1. Circulatory Arrest Cooper University Hospital School of Perfusion 2015
Michael F. Hancock, CCP

2. Aneurysms
Aneurysms- dilation of the wall of the aorta causing a weak point in the tissue
Layer most affected is the Tunica Media
“True Aneurysms”- an abnormal widening that involves ALL THREE layers of its wall
50% over its normal diameter
Thinned Fibrous Endocardium
“False Aneurysm”- usually caused by trauma consisting of only Adventitia and Clot
Much more dangerous aneurysm

3. Aneurysms 2 Types: Fusiform- most common Saccular-
Expands evenly around the aorta
Most are True Aneurysms
Symmetrical
Saccular-
Involves a portion of the circumference and consists of an out pocketing
Asymmetrical
Most are False Aneurysms

4. Causes of Aneurysms Atherosclerosis- most common
Cystic Medial Degeneration
Ie. Marfan’s Syndrome
Degeneration of the elastic and smooth muscle fibers of the tunica media
Trauma
HTN
Infections

5. Locations of Aortic Aneurysms
Thoracic Aorta- parts of aorta above the Diaphragm
Ascending Aorta- 50%
Aortic Arch- 10%
Descending Thoracic Aorta- 40%
Abdominal Aorta- parts of aorta below the Diaphragm

6. Thoracic Aortic Aneurysms
Thoracic Aorta-
Account for 25% of aortic aneurysms
Cause-
Atherosclerosis
Marfan’s Syndrome
HTN- leads to growth of aneurysm size
Symptoms-
Back or Neck Pain
Coughing, Edema
50% Asymptomatic
Detection- CAT Scan or MRI
Rupture- leads to hypovolemic shock and death

7. Ascending Thoracic Aortic Aneurysms
Ascending Thoracic- 1st most frequent site of Thoracic Aneurysms
Most common cause is atherosclerosis
Most common location- Just distal to the Aortic Valve
Leads to dilation of the aortic root and aortic insufficiency, leading to LV failure
Fix- Bental Procedure- aortic valved conduit with reimplantation of the coronary arteries
Does not require Circulatory Arrest unless the Aortic Arch is involved or Cross-Clamping the Aorta isn’t possible

8. Descending Thoracic Aortic Aneurysms
2nd Most frequent site of Thoracic Aortic Aneurysm
Usually Fusiform- symetrical, expands evenly around aorta
Cause- Atherosclerosis
Symptoms:
Coughing, Weezing, Chest Pain, Some Asymptomatic
Fix- > 10 cm = Surgery
Decceleration Injury- Motor Vehicle Accidents
Causes a traumatic Saccular Aneurysm (False) at the level of the Ligamentum Arteriosum (5 cm below Left Subclavian Artery)
Patient usually dies on the scene or within 4 hours of injury
Surgery-
Use of Left Heart Bypass (LAFA) or Gott Shunt to perfuse distal to the injury during the surgery

9. Abdominal Aortic Aneurysms
AKA- (AAA)- Abdominal Aortic Aneurysm
Accounts for 75% of all aortic anerysms
Causes-
Atherosclerosis
HTN
Smoking (4x ↑ Risk)
Symptoms-
Asymptomatic
Abdominal Pain
Lower Back Pain
Abdominal Aorta Size-
Normal- 2.5 cm
Die within 4-5 years- 4-6 cm
Die within 1 year- > 6.0 cm
Fix- Don’t want aneurysm to rupture
Surgical stenting of the aorta by an open AAA procedure or an endovascular stent graft

10. Aortic Dissections Aortic Dissection-
Tear in the Tunica Intima, separating the intima from the surrounding media and/or adventitia, creating a false lumen for blood to travel through and create a hematoma
False lumen fills with blood which can cut off blood flow to other vessels
Causes:
HTN- biggest cause of acute aortic dissection
Atherosclerosis
Cystic Medial Degeneration, ie. Marfan’s Sydrome
Family History
Cocaine abuse (↑ BP)

11. Aortic Dissections Classifications- 5 P’s of Diagnosing Dissections
Debakey Classification
Type I- Ascending and Descending and Arch
Type II- Ascending Only
Right Lateral Wall of Ascending Aorta most common location
Type III- Descending
Stanford Classification
Type A- Ascending
Sx: Chest Pain
Type B- Descending
Sx: Back Pain
5 P’s of Diagnosing Dissections
Pain
Pallor (skin color, pale)
Pulselessness
Parasthesia (skin numbness or tingling)
Paralysis

