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1

What are the key components in a CPB machine?

Simplified version to know;

  • Drainage canula drains blood from body
  • Reservoir to collect blood
  • Pump to move blood forward back to the patient
  • Oxygenator/heat exchanger combo
    • oxygenates the blood
    • warms/cools blood
  • Arterial cannula for return

2

Anesthesia responsibilites at the beginning of CPB case?

Bring patient into OR and induce and place lines.

  • Induction and lines
    • A-line (x 2)
    • Central line
      • vasopressors
      • volume requirements
    • PA line
      • managing pt post operatively
  • Monitoring
    • Sat probes – sometimes each side of body or upper and lower body
    • NIRS (Cerebral Oximetry)              
      •  used as a trending device – determine perfusion problems
      • Noninvasive monitor for tissue oxygenation
    • Temperature (x 2)
      • Esophageal
      • core temp (bladder/rectal/or PA cath) – monitor for cooling and rewarming.
  • Sedate and Paralyze
    • Reduce metabolism
      • Allows for lower CPB flows than normal CO

3

What are some drugs you want available for CPB case?

  • *Phenylephrine – often used by perfusionists when on by-pass
  • The rest of the drugs are more likely to help pt transition off bypass and to be used afterward
    • Epinephrine,
    • Vasopressin
    • Dobutamine
    • Dopamine
    • Isoproterenol
    • Norepinephrine
    • Milrinone
    • Nicardipine
    • Lidocaine
    • Amiodarone
  • Refractory Vasoplegia: HoTN refractory to vasopressor therapy (rare) 
    • Tx:
      • Methylene Blue
      • Hydroxocobalamin (Vit B12)

4

What do we need to do to prepare for sternotomy?

  • Step 1: Opening the chest
    • “Lungs down” for sternotomy
      •  Fx: deflate lungs and move the heart farther from chest wall

5

What are some perfusionist responsiblities pre bypass?

  • Prime (de-air) the CPB Circuit
    • balanced electrolyte solution – most important task
      • Plasmalyte A/Normasol/ LR
  • Then drugs are added to circuit based on institution and pt need:
    • Ex: Heparin, Bicarb (Na), Mannitol, Cefazolin, Albumin, TXA/ Amicar (antifibrinolytic)
  • Determine if  PRBCs/FFP needed
    • Predicted diluted Hct < 24%
    • Ex: if pt has low Hct before bypass or predicted dilutional Hct low (< 24%) → add PRBCs
  • Never prime circuit w/ plts OR cryo
    • No cryo –don’t want to promote clotting (why you give heparin)
    • Arterial blood pump would destroy platelets
  • Perfusionist get baseline ACT
    • Baseline Activated Clotting Time (ACT)
    • Normal: 70-120 sec
      • Goal is to return to this baseline after bypass
  • Perfusion will set up a cell Saver blood is obtained from
    • opening of the chest
    • blood is collected prior to heparinization
  • Crystalloid prime will REDUCE colloid oncotic pressure (during initiation of CPB)
    • → fluid shifts and hypotension will likely follow

6

How do perfusionist determine the patient's hematocrit after pump initiation?

Calculation:

  • Post-dilutional HCT = RBCV / TCBV + prime volume
    • RBCV= Red blood cell volume
      • TCBV x Hct
    • TCBV= Total circulating BV
      • 70-80 ml/kg
    • Prime volume= ~ 500-1000 ml
  • Example:
    • 70 kg Male
    • Hct 35%
    • Prime volume 700 ml
      • Answer: Post-Dilutional Hct → 31% (0.306)
    • Same pt but starting Hct 28% → 24% (0.245%)
      • Will probably add PRBC to circuit
  • RBCV (TCBV x Hct) / TCBV (total circulating blood volume) + prime (usually 500-1,000 ml)

7

Considerations with heparin load prior to initiation of bypass?

