CV complications

Question 1

MAP =

Answer 1

= CO x SVR
= (SV x HR) x SVR

where SVR is systemic vascular resistance

Question 2

CO in terms of VO2 (minimum oxygen consumption), CaO2 (arterial oxygen content), and CvO2 (mixed venous oxygen content)

What is the interpretation of this equation?

Answer 2

CO = VO2/(CaO2 - CvO2)

=> cardiac output is influenced by the oxygen demand of the tissues, and how much oxygen i bring to the tissues, and how much oxygen leaves the tissues
> the requirements of the tissues are met by the oxygen that is left there

> > when you run, the heart it is told by the tissues, “we need more oxygen”, and this is done by increasing HR or SV (CO = HR x SV)

Question 3

possible CV complications

Answer 3

1. Rate and Rhythm
   * Rate
   * Regular or irregular
2. Arterial blood pressure
3. Circulating volume

Question 4

normal HR vs tachycardia for dog

Answer 4

normal: 60-140
tachycardia: >180

Question 5

normal HR vs tachycardia for cat

Answer 5

normal: 100-160
tachycardia: >240

Question 6

normal HR vs tachycardia for horse

Answer 6

normal: 28-40
tachycardia: >60

Question 7

normal HR vs tachycardia for foal

Answer 7

normal: 60-90
tachycardia: >110

Question 8

normal HR vs tachycardia for cow

Answer 8

normal: 50-80
tachycardia: >100

Question 9

what do we want to see on a normal electrocardiogram?

Answer 9

Make sure rhythm is sinus
* Only possible if ECG monitoring
* All waves should be present
- A “P” wave for every “QRS”
- A “QRS” for every “P” wave

Question 10

pathophysiology of a normal to slow HR

Answer 10

Adequate diastolic filling- stroke volume
Too slow- negative effect on MAP, CO

Question 11

pathophysiology of a fast HR

Answer 11

> Inadequate diastolic filling- stroke volume
Too fast- negative effect on MAP, CO
Myocardial hypoxia

Question 12

what four factors contribute to stroke volume?

Answer 12

-preload
-afterload
-contractility
-rhythm

Question 13

influence of high vascular resistance on cardiac output

Answer 13

high resistance may drop cardiac output

=> CO = MAP/SVR

Question 14

animal species have different normal blood pressures. If pressures tend to be high, cardiac output tends to be….

Answer 14

low
-and vice versa; low pressures correspond to high cardiac outputs

Question 15

CO relationship to MAP and SVR

Answer 15

CO = MAP / SVR

Question 16

when might we see bradycardia with hypotension? what can trigger it? what drugs might cause this?

Answer 16

Increased parasympathetic activity
* Increased Vagal tone

Can be triggered by
* Oculocardiac reflex (trigeminovagal)
* Atrioventricular blocks and/or impaired SA to AV node conduction
– Heart disease (e.g.,Sick sinus syndrome)

• Drug induced
  – Opioids (morphine, butorphanol, hydromorphone, fentanyl)

Question 17

hypothermia and electrolyte abnormalities, specifically hyperkalemia, can cause what cardiac issues

Answer 17

bradycardia with hypotension or normal MAP

> if hyperkalemia caused by eg. urethral obstruction, may not see bradycardia due to counteracting effects of pain

Question 18

when might we see bradycardia with hypertension? what is the root cause of this? what drugs can cause this?

Answer 18

§ Increased parasympathetic activity

• Drug induced
  > Alpha 2-agonists (xylazine, romifidine, detomidine, dexmedetomidine)- due to hypertension that increases vagal tone
• Baroreflex response to hypertension
  > Vasoconstrictors that increase MAP
  – Phenylephrine, Norepinephrine
  – Increased intracranial pressure
  » Cushing’s response or ischemic response to an increase in intracranial pressure (ICP)

HYPERTENSION FIRST and then BRADYCARDIA

Question 19

when do we treat bradycardia?

Answer 19

§ Treat if marked bradycardia
§ Treat if hypotension or low cardiac output is associated with it
§ Treat if rhythm is markedly irregular and/or arrhytmias are also present

dont treat if hypertension => might exacerbate and decrease further the cardiac output

Question 20

how can we treat bradycardia with hypotension, or no change in MAP?

Answer 20

depends on the reason for it, but in general, anticholiergics are effective
-for sick sinus syndrome, also can install pacemaker. anticholinergic may not be effective here.
- generally, treat underlying cause too if possible

Question 21

how can we treat bradycardia with hypertension?

Answer 21

depends on the reason:
-if due to a2-agonist, anticholinergic may further decrease cardiac output
>can use reversal (atipamezole), and lidocaine also works

-if due to increased ICP, can use osmotic (mannitol or hypertonic saline)

Question 22

what can cause tachycardia?

