This document discusses preparation for weaning a patient from cardiopulmonary bypass (CPB) during cardiac surgery. It emphasizes the importance of general preparations like ensuring rewarming, optimizing blood chemistry, and removing air from the heart. Preparing the lungs and heart is also important. This involves reinflating the lungs, optimizing the heart's rhythm, rate, contractility, afterload and preload. Electrical pacing may be needed to establish an effective cardiac rhythm before terminating CPB. Inotropic support can be provided if low contractility is detected. The goal is to have the heart in the best condition possible before ending CPB support.

1. Preparation for weaningPreparation for weaning
from CPBfrom CPB
Abeer elnakeraAbeer elnakera
Anesthesia lecturerAnesthesia lecturer
20132013

2. objectivesobjectives
• To emphasize the importance
for preparation to wean from
CPB which include
–General preparations
–Preparing the lungs
–Preparing the heart
–Final preparations

3. General preparationsGeneral preparations
1. Ensure rewarming
2. Restoration of MAP at
normothermic levels
3. Ensure adequate anesthesia and
muscle relaxation
4. Blood chemistry optimization
5. Determine factors that may make
termination of CPB difficult
6. Removal of intracardiac air

4. 1-Ensure rewarming1-Ensure rewarming
• By increasing perfusate temperature with
heat exchanger
• Equilibration of the bladder or rectal
temperature and the nasopharyngeal
temperature at 36–37◦C is desired.
• Excessive heating is dangers as it
cause:
1. Plasma protein denaturation
2. Cerebral hyperthermia
3. Expand gas bubbles

5. Ensure rewarmingEnsure rewarming
• The rate of rewarming is important, as increased
cerebral oxygen extraction has been noted in
adults which is associated with subsequent
cognitive defects
• Better cognitive outcome is achieved following
coronary artery bypass surgery in adults
when slow rewarming (2◦C difference between
nasopharyngeal and CPB perfusate temperature) is
compared to more standard rewarming
(4–6◦C difference between nasopharyngeal and CPB
perfusate temperature)

6. Ensure rewarmingEnsure rewarming
• Despite homogeneous core rewarming, it is not
uncommon for the patient’s core temperature to
drop 2–3◦C in the hour after termination of CPB.
( temperature after drop ) This is due to
reperfusion of the cold extremities, which results
in a re-equilibration of the patient’s temperature
at a lower core temperature.
• This temperature afterdrop may result in arterial
vasoconstriction and shivering, which will
increase myocardial oxygen consumption.

7. Ensure rewarmingEnsure rewarming
• Vasodilatation is physiological process due to
rewarming necessating increasing the pump flow that
improves the rewarming quality
• Infusing sodium nitroprusside or providing vasodilatation
with an inhalational anesthetic while maintaining MAP
greater than or equal to 50–70mmHg by increasing
pump flow has been advocated as a method of
decreasing afterdrop. This method allows the poorly
perfused cold extremities to be perfused with warmed
blood before termination of CPB. Therefore, the caloric
load of peripheral rewarming is in large part assumed by
the heat exchanger and not the patient

8. Ensure rewarmingEnsure rewarming
• measures to keep the patient warm such
as fluid warmers, a circuit heater-
humidifier, and forced-air warmers should
be set up and turned on before weaning
from CPB. The temperature of the
operating room may need to be increased
as well; this is probably an effective
measure to keep a patient warm after
CPB, but it may make the scrubbed and
gowned personnel uncomfortable.

