Treatment of hypoperfusion

Question 1

Which factors are considered in early goal directed therapy

Answer 1

• mean arterial pressure >65mmHg
• Urine output >0.5ml/kg/hr
• Central venous oxygen saturation >70%
• HCT >30%, Hb >10g/dl
• Lactate <2mmol/l (or reduced by 10%)
• CVP 8 -12cmH2O

Question 2

what is permissive hypotension?

Answer 2

• some evidence with haemorrhage for better outcome using low volume resusitation targetting a MAP of 60mmHg
• suggests reduced end organ damage

Question 3

What are the recommended bolus doses and maximums for crystalloids

Answer 3

Dogs:
- 10-20ml/kg increments
- maximum 60 -90ml/kg volume.

Cats:
- 5-10ml/kg increments
- maximum 40-60ml/kg volume

Question 4

How are crystalloids redistributed

Answer 4

Rapidly redistributed into the extravascular space with only 25% remaining in the vessels 30 minutes after bolus

Question 5

What arepoptential problems from crystalloid administration

Answer 5

• volume overload
• pulmonary oedema
• coagulopathies
• anaemia
• Hyproproteinaemia

Question 6

Isotonic crystalloids vs saline

Answer 6

• isotonic contains buffer so best for correcting acidosis
• SALTED and SMART, human studies suggesting improved outcomes with isotonic.
• 0.9% NaCL still best for hypochloraemic metabolic alkalosis or TBI

Question 7

Hypertonic saline

What are the doses and what considerations should be given to speed of administration

Answer 7

• Ideally 3% or 5%, 7.2% may be acceptable.
• dogs 3-7ml/kg, cats 2-4ml/kg
• given over no less that 5 minutes (aim for at least 1ml/kg/min rate) to avoid hyperosmolar induced hypotension.

Question 8

How does hypertonic saline work?

Answer 8

• causes a transient osmotic shift of fluid from the intravascular to extravascular compartment
• also some evidence that reduces vascular endothelial cell swelling, improves contractility and reduces inflammation.

Question 9

When might hypertonic saline be useful

Answer 9

• large animals when they need large fluid volumes faster that the pump can deliver
• useful in low volume resusitation protocols
• TBI to combat cerebral oedema.
• rapidly redistributes so need ongoing replacement fluid and not appropriate in dehydrated.

Question 10

what are the main categories of colloids and their general dose

Answer 10

• starches, gelatins and dextrans (als natural)
• 5 - 15ml/kg dog and 3-8ml/kg cat

Question 11

What are synthetic colloids

Answer 11

contain molecules (glucose polymers, starches) which do not cross the vascular membrane, suspended in a crystalloid solution.

Question 12

What is the theory for the benefits of colloids

Answer 12

• cause a fluid shift from the extravascular into the intravascular space, causing volume expansion > than the infused amount.
• molecules should exert a colloid oncotic pressure helping this fluid to remain in the intravascular space.

Question 13

What are the limitations/risks of colloids

Answer 13

• Volume expanding effect may not be as great as once thought as patients have damaged vascular endothelium.
• failure to find prognostic benefit.
• gelatins associated with high incidence of anaphylactic reactions.
• side effects: coagulopathies, volume overload, renal injury, anaphylaxis

Question 14

where are blood products useful in shock

Answer 14

• in haemorrhagic shock were crystalloids further dilute RBC mass and coagulation factors.
• use of alubumin containing fluids eg FP as an alternative to colloids
• HSA - not recommended due to reactions. canine serum albumin not availible UK.

Question 15

What is the significance of hypoperfusion persisting despite fluid resusitation?

What are your initial actions?

Answer 15

• persitent hypoperfusion mains likely a distributative component - assess patent for vasodilation.
• investigate for source of inflammation or infection.
  -these may have increased vascular permeability = increased risk of interstitial and pulmonary oedema
  ** evaluate cardiac contractility and vasomotor tone - is inotrope or pressor needed**

Question 16

what is the effect of drugs that act on a-adrenoreceptors and b-adrenoreceptors

Answer 16

a-adrenorecptors: vasopressors, vasoconstriction
b-adrenoreceptors: Inotropes, increase cardiac contractility

Question 17

can you list the common vasopressors and how much alpha/beta-adrenergic activity they have.

Answer 17

norepi 1st line

Question 18

how does vasopressin act

Answer 18

another pressor which acts on vascular smooth muscle via the v1 receptor. may be a good second line as vasopressin deficiency can be cause for low vasomotor tone

usually hard to get and cost prohibitive

Question 19

Explain the rational for the use of steroids when hypotension persists.

Answer 19

• hypothalmic pituitary shock response, production of cortisol
• prolonged overstimulation or injury of the HPA could cause relative adrenal insufficency
• could supplement physiological doses of HYDROCORTISONE in some.