Anesthesia for Cardiac Surgery Flashcards
Labs you want prior to cardiac surgery
Pretty much your standard things + cardiac enzymes:
CBC (tells you O2 carrying capacity and ABL)
Electrolytes
Cardiac Enzymes (ensure that MI isn’t actively happening)
BUN/Cr
Coags (pt will be given heparin prior to placement on CPB)
T&C (PRBCs must be available! Usually ask for 4units on hold. 6-8 units for a re-do surgery)
This is the most preferred biomarker for myocardial damage
Cardiac troponin. This is ONLY found in cardiac tissue. Thus, its presence reflects even microscopic amount of myocardial necrosis.
Should premedication be given to pts undergoing cardiac surgery?
YES! Premedication assists in providing a calm and hemodynamically stable pt who is ready for surgery.
Inadequate sedation may predispose to HTN, tachycardia, or coronary vasospasm, and precipitate an myocardial ischemia.
Monitoring needed for cardiac surgery
Pulse-ox
EKG
–> can help detect regional ischemia
IABP
–> Usually radial, but sometimes femoral
CVP
–> Central line needed for vasoactive drug infusion. CVP can also help estimate RV filling pressure.
PA Cath
–> Indications vary. Some institutions place them all the time, and others may only place if severe cardiac dysfunction or pulm HTN. Despite the controversy surrounding PA cats, there needs to be SOME way to measure CP and ventricular filling pressures, whether it’s with a PA cath or TEE
–> The catheter can migrate with cardiac manipulation before and after CBP and with acute preload changes. May want to pull out a few cm before CPB started so that permanent wedging or PA rupture doesn’t occur.
TEE
–> Can detect real time ischemia by looking for new wall abnormalities and assessing valvular function. Can also detect filling volumes to direct fluid therapy.
EKG Leads and where they detect ischemia
Inferior myocardium (RCA) - II, III, AVF
Anterior Myocardium (LAD) - V4, V5
Lateral LV Myocardium (L circumflex)
- I, AVL
TEE provides intermittent pulses at a frequency of ____
2.5-7.5MHz
Preparing the room for cardiac surgery
Usual MSMAID things
Pacemaker with batteries
Heparin drawn up and ready to go (in case the pt needs to go on bypass emergently)
Coag monitoring capability (ACTs)
PRBCs available and in the room
Vascular access equipment (a-line, central line, ultrasound for central line placement)
Drips (usually have hypertensives on one side and hypotensive on another):
- NTG/NTP
- Epi/Norepi
- Phenylephrine/ephedrine
- Dopamine/dobutamine
- Antidysrhythmics (lidocaine, esmolol, amio, magnesium)
- The drips you need to have ready to go will vary from site to site
These are the most stimulating parts of cardiac surgery
Tracheal intubation, incision, sternotomy, pericardiotomy, and manipulation of the aorta.
Volatile agents in cardiac surgery are used as
Primary agents, or can be used as adjuvants in the prevention and treatment of breakthrough hypertension.
Opioids in cardiac surgery
Fentanyl and fentanyl-like drugs
- -> Fentanyl 50-100mcg/kg
- -> Sufentanil 10-20mcg/kg
Aside from bradycardia, they are relatively devoid of CV effects. They lack negative inotropic effects.
Although high-dose opioids cause loss of consciousness, recall is not totally eliminated. Therefore, benzos are often added.
High dose opioids do not consistently prevent a hypertensive response to periods of increased surgical stimulation. Volatile anesthetics can be added to prevent/treat this.
Fentanyl + benzo can cause a drop in SVR.
High dose opioids can cause chest wall rigidity. Can prevent with low dose NDMR.
Brady with opioids may be worsened with vecuronium or cisatracurium. Pancuronium can help offset the brady.
Is N2O used in cardiac surgery?
No, not really. It causes an increase in PVR, especially in those with pre-existing pulm HTN.
N2O is also a myocardial suppressant and also causes a SNS mediated increase in SVR. These slight changes may not be tolerated by those with minimal cardiac reserve.
Also, air introduced by CPB may be expanded.
Induction agents for cardiac surgery
Benzos, barbs, propofol, and etomidate can all be used as sole anesthetic induction agents or as adjuncts to opioid and/or volatile technique. Usage depends on degree of ventricular function and baseline sympathetic tone.
Etomidate is favored for those with limited cardiac reserve, but is rarely used d/t the adrenal dysfunction.
NMBs in cardiac surgery
Needed for intubation, prevention of opioid-induced chest wall rigidity, and attenuation of muscle contraction during defibrillation.
Considerations for the pre-induction period of cardiac surgery
Pretty much typical stuff.
