Flashcards in Fluid therapy Deck (48)
Reasons for fluid therapy - 4
Replace excessive fluid losses, restore organ perfusion, correct metabolic disturbances, nutritional support, enhance excretion of a toxin (if it can be cleared by the kidneys) if inducing diuresis (e.g. if the animal is azotaemic; especially useful if the underlying cause of the azotemia is kidney hypoperfusion, as fluid therapy will restore perfusion and induce diuresis)
Reasons - fluid loss - 5
Bleeding, vomitting, diarrhoea, third-space pooling (thorax, abdomen or GIT), dehydration
Define fluid resuscitation
Re-expansion of the intravascular fluid volume
Describe the physical exam findings associated with dehydration and hypovolaemia
DEHYDRATION (fluid deficit in interstitial and intercellular spaces) -oral mucous membranes (dryness), skin turgor, and eye moisture. Severe cases - weak rapid pulse, acute weight loss
HYPOVOLAEMIA - cardiovascular signs more prominent - assess heart rate (tachycardia), CRT, mucous membrane colour and peripheral pulses
How does anaesthesia affect vasomotor tone?
It causes vasodilation (dramatic; i.e. decreased vasomotor tone) --> volume depletion, hypotension and possibly hypoperfusion
Other causes of decreased vasomotor tone.
Pathological conditions - anaphylaxis and sepsis. Leads to maldistributive shock
Composition of fluids - 3
Water, electrolytes and +/-buffers, +/- dextrose
Why is metabolic acidosis often corrected with fluid therapy?
Metabolic acidosis also tends to be related to perfusion problems
Suggest some agents that are administered via fluids
-Drugs that need to be delivered at a constant rate infusion (insulin, metoclopramide, lidocaine, catecholamines)
-glucose infusions (2.5-5% dextrosefor hypoglycaemia correction)
Differentiate enteral and parenteral nutrition
Enteral = fed using the GIT
Parenteral (PN) = animal is fed not using the GIT but intravenously, not commonly used in general practice
What does PN contain? (3)
amino acid solution, concentrated dextrose and lipids. can be adapted to meet specific energy and protein needs of patient
2 forms of PN = ? What are the advantages of each?
-Total PN (TPN) = meets virtually all energy and nutrient requirements, administered centrally (via jugular catheters)
-Partial PN (PPN) = meets 40-70% of an animal's energy needs. Advantages over TPN are that it has a lower osmolarity, can be administered via peripheral catheters (versus TPN which is only administered centrally), less expensive.
Indications of commercial ready-to-use preparations of glucose and amino acids
general practice, <50% required calories provided (when administered at maintenance fluid rate), short term or interim nutritional support
How can fluids be described? (4)
-electrolyte content (hyper/iso/hypo - tonic)
-presence of large particles (crystalloids= smaller, colloids = larger)
-nature of the particles present (natural vs. synthetic colloids)
-physiological purpose (replacement, maintenance, nutrition)
Distinguish crystalloids and colloids (about 5 each)
CRYSTALLOIDS: contains only small particles (electrolytes, glucose, buffers; irrespective of their concentrations), freely permeable through capillary membranes, distribute largely by diffusion and this is rapid when administered intravenously, can dilute the concentration of natural colloids (albumin, immunoglobulins) and therefore lower the patient's COP which decreases the host's ability to retain fluid within the intravascular space (increasing the risk of peripheral oedema)
COLLOIDS: particles larger than 30kD (plasma proteins, synthetic polymers), largely restricted from diffusing through capillary membranes, impart an oncotic pressure which interferes with fluid dynamics, the colloidal particles act as 'little sponges' and help hold fluid within the intravascular space, do not 'pull fluids' from other compartments, tend to persist within the intravascular space longer and so achieve more effective and longer lasting intravascular volume expansion
Advantages - colloid therapy
-preserving/increasing plasma COP (this increases intravascular fluid retention, necessitating smaller volumes of fluids required for recussitation)
Disadvantages - colloid fluids
risk of complications
Natural colloids for vet use (3)
-Blood products - whole blood, packed RBCs, fresh frozen plasma (Packed RBCs exert little oncotic pressure (approx. 5mmHg) and is not expected to affect plasma COP)
-Concentrated albumin products (human/canine/feline albumin - latter two not widely available)
When are human albumin solutions (5%, 25%) used?
-potential to cause anaphylactic reactions with repeated use
-successful one-time use in dogs reported
Synthetic colloids are commonly used to increase COP in vet practices - examples?
-Starchy ones (Hetastarch, dextrans, pentastarch, tetrastarch)
-Haemoglobin-based oxygen carrying fluids (Oxyglobin Biopure)
-Other synthetic colloids
Characteristics of all synthetic colloids (2)
-Heterogenous mixtures of molecules
-various molecular weights (range 100kD (better intravascular expansive properties and longer intravascular persistence.
Distinguish fluids intended for replacement and maintenance
REPLACEMENT (e.g. rehydration and shock resuscitation): include crystalloids and colloids, contain electrolyte concentrations similar to normal plasma concentrations and are referred to as replacement fluids
MAINTENANCE - if only requiring replacement of daily sensible and insensible water and electrolyte losses, typically contain half of the sodium content of plasma, since they are hypotonic ot normal plasma - dextrose is added as a 2.5% concentration to restore tonicity to normal. As animal metabolises the dextrose, a greater amount of free water is delivered.
N.B. generally all animals can be treated with conventinal replacement fluids and there is rare need for maintenance fluids.
Examples of hypertonic solutions (3).Indications?
Supraphysiological concentrations of electrolytes (7% saline), or other osmotically active particles (20% mannitol, 50% dextrose)
High osmotic particle concentration imparts high osmotic pressure --> drives fluid shidts form the intracellula rand intersitital compartments to the intravascular compartment. Thus commonly used in resuscitation of severely hypovlaemic animals with normal interstitial hydratiion (e.g. trauma patients). Also used in patients with intracranial hypertension or cerebral oedema (to shift fluids to intravascular compartment for later excretion)
How to estimate daily maintenance fluid requirements and for critically ill patients.
40-60ml/kg/day. A common practice is to multiply this by a multiplier (1.5-3) for critically ill patients but this is often not ideal (can result in under- or over-hydration of many patients. More appropriate way = calculate fluid therapy to account for the hydration deficit (sensible+insensible fluid losses, +ongoing (contemporary fluid losses e.g. V/D/PU).
When can you discontinue fluid therapy?
When the animal voluntarily consumes enough water to meet its fluid requirements and maintain adequate hydration.
How much fluid is in the different body compartments? How do you calculate blood volume?
Total body water = 60% total body weight=TBW(kg)
ECF = 1/3 TBW and ICF is 2/3 TBW. This is divided into interstitial fluid (3/4 ECF, assessed by skin tent and mucous membrane colour) and plasma/intravascular volume (1/4 ECF)
How do you calculate blood volume?
Blood volume = Plasma volume/(1-haematocrit)
How do you decide if fluid therapy and how to administer it?
Clinical history AND PE findings. Lab tests can support decision but shouldn't be used alone to determine if needed
What do tall and narrow pulses indicate?
A large difference between systolic and diastolic beats. high sympathetic drive to the heart.