9. 22--Restoration of MAP atRestoration of MAP at
normothermic levelsnormothermic levels
– It is advisable to gradually increase MAP to 60-80
mmHg to avoid myocardial ischemia and systemic
hypo perfusion
– it is best to accomplish this by maintaining a
calculated SVR in the range of 1000–1500 dynes
s/cm5 and adjusting pump flows accordingly. SVR
can be varied with the use of either phenylephrine or
nitroprusside as needed.( how to calculate?)
– There is a discrepancy between radial and central
aortic measurement of MAP WITH THE END OF
CPB ( how to deal )

10. 33--Ensure adequate anesthesiaEnsure adequate anesthesia
and muscle relaxationand muscle relaxation
• Adequate anesthesia : during rewarming
For the potential of pt. awareness
This can be dealt with by:
1.Preoperative discussion of the possibility of
awareness with the pt.
2.Use of volatile agents or midazolam for their
amnestic properties
3.Postoperative communication of the pt. and
psychological support

11. Ensure adequate anesthesia andEnsure adequate anesthesia and
muscle relaxationmuscle relaxation
• Adequate ms. Relaxation:
To avoid catastrophic disconnections
• BIS index is beneficial
• Sweating after emergence from CPB is
indication of awareness

12. 44--Blood chemistryBlood chemistry
optimizationoptimization
• Arterial blood gas analysis should be
obtained before weaning from CPB and
any abnormalities corrected.
• Severe metabolic acidosis depresses
the myocardium and should be treated
with sodium bicarbonate
• Optimization of oxygenation and
maintenance of normocapnia are needed

13. Blood chemistry optimizationBlood chemistry optimization
• A serum potassium level of
approximately
5 m Eq/L decreases the defibrillation threshold
compared with levels approximately 0.5 mEq/L
lower.
• If defibrillation is unsuccessful in the
presence of a low serum potassium,
potassium administration should be
considered.

14. Blood chemistry optimizationBlood chemistry optimization
• A serum potassium level 6 mEq/L˃ will
increase the incidence of dysrhythmias
and conduction abnormalities
• Keep in mind the reversible
extracellular shift of potassium
occuring with rewarming and reversed
after rewarming end

15. Blood chemistry optimizationBlood chemistry optimization
• Immediate treatment of elevated serum
potassium with electrocardiogram (ECG)
changes is indicated. IV calcium chloride 10
mg/kg or calcium gluconate 50 mg/kg, sodium
bicarbonate 0.5–1.0 mEq/kg, or 1 mL/kg of 50%
dextrose and 0.1 unit/kg of regular insulin all
work immediately to reduce serum potassium by
shifting it intracellularly.Where severe
hyperkalemia exists, diuretic therapy will be
necessary

16. Blood chemistry optimizationBlood chemistry optimization
• In patients with compromised renal function,
efforts must be made to avoid hyperkalemia resulting
from use of potassium cardioplegia. It is possible to
scavenge the cardioplegic solution from the coronary
sinus so that it does not end up in the pump and
elevate the serum potassium. In addition, it also is
possible to use cold crystalloid cardioplegia without
potassium in these patients. ultrafiltration may also be
used to reduce serum potassium prior to termination
of CPB in these patients.

17. Blood chemistry optimizationBlood chemistry optimization
• Hypomagnesemia occurs in up to 70% of
patients after CPB and may predispose
ventricular and supraventricular
tachyarrhythmias. As a result, some
centers supplement magnesium
(2.0–4.0 g or 100 mg/kg in children) before
or immediately after termination of CPB.

18. Blood chemistry optimizationBlood chemistry optimization
• The ionized calcium level should be measured,
and significant deficiencies corrected before
discontinuing CPB. ( after reasonable period of
reperfusion to the myocardium )
• calcium chloride 5–10 mg/kg or calcium
gluconate 25–50 mg/kg
• Many centers give all patients a bolus of calcium
chloride just before coming off CPB. However, it
has been argued that this practice is to be
avoided because calcium may aggravate
reperfusion injury.

