Cardiac Anesthesia Flashcards
Trace the coronary blood supply and possible presentation with occlusion
Dominance is determined by which artery gives rise to the Posterior Descending Artery (supplies the inferior wall of LV)
(A) Right-sided: right coronary artery
- ~80% of the population
- supplies SA node, AV node, RV –> bradycardia or AV blocks
- ECG: inferior wall - II, III, aVF
(B) Left-sided: left circumflex artery
- supplies AV node, SA node (in 40%), septum
- ECG: septal, anterior, apical, lateral wall
What are the clinical risk factors for a major perioperative cardiac event (MACE)?
Revised Cardiac Risk Index (RCRI) - noncardiac sx
- HR surgical procedures: intraperitoneal, intrathoracic, supra-inguinal vascular
- IHD
- CHF
- CVD
- Insulin-requiring DM
- Serum creatinine > 2mg/dl
*Gupta scoring - both cardiac and non-cardiac
What is the metabolic equivalent for adequate cardiac reserve?
At least 4 METs:
- able to climb 2-3 flights of stairs without symptoms
What are considered active cardiac conditions?
1) Unstable coronary syndromes
2) Decompensated HF
3) Arrhythmia: symptomatic bradycardia/ventricular arrhythmia, high-grade AV block
4) Severe valvular disease: symptomatic MS, severe AS
A patient, S/P PCI, presents for an elective surgery. What are important concerns?
S/P PCI patients are on dual anti-platelet therapy
Continue ASA
Hold clopidogrel 5-7 days
Delay elective surgery
- Balloon angioplasty: at least 2 weeks
- BMS: 6 weeks
- DES: 1 year
A patient with a history of MI presents for an elective surgery.
Recent - < 30 days
Prior - > 30 days
*ideally hold elective surgery for at least 4-6 weeks d/t risk of reinfarction
*more important to establish functional capacity post-MI
*if symptomatic –> candidate for revascularization prior to elective SX
What information may be derived from the pressure-volume loop?
Pressure-volume loop describes heart function; plots LV pressure vs volume in 1 cardiac cycle
EDV
ESV
SV
EF = SV/EDV
How does the Frank-Starling Law apply to the heart?
Length-tension relationship in cardiac muscle fibers (force or tension developed in a muscle fiber depends on the extent to which it is stretched) aka more volume more stretching
~ VR = EDV = SV & CO
*until optimal stretch is reached
How does the Laplace Law relate to the heart?
Wall tension = intracavitary pressure x radius / wall thickness
a) pressure overload –> concentric hypertrophy –> INC wall tension during systole
b) volume overload –> eccentric hypertrophy –> INC wall tension during diastole
- increasing wall tension –> increasing myocardial demand
How to balance myocardial demand and supply?
Demand
- wall tension: high preload/afterload
- contractility: high HR
Supply
- O2 content: anemia, hypoxemia
- blood supply: high LVEDP, LVH, high HR
Differentiate systolic from diastolic dysfunction
SYSTOLIC - ineffective contraction during heartbeats
- low EF, low exercise tolerance –> more symptomatic
DIASTOLIC - ineffective relaxion in between heartbeats
- impaired ventricular relaxation, decreasing LV compliance –> DX relies on 2D echo
- increased LA filling pressures, becomes atrial-dependent, prone to AF
- sensitive to volume-overload ‘flash pulmonary edema’
Which anesthetic agents have the most profound myocardial depression?
Barbiturates
Propofol
High dose volatile agents
Considerations for a patient with decompensated HF presenting for emergent surgery
Ideally, optimize for a few days w/ IV inotropes, LV assist device (considered full stomach -> RSI)
Invasive monitors: A-line, PA catheter, TEE
Opioid-based +/- low-dose volatile agent
*Ketamine - will act as a negative inotropic agent
Inotrope: dopamine
Inodilator: dobutamine, milrinone
Describe Intra-Aortic Balloon Pump
IABP
- temporary invasive hemodynamic support
- uses helium
- inflates during diastole: to increase diastolic pressure –> increase coronary perfusion
- deflates during systole: to decrease afterload and increase SV
- timing is important: inflated at R wave or before dicrotic notch (AV closure –> diastole)
Hemodynamic goals for aortic dissection
Lower the shear stress to avoid rupture:
Preload - increase if acute
Afterload - decrease (SBP <100-120 mmHg)
HR < 60-80 bpm
If w/ AF - control VR
A 75/M with a history of syncopal and anginal episodes presents for elective TURP. On PE, he has a systolic murmur radiating to the carotids. What are the appropriate hemodynamic goals?
