Dissection vs. Aneurysm
dissection- occurs when blood penetrates the intimate of the aorta, expanding medial layers, true lumen gets smaller, branching vessels may not be affected
aneurysm- dilation of all 3 layers
Aortic Dissections
=Intimal Tear! - at weak spots or areas with high shear force
- risk factors HTN (90%), age (>60), male, Marfan’s, CHD, prego
- causes- high physical activity, emotional stress, trauma (deceleration injury- MVA—most common occurring distal to left subclavian at lig. arteriosum, 2nd most common at ascending aorta distal to aortic valve), cannulation/CPB
- propagation- spreading driven by pulse pressure and ejection velocity
DeBakey Classification
-based on intimal tear origin and sections involved
Type 1- tear in asc. aorta, includes rest of aorta
Type 2- tear in asc. aorta, stays in asc. aorta
Type 3a- tear in desc. aorta, dissection stays above diaphragm
Type 3b- tear in desc. aorta, dissection goes below diaphragm
Standford (Daily) Classification
- doesn’t matter the origin, just where it is
Type A- if it involves the asc. aorta (regardless of how far it propagates
Type B- distal aorta (past left subclavian)
Dissection causes of death
- rupture of false lumen into pleural or pericardium space!
- or HF, MI, stroke, bowel gangrene
Aneurysm Etiology and Shape
-is site dependent
-Asc. = congenital (marfans), post-stenotic dilation
-arch= isolated (atherosclerosis)
-desc.= atherosclerosis (intimal disease)
Shape= fusiform (circumference gets bigger), saccular (sac bulges out-most common)
Crawford Classification
- to classify thoracoabdominal aortic aneurysms
Extent 1- desc. thoracic aorta and upper abdominal aorta (above diaphragm)
Extent 2- desc. thoracic aorta to infrarenal
Extent 3- distal second half of desc. aorta and down
Extent 4- abdominal aorta and down
Indications for surgery- Ascending aorta
- dissection= acute type A (high mortality)
- aneurysm= pain, MI, angina, expanding, >5-5.5 cm
Indications for surgery- Aortic Arch
- dissection= acute, limited to arch (rare)
- aneurysm= persistant symptoms, > 5.5-6 cm, expansion
Indications for surgery- Desc. aorta
- dissections= HTN, pain, enlargement, neurological deficit, renal/GI ischemia
- aneurysm= >5-6 cm, expanding, leaking, chronic pain
CPB with DHCA and ACP
- DHCA= blood less filed, uncluttered field, BUT brain ischemia and accumulation of waste, must monitory temps and brain
- Drugs= Mannitol 25 g and steroids before going off= cerebral protection
- cannulation= axillary and bicaval
- cooling= 10 degree drop in temperature = reduces O2 consumption rate by 50% and 20-25% increase blood viscosity
- hemodilute HCT<25% (keep low until rewarming)
- at firbrillation= give retrograde CPG
- cool for at least 25 min before circ arrest, want brain temp 18-20, NO lower than 15 until no EEG= give pentobarbital, head in ice and Trendelenburg
- flow off= drain patient
- innominate artery is snared= ACP at 10 ml/kg/min at 90 mmHg= NEED suction at distal arch (because some blood will flow back into left carotid and subclavian
- after DHCA= there will be low platelets and hypothermia
Retrograde Cerebral Perfusion
-cerebral cooling, was out air, debris, wastes, prevent aggregation, delivery of oxygen and nutrients
=goes retrograde up venous line into SVC
=pressure no higher than 25 mmHg
Antegrade Cerebral Perfusion
-most popular right now= maintains jugular venous sats and cerebral oxygen extractions
Complications of Aortic Surgery and DHCA
air, clots, LV dysfunction, MI, renal failure, respiratory failure, coagulopathy, hemorrhage
TEVAR
Thoracic Endo Vascular Aortic Repair
- femoral access, graft, fluoroscopy
- advantages= lowered death, less blood loss, quicker recovery
- complcations- bad if you need to convert to open heart if something goes wrong, bleeding, endo-leakage, stroke
Left Heart Bypass
- shunts around aneurysm
- venous cannula LA, cent pump (2/3), arterial in descending aorta
- heart is still beating
- still use lungs to oxygenate
- no reservoir, H/E, filters
Marfan’s Syndrome
connective tissue disorder= weak arteries and aorta= can dilate or tear
Aortic Debranching and Endovascular Repair
-to repair arch aneurysm
make graft from aorta to head vessels and deploy endograft in arch and occult head vessels
Embolic Events with CPB
50% of CABG patients have cerebral infarct BEFORE surgery
- 30% new infarcts after CPB
- stroke post CPB 1-5%
Embolus
carried by blood and occludes vascular system
- deformable (conformal)= GME, fat
- non-deformable= bone chip, calcific particle
- sources= circuit component, drugs, blood/surface interactions, perfusionists/surgeon (major cause!)
- types= foreign material (cotton fibers, plastic, filter, tubing, metal, bone wax), gaseous (cannula, de-airing, low reservoir, damaged circuit, ,suction, vacuum), biological (blood born-thrombin, aggregates, proteins, bone, muscle, fat)
Biologic Emboli areas for risk and circuit
areas for risk= low flow, stagnant, turbulence, cavity, rough surface
areas in circuit= connections, oxygenators, AF, reservoir
Opportunity for Embolic Events
- greatest period of risk= insertion of arterial cannula, initiation of bypass, cross clamp
- BRAIN is at greatest risk (15-20% don’t have circle of willis)
Prevention of Biological, Foreign Material, and Gaseous Emboli
- Biological= transfusion filters, anticoagulants properly, decrease circuit SA, lower WBC activation
- Foreign Material= good circuit, prime, prebypass filter, reservoir filters
- Gaseous= components secure, co2 flush, retrograde ALF priming, safety device, purge lines, pressure valves, watch for air, vents, trendelendburg, TEE, suction,
- –X clamp types= Bahnson (, Fogarty L
Safety Devices
low level alarm, bubble detector, filters, one way valves, communication protocols, checklists