12. Repair of Aneurysms and Dissections
Location determines which surgical procedure and which type of circulatory support will be needed for repair
Descending/Abdominal Aorta-
AAA can be repaired by an open procedure using a dacron graft or by inserting an Endovascular Stent Graft
Ascending Thoracic Aorta-
Fix depends on if the aortic valve, coronaries, and arch are involved
Surgery- Dacron graft with or without a new aortic valve attached
If the coronaries are involved, Bental Procedure must be done
Perfusion- normal CPB circuit as long as surgeon can cross-clamp aorta
Descending Thoracic Aorta-
Fix depends if the Arch is involved
Surgery- Clamp proximal and distal to the affected area and replace native aorta with a dacron graft
Use Clamp and Go method, Left Heart Bypass, or Gott Shunt
Perfusion- Left Heart Bypass (LAFA)

13. Repair of Aneurysms and Dissections
Aortic Arch Repair-
Depends on the aneurysm’s degree of involvement of the arch
Surgery-
May do an island procedure if the individual head vessels are not affected
May have to use a Trifurcated Graft if the individual head vessels are affected
May do a combination of the above methods
Perfusion-
Complete CPB with Deep Hypothermic Circulatory Arrest is needed
With or without Cerebral Perfusion (Surgeon’s Choice)
Antegrade or Retrograde Cerebral Perfusion

14. Deep Hypothermic Circulatory Arrest
Uses:
Congenital Defects (ie. HLHS- Norwood)
Aortic Arch Aneurysms
Purpose:
Lower metabolic demands of the brain enough to sustain a prolonged ischemic period
Temperatures below 20° allow cessation of circulation for mins without detectable organ injury
Factors that influence “Safe Period”
Hypothermia- lower temperatures decrease metabolic demand
Intracellular pH- hypothermic tissues have higher levels of energy rich phosphates which allow toleration of longer ischemic periods

15. Hypothermia Decreases patient’s metabolism
Decreases body’s oxygen demand (VO2 ↓)
for every 1˚ drop, there is 7% reduction in demand
Reduction in energy production (ATP ↓)
Increases blood viscosity
For every 10° decrease in temperature, blood viscosity increases 25%
More hemolysis
Poor tissue perfusion
Hemoglobin holds onto oxygen more (shift to left)
Increased solubility of gases

16. Hypothermia Degrees of Hypothermia Mild- 35 - 32˚ Moderate- 32 – 26˚
Deep- 26 – 18˚
Profound- 18 – 0˚
“Safe Period”
*for every drop of 5º the safe period doubles*
37˚ 3 mins
32˚ 6 mins
27˚ 12 mins
22˚ 24 mins
18˚ 48 mins

17. Hypothermia and Cerebral Blood Flow
During hypothermia, less cerebral oxygen consumption takes place so less cerebral blood flow is acceptable
CBF decreases linearly as temp drops
CMRO2 (cerebral metabolic rate of O2) decreases exponentially as temp reach deep hypothermic temperatures
Normothermia CBF:CMRO2 = 20:1
Deep Hypothermia CBF:CMRO2 = 75:1
CBF of 10cc/kg/min is acceptable flow

18. Cooling
Cooling
Rate of Cooling- wide gradiants between body and perfusate temperature correlate with cell necrosis
We do not use any specific guidelines for cooling, we cool down fast, and warm up slow
Brain Temperature Monitoring Sites
Nasopharyngeal- most used
Tympanic
EEG (Electroencephalographic) Monitoring
Used to determine cessation of brain activity which determines the ideal end-point of the cooling process
No peripheral body temperature will consistently predict this point
If no EEG is available, cooling for at least minutes to a temp of 18-20° is ideal
~25° if using Antegrade/Retrograde Cerebral Perfusion
Surgeon dependant
Once desired end-point temperature is reached, pump is turned off, cannula removed, and systemic circulation ceases

19. Monitoring during Circ. Arrest
Cerebral ice-packs are optional, not often used.
Cerebral Oximetry measurements are recommended.
Continuous Pump SvO2 measurements is considered a perfusion standard with DHCA
EEG, optional
BIS
Core Temperature
Brain Temperature- Nasopharyngeal
Arterial Temperature
Venous Temperature

20. CPB Circ Arrest Timeline
Routine cardiopulmonary bypass is established with or without Bi-caval cannulation.
Cooling is initiated to reach desired end-point cooling temp., ~25° for Dr. Bowen due to him using ACP
If we are able to apply Cross-Clamp:
Cardioplegia is given every min or when activity is noted until end-point cooling temp. is reached, usally a dose of plegia will be given right before circ. arrest
Deliberate hemodilution should be used to reduce the hematocrit to match the end-point cooling temp. to prevent sludging in the cerebral microcirculation.
Ie. Cooling temp = 25°, HCT = <25
When temperatures are reached or we notice cessation of brain activity, circ. Arrest drugs are added
1g Methylprednisone, mg Lasix, 25g Mannitol, 2g Magnesium
Sodium Pentothal used to be given by anesthesia, now they will give Fentanyl or let us give it

