CARDIOPULMONARY BY-PASS

Dr. Md. Rezwanul Hoque MBBS,MS,FCPS, FRCSG, FRCS Ed

Associate Professor( Cardiac Surgery)BSMMU, DhakaBangladesh

.

DEFINITION:

CPB is the process by which the

pumping action of the heart & the

gas exchange function of the lung are

replaced temporarily by a mechanical

device -the pump oxygenator-

attached to the patient’s vascular

system.

HISTORICAL BACKGROUND

Experiment on hypothermia with TCA & hypothermia with CPB went on parallel.

Gibbon (1939) demonstrated support of circulation using pump oxygenator.

Bigelow(1953), Lewis and Taufic(1953), Swan used TCA by surface cooling for intracardiac repair.

Gibbon ( 1953) repaired ASD using CPB. Lillehi(1954) used controlled cross-circulation

based on Azygos flow principle and one parent as oxygenator for cardiac defect correction.

Sealy, Brow & Young(1958) combined TCA with CPB(core cooling & rewarming)

TYPES OF CPB:

Total CPB-Systemic venous return diverted completely to pump oxygenator, then to arterial circulation, pts own cardiac & pulmonary function remain completely suspended.

Partial CPB-Pt’s own heart & lungs participate and are being assisted by pump-oxygenetor.

TYPES OF CPB

Veno-Arterial• Total• Partial (e.g. perfusion of lower half of the

body) Arterial-Arterial with pump• Omit oxygenator• Omit Heparin( heparin bonded tubing) Arterial-Arterial without pump( Heparin

bonded tubing)• Thoracic aneurysm operation• Aortic transection operation

USES OF PARTIAL CPB:

In conventional CPB before application & after

release of aortic cross clamp.

Femoro-Femoral bypass- Total/ Partial

• Used in descending thoracic/ thoraco-abdominal

operation for spinal cord protection .

• Rapid warming of patient with hypothermic cardiac

arrest maintaining CPB support

LA-Femoral bypass( Oxygenator omitted) used in

descending thoracic & thoraco- abdominal aortic

operation.

CONTD.

LVAD , RVAD , BVAD use centrifugal pump to support the circulation bypassing sick ventricle.

( LVAD : LA PUMP AORTA . ) ECMO:• Veno-Arterial for bypass support of heart &

lungs.

RA/JV Pump Oxygenator RCCA• Veno- Venous ( IJV/ SVC Pump

Oxygenator FV/ IVC RV lung LV ).

CONTD.

Veno-Venous by pass- vascular isolation for difficult IVC procedure

Anhepatic phase of liver transplant Resection of renal & adrenal tumor with caval

involvement Repair of traumatic injury to retrohepatic IVC IMV+ FV PumpRA or Axillary vein** Rt. Renal tumor involving intracardiac IVC or

RA needs total CPB and TCA

CPB CIRCUIT

COMPONENTS & CIRCUITRY OF PUMP OXYGENATOR.

Arterial Pump :A. Roller pump Non - Pulsatile mode .• Flow proportional to ID of boot tube & RPM .• Partially occlusive• Haemolysis more due to more stress • Flow independent of downstream resistance ( Arterial

line pressure if more than 300 mm Hg, line disruption/ cavitation may occur).

Pulsatile mode Can produce pulsatile flow e.g. 80/min to maintain body

physiology.

COMPONENTS & CIRCUITRY OF PUMP OXYGENATOR

B. Centrifugal Pump :• Incorporates impeller with vanes rotated by electric

motor within a housing• Flow generated by vortexing blood by impeller,

blood enters central low pressure zones, exit through housing outer perimeter by centrifugal force

• Non-occlusive• Flow depends on upstream/downstream resistance (

stops at ±500mm Hg)• Less haemolysis• Non-pulsatile• Used for long bypass e.g. > 6 hours

CENTRIFUGAL PUMP

HEART-LUNG MACHINE

SCHEMA OF CPB

COMPONENTS & CIRCUITRY OF PUMP OXYGENATOR

C. Cardioplegia delivery pump.

D. Cardiotomy Sucker pump 2 in number, may be used as vent sucker.

COMPONENTS & CIRCUITRY OF PUMP OXYGENATOR

E . Heat- Exchanger Heating- cooling machine is connected by ½

inch water lines to inlet and outlet ports on the heat exchanger. Heat exchanger water flow is started and checked for leaks for the water compartment to the blood compartment.

Oxygenator is discarded if water is present in the blood compartment.

