Lecture 17 11/7/24

Question 1

What are the primary goals for a general anesthesia event?

Answer 1

-minimize complications
-client satisfaction

Question 2

What are the common complications of general anesthesia?

Answer 2

-hypoxia
-hypotension
-hypoxemia
-hypothermia
-hypoventilation
-hemorrhage
-pain
-myopathy
-neuropathy

Question 3

What are the “4 Hs” that must be considered for every animal during every anesthetic event?

Answer 3

-hypoxia
-hypotension
-hypothermia
-hypoventilation

Question 4

What is hypoxia?

Answer 4

-an imbalance between the oxygen supply and oxygen demand of the body
-DO2 < VO2
-oxygen delivery/supply is less than oxygen demand/consumption

Question 5

What is oxygen supply?

Answer 5

DO2; oxygen delivery to tissues

Question 6

What is the equation for DO2?

Answer 6

DO2 = CaO2 x CO

Question 7

What does cardiac output represent?

Answer 7

pumping of blood to the tissues

Question 8

What does arterial oxygen content represent?

Answer 8

the carriage of oxygen into the tissues/to the cells

Question 9

What can lead to hypoxia?

Answer 9

decrease in either cardiac output or arterial oxygen content

Question 10

What are the characteristics of mean arterial pressure/MAP?

Answer 10

-used in vet med as a surrogate for cardiac output
-MAP = CO x SVR
-dilated vessels leads to low SVR and low MAP
-vasoconstriction leads to high SVR and high MAP

Question 11

What is the MAP “sweet spot” for tissue autoregulation?

Answer 11

50 to 150

Question 12

What are the characteristics of blood pressure in horses and large ruminants?

Answer 12

-MAP is important in understanding muscle blood flow
-external weight when in recumbency leads to compression of muscles
-want MAP greater than 70 mmHg to decrease incidence of myopathy

Question 13

What are the characteristics of hypotension?

Answer 13

-MAP less than 60-65 mmHg
-SAP less than 85-90 mmHg
-treatment depends on underlying mechanism

Question 14

What is the equation for cardiac output?

Answer 14

CO = heart rate x stroke volume

Question 15

How does a decreased heart rate impact MAP?

Answer 15

decreases MAP by causing decreased CO

Question 16

When should bradycardia be treated?

Answer 16

-concurrent hypotension and bradycardia
-absolute bradycardia

Question 17

What are the characteristics of preload?

Answer 17

-stretching of cardiac myocytes prior to contraction
-ventricular end diastolic volume
-stretching from increased venous return to the heart

Question 18

What are the clinical signs of decreased preload?

Answer 18

-concurrent hypotension and tachycardia
-clinical suspicion; vomiting, dehydration, etc.

Question 19

What is the treatment for decreased preload?

Answer 19

-fluid therapy
-decrease intra-thoracic pressure

Question 20

What are the characteristics of dobutamine?

Answer 20

-positive inotrope
-inodilator/vasodilator
-acts on beta1 and beta2 receptors
-indicated in systolic dysfunction

Question 21

What are the characteristics of dopamine?

Answer 21

-dose dependent effects
-positive inotrope
-vasoconstrictor at higher doses
-indicated for inotropy and vasoconstriction
-acts on alpha1, alpha2, beta1, beta2, D1, and D2 receptors

Question 22

What are the characteristics of ephedrine?

Answer 22

-direct effects on heart
-indirect effects via increased norepinephrine
-positive inotrope
-possible vasoconstriction
-increases uterine blood flow
-crosses blood brain barrier
-given as single bolus or CRI
-acts on alpha1, alpha2, beta1, and beta2 receptors

Question 23

Which drugs have the potential for use when treating hypotension?

Answer 23

-dobutamine
-dopamine
-ephedrine
-phenylephrine
-norepinephrine
-epinephrine
-vasopressin

Question 24

What are the characteristics of epinephrine?

Answer 24

-positive inotrope
-causes vasoconstriction
-increases heart rate
-final line of defense for refractory hypotension
-used in CPR
–acts on alpha1, alpha2, beta1, and beta2 receptors

Question 25

How is epinephrine reversed?

Answer 25

acepromazine blocks alpha receptors so epinephrine cannot bind there

Question 26

What are the characteristics of afterload?

Answer 26

-load that heart has to push against
-occurs with dx such as subaortic stenosis
-increased afterload decreases cardiac output
-not managed as a primary condition

Question 27

What are the characteristics of systemic vascular resistance?

Answer 27

-decreased SVR leads to decreased MAP
-vasodilation can occur with inhalants, acepromazine, propofol, and alfaxalone

Question 28

What is the general treatment for decreased systemic vascular resistance?

Answer 28

vasoconstriction

Question 29

What are the characteristics of phenylephrine?

Answer 29

-causes vasoconstriction
-can have reflex bradycardia
-indicated in vasodilatory shock and hypotension refractory to acepromazine
-first line drug for cats with HCM
-used in equine if dobutamine does not work first
-acts on alpha1 and alpha2 receptors

Question 30

What are the characteristics of norepinephrine?

Answer 30

-causes vasoconstriction
-less tachyarrhythmia risk compared to dopamine
-can decrease splanchnic and peripheral blood flow
-indicated in refractory hypotension and vasodilatory shock/sepsis
-acts on alpha1, alpha2, beta1, and beta2 receptors

Question 31

What are the characteristics of vasopressin?

Answer 31

-causes vasoconstriction
-works well in acidic environments
-beneficial when adrenergic receptors are down-regulated
-indicated in refractory hypotension, vasodilatory shock/sepsis, and CPR
-acts on special receptors (V)

Question 32

What is the clinical approach to hypotension?

Answer 32

-consider heart rate and BP together
-if heart rate and BP are both low, treat with anticholinergics
-if heart right is high, give fluids; consider dehydration and blood loss
-if HR is normal, consider if low BP is anesthesia induced
-if HR is normal, identify if patient has DCM, HCM, or vasodilatory shock/sepsis