Preop Eval for Cardiac Surgery on Ischemic Pts Flashcards
What is the definition of a MET?
amount of O2 consumed while seated at rest
A MET is equal to how many mL of O2 per kg of body weight per minute?
3.5 mL
We want at least ___ METs in our patients?
> or = to 4
What is an example of 1 MET?
can you take care of yourself, eat, dress, toilet
What is an example of 2 METs?
Walk a block or two on ground level at 2-3 mph
What is an example of 4 METs?
Do light housework? Climb a flight of stairs? Walk on ground level at 4mph?
What is an example of 7 METs?
biking at 12 mph/moderate sports
Is heavy housework like scrubbing >4 METs?
yes
What is the MET score of participating in strenuous sports?
10
What is the MET score of participating in moderate strenuous sports such as golf, bowling, double tennis, or throwing a football?
around 9
What are 4 categories of active cardiac conditions for which the patient should undergo evaluation and treatment before noncardiac surgery? Also, what is the level of evidence for that recommendation?
unstable coronary syndromes (unstable angina, recent MI), decompensated heart failure (functional class IV, new or worsening HF), significant arrhythmias (high grade AVB, Mobitz II, 3rd degree block, uncontrolled AF RVR, supraventricular arrythmias, symptomatic or newly recognized VT, symptomatic bradycardia), severe valvular disease (AS with pressure gradient >40, valve area
Sx of mitral valve stenosis?
progressive DOE, exertional presyncope, HF
Sx of severe AS?
angina, syncope, PND, dyspnea on exertion, fatigue, palpitations
If a patient has active cardiac conditions but needs non cardiac surgery, should you proceed?
if it’s an emergency, yes. if not an emergency, try to treat active cardiac conditions and then consider OR, for low risk surgery it’s ok to take pt to surgery. if METs> 4 or not symptomatic go to OR
If a pt has
consider testing if it will change the way you manage the pt
If a pt has4
proceed w planned surgery w HR control or consider noninvasive testing if it will change management
If a pt has
proceed w planned surgery w HR control or consider noninvasive testing if it will change management
If a pt has
yes
What are some examples of high risk surgeries?
emergent surgeries, particularly in the elderly, aortic and other major vascular surgery, peripheral vascular surgery, anticipated long surgeries associated w large fluid shifts and blood loss
What are some examples of intermediate risk surgeries?
CEA, head and neck, orthopedic, prostate, intraperitoneal and intrathoracic surgery
What are some examples of low risk surgeries?
endo procedures, superficial procedures, cataract surgery, breast surgery
What did Dr. White say is the rule of thumb regarding ASA and plavix if the surgeon is concerned w bleeding?
hold plavix, continue ASA
Out of supply and demand, what can the anesthetist control?
both
4 GENERAL ways to control supply and demand?
drugs, ventilation, fluids/blood, vigilance
3 ways to control supply?
drugs to maintain homeostasis, management of ventilation, coronary vasodilation (?)
2 ways to control demand
keep workload low (low HR, low BP, low SVR); lower BMR
Oxygen supply to the myocardium depends primarily on?
myocardial blood flow and the O2 content of the blood
An increase in oxygen extracted by the myocardium must be accomplished how?
improved flow/increased coronary blood flow
What’s the equation for calculating coronary blood flow (CBF)?
CPP (coronary perfusion pressure)/CVR (coronary vascular resistance)
This is the degree of vasoconstriction of coronary arterioles?
coronary vascular resistance
How do you calculate CPP?
diastolic BP- LVEDP
What are the goals of therapy for each: diastolic BP, LVEDP, hr? Which of these allow more time for filling?
normal to high DBP, low LVEDP, low HR; low LVEDP and low hr
What is the most vulnerable part of the heart to ischemia?
subendocardial layer
Flow is ___________ and only occurs during _________?
intermittent; diastole
3 metabolic lab values that increase coronary vascular resistance?
increased oxygen, decreased CO2, decreased H
2 autonomic ways to increase CVR?
increase alpha adrenergic tone and increase cholinergic tone
3 hormones which will increase CVR?
increased vasopressin, angiotensin, and thromboxane
5 metabolic things that decrease CVR?
