31. Cardiopulmonary Bypass Pitfalls-Clinical Scenarios

Juan G. Penaranda, MD, and Harold M. Burkhart, MD

Concept

  • Establishing access for CPB
  • Initiating CPB
  • Maintaining CPB
  • Separating from CPB
  • Pitfalls that arise in each of the above steps

Chief complaint

“A 77-year-old diabetic man is undergoing a CABG AVR. Describe any preoperative workup relevant to CPB.”

Differential

Non applicable

History and physical

Any patient requiring CPB needs to have a comprehensive systems-based history and physical to identify history of stroke, renal disease, coronary lesions, intestinal angina, respiratory problems, bleeding disorders, or peripheral vascular disease.

Tests

  • Comprehensive labs (CBC, BMP, Coags, LFTs)
  • Head CT if recent stroke
  • Carotid duplex if stroke or bruits
  • Mesenteric duplex if evidence of intestinal ischemia
  • ABIs for evidence of peripheral vascular disease
  • Coronary angio to identify critical lesions
  • PFTs for history of respiratory problems
  • Chest CT scan for any patient with calcification on CXR

These tests allow risk stratification, identification of lesions that require preoperative intervention and identification of lesions that modify the lowest acceptable MAP on CPB.

Index scenario (additional information)

“The patient has a creatinine of 1.7, and a carotid duplex showing a 60% asymptomatic left carotid lesion. Chest CT shows a normal appearing aorta without calcification.”

This patient will require CPB in order to perform the combined CABG AVR. His MAP should be kept at the upper range of normal to ensure adequate renal and brain perfusion. A useful rule of thumb is MAPs = decade of age (i.e., 77 = 70-80 mmHg). Mild hypothermia (32-34° C) can be considered to decrease the tissue oxygen demand.

Operative steps

Cannulation

  • Median sternotomy.
  • Palpate the aorta for calcification.
  • Ensure you are high enough to complete all your proximal procedures.
  • Give Heparin (400 Units/kg).
  • Place purstrings.
  • Check your systemic pressure (ideally < 70 mmHg).
  • Cannulate the aorta with a 21-24 F arterial cannula and secure the cannula.
  • Check your line (assess the swing and line pressure with a test transfusion). Visualize the proximal aorta with the test transfusion.
  • Cannulate the RA with a dual stage cannula that drains both the RA and IVC.
  • Alternative venous cannulas include right angled IVC/SVC cannulas, 3 stage SVC cannula, or long femoral vein cannulation.
  • ABC’s – A: anticoagulate B: be sure you are high enough C: calcification.

Initiation

  • Check your ACT and make sure you are > 480.
  • Go on CPB – forward flow is initiated to ensure there is no obstruction.
  • Empty out – drain the heart once forward flow is confirmed.
  • Hold ventilation.
  • Flush cardioplegia, specify your desired temperature, and complete any required dissection prior to cross clamp and arrest.
  • Specify your temperature.
  • ABC’s – A: ACT B: breathing – hold ventilation C: circulation (forward flow and drainage, PAPs, CVP should be low).

Maintenance

  • Check for asystole (clamp, antegrade/retrograde).
  • Aortic vent on.
  • Check for optimal MAPs (usually 50-80 mmHg) – higher age or greater atherosclerotic burden may require higher MAPs.
  • Flow is usually 2.1-2.5 L/min.
  • Assess perfusion via lactate, venous saturation, urine output.
  • Cooling to mild hypothermia (32-34°C) may allow a decrease of flow and MAPs when needed.
  • Check drainage – heart should be empty, CVP and PAP should be low.
  • Check sats, ABG, oxygenation, visual inspection of arterial blood – should be bright red).
  • ABC’s – A: asystole B: breathing (oxygenation) C: circulation (forward flow, drainage).

Releasing the cross clamp

  • Deair the left atrium and root.
  • Administer hot shot cardioplegia (institution specific).
  • Drop your flows, vent on, head down, release the clamp, resume your flows.

Weaning from CPB

In general, you need to be warm, have rhythm and be ventilating in order to come off.

