Patient criteria that may require left heart bypass
Benefits of vortex pumps for left heart bypass
Cannulation sites for left heart bypass
Significance of Patent Foramen Ovale
Pressure monitoring in left heart circuit
Partial left heart bypass for surgery to the aorta
Transfer of circulation from cardiopulmonary bypass to left heart circulation
1.
Indications in left
ventricular failure
a) CI < 1.8 - 2.0 l/m2/min
b) PCWP (left ventricular filling pressure) > 18 - 25 mmHg
c) MAP < 70 mmHg despite inotropes & IABP
d) But reasonably functioning right side
2.
Post cardiotomy
cardiogenic shock (PCCS) — Short term ventricular assistance
a) PCCS occurs in 2% — 6% of all patients undergoing CABG or valvular surgery
b) Used to resuscitate stunned myocardium and maintain adequate systemic and pulmonary function
c) If myocardial recovery does occur; occurs within a week
d) Preoperative predictors of need for circulatory assistance:
i) Prior myocardial infarction with depressed ventricular function
ii) Severe valvular dx with endstage myocardial involvement
iii) Coronary artery grafting that is only partially amenable to grafting with poor LV function
iv) Anticipated long CPB time
e) Preoperative predictors of need for circulatory assistance:
i) Inadequate myocardial protection
ii) Reperfusion injury
iii) Prolonged CPB
iv) Air or particulate emboli in coronary artery
v) Large ventriculotomy or aneurysm resection
f) Contraindicated:
i) Patients who have had incomplete revascularisation or imperfect operation as are not likely to recover
ii) Patients sustaining very large perioperative infarct
iii) Right ventricular failure
3.
Ventricular failure
after MI
a) Role of VAD not evaluated
b) Greater role for IABP
4.
Bridge to
transplantation — Long term ventricular
assistance
a) Used for patients with no likely hood of myocardial recovery ie end stage cardiomyopathy
b) Circulatory support is required until heart transplantation
c) Up to 1/3 die before receiving new heart
5.
Descending aorta
surgery
a) Left atrium to femoral artery
1. Pressure sensitive
a) Increases flow when preload increases or afterload decreases
b) Decreases flow when preload decreases or afterload increases
c) As are sensitive to afterload pressure
i) Catastrophic pressure buildup in arterial line (eg kinked tubing) cannot happen as flow decreases as pressure increases
2. Tendency to not pump accidentally introduced air
a) Bubbles tend to remain at the low pressure inlet point
b) Massive introduction of air unprimes pump, stopping flow
3. Better blood handling characteristics
a) Less haemolysis, complement activation, white cell activation & platelet activation [controversial]
4. Absence of tubing trauma prevents spallation & associated particulate embolisation
5. Not suitable for long term use due to heat produced in the bearing housing predisposing to thrombus formation in this area
1. Post cardiotomy cardiogenic shock (PCCS) — Short term ventricular assistance
a) Outflow
i) ascending aorta
ii) femoral artery
b) Inflow
i) left atrium via a tube attached to venous line via a 1/2 1/2 3/8 connector
ii) Clamp off the RA cannula
2. Bridge to transplantation — Long term ventricular assistance
a) Outflow
i) ascending aorta
b) Inflow
i) left ventricle; aids in ventricular decompression
3. Descending aorta surgery
a) Outflow
i) Femoral artery
b) Inflow
i) Left atrium
4. Tubing length
a) Centrifugal pump or roller pump
i) pump mounted away from patient; longer tubing required
b) LVAD
i) pump mounted on patient; shorter tubing required
1. Dangers of diastolic vacuum
a) Patent Foramen Ovale
i) Occurs in 25% of general population
ii) Can cause severe R®L intracardiac shunting if left atrial pressure is reduced below right atrial pressures
iii) Should always be diagnosed (TOE; visual) and surgically closed prior to insertion of LV CPB cannula
b) Open Chest
i) Diastolic vacuum may draw air into the circulation prior to closure of the chest
ii) Negative inflow pressures generated by centrifugal pumps or excessive venous drainage has the potential to draw air into the circulation at suture lines or central venous catheters
iii) Use soft shell reservoir; try not to direct draw
