This document discusses extracorporeal circulation, specifically cardiopulmonary bypass (CPB) used during open heart surgery. It describes the basic CPB circuit including components like the venous cannula, reservoir, pump, heat exchanger, oxygenator, and arterial cannula. It outlines the steps of CPB including priming, anticoagulation, cannulation, initiating bypass, maintenance on bypass, weaning from bypass, and potential complications. CPB temporarily takes over the functions of the heart and lungs to provide a still, bloodless field for cardiac surgery using mechanical devices placed outside the body.

1. Extra corporeal circulation
Dr. Arati Mohan Badgandi

2. Introduction
• A procedure in which blood is taken from a
patient's circulation to have a process
applied to it before it is returned to the
circulation
• All of the apparatus carrying the blood
outside the body is termed extracorporeal
circuit

3. Extra corporeal circulation
• Hemodialysis
• Hemofiltration
• Plasmapheresis
• Extracorporeal membrane oxygenation
(ECMO)
• Cardiopulmonary bypass during open
heart surgery

4. CPB
CPB

5. Introduction
• CPB involves the temporary substitution of
the functions of the heart and lungs with
mechanical devices, placed outside the
human body
• Dr. John gibbon - Performed first
successful intracardiac operation with the
aid of heart lung machine in 1953

6. Goals of CPB
• To provide a stilled bloodless heart with
blood flow temporarily diverted to an extra
corporeal circuit that functionally replaces
the heart and lungs
• Respiration
– Ventilation
– Oxygenation
• Circulation
• Temperature regulation

7. Indications
• Surgical correction of congenital, ischemic or
valvular heart diseases
• Coronary artery bypass
• Valve replacement
• Correction of septal defects
• Advances of CPB technology have been
utilized in the development of other complex
medical devices like
– Artificial hearts
– ECMO
– Ventricular assist devices

8. Basic CPB Circuit

9. CPB Circuit in Real Setting

10. Venous Cannulas

11. Venous cannulae
• These drain blood from the
patient into the CPB circuit
• One or two cannulae are
used, depending on the type
of cardiac surgical
procedure or surgeons
preference
• These drain the blood by
gravity

12. Venous Reservoir

13. Blood reservoir
• This stores the blood
• It can be of two types
• Venous reservoir - collects the blood drained
from the patient
• Arterial reservoir – collects the oxygenated
blood coming from the oxygenator

14. Pump

15. Pump
• These are the devices, which are used to
generate the pressure required to return the
perfusate to the patient
• These are driven by electrical motors
• There are two types
– Roller pump
– Centrifugal pump

16. Heat Exchanger

17. Heat exchanger
• It adjusts the temperature of the perfusate to
provide moderate systemic hypothermia
during the period of cardiac repair and
gradually rewarms the blood during the
discontinuation of CPB
• Water circulates within the heat exchanger in
a counter current fashion to the flow of blood
at temperatures between 1-2°C and 42°C
• The temperature gradient between the water
and blood is kept at 10°C or less

18. Oxygenator

19. Oxygenators
• It is an apparatus where O2 and Co2
exchange takes place
• There are two types
– Bubble oxygenator
– Membrane oxygenator

20. Bubble oxygenator
• This type of oxygenator is used when CPB is
needed for less than 2hours
• In this, O2 is directly infused into a column of
systemic venous blood through a diffusion
plate
• The diffusion plate produces thousands of
small O2 bubbles within the blood
• Gas exchange occurs across a thin film at the
blood gas interface around each bubble
• Co2 diffuses into the bubble and O2 diffuses
into the plasma

21. Membrane oxygenator
• This type of oxygenator is used when CPB is
needed for more than 2-3 hours
• In this type of oxygenator, gas doesn’t come
in direct contact with the blood
• A membrane, made up of silicon rubber or
polypropylene or Teflon, separates blood and
gas compartments
• Blood is made to flow in small streams
(hollow fibers) or thin sheets over the
membrane
• CO2 diffuses outwards and O2 diffuses into
the blood

22. Filters

23. Filters
• These are designed to trap particulate
matter and gaseous emboli
• In the suction line - Prevents the debris
from the operating site from reaching the
oxygenator
• Arterial filter - This removes the emboli
from the blood in the arterial tubing prior to
entering the body
• Venous filler - Remove the particulate
matter from the cardiotomy suction
devices

