Lecture 17 11/7/24 Flashcards
What are the primary goals for a general anesthesia event?
-minimize complications
-client satisfaction
What are the common complications of general anesthesia?
-hypoxia
-hypotension
-hypoxemia
-hypothermia
-hypoventilation
-hemorrhage
-pain
-myopathy
-neuropathy
What are the “4 Hs” that must be considered for every animal during every anesthetic event?
-hypoxia
-hypotension
-hypothermia
-hypoventilation
What is hypoxia?
-an imbalance between the oxygen supply and oxygen demand of the body
-DO2 < VO2
-oxygen delivery/supply is less than oxygen demand/consumption
What is oxygen supply?
DO2; oxygen delivery to tissues
What is the equation for DO2?
DO2 = CaO2 x CO
What does cardiac output represent?
pumping of blood to the tissues
What does arterial oxygen content represent?
the carriage of oxygen into the tissues/to the cells
What can lead to hypoxia?
decrease in either cardiac output or arterial oxygen content
What are the characteristics of mean arterial pressure/MAP?
-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
What is the MAP “sweet spot” for tissue autoregulation?
50 to 150
What are the characteristics of blood pressure in horses and large ruminants?
-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
What are the characteristics of hypotension?
-MAP less than 60-65 mmHg
-SAP less than 85-90 mmHg
-treatment depends on underlying mechanism
What is the equation for cardiac output?
CO = heart rate x stroke volume
How does a decreased heart rate impact MAP?
decreases MAP by causing decreased CO
When should bradycardia be treated?
-concurrent hypotension and bradycardia
-absolute bradycardia
What are the characteristics of preload?
-stretching of cardiac myocytes prior to contraction
-ventricular end diastolic volume
-stretching from increased venous return to the heart
What are the clinical signs of decreased preload?
-concurrent hypotension and tachycardia
-clinical suspicion; vomiting, dehydration, etc.
What is the treatment for decreased preload?
-fluid therapy
-decrease intra-thoracic pressure
What are the characteristics of dobutamine?
-positive inotrope
-inodilator/vasodilator
-acts on beta1 and beta2 receptors
-indicated in systolic dysfunction
What are the characteristics of dopamine?
-dose dependent effects
-positive inotrope
-vasoconstrictor at higher doses
-indicated for inotropy and vasoconstriction
-acts on alpha1, alpha2, beta1, beta2, D1, and D2 receptors
What are the characteristics of ephedrine?
-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
Which drugs have the potential for use when treating hypotension?
-dobutamine
-dopamine
-ephedrine
-phenylephrine
-norepinephrine
-epinephrine
-vasopressin
What are the characteristics of epinephrine?
-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
How is epinephrine reversed?
acepromazine blocks alpha receptors so epinephrine cannot bind there
What are the characteristics of afterload?
-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
What are the characteristics of systemic vascular resistance?
-decreased SVR leads to decreased MAP
-vasodilation can occur with inhalants, acepromazine, propofol, and alfaxalone
What is the general treatment for decreased systemic vascular resistance?
vasoconstriction
What are the characteristics of phenylephrine?
-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
What are the characteristics of norepinephrine?
-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
What are the characteristics of vasopressin?
-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)
What is the clinical approach to hypotension?
-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
