by vomiting and diarrhoea.

Ongoing losses = Amt.per loss(ml/Kg) X BW(Kg) X No.of losses

1,2 and 3 will be added together for total fluid requirement in a 24 hr period as

x/24 = y (fluid required by 1 hr)

y/60 = z(fluid required by 1 minute)

z/60 = α (fluid required by 1 second)

β (drops per second) = α X set factor

Monitoring of fluid therapy:

1.      Observe urine output.

2.      PCV and TPP estimation.

3.      Colour and hydration of mucous membrane.

4.      Monitoring of blood pressure.

5.      Importance of observing signs of pulmonary edema/ascites.

6.      It should not be stopped until patient is able to maintain normal hydration status independently.

Special considerations for fluid therapy:

1.      Shock

2.      Anaesthesia

3.      Cardiac disease

4.      Hepatic disease

5.      CNS disease.

1.Shock:   a) Hypo volemic—Isotonic crystalloids.

                 b) Cardiogenic—Animal already volume overload, so treat with diuretic.

c)Vascular—either obstructive or distributive, obstructive treated by the removal     of obstruction.        

2.Anaesthesia:  Most anaesthetics will alter fluid homeostasis so even in healthy animals fluids are administered. Anaesthetic induced hypotension is created. Warm the fluids in cool temperature.

3.Cardiac disease: Fluid overload should be prevented in cardiac compromised patients.

4.Hepatic disease: Alteration in protein levels and clotting factors. Proteins carry anaesthetic drugs, in hypo proteinemia, low carrying capacity of anaesthetics. In low level of clotting factors, blood transfusion may be necessary.

5.CNS disease: Animal with head trauma/ increase in intracranial pressure, susceptible for excess fluid loading. Fluids with glucose should be avoided.

Coclusions for fluid therapy:

1.Determine volume deficit by history, physical exam, lab exam for PCV and TPP estimation, urea and creatinine estimation.

2. Estimate continuing loss requirement.

3.Decide the nature of fluid requirement.

4.Deterimine potassium status and requirement.

5.Determine acid-base status and bicarbonate requirement.

6.Calculate daily maintenance requirement.

7.Add all requirement together and divide by no of available hrs to determine hrly rate of fluid administration.

Cautions for fluid therapy:

1.Heart disease.

2.Respiratory disease.

3.Anuria with volume overload( Obstruction to pass urine).

4.When edematic consequences are a problem like in head trauma, pulmonary contusions.