Fluid Therapy Flashcards
What is the definition of Osmolality and Osmolarity?
Osmolarity refers to the number of solute particles per 1 L of solvent (mOsm/L)
Whereas osmolality is the number of solute particles in 1 kg of solvent (mOsm/kg)
What are the pressures and forces driving movement of fluid at the arteriole and venule end of the capillary?
- Fluid exits/ filtered through the arteriole end of the capillary due to greater hydrostatic pressure (35 mmHg) than the blood colloidal osmotic pressure (25 mmHg)
- Fluid re-enters/ reabsorbed at the venule end of the capillary due to capillary hydrostatic pressure (18 mmHg) being less than the blood colloidal osmotic pressure (25 mmHg)
How can you calculate a patient’s plasma Osmolarity when presented with a basic blood panel?
Dorwart-Chalmers Equation:
Plasma(osm) = 2[Na+] + 2K+ + [glucose (mmol/L)] + [BUN (mmol/L)]
normal for dogs and cats = 290 - 310 (in dogs) or 330 (in cats) mOsm/L
below this = hypo-osmotic
above this = hyper-osmotic
note:
Plasma osmolarity of some reptiles, especially those from a freshwater aquatic environment may be lower than that of mammals (e.g. < 260 mOsm/L) during favourable conditions. Consequently, solutions osmotically balanced for mammals (e.g., 0.9% normal saline) are likely to be mildly hypertonic for such animals. Many arid species of reptiles and hibernating uricotelic species allow major elevations of plasma osmolarity (e.g. > 400 mOsm/L) that could be fatal to some mammals.
What is the definition of Osmotic Pressure?
The pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution.
What is the definition of Tonicity?
Tonicity is the relative concentration of solutes dissolved in solution which determine the direction and extent of diffusion
The ability of an extracellular solution to make water move into or out of a cell by osmosis is known as its tonicity
e.g. Hypertonic, Isotonic, Hypotonic
What is the definition of Oncotic Pressure?
Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure induced by proteins, notably albumin, in a blood vessel’s plasma (blood/liquid) that displaces water molecules, thus creating a relative water molecule deficit with water molecules moving back into the circulatory system within the lower venous pressure end of capillaries
A solution with an osmolarity of 300 mOsm/L is ________
Isotonic
A solution with an osmolarity of 700+ mOsm/L is ________
Hypertonic
note: must be administered via a central line
What is the daily fluid requirement “maintenance” of a normal healthy animal?
50 - 60 mL/kg/day
= 2.5 mL/kg/hour
What are the 3 ways you can describe a fluid by?
1) Content = crystalloid vs colloid
2) Tonicity = isotonic vs hypertonic vs hypotonic
3) Function = Resuscitation, replacement, maintenance, alkalinizing, acidifying or a combination of these
What is included in a crystalloid solution?
What is included in a colloid solution?
- Crystalloid
Water + Electrolytes +/- Glucose = can readily move from vascular to interstitial space, and if it contains glucose then it can diffuse into the intracellular space - Colloid
Water + Electrolytes + Large molecules in large quantities = take longer to leave the intravascular space
What is the definition of a Resuscitation fluid therapy?
Re-establishes hemodynamic stability through restoring intravascular volume
What is the definition of a Replacement fluid therapy?
Provides daily maintenance requirements and replacement of any ongoing abnormal losses
What is the definition of a Maintenance fluid therapy?
Provides daily maintenance requirements
A patient requires Resuscitation fluid therapy, what fluids are available?
Balanced Crystalloid:
- Hartmann’s solution
- Ringer’s acetate
- Plasma-Lyte 148
Crystalloid:
- 0.9% sodium chloride
A patient requires Replacement fluid therapy, what fluids are available?
Balanced Crystalloid:
- Hartmann’s solution
- Ringer’s acetate
- Plasma-Lyte 148
Crystalloid:
- 0.9% sodium chloride
A patient requires Maintenance fluid therapy, what fluids are available?
- 0.18% sodium chloride/ 4% dextrose
- 0.45% sodium chloride
- 5% dextrose
What are the commonly used Crystalloid fluids?
- CSL = Compound Sodium Lactate (common at UCD): used as a replacement and alkaliniser fluid
- Lactate Ringers Solution (LRS)
- Ringers Solution
- Plasmalyte A or Normosol R
- Normal Saline (0.9% NaCl)
- D5W
- Hypertonic Saline (7.5% NaCl)
What are the commonly used Colloid fluids?
- Synthetic
- Semi-synthetic: Gelatins, Dextrans and Hydroxyethyl starches
- Natural: Plasma, blood products, albumin
A patient comes in dehydrated, hypovolemic or with metabolic acidosis, which fluid therapy is recommended?