Heparin loading dose

  • Reduce clotting from blood exposure to foreign surfaces of CPB circuit
  • Dose: 300-400 units/kg
    • Admin via central line or by surgeon directly into R atrium
    • Dose is facility dependent
      • Ex: 70 kg pt → 28,000 units (or round up to 30,000 units)
      • Once the chest and pericardium are open and surgeon is happy with exposure, they will ask the anesthesia provider to give heparin via IV or will give it directly into the right atrium
  • Considerations:
    • May need to increase dose if previous exposure
    • Large heparin bolus can cause transient hypotension – d/t decreased viscosity
      • HoTN d/t decrease viscosity (SVR 10-20%)
  • Peak affect = 1-2 min after admin
    • After 3-5 min of heparin circulation → draw blood for perfusionist to run ACT

8

What is an ACT? What is the goal for ACT on CPB?

What are pump suckers?

  • Goal ACT: 480 sec
    • provides acceptable margin of safety
  • Avoid under heparinized
    • will clot circuit
    • prevent consumption of clotting factors (won’t be available when needed after CPB termination)
  • Avoid over heparinized – prevent bleeding,
  • Pump suckers – kind of like yankauers for surgical field
    • started after ACT at >300 sec (these take blood in the surgical field and pull into pump to be delivered back to patient

9

How does heparin work?

  • Heparin binds to antithrombin III (ATIII) and potentiates its activity
    • ATIII: a natural thrombin inhibitor
    • Increases ATIII activity from 1,000 -10,000 x
  • Antithrombin III inhibits thrombin and other serine proteases by binding to the active site.
  • Inactivates factor Xa & thrombin → disrupting the formation of fibrin clot
  • Also works on factors VII (?), IX, XI, XII

10

What are some considerations if the ACT does not reach a therapeutic level after administration of heparin?

Look for ATIII level from preop labs

  • Sometimes ACT will not reach the goal of 480 seconds with the loading heparin dose alone, when this happens the first step is for the perfusionist to provide the anesthesia provider with a second, smaller dose of heparin in hopes of getting closer to goal ACT
  • Increasing heparin dose w/ increasing body wt is only effective to some degree bc the heparin is mainly distributed in plasma.
  • Once the additional heparin reaches > 600 units/kg and the pt is still < 300 seconds → pt is “heparin resistant”
  • Heparin does need anti-thrombin 3 as a co-factor to work
    • so even additional heparin will not provide enough anti-coagulation because of an anti-thrombin 3 deficiency.
  • This can be inherited or acquired r/t prior heparin exposure.
    • Why it’s helpful to get pre-op ATIII level so a poor response to heparin can be anticipated and prepared for.
  • In cases when you have ATIII deficiency → Administer:
    • recombinant anti-thrombin (thrombate) or
    • FFP (contains ATIII)

11

What is the treatment for heparin resistance?

  • Additional heparin
  • Thrombate
    • From pharmacy (not kept in OR, $$$)
    • preferred over FFP
      • Give thrombate + additional heparin → recheck ACT
    • Dosing thrombate: 
      • Dose (IU) = (Desired ATIII level – Actual ATIII) x kg / 1.4 = thrombate units to admin
      • Desired ATIII level: 80-120%
        • admin dose while redosing heparin
  • FFP 
    • Inconvenient (must thaw and want to avoid blood product during CV sx)
    • 1 unit of ATIII per mL of FFP
      • ~ Adult: usually 2 units of FFP
  • Perfusionist will avoid going on bypass unless your ACT is at least > 300 seconds.

12

What is an heparin alternative that can be used for CPB? Consideraitons?

  • Bivalirudin (Angiomax) → Heparin alternative
    •  takes a lot of planning and is usually not done on the fly.
  • Requires a constant infusion d/t short half-life (24 minutes)
    • No reversal required*
  • No easy anticoag monitoring with bivalirudin.

13

Where can the arterial cannulation be inserted?

Considerations for arterial cannulation?

After heparin is giving and we have adequate ACT → cannulation can begin.

