THORACIC AND AORTIC SURGERY Flashcards
Ascending Aorta:
Begins at the AV annulus and extends to the proximal innominate artery
Transverse Arch
Where 3 brachiocephalic
branches arise
Treatment for Ascending and Transverse Arch are very similar.
Descending Thoracic and Thoracoabdominal Aorta
Lies just beyond the subclavian to the aortoiliac bifurcation
Dissection
Occurs when blood penetrates the intima of the Aorta Creates an expanding hematoma between medial layers True lumen is not usually dilated
Compressed by dissection Branching vessels may not be affected
Aneurysm
Dilation of all 3 layers
AORTIC DISSECTIONS
Incidence
According to European Autopsy Study Occurs in 3.2 dissections per 100,000 autopsies Results in more deaths than aneurysm rupture
AORTIC DISSECTIONS risk factors
Hypertension, advanced age, male sex, Marfan’s Syndrome, Coarctation, Bicuspid AV, Pregnancy
AORTIC DISSECTIONS
Causes (Inciting Events)
Increased Physical Activity Emotional Stress Blunt Trauma
Can also occur without any physical activity Ie. Cannulation for bypass
AORTIC DISSECTIONS
Mechanism
Intimal Tear Presence of a weakened aortic wall Areas experiencing greatest mechanical shear forces
Points where the aorta is fixed, there is increased shear stress applied to the aortic wall.
aoritc dissections prevalence based on location
Ascending (61%) Descending (24%)
Isthmus (Distal to Left Subclavian) (16%) Arch (9%) Abdominal (3%) Other (1%)
AORTIC DISSECTIONS
Propagation
Occurs within seconds Driven by pulse pressure and ejection velocity
Origin of arteries (including coronary arteries) may be involved in
Aortic Dissections
Vessel occlusions can also occur Due to compression by the false lumen.
DeBakey Classification
3 types based upon location of intimal tear and which section of the aorta is involved
DEBAKEY CLASSIFICATION
Type I
Intimal Tear: Asceding Aorta
Dissection: All parts of thoracic aorta (ascending, arch, and descending)
DEBAKEY CLASSIFICATION
Type II
Intimal Tear: Asceding Aorta
Dissection: Ascedng Aorta only Stops before innominate artery
DEBAKEY CLASSIFICATION
Type IIIA
Intimal Tear: Descending Aorta
Dissection: Descending Thoracic only distal to left subclavian, ends above diaphragm
DEBAKEY CLASSIFICATION
Type IIIB
Intimal Tear: Descending Aorta Dissection: Below diaphragm
“Easier” Classification system
Type A
Ascending Aorta Any involvement regardless of where tear is
Regardless of how far it propagates Usually emergent/ urgent cases More virulent course
Easier” Classification system
Type B
Distal aorta Any part of aorta distal to left subclavian
Prognosis for untreated ascending dissection DISMAL
2 day mortality = 3 month mortality=
50%,90%
usual cause of death from dissection
Rupture of the false lumen into the pleural space or
pericardium
Lower incidence with DeBakey Type III or Stanford B dissections
Other causes of death from dissections
Progressive heart failure (AV involvement) MI (Coronary Involvement) Stroke (Occlusion of cerebral vessels) Bowel Gangrene (Mesenteric artery occlusion)
AORTIC DISSECTIONS
Surgical Mortality
3-24%
Depends on affected section of aorta Aortic Arch – Highest mortality Descending Thoracic – lowest mortality
ANEURYSMS
Incidence:
European Studies show 460/100,000 Thoracic Aneurysms
aneurysm percentage by location
45% Involved Ascending Aorta 10% Involved Arch 35% Involved Descending Aorta 10% Thoracoabdominal
fusiform aneurysm
Entire circumference of the aortic wall
saccular aneurysm
Involves only part of the circumference of the aortic
wall
ARCH aneurysms are typically
saccular
ANEURYSM – CRAWFORD CLASSIFICATION
Used to classify Thoracoabdominal Aortic Aneurysms
Used to describe the extent of the aorta requiring replacement
ANEURYSM – CRAWFORD EXTENT I
Extent I :
Involves most or all of the descending thoracic aorta and upper abdominal aorta.
