Physiology for fluid therapy and patient assessment

Question 1

Fluid distribution in the body

Answer 1

60% body weight = water
of this
5% = intravascular compartment - inside blood vessels
- for delivery of O2, nutrients and transport of waste

55% = extravascular compartment - outside blood vessels
- 40% H2O inside cells
- 15% H2O between cells

Question 2

Fluid movement

Answer 2

Fluid is not static
movement between intravascular and extravascular compartments is influenced by starlings forces

Question 3

Fluid distribution around body

Answer 3

Plasma proteins and hydrostatic pressures influences distribution of fluid around the body

Question 4

What causes fluid balance to get disrupted?

Answer 4

Changes in volume e.g dehydration and hypovalemis
Changes in content e.g. electrolyte disturbances, changes in blood glucose, changes in blood protein levels
Changes in distribution e.g. Third spacing

Question 5

Increase vs decrease in fluid volume

Answer 5

Increase in fluid volume: Hypervolaemia - can lead to volume overload

Decrease in fluid volume = Hypovalemia (inside the blood vessels), dehydration (outside the blood vessels)

Question 6

What is hypovolaemia?

Answer 6

• Fluid is lost quickly from the intravascular space
• This results in tissue hypo perfusion aka ‘shock’
• so decreased delivery of O2 and removal of waste
• e.g. bleeding following an RTA

Question 7

What is dehydration?

Answer 7

• Fluid is lost slowly from the extravascular compartment - patient is unable to keep up its ‘ins’ with its ‘outs’
• There is time for fluid to be distributed across all body compartments
• Results in water being lost equally from all compartments from the body
• e.g. an animal without access to fluid and water

Question 8

Physiological consequences of hypovolaemia

Answer 8

Blood loss
Reduced pre-load (amount of blood returning to the heart)(endiastolic volume decreases)
Reduced stroke volume
Decreased cardiac output
Vasoconstriction (increases total peripheral resistance) and tachycardia (fall in BP to compensate)
Leads to
Maintenance of BP to heart, brain and lungs
Changes in mucus membrane colour and CRT

Question 9

How to asses a patient’s intravascular volume?

Answer 9

• heart rate
• Pulse quality
• Mucus membrane colour
• Capillary refill time - normal = 1.5-2s
• Blood pressure
• Mentation = mental awareness
• (Temperature)

Question 10

Hypovolaemia peramaters canine
Normal

Answer 10

HR= 6-120
Mucus membrane colour = pink
CRT = <2
Pulse quality = ‘normal’
Systolic BP (mmHg) = >90
Mentation = Normal

Question 11

Mild shock (compensatory)

Answer 11

HR = 130-150
MMc = Normal to pinker
CRT = <1
Pulse quality = Bounding
Systolic BP (mmHg) = >90 (factors above all adjusted to keep BP 90)
Mentation = Normal

Question 12

Moderate shock

Answer 12

HR = 150-170
MMc = Pale pink
CRT = 2
Pulse quality = weak
Systolic BP (mmHg) = >90
Mentation = Normal -obtunded (diminished response to stimuli)

Question 13

Severe shock (decompensatory) - no longer able to maintain perfusion to vital tissues

Answer 13

HR = 170-220 - if above 220 be suspicious of tachyarythmia as a cause
Mmc = Pale pink - white
CRT = >2
Pulse quality = very weak
Systolic BP (mmHg) = <90
Mentation = obtunded - disminished response to stimuli

Question 14

Why will the body never have a HR of above 220?

Answer 14

<220 will mean the heart can’t properly fill with blood as not enough time so it would actually decrease CO

Question 15

How to assess a patients extravascular volume?

Answer 15

• Moistness of mucous membranes
• Skin tutor e.g. skin tenting (cat and dog above hear, horse and cattle skin above eye)
• Weight
• Globe position
• (urine output)

Question 16

Assessing dehydration (extravascular volume)

<5% body weight dehydrated

Answer 16

Not clinically detectable, suspected from clinical history e.g vomiting, inappetence, lethargy etc.

Question 17

5%- 6% body weight

Answer 17

Tacky mucous membranes, mild delay in skin tent return

Question 18

6%- 8% body weight

Answer 18

Dry mucous membranes, milt increase in CRT, mild to moderate delay in skin tent, +/- sunken eyes

Question 19

> 10% - 12% body weight

Answer 19

Dry mucous membranes, CRT >2-3s, +/- signs of shock, marked prolongation/ standing skin tent, sunken eyes

Question 20

> 15% body weight

Answer 20

Incompatible with life

Question 21

Complications is assessing dehydration

Answer 21

Hypersalivation, amount of subcutaneous fat, skins collagen content

e.g lost weight rapidly so less submit fat, increased skin tent
e.g. older animal less collagen so increased skin tent

Question 22

Clinicopathological features to assess dehydration

Answer 22

From haematology, biochemistry and urinalysis
- increased packed cell volume/ total solids
- Urea and creatinine - pre renal asetemia
- Urine specific gravity

Question 23

Hypovolaemia and dehydration can commonly occur at the same time

Answer 23

never rely on a singular perameter to assess

Question 24

What happens if you give a case of dehydration fluids quickly?

Answer 24

Leads to an increased blood volume and atrial pressures
Triggers atrial and baroreceptors increasing the production of diuretic hormones
Will increase the urine output and will remain dehydrated