  • 1st: arterial cannulation bc how blood can be returned to patient.
    • If BP drops/bleeding → perfusionist can rapidly transfuse from bypass circuit
  • Sites:
    • Aorta Ascending: (most common site) proximal to innominate artery
    • Femoral artery: retrograde flow up the descending aorta
      • Alternative if aorta is calcified or if a “re-do” where concern for adhesion to chest wall and reopening the sternum poses risk to aorta or LV
      • Considerations:
        • Cannula in DESCENDING aorta and perfuses upper body and head via retrograde flow
          • having a femoral cannula in allows for rapid initiation of CPB if needed
        • Also have the option of going on CPB prior to opening the chest to decompress the heart and move it away from the chest wall (easier for opening)
    • Axillary artery: selective cerebral perfusion
      • Used in special circumstances

14

What are some considerations with the arterial cannula size?

What occurs immediately around arterial cannulation?

How should we treat hypotension during this process?

  • Arterial cannula size
    • Too small → limit flow due to increased resistance and then jetting of blood (high pressure) – this can potentially cause an aortic dissection, biggest risk of cannulation
    • Too large → cause vessel damage
      • Need balance
      • Adult Cannula Size: 22 - 24 French aortic canula
  • Sucker bypass utilization
    • Bleeding during cannulation period → Sucker bypass collection system allows blood lost to be pumped from chest and taken back to immediately re-tx volume
  • Once the arterial canula is in place, the perfusionist will check the arterial line pressure is reading as this is a reflection of the [aortic] root pressure
    • excessively high = sign of aortic dissection.
    • Perfusionist will check for pulsatility so some fluctuation up and down in the pressure on the A-line, and can give a test transfusion of a small amount of volume to ensure the pressure doesn’t jump up.
  • The surgeon wants the pressure on the LOWER side for canulation to avoid additional bleeding during this period.
    • The pt will lose blood during cannulation, but this is only temporary.
  • Hypotension should be treated with VASOPRESSORS not volume.

15

Where can the venous cannula be placed during CPB surgery?

/

There a few different types of venous canulation types depending on the surgery being performed.

  • Size is important as it needs to ensure adequate drainage,
    • b/c what drains out is what is returned to the patient so if not enough is drained, we can’t return enough to get good flow
  • Single
    • Dual Stage: RA, IVC
    • A single venous canula can be used in the right atrium to drain the heart in the case of aortic valve repair, arch repair, or CABG.
    • These cannulas are considered dual stage and usually have multiple holes spaced out to drain from different locations like the right atrium and IVC
  • BiCaval Canulation = two separate venous cannulas
    • SVC and IVC cannulated
      • Y-ed together and attached to venous drainage line
        • SVC: 1/3 drainage (smaller)
        • IVC: 2/3 drainage (larger size)
    • This form of drainage is utilized if the right heart needs to open for repair:
      • Ex: tricuspid valve, pulmonary valve, mitral valve, ASDs, PFO
    • Snares around each cannula → “Total Bypass”Total Bypass = obtained if snares are tightened around each venous canula used for bicaval, so then only bronchial return can enter heart. Allows for better visualization of chambers
  • Femoral canulation: via femoral vein
    • Drains Right heart via IVC
      • Redos
      • Minimally invasive

16

What occurs during CPB initiation?

  • Simultaneously drain the heart while returning blood via the arterial cannula
    • Pt already heparinized, arterial perfusion cannula, and venous drainage cannula → bypass
    • Perfusionist will slowly release the clamp on the venous line to allow the heart to empty while coming up on the arterial flow to return blood to the patient
    • GOAL:
      •  empty the heart and still provide enough flow to maintain pressure
  • “Fullflow”→ stop ventilating
    • Bypass has taken over lung role
    • The perfusionist will also take over the continuous administration of isoflurane using a vaporizer, usually will run it at 0.5 -1% in a case
      • if you have concerns about the adequacy of anesthetic depth, discuss with perfusionist.
  • Loss of arterial line waveform
    • A-line flattens but ideally MAP
    •  stays around 60-65 mmHg
  • Begin cooling patient
  • Perfusionist responsible for:
    • Administering anesthetic gas
    • Monitoring and responding to pressure changes – Monitoring and correcting blood gases
    • Administering medications
    • Managing patient temperature
    • Taking over the role of the heart and lungs

17

What is the reservoir in the bypass circuit?

