Weaning from cardiopulmonary bypass (CPB) requires optimizing several cardiovascular parameters to ensure a smooth transition back to native heart function. Key factors to address include adequate rewarming, hemodynamic stability, cardiac contractility, oxygen delivery, electrolyte/acid-base balance, and removal of air from the heart. The sequence of events involves gradually reducing pump flow while monitoring pressures and cardiac function. Inotropic support may be needed for patients at high risk of low output. Complications can include low cardiac output, arrhythmias, hypotension or hypertension, and end-organ dysfunction if not managed appropriately.

1. WEANING FROM
CARDIOPULMONARY BYPASS
MODERATOR: DR RANJAN
PRESENTOR: DR MITHRA

2. Introduction
• Weaning from CPB should represent a smooth transition from the mechanical pump back to the patient’s heart and lungs
as the source of blood flow and gas exchange
• Optimize cardiovascular status
• Avoid myocardial injury or damage to major organs.

3. TOPICS FOR DISCUSSION
 Preparation for termination of bypass: central venous pressure (CVP or C6V4P6)
mnemonic
 Sequence of events immediately before terminating cardiopulmonary bypass (CPB)
 Sequence of events during weaning from CPB
 Sequence of events immediately after terminating CPB
 Cardiovascular considerations after successful weaning from CPB
 Complications in post CPB

5. COLD:
• Core temperature should be greater than 36 degree Celsius before terminating CPB.
• Rectal or bladder temperature should be 350 to 360
• Ending CPB when cold causes prolonged hypothermia
• Nasopharngeal temperature not exceeed 370: Post operative CNS dysfunction.
• Rectal temperature is two degree lower :Larger than four degrees gradient between the nasopharyngeal and rectal temperatures is indicative of
inadequate rewarming or increased vasoconstriction
• Vasodilator ---- warming blankets .
CONDUCTION:
RATE:
HR of 80 -100 beats/min
• Bradycardia-- epicardial pacing or atropine or inotropic drug.

6. Tachycardia should be avoided > 120/min.Causes
1) Hypoxia
2) Hypercapnia
3) Medications (inotropes, pancuronium, )
4) Light anesthesia, awareness
Fast track” anesthesia with its lower medication additional dose of narcotic and benzodiazepine, or hypnotic (propofol infusion) should be given
during the rewarming period or if tachycardia is present.
(5) Anemia
(6) ST and T-wave changes indicative of ischemia
Rhythm
• Sinus rhythm is preferable, particularly in patients with poor LV compliance, who are especially dependent on an “atrial kick” to achieve adequate filling.
If supraventricular tachycardia is present, direct synchronized cardioversion .
pharmacologic therapy with amiodarone, esmolol, verapamil, or adenosine may be used in the initial treatment of or to prevent the reoccurrence of
supraventricular tachycardia.
Stabilize parameters • Defib • Pacing • Then only anti arrhythmic drugs
•

7. Cells
• The hemoglobin concentration should be measured after rewarming
.• If it is less than 6.5 to 7 g/dL before terminating CPB– blood administration to maintain o2 carrying capacity after CPB.
10 gm is acceptable in many centres.
• 2 units of PRCs, 6 units ready
• Salvaged blood –ready.
• COPD, cyanosis ,residual stenosis, low output ---- aim for higher hematocrit

8. Cardiac output or “contractility.
• Following unclamping ,an adequate reperfusion period must be permitted.
• allows the heart to replenish metabolic substrates, specifically high-energy phosphates (ATP), and “washes out” the products of anaerobic
metabolism,
• Contractility may be estimated from TEE and cardiac output can be measured with a PA catheter. -- 3 minutes interval
Coagulation
the prothrombin time,
• partial thromboplastin time,
• platelet count
• ACT
RISK ::
• long CPB times;
• extreme hypothermia,
• chronic renal failure.
Platelet function tests may be useful in patients taking platelet inhibitors such as clopidogrel or aspirin.
Platelets,FFP,fibrinogen concentrated or cryoprecipitate should be available

9. Calcium
• The concentration of calcium in the plasma may be reduced by large volumes of citrated blood, leading to impaired
contractility and vasodilatation.
• Ionized calcium should be maintained above 1.0 mmol/l.
• Calcium – culprit in reperfusion injury – correct only after establishing serum values

10. VENTILATION
• Adequate oxygenation and ventilation
• Arterial pH between 7.3 and 7.5
• Reexpand lungs with two to three sustained breaths to peak pressure of 30 cm of water.
• Inspired fio2 : 100%.
• Avoid nitrous oxide.
• A venous oxygen saturation of 75% and a minimum venous PO2 of 35mmHg are satisfactory to start weaning from CPB.
• Auscultation of breath sounds.
VISUALIZATION OF HEART
• TEE
• Evaluates contractility, distension of chambers, Residual air, Conduction and valvular function.

11. VAPORIZER:
Should be turned down 10 minutes before terminating CPB.
They decrease contractility.
VOLUME EXPANDERS:
Albumin or Crystalloid solutions to increase preload.

