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Anesthesia for the Heart

Physiology Review

Physiology Review

DO2 = CO X CaO2 (blood O2 content)

CO = HR X SV

  • SV depends on...Contractility, PL & AL
  • Increase PL --> Increased CO
  • Increased AL --> Decrease CO
  • Increase contractility --> Increase CO

Ultimate goal = O2 delivery to tissues!

Drug targets

Manipulate SV & HR --> Better CO!

Heart rate:

  • If too low...Decreases CO...Give Anticholinergics
  • If too high or irregular...Decreases CO...Give Antiarrhythmics

Contractility:

  • If too low...Decreases CO...Give Positive inotropes

Afterload/Preload (Vasopressors):

  • Most anesthetic drugs cause...Vasodilation
  • Needs adequate intravascular volume

Drugs for the heart

Drugs

  • Decreases parasympathetic tone
  • Increases firing rate @ SA node & Chronotropy (HR)
  • Indication = bradycardia 2nd to increased vagal tone caused by...
  • Intubation
  • Opioids
  • Brachycephalics
  • Heart SE = Paradoxical bradycardia & can potentially cause AV block
  • Drugs = Atropine & Glycopyrrolate
  • Atropine --> Emergency use, transient tachycardia, cross BBB (mydriasis)
  • Glyco --> Less tachycardia, doesn't cross BBB

Anticholingergics

Anti-Arrhythmics

  • Class 1B = Lidocaine
  • Indication --> Ventricular arrhythmias (Multifocal VPC, HR >180)
  • Class II = Beta-blockers
  • Rare to use during anesthesia unless...Tachycardia associated with pheochromocytoma

Adrenergics

  • Dopamine
  • @ Low dose --> Increases Inotropy (CON) & Chronotropy (HR)
  • @ High dose --> Above + Vasoconstrictor
  • Common 1st drug for hypotension!
  • Epinephrine
  • Primary alpha
  • Can see reflex bradycardia due to vasoconstriction effects
  • **Less effective after 2-3 doses & can cause CNS stimulation (increases MAC)**
  • Norepinephrine
  • Primary alpha
  • Indication = refractory shock OR non-responsive hypotension
  • Epinephrine
  • Non selective (alpha, beta 1 & 2)
  • For CPR & causes V-Fib
  • Phenylephrine
  • Alpha 1 agonist ONLY = vasoconstriction & increases BP BUT...decreases CO & perfusion & causes splenic contraction
  • Used for horses to prevent nasal edema
  • Dobutamine
  • Beta-1 primarily --> Increases inotropy BUT minimal chronotropy
  • Vasopressin (non-adrenergic sympathomimetic) --> Vasoconstriction @ V1 receptor
  • Indication = Refractory shock OR Non-responsive hypotension (CRI)
  • Monitory closely! --> Can cause profound vasoconstriction --> Decrease CO & Increase BP

Hypotension :(

How can we fix it??

1. Decrease Vaporizer if patient is too deep

  • If bradycardic & hypotensive = Anticholinergic
  • If patient is too light...Add MAC sparing drug & then turn down vaporizer
  • MAC sparing drugs = Opioid, Benzo, Lidocaine, Ketamine

2. Give Crystalloid fluid bolus

3. Either Vasopressor (Vasodilation) OR + Intrope (decrease contractility)

Valve Regurgitation

  • Mitral valve regurgitation --> Increases valvular contraction
  • (-) Intrope (most anesthestics) --> Not high risk for these patients

  • Pre-Anesthetic:
  • AVOID severe Bradycardia
  • Morphine & Fentanyl preserves cardiac function & better analgesia BUT can cause severe bradycardia
  • High ACE --> Hypotension --> Tissue ischemia in end stage Heart Disease
  • Induction:
  • Propofol
  • Etomidate --> Maintains normal CV function & good in severe valvular insufficiency
  • Maintenance:
  • Adding a MAC sparing drug can be beneficial to help decrease heart side effects
  • Goal = Improve myocardial contraction & Decrease PL, AL
  • **CONTINUE PIMOBENDAN** (+ inotrope & arterial dilator)

  • Pre-med: Benzo & Opioid combo
  • If use ACE...Use LOW dose (high dose =prolonged hypotension)
  • **NO ALPHA-2**
  • Bradycardia
  • Myocardial depression
  • Arrhythmogenicity
  • Induction:
  • Propofol --> Can decrease myocardial contraction
  • Ketamine (+ inotrope) --> Good for induction but increases O2 demand
  • Inhalant: They cause dose-dependent decrease myocardial contraction
  • ADD CRI low dose ketamine, benzo or opioid to decrease inhalant concentration
  • **MONITOR = BP & careful not to fluid overload (L CHF)***

DCM

  • Goals for HCM cat:
  • Maintain preload (in cats w/o CHF)
  • Increase AL
  • DON'T increase myocardial contractility
  • Maintain normal HR & sinus rhythm
  • Avoid increase in myocardial O2 consumption
  • Pre-med = Opioid-Benzo combo
  • Butorphanol & midaz OR morphine & midaz
  • **AVOID**
  • Ketmaine...Increase CON, HR & O2 demand
  • High ACE...Vasodilation --> Augment outflow obstruction
  • Stress..Will increase HR & CON
  • DON'T STOP heart medications

HCM

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