Cardiopulmonary Bypass

Cardiothoracic & Vascular Surgery Department-SulaimaniyaBy :- Dr. Allaa S. Abdel Majeed

History

Dr.Gibbons, inventor of the Heart & Lung machine Also known as, cardio-pulmonary bypass machine (CPB).

•1935 –maintained a cat’s circulation on CPB while closing the pulmonary artery.

1953 –Cecelia Bavolek First patient to undergo open heart surgery using CPB to repair an atrial septal defect

More than 40 years of Innovation, Research, and Hard Work

General Comments

CPB involves an extracorporeal circuit that provides oxygenated systemic blood flow.

Is accompanied by normovolemic hemodilution and nonpulsatile flow.

The contact of blood with the extracorporeal circuit results in the activation of numerous cascades.

Among the consequences of this contact are thrombin generation, the release of proinflammatory cytokines.

This systemic inflammatory response may lead to multiple organ system compromise.

Use of membrane oxygenators, biocompatible circuits, centrifugal pumps, leukocytes filtration and intraoperative steroids may reduce the inflammatory effects of CPB, but have not had a significant impact on clinical outcomes.

Despite adequate heparinization, the bypass circuit is a potent activator of the coagulation system with generation of factor Xa and thrombin.

A coagulopathy may develop from activation of platelets and the fibrinolytic system, as well as from dilution of clotting factors and platelets during bypass.

Circuits coated with the Carmeda BioActive surface, heparin (DurafloII) have been shown to improve biocompatibility, with reduce platelet activation and less release of proinflammatory mediators.

Why CPB

To facilitate a surgical intervention Provide a motionless field

Provide a bloodless field

To whomCoronary Artery Disease (CAD)

Valve Disease

Congenital Heart Defects

Dissections

Aneurysms :- Aortic, ventricular, giant cerebral

Transplants :- Heart, liver, lung, trachea

Others: limb cancer, hypothermic rescue

Principle of CPB

Deoxygenated blood (Venous Return) taken away from the body to the CPB machine.

Then pumped and oxygenated to returned back to the body (Arterial system)

Components of CPB Venous and arterial cannulas

Venous Reservoir

Centrifugal pump

Oxygenator, heat exchanger , venous reservoir

Microfilter bubble trap on the arterial side

Suction system for cardiotomy reservoir and filter returns to venous reservoir

Field blood washed in a cell saver system returned as packed RBCs.

Partial and occluding clamps to direct and regulate flow

Various ports in the system to obtain blood samples.

Cardioplegic system, LV Vent.

Venous Drainage and Cannulation

Venous cannulas:- Size determined by patient size, anticipated flow rate, flow characteristics and resistance

Usually 30F in SVC and

34F in IVC or a single 42F

3 basic approaches:-

Bicaval, single atrial, cavoatrial(2-stage Cannula)

Augmented /Assisted Venous Return Negative pressure can be applied using roller pump,

centrifugal pump or regulated vacuum. Augmented negative pressure increases risk of aspirating air , cerebral injury & hemolysis.

Complications of Venous drainage Arrhythmias Atrial or caval tears Bleeding Air embolization Unexpected decanulation Improperly placed purestring sutures may obstruct cava

when tied.

Arterial CannulationAscending Aortic

Tip of arterial cannula is narrowest part of the perfusion system

Distal ascending aorta is preferred due to ease of placement and fewest complications.

The outflow should be directed into the arch, not into the innominate artery.

Complications of AA Cannulation Difficult insertion, bleeding, tear in aortic wall, intramural or

malposition of cannula tip, air emboli, plaque emboli, aortic dissection

•Atherosclerosis of the ascending ,dislodgement of plaque/debris lead to Peri-operative Stroke

Aortic dissection0.01-0.09%.Common in aortic root disease :-discoloration beneath

adventia near cannula site, increase in art line pressure, sharp reduction in return to venous reservoir.

Emergency Management: Cannulate peripheral artery or uninvolved distal aorta.Control BP pharmacologicallyTemperature to < 20 ºCCirculatory arrest and repair aorta.

Femoral Cannulation

First alternative to aortic cannulation Indicated for initiating CPB quickly in cardiac arrest, acute , dissections, limited access

Complications Retrograde arterial dissection (0.2-

1.3%) most serious one with 50% mortality.