12. • Predictors and factors contributing to adverse cardiovascular outcome:
1.Risk factors for difficult weaning:
 LVEF<45%
 Renal disease
 Female patient undergoing CABG.
 Elderly patient.
 CCF
 Emergent surgery:1.Ischemia or infract
2. Failed closed interventions
 Prolonged CPB duration
 Inadequate surgical repair: 1. Incomplete coronary revascularization: small vessels, Distal disease
2. Valvular disease: valve replacement with very small valve, suboptimal valve repair

13.  Incomplete myocardial preservation during cross-clamping: 1. Incomplete diastolic arrest
2. Prolonged ventricular fibrillation before cross clamping
3.Warm myocardium
LV hypertrophy
High grade coronary
stenosis
Grafting order Noncoronary
collateral flow
washing out
cardioplegia
Poor LV venting
causing cardiac
distension
Inadequate
topical cooling
L sided SVC with
retrograde cardioplegia

14.  Prolonged ventricular failure
 Impaired myocardial perfusion before and after cross clamping: 1.Sustained low perfusion pressure on CPB
2. Ventricular distension
3. Emboli from ventriculotomy or improper deairing of coronary grafts.
2.Additional preparations for high risk patients: 1 Ephedrine (5 mg/ml)or epinephrine (4 to 10 mcg/ml)
2.Invasive monitoring(LA or central aortic catheter)
3.Inotropes
4.IABP
5. First attempt
6.Ischemic pre conditioning and post conditioning.

15. PROTAMINE:
• 3-4 mg/kg or 1 mg for 100 units of heparin administered •
• Slow
PRESSURE:
ARTERIAL PRESSURE AND PA PRESSURE
• Calibration and re zeroing are accomplished shortly before starting to wean the patient from CPB.
• Any discrepancy between distal (usually radial) arterial pressure and central aortic pressure should be recognized.

16. • PRESSORS AND INOTROPES
• Phenylephrine • • Norepinephrine • Terlipressin • NTG
• Methylene Blue (1.5 mg/kg)
• Catecholamines
• Low SVR -- noradrenaline or vasopressin
• Low cardiac output syndrome- Adrenaline , dopamine, dobutamine, milrinone and
levosimendan

17. LOW CARDIAC OUTPUT SYNDROME
• Defined as cardiac index less than 2.4L/min/m2, elevated
lactate levels and urine output less than 0.5ml/kg/hour
• Preload optimized and the afterload help maximise cardiac
function
• Arryhthmias are treated
• Sedation and muscle relaxation maintained to decrease pain
and O2 demand 25-30%

18. Risk factors

21. PACING
• Epicardial pacing is commonly required in the immediate and early post-CPB period.
• Atrial (AV node ) , / ventricular ( chronic AF)
• If cardiac function is adequate after weaning from CPB, pacing may not prove necessary.
pH
pH of 7.4 and a PCO2 higher than 35 mmHg are mandatory to safely disconnect a patient from the pump.
• Any degree of acidosis should promptly be corrected because it depresses myocardial contraction, diminishes the
action of inotropes, and increases pulmonary vascular resistance.
• Acidosis → sympathetic activity → beta blockers ( preop )

22. Potassium
• hypokalemia may contribute to dysrhythmias
• hyperkalemia may result in conduction abnormalities.
• Hypo more a common problem – patients on diuretics
• Off bypass – usually in the range of 2.5
• magnesium (2 to 4 g) is generally administered before CPB is terminated.: risk of arrhythmias ,coronary vasospasm and
postoperative hypertension.
Glucose (4.0–7.8 mmol/l) • Tight glucose control in the postoperative period has been shown by some investigators to
improve outcome after cardiac surgery.
Hyerglycaemia : CNS dysfunction,poor wound healing and cardiac morbidity.
• Hypoglycemia is rare except in liver diseases
• Lactate may be high (> 2.5 mmol/l) – usually no treatment

23. Surgeons preparation
• Removal of intracardiac cathethers and repair of cathether entry sites.
• Removal of intracardiac air present in left sided chambers of heart by meand of aortic root vent
• Placement of epicardial pacing wires in RA and RV
• Final visualisation of surgical repair and maintain hemostasis

24. Perfusionist preparation
• Ensuring adequate rewarming in avoiding hyperthermia
• Treatment of anemia by cell salvage technique
• Discontinue unnecessary venting of blood from surgical field and vacuum assistance for venous drainage.

