Mod2: CARDIAC SURGERY AND ANESTHESIA CONSIDERATIONS Flashcards
CORONARY ARTERY DISEASE
What’s the leading cause of death in the US?
Coronary Artery Disease
CORONARY ARTERY DISEASE
What’s the leading cause of death after anesthesia and surgery?
Perioperative Cardiac morbidity
CORONARY ARTERY DISEASE
Why is it our goal to either prevent it or to promptly identify it and treat myocardial ischemia?
Because CAD is the leading cause of death in the US and
Cardiac morbidity is the leading cause of death after anesthesia and surgery
CORONARY ARTERY DISEASE
T/F: When patients do develop CAD, supply and demand becomes a balancing act
True
PATHOPHYSIOLOGY OF ISCHEMIA
When does Myocardial ischemia occur?
When there is a relative lack of O2 supply to the myocardium and
Reduced metabolite removal for the heart for a given O2 consumption
PATHOPHYSIOLOGY OF ISCHEMIA
How is Myocardial ischemia Classically noted?
Classically noted as symmetrical T-wave changes
This is a Dynamic state the heart can go in and out of
Occurs at the cellular level
As a result of imbalance between supply and demand
PATHOPHYSIOLOGY OF ISCHEMIA
Ischemia that causes potentially reversible damage to the myocardium, which causes it to depolarize and repolarize incompletely is also known as:
Myocardial injury
PATHOPHYSIOLOGY OF ISCHEMIA
How is Myocardial injury classically noted as?
Myocardial injury is Classically noted as ST changes
Also known as “stunned myocardium” or “stoned heart”
PATHOPHYSIOLOGY OF ISCHEMIA
What event do we have when Myocardial ischemia continues and results in tissue death/necrosis?
Myocardial infarction
Occurs with a reduction in coronary blood flow that persists longer than 20-40 minutes
PATHOPHYSIOLOGY OF ISCHEMIA
T/F: Ischemia can affect different layers of the heart muscle
True
PATHOPHYSIOLOGY OF ISCHEMIA
Ischemia that affects the superficial outer layer of the ventricle is known as:
Subepicardial ischemia
PATHOPHYSIOLOGY OF ISCHEMIA
Ischemia that results in injury or infarction of only the inner half of the heart muscle is known as:
Subendocardial ischemia
As previously mentioned, because autoregulation is lost, this area becomes pressure dependent so it has the highest risk of ischemia
- Manisfest as Flipped t-wave* or ST depression
- Q-wave will be absent in Subendocardial ischemia?!*
- Recent studies suggest that Q-wave could be present in both Subendocardial and Transmural ischemia*
PATHOPHYSIOLOGY OF ISCHEMIA
How does Subendocardial ischemia manifest on the ECG?
Flipped t-wave, or
ST depression
PATHOPHYSIOLOGY OF ISCHEMIA
Ischemia that results in injury or infarction of the full thickness of the ventricle is known as:
Transmural ischemia
PATHOPHYSIOLOGY OF ISCHEMIA
How does Transmural ischemia presents on the ECG?
ST elevation
Some sources say Q-wave
- Q-wave will be absent in Subendocardial ischemia?!*
- Recent studies suggest that Q-wave could be present in both Subendocardial and Transmural ischemia*
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
What % of patients with CAD may have a normal resting EKG?
25-50%
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
What % of patients have a baseline defect that makes it non-interpretable for ischemia?
25%
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
Why do EKG have increased importance in the postoperative period?
Because 80% of MI’s occur in the postoperative period
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
Why might ST segment changes on the EKG be considered late sign of ischemia?
Because patients with baseline defect (LBB, WPW) make it non-interpretable
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
Which ECG change is seen WPW?
T-wave inversion
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
How does LBB appear in V1?
As a Q-S complex
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
How is intraoperative ischemia detected via PA catheter?
Increased demand, leads to a decreased compliance
Decreased compliance manifests as:
=> Sudden ↑ PA pressure/PCWP (ventricular dysfunction)
=> Large a waves ( ↓ ventricular compliance)
=> Large v waves ( ischemia induced papillary muscle dysfunction)
=> Is Not specific
DETECTION OF INTRAOPEARTIVE MYOCARDIAL ISCHEMIA
Why is the Intraoperative TEE considered the best choice for detecting ischemia intraoperatively?
Very sensitive and more specific than EKG or PAC
Will detect development of new global and regional wall motion abnormalities
First detectable change in the left ventricle during ischemia
TEE changes are more common and more predictive of MI than ECG
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What does the QRS complex on the EKG represent?