  • Venous cannula → venous line → reservoir
    • Once blood is drained by venous canula it then travels down the venous line (3/8 to ½ inch tubing) and enters the venous reservoir aka the “cardiotomy”
      • → allows the blood to settle so less bubbles enter circulation.
  • “Storage” for venous blood, pump sucker return, vent return, and any additional fluid added to circuit (Ex: fluid, drugs)
    • Must maintain a minimum operating volume in reservoir to prevent air from entering the pump [next component]
  • Filters and Defoamers
    • Blood travels through these to prevent gaseous and particulate micro-emboli from entering circuit
    • Always placed first, before the arterial pump and oxygenator

18

What is the arterial pump in the bypass machine? What are the types of pump?

  • Venous Cannula → Venous Line → [[filter/defoamer]] Reservoir à Arterial Pump
  • Pulls volume from the reservoir and forces it forward against resistance of circuit components and the patient
  • TYPES: 2
    • Centrifugal
      • Preload, afterload dependent
    • Roller
      • Preload, afterload independent

19

What are some characteristics of a centrifugal pump? With what patient population is this normally used?

  • frequently used in adults,
  • kinetic pump that creates a vortex using rapid revolutions (RPMs), pulls blood into center of pump and forces it to sides where it leaves to go to patient.
    • Pump comes with a risk of retrograde flow if < 1000 RPM
      •  Normal RPM = 3000 range
    • Pump will be set to certain number of revolutions per minute (RPM)
      • Resistance increases → flow will decrease unless RPM is manually increased
      • Resistance decreases → flow will increase unless RPM is manually decreased
        • RPM have to increase to maintain the same flow you had at a lower pressure → this can result in more hemolysis is resistance is not corrected
  • Several benefits:
    • less chance of air getting to the patient
    • reduces hemolysis
  • Pre-load and afterload dependent:  
    • Pre-Load: requires fluid (blood) for centrifugation to occur.
      • *If air were to enter the pump, it would not be able to overcome atmospheric pressure and pump the air forward – good safety mechanism.
    • Afterload: it is like a beating heart → if it has to pump against a high resistance (higher blood pressure, smaller circuit components) must work harder to achieve the same flow.

20

What is a roller pump? Characteristics? Patient population that uses it?

  • Positive displacement pump
    • Positive displacement means that tubing is occluding by two roller heads that rotate counterclockwise and these roller heads squeeze the blood forward.
      •  ½  inch, 1 foot long tubing
      • push forward from each revolution: ~ 40 mL
        • ~ 4 L/min flow (less revolutions/min than centrifugal pump)
  • Preload and afterload INDEPENDENT
    • RISK: If air in circuit → air pushed forward unless stopped by perfusionist
  • Considerations:  
    • If pump encounters higher pressure → it will continue to press forward anyway and can damage vessels or can cause the CPB circuit to come apart (dangerous)
    • More precise control of flow (benefit)

21

What is the oxygenator in a bypass circuit? Types of oxygenator?

Venous Cannula → Venous Line → [[filter/defoamer]] Reservoir à Arterial Pump --> Oxygenator [heat exchanger, arterial line filter]

  • “Artificial lung”
    • FUNCTION:
      • Gas exchange (O2, CO2)
        • Utilize Membrane oxygenators: made up of small fibers that gas runs through while blood runs around these fibers so that gas can exchanged via a gradient
        • Driving pressure causes the gas to diffuse from areas of high pressure to lower pressure
      • Anesthetic gas administration
    • SA= 2-2.5 sq meters (human lung 70-1000 sq meters)
  • Oxygenators can be: 2 types
    • 1. Integrated: contains arterial line filter [ALF]
      • reduces prime volume
    • 2. Non-integrated: requires external ALF
  • ALF/arterial line filter
    • filtering device for particles and emboli from the blood, last line of defense before blood returns to pt
  • External ALF
  • Includes stainless steel heater-exchanger:
    • cool and re-warm blood/pt (water outside membrane set to any temp and blood w/in membrane)
  • Specifications:
    • Typical prime volume for oxygenator = 260 ml
    • Rated max flow= 7 L/min
      • Can run flow higher but gas exchange less effective

22

How is blood returned to the patient from the bypass machine?