21. CPB Circ Arrest Timeline
Once drugs have recirculated, the surgeon will give the command to “Circ. Arrest” or “Pump Off”
Arterial line clamped, and controlled exsanguination is allowed via the venous line.
Send excess volume up to your spike bags and venous sequester bag
Leave your venous line unclamped to allow drainage throughout the circ. Arrest period, especially if you are using ACP
Start your Circ. Arrest clock to keep track of ischemic time
At this point, you will begin your cerebral perfusion, usually by ACP using the 18/20 fr. Optisite cannula sitting in the Innominate Artery
He will snare the proximal part of the Innominate Artery preventing your flow from reaching the systemic circulation, forcing blood into the Right Common Carotid Artery and Right Subclavian, he may snare the sublcavian as well
He will say to start ACP or “Flow to the brain”
Reduce RPMs to about 1500 and open arterial line clamp, come up to flow slowly
He wants flow of 10cc/kg/min usually coming out to be cc of flow
Watch your arterial line pressure and don’t let it get too high, that will dictate your flow
Watch your cerebral SATs, right should be higher, and notice if you have a Right Radial Line, you will get a BP during this time if he did not snare the subclavian

22. Circ. Arrest Timeline You will flow ACP the entire time
He may give some doses of plegia, let him know at 20 mins or so
Once he is done his distal anastomosis and/or Arch work is complete, he will clamp the proximal end of the dacron graft (the new ascending aorta) and de-air the graft
He will then re-establish full bypass perfusing the entire systemic circulation by removing his Innominate snares
You will work your way up to full flow, dropping the volume that you sequestered as needed and start to warm watching your temp. gradients
You will give a dose of plegia, take a blood gas and treat any issues, usually some acidosis

23. Circ. Arrest Timeline
From this point on it is a normal case, giving plegia every minutes and warming
Once his proximal anastamosis is complete, he will ask you to “Fill the root” at which point you will turn on your ANTEGRADE cardioplegia and run it very hard to pressure the new root
He is doing this to de-air his graft and test the suture lines
At this point he can take off the cross-clamp if he wishes, which he will do even if you are still cold
Proceed from here as if it were a normal case
Ask if he wants blood products which he usually will
These cases bleed a lot due to all of the suture lines
Usually order 2 Platelets, 4 FFP, 20 Cryo

24. Antegrade Cerebral Perfusion
Cannulate the Innominate Artery
Perfuses brain through right common carotid and right vertebral artery
Snare distal to the cannulation or snare the bracheocephalic arteries and descending thoracic aorta to prevent flow
NIRS- used to monitor cerebral saturations
Left Side of brain will be hypoperfused, only flow coming from Circle of Willis

25. Retrograde Cerebral Perfusion
Started as a treatment for massive air embolism
Can extend safe periods up to 60 minutes
Washes out metabolic waste products, embolic debris, air bubbles and delivery of O2 and nutrients to the ischemic brain during HCA
Optimal pressure for RCP is mm Hg
Flows of 10-30cc/kg/min
Infusion temperature should match the desired core temperature
Cannula placed in SVC and blood return from aortic root is retrieved by suckers

26. Left Heart Bypass Uses: Goal: Circuit:
Descending Thoracic Aneurysms/Dissections
Thoracoabdominal Aneurysms/Dissections
Goal:
To perfuse the body distal to the clamp placed near the aneurysm/dissection
Circuit:
Inflow and Outflow cannula
3/8” tubing
Centrifugal Pump
NO heat exchanger or oxygenator needed
NO heparin needed, some places will give 100 u/kg to maintain patency of small intercostal arteries and spinal arteries
Heparin administration causes excessive bleeding around suture sites and in pre-existing traumatic locations

27. Left Heart Bypass Cannulation: Monitoring:
Proximal cannulation in the Left Atrium via the left atrial appendage or either of the left pulmonary veins (usually L. Inferior PV)
Distal cannulation in the femoral artery or in the descending aorta distal to the clamp
Monitoring:
Arterial pressure lines placed in the Right Radial Artery and the Right Femoral Artery to monitoring both methods of perfusion during LHB
Right Radial measures proximal pressures
Used in case Left Subclavian Artery is aneurysmal and has to be clamped and re-anastomosed
Right Femoral measures distal pressures
Used because L. Fem. Artery can be used for cannulation

28. Left Heart Bypass Perfusion:
Area proximal to clamps are perfused by the heart ejecting normally into the ascending aorta
Area distal to clamps perfused by the LHB machine
Increasing LHB flow rate will steal more volume from LV and reduce proximal BP, but will increase distal BP
Vasodilators, LHB flow rate, and addition of fluids are most common practices of maintaining both BPs