Tears, late stenosis, thrombosis, bleeding, lymph fistula, infection in groin, cerebral or coronary

Axillary Cannulation

Increasing use in Aortic surgery, circulatory arrest cases

Advantage :- freedom from atherosclerosis, antegrade flow into arch vessels, protection of arm and hand by collateral flow

Disadvantage: Risk of brachial plexus injury, axillary artery thrombosis

Venous Reservoir

Placed immediately before arterial pump

Reservoir is high capacitance (low pressure) receiving chamber for Venous Return

Facilitates gravity drainage

Can add drugs, fluids, or blood

Can hold 1-3L of blood when patient on full CPB

Pumps

Centrifugal pump Propel blood by centrifugal

force. Can pump small amounts of

air but stopped if > than 50mL of air enters blood chamber

Produce pulseless blood flow

Roller Pumps Forward flow generated by roller compression

Produces a sine wave pulse blood flow at 5mmHg

No evidence to produce pulsatile perfusion during short/long-term CPB

Heat Exchangers

Control body temperature.

Gasses more soluble in cold than warm blood.

Rapid rewarming may cause bubble emboli.

Temperature difference between body and perfusate kept <10.

Temp kept < 40ºC to prevent denaturation of proteins.

Cardioplegia requires separate heat exchanger.

Oxygenator Membrane Oxygenators imitates

natural lung by providing a thin membrane between the gas and blood phases

Plasma filled pores prevent gas from entering blood but allows exchange of Oxygen and CO2.

Produce up to 470mL of O2 and remove 350mL of CO2 / minute at 1-7L of flow.

Malfunctioning of oxygenators occurs in 0.02-0.26% of cases most common due to abnormal resistant of blood.

Monitoring of blood gasses is very important to ensure adequate removal of CO2 and oxygenation.

Heparin Coated Circuits

Can be attached to blood surfaces of all components of the CPB.

An ACT of 350 will be satisfactory for this types of circuits.

No evidence that heparin-coated perfusion circuits reduce need for systemic heparin, or reduce bleeding or thrombotic problems associated with CPB.

Cardiotomy Reservoir / Field Suction

Blood aspirated from surgical wound maybe directed to cardiotomy reservoir filtered and added to perfusate

Negative pressure for suction generated by roller pump.\

Suction is major sources of hemolysis, emboli, platelet injury, thrombin generation, fibrinolysis.

Alternate option is cell saver

Field aspirate blood is diluted with saline and saline removed to return only pRBC to perfusate

Venting the Heart

RV distention rarely a problem during cardiac arrest.

LV distention is a problem due to:-

Blood atrial or venous cannulasBlood from coronary sinus.Bronchial arterial and venous blood.Blood from Aortic Valve regurgitation.Unknown sources (PFO, PDA).

Left Heart Venting:-

Multihole, soft-tip catheter (8-10F) inserted into RPSV and LA and into LV then connected to cardiotomy reservoir

Cardioplegia System Solution contains 8-20 Meq/L of K+,

Mg++, and other components

Given Anterograde and/or Retrograde.

Temp varies (4-37ºC)

Normothermic circulation continuous

Cold circulation use intermittent

Delivered through separate perfusion system that includes a reservoir, heat exchanger, roller pump and bubble trap.

The CPB Team Role Surgeon:- Determines the planned operation, target

perfusion temperatures, methods of cardioplegia, cannulations.

Communicates procedural stepsConnecting/disconnecting CPB, perfusion management, surgical

exposure

Perfusionist:- Setting up and priming the CPB machine, safety checks, monitoring anticoagulation, adding prescribed drugs, maintaining records.

Anesthetist:-“Troubleshooter” of complex procedures

CPB Physiology

Hemodilution

Anticoagulation

Hypothermia.

Flow rate & Blood Pressure.

Blood gas control

Priming & Hemodilution

Adult circuits require 1.5-2L of balanced electrolyte solution.

Volume ~40% of patient’s blood volume↓ HCT by 1/3 of pre-op value Sometimes banked blood added to raise HCT.

Decreased viscosity results in increased tissue perfusion.

No consensus on optimal HCT usually 20-25%.

Hct of less than 20% may be associated with significant increase in risk of renal injury and that less than 15% may lead to maldistribution of coronary flow away from the subendocardium in the presence of residual coronary stenosis

Dilution may also ↓ O2 carrying capacity if this occurs, need to transfuse or increase pump flow.