A more detailed but useful mnemonic follows:

A – Anastomosis

B- Beat of the heart (fibrillation, pacing wires), Breathing – ventilation

C- Circulation (fill up the heart and eject), assess Contractiliy

D- Degrees (36° C)

E- Echo (function, valves, air), Electrolytes

F- Flows (gradually reduce while observing function and hemodynamics)

G- Gases (ABG)

H- Hypertension (vasodilate)

I – Inotropes

J- Juices (urine output throughout the case)

Potential questions/alternative scenarios

“5 minutes after the cross clamp is released the heart begins to over distend. You notice a lack of spontaneous contraction. What do you do?”

There are 2 considerations – one is that the valve has a leak of some degree and the second is that the heart is not ejecting to overcome any regurgitant volume. Usually the first maneuver will be to squeeze the heart to get it to decompress from the apex up towards the LVOT. Check your PAP which will give you a clue as to how effectively you are decompressing. Try to pace or tap the heart to encourage ejection but ultimately the solution may be to cross clamp.

“You attempt to pace but have no capture despite well placed leads. Anesthesia tells you there is 1+ central AI. Perfusion tells you that the potassium has been 7 meq/L and they have struggled to bring it down. The patient has not made urine during the case. You cross clamp the aorta, turn up the root vent and empty out the heart. After 10 minutes the potassium starts to decrease and the heart contracts.”

Now you know the etiology. There is some leak, but it is hard to truly estimate it without contractility. Knowing the electrolytes is an important component of the weaning process as is the production of urine output. If the potassium does not decrease options include hemoconcentration, IV insulin and glucose, lasix, or bicarb. Usually the perfusionist can get the potassium down but it may take some time. Another option would be to vent the heart while you wait for the K to resolve. While you wait it would not be unreasonable to open the aortotomy and explore the aortic valve for any major defects especially if you were told that the AI was moderate-severe. But in the absence of something obvious and only 1+ AI, wait until you are ejecting to analyze the valve and decide on replacing or not. Once you are ready, release the cross clamp, pace prn, ventilate, fill up the heart, eject, wean your flows and check the echo carefully.          

“A 60-year-old male patient has just undergone a mitral valve repair. You release the cross clamp. The heart begins to fibrillate. The echo does not demonstrate anything more than a trace to 1+ central aortic jet. You try to defibrillate but are unable to cardiovert. Describe your approach to defibrillating the patient.”

Internal paddles are set at 10 – 20 Joules and gradually increased. If you cannot cardiovert give IV lidocaine and or amiodarone (150 mg IV) and try again. There are several issues that can make it hard to cardiovert: distention, air, low systemic pressures, electrolyte abnormality, poor oxygenation, and hypothermia. In addition, consider coronary ischemia or valvular incompetence. If the heart appears distended and or the PAPs are elevated, the initial step is to manually squeeze the heart while emptying out with CPB. If the heart continues to over distend then place a PA vent or LV vent. After placing the vent and decompressing the heart you should be able to cardiovert to sinus rhythm. Make sure the root vent is on to evacuate any air. Increase your perfusion pressures to > 75 mmHg both for improved coronary perfusion and to flush out any air that may have embolized. Give lidocaine and or amiodarone. Optimize your oxygenation, electrolytes and temperature. Check the echo to ensure that you do not have AI. Anything greater than 1+ warrants consideration for replacement (see previous scenario). On the differential, is damage to the non-coronary leaflet with placement of the mitral stitches. If this appears to be the problem by echo, arrest the heart and explore the aortic valve. If there is evidence of coronary ischemia as evidenced by ST changes or new regional wall motion abnormalities, then bypass with a vein graft. If you cannot defibrillate even after venting and reversing all the above then clamp, arrest and try again.


“Describe the components of the CPB machine.”

Blood drains into the venous reservoir by gravity or vacuum assist. It is then pushed by centripetal or centrifugal pumps into the oxygenator/heat exchanger. It then continues to the arterial air filter and back to the patient.

“You are starting a mitral valve repair and ask the anesthesiologist to give the heparin. After the cannulas are in you ask your perfusionist if the ACT is adequate for bypass. He is having trouble and tells you a standard dose of heparin has been given and the ACT is only 200 seconds and is not going up. How do you deal with this issue?”

Antithrombin III deficiency is the most common reason for an inadequate ACT despite appropriate heparin dosing. An additional dose of heparin solves the problem in most cases. If the ACT does not respond appropriately to a second dose of heparin, one should consider administering either fresh frozen plasma or recombinant antithrombin III.

