CPB weaning, preparation for anesthesia, surgery and cardiopulmonary bypass

01

Preparation by the anesthesiologist

Checklists ensure that critical work has been done before attempting to go offline, that correctable exceptions have been addressed, and that important information
is communicated to each other among team members.
For example, the following list is called "WAAARRRRRMM" for memorization purposes:

●Warm – In general, rewarming should be done slowly prior to weaning, with a target nasopharyngeal temperature of 37.
0°C (but not higher than 37.
0°C) and a bladder (core) temperature of around
35.
5°C.
The target temperature of the nasopharynx should not be exceeded as this may lead to brain damage
.

●Anesthesia – Develop an anesthesia plan
after weaning.
Volatile anesthetics are usually given through an evaporator attached to the CPB loop, or anesthesia
is maintained during CPB by relying entirely on intravenous anesthesia.
Subsequently, during the CPB weaning, the volatile anesthetic is re-administered through an anesthesia machine or TIVA technology
is continued.
Additional monitoring, such as bispectral index (BIS) monitoring, during and after weaning, may help guide dose adjustment
of inhalation and/or intravenous anesthetics.

●Adjuvant drugs – Prepare medications that may be required during CPB weaning in advance so that they are readily available, such as antiarrhythmics, inotropes, and vasoactive drugs for infusion, to avoid distractions
during weaning.
Protamine, with the exception, should only be formulated before administration to avoid accidental use and premature neutralization of the action of
heparin.

●Air – Air in the heart chambers is cleared by the surgeon and assessed for adequacy
by transesophageal echocardiography (TEE) monitoring and close communication with the anesthesiologist.

Intraoperative air may accumulate at the aortic root, left ventricle, and left atrium, especially if the left chamber is opened, and systemic embolism
may occur after removal of the aortic transection forceps.
If the lung is inflated again and mechanical ventilation resumes, pulmonary venous blood is transferred to the left atrium, along with air bubbles trapped in the pulmonary vein
.
Coronary embolism may lead to myocardial ischemia, arrhythmias, and ventricular insufficiency, while cerebral circulatory embolism may lead to neurologic dysfunction
.

The goal of air exclusion is to minimize cerebral and systemic air embolism
.
The anesthesiologist usually places the patient in a supine position with their head down and feet high during the removal of air, as this reduces the amount of
gas entering the cerebral circulation.

●Rhythm – Rhythm should be restored prior to weaning
.
Normal sinus rhythm is best restored, or temporary epicardial pacing
may be used if this is not possible or to treat bradycardia.
If AV conduction is normal, atrial pacing (A)
is used.
Otherwise, atrioventricular sequential pacing (AV) is preferred over ventricular pacing (V) to maintain optimal atrioventricular synchronicity and ventricular preload
.

●Rate – To maximize cardiac output without reducing diastolic coronary perfusion time, a heart rate of 80 to 90 beats per minute is optimal.

●Resistance – Vasodilation with hypotension in patients with normal or elevated cardiac output (pump velocity) indicates low systemic vascular resistance (SVR) requiring vasopressors
.
The use of vasopressors during CPB suggests that they may also be needed during weaning
.

●Respiration – Adequate ventilation and oxygenation of one's own lungs by restarting positive pressure mechanical lung ventilation
.
Respiratory problems that may manifest after resumption, such as bronchospasm or high airway
pressure, should be addressed before weaning.

●Metabolism/laboratory markers – Corrects hemoglobin to appropriate levels, typically 7 to 8 g/dL
>.
The decision to transfuse depends on the volume of the blood reservoir and the amount of
red blood cells.
Through central laboratory testing or point-of-care testing, electrolytes (potassium, calcium, etc.
) or acid-base balance abnormalities are checked and corrected in
time.
The concentration of ionized calcium should be between 1.
09-1.
3mmol/L and the serum potassium concentration should be between 4-5.
5mmol/L to maintain normal
myocardial function.

Monitoring – Ensure that all monitoring equipment is operating normally
.
The volume of the pulse oximeter should be adjusted so that it can be heard
.
Calibrate the pressure sensor to ensure the accuracy of the
"zero point" and reference values.
Additional monitoring equipment, such as femoral artery catheter, may be required; If so, you should be prepared before going offline to reduce distraction
during the actual offline process.

02

Preparation of the surgeon

The surgeon's responsibilities in preparation for weaning include:

●Removal of cardiac catheters that are no longer needed (eg, coronary sinus catheters for retrograde cardiac arrest fluid, left ventricular drains) and repair the catheter puncture opening
.

●Exclude residual gas
in the left heart chamber.
The surgeon "vents" primarily by anterograde perfusion catheter (called "
aortic root venting") with cardiac arrest fluid within the ascending aorta or other drainage catheter in the left heart.
In addition, surgeons usually "massage" the heart, forcing air out of the left heart chamber
.
The anesthesiologist assists in the process of
air removal through TEE monitoring.

●Place epicardial pacing leads directly in the right atrium and right ventricular myocardium for atrial pacing, ventricular pacing, or atrioventricular sequential pacing
as needed.

●Finally, the surgical repair is examined under direct vision and attention is paid to hemostasis
.

03

Preparation by a cardiopulmonary bypass doctor

The cardiopulmonary bypass doctor's work must be done
before the first attempt to wean.
These include:

●Ensure adequate reheating while avoiding overheating
.

●Treatment of anemia (ie, hemoglobin level < 7 to 8 g/dL): If the volume of the venous blood storage device is large, hemoconcentration therapy can be done by adding recovered autologous blood to the venous blood storage device or, if necessary, allogeneic blood
.

●Stop unnecessary surgical blood aspiration and negative pressure-assisted venous drainage
.

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