ANEURYSM – CRAWFORD EXTENT II
Involves most or all of descending thoracic aorta and extends into infrarenal abdominal aorta
ANEURYSM – CRAWFORD EXTENT III
Involves the distal 1⁄2 or less of descending thoracic aorta and varying portion of abdominal aorta
ANEURYSM – CRAWFORD EXTENT IV
Involves most or all abdominal aorta
ANEURYSMS
Natural History
Progressive dilation
More than 1⁄2 of aortic aneurysms rupture
Untreated 5 year survival of a thoracoabdominal aortic aneurysm is
13-39%
Other complications of aneurysm include:
Mycotic infection Atheroembolisation Dissection (rare)
ANEURYSMS
Predictors of poor prognosis:
Larger size (less than 10cm max transverse diameter)
Presence of other symptoms
Associated CV Disease CAD MI CVA
THORACIC ARTERY TEARS - ETIOLOGY
Majority occurs after
a trauma. Involve deceleration injury (MVA)
Large shear stress on points of aortic wall that are relatively immobile.
thoracic artery tear leads to
immediate exsanguination and death 10-15% are lucky
Maintain the integrity of the adventitial covering of the aortic lumen
Survive to emergency care
THORACIC ARTERY RUPTURE - LOCATION
Most occur distal to the origin of the left subclavian artery
Due to fixation at the point of the ligamentum arteriosum
2nd most common site
Ascending aorta just distal to the Aortic Valve.
diagnosis for dissection aneurysm and trauma rupture
Dramatic onset, Asymptomatic until late in course
Medical evaluation for unrelated problem or complication of aneurysm
If they survive trauma Signs/symptoms similar to descending aortic aneurysm
INDICATIONS FOR SURGERY – ASCENDING AORTA
Dissection
Acute Type A Virulent Course High Mortality
Aneurysm Persistent pain despite small aneurysm AV Involvement creating MI Angina Rapidly expanding Greater than 5-5.5 cm diame
INDICATIONS FOR SURGERY – AORTIC ARCH
Dissections Acute, limited to arch (rare)
Aneurysm Repair of arch aneurysm is more complicated
Carries increased morbidity and mortality Persistent symptoms Greater than 5.5-6cm Progressive expansion
INDICATIONS FOR SURGERY – DESCENDING AORTA
Dissection Medical management in acute phase Failure to control hypertension medically Continued pain Enlargement on CXR, CT, Angio Neurologic deficit Renal/ GI Ischemia
Aneurysm Greater than 5-6cm Expanding Leaking Chronic, causing persistent pain.
PERFUSION – AORTIC SURGERY
Considerations
Where is the aneurysm located? Where do we need to cannulate? Do we need to circ arrest? Median sternotomy versus Thoracotomy? Full CPB or Left heart bypass?
CPB W/O CIRC ARREST
Very proximal aneurysms limited to the Aortic Root or Ascending Aorta.
Cannulate in the ascending aorta or transverse aorta, and Dual stage in RA or Bicaval
Cross clamp proximal to the Innominate Artery
If patient is unstable prior to sternotomy – cannulate femoral to go on CPB prior to sternotomy
Normal LV/PA Vent Normal CPG
Ie. NORMAL CBP CASE!
CPB W/ DHCA AND ACP
Bloodless field Uncluttered by clamps and cannulas
Studies have shown it doesn’t necessarily abate cerebral metabolic demands
Significant cerebral metabolic activity occurs
at temperatures at which DHCA is initiated.
Promotes brain ischemia Accumulation of metabolic wastes.
Perioperative neurologic complications
Higher when DHCA was
greater than 40 minutes
Mortality
Increased dramatically when DHCA
was greater than 65 minutes.
RETROGRADE CEREBRAL PERFUSION
Gained popularity in the and was first done
‘90s. 1st done in 1980 by Milles and Ochsner
Treating massive air embolism
benefits of rcp
Homogeneous cerebral cooling Air bubble wash out Wash out of embolic debris Wash out of metabolic wastes Prevent cerebral blood cell micro aggregation Delivery of oxygen and nutrients to brain.