Ventricular depolarization
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What does the the first downward or negative deflection of the QRS complex represent?
the Q wave
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What does the First upward or positive deflection of the QRS complex represent?
the R wave
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What does the negative deflection that occurs after the R wave of the QRS complex represent?
the S wave
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
On the EKG tracing below, what do 4 and 8 represent?
4: Q-wave
8: QS complex (Can’t tell if it’s a Q or an S wave)
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What happens to the S & R wave amplitudes as the QRS complex progresses in the precordial leads from V1 to V6?
S wave amplitude decreases
R-wave amplitude increases
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
Which phase of cardiac action potential does the T wave represents?
Ventricular repolarization
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
In which leads is the T wave normally upright?
In leads I, II, and V3-6
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
In which leads is the T wave normally inverted?
in aVR
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What’s the T wave orientation in leads other than I, II, V3-6, and AVR?
Variable
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA: OVERVIEW
What happens to the T wave amplitude as we progress along the precordial leads V1-6?
Amplitude should increase along with R-wave
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
Which two changes can ischemic EKG have?
Indicative changes
Reciprocal changes
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
Changes that occur in leads that are facing the ischemic/infarcted area are categorized as:
Indicative changes, include:
- Inverted T-wave*
- Elevated ST segments,*
- Abnormal Q-waves or*
- Loss of R wave amplitude*
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
Changes that occur in leads facing away from the ischemic or infarcted area are categorized as:
Reciprocal changes
They record a mirror image of the indicative changes and provide indirect evidence of ischemia
They are sometimes seen first
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
Given a list of some Reciprocal changes:
Upright, tall or peaked T-waves
Depressed ST segments
Absence of normal Q-wave in the lateral leads
Increased R-wave voltage
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
Summary table of Indicative/Facing vs Reciprocal changes:
(See table)
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
What’s the signature of an MI on the EKG?
Decreased R-wave amplitude, and
Pathologic Q-waves
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
What causes pathologic Q waves?
Absence of electrical activity
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
An MI can be thought of as an electrical whole; why is that?
Because scar tissue is electrical death
Therefore results in pathological Q wave
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
When are Q waves considered diagnostic?
It they are more than 0.04 sec in V2-V3, or
QS complex in V2
IDENTIFICATION OF INTRAOPERATIVE ISCHEMIA
T/F: Q waves in V1-2 are always abnormal
True
SELECTION OF ANESTHETIC AGENT
T/F: No “one ideal” anesthetic
True
SELECTION OF ANESTHETIC AGENT
Choice dependent primarily on:
Degree of myocardial dysfunction
Pharmacological properties of drugs themselves
SELECTION OF ANESTHETIC AGENT
Volatile agents might be the anesthetic of choice for a pt with which LV assessment?
Good LV function
(meaning EF >40%, LVEDP <12, normal CO)
Volatile agents will contribute to coronary vasodilation
Volatile agents can potentially cause preconditioning which will protect the myocardium from hypoperfusion and ishemia
SELECTION OF ANESTHETIC AGENT
High-dose opioid technique might be the anesthetic of choice for a pt with which LV assessment?
Poor LV function
(Meaning EF <40%, LVEDP >18, Decreased CO, multiple areas of dyskinesia)
Opioid-based technique lack myocardial depression so hemodynamics remain stable
SELECTION OF ANESTHETIC AGENT
What’s a disadvantage of opioid based technique?
Prolonged mechanical ventilation
Delayed extubation
Whereas the goal is to fastrack (extubate within 6-hrs) most of theses pts
SELECTION OF ANESTHETIC AGENT
What’s the perfect anesthetic combination for theses patients?
Volatile agents + opioid-based technique = Both together
TREATMENT OF INTRAOPERATIVE ISCHEMIA: NITRATES
What’s the effect of Nitrates like nitroglycerine on vascular smooth muscles?
Relax vascular smooth muscle
Venous > arterial
Reduce venous and arteriolar tone
=> reduce circulating blood volume
Reduction in preload and wall tension afterload => reduces MVO2
Dilation of coronary arteries
This reduces cardiac oxygen demand by decreasing preload and afterload
TREATMENT OF INTRAOPERATIVE ISCHEMIA: NITRATES
Why are Nitrates the drugs of choice for acute coronary vasospasm?
Because they preferentially increases blood flow to Subendocardial layers
TREATMENT OF INTRAOPERATIVE ISCHEMIA: NITRATES
How do Nitrates decrease pulmonary HTN?
By reducing pulmonary vascular resistance
TREATMENT OF INTRAOPERATIVE ISCHEMIA: NITRATES
Nitrates are great at improving collateral flow to ischemic regions. However, they must be used with caution. Why is that?