Is your premed working? Is the patient adequately relaxed?
Attach your monitors
Pre-oxygenate
Do you have all your venous access? At least 2 large bore IVs
Invasive monitoring ready to go?
–> Consider post vs. pre-induction placement of monitors. In severe disease, get invasive monitoring prior to induction. If doing pre-induction, place a NC in the patient while getting access.
Remind the patient to report any CP or SOB. Treat CP with O2, additional sedation, and/or IV NTG. If due to severe anxiety associated with tachycardia and HTN, give BB and consider inducing general anesthesia if possible.
Induction and Intubation
We want a smooth induction, avoiding coughing, laryngospasm, and tranquil rigidity. Obviously, we want to avoid hyper/hypotension and tachycardia as well.
Achieve a deep plane of anesthesia for DVL.
Try to make DVL as quick as possible to minimize stimulation.
The induction period is part art and part science in determining what combination of medications to be given, what amounts, and at what speed to deliver them.
Be aware that in those with a slow HR prior to induction, their response to DVL will most likely be vagal in nature and severe brady can occur.
Pre-incision period
This is after the pt has been induced and intubated. The pt is being prepped, draped, etc –> all things with minimal stimulation. Hypotension may result regardless of anesthetic used. May need to reduce anesthetic depth or give vasoconstrictor. Remember to increase the depth again before incision!!!
Recall at this point is rare unless severe hypotension occurs in the face of a purely opioid technique.
The incision to bypass period
This is a critical period, with moments of intense surgical stimulation (incision, sternotomy, vascular harvesting, etc). This stimulation can cause HTN, tachycardia, and induce myocardial ischemia. We can try to anticipate these and increase anesthetic depth, but often a vasodilator or other adjuvant is also necessary.
Also, hypotension may occur during the less stimulating parts, or may occur with cardiac manipulation while attempting to cannulate the atrium.
As mentioned, this is a critical period and continuous observation of the surgical field is essential.
Surgeon also needs to be aware if any signs of new ischemia occur, and it should be treated promptly. There needs to be open communication btw surgeon and anesthesia so that they both know what’s going on and so that the heart gets periodic rests.
What needs to be done before the sternotomy?
Drops the lungs!!
When is the pt heparinized?
Immediately before CPB
How much heparin is the pt given and when does it peak?
200-300 units/kg
Peaks in 2 minutes.
What does ACT stand for? What is the normal range, and what is our goal for CPB?
Activated clotting time
Normal is around 80-160 seconds
Goal for CPB is generally greater than 400. Usually 400-500.
How does heparin work?
It binds to and activated Antithrombin III. AT III then goes on to thrombin and Factor Xa, which are essential to the clotting cascade.
How should heparin be administered?
Through a central line or directly into the RA.
Side effects of heparin
SVR and BP can decrease by 10-20%
Bleeding
Rare: HIT syndrome (heparin induced thrombocytopenia)
When should the next ACT be checked after heparin administration.
After 3-5 minutes. Remember that heparin peaks in 2 minutes.
Events that need to occur immediately before bypass
1) Cannulation of the aorta (arterial) and the RA (venous)
- -> Need to drop BP for cannulation (MAPs of 50-60)
- -> During RA cannulation, BP may drop and arrhythmia may occur
- -> The perfusionist is able to give fluids though the arterial (aorta) line
2) Cannulation of the coronary sinus for retrograde cardioplegia
- > Cannulation here can also cause low BP
3) Medicate the pt with fentanyl and versed
- -> CPB will increase the Vd of your drugs, resulting in risk of recall at this point
Process of starting CPB
1) Cease ventilation and deflate the lungs
2) Shut off your IV fluids (perfusionist now in control of this)
3) Turn off your anesthetic and ensure the perfusionist has started theirs
5) Pull back on your PA Cath, as it may migrate forward during institution of CPB
6) Give NDMR to prevent shivering (surgeon wants a still field!)
7) Surgeon may want more antibiotic at this point
Cardioplegia Solution
Very cold (4 degrees C)
–> V-fib will occur at 25-30C. Heart will fibrillate for a bit and then stop.
Contains K+ (depolarizes and stops the heart)
Changes that occur with institution of bypass
Rapid dilution of catecholamines and significant drop in BP
Hemodilution and decreased blood viscosity
Rapid cooling to the brain, heart, and liver
Aortic crossclamping prevents systemic spread of the cardioplegic solution.
Solution used to prime the CPB circuit
Takes about 2L of crystalloid to prime.
Heparin (to maintain anticoagulation), mannitol (to promote diuresis), bicarb, albumin (to decrease post-op edema), corticosteroids, calcium (to prevent hypocalcemia d/t citrate in transfused blood), and antifibrinolytics such as aminocaproic acid (Amicar) are also added depending on institutional preferences.