Sometimes, 12.5-50g of mannitol added to stimulate diuresis.

Addition of Glucose/Lactate avoided because shown to increase neurologic deficits.

Other additives to the prime may include calcium, and pharmacologic agents such as heparin and aprotinin.

Anticoagulation 300 – 400 Units/Kg IV heparin given before arterial and venous

cannulation

Measure ACT 3 minutes after dose.

ACT must >480 to begin cannulation.

During off-pump surgery, ACT should reach 250 seconds.

If ACT not increasing need to increase heparin dose to 500U/kg

May need FFP (antithrombin)

ACT measured every 30min.

Usually 1/3rd of initial heparin dose given every hour to maintain target ACT

Reversal

Protamine (1mg/100U of heparin) given

Heparin-protamine complex activates complement pathway & lead to hypotension.

May need to add Calcium (2mg/1mg of protamine)

After 1/3rd of protamine dose administered blood must not be returned to the cardiotomy reservoir from the surgical field

Neutralization of heparin must be confirmed by an ACT

Hypothermia Reduces metabolism and oxygen demand especially by

brain.

Allows less blood trauma.

Myocardial protection & Systemic organ protection.

Provides a margin of safety in the event of equipment failure.

Types of Acceptable hypothermias:- Mild 37° - 32°C < 5 min 32° Moderate 32° - 28° < 20 min 28 ° Deep 28 ° - 18 ° < 45 min 18 ° Profound < 18 ° < 60 min

Outgassing {Air Emboli}

Occurs at tissue level when cooling.

Occurs at heat exchanger when rewarming.

Maintain a 12°C gradient when rewarming.

Cool at a rate of 1°C per 1 minute

Rewarm at a rate of 1°C per 3 minutes

Protein denaturation occurs at. 42°C

Blood flow rate/Arterial pressure Basic CO2 determined by O2 consumption (250ml/min).

systemic flow rate is calculated based on the BSA and modified by the degree of hypothermia and the venous oxygen saturation (SvO2).

Generally accepted flow rate with HCT 25%, deeply anaesthetized, muscle-relaxed patient = 2.4L/min/m.sq.

Also ↓flow = ↓O2 consumption.

in most practices, as long as the SvO2 exceeds 70%, the flow rate is considered to be adequate.

Cerebral autoregulation maintenance cerebral blood flow down to a MAP of 40–50mmHg, but may be inadequate in HT or DM, in whom may need high MAP.

At 24% HCT, MAP between 55-60mmhg, adequate to maintain autoregulation.

In older patients with vascular disease, MAP generally maintained between 70-80mmhg.

At lower temperatures, a mean pressure of 35 mmHg is still generally accepted as safe

Higher MAPs undesirable as it increases blood in the operative field.

Hypotension – causes are low pump flow, aortic dissection, vasodilation

Phenylephrine, vasopressin

Hypertension nitroprusside (arterial dilator) nitroglycerine (venodilator and pulmonary vessel)

Blood Gas Strategies

pH stat maintain normal temperature corrected values for pH and PaCO2

As blood temperature decreases, CO2 becomes more soluble

2 Strategies:-

pH-stat – maintains pH at 7.40 at all temperatures.

Requires addition of CO2 while cooling

Cerebral blood flow is higher, and uncoupled to cerebral oxygen demand

Recommended for pediatric surgery

Alpha-stat – pH allowed to increase during cooling

Blood becomes alkalotic.

Cerebral blood flow is lower, autoregulated, and coupled to cerebral oxygen demand.

Total CO2 remains constant.

pH changes as temperature changes.

PaO2:- >150mmHg to assure complete arterial saturation

Seven Steps for CPB

Step 1 for CPB

Heparin

Step 2 for CPB

Exposure of the heart & Check Aorta.

Pericardial cradle/sutures.

Step 3 for CPB Check ACT

Aortic Cannulation Concentric 2-0 Ethibond stitches with

sliders11 Blade and cannula insertion Snare both stitches securely and tie to

cannula Connect cannula to arterial line.Check for any bubbles Ask for pulse pressureSecure aortic cannula (skin stitch and/or

towel

Remove arterial clamp.

Step 4 for CPB Atrial (venous) Cannulation Single Prolene or Ethibond stitch for RA appendage followed by

slider. Make incision/dilate.Insert cannula with hand over the IVC for accurate positioning.Secure cannula with slider and tie. Connect to venous line.