“You end up giving a dose of AT III and the ACT is now adequate for bypass. Soon after going on CPB, the perfusionist alerts you of a high aortic line pressure. What is your checklist for this situation?”

  • Obstruction on the arterial circuit (kink in or clamp on line)
  • Malposition of the aortic cannula
  • Cannula too small for full CPB
  • Evidence of aortic dissection: systemic pressure will be low, and the ascending aorta will be abnormal

“You checked the systemic pressure and it is normal. You inspect the ascending aorta and it looks normal without evidence of swelling or discoloration. You trace out the arterial line and there are no kinks in the circuit. Upon inspection of the cannulation site you notice there is an excessive angulation of the cannula suggesting that the tip is against the lateral aspect of the innominate artery. You reposition the cannula and the line pressure comes down. Your perfusionist now tells you there is poor venous return and a drop in venous reservoir volume after snaring the caval tapes. The right atrium is not distended, and the PAP is low. The CVP is elevated Your perfusionist lowers the CPB flow to protect the level of venous reservoir. What are some of the maneuvers to manage inadequate venous drainage?”

  • Check for air locks
  • Ensure good position of the venous cannula
  • Elevate the level of the patient in relation to the reservoir if relying on gravity
  • Use suction drainage
  • Increase cannula size
  • Reduce flows if still within ideal MAP range (may need to cool 32-34° C)
  • Exclude other sources of blood flow into the heart especially in the setting of distention (aortic regurge – vent, azygous vein – adjust snares, left sided SVC – snare or cannulate)
  • Consider other sites of volume loss (i.e., retroperitoneal or peritoneal hemorrhage) – check abdominal girth, H/H

“In this case the IVC right angle cannula has rotated before snaring the caval tapes and is now pointing towards the right atrium occluding the IVC drainage. You release the snare and reposition the cannula solving the problem. You also noticed that the SVC cannula was inserted into the azygos and reposition accordingly. After re-instituting CPB, your perfusionist cannot get the mean blood pressure above 40 mmHg. The anesthesiologist tells you the patient was on a high dose of ACE inhibitor preoperatively. What do you do next?”

Vasoplegia can be seen in patients on numerous antihypertensive medications, in particular ACE Inhibitors. In this situation, phenylephrine, norepinephrine, vasopressin or even methylene blue are options that can be used to increase the systemic pressure. This scenario may arise in the postoperative period as well.

“You placed a coronary sinus catheter for retrograde cardioplegia because the patient has moderate aortic regurgitation. As you start your retrograde infusion, the pressure within the coronary sinus seems to be very low. You inspect the inferior aspect of the heart to make sure there has been no rupture of the coronary sinus or malposition of the catheter. You take out the catheter and the balloon is intact. You place the catheter in again and confirm its position by palpation. Despite this, the pressure remains low and the heart is not arresting. What are the causes of this problem?”

Inadequate retrograde cardioplegia delivery may be due to:

  • Catheter displacement into the right atrium
  • Rupture of coronary sinus
  • Balloon rupture
  • Persistent left sided superior vena cava (LSVC)

“You lift the heart to the right and discover a LSVC. You place a snare to occlude it since there is a large innominate vein and you are now able to arrest the heart.”

If there is not a persistent innominate vein you can cannulate the LSVC separately.

“You finished your mitral valve repair and wean the patient off bypass. After a few seconds, the blood pressure drops, there is ST elevation on the EKG and the right ventricle distends. You suspect air has entered the right coronary artery. What are some of the maneuvers you use to overcome this problem?”

The right coronary ostium is anterior and susceptible to air embolism. It can be seen after valvular or other cardiac surgery and usually causes transient right ventricular dysfunction and distention. In this case, re-instituting CPB with a high perfusion pressure will help to support cardiac function and push the air through the coronary artery into the venous circulation. De-airing the heart through an aortic root vent will prevent further air migration into the coronary arteries. Consider evacuating air through the apex with a large bore needle if there is a large collection of air at the apex.

“The patient is now off bypass and you and the cardiologist are assessing the mitral valve repair with transesophageal echo (TEE). Your assistant points out to you that the aorta suddenly developed a bluish discoloration. Upon inspection, you notice there is an expanding hematoma in the ascending aorta. On TEE there is a dissection flap in the ascending aorta and the aortic valve is competent. What do you do now?”