19. Blood chemistry optimizationBlood chemistry optimization
• Hematocrit
Generally, a hematocrit greater than 25% is sought
as CPB terminates. This can be achieved by
– Reduction of the prime volume may be needed for some
patients,
– diuresis during CPB may result in hemoconcentration
– , the use of an ultrafiltration device during CPB .
– Transfusion of red blood cells may be necessary if these
methods fail or are not appropriate due to low venous
reservoir levels on CPB.
• Low hematocrit levels (<22%) as CPB terminates at
37◦C may result in low SVR and myocardial ischemia

20. 66--Removal of intracardiac airRemoval of intracardiac air
• To avoid cerebral and coronary emboli
With aortic clamp still applied :
1. Allow the heart to refill
2. Lt atrium and ventricle are ballotted to dislodge
air bubbles through vent
3. Ventilation then valsalva maneuver to squeeze
pulm. Veins
4. Head down position and carotid compression
(controversial)
TEE IS HIGHLY BENEFICIAL MONITORING

21. Removal of intracardiac airRemoval of intracardiac air
The first manifestation of small amounts of
ejected air may be ST segments elevations in
the territory of the anterior right coronary
artery (leads II, III, aVF).
In the cases of anteriorly placed coronary
artery bypass grafts the distribution will tend
to be more global.

22. General preparationsGeneral preparations
1. Ensure rewarming
2. Restoration of MAP at
normothermic levels
3. Ensure adequate anesthesia and
muscle relaxation
4. Blood chemistry optimization
5. Determine factors that may make
termination of CPB difficult
6. Removal of intracardiac air

23. Preparation of the lungPreparation of the lung
• Suction trachea and endo tracheal tube even
with lavage if needed
• Relief abdominal distension if present
• The lungs are reinflated by hand gently and
gradually, with sighs using up to 30 cmH2O
pressure, and then mechanically ventilated with
100% oxygen. Care should be taken not to allow
the left lung to injure an in situ internal mammary
artery graft as the lung is reinflated.
• The compliance of the lungs can be judged by
their feel with hand ventilation,

24. Preparation of the lungPreparation of the lung
• both lungs should be inspected for
residual atelectasis, and they should be
rising and falling with each breath.
• The surgeon should inspect both pleural
spaces for pneumothorax, which should
be treated with chest tubes.
• Any fluid present in the pleural spaces
should be removed before attempting to
wean the patient from CPB.

25. NowNow
Aorta declampingAorta declamping
= end of ischemic time
= beginning of reperfusion time

26. Preparation of the heartPreparation of the heart
• optimizing the five hemodynamic
parameters that can be controlled:
1. rhythm,
2. rate,
3. contractility,
4. after load,
5. preload

27. 11--RhythmRhythm
• Our aim is to obtain
an organized, effective, and stable cardiac
rhythm
This can occur spontaneously after removal
of the aortic cross-clamp

28. RhythmRhythm
• the heart may resume electrical
activity with ventricularventricular
fibrillationfibrillation
VFVF

29. RhythmRhythm
• If the blood temperature is greater than
30°C defibrillate (10 -20J)
• If ventricular fibrillation persists or recurs
repeatedly ant arrhythmic drugs
such as lidocaine or amiodarone may be
administered
VFVF

30. RhythmRhythm
• Recurrent or persistent VF after several minutes
of aorta declamping should prompt concern
about impaired coronary blood flow.
• Coronary perfusion pressure and the duration of
reperfusion after aortic cross-clamp removal are
important.
• mean aortic blood pressure of at least 50
mmHg for greater than 5 minutes is likely to increase
the success of defibrillation.
• Never forget K, Mg, Hb, ABG and blood
sugar optimization
VFVF

31. RhythmRhythm
• Inability to defibrillate a heart of a patient in
whom conditions have been optimized suggests
ongoing myocardial ischemiaongoing myocardial ischemia from poor
revascularization or from coronary air or
particulate emboli.
• Increasing MAP on CPB will increase coronary
perfusion pressure to break up bubbles and
move them through to the venous side of the
circulation. . This in combination with
nitroglycerine administration
VFVF

32. RhythmRhythm
• Because it provides an atrial contribution
to ventricular filling and a normal,
synchronized contraction of the ventricles,
normal sinus rhythm is the ideal cardiac
rhythm for weaning from CPB.
Potentially per fusingPotentially per fusing
rhythmrhythm
Potentially per fusingPotentially per fusing
rhythmrhythm