Venous Cannula → Venous Line → [[filter/defoamer]] Reservoir --> Arterial Pump --> Oxygenator [heat exchanger, arterial line filter] --> Arterial Line --> Arterial Cannula (Aorta)

 Arterial Line à Arterial Cannula

  • Final stage of CPB circuit
  • Once blood leaves the oxygenator/ ALF/ Heat- exchanger → it travels up the arterial line and back to the patient’s aorta via the arterial cannula

23

What is the function of cardioplegia?

What are the routes for cardioplegia?

Alternative to cardioplegia?

  • CPB circuit also includes a cardioplegia pump.
  • Function:
    • Helps provide a motionless field
    • Solution used to arrest the heart once the cross-clamp placed – prevent flow to systemic circulation
      • Loss of EKG activity
        • EKG activity disappear quickly if going well
        • NO EKG activity while cross clamp period
        • If EKG activity is suspected:
          • 1st: r/o interference
          • 2nd: notify surgeon
          • 3rd: re-dose cardioplegia
  • Routes:
    • Anterograde cardioplegia: via aortic root cardioplegia needle to both coronary arteries simultaneously
    • Retrograde: via coronary sinus
      • Commonly used with AI
      • Keep CS pressure < 40 mmHg
      • Less R heart protection
    • Ostial: olive tip cannulas held directly to coronary ostia
      • Aortic sx
  • Induced fibrillation: XC alternative for PVRs, TVRs
    • alternative to cardioplegia sometimes used in place of placing a cross clamp for procedures on the right side of the heart
      • ex: pulmonary valve, tricuspid valve
      • Fx: help avoid ischemia.
    • We induce fibrillation by rapidly cooling to < 30 degrees or we can use a fibrillatory device

24

What is antegrade cardioplegia?

via coronary arteries (most common)

  • Delivered to both coronary arteries simultaneously via the aortic root cardioplegia needle
  • Cardioplegia needle → inserted into the aorta above aortic valve.
  • Cross clamp → placed on the aorta, above the cardioplegia needle.
  • Once the cross clamp is applied, administration of the solution from the pump beings immediately
    • Flow must be fast enough to build enough pressure to close the aortic valve (150-250 mmHg) but it can’t be so fast that it would cause dissection of the coronaries/myocardial edema
  • Once the aortic valve is closed, the solution cannot enter the heart (closed valve), cannot enter the aorta (cross clamp) so must go down the coronary arteries.
  • Will usually be flowing 250- 400 mL per minute with this form of delivery
    • will take several minutes to deliver.
  • The cardioplegia will then exit the coronary arteries via the coronary sinus into the RA

25

What is retrograde cardioplegia?

  • A retrograde canula is placed through the atrium and into the coronary sinus, there is a balloon at the tip of the canula to prevent cardioplegia leakage back into the RA
  • So then the flow has to go retrograde into the coronary arteries and empties into the aortic root. The aorta will be vented in this case (drained)
  • Retrograde:
    • less right heart protection, because the right coronaries drain into the right atrium via the small cardiac veins and not the coronary sinus
      • good left heart protection
      • poor right heart protection
  • This form is utilized in cases of aortic insufficiency, because the anterograde method will leak through the incompetent valve into left ventricle and this will prevent an adequate arrest
  • Considerations:
    •  monitor the sinus pressure because it is very bad to rupture the coronary sinus as it’s hard to repair because its on the back of the heart
    • Surgeon will hand you (anesthesia provider) a line to attach to CVP transducer and this is how the perfusionist can monitor coronary sinus pressure during retrograde cardioplegia
      • (max = 40 mmMg), flowing 200 mL/min
  • If retrograde cardioplegia is given, you may also see an additional dose of cardioplegia given directly via the R ostia for better right heart protection

26

What is direct ostial cardioplegia?