- CSL (Compound Sodium Lactate)
- Lactated Ringers Solution
- Plasmalyte A or Normosol R
A patient comes in for routine surgery and anesthesia, which fluid therapy is recommended?
CSL (Compound Sodium Lactate)
- Patients usually become acidemic during anesthesia, and CSL is an alkaliniser
A patient requires blood products, which fluid therapy CANT it have?
CSL (Compound Sodium Lactate)
CSL contains Ca++ which counteracts the anticoagulant and can lead to microthrombi formation
A patient is hypercalcemic, which fluid therapy CANT it have?
CSL (Compound Sodium Lactate)
CSL contains Ca++
Compound Sodium Lactate (CSL) is very similar to ________ and ________ and ________
Lactated Ringers Solution (LRS)
Ringers Solution (just without the lactate)
Plasma-Lyte A or Normosol R
A patient is experiencing vomiting, diarrhea or metabolic alkalosis, which fluid therapy is recommended?
Lactated Ringer’s Solution +/- K+
- Isotonic
A patient has Diabetic Ketoacidosis, which fluid therapy CANT it have?
Plasmalyte or Normosol R
Contains acetate which is a ketone precursor and can worsen the condition
A patient presents with one or more of the following, which fluid therapy is indicated?
Dehydrated
Hypovolemia and/or Hyponatremia
Hypochloremia
Hypercalcemia
Metabolic alkalosis (e.g. in pre-pyloric obstruction)
Hyperkalemia
Normal Saline (0.9% NaCl) \+/- potassium depending on the situation
A patient presents with heat stroke, hypernatremia, hypodipsia (not drinking), diabetes insipidus, or overall primary water depletion what fluid therapy is indicated?
- D5W (Dextrose 5% Water) +/- colloid
- 0.9% NaCl + 5% Dextrose +/- colloid
D5W is almost isotonic, but once the glucose is metabolized it can become hypotonic
A patient comes in with shock or increased intracranial pressure, which fluid therapy is indicated?
Hypertonic Saline (7.5% NaCl) hypertonic fluid will pull water out of the intracellular space, and into the vessels leading to vessel expansion, increased microcirculation and microperfusion
Caution: will shrink red cells
Caution: will cause intracellular dehydration, therefore must follow with isotonic solution to restore this once circulation stability is achieved
What are the disadvantages/ cautions of using hypertonic saline?
- Short duration of action
- Causes a hyperchloremic metabolic acidosis, which can be detrimental to the myocardial and cellular function
- Is irritating to the veins
- Can cause intravascular hemolysis
- Can cause ventricular arrhythmias
- If administered rapidly, can cause a vagally mediated bradycardia, hypotension and bronchoconstriction
A patient requires plasma volume support/ expansion, or is hypoproteinemic, which fluid therapy is indicated?
Colloids
What is the effect of using Colloid fluid therapy?
- Increase intravascular colloid osmotic pressure
- Fluid will diffuse from the interstitium into the intravascular space
- Resulting in an increased circulating volume
Will have to follow up with a crystalloid in order to rehydrate cells
What is the most commonly available Semi-synthetic Gelatin Colloid solution?
Gelofusine- a succunylated bovine gelatin in NaCl solution
- Improves water retention and expansion within the circulation for around 3 hours
- Excreted in the urine
What are the cautions/ adverse effects of using Gelatins in fluid therapy?
- Anaphylaxis: higher incidence than any other colloid
- Hemodilution when used in large volumes
- Volume overload + Hypertension
A patient presents with dehydration or risk of thrombosis, which fluid therapy is indicated?
Dextrans (semi-synthetic) colloid solution
How much volume of fluid therapy is needed for a 10kg dog that is 8% dehydrated?
1) Maintenance volume = this is the volume necessary to meet insensible losses (if oral intake is not adequate) + volume necessary to meet ongoing sensible losses = 50 - 60 ml/kg/day (lets go with 50 for ease)
2) Replacement volume = %dehydration x body weight (kg) x 10 = 8% x 10 x 10 = 0.8 litres = 800 mL
Total:
maintenance: 50 x 10 = 500 mL
replacement: 800 mL
= 1300 mL
= 1.3 L over 24 hours to replace the fluids lost
note: dehydration should be corrected slowly (over 12-36 hours). Meanwhile hypovolemia needs to be corrected rapidly
What rate of IV fluid administration should be given to a mild, moderate and severely dehydrated animal?
- Mild dehydration (<5%): 15-30 ml/kg/hr
- Moderate dehydration (5-7%): 50 ml/kg/hr
- Shock/ Severely dehydrated (7 -10%): 90 ml/kg/hr
What is the fluid rate for subcutaneous administration and when would you use this administration?