Remove venous clamp

Command “On bypass”

Turn lungs ventilation off.

Step 5 for CPB Place cardioplegia cannula (retro/ante).

Reduce pump flow/Clamp aorta.

Resume full flow/check line pressure.

Start cardioplegia.

Set pt. temperature with perfusionist.

Step 6 for CPB Release cross-clamp after warm cardioplegia.

Remove all air from heart.

Begin respirations (start lungs).

Check Good contractility & Stable heart rhythm.

No bleeding.

Desired patient temperature.

Step 7 for CPB

Wean slowly from CPB.

Begin Protamine assessing BP, CVP.

When stable: Clamp venous line and remove.

Remove vent/cardioplegia.

Be alert for hemodynamic reactions.

Remove arterial cannula after all protamine in.

Keep lines clamped and ready for any emergency.

Weaning off bypass Flow rate gradually decreased.

Venous line gradually occluded.

As flow rate approaches zero, volume is added/removed to keep arterial and venous pressures within physiologic range.

Cardiac filling, contractility, and repairs are assessed while weaning.

Once Sats near 100%, ETCO2 >25mmHg, and SvO2 >65% mean satisfactory circulation.

If all satisfied, can give protamine.

Patient Monitors Radial/brachial/femoral arterial catheter.

CVP via jugular venous catheter.

Routine use of Swan-Ganz PA cath controversial.

TEE – important tool for cathether and vent insertion, aortic atherosclerosis, thrombi and air assessment, contractility, valve function, diagnosis of dissection.

Urine output.

Temperature – Nasopharyngeal or tympanic membrane temp used more commonly.

Arterial line temp. correlates best with jugular venous bulb temp (best surrogate for brain temp).

Before CPB there is electrical activity on the EKG

positive pressures from blood present in the right side of heart

pulsatile arterial blood pressure.

On CPB, the hearts electrical activity can be suspended.

Therefore the arterial blood pressure will be nonpulsatile.

The right side of the heart will be empty.

Emergencies in CPBAortic Dissection with cannulation

Massive Air Embolism Stop CPB Place pt in steep head-down position Remove aortic cannula from asc. Aorta Purge asc. aorta of air and refill arterial line Begin retrograde SVC perfusion for 2-3 min until air is cleared Return cannula to aorta for systemic cooling and ?pharmacologic brain

protection Post-op-Hyperbaric O2 & hyperventilation.

Clotted Oxygenator Decreasing PaO2 with metabolic acidosis Check O2 supply/blender Emergency oxygenator change-out may be necessary

Severe Protamine Reaction

Anaphylactic reaction with pulm HTN, edema and systemic hypotension.100%O2, IV fluids, steroids, antihistamines, vasoconstrictors and

bronchodilators.

Inadequate CPB Flow Directly proportional to venous saturation/acid-base status.Possible reasons:-

Inadequate CPB volume Aortic dissection

Cannula problems (aortic or venous) Oxygenator thrombus

Pump head malfunction

Systemic Complications

CardiacDifficult to decipher post-op cardiac dysfunctionSubject to emboli, cytotoxinsMyocardial “stunning ”reperfusion injury.

Lung Pulmonary edema (complement activation ) CPB reduces effect of natural surfactant . CPB increases shunts, reduces compliance and FRV. ARDS

KidneyHemodilution, microemboli, catecholamines, diuretics, hypothermia,

aprotinin all impair renal function.

GIPeptic ulcers (surgical stress).Pancreatitis and mild jaundice.Gastroenteritis (increase inflammatory response).

BrainMost sensitive organ exposed to injury by CPB.Difficult to assess with difficult outcomes as stroke, delirium &

coma Risk increases with age (>60), Proximal aortic atherosclerosis or PHx

of neurologic disease ↑ ↑ ↑ ↑ riskMechanism –microemboli (air, debris, fat) or hypoperfusion.Protection strategies Mild hypothermia, HCT>25%, cerebral perfusion,

off-pump.

CPB in Pregnancy In additional to effect of (CPB), pregnant women circulation already altered.

These effects are relatively well tolerated by the mother.

Pregnant women mortality during CPB is almost similar to that in nonpregnant.

 Cooling and rewarming phases are associated with increased sustained uterine contractions.

Higher fetal mortality rate with hypothermic than with normothermic CPB.