Answer 22

§ CNS stimulation
* Increased sympathetic activity
»
* Hypercapnia
* Drug induced
– Ketamine
– Sympathomimetics (dobutamine, dopamine, ephedrine, epinephrine)
– Anticholinergics (glycopyrrolate, atropine)
* Superficial anesthetic plane and pain
* Shock/hypotension
– Sympathetic response
* Phaeochromocytoma
* Hyperthyroidism
* Heart disease

Question 23

how can we cure increased sympathetic activity due to hypercapnia?

Answer 23

• Adjust ventilation: RR x VT, flows, soda lime freshness

Question 24

how can we treat drug induced increases in sympathetic activity? what drugs could cause this?

Answer 24

could be due to ketamine, sympathomimetics, or anticholinergics
* Wait and/or stop administration

Question 25

how can we treat tachycardia due to superficial anesthetic plane and pain?

Answer 25

* Analgesia, adjust depth

Question 26

how can we treat tachycardia due to shock or hypotension?

Answer 26

* Treat underlying cause- fluids

Question 27

how can we treat tachycardia due to phaeochromocytoma?

Answer 27

* Beta-blocker

Question 28

how can we treat tachycardia due to hyperthyroidism?

Answer 28

regulate thyroid function

Question 29

how can we treat tachycardia due to heart disease?

Answer 29

* Improve cardiac output- inotropes, control volume

Question 30

what is commonly associated with AV blocks

Answer 30

-bradycardia § Conduction from atria to ventricles is impaired * Slow conduction (1st degree AV-block); not a great worry * P waves not followed by QRS complex (2nd and 3rd degree)

Question 31

what can cause AV blocks?

Answer 31

§ Drug induced * Alpha2-agonists * Underdosed anticholinergic drugs > Elicit increased parasympathetic tone (transient effect) § Organic disease

Question 32

how can we treat AV blocks?

Answer 32

depends on cause: * Reversal of alpha2-agonist * Anticholinergics * Isoproterenol * 2nd type II and 3rd degree can only be treated with artificial pacemaker *can also give lidocaine

Question 33

how can we treat atrial fibrilation in small animals? how does it arise?

Answer 33

§ Small animals: Can occur suddenly in dogs of large breeds. § Not always treated if the patient is able to maintain normal hemodynamic function § Diltiazem, Atenolol

Question 34

how can we treat atrial fibrilation in a horse?

Answer 34

§ Quinidine § Transvascular electrical conversion

Question 35

what is a ventricular premature contraction? what do we see on an electrocardiogram?

Answer 35

§ Ectopic focus in ventricle originates the ventricular depolarization § Not associated with atrial activity * No P wave * Premature * Bizarre QRS

Question 36

why are ventricular premature contractions a problem?

Answer 36

§ Premature nature prevents adequate diastolic filling * Pulse deficit

Question 37

causes of ventricular premature contractions?

Answer 37

* Heart disease- Hypertrophic-, Dilated cardiomyopathy * Myocardial hypoxia * Myocardial depressant factors (GDV, splenic tumors) * Arrhythmogenic drugs (thiopental, B1-agonists- sympathomimetics) * Irritation of ventricles (cardiac catheterization)

Question 38

how to treat ventricular premature contractions?

Answer 38

1. lidocaine. the rest is supportive * Prevents ectopic activity by blocking sodium channels during action potential -oxygenation, control underlying cause, improve contractility – VPCs may not be eliminated despite efforts * Attempt to maintain MAP and CO within acceptable values

Question 39

what is ventricular tachycardia? what happens if it is not treated? how do we treat?

Answer 39

§ More than 3 VPCs in sequence § Can become ventricular fibrillation if untreated § Tachycardia is part of this arrhythmia * Some VT with slower rates (HR <100) in dogs do not result in extreme adverse hemodynamic function § Same etiology and treatment as for VPCs * More aggressive

Question 40

a low blood pressure may mean what about perfusion?

Answer 40

* A low blood pressure may mean inadequate perfusion

Question 41

When is hypotension a concern? why?

Answer 41

* Deep plane of anesthesia * Dehydrated patient * Shock * Associated with arrhythmias * Weak pulses * Abnormal blood gases § If any of these are present, then: * Hypotension is associated with decrease blood flow to vital organs

Question 42

how do we treat hypotension, generally?

Answer 42

§ Correct volume * Fluids § Enhance contractility * Sympathomimetics (inotropes) * Decrease anesthetic depth § Vasodilatory shock * Increase vascular resistance § Control arrhythmias § If associated with bradycardia * Anticholinergics § If associated with tachycardia * Analgesia, anesthetic plane, B1-blocker

Question 43

what must we assess for hypotension treatment? (3)

Answer 43

-anaesthetic depth -volemia -contractility