33. RhythmRhythm
• Atrial flutter or fibrillationAtrial flutter or fibrillation, even if
present before CPB, can often be
converted to normal sinus rhythm with
synchronized cardio version, especially if
ant arrhythmic drugs are administered.
• It is often helpful to look directly at the
heart when there is any question about the
cardiac rhythm.
Potentially per fusingPotentially per fusing
rhythmrhythm

34. RhythmRhythm
• Ventricular arrhythmiasVentricular arrhythmias should be
treated by correcting underlying causes
and, if necessary, with ant arrhythmic
drugs such as amiodarone.
Potentially per fusingPotentially per fusing
rhythmrhythm

35. RhythmRhythm
• Wait for 10 minutes allowing adequate
perfusion (avoid distention or collapse)
• Atropine 3mg
• Calcium chloride iv if needed
• Adrenaline
• Electrical Pacing
asystole or
complete heart block

36. RhythmRhythm
• electrical pacingelectrical pacing with temporary epicardial pacing
wires may be needed to achieve an effective rhythm
before weaning from CPB.
– If atrioventricular conduction is present, atrial pacing( AOO)
should be attempted because, as with normal sinus rhythm, it
provides atrial augmentation to filling and synchronized
ventricular contraction.
– Atrioventricular sequential pacing (DOO) is used when there is
heart block.
– Ventricular pacing (VOO) remains the only option if no organized
atrial rhythm is present, but this sacrifices the atrial “kick” to
ventricular filling and the more efficient synchronized ventricular
contraction of the normal conduction system.
asystole or
complete heart block

37. RhythmRhythm
• Asynchronous (nonsensing) pacingAsynchronous (nonsensing) pacing is
used post-CPB to avoid electromagnetic
interference (EMI) from electrocautery
• The current output (mill amperes) of the
pacemaker is increased slowly until the
desired cardiac chamber is captured.
Each pacemaker spike must result inEach pacemaker spike must result in
appropriate atrial and/or ventricularappropriate atrial and/or ventricular
capture and contraction.capture and contraction.
asystole or
complete heart block

38. RhythmRhythm
Aorta declamped
VFPPR
asystole or
HB
Sinus rhythm

39. 22--RateRate
• In most situations for adult patients, HR
should be between 75 and 95 beats75 and 95 beats per
minute for weaning from CPB
• Lower ratesLower rates may theoretically be
desirable for hearts with residual ischemia
or incomplete revascularization
• Higher HRsHigher HRs may be needed for hearts
with limited stroke volume, such as after
ventricular aneurysmectomy.

40. RateRate
• Slow HRsSlow HRs are best treated with electrical
pacing, but β-agonist or vagolytic drugs
also may be used
• TachycardiaTachycardia: treatable causes such as
inadequate anesthesia, hypercarbia, and
ischemia should be identified and
corrected. The HR often decreases as the
heart is filled in the weaning process

41. RateRate
• Supraventricular tachycardiasSupraventricular tachycardias should
be electrically cardioverted if possible, but
drugs such as β-antagonists or calcium
channel antagonists may be needed to
control the ventricular ratecontrol the ventricular rate if they
persist, most typically occurring in patients
with chronic atrial fibrillation. If drug
therapy lowers the rate too much, pacing
may be used.

42. 33--ContractilityContractility
• Determine factors that may make termination
of CPB difficult:
– poor preoperative systolic function,
– a history of congestive heart failure,
– pre- or intra operative inotropic support,
– poor myocardial preservation,
– a long cross-clamp time,
– incomplete revascularization,
– advanced age,
– female gender

43. ContractilityContractility
• A heart with good contractilitygood contractility often has a
vigorous snap with contraction that can be seen
while on CPB, in contrast to the weak
contractions of a heart with impaired contractility,
but it may be difficult to assess global ventricular
function while the heart is empty and on CPB.
• If significant depression of contractilitysignificant depression of contractility is
likely, inotropic support can be started before
attempting to wean the patient from CPB.
•

44. ContractilityContractility
• If depressed myocardial contractilitydepressed myocardial contractility
becomes evident during weaningbecomes evident during weaning, the safest
approach is to prevent cardiac distention by
resuming CPB, resting the heart for 10 to 20
minutes while inotropic therapy with
• a catecholamine or phosphodiesterase inhibitor
drug is started.
• Extreme depression of contractile functionExtreme depression of contractile function
of the myocardiumof the myocardium may require mechanical
support with an intra-aortic balloon pump (IABP)
or ventricular assist device (VAD).

45. 44--After loadAfter load
• An important component of afterload in patients
is the systemic vascular resistance (SVR).systemic vascular resistance (SVR).
• While on CPB at full flow,, mean arterialmean arterial
pressure (MAP) is directly related to SVRpressure (MAP) is directly related to SVR and
indicates whether the SVR is appropriate, too
high, or too low.
• Low SVRLow SVR after CPB can cause inadequate
systemic arterial perfusion pressure, and
• high SVRhigh SVR can significantly impair cardiac
performance, especially in patients with poor
ventricular function.

46. After loadAfter load
• SVR is usually within a reasonableSVR is usually within a reasonable
range when the arterial pressure isrange when the arterial pressure is
betweenbetween 60 and 80 mmHg60 and 80 mmHg at full pump
flow. If below that range, infusion of a
vasopressor may be needed to increase
SVR before attempting to wean from CPB.
If the MAP is high while on CPB,
vasodilator therapy may be needed.

47. 55--PreloadPreload
• In the intact heart, the best measure of preloadthe best measure of preload
is end-diastolic volume.is end-diastolic volume.
• Less direct clinical measuresclinical measures of preload
include left atrial pressure (LAP), pulmonary
artery occlusion pressure (PAOP), and
pulmonary artery diastolic pressure.
• Transesophageal echocardiography (TEE)Transesophageal echocardiography (TEE) is
a useful tool for weaning from CPB because it
provides direct visualization of the end-diastolic
volume and contractility of the left ventricle.[

48. PreloadPreload
• The process of weaning a patient from CPBThe process of weaning a patient from CPB
involves increasing the preload (i.e., fillinginvolves increasing the preload (i.e., filling
the heart from its empty state on CPB) untilthe heart from its empty state on CPB) until
an appropriate end-diastolic volume isan appropriate end-diastolic volume is
achievedachieved. (vary with each patient)
• The filling pressures before CPB mayThe filling pressures before CPB may
indicate what they need to be after CPBindicate what they need to be after CPB;
• a heart with high filling pressures before CPB
may require high filling pressures after CPB to
achieve an adequate preload.

49. Final preparationsFinal preparations
• anesthesiologist preparations include:
– leveling the operating table,
– re-zeroing the pressure transducers,
– ensuring the proper function of all monitoring
devices, ( TEE.,PAOP, CVP)
– confirming that the patient is receiving only intended
drug infusions,
– ensuring the immediate availability of resuscitation
drugs and appropriate fluid volume, and
– verifying that the lungs are being ventilated with 100%
oxygen

50. Final preparationsFinal preparations
• Surgeon preparations include:
– Macroscopic collections of air in the heart should be
evacuated
– Major sites of bleeding should be controlled,
– cardiac vent suction should be off,
– all clamps on the heart and great vessels should be
removed,
– coronary artery bypass grafts should be checked for
kinks and bleeding,
– and tourniquets around the caval cannulas should be
loosened or removed before starting to wean a
patient from CPB

51. •? ? ? ? ? ?? ? ? ? ? ?

52. SummarySummary
• Preparation for weaning from CPB include
• General preparation: Ensure rewarming, Restoration of
MAP at normothermic levels,Ensure adequate anesthesia and
muscle relaxation,Blood chemistry optimization,Determine factors
that may make termination of CPB difficult,Removal of
intracardiac air
• Lung preparation
• Heart preparation : rhythm,rate,contractility, afterload and
preload
• Final preparation

53. • Thank you