Physiology and Patient Assessment

Physiology
1. 60% body weight is water
  1. 20% extracellular
    1. 5% intravascular
      1. Small amount of circulating fluid c.f. total volume
      2. Only a small volume we can control with fluids, which in turn affects other fluid compartments
    2. 15% interstitial
  2. 40% intracellular
  3. Higher in young and male animals, lower in older and female animals
    1. Related to fat content
2. Electrolytes controlled by kidney
  1. Sodium and chloride main extracellular ions
  2. Potassium main intracellular ion
  3. Also used glucose and urea to control osmolality of fluid
3. Osmotic pressure controlled by large particles
  1. e.g. albumin
  2. Draw water into vessel
4. Hydrostatic pressure
  1. Physical pressure on vessel walls
  2. Push water out of vessel
5. Water inputs
  1. Food
  2. Small amount from metabolism
  3. Drinking water
    1. Water supply enough to cover normal losses
      1. 40-60ml/kg/24 hrs
6. Water outputs
  1. Sensible
    1. Urine
    2. Faeces
  2. Insensible
    1. Respiratory tract
    2. Skin evaporation
      1. Minimal in dogs and cats
      2. Greater in animals that sweat
        e.g. horses and cattle
    3. Influenced by external factors
7. Increased water requirement
  1. Immature animals
  2. Lactation
  3. Pyrexia
  4. High ambient temperature
Patient Assessment
1. Does the patient need fluid therapy?
  1. If so, are you treating hypoperfusion, dehydration, hypovolaemia, or maintenance?
    1. Assess perfusion and hydration status
      1. Perfusion – to do with loss from circulation
      2. Hydration – to do with total loss from body
2. Does the patient have inadequate intake and/or excessive losses?
3. What type of fluid has been lost?
4. Choose a type of fluid
5. Choose a route of administration
6. Calculate amounts and rates of fluids
7. Hypovolaemia
  1. Deficit in blood volume
    1. Can lead to hypoperfusion (inadequate tissue blood flow)
  2. Reduced oxygen delivery to tissues
  3. Failure to remove metabolic waste products
  4. Causes
    1. Reduced cardiac output
    2. Maldistribution of blood flow
    3. Reduced volume
    4. Haemorrhage
    5. Fluid loss in excess of intake
      1. Vomiting
      2. Diarrhoea
      3. Polyuria
    6. Loss of plasma may be internal
      1. Transduction
      2. Exudation to third space
8. Dehydration
  1. Reduction in water content of body
  2. Often used to refer to combined water and solute losses in excess of intake
  3. Can lead to hypovolaemia and hypoperfusion
9. Calculating amount of fluid required - consider continual losses
  1. Insensible losses
  2. Sensible losses
  3. Number of vomits per day
  4. Volume of diarrhoea
    1. No amount of renal compensation
Types of abnormal fluid loss
1. Hypotonic
  1. e.g. cat shut in garage
  2. Loss of fluid (urine, sweat) without replacing it
2. Isotonic
  1. e.g. haemorrhage
  2. First 6-8 hours of blood loss
    1. Little fluid movement to compensate
    2. Blood composition similar
    3. Total volume reduced
  3. High impact on blood pressure
    1. High heart rate
    2. High pulse
      1. Thready/no peripheral pulse
3. Hypertonic
  1. e.g. diarrhoea, vomit
  2. Loss of water, electrolytes/salts
    1. Lose more electrolytes than water
      1. NaCl
      2. Mg
      3. Effect on cardiac function
  3. Retaining circulation is more dilute (hypotonic)
  4. Water moves from circulation to interstitial and intracellular spaces
    1. Oedema
  5. Greater impact on fluid loss than interstitial loss
  6. Death can come quickly
    1. Very rapid loss of electrolytes
Dehydration and hypovolaemia
1. Hydration status
  1. Mucous membranes - moist?
  2. Skin turgor
    1. e.g. skin tenting
    2. Careful in older/emaciated animals
      1. Loss of skin elasticity
  3. Retraction of the globe
  4. Most animals between 7-10%
    1. Likely to make little difference if it is 7.5 or 8.5
    2. Add on maintenance
    3. Administer over 24 hours
      1. Make sure signs are getting better
2. Hypoperfusion
  1. Mucous membrane colour
  2. Capillary refill time
  3. Pulse quality
    1. Area under curve
  4. HR and BP change more with severe hypoperfusion
    1. Normal HR 60-120 depending on size of dog
    2. 160-200 cats
  5. Difficult to differentiate hypovolaemia from other causes of hypoperfusion from these signs
    1. Other tests may be useful
      1. Urine specific gravity, urine output
        Normal > 1.030 and 1-2 ml/kg/hr
      2. Packed cell volume
        Increase if fluid loss not including cells
      3. Body weight
      4. Urea
      5. Electrolytes
        Increase of pure water deficit, may be deficits depending on type of loss
      6. Central venous pressure
      7. Useful to observe trends c.f. single result
3. Dehydration
  1. Dryness of mucous membranes
  2. Retraction of the globe
  3. Third eyelid comes across
    1. At this point, will tend to have skin tenting
Clinical assessment and monitoring
1. Monitor input and output
  1. Input
    1. IV fluids
      1. Bags used
      2. Volumes recorded on pumps
    2. Intake from drinking, wet food
  2. Output
    1. Urine
    2. Vomit
    3. Dirrhoea
      1. Approx 20ml per 10cm puddle
  3. Aim for input slightly over output
    1. 10%
    2. Allow for respiratory and other non-measurable losses
    3. If out>in, increase input/fluids
    4. If in is significantly greater than out, decrease fluids and try to work out why
2. Volume depletion and overload
  1. Depletion
    1. Weak, rapid pulse
    2. Pale, dry/tacky mucous membranes
    3. Slow CRT
    4. Poor skin elasticity
    5. Cool extremities
    6. Sunken eyes
    7. Reduced urine output
    8. Radiographically small heart
  2. Overload
    1. Coughing
    2. Increased respiratory rate
    3. Oedema
    4. Ascites/pleural effusion
    5. Chosis
    6. Serous nasal discharge
    7. Exopthalmus
    8. increased urine output
    9. Vomiting
  3. Stop fluids if signs of overinfusion
3. HR decreasing
4. Pulse quality improving
5. Mucous membranes colour, moistness, CRT
6. Reduced skin tenting
7. Urine output
  1. 1ml/kg/hr indicates renal perfusion may be inadequate
  2. 1-2 ml/kg/hr = normal
  3. >2ml/kg/hr = overinfusion
8. Central venous pressure 1-5cm H2O
  1. Trends more important
9. PCV/ total protein
  1. Useful in serial measurements
  2. Care in anaemia, haemorrhage
10. Urine, creatinine, electrolytes
  1. Renal perfusion
11. Arterial blood pressure
  1. Systolic 100-120 mmHg
  2. Mean 80mmHg
    1. Less than 60mmHg - poor renal perfusion
12. When heart rate, blood pressure, pulses, CRT etc are normal
  2. Maintenance phase fluid required
13. Once electrolytes normal, the parient is eating, drinking, with normal gastrointestinal and urinary function
  1. Stop fluids and return to normal intake
Aims of fluid therapy
1. Restore circulating blood volume
2. Replace pre-existing losses
3. Allow for ongoing abnormal losses
4. Aim to replace like for like
  1. Decide on type of fluid
5. Supply normal maintenance requirements

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Physiology and Patient Assessment

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	Created by Jess Pope over 7 years ago