The patient has developed an iatrogenic Type A dissection. Establish arterial access within the true lumen (axillary), cool, circ arrest, replace the ascending, resume flow(refer to chapter on iatrogenic aortic dissections).

“You are doing a mitral valve repair in a 42-year-old woman with asymptomatic severe mitral regurgitation. You performed aortic and bi-caval cannulation, instituted CPB and cooled to 32° C. After placing the aortic cross clamp and arresting the heart, the perfusionist alerts you of poor venous drainage. You notice a large amount of air in the aortic cannula. You are certain air has entered the aorta and suspect it has embolized to the brain. The level of the venous reservoir has gone down too low and air has been pumped into the arterial line. What do you do at this point?”

Even though massive air embolism after initiation of cardiopulmonary bypass is a rare complication (incidence less than 0.2% of cases), it has a high mortality and high incidence of neurologic injury. It most commonly happens if the blood level in the venous reservoir and oxygenator gets too low allowing air to be introduced into the arterial circuit. Rapid implementation of an algorithm may save the life of the patient or prevent significant neurologic damage.

A useful algorithm in this situation includes:

  • Perfusionist:
    • Discontinue CPB
    • Clamp arterial and venous lines
    • De-air bypass circuit
    • Add necessary volume to the reservoir
  • Anesthesiologist:
    • Steep trendelenburg
    • 100% oxygen
    • Steroids/Barbiturates/Mannitol
    • Support circulation with vasopressors
  • Surgeon:
    • Aspirate air from aortic root
    • Retrograde cerebral perfusion
  • Reinstitute CBP and cool the patient down for cerebral protection
  • Massage coronary arteries to displace air
  • Complete surgical procedure and de-air heart in usual fashion
  • Consider hyperbaric chamber postoperatively
  • ICU:
    • Consider deep sedation for cerebral protection
    • Consider hyperbaric chamber

“You ask your perfusionist to stop the pump and clamp both the aortic and venous lines. You place the patient in trendelenburg and aspirate the air from the ascending aorta. Next you disconnect the arterial line from the cannula, de-air the line and connect it to the SVC cannula to start retrograde cerebral perfusion. 300 mL/min of flow directed up to the vena cava is started and after two minutes of perfusion you start seeing bubbles at the ascending aorta which are removed by an aortic root vent you have placed. You then reinstitute CPB and cool the patient down to 28° C for cerebral protection. You complete your aortic valve replacement quickly. The patient is weaned off bypass after 50 minutes and transferred to the ICU. The anesthesiologist gives steroids and barbiturates to the patient and keeps him in deep anesthesia for two days. A CT scan is performed and is negative for any intracerebral injury. The patient is discharged neurologically intact after 10 days in the hospital.”

Pearls/pitfalls

  • Patients undergoing CPB require a comprehensive workup to minimize the risk of end organ injury.
  • Phases of CPB are Induction > Maintanence > Seperation: be familiar with critical elements of each of these phases.
  • Target MAP is roughly equivalent to the patient’s age (i.e., 63 yo = 60 mmHg, 83 yo = 80 mmHg).
  • Air embolism, dissection, and venous perforations are major adverse events that can occur during CPB. Be prepared to anticipate, prevent and deal with these complications if they occur.
  • Poor drainage can result from air locks, inappropriately positioned cannulas, persistent LSVC. An empty heart and poor drainage suggests loss of blood volume (i.e., retroperitoneal or peritoneal hematoma).

Suggested readings

  • Bojar RM. Cardiopulmonary Bypass. Chapter 5. Manual of Peri-operative care in adult cardiac surgery, 4th Edition 2005.
  • Millls NL, Ochsner JL. Massive air embolism during cardiopulmonary bypass: causes, prevention and management. J Thorac Cardiovasc Surg 80:708-717, 1980.
  • Svensson LG and Crawford ES. Cardiovascular and Vascular Diseases of the Aorta. WB Saunders Company 1997.
  • Brodie JE, Johnson RB. The Manual of Clinical Perfusion, 2nd Edition 1997.

Kincaid EH, Hammon JW. Cardiopulmonary bypass. John Hopkins Manual of Cardiothoracic Surgery. 2007.

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