Once the pt in on bypass, blood flow is no longer pulsatile. What determines BP at this point?
Flow and SVR.
Typical flow rates and pressures during CPB
Flows are usually maintained at 50-60ml/kg/min, and BP is maintained at 50-60mmHg. Some believe that older patients may benefit higher BP around 70mmHg.
Lower BP is good for hematology, while higher BP is good for stroke patients.
What should CVP be reading during CPB?
CVP should be 0.
If it’s higher, there may be a kink in the perfusionist’s lines.
Hematologic effects of CPB
Has effects on both the intrinsic and extrinsic coagulation pathways:
Factor XII gets converted to Factor XIIa on various surfaces of the CPB circuit (there is no way to prevent this)
CPB also directly impairs platelet function.
- -> Plasma proteins such as vWF and fibrinogen rapidly adhere and begin to conform
- Platelets aggregate and detach d/t shearing forces
This is why anticoagulation with heparin is initiated proper to CBP
Prophylaxis against bleeding during cardiac surgery
Prophylaxis reduces bleeding and need for transfusion
1) Synthetic Lysine Analogues
- -> Aminocaproic Acid (Amicar)
- -> Tranexamic Acid (80x stronger than Amicar)
2) Serine Protease Inhibitors
- -> Aprotonin (taken off the market, but now being researched again in Canada)
What is the most common cause of post-op neurologic complications?
Emboli (air, atheroma, or other particulate matter).
Overt strokes are d/t macro emboli, whereas subtle cognitive changes are usually due to micro emboli.
Methods of cerebral protection during CPB
Arterial line filters to prevent emboli (although has unproven benefit)
Hypothermia (decreases metabolic rate and increased ischemic tolerance)
Sodium Thiopental (cerebroprotective for intracardiac procedures, but not CABG)
ABG Management by perfusionist
Adequate perfusion to brain (BP and flow)
Monitoring of cerebral oximetry
Fluid management for cardiac surgery
Minimize fluids (minimize crystalloid usage to 1-1.5L) Replace blood loss with colloids, cell saver, or PRBCs
Anesthetic requirements are (increased/decreased) during hypothermia
Decreased
When does the process of rewarming begin?
Prior to removal of the aortic cross-clamp
OR
With the last distal anastomosis in an angioplasty procedure
OR
Once all valve sutures are in and the knots are being tied down
Why is recall a risk during rewarming?
Anesthetic requirements begin to increase again as the hypothermia is reversed.
A gradient of __-__ degrees C should be maintained between the patient and perfusate to prevent formation of gas bubbles within the blood
4-6 degrees C
How long does rewarming take?
30-40 minutes
Rate of rewarming
1 degree C every 3-5 minutes
Hemodynamic changes during rewarming
Vasodilation occurs, resulting in a drop in SVR
Prior to discontinuation of CPB…
Pt must be adequately warmed
Surgical field should be dry
Lab values should be checked and looking good
Begin ventilating lungs and assessing pulmonary compliance (we will be asked to vigorously ventilate the lungs to help remove air from the pulmonary veins)
Heart beat is begun by pacing, defibrillating, or is induced pharmacologically
The venous cannula is then incrementally occluded, and sufficient pump volume is given to the patient while the flow is continuously decreased.
During this time, cardiac function is constantly evaluated from hemodynamic data, TEE, and direct inspection of the heart. The need for fluids, vasoactive, and cardioactive drugs is continuously assessed.
Dosage of protamine
2-4mg/kg
OR
1-1.3mg for every 100units heparin given
Can check ACT and give more if needed
Risk of protamine
Anaphylaxis can occur!
- -> Can occur with previous exposure
- -> Can also occur with patients on NPH insulin (nedutral protamine Hagedorn), as this is also considered prior exposure.
Can also cause vasodilation. Give it slowly over 5 minutes.
What to do if patient is allergic to protamine
Can consider using an alternative to protamine, perform bypass with an alternative to heparin, or just plan on not reversing the heparin.
Examples of non-protamine heparin reversal agents
PF4
Heparinase
Post-op considerations
Pt will go to ICU
About 4-10% will go back to the OR d/t bleeding (risk for cardiac tamponade)
Pain control (sternotomy is very painful)
What will happen to BP with chest closure?
It drops
General rules for minimally invasive (off-bypass) cardiac surgery
Reduce the HR and increase preload (thus reducing motion for the surgeon while preserving CO) Avoid and treat arrhythmias Lower TVs (again to reduce motion) Give heparin just in case the pt needs to go on bypass emergently. Heparin reversal will differ by institution.