EFFECT OF THERMAL CHANGE ON METABOLISM

Vant Hoffs Law : The logarithm of a chemical reaction is

directly proportional to temperature. Q10 : Temperature change of 10°c changes

metabolic rate by 50% (Q10=2)

During hypothermia , temperature fall should be1°c / min.

But during rewarming , temperature rise should be 1°c / 5 min.

PRINCIPLE OF THERMAL MANIPULATION

Reduction of myocardial temperature from 37°c to 27°c profoundly decreases ischemic and reperfusion myocardial injury, further reduction is less advantageous.

A temperature gradient of less than 10°c between arterial & venous blood should be maintained, otherwise gas bubble may come out

Water temperature should not exceed 42°c,mixed-blood temperature should be less than 39.5°c during rewarming

During cooling water temperature should not be less than 5°c, as it should not be less than 15°c in case of mixed arterial blood.

WARM HEART SURGERY

Continuous cardioplegic perfusion of heart at 37°c reduces oxygen consumption by 90%, so further cooling of heart is unnecessary.

Using this principle, operation can be safely done at 32°c to 34°c even at 37°c.

TOTAL CIRCULATORY ARREST

More than 60 minutes of profoundly hypothermic (<20°c) TCA produces some brain damage whereas duration below 45 minutes is quite safe

TCA is done at 18°c to 20°c, below 15°c causes brain damage.

COMPONENTS & CIRCUITRY OF PUMP OXYGENATOR

F. Venous reservoir Venous reservoir bag: PVC made, closed system, high safety profile as

venous occlusion stops pump making alarming sound but air evacuation and volume management are difficult, drainage is bad and needs separate cardiotomy reservoir

Hard-shell venous reservoir: Open system to air, cardiotomy reservoir

built-in/separate, greater volume capacity, emptying of heart better, air handling easy but do not make alarming sound on emptying

HARD-SHELL VENOUS RESERVOIR

COMPONENTS & CIRCUITRY OF PUMP OXYGENATOR

G. Oygenators Animal/ human lungs are used as oxygenator in

controlled cross-circulation, in heart-lung pack oxygenators are artificially made. Two types:

Bubble oxygenator Venous inlet heat exchanger( gas exchange,

oxygen bubbling) defoamer arterial reservoir pump arterial line

Membrane oxygenator Venous reservoir pump heat exchanger

oxygenator filter arterial line

MEMBRANE OXYGENATOR

Rolled flat plate membrane Silicone made, long term use in ECMO e.g.

AvecorFlat plate membrane Polypropylene made e.g. Cobe, CMLHollow fibre membrane Polypropylene made, blood flow outside &

gas flow inside is better than vice versa e.g. Affinity NT, Quantum ICVR etc.

Each oxygenator has its own rate of flow (LPM), prime volume (ml), surface area Sq. m, Oxygen transfer (ml/min@LPM

CIRCUITS:

A circuit consist of all disposable elements used on heart-Lung machine.

Tubing volume

Tubing ID ml/ft.

1/4 inch 09.65 ml

3/8 inch 21.71 ml

1/2 inch 38.61 ml

5/8 inch 48.00 ml

TUBING SIZE IN ADULT

Line ID (inch)

Venous line 1/2

Arterial pump line 3/8

Boot tubing 1/2

Arterial outlet line 3/8

Sucker & vent line 1/4

Cardiotomy line( connects CR to VR) 3/8

Quick prime line 3/8 or 1/4

Gas line( connects gas flow system, O2/air blender) to oxygenator

1/4

MANIFOLD SYSTEM

Three or four stop cock with tubing to connect arterial & venous sampling port.

Manifold system must be kept closed when not on bypass and prior to coming off bypass.

FILTERS:

Used in extracorporeal circuit for removal of microbubbles, microparticles & made of glass wool , dacron wool or polyurethane foam.

Blood filter: Arterial line filter( 20-40 micron), priming volume 150-250ml

Cardiotomy filter.

Filters for banked blood

Non-blood filters Pre-bypass filters- 5 micron

Gas filters- 0.2 micron

Cardioplegia filters-0.2 micron ( Crystalloid CP only)

Blood CP filters- for leukocyte depletion

FILTERS

FILTERS ( CONTD)

Screen filters- Filtration depends on

pore size, made of mesh material

( Dacron)

Depth filters- Glass wool, Dacron

wool or polyurethane foam through

which blood must pass.

Combination of two.

ARTERIAL CANNULA

Size of the cannula is selected by evaluating the flow and pressure drop chart. The accepted limit of pressure drop ( difference between pressure entering the cannula and that leaving) is 100mm Hg. Arterial cannula may be straight, curved-tip, metal or PVC-tipped, and may be for femoral cannulation, high arch cannulation etc.