low oxygen, high CO2, increased H, adenosine, lactate
Does lung protective ventilation increase or decrease CVR?
decrease
What is an autonomic way to decrease CVR?
increase beta adrenergic tone
What is a hormone that will decrease CVR?
increased prostacycline
What are 3 endothelial mediated substances that will decrease CVR?
increased nitric oxide, increased endothelium derived hyperpolarizing factor, and increased prostaglandin I2
Anatomically speaking, what are 2 ways that CVR can be decreased?
capillary: myocyte ratio, coronary collaterals
What do stenotic lesions do to CBF and CVR?
decrease CBF, increase CVR
What is Pouiseuille’s equation? What are P, R, L, and N iin reference to this equation?
{P x pi x r to the 4th}/ (8 x l x n); P= pressure, R= radius, L= distance, N= viscosity
A 50% reduction in vessel diameter decreases flow by what fraction? What type of symptoms would be seen in this patient?
1/16; angina on exertion
A 75% stenosis is > ___% reduction in flow? What symptoms will this patient have?
98; unrelenting angina not controlled with nitrates
Sequential lesions are important for us to know about why?
they additive in flow reduction so if proximal lesion (near aortic ostia) that is 50% (flow cut by 75%) and further down there is 75% lesion, so flow past 75% lesion is >98% restricted. that distal tissue really at risk for ischemia
Lesions where restrict flow more than others?
left main, high grade proximal lesions of the left main and LAD
What is a left main equivalent?
if high grade proximal lesions of the circumflex and LAD occur in tandem (she mentioned >75% stenosis of both but not sure if that disqualifies you from left main equivalent status if its
How can you increase oxygen supply (hint: vital signs)?
low heart rate, low RA or PAP, high MAP, normal Hgb, high SaO2 and PaO2, low CVR
How can you decrease oxygen supply (hint: vital signs/numbers)?
high heart rate, high RA or PAP, low MAP, low O2 content, low Hgb, high CVR
What are the 3 primary determinants of myocardial oxygen demand?
LV wall tension, HR, and contractility
Wall tension is directly proportional to?
pressure in ventricle during contraction (afterload), size of ventricle (preload), and wall thickness
What is the Law of LaPlace equation?
wall tension = pressure x radius/ (2 x wall thickness)
What is the goal for PAWP, RA, and MAP values for maintaining appropriate wall tension? What is the exception?
low PAWP, RA and low to normal MAP; AS
This is the intrinsic vigor of the myofibril shortening?
contractility
How can you measure contractility?
direct observation when pericardium is opened, brisk upstroke of a line tracing
How do you control contractility?
not really any drugs that lower it but can avoid those agents that increase it. anesthetic gasses lower contractility
2 indications for an IABP?
left main or left main equivalent and unstable angina
When is the IABP inflated and deflated?
inflated at onset of diastole, deflated at onset of systole
Tachycardia is undesirable for what 3 reasons?
decreases filling time, decreases time in diastole, decreases perfusion of subendocardium
General anesthesia reduces BMR by?
30-40%
A drop in core temp by 1 degree C causes a what percentage reduction in BMR?
10%
Decreasing BMR by this much reduces oxygen demand on the myocardium?
40%
Some downsides to hypothermia?
delayed drug metabolism, prolonged recovery from anesthesia, impaired coagulation, prone to arrythmias, impaired wound healing, shivering which you see on SVO2 cath
What are the temperature goals before, during, and after bypass?
lower temp prior to going on bypass, cool during bypass, active warming post bypass
Why do you see a downward drift in temperature after the patient has been warmed post bypass?
the cold blood that was in the periphery is now circulating back through the core
What do benzos and narcs do to coronary vasculature?
vasodilate
In general, the anesthetic gasses do what to vasculature and coronary vasculature?
dilate; unfortunately they cause profound systemic vasodilation
What is unique about halothane and the myocardium?
it’s a direct depressant of contractility and it sensitizes the myocardium to catecholamine effects and arrythmias associated with catecholamines
4 HD goals for cardiac surgery?
prevent ischemia, prevent tachycardia, HTN is better than hypotension, slow, small, and richly perfused (wtf?)