25. SEQUENCE OF EVENTS IMMEDIATELY BEFORE TERMINATING
CPB
• FINAL CHECKLIST BEFORE TERMINATING:
1 Confirm
 ventilation
 rewarming
 deairing
 metabolic conditions
 Medications and equipments ready.
• WHAT TO LOOK DURING WEANING
• Invasive pressure display: Pressure waveforms
1.Arterial pressure
2.CVP
3.PA pressures: TEE,ECG, DIRECT VISUALIZATION,VENTILATION AND OXYGENATION

26. SEQUENCE OF EVENTS DURING WEANING FROM CPB
Impeding venous return to the pump:
1.Consequences of partial venous occlusion:
Slowly the venous line is occluded : increase in resistance-RA pressure rises- diverts blood to RVincrease in CO as preload increases
 ejects blood more forcefully
2.Preload: adjusted to maintain LVEDV
Estimate preload: TEE, Central venous or PA cathether.
Optimal preload
Typical weaning filling pressures: PCWP :8-12 mm hg or CVP 6-12 mm hg.
CVP/LAP ratio

27. • Lowering pump flow into aorta
Attaining partial bypass
Reduced pump outflow requirement
Readjusting venous line resistance
• Terminating bypass
Adequate systolic pressure with acceptable preload with pump flow of 1l/min bypass is terminated
Pump stopped and venous cannula stopped

28. SEQUENCE OF EVENTS IMMEDIATELY ATER
TEMINATING CPB
• Preload: Infusing blood from the pump:
50 to 100 ml from venous pump reservoir to patient
Bp=CO*SVR if SVR constant then BP= CO
• Measure cardiac function:
1.Derived cardiac index= CO/ body surface area
Stroke volume index: CI/HR
2.Measuring patient perfusion:ABG,PH,SVO2, Urine output
3.Afterload and aortic impedence: avoid elevated afterload,maintain BP:100-130 mm hg
• Removing the cannulas
Allows for reprime the pump and further volume infusion
• Cardiac decompensation
LV failure
RV failure
Inapproriate vasodilation: vasoplegic syndrome

29. Vasoplegia
• Characterized by hypotension associated with profound vasodilation unresponsive to conventional catecholamines or vasopressors.
• Treatment was with vasopressin and methylene blue
RESUMPTION OF CPB
• Risks: (inadequate heparinization, hemolysis, worsening coagulopathy, and vasoplegia after a second bypass run). But CPB must be restarted before
permanent ischemic organ damage occurs (heart, brain, kidneys)
• Rapid return to full CPB
• Full dose of heparin
• Maintain coronary and cerebral perfusion
• Discontinue inotropes and vasopressors
• Recovery and reversal of damage if heart is rearrested.
• Correct mechanical factors
• Monitor LVEDP
• If second attempt is unsuccessful: maintain preload and afterload.

30. Cardiovascular considerations after successful weaning
• Reperfusion injury
Functional, structural and metabolic alterations that results from reperfusion of myocardium after a period of temporary ischaemia.
Rx: reoxygenation with warm blood to start aerobic metabolism
• Decannulation
Blood loss and atrial dysrhythmias
Significant blood loss during aortic cannula removalcannula reinserted into right atriumvolume infused achieve stability
• Manipulation of heart
Impaired venous return,arrythmias, decreased ventricular ejections systemic hypotension
• Myocardial ischaemia
Coronary spasm, mechanical obstruction, air in grafts,inadequate revascularization.
• Chest closure

31. Complications in post CPB
• Awareness
• Hypothermia
• Low cardiac output syndrome
• Right heart failure
• Vasoplegia
• Dysrhythmias
• Hypertension
• Renal insufficiency
• CNS dysfunction
• Respiratory insufficiency
• Metabolic disturbances
• Pain
• Bleeding and coagulopathy

32. KEY POINTS
1. Core temperature (nasopharyngeal or bladder) should be greater than 36°C before terminating cardiopulmonary bypass (CPB).
Discontinuation of CPB at temperatures less than 36°C increases the risk of rebound hypothermia in the intensive care unit (ICU).
However, the nasopharyngeal temperature should not exceed 37°C, as this will increase the risk of postoperative central nervous
system dysfunction. Using nasopharyngeal temperature to avoid hyperthermia and the rectal/ bladder temperature to assure adequate
rewarming may be the safest technique.
2. Visualization of the heart, directly to assess right ventricular (RV) function and volume status, as well as with transesophageal
echocardiography (TEE) to rule out air and to assess valve and ventricular function is important before terminating CPB

33. • 3.The first attempt to terminate CPB is usually the best one. Optimize all central venous pressure (CVP) mnemonic parameters before
CPB termination. Consider prophylactic inotropes in patients with markedly reduced ventricular function.
• 4. Protamine should not be given until the heart has been successfully weaned from CPB. A struggling heart after CPB
discontinuation could require reinstitution of CPB.
• 5.Vasoplegic syndrome is a severe form of post-CPB vasodilation characterized by low arterial pressure, normal to high cardiac
output (CO), normal right-side filling pressures, and low systemic vascular resistance (SVR) that is refractory to pressor therapy.
• 6. When evaluating hypoxemia after CPB, the possibility of a right-to-left shunt through a patent foramen ovale must be considered
and evaluated with TEE.
• 7. New-onset renal dysfunction requiring dialysis after CPB increases mortality almost eightfold. Maintenance of a higher mean
arterial pressure (MAP) on pump in patients with preexisting renal insufficiency may be protective in some patients

34. REFERENCES
• Millers anesthesia
• Cardiac anesthesia by Deepak Tempe
• Cardiac anesthesia by Gravlee.

35. • Thank you.