SQ: 10 - 12 ml/kg per spot
Only used for mild dehydration and must ONLY use isotonic fluids
What are the clinical consequences of volume overload?
- Increased urine output
- Restlessness + coughing + increased respiratory rate
- Vomiting!
- Exopthalmos
- Serous nasal discharge
What can you do to monitor the status of hydration and effectiveness of fluid therapy?
- Skin turgor
- Thoracic auscultation: an animal that is getting fluid overload or cant handle fluids will get pulmonary edema
- Weight changes: if the animal is not excreting the fluids it will gain weight
- Hematocrit
- Total Protein
- Urine outpur
- Central venous pressure
What is the maintenance needs of Potassium salts of a patient?
1-2 meq/kg/day if no oral intake (i.e. not eating)
Thus at a maintenance fluid rate of 60 ml/kg/d in a dog, the K+ concentration should be 30-35 meq/litre
- UCD likes to put 20 meq in 1L of LRS for fluids at maintenance
- Use less potassium if fluids are to be given above maintenance
- NEVER administer K+ supplemented fluids faster than 0.5 meq/kg/hr
A dog has been vomiting, what dose and rate of fluids are needed to replace the fluids lost from vomiting ?
4-5 mL/kg/vomit
A dog has had 5 episodes of diarrhea, what dose and rate of fluids are needed to replace the fluid lost from the diarrhea?
5 mL/kg/episode
A 10 kg dog is 5% dehydrated and has had 4 vomits in the last 24 hours, how much volume of fluid therapy is needed?
- Maintenance: 50 - 60 ml/kg/day (lets go with 50 for ease)
50 x 10 = 50mL - Replacement: %dehydrated x body weight x 10
5 x 10 x 10 = 500mL - Loss from vomiting: 4-5 mL/kg/vomit
5 x 10 x 4 = 200mL
Total = 750mL over 24 hours
A 10kg DOG comes in with hypovolemic shock, what fluid therapy and at what rate is required?
- Isotonic crystalloid
- Total Volume: 80-90 ml/kg: 90 x 10 = 900 mL
- Administer in aliquots of 20ml/kg as a bolus, and re-assess patient: 20 x 10 = 200mL bolus (as fast as possible)
OR
- Colloid rapidly IV
- Total Volume: 20ml/kg: 20 x 10 = 200mL
A 4kg cat comes in with hypovolemic shock, what fluid therapy and at what rate is required?
- Isotonic crystalloid
- Total Volume: 60 ml/kg: 60 x 4 = 240 mL
- Administer in aliquots of 20ml/kg as a bolus, and re-assess patient: 20 x 4 = 80 mL bolus (as fast as possible)
OR
- Colloid rapidly IV
- Total Volume: 10ml/kg: 10 x 4 = 40mL
Patients with congestive heart failure, renal disease, urethral obstruction, pulmonary edema, hypoalbuminemia or cats that are hypothermic are at particular risk of _______
Over-infusion of fluids leading to fluid overload
- Usually given a fluid rate too high, rather than too much volume
How can fluid overload be avoided in a patient undergoing fluid therapy?
- Dont exceed 90 ml/kg/hr in DOGS
- Dont exceed 50 ml/kg/hr in CATS
- Ensure urine output
- Ensure no cardiac disease
- Ensure no anemia
How do you know if youve given enough fluids to a patient?
- Monitor urine output: normal output is 1-2 ml/kg/hr
- Weigh the patient
- Serial blood samples: PCV, TPP, Electrolytes
- Clinical Exam: recheck the cardiovascular and respiratory system, mucous membranes, and temperature
What are the indications for supplementing Potassium (K+) in a fluid therapy?
Patient has low plasma K+
- prolonged inappetence
- V/D
- Increased urine output
- alkalosis
- all animals receiving maintenance fluids
When is Lactated Ringer’s Solution (LRS) or Compound Sodium Lactate (CSL) contraindicated?
- Alkalosis: the lactate will add to the alkalosis
- Hepatic encephalopathy: the liver will be unable to metabolize lactate thus can lead to severe acidosis
- Long term maintenance
What are the features of Lactated Ringer’s Solution (LRS)?
- Isotonic
- Polyionic
- Crystalloid
- Replacement
- ECF alkaliniser
What are the side effects of over-administering crystalloid fluids?
What are the side effects of over-administering colloid fluids?
- Crystalloid
Peripheral edema
Pulmonary edema
-Colloid
Allergic reactions
Coagulopathies
Renal failure (especially in septic patients)