Aortic Stenosis - fixed outflow obstruction
a) adequate preload - for the non-compliant LV
b) maintain afterload - to ensure coronary perfusion
c) low-normal HR, SR
Anesthetic concerns during TAVR
Invasive monitors: PA catheter, A-line, TEE
Agents with minimal effects on hemodynamics:
- induction: fentanyl, etomidate, rocuronium
- maintenance: volatile agent e.g. sevoflurane
Maintain BP in the normal range
Rapid pacing at 160-180bpm during the repair/replacement
Why is there a need for rapid pacing in TAVR?
HR 160-180bpm: low MAP with minimal pulsation –> valvuloplasty and valve replacement can be done
‘clear surgical field’
A 25/M was diagnosed with HCOM. What are important hemodynamic targets for him?
Maintain preload
Maintain or increase afterload
Decrease contractility
Low-normal HR, SR
A 60/F has progressive dyspnea. PE shows a diastolic murmur. On 2D echo, there is LVOT. What are hemodynamic goals?
Aortic Regurgitation
GOAL: maintain forward flow & decrease regurgitant volume
- high preload (to augment CO)
- lower afterload > > forward flow
- high normal HR > > limits regurgitant time
Most common rheumatic-related valvular lesion
Mitral Stenosis
- secondary to rheumatic disease in 80-90%
- critical stenosis occurs 10-20 years after
What hemodynamic changes occur in MS?
- LV is underfilled (low EDV) –> low CO
- LA pressure increases –> increasing PVR –> pulmonary hypertension –> eventual RV failure
- LA overdistention –> prone to AF
Anesthetic considerations for MS
1) adequate preload to maintain flow
2) low-normal HR to allow for ventricular filling
3) sinus rhythm for adequate filling (atrial systole accounts for 30% of SV)
4) maintain afterload
5) low PVR: avoid/treat hypoxia, hypercarbia, acidosis
Why is the anterior spinal cord at risk for ischemia during thoracic aneurysm repair?
Single artery to the anterior spinal cord
What are considered contraindications for heart transplant?
active malignancy
active infection
high, irreversible pulmonary vascular resistance
alcohol or IV drug abuse
Anesthesia considerations during organ retrieval
Monitor volume status, arterial & CVP
FiO2 1.0 - optimal for organ viability EXCEPT for lungs (lowest FiO2 to maintain PaO2 > 100 mmHg)
NMDR to prevent spinal reflex-mediated movements
Administer heparin
<4 hours ischemia time - for optimal myocardial function
CPB vs ECMO
CPB - for a bloodless surgical field
ECMO - temporizing support i.e. VV or VA
Considerations during cannulation in CPB
aortic cannulation - avoid hypertension (SBP 110 mmHg or less)
venous cannulation - low TV
Physiologic effects of CPB
When blood comes into contact with the CPB circuit:
- release of stress hormones
- activation of: complement cascade, coagulation cascade, systemic inflammatory response
- platelet activation & dysfunction
- hemodilution
Why is cardioplegia necessary in CPB?
Cardioplegia induces diastolic electromechanical dissociation
- myocardial requirements are lowered to cellular maintenance
- typically a hyperkalemic solution with metabolic substrates
What is the purpose of priming solutions in CPB?
Either crystalloid, colloid or blood
- ‘prime’ the circuit (avoid air embolism)
*Lower priming volume –> lower inflammatory response and transfusion requirements
(traditionally 1.5 - 2L vs currently <1L)
Heparin dose before start of bypass
300-400 u/kg
Reversal with protamine: 1 mg/100 u
Checklist prior to termination of CPB
- normothermia (rewarm to 37C)
- correct acid-base & electrolyte, Hgb/Hct
- evaluate cardiac rate & rhythm, pacing may be required
- check ECG and TEE
- complete de-airing of the heart before removal of cross-clamp
- resume inotropic support
- initiate lung ventilation
Target (immediate post-CPB):
- HR 100-120 bpm
- MAP > 65 mmHg
- low CVP, PCWP
A post-cardiac transplant patient is scheduled for an elective surgery. What important concerns?
Transplanted heart is denervated:
- preload-dependent
- high resting HR
- loss of vagal tone
- delayed response to circulating catecholamines
- indirect-acting agents are ineffective e.g. atropine, ephedrine
- must use direct-acting vasoactive drugs: epinephrine, isoproterenol
