Automation in Heart-Lung Machine

Prepared by:-Makwana Hiren J.

Shah Manthan M.

Introduction

The Heart-lung machine is a device which is used to provide blood circulation and oxygenation while the heart is stopped during the open heart surgery.

Heart-lung machine consists of three main functional units, the pump, the oxygenator and heat exchanger.

To function, the heart-lung machine must be connected to the patient in a way that allows blood to be removed, processed, and returned to the body.

HistoryThe researchers searched mainly for a means to

provide oxygenated blood to organ preparations. They filtered the blood through various screens and membranes and even pumped it through the lungs of dogs or monkeys, but their problem was not to be solved, though this may be considered the beginning of research into a heart-lung device.

The first successful open heart procedure on a human utilizing the heart lung machine was performed by John Gibbon in 1953. He repaired an atrial septal defect in an 18-year-old woman.

Purpose of Heart-lung machine:-

The heart-lung machine provides the benefit of a motionless heart during open heart surgery.

The heart-lung machine is valuable during this time since the patient is unable to maintain blood flow to the lungs or the body.

Surgical procedures in which Heart-lung machine is used:-

Coronary artery bypasses surgery.Cardiac valve repair and/or replacement

(aortic valve, mitral valve, tricuspid valve, pulmonic valve)

Repair of large septum defects (atrial septum defect, ventricular septum defect, atrioventricular septum defect)

Transplantation (heart transplantation, lung transplantation, heart–lung transplantation)

Implantation of heart.

Block diagram:-

Components of Heart-lung Machine:-

CardioplegiaCannulaBlood reservoirHeparin PumpRoller pumps/Centrifugal pumpOxygenatorsHeat Exchanger

Cardioplegia

Heart-lung machine circuit consists of a separate circuit for infusing a solution into the heart itself to produce cardioplegia to stop the heart from beating, and to provide myocardial protection (to prevent death of heart tissue).

Cannula

A venous cannula removes oxygen deprived blood from a patient's body. An arterial cannula is sewn into a patient's body and is used to infuse oxygen-rich blood.

A cardioplegia cannula is sewn into the heart to deliver a cardioplegia solution to cause the heart to stop beating

Blood reservoir

The blood reservoir serves as a receiving chamber for venous return, facilitates a venous bubble trap, provides a convenient place to add drugs, fluids, or blood, and adds storage capacity for the perfusion system.

Reservoirs may be rigid (hard) plastic or soft, collapsible plastic bags.

Heparin Pump

Once using a heart-lung machine during open-heart surgery, A powerful anticoagulant, Heparin should be given to the patient in order to reduce the blood's ability to clot, reducing the risk of clots forming in the heart-lung machine.

Pumping system

1. Roller pumps Roller pumps compress a segment of the blood

filled tubing. Blood is then pushed ahead of the moving roller.

Roller pumps consist tubing, which is compressed by two rollers 180° apart. Forward flow is generated by roller compression and flow rate depends upon the diameter of the tubing, rate of rotation.

Excessive compression of the tubing in a roller pump increases the risk of hemolysis.

Conti

Fig: Diagrams of blood pumps. (A) Roller pumps with two rollers, 180 degrees apart. The compression of the rollers against the raceway is adjustable. Blood is propelled in the direction of rotation. (B) The impeller pump uses vanes mounted on a rotating central shaft. (C) The centrifugal pump uses three rapidly rotated, concentric cones to propel blood forward by centrifugal force

2 Centrifugal pump

Centrifugal pump have replaced roller pumps at many institutions; mainly because they cannot over pressurize the heart-lung machine system.

It consists of smooth plastic cones, which when rotated rapidly, propel blood by centrifugal force. An arterial flow meter is required to determine forward blood flow, which varies with the speed

of rotation and the after load of the arterial line.

Oxygenators Oxygenators not only supply vital oxygen for

the blood, but also transport carbon dioxide, anaesthetics and other gases into and out of the circulation.

There are three types of oxygenator

1. Membrane oxygenators2. Bubble oxygenator

3. Film oxygenator

1.Membrane oxygenators Membrane oxygenators imitate the natural lung by a thin

membrane of either micro porous polypropylene or silicone rubber between the gas and blood phases.

Diagram of a hollow fiber membrane oxygenator and heat exchanger unit. Oxygen enters one end of the bundles of hollow fibers and exits at the opposite end. The hollow fiber bundles are potted at each end to separate the blood and gas compartments. Oxygen and carbon dioxide diffuse in opposite directions across the aggregate large surface of the hollow fibers.

2.Bubble oxygenator

In bubble oxygenators, venous blood drains directly

into a chamber into which oxygen is infused through a

diffusion plate. The diffusion plate produces

thousands of small oxygen bubbles within blood. Gas

exchange occurs across a thin film at the blood-gas

interface around each bubble. Carbon dioxide diffuses

into the bubble and oxygen diffuses outward into

blood.

Heat ExchangerControl body temperature by heating or cooling blood passing through the perfusion circuit.In heat exchanger, blood flows through

spiralling coils made of stainless steel. The inner walls of the coils are coated with polymers to limit blood-surface interactions. The circulating water is chilled to nearly 0 0C in an ice bath and heated by an electric resistance coil to an absolute maximum of 42 0C.

Stopping of Heart-lung machine

Once operation is completed, The surgeon

gradually occludes the arterial pressure and

pulse, and central venous pressure are monitored and adjusted. When cardiac performance is satisfactory and stable, protamine is given to reverse cardioplegia and blood return from the surgical field is discontinued.

ComplicationsHaemolysisCapillary leak syndromeClotting of blood in the circuit – can block the

circuit or send a clot into the patient.Air embolismLeakage – lose blood perfusion of tissue if a line

becomes disconnected.1.5% of patients that undergo Heart-lung machine

are at risk of developing Acute Respiratory Distress Syndrome.

Why Automation in the Heart-lung Machine needed?

During open heart surgery, Per fusionists take care of the connection procedