Preparation for separation 2010 final

Preparation for weaning Preparation for weaning from CPB from CPB

Abeer elnakeraAbeer elnakera

Anesthesia lecturerAnesthesia lecturer

20132013

objectivesobjectives• To emphasize the importance

for preparation to wean from CPB which include–General preparations–Preparing the lungs–Preparing the heart–Final preparations

General preparationsGeneral preparations1. Ensure rewarming2. Restoration of MAP at

normothermic levels3. Ensure adequate anesthesia and

muscle relaxation4. Blood chemistry optimization5. Determine factors that may make

termination of CPB difficult6. Removal of intracardiac air

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 denaturation2. Cerebral hyperthermia3. Expand gas bubbles

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 followingcoronary artery bypass surgery in adultswhen slow rewarming (2◦C difference betweennasopharyngeal and CPB perfusate temperature) is

compared to more standard rewarming (4–6◦C difference between nasopharyngeal and CPB

perfusate temperature)

Ensure rewarmingEnsure rewarming• Despite homogeneous core rewarming, it is notuncommon for the patient’s core temperature todrop 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.

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

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.

22--Restoration of MAP at Restoration 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 )

33 - -Ensure adequate anesthesia Ensure adequate anesthesia and muscle relaxationand muscle relaxation

• Adequate anesthesia : during rewarmingFor 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

Ensure adequate anesthesia and Ensure 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

44--Blood chemistry Blood 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

Blood chemistry optimizationBlood chemistry optimization

• A serum potassium level of approximately5 m Eq/L decreases the defibrillation thresholdcompared with levels approximately 0.5 mEq/Llower.

• If defibrillation is unsuccessful in the presence of a low serum potassium, potassium administration should beconsidered.


• 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


• 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


• 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.


• 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.


• 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.


• HematocritGenerally, a hematocrit greater than 25% is soughtas 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 at37◦C may result in low SVR and myocardial ischemia

66--Removal of intracardiac airRemoval of intracardiac air

• To avoid cerebral and coronary emboli With aortic clamp still applied :

1. Allow the heart to refill2. Lt atrium and ventricle are ballotted to dislodge

air bubbles through vent3. Ventilation then valsalva maneuver to squeeze

pulm. Veins 4. Head down position and carotid compression

(controversial)

TEE IS HIGHLY BENEFICIAL MONITORING

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.

General preparationsGeneral preparations

1. Ensure rewarming2. Restoration of MAP at

normothermic levels3. Ensure adequate anesthesia and

muscle relaxation4. Blood chemistry optimization5. Determine factors that may make

termination of CPB difficult6. Removal of intracardiac air

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,

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.

NowNow

Aorta declampingAorta declamping

= end of ischemic time

= beginning of reperfusion time

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

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

RhythmRhythm

• the heart may resume electrical

activity with ventricular ventricular fibrillationfibrillation

VFVF

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

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

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

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


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.


RhythmRhythm

• Ventricular arrhythmiasVentricular arrhythmias should be treated by correcting underlying causes and, if necessary, with ant arrhythmic drugs such as amiodarone.


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

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.


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 in Each pacemaker spike must result in appropriate atrial and/or ventricular appropriate atrial and/or ventricular capture and contraction.capture and contraction.


RhythmRhythm

Aorta declamped

VFPPRasystole or

HB

Sinus rhythm

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.

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

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.

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

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.

•

ContractilityContractility

• If depressed myocardial contractility depressed 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 function Extreme 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).

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 arterial mean 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.

After loadAfter load

• SVR is usually within a reasonable SVR is usually within a reasonable range when the arterial pressure is range 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.

55 - -PreloadPreload

• In the intact heart, the best measure of preload the 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.[

PreloadPreload

• The process of weaning a patient from CPB The process of weaning a patient from CPB involves increasing the preload (i.e., filling involves increasing the preload (i.e., filling the heart from its empty state on CPB) until the heart from its empty state on CPB) until an appropriate end-diastolic volume is an appropriate end-diastolic volume is achievedachieved. (vary with each patient)

• The filling pressures before CPB may The 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.

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

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

•? ? ? ? ? ?? ? ? ? ? ?

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

• Thank you

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Preparation for separation 2010 final