Experimental and clinical data do not consistently support the efficacy of
RCP for cerebral protection
Flow may not be adequate to meet the metabolic needs
RCP provide flow to brain microvasculature?
HOW TO DO A CIRC ARREST CASE
Need to monitor temperatures
Nasopharyngeal / Bladder Arterial Venous
Water
HOW TO DO A CIRC ARREST CASE. Need to monitor the brain
EEG – Brain activity
Electrocerebral silence dictates adequate cerebral cooling
drugs for circ arrest
Mannitol (25g) and Steroids Enhances cerebral protection Put in the pump prior to turning off the pump (Prime?)
cannulation for circ arrest
Axillary Cannulation is preferred Artery is usually exposed prior to sternotomy After heparin is given,
8mm graft is sewn to the artery Cannula is placed in the 8mm graft. In an emergency – femoral artery is used
If it’s a dissection, make sure that the cannula is in the true lumen!
Venous cannula – RA, Bicaval, Femoral Depends on need and access
HOW TO DO A CIRC ARREST CASE
CPB is initated
Assess adequacy of perfusion Especially important for femoral artery cannulation
10°C drop in temperature – reduces rate of oxygen
consumption by
50%. Pump flows can be reduced to a CI of 1.6-1.8 L/min/m2
A 10°C decrease in tempearture causes a _____increase in blood viscosity
20-25%
Hemodilution to a
hct of less than 25 % to avoid stroke
Hct kept low until
rewarm
Hemoconcentrate
hemodilution reduces o2 carrying capacity but
overall oxygen delivery improves
Decreased viscosity enhances the flow in the microcirculation.
HOW TO DO A CIRC ARREST CASE
At fibrillation
Give CPG via retrograde cannula
Remember aneurysm/dissection is probably in the ascending aorta or arch, therefore no antegrade CPG.
If the AV is competent and a AoXC can be safely put on the aorta w/o damaging tissue
Give antegrade CPG Arrest is maintained with deep hypothermia
HOW TO DO A CIRC ARREST CASE
Keep cooling until
EEG shows no cerebral electrical activity
Usually takes about 20-25 min. Brain Temp 18-20°C Cool no lower than 15°C
when not using an eeg cool to
for at least 25 min to a target core temp of 18-20°C
At EEG silence
Give pentobarbital Circulate for 3 minutes
Head is packed in ice to facilitate
surface cooling
what position of the patent for circ arrest
Trendelenburg position
HOW TO DO A CIRC ARREST CASE
Flow is turned off. Patient is drained
Innominate artery is snared
nitiate ACP – 10mL/kg/min
Right axillary – innominate artery – snare diverts blood antegrade through right common carotid – brain.
when aorta is opened
Bleed back from the L. Common Carotid and L. Subclavian obscure field view
Cardiotomy suction in distal arch Possible use of balloon occluder in both vessels.
HOW TO DO A CIRC ARREST CASE
End of graft is sewn
to proximal descending thoracic aorta, transverse arch or distal ascending aorta
Attach head vessels Island
Branched graft
Put patient in steep
Trendelenburg
Cardiotomy suction placed in unattached graft
Release tourniquet on innominate
Slowly increase flow to full flow (50mL/kg/min) as the aorta and graft are deaired
If cannulated femorally, move the cannula to the arch Systemic circulation re-estabilished.
HOW TO DO A CIRC ARREST CASE
Proximal graft attached Slowly rewarm to
36.5°C
Not to exceed a 10°C gradient between arterial blood and nasopharyngeal / bladder
Proximal complete Deair with venting needle through graft AoXC removed
TEE is utilized to make sure there is no air present
CPB is terminated
OFF PUMP
Want systolic BP
appx 100-120mmHg
off pump mean
70-90mmHg
off pump HR
60-80 BPM
OFF PUMP CI
2.0-2.5 L/min/m2
Will see a coagulopathy after bypass, especially with DHCA SUCH AS
Platelet dysfunction secondary to extreme hypothermia
Usually requires FFP/ Platelets/ Cryo? Often resort to Factor VII and IX Usually use an antifibrinolytic to help with bleeding.