a) Minimise cavitation
b) Able to add volume more effectively
c) Normally (without PFO) CVP: keep >10 to prevent cavitation
i) control by adding volume; no partial clamp
ii) If underfilled, unable to flow
a) (using a soft shell reservoir + bimedicus pump) -> unable to maintain systemic blood pressure
b) Rollerpump: potential for cavitation also if no soft shell reservoir
iii) PA to be zero: resting left side of heart; do not want to eject
1. Short term VAD
a) Continuous IV heparin
b) ACT: 200-250 seconds
2. Long term VAD
a) Initially continuous IV heparin; dextran
b) Long term maintenance with Warfarin ± dipyridamole
c) Balance between haemorrhaging and thromboembolism
3. Carmeda
a) ACT: 150-200 [assuming flows > 2l/min]
b) Boluses heparin
c) Monitor from circuit (not patient)
1. Centrifugal pumps during left heart assist
a) Pump rate is adjusted so that the pump maintains adequate pressure on its outflow side while effecting adequate decompression on its inflow or venous side
b) Left atrial pressures kept below an acceptable maximum value to rest left side
i) >0 but < 5 mmHg
ii) But not too low: danger of air entrainment
c) MAP kept at an acceptable minimum value
d) CVP keep filled
2. Centrifugal pumps during right heart assist
a) RA -> PA
b) CVP kept at a reasonable safe maximum
i) >0 but < 5
ii) To rest right side
c) MeanPA or LAP kept at a reasonable minimum
3. Accomplished by adjusting pump speed & blood volume
4. Note that the centrifugal pump needs continuous vigilence as its output is affected by changes in afterload
5. Note prior to RVAD or LVAD should assess whilst using CPB to determine suitability for long term LVAD -RVAD(eg 1 hour) looking for ventricular failure of the opposite side of the heart
1. Surgical approaches to repair descending & thoracoabdominal aortic disease
a) Simple cross-clamp
b) Left atrium to left femoral artery bypass
c) Left ventricle to left femoral artery shunt
d) Partial CPB (femoral vein to femoral artery)
e) Total CPB (femoral vein to femoral artery)
f) Passive shunt (Gott shunt) (Proximal aorta to distal aorta)
2. Left atrial to left femoral artery partial CPB
a) Centrifugal pump
b) No oxygenator to reduce haemodilution & cost (One lung should be oxygenating - but advantage of using an oxygenator is the use of a heat exchanger and to cover any oxygenator problems)
c) Minimum heparinisation (especially if Carmeda)
d) Possible add heat exchanger
e) Soft shell reservoir - avoid direct suction unto a vessel, reducing cavitation, shearing, difficult to add volume, mechanical shut down if run out of volume
f) Drainage to the pump comes from the preload chamber of the left ventricle
i) Increasing pump flow decreases ventricular filling, cardiac output, & proximal systemic pressure
ii) Must monitor upper & lower body pressures simultaneously
iii) Improper drainage of the left atrium may lead to upper-body hypotension leading to cerebral & cardiac ischaemia
g) Not recommended for routine use
h) Recommended for patients with poor ventricular &/or renal function
3. Femoral vein to femoral artery
a) Oxygenator
b) Full heparinisation
c) Hypothermia
d) ± Circulatory arrest
e) Indicated for extensive thoracoabdominal aneurysms
i) Allows prolonged intercostal and visceral ischaemia with reduced post operative paraplegia and bowel infarcts
f) Associated with increased incidence of coagulopathies & post op bleeding
LVAD
1. Insert cannula standard single stage [30 F] cannula into left atrium and attach via 3/8” to a 1/2-1/2-3/8 connector attached to venous line - clamp off right atrial line on normal CPB
2. Assess patient’s suitability for LVAD by staying at this state for at least an hour and observe for failure of right side; if patient doesn’t get any worse continue LVAD
3. Set up centrifugal + soft shell circuit, hand 3/8 line to table, both ends of line handed back to be inserted into reservoir & pump head [no oxygenator or arterial filter] and primed - pump off & cannulated
RVAD
1. RA -> PA
2. See above
3. Ideal left atrial line for monitoring
4. Need to have enough left sided filling for ejection
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