Problems of arterial cannulation may be injury, dissection, air or atheromatous embolism, accidental selective cannulation, aneurysm formation etc.

ARTERIAL CANNULA

VENOUS CANNULA

Drainage may be by gravity or vacuum assisted venous drainage( VAVD)

Single stage- separate SVC & IVC cannula Two stage- IVC & RA drainage by one cannula Thin right angled metal cannula- for selective

SVC/ IVC cannulation Problems of venous cannulation include

injury, air locking, poor drainage, flooding of operation field, problems with PLSVC, post-operative bleeding

VENOUS CANNULA

CANNULA( CONTD)

Cardioplegia cannula Aortic root cannula Selective coronary cannula Retrograde cannula- automatic or manual balloon

inflation

Vent cannula Aortic root vent LV vent- through RSPV, RIPV, IAS, LV apex PA vent

CARDIOPLEGIC CANNULA

PURSE STRING & CANNULATION SITE

ARTERIAL CANNULA FLOW CHART: PRESSURE GRADIENT( MM HG)

Size inFrench scale

Flow ( L/ Min)

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

10 60 175 350

12 40 100 225 325

14 25 60 140 240 350

16 25 60 90 150 200 260

18 20 40 60 80 120 150 200

20 25 40 60 80 100 120

22 25 40 50 60 75 90

24 40 50 60 70 80

VENOUS CANNULAS FOR VARIOUS FLOWS

Total flow( L/Min)

Cannula size

Pacifico angled metal

≤ < Single tygon Single USCI Two Tygon TwoUSCI

SVC IVC

0.9 3/16” 20Fr 16Fr 16Fr 20Fr

0.9-1.75 4/16” 24Fr 3/16”

0.9-1.2 20Fr 20Fr 24Fr

1.2-1.6 22Fr 20Fr 24Fr

1.6-1.75 24Fr 24Fr 24Fr

1.7-2.2 4/16” 28Fr 4/16” 28Fr 24Fr 28Fr

2.2-2.8 5/16” 4/16” 30Fr 28Fr 28Fr

2.8-3.2 5/16” 5/16” 32Fr 28Fr 28Fr

3.2-3.7 6/16” 5/16” 34Fr 28Fr 32Fr

3.7 8/16” 6/16” 36Fr 32Fr 32Fr

SELECTION OF ARTERIAL CANNULA :

Size selected by evaluating the flow & Pr. drop chart.

Pr. Drop means difference between pressure entering the cannula & that leaving the cannula, accepted limit of Pr. Drop is 100 mm Hg .

@ BSA x 2 . 5 = Full flow ( at 37 degree Centigrade)

@ BSA X 2 .2 = Flow at 34 degree.

@ BSA X 1.8 = Flow at 28 degree.

BSA= √ Ht( cm) x Wt( kg) / 3600

PRIME :

To deair the oxygenator & partially fill up the circuitry, crystalloid or colloid is taken as prime volume, just before starting CPB.

Haemic Priming.

Non-Haemic Priming. e.g. Polycythemia, profound hypothermia with TCA.

Priming volume -20-30 ml/ Kg BW. Includes oxygenator priming volume+ filter volume+ tubing

volume

Cont.

COMPOSITION OF PRIMING VOLUME

Ringers solution 1000-1500ml

CPD blood 1-3 unit( Hct kept at 0.25-0.30)

Mannitol 20% 200-300ml

NaHCO3( 8.4%) 10ml/500ml CPD blood

Heparin for circuitry 5000 unit

Antibiotics

Heparin for blood 6unit/ ml of blood added

CaCl2( added last) 10ml/ unit of CPD blood

Albumin 25% To preserve COP

HAEMATOCRIT MANAGEMENT DURING CPB

Normal Hct - 0.4-0.5 at 37 degree ( ↑Hct ↑ viscosity) During CPB acceptable Hct- 0.25-0.30

** Mitochondrial PO2 ▬ 0.05-1 mm Hg, Intracellular PO2 ▬5mm Hg, PVO2▬ 40 mm Hg( SVO2 ▬75%), PAO2▬ 90-104 mmHg ( SAO2- 98%)

Pt. blood volume = body wt. In Kg X factor (80) = 60 x 80 =4800 ml.

Red cell volume = Pt’s B.V. x Hct .= 4800 x .36= 1728 ml.

Total circulatory volume = BV + Prime vol.=4800 + 1200 =6000ml.

Pt’s Hct = RBC Volume/TCV = 1728 /6000 =0.28 = 28 % .

