Ch 67 Anesthesia for Cardiac Surgical Procedures Flashcards
Which ECG lead is most sensitive for detecting ischemia by itself?
V5 (75% sensitivity).
With Lead II added, 80% sensitivity. With V4, nearly 100%
Name conditions when your PCWP would be greater than your LVEDP (i.e., would overestimate your LVEDP)
PPV PEEP Increased intrathoracic pressure PAC not in West lung zone III COPD Increased PVR LA myxoma MV disease
Name conditions when your PCWP would be less than your LVEDP (i.e., would underestimate your LVEDP)
Noncompliant LV
Aortic regurgitation
LVEPD >25
What are absolute contraindications to using a pulmonary artery catheter?
Tricuspid Stenosis Pulmonary Stenosis RA or RV masses Tetralogy of fallot (Relative contraindications include severe arrhythmias, newly inserted pacemaker wires)
What is the risk of post-op stroke after isolated CABG?
1.2% (2009), 1.6% (2000)
What is thought to be the most common cause of CNS injury/dysfunction after cardiac surgery? What are the other influencing factors?
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
Which parts of the aorta are in the TEE probes “blindspot” and how can they be imaged preoperatively?
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)
How does cerebral oximetry work?
Like pulse oximetry, uses near-infrared spectroscopy
What values of cerebral oximetry are associated with increased incidence of adverse postoperative outcomes?
Decrease in rSO2 to less than 80% of baseline or to absolute of less than 50%
Why might EEG not be great for monitoring for cerebral ischemia during cardiac surgery?
Cofounding factors: hypothermia, pharmacologic suppression of EEG signals, interference with pump mechanics, only measures cortical activity (would miss ischemic or embolic injury below cortex)
What are 6 major injury pathways of cardiac-surgery associated AKI?
toxins (endogenous and exo) metabolic ischemia-reperfusion neurohormonal inflammation oxidative stress
Name an independent risk factor for AKI in cardiac surgery
Atherosclerosis of ascending aorta
What level should blood sugar be kept below in the perioperative period for cardiac surgery?
10 mmol/L (180mg/dl)
What is the mechanism for heparin anticoagulation?
Binds antithrombin (AT) and thrombin. Allows AT to inhibit the procoagulant effect of thrombin with 1000x more potency. Heparin also inhibits Factor Xa
What is the dose of heparin for CPB? What is the target ACT?
300-400u/kg
Target ACT 480
What factors (besides heparin) might prolong ACT?
Hemodilution (if already heparinized) Hypothermia Thrombocytopenia Platelet inhibitors Surgical stress SHORTENS ACT
What is the dose of protamine?
1-1.3mg protamine per 100 units of heparin (total amount given)
How does CPB affect intrinsic and extrinsic clotting pathways?
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
How does CPB impair platelet function?
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
What are causes of heparin resistance?
- congenital
- Antithrombin (aka antithrombin III) deficiency
- acquired conditions: sepsis, activated platelets, increased levels of heparin-binding proteins (pre-op heparin therapy)
What can be done to treat altered heparin responsiveness (aka heparin resistance)?
- Treatment with antithrombin concentrate or recombinant AT
- supplemental heparin
What is heparin rebound?
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.
What are options for a patient that has HITT and needs Cardiac Surgery?
- 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
What are the different classifications of protamine reactions:
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