24. Filters

25. Filters

26. Aortic cannulas

27. Arterial cannulae
• These cannulae return the blood from the
CPB circuit to the patient
• Commonly ascending aorta is the site for
arterial cannulation

28. Priming
• The composition of the fluid used for priming, varies
according to the preference of institutions
• But its composition should be close to that of ECF
• The volume depends upon the capacity of the CPB
circuit
• The prime for most adult perfusions contains, a
balanced salt solution
• Individual recipes add
– Albumin
– Mannitol
– Heparin
– Bicarbonate
– Calcium

29. Conduct of CPB
• Various steps associated with conduct of
CPB
1. Pre bypass preparations
2. Initiating CPB
3. Maintenance of extracorporeal circulation
4. Weaning from CPB

30. Pre by pass preparations
• The heart lung machine should be partially
assembled 45-60min before bypass is
scheduled to begin
• The system is primed with priming solution
and recirculated for several minutes
through a sterile 0.5u filter to remove all air
bubbles and particulate emboli from
system
• The patient positioned in trendlenberg
position & anesthesia induced
• The surgeon prepares the sites for arterial
and venous cannulation

31. Anticoagulation
• As bypass circuits are thrombogenic,
appropriate systemic anticoagulation is a
must before initiating bypass
• Heparin 300-400Ukg-1 or 2-3 mg/kg given
into the central vein / directly into the right
atrium
• Activated clotting time is measured 2-
5minutes later and additional heparin
given as required
• Supplemental dose of heparin given every
hourly at the dose of 1/3 of initial dose

32. Cannulation
• After full heparinization, cannula’s are placed
• Arterial cannula is usually placed first
because, it is technically more difficult to do
& after placement, perfusionist can give
additional volume via arterial cannula to
support the patients BP
• The ascending aorta is most often used
• Reduction of systemic BP to 90-100mm Hg
systolic facilitates placement of aortic
cannula

33. Cannulation
• The anesthesiologist should palpate both
carotids to confirm cannula is not
obstructing right-sided carotid blood flow
• Once the surgeon, perfusionist &
anesthesiologist are satisfied with
functioning & placement of arterial line,
venous cannula is then placed

34. Initiating CPB
• Bypass begins when surgeon unclamps
venous lines & blood begins to enter
extracorporeal circuit
• As blood starts to fill up venous reservoir of
oxygenator, arterial pump is turned on
• The perfusionist gradually increases bypass
flow rates until all systemic perfusion is
machine generated
• Left ventricular vent introduced through right
superior pulmonary vein & tapes around SVC
& IVC are tightened

35. Initiating CPB
• Once machine is at full flow, all venous
blood is bypassing cardiopulmonary
circulation
• Ventilation at this point is discontinued
• Once circulation begins, aorta is cross-
clamped & cardioplegic myocardial
protection given before surgical correction
is undertaken

36. Maintenance of bypass
• The primary goal of this period is to obtain
desired levels of hypothermia, maintain
adequate systemic perfusion, tissue
oxygenation & manage arterial blood
gases
• Ischemic depletion of high energy
phosphate compounds & accumulation of
intracellular calcium, depletes the energy
stores of myocardium

37. Maintenance of bypass
• To maintain normal myocardial cellular
integrity and function during CPB, the
available high energy phosphate
compounds have to be spared
• This is accomplished by
– Hypothermia
– Cardioplegia
– Intermittent periods of myocardial perfusion

38. Hypothermia
• Hypothermia of 20-30°C is routinely used
for CPB
• O2 consumption is reduced 5-7% per
degree centrigrade decrease in
temperature
• 10°C drop in temperature will halve the
BMR

39. Cardioplegia
• A number of different solutions are
described
• Most common compounds are
– Potassium = 15-40 meq/l
– Sodium = 100-120 meq/l
– Chloride = 110-120 meq/l
– Calcium = 0.7 meq/l
– Magnesium = 15 meq/l
– Glucose = 28mmol/l
– Bicarbonate = 27mmol/l

40. Cardioplegia
• 14G needle is inserted into the aortic root
below cross clamp
• 1 litre of cold (0-40C) cardioplegic solution
is rapidly infused through needle
• In presence of aortic incompetence, the
infusion is done directly through cannulae
inserted into each coronary osteum