HEPARINISATION:UAB PROTOCOL

• Baseline ACT

• Heparin administered at a dose 300 u/kg

• ACT checked prior to CPB to ensure> 480 sec

• On CPB, ACT is checked every 30 minutes, Heparin added (100 units/ kg) as required.

• Reversal of heparin 1 .5 mg protamine / 100 unit initial heparin dose.

• For infants, initial dose and heparin doses are added to pump prime

• ACT checked, if prolonged ACT tested with heparinase, more protamine added

HYPOTHERMIA :

Use of hypothermia in association with CPB which allow low perfusion flow rate because of reduced oxygen consumption.

Classification

Type Temp( degree centigrade)

TCA (min) at temp

Mild 37-32 10min at 32

Moderate 31-28 10-15min at 28

Deep 28-18 16-45 min at 18

Profound 18-0 46-60 min at <18

GAS/BLOOD FLOW RATE AT HYPOTHERMIA: BLOOD FLOW MUST BE KEPT GREATER THAN BLOOD FLOW RATE, OTHERWISE GAS EMBOLISM MAY OCCUR

Temp( degree centigrade)

Cardiac index FIO2 Gas/Blood flow ratio

37 2.4 L .80 1:1

34 2.2 L .70 .8:1

30 2.0 L .65 .7:1

28 1.8 L .60 .6:1

22 1.6 L .50 .5:1

18-20 1.0 L - -

0.5L/min/ Sq.M is adequate for 30-60 minutes

ACCEPTABLE DATA DURING CPB :

PH-- 7.4 .

Po2--- 100 - 250 mm Hg.

P co2--40 mmHg.

Glucose concentration of the prime < 350mg/dl

Perfusion Pr.-- 50-60 mm Hg.( If < 40 mm Hg

cerebral damage, If > 100 mm Hg -SVR raised so, microcirculation impaired.

Perfusion flow 2.2-2.5 l/m/m sq . are adequate. hypothermia allows lesser flow rate.

PRE BYPASS CHECK LIST

Gas lines connected Exhaust cap removed O2 source operable Water lines connected Water heater-cooler operable

& warming Oxygenator checked for

water leak before priming Arterial occlusion set on

roller head pumps Arterial filter primed Pressure transducer zeroed Stopcocks closed properly Luer connection tight Pump flow rates set

Sucker and vent in proper direction in housing Vent valve in proper direction Cardioplegia present with proper drug added Drugs in prime Bubble detector operable Level detector operable Back-up power present Temperature probes connected BSA & flows calculated

CHECK LIST DURING BYPASS

O2 flowing Arterial line pressure is not excessive Pump flow correct Patients arterial pressure acceptable Temperature of water-heater correct Coagulation status acceptable ACT> 480

secs

Bubble detector on Level detector on Urine in Foleys emptied, monitored during

case Manifolds open Required drugs given

MONITORING DURING BYPASS

Anaesthesiologist• ABG• PA pressure, PAWP, MVO2• BP• PETCO2

Surgeon• Observes distension of PA• Detects failure of venous

drainage• Manually confirms arterial

pressure• Observes aorta for dissection

Perfusionist• SaO2• SVO2• Hb%• Blood level in oxygenator

reservoirs• Coagulation status• S. Electrolytes • ABG

MYOCARDIAL PROTECTION

Mild to moderate hypothermia with cardioplegic arrest of heart

under CPB

Continuous or intermittent antegrade cardioplegia with

normothermic CPB in warm heart surgery .

Profound hypothermia ( <20degree centigrade ) with TCA

Intermittent cross clamping with CPB, 2 minutes release after

every 12 minutes X-clamp in fibrillating heart, no CP

Fibrillating heart with CPB, no X-clamp

Empty beating heart with CPB, no X-clamp

Inflow occlusion for short procedure e.g. PA valvutomy

Beating heart surgery (CABG)

CARDIOPLEGIA

Regime-1DBL (20 ml) 16mmol K+

16mmol Mg++

+ 2 ampoules KCl (20 ml) 40mmol K+

Each ml contains 56/40= 1.40 mmol K+/ml

6ml purge gives 6x1.40= 8.40mmol K+

150ml/hour (2.50ml /min) for 2 min, 5x1.40= 7.00mmol K+

Blood contain 4.50 mmol K+

Total 20.00mmol/L

CARDIOPLEGIA

Regime-23.5 ampoule KCl+ 1.5 ampoule MgSO4=

35ml+7.5ml=42.5ml

K+ concentration, 70/42.5= 1.64mmol/ml

5.50ml purge, 5.50X1.64= 9.02mmol K+

150ml/hr, 2.5ml/min, for 2 min, 5X1.64= 8.20mmol K+

Blood contains 4.50mmol K+

Total 21.72mmol K+

CARDIOPLEGIA

Routes of administration• Antegrade- aortic route/ selective

• Retrograde- coronary sinus (alternating and/or simultaneous)