Too high doses of Nitrates can cause systemic hypotension and impair coronary perfusion pressure
TREATMENT OF INTRAOPERATIVE ISCHEMIA: NITRATES
T/F: High dose Nitrates could cause Methemoglobinemia
True
TREATMENT OF INTRAOPERATIVE ISCHEMIA: SNP
Which type of drug is SNP classified as? What are its effects?
Direct-acting nonselective peripheral vasodilator
Relaxes both arterial and venous vascular smooth muscles
Enhances ventricular function by decreasing impedance to ventricular ejection
Reduction in pulmonary vascular resistance (Effective for use against PHTN)
Decrease SVR and PVR, preload, and also reduces platelet aggregation
TREATMENT OF INTRAOPERATIVE ISCHEMIA: SNP
SNP reduces platelet aggregation. Why would this be a concern?
Reduction of platelet aggregation would be a benefit before surgery but a disadvantage after
After surgery, when aggregation is important to reduce post op bleeding, this could potentially cause problems
TREATMENT OF INTRAOPERATIVE ISCHEMIA: SNP
SNP could cause the diversion of blood away from ischemic areas. What is this phenomenom called?
Coronary steal
TREATMENT OF INTRAOPERATIVE ISCHEMIA: SNP
Which disadvantages of Sodium Nitroprousside make NTG the preferred drug of choice after acute MI?
Coronary steal, which results in the diversion of blood away from ischemic areas where blood vessels are already maximally dilated
Can also cause reflex tachycardia by stimulating baroreceptor-mediated response
Decreases in PaO2 as a result of the inhibition of hypoxic pulmonary vasoconstriction
Cyanide toxicity
Methemoglobinemia
Thiocyanate toxicity
Reduces platelet aggregation
TREATMENT OF INTRAOPERATIVE ISCHEMIA - VASOCONSTRICTORS
What role do vasoconstrictors play in the management of intraoperative ischemia?
Maintain diastolic blood pressure
Indicated during episodes of systemic hypotension
Increase coronary perfusion pressure (alpha-adrenergic)
- However, they also increases afterload, preload, and MVO2*
- NTG added to counteract increased preload*
- More often then not, increased CPP offset increased wall tension*
TREATMENT OF INTRAOPERATIVE ISCHEMIA - VASOCONSTRICTORS
Which vasoconstrictors are most commonly used in the intraoperative phase of surgery prior to bypass grafting?
Phenylephrine
Norepinephrine
Vasopressin
TREATMENT OF INTRAOPERATIVE ISCHEMIA - VASOCONSTRICTORS
What makes Phenylepherine is an excellent drug for the treatment of intraoperative ischemia?
It has alpha agonist activity
Minimal to no inotropic or chronotrpic stimulation
Its administration activates the baroreceptors, reducing heart rate
However, the increase in SVR could potentially increase the work of the heart and reduce myocardial O2 demands
TREATMENT OF INTRAOPERATIVE ISCHEMIA - VASOCONSTRICTORS
How could Norepinepherine decrease myocardial oxygen supply?
by increasing myocardial contractility
via mild stimulation of Beta-1 cells
TREATMENT OF INTRAOPERATIVE ISCHEMIA - VASOCONSTRICTORS
Why should Vasopressin be used cautiously in patients with coronary artery disease?
Because of its powerful vasoconstrictor response
Could also constrict the coronary arteries
TREATMENT OF INTRAOPERATIVE ISCHEMIA - VASOCONSTRICTORS
T/F: although vasoconstrictive agents are effective in treating systemic hypotension during intraoperative ischemia, they should be used with caution
True
TREATMENT OF INTRAOPERATIVE ISCHEMIA
A balance of supply and demand involves controlling heart rate and contractility. Which drugs reduce heart rate, and myocardial contractility in hyper-dynamic states?
Beta blockers
TREATMENT OF INTRAOPERATIVE ISCHEMIA
Why should Beta blockers be administered prior to CABG (According to quality measures)?
Because they have been shown to reduce the risk of death following surgery
They should be administered to all patients who are 18 years of age with no contraindication present
Administration within 24 hours prior to surgery is a quality measure unless contraindicated
TREATMENT OF INTRAOPERATIVE ISCHEMIA
Which drugs selectively relax arterial resistance and thus cause coronary vasodilation?
Calcium channel blockers
Also decrease myocardial demand by decreasing contractility
TREATMENT OF INTRAOPERATIVE ISCHEMIA
Which Calcium channel blockers have greater effects on cardiac contractility, but should be used cautiously in patients with ventricular dysfunction, conduction abnormalities
Verapamil and Diltiazem
TREATMENT OF INTRAOPERATIVE ISCHEMIA
Which calcium channel blocker is frequently used in the operating room and is thought to be the first-line treatment for cardiac patients who have acute hypertension that requires immediate control? and why is it the first-line treatment?
Nicardipine
Because of its minimal side effects