41. Mechanism of action
Increased extracellular potassium
↓
Decrease in transmembrane potential
↓
Impairment of Na+ transport
↓
Abolition of action potential generation
↓
Cardiac arrest in diastole

42. Intermittent periods of myocardial perfusion
• Intermittent arotic cross clamping
• Intermittent coronary perfusion with
arterialized blood from heart – lung
machine via 2 small cannulae inserted into
coronary ostia
• Alternating ventricular fibrillation with
defibrillation to allow heart to beat
intermittently

43. Blood gas management
• Acid base management during CPB is
done by two methods
– Alpha stat method
– pH stat method

44. Alpha stat method
• It considers alkaline pH seen during CPB
is physiological (increased solubility of
carbon dioxide seen during hypothermia
raises pH)
• Hence no additional measures to correct
pH/Pco2 levels is undertaken
• This is more commonly used method & it
appears to preserve cerebral
autoregulation & improve myocardial
preservation

45. pH stat method
• In this, pH & Pco2 are maintained at
normal values regardless of body
temperature
• In order to maintain Pco2, Co2 is added to
ventilating gas mixture
• This method is not preferred because
patients tend to have higher CBF because
of increase in Co2 content and there will
be loss of cerebral autoregulation

46. Blood pressure & flow rate management
• A 50 —60 ml/kg of flow rate maintains mean
arterial pressure at 40- 60 mmHg
• To preserve CNS function MAP should be
maintained >50mmHg
• As the patient is rewarmed, MAP should also
be increased accordingly, to ensure adequate
CBF
• Renal function is maintained with pump flows
of more than1.6L/min

47. Rewarming
• When the surgeon begins last phase of
procedure,perfusionist begins to rewarm
patient
• The rewarming should be gradual & is done
over a 30 minute period
• A gradient of I0°c is maintained between
patient & perfusate to prevent formation of
gas bubbles due to their increased solubility
as blood gets warmed
• Anaesthesiologist should ensure amnesia of
patient by administering additional doses of
benzodiazepines

48. Rewarming
• Upon completion of the surgical repair, any
residual air in ventricles to be removed
• The anaesthesiologist vigorously inflates
lungs to remove air from pulmonary veins
& aids in filling of cardiac chambers
• TEE assesses the effectiveness of
deairing process
• The aortic clamp removed to resume
myocardial perfusion
• The heart is defibrillated & allowed to beat
empty

49. Weaning from CPB
• Ensure that patients are rewarmed
adequately & myocardial contractility rhythms
are acceptable
• If necessary, heart rate & rhythm can be
regulated either pharmacologically or
electrically with appropriate pacing
• Ventilation begun with 100%-O2
• Venous drainage lines are gradually
occluded, allowing, arterial return to
progressively raise the circulating volume
• Venous cannulas are removed following a
satisfactory interval of stable hemodynamic
functions

50. Weaning from CPB
• Reversal of anticoagulation done with
protamine
• Dose - 1 to 1.3ml (10mg/ml) for every
1000U of heparin or dose is calculated
based on the heparin dose response curve
• Arterial cannulas remain in place for
continued transfusion of pump contents
• When this is completed & bleeding is
controlled, arterial cannula is removed &
chest is closed

51. Post bypass period
• Patient should be shifted to the ICU, kept on
mechanical ventilatory support
• He should be continuously monitored for his
haemodynamic stability & cardiac electrical activity
• SBP should be maintained at 90-110mmHg, HR -
70-80bpm & Hct kept at 25-30%.
• Hypertension may be due to pain & should be
treated with analgesics & sedatives
• Extubation considered when muscle paralysis has
been worn off and patient is hemodynamically
stable
• Most patients can be extubated by following
morning

52. Complications
Physiologic
• CNS - Intracranial Haemorrhage (14%),
bleeding,seizures
• Respiratory - Pulmonary oedema, pulmonary
haemorrhage
• CVS - hypo/hypervolemia leading to hypo/HTN
• Alteration in R-Angiotensin – aldosterone cycle,
secondary to the non pulsatile perfusion, may lead to
Renal complications
• Haematologic - Anaemia,
leucopenia,thrombocytopenia (because of
consumption in membrane oxygenator)
• Infections

53. Complications
• Mechanical
• Failure of pump
• Rupture of tubing
• Failure of the membrane
• Difficulties with cannulas