COMPLICATIONS OF AORTIC SURGERY AND DHCA
Air Emboli Clots LV Dysfunction MI (Reimplanting coronaries) Renal Failure Respiratory failure Coagulopathy Hemorrhage
OTHER PROCEDURES OF AORTIC CONDTIONS
Endovascular Repair Left Heart bypass
ENDOVASCULAR REPAIR HISTORY
1st done in 1991 on abdominal aortic aneurysm
Now we can do it on thoracic aneurysms due to increased technology which allows precise placement in a high pressure system
Before only open repairs
Thoracic EndoVascular Aortic Repair (TEVAR)
Requires femoral access Flouroscopy Graft self-deploys
Req’s flouroscopy to check position Requires systemic heparinization
ENDOVASCULAR REPAIR (TEVAR) Requires proximaL
“Landing Zone” of 15mm length
Distal end needs to be non-aneurysmal
ENDOVASCULAR REPAIR (TEVAR) CON
Side branches – possibility of occluding a
vessel that branches off the aorta
ENDOVASCULAR REPAIR (TEVAR) Considerations:
Aortic Tortuosity, calcification, atherosclerosis
TEVAR
Advantages:
Reduces mortality Reduces morbidity Less blood loss Quicker recovery Hemodynamic stability
Pulmonary and cardiac comorbidities that may have not made them a candidate for open surgeries, allow them to have this option.
TEVAR
Complications
Conversion to open procedure Aortic Rupture / dissection Malposition – causing visceral ischemia
Bleeding Endoleak
Blood flows back into the aneurysmal sac after the endovascular graft is placed
Usually observe and hope it spontaneously resolves Stroke
Paraplegia Contrast Nephropathy
LEFT HEART BYPASS
Basically, a shunt around the aneurysm/ dissection
Used on Descending legions
Heart pumps blood to the lungs Lungs oxygenate Venous cannula places in LA/ L. Pulmonary veins
Risk of air embolism
Move tip of cannula – impair drainage
Could cannulate Apex of LV Great flow Risk of LV injury
Arterial cannula placed in descending aorta
LEFT HEART BYPASS
ECC Circuit
Tubing
Centrifugal pump No Reservior NoH/E No Bubble Trap
Excluding those help minimize the heparinization required.
LEFT HEART BYPASS
If the patient needs volume
Anesthesia must give
LEFT HEART BYPASS Heart pumps blood to the vessels p
proximal to the clamp (usually the head vessels)
LEF HEART BYPASS ECC pumps
distal to clamp 2/3 of CO to lower body
LEFT HEART BYPASS arterial pressure
Monitored at radial or brachial artery (upper body) Monitored at femoral artery (lower body)
CLINICAL APPLICATIONS – MARFAN’S SYNDROME
Connective Tissue Disorder
Connective Tissue provides strength and support to tendons, ligaments, cartilage, blood vessel walls, and heart valves.
They aren’t as stiff as they should be Arteries are weakened, particularly the aorta Aorta dilates – weakens Under exertion the aorta can tear – dissection Also have MV prolapse and AI
CLINICAL APPLICATIONS – AORTIC DEBRANCHING AND ENDOVASCULAR REPAIR
To repair an arch aneurysm Can do an extra-anatomic bypass
Connect the aorta to the Innominate artery, L. Carotid, and L. subclavian arteries
Then, deploy an endograft in the arch and occlude the head vessels.
Head vessels get flow via the graft, and the aneurysm/ dissection is treated via the endograft.
CLINICAL APPLICATIONS – CASE REPORT AORTIC DEBRANCHING
64y/o male
Acute type A dissection
Emergency AV replacement and hemiarch replacement
Post op day 4, CT showed expansion of the false lumen of the arch distal to the hemiarch graft
Did an extra-anatomic bypass to the innominate and left carotid. Access to the left subclavian was problematic
Deployed and endograft antegrade into the prior hemiarch graft.
Larger to cover/pass the graft No endoleak.
