CV anesthesia Flashcards
How do you reduce anesthetic risk with CV cases
Accurate diagnosis
Identify cardiac disease and known relevant pathophysiology
Treat reversible risk factors
Know cardiovascular therapy and possible interactions with anaesthetics
Continue administering prescribed drugs
Use anaesthetic protocol: that does not aggravate the hemodynamic effects of the CV condition
Understand adverse hemodynamic effects of surgery
Risk vs benefit calculation wiht anaesthsia
Anesthesia is risk because it upsets hemostasis
Risk vs benefits calculation is always influenced by availability of
Monitoring
Supportive care
Organized planning increases chances of a favourable outcome
Minimize anesthesia time - Keep it short!
Monitoring and supportive care for CV patients
Preoxygenation
IV access (mandatory)
Anticipate and prepare for complications
CV support drugs (dobutamine, ephedrine,..)
Increased vigilance of patient monitoring
Have one person dedicated to monitor patient
Electrocardiogram
Arterial blood pressure (doppler, oscillometric)
Pulse ox
Capnograph
Pharmacokinetic effects of CV disease
Poor peripheral perfusion
- Lower drug bioavailability after IM, SC
Reduced drug volume of distribution
- Greater sensitivity to injectable anesthetics
Slower circulation time
-Slower response after IV injection
Reduced Cardiac Output
- Increased rate of inhalation anesthetic uptake
Increased V/Q mismatch
- Slower onset and response to altered concentrations of inhalation anesthetics
Reduced renal perfusion and hepatic blood flow
Effects of anesthesia
Alteration of systemic vascular resistance
- Vasodilation: Inhalants, acepromazine, propofol, alfaxalone
- Vasoconstriction: dexmedetomidine, ketamine
Alteration in heart rate and rhythm
- Tachycardia: Anticholinergics, ketamine
- Bradycardia: opioids, alpha-2
Impairment of calcium utilization
- Inhalants
Development of intracellular acidosis
- Respiratory depression (propofol, alfaxalone, opioids,..)
What are the goals for anaesthesia
Pre-anesthetic exam: Assess individual baseline values
Maintain a stable cardiovascular system
Maintain a ‘normal’ heart rate
Avoid further depression of myocardial function
Maintain cardiac output and oxygen delivery
Avoid alterations of arterial blood pressure
Avoid increasing myocardial workload
Avoid increases in SNS tone
Choose anesthesia protocol adequate for cardiac condition
Keep anesthesia time as short as possible
General anesthesia or sedation
Sedation
- Adequate sedation for appropriate immobilization is often heavy and requires drugs with unfavorable cardiovascular effects
- Inadequate sedation increase patient stress: increase in catecholamines → increased myocardial O2 demand → increased risk of arrhythmias
- Fewer options for monitoring and support
General anesthesia
- Allows endotracheal intubation: secures airway and facilitates O2 administration
- Easier to apply monitoring
Degenerative mitral valve disease: review of disease process
Degenerative valve disease common in elderly small breed dogs
Begins asymptomatic (preclinical stage)
Anesthetic risk depends on severity
Degenerating valves become incompetent → mitral regurgitation
Decreased forward stroke volume → increases left atrial volume and pressures
Chronic volume overload of left heart → LV hypertrophy
Pulmonary venous hypertension (congestion, edema, tachypnea)
What are the hemodynamic goals for DMVD
Goal
- To maintain or improve forward blood flow
- Avoid increases in regurgitant flow through the mitral valve
Avoid increase in afterload due to vasoconstriction
- Vasodilation improves forward blood flow – inhalant anaesthetics are great vasodilators
Maintain a high normal HR
- Bradycardia allows overfilling of the ventricle and increases regurgitant volume
Maintain adequate IV volume. But avoid fluid overload
Anesthetic considerations with CVD
Consider temporarily discontinuing ACE-inhibitors just prior to anesthesia
Continue
- Inotropes (pimobendan) and other PDE-3 inhibitors (sildenafil)
- Diuretics (furosemide)
- Chronic vasoactive drugs such as amlodipine or hydralazine
Do not increase myocardial oxygen requirement (tachycardia)
- Avoid stressful situations
- Avoid hypothermia, shivering
Consider pre-hospital anxiolytics (trazadone and gabapentin)
Avoid fluid overload: Fluid rate: 3-5ml/kg/h
Anesthetic considerations for those with DMVD
Ensure adequate volume status and hydration–correct deficits
Management of hypotension
Use a balanced anesthetic drug plan to keep inhalant delivery at minimum
Use anticholinergics to maintain HR as necessary
Dobutamine (beta-selective catecholamine that increases cardiac contractility)