Pulsatile flow in contrast to nonpulsatile flow, preserves endothelial NO synthesis, decreases the activation of the fetal renin-angiotensin pathway and preserve lactate level stable.

the fetal mortality rate during maternal cardiac surgery with CPB ranges of 16% -- 33%.

Current evidence favors maintaining normothermic CPB, high HCT , high pulsatile flow and avoiding the use of vasoconstrictors .

CPB in Renal failure Pt. Patients requiring long-term hemodialysis are known to be at a high

risk for both mortality and morbidity during heart surgery

In the literatures, the mortality of cardiac surgery from CPB is 3.5% for RF pt.

The most important electrolyte imbalance in CPB operations is that of potassium.

Renal insufficiency with creatinine levels higher than 2.5 mg/dL increases the risk of postoperative dialysis and prolongs the length of hospital stay.

Careful intraoperative techniques, such as avoiding myocardial depressants & low perfusion pressure with using low-dose dopamine, may be useful for a good operative outcomes.

The use of intraoperative hemodialysis was advocated by some centers.

Special Types of Extracorporeal Circulations

A. Deep hypothermic circulatory arrest (DHCA)

Indications for DHCA include:Severe aortic atherosclerosis Type A dissections & intraoperative ones.Descending thoracic aortic surgery.Resection of IVC tumors.

patient is cooled systemically to 18 C to achieve (EEG) silence.

The head is packed in ice, and methylprednisolone 20 mg/kg is also given.

The arterial line is clamped and blood is drained from the circulation, taking care not to allow air entry in the lines.

Measures that may extend the acceptable period of DHCA Include antegrade (Axillary Art.) or retrograde (IJV) cerebral perfusion.

Extensive cooling and rewarming are often associated with a coagulopathy.

gradient between the arterial inflow and the patient’s temperature should be no more than 10 –12 C to prevent generation of gaseous emboli.

B. Left-heart bypass for thoracic aortic surgery

Indicated in aortic procedure involving descending aortic cross-clamping with risks of paraplegia and renal dysfunction.

Left-heart bypass entails drainage of oxygenated blood from the left side of the heart and returning it more distally in the arterial tree.

The blood does not pass through an oxygenator, although one can be placed in the circuit to improve oxygenation

Minimal heparinization is necessary for this setup (about 5000 units to achieve an ACT of 250 seconds).

Flow rates of up to 3 L/min can be used, with monitoring of lower-extremity mean pressures in the femoral artery that should approximate 50mmHg.

C. Assisted right-heart bypass for off-pump surgery.

During manipulation of the heart for off-pump surgery, especially with hypertrophied hearts, there may be compromise of right ventricular filling.

Several devices have been designed that provide right-heart assist by draining blood from the right atrium and pumping it into the pulmonary artery during these procedures

D. Extracorporeal membrane oxygenation (ECMO)

Is a means of providing a prolonged period of cardiopulmonary bypass.

It is applicable to patients with severe hypoxemic respiratory failure, severe myocardial dysfunction and CDH Pt.

Arterial line usually placed through a side graft sewn to the femoral artery to ensure distal perfusion of the leg, and venous cannulas in the femoral and/or jugular vein.

Either arteriovenous or venovenous access can be used in the patient with respiratory failure.

E. Ventricular assist devices (VADs)

consist of extracardiac circuits and pumps that provide hemodynamic support to patients with severe ventricular dysfunction.

This may be noted with postinfarction or postcardiotomy cardiogenic shock, or in patients with end-stage heart failure.

These devices may be used as a bridge to recovery or transplantation.

They function solely for hemodynamic support.

They do not provide oxygenation.

References

SABISTON & SPENCER SURGERY OF THE CHEST-8th ed.

MANUAL of PERIOPERATIVE CARE in ADULT CARDIAC SURGERY 5th ed--Robert M. Bojar.

Cardiopulmonary Bypass Mora CT.

Cardiac Surgery during Pregnancy. Anish Patel, MRCS, Sanjay Asopa, MRCS, Augustine T.M. Tang, MD, FRCS (CTh), and Sunil K. Ohri, MD, FRCS (CTh).

Cardiac surgery with cardiopulmonary bypass in patients with chronic renal failure. Isa Durmaz, MDa, Suat Büket, MDa, Yüksel Atay, MD, Tahir Yağdı, MDa, Mustafa Özbaran, MDa, Mehmet Boğa, Mda.

Thanks for your attention