  • When small cannulas are placed directly up to left and right coronary ostia, this form does not require competent aortic valve but it does require optimal positioning of the cannulas and slower delivery (50-100 mL/min)
  • often surgeons are too impatient for this
  • can see direct ostial cardioplegia to re-dose after retrograde flow
  • Another time you might see direct ostia cardioplegia is during aortic surgery cases requiring the opening of the aorta.
    • Basically any dose beyond the first in aortic valve repair, replacement, arch repairs, might be direct ostia cardioplegia

27

What makes up cardioplegia solution?

  • Delivered cold (2-4 oC)
    • Ideally keep myocardial temp < 10 oC
      • (myocardial temp probe)
    • Ice slush in chest
  • Blood vs Crystalloid
    • Some solutions are all crystalloid and some include a ratio of pt’s blood
  • K+ most common arresting agent
    • 20-40 mmole/L K
    • Prevents repolarization of heart
      • You do need to be aware of high potassium during and after CPB but the goal is for the perfusionist to correct this prior to coming off of CPB
    • Cardioplegia solutions can also include: lidocaine, mannitol, magnesium, bicarb, glucose, calcium, sodium. A common one is called “Del Nido”
  • Standard dosing:
    • Arresting dose: 1000 ml
    • Subsequent doses: 500 ml
      • Frequency: Dependent on soln
        • q 20 min-q 2hrs

28

What happens after cross clamp removal?

  • Trendelenburg + Ventilate/Valsalva
    • Perfusionist will fill heart or fill heart by turning off LV vent
    • De-air the heart (compress heart and force de-airing and avoid air to cerebral vasculature)
      • Clamp removed → stop ventilation again and come out Trendelenburg.
  • MgSO4: ~ 50 mg/kg (into circuit)
    • Transmembrane electrolyte control (Na, Ca, K)
      • Reduces risk of arrythmia, lidocaine can also be given at this time
  • Mannitol: ~12.5 g
    • Scavenge O2 free radicals
  • Occasionally the heart may fibrillate when the cross clamp is removed so the surgeon may use paddles to defibrillate

29

What are vents?

  • Decompress the heart
    • Prevent distention (help avoid excess blood collection → typically LV)
  • LV Vent
    • Venous cannula can remove blood returning to RA, but Still bronchial venous return that will enter heart via pulm veins (LA) ~ 1-3% CO → obstruct view
      • LV vent into right superior pulm vein (goes across MV and into LV) where can collect blood and air
  • Aortic Root Vent:
    • De-air heart post CX removal
      • usually part of the cardioplegia catheter and is placed in the ascending aorta above the aortic valve before the cerebral vasculature and the goal is that it will collect any air ejected from the left ventricle and the air will go to the vent which is connected to suction instead of any cerebral vessels

30

What is the hemoconcentrator/ultrafiltrator in the bypass circuit?

What are some benefits to its use?

Another additional component is the hemoconcentrator, it is not exactly like dialysis because there’s no dialysate solution used but the goals are similar

  • Ultrafiltration
    • Utilizes Pressure differential:
      • Blood side
      • Atmospheric pressure (ultrafiltrate side)
    • Remove plasma water and LMW solutes via semi-perm membrane
      • Retain larger plasma proteins (coag proteins, plts, albumin)
        • *hemoconcentrators pull off % of drugs admin (ex: heparin, bicarb, Mg, Ca)
        • Consequences: possibly make pt acidotic or reduce anti-coag during bypass
    • Increase HCT
  • Benefits:
    1. Reduce non-RBCV → Avoid donor RBC
      • Decrease hypervolemia
      • Increase Hct
        • *pt w/ low starting Hct but anticipate may have extra volume on board (MV pts) → avoid priming w/ blood and instead hemo[] that pt to increase Hct to acceptable level
    2. Correct electrolytes (esp K after cardioplegia soln)
    3. Remove inflammatory mediators
      • Help avoid pulm edema after CPB
    4. Help support kidneys (esp w/ inadequate UO)