Ephedrine
Avoid drugs that mainly activate alpha receptors and cause vasoconstrictors
Prehospital treatment with trazadone
Avoid dexmedetomidine and acepromazine
Benzodiazepines (midazolam, diazepam) could cause paradoxical excitement
Alfaxalone IM
Use Opioids
What opiods are ok to use with animals with DMVD
Hydromorphone (0.1mg/kg, IM)
Methadone (0.2-0.5mg/kg)
Choice depends on expected pain from surgical procedure
Analgesia and sedation
Consider application of EMLA cream (local anesthetic) to facilitate IV catheter placement
Induction of anaesthesia for those with CVD
Pre-oxygenate (stress-free)
Titrate to effect (long circulation time)
Alfaxalone (or Propofol) co-administered with Benzodiazepines
Anesthetic sparing effect–less side effects
Give ¼ of propofol/ alfaxalone first and wait for effect
Then administer benzodiazepine
Diazepam/Midazolam (0.2mg/kg) IV
Top up with propofol/alfaxalone to effect
Alternative: Ketamine/Diazepam (tachycardia, increase in myocardial contractility, not recommended for advanced heart disease)
How do you mainitn GA for animals with CVD
Isoflurane/Sevoflurane: high doses should be avoided
Balanced anesthesia technique
Fentanyl CRI: 5-40μg/kg/h
Dental blocks with bupivacaine
MONITORING: ECG, BP, SpO2, capnography, temperature
How do you recover animals with CVD
Provide external heat support
Provide O2 until patient is breathing adequately
Analgesia
Minimize stress-provide optimal recovery conditions-TLC
Hypertrophic cardiomyopathy is
Characterized by an abnormal thickening of ventricular wall (hypertrophy)
Often asymptomatic
First sign: pulmonary edema or sudden death during anesthesia
Left ventricular hypertrophy and fibrosis lead to LV diastolic dysfunction and reduced cardiac output
Hypertrophy is not matched by coronary perfusion
Myocardial hypoxia, arrhythmias
What is Dynamic Left Ventricular Outflow Tract Obstruction (DLVOTO)
Ejection of blood from left ventricle can be impeded
Mitral valve is displaced against the inner wall of ventricle and septum → partially obstructing the passage
Effects of DLVOTO are greater when:
Heart rate and myocardial contractility are increased
Left ventricular diastolic volume and afterload are decreased
In humans, this is associated with an increased risk of sudden death.
What are the hemodynamic goal in a patient with HCM
Do not increase myocardial contractility
Avoid increases in myocardial oxygen consumption
Maintain normal (low) HR, avoid tachycardia
Maintain or increase systemic vascular resistance
Avoid drugs decreasing afterload (will worsen DLVOTO)
HCM: anaesthetic implications
Avoid stress (catecholamine release)
Administer 50-100mg Gabapentin 2-3 h beforehand
Tx should be administered the day of GA (Beta blocker or Ca++ channel blocker)
Pre-oxygenate
Avoid anticholinergics (atropine/glycopyrrolate)
Avoid ketamine (sympathomimetic effects)
What sedatives can you use with HCM
Opioids:
- Minimal effects on myocardial contractility, preload/ afterload
-Minimal sedation in cats, euphoria
Dexmedetmidine
- Controversial, use low doses (5-7μg/kg)
- Beneficial in cats with DLVOTO: may eliminate outflow tract obstruction
Midazolam:
- Minimal cardiovascular depression
- Paradoxical agitation, useful as an adjuvant
Acepromazine:
-Vasodilation resulting in augmentation of DLVOTO and hypotension
Alfaxalone
HCM and anaesthesia
Mask/Chamber induction?
- Stress of induction may be detrimental
-Should be avoided
Propofol
- Dose-dependent vasodilation
Alfaxalone
-Preserves heart rate, minimal vasodilation
Hypotension:
-Difficult to treat
- Balanced anesthesia
- Avoid hypovolemia, decrease in afterload
-Appropriate, but judicious fluid therapy
- Treat with alpha-1 agonist (phenylephrine 0.1-2μg/kg/min)
- Avoid beta-1 agonist (dobutamine)
How does ace work
Max sedation after 30-40 min
Long lasting (6-8 hours)
Reduces dose of major anesthetic agent by 30%
No reversal
Alpha 1 antagonist → peripheral vasodilation
Dogs: 0.01-0.05mg/kg
Low dose may be beneficial in patients with low degree MVI
Characteristics of dexmed
Most selective alpha 2 agonist available
Profound sedation
Analgesia
Muscle relaxation
Significant drug sparing effect
Recommended only for young, healthy patients
Vasoconstriction and bradycardia
Reversal with atipamezole (same volume)
Contraindicated in patients with MVD → increases mitral valve regurgitation
Last 60-90 min
Characteristics of midazolam
0.1-0.2mg/kg
Variable side effects
Can cause paradox excitement
Minimal cardio effects
Characteristics of alfax
IV induction agent
Can be used IM for sedation
Minimal cardioresp effects
1-1.5mg/kg
