Ch 67 Anesthesia for Cardiac Surgical Procedures

Question 1

Which ECG lead is most sensitive for detecting ischemia by itself?

Answer 1

V5 (75% sensitivity).

With Lead II added, 80% sensitivity. With V4, nearly 100%

Question 2

Name conditions when your PCWP would be greater than your LVEDP (i.e., would overestimate your LVEDP)

Answer 2

PPV
PEEP
Increased intrathoracic pressure
PAC not in West lung zone III
COPD
Increased PVR
LA myxoma
MV disease

Question 3

Name conditions when your PCWP would be less than your LVEDP (i.e., would underestimate your LVEDP)

Answer 3

Noncompliant LV
Aortic regurgitation
LVEPD >25

Question 4

What are absolute contraindications to using a pulmonary artery catheter?

Answer 4

Tricuspid Stenosis
Pulmonary Stenosis
RA or RV masses
Tetralogy of fallot
 (Relative contraindications include severe arrhythmias, newly inserted pacemaker wires)

Question 5

What is the risk of post-op stroke after isolated CABG?

Answer 5

1.2% (2009), 1.6% (2000)

Question 6

What is thought to be the most common cause of CNS injury/dysfunction after cardiac surgery? What are the other influencing factors?

Answer 6

Most common cause: particulate or micro gaseous emboli.
Influencing factors:
-aortic atheromatous plaque
-Cerebrovascular dx
-Altered cerebral regulation
-hypotension
-intracardiac debris
-air
cerebral venous obstruction on bypass
-CPB circuit surface
-reinfusion of unprocessed shed blood
-cerebral hyperthermia
-hypoxia

Question 7

Which parts of the aorta are in the TEE probes “blindspot” and how can they be imaged preoperatively?

Answer 7

distal ascending aorta and proximal midportion of aortic arch can’t be seen with TEE. Can do handheld epiaortic echocardiography intraoperatively (place sterile probe in field to directly U/S aorta)

Question 8

How does cerebral oximetry work?

Answer 8

Like pulse oximetry, uses near-infrared spectroscopy

Question 9

What values of cerebral oximetry are associated with increased incidence of adverse postoperative outcomes?

Answer 9

Decrease in rSO2 to less than 80% of baseline or to absolute of less than 50%

Question 10

Why might EEG not be great for monitoring for cerebral ischemia during cardiac surgery?

Answer 10

Cofounding factors: hypothermia, pharmacologic suppression of EEG signals, interference with pump mechanics, only measures cortical activity (would miss ischemic or embolic injury below cortex)

Question 11

What are 6 major injury pathways of cardiac-surgery associated AKI?

Answer 11

toxins (endogenous and exo)
metabolic
ischemia-reperfusion
neurohormonal
inflammation
oxidative stress

Question 12

Name an independent risk factor for AKI in cardiac surgery

Answer 12

Atherosclerosis of ascending aorta

Question 13

What level should blood sugar be kept below in the perioperative period for cardiac surgery?

Answer 13

10 mmol/L (180mg/dl)

Question 14

What is the mechanism for heparin anticoagulation?

Answer 14

Binds antithrombin (AT) and thrombin.  Allows AT to inhibit the procoagulant effect of thrombin with 1000x more potency. 
Heparin also inhibits Factor Xa

Question 15

What is the dose of heparin for CPB? What is the target ACT?

Answer 15

300-400u/kg

Target ACT 480

Question 16

What factors (besides heparin) might prolong ACT?

Answer 16

Hemodilution (if already heparinized)
Hypothermia
Thrombocytopenia
Platelet inhibitors
Surgical stress SHORTENS ACT

Question 17

What is the dose of protamine?

Answer 17

1-1.3mg protamine per 100 units of heparin (total amount given)

Question 18

How does CPB affect intrinsic and extrinsic clotting pathways?

Answer 18

Intrinsic: contact activation and conversion of factor XII to XIIa
Extrinsic: tissue factor generation from wound and circulating tissue thromboplastin causes increased generation of thrombin

Question 19

How does CPB impair platelet function?

Answer 19

Components of bypass circuit have circulating proteins adhered to their surface. This serves as foci for platelet attraction/adherence which then release their contents. This can serve as localized source of thrombin generation or may embolize to initiate microvascular thrombosis

Question 20

What are causes of heparin resistance?

Answer 20

• congenital
• Antithrombin (aka antithrombin III) deficiency
• acquired conditions: sepsis, activated platelets, increased levels of heparin-binding proteins (pre-op heparin therapy)

Question 21

What can be done to treat altered heparin responsiveness (aka heparin resistance)?

Answer 21

• Treatment with antithrombin concentrate or recombinant AT

- supplemental heparin

Question 22

What is heparin rebound?

Answer 22

Clinical bleeding that occurs within 1 hour of protamine neutralization. Rare, but can be mostly prevented by giving a protamine dose in relation to “total heparin” rather than “residual heparin” at the end of CPB. This will result in a relative “overdose” and less likely to have rebound.

Question 23

What are options for a patient that has HITT and needs Cardiac Surgery?

Answer 23

• If possible, wait until antibody titers are undetectable or weakly positive (may take 90 days)
• LMWH or heparinoid (test first)
• Alternative thrombin inhibitor (hirudin, bivalrudin, agatropban)
• Ancrod (Viprinex) not available in any country

Question 24

What are the different classifications of protamine reactions:

Answer 24

Type I: isolated hypotension; mild
Type II: moderate to severe hypotension with features of anaphylactoid reactions (e.g., bronchoconstriction). IgE, IfG or complement mediated
Type III: severe hypotension, elevated PA pressures leading to acute RV failure. Caused by large heparin-protamine complexes lodged in pulmonary circulation

Question 25

Risk factors for protamine hypersensitivity reactions?

Answer 25

-use of NPH insulin, other medical allergies, fish allergy