• Combined

• Through anastomosed vein graft

Composition• Crystalloid CP

• Blood CP

• High K+(>20mmol K+/L) for induction

• Low K+(<10 mmol K+?L) for reperfusion

Timing• Intermittent

• Continuous

Temperature• Cold CP (4 degree C)

• Warm blood CP( Perfusate temp)

• Warm induction( ante or retrograde) warm reperfusion( low K+ plus substrate)

• Blood CP & Non cardioplegic cold blood reperfusion

Antegrade CPGiven at 70mm Hg pressure, 200ml/min, 15-20ml/kg BW, at 20 minutes interval

Retrograde CPGiven at 25-40mm Hg pressure, 100-200ml/min,15-20ml/kg BW

CP in children500XBSA / 1.5

Antegrade CP is less effective in severe multivessel disease and acute coronary occlusion

CP- COMPOSITION

K+ 15-30mmol/L Ca++ ≈ 0.5-1.0mmol/L Na+ ≈ 100-140mmol/L PH ≈ 7.6 Osmolality ≈ 380mosm Glucose>100mg/dl ± Red blood cell ± Magnesium Aspartame, Glutamate, GTN, Procaine/ Lidocaine,

energy enriching compound, Buffer-HCO3,TRIS,THAM,EDTA,

Blood, albumin, mannitol etc.

Newer additives for reperfusion Adenosine, lidoflazine, Myoflazine Free radical scavengers e.g.

SOD± catalase

SOD with polyethylene glycol

Desferoxamine

Glutathione

Ascorbic acid

Tocopherol

ACID BASE MANAGEMENT ( CPB ): Maintenance of physiological level of arterial Pco2

& Po2 ( 35-40 mm Hg & less than 200 mm Hg

respectively ) ought to be the goal during CPB . All perfused tissues , O2 needed for cell

metabolism & to remove CO2 ( produced by cell metabolism ) .

Metabolic acidosis occur during CPB due to poor tissue perfusion if arterial flow is low.

In metabolic acidosis , peripheral vasoconstriction may results.

So, correction of acidosis & alkalosis is essential on the basis of blood gas report during CPB .

EFFECT OF HYPOTHERMIA ON ACID-BASE BALANCE- ↑SOLUBILITY OF CO2,↑PH,↓PCO2

PH stat strategy

PH 7.4 and PCO2 40mm Hg should be maintained regardless of temperature.

PH is measured as if it is at 37 degree C, 5% CO2 is added to adjust PH to 7.4

Alpha stat strategy• PH is made alkaline, PCO2 is decreased at

hypothermia

• No CO2 is added• Refers to the fraction of unprotonated imidazole group

of histidine, this fraction stays constant as temperature decreases

WEANING : Deairing of heart is done before removal of X-clamp Volume is added gradually Inflow of blood is increased Outflow of blood is decreased Arterial BP is optimised CVP, LA pressure is optimised Patient is made normothermic Heparin is neutralized by protamine Haemodynamic stability is ensured by inotropes/

vasodilator/ pressors Rhythm and contractility optimised by

pharmacological means and pacing

PATHOPHYSIOLOGIC RESPONSE TO CPB

Catecholamine-Eph ↑ NE ↑ due to ↓pulm. blood flow Cortisol ↑↑ Renin-angiotensin-aldosterone ± T3 ↓ ANF ± Cytokines- IL1,IL6, IL8↑↑ Protease release ↑ Elastase ↑

Partial coagulation activation.

Compliment activation, mainly by alternate pathway

Arachidonic acid activation .

Fibrinolytic activation .

Kallikrein-bradykinin activation.

DAMAGING EFFECTS OF CPB :

Air embolism.

Bleeding disorder .

Constrictive pericarditis .

Infection.

Microembolism .

Mediastinal tamponade.

Cholecystitis

Intestinal ischemia/infarction

Cont.

Myocardial depression & LOS.

Neurological dysfunction .

Pancreatitis .

SIRS & MOF .

Pulmonary & Vascular injury .

Post cardiotomy syndrome

ISCHEMIA/ REPERFUSION INJURY

Myocardial consequences of global ischemia• Cell depolarization• Calcium loading• ATP hydrolysis• Acidosis• Potassium leakage• Sodium loading• Contracture

Reperfusion abnormalities• Cell swelling• Calcium loading• High energy phosphate precursor loss• Oxygen wasting• Free radical injury• Mitochondrial dysfunction