Cardiac Anesthesia Resident Rotation
Guide to Managing Cardiopulmonary Bypass – “The Pump”
Lots of things happening. This is only a cursory overview
Different mnemonics available, or use a systems-based approach, or scan left to right
Immediately prior to CPB
- Anticoagulation: Heparin dosed to achieve ACT >450sec and heparin concentration >3u/mL + antifibrinolytics (ie, Amicar) administered
- Cannulae and emboli: ensure appropriate position. Check there are no bubbles in the arterial cannula
- Support hemodynamics (vasopressor) if autologous priming of CPB pump is requested
Checklist immediately after going on CPB
- Observe arterial inflow cannula color (bright red = oxygenated)
- Confirm adequacy of CPB flow. Confirm adequacy of “perfusion pressure” (ie, MAP)
- Stop mechanical ventilation (ventilator and volatile off)
- Adjust monitor alarms and tone modulation of pulse oximetry
- Observe head and face, CVP and cerebral oximetry for evidence of inadequate SVC drainage
- Administer additional anesthesia and analgesia per preference (midazolam, rocuronium, fentanyl commonly redosed)
- Check urine output – communicate total to perfusionist. Update them every q30-60mins
- Adjust infusions: vasoactive infusions usually paused unless patient is unstable. Notable exception is NTG used continuously during CABG
- Chart commencement of CPB. Other time points to be documented may include aortic cross clamp on/off, circulatory arrest, defibrillation
Checklist during CPB
- If any concern for malperfusion (cerebral oximetry, urine output, acid-base balance and SvO2) immediately alert attending and perfusionist
- Follow serial ABGs (perfusionist will send q30-60min)
- Monitor CPB cardiac index (flow via pump circuit). This should be >2.2-2.4L/min/m2. If perfusionist voices concerns about flow, may need vasodilation or other maneuvers that we will assist with. Immediately discuss with your attending
- Nadir allowable hematocrit varies based on procedure, risk of bleeding, comorbidities. Usually maintained >20-21%
- Plan for post-CPB coagulation needs while still on CPB. Talk with your attending. Some patients require no additional products. Some require a lot or special factor concentrates from pharmacy. May be useful to send a TEG (thromboelastogram) while on CPB
- Plan for post-CPB hemodynamic support. Talk with your attending. May require no hemodynamic support, or may require multiple inotropes/vasoactives and mechanical support
- Nitroglycerin may be used during rewarming phase – check with your attending
Weaning from CPB
WRMVP (Wide Receiver Most Valuable Player)
Useful mnemonic from Dr Wallace (cardiacengineering.com).
Brodt modification below.
- Warm: What is the bladder/core and blood temp? Usually acceptable if >36-36.5C (risk of afterdrop and postoperative hypothermia if inadequately rewarmed)
- Rhythm: Will the patient be hemodynamically stable post-bypass in this rhythm? What is the native rhythm? Is epicardial pacing required? Any intrinsic AV conduction?
- Monitors: Turn pulse oximetry tone and appropriate alarms back on. Ensure alarm limits reactivated and pulse oximetry tone is audible
- Ventilation/Volatile: Ensure adequate minute ventilation + anesthesia (mild respiratory alkalosis preferred). Set appropriate minute ventilation and oxygen delivery is set. While you’re adjusted the ventilator, ensure volatile agent is also back on
- Perfusion/Potassium: Confirm appropriate vasoactive support infusing and
electrolytes within acceptable range. Patient should not be acidotic. Potassium should be >4mEq/L, usually closer to 5, rarely as high as 6mEq/L. Ensure remainder of acid-base and metabolic panel is acceptable
Post-CPB period
There are many critical aspects during this time. Summarized below
- If uptitration of inotropic/vasoactive support is necessary (or you have to turn off vasodilators), alert attending and do not remove the TEE probe
- Heparin reversal: protamine is administered only after surgeon requests. “Test dose” of 10mg (1mL) should be given and announced clearly with verbal confirmation from perfusionist and surgeon that they know you gave it. Watch for systemic hypotension, anaphylaxis or acute pulmonary hypertension. Perfusionist will recommend the total protamine dose for full heparin reversal. After 1-2 circulation times, continue administration of protamine to 1/3 of the total reversal dose. Announce clearly that “1/3 of protamine is in”. Perfusionist will state “Last call” or “suckers are off” indicating that no further suction from the surgical field will go into the CPB circuit (to avoid clotting off circuit with protamine – occasionally patient instability necessitates crashing back onto bypass)
- Coagulopathy management: FFP/platelets/cryoprecipitate or factor concentrates may be administered. This is typically managed based on assessment of coagulation tests, underlying coagulopathy, empiric management of likely coagulopathy, and clinical assessment
- Hemodynamic management: titration of inotropic support may be required if either/both ventricles show impaired function, or if systemic BP is too high (risk of life threatening bleeding) or too low (risk of malperfusion/ischemia)
- Acid-base management: check ABGs q30-45mins. Remember NaHCO3 is a temporizing drug, it does not fix the cause of the acidosis
- Electrolyte management: Potassium should be >4mEq/L to minimize risk of arrhythmias. Note major trends in other electrolytes, discuss with attending PRN
- Beware potential for urgent recommencement of CPB if ventricular failure or massive bleeding ensues. Always have a backup vial of heparin available
- Hypotension on transfer from OR table to ICU bed is common. Have volume and vasoactives available. Do not move if unstable. Do not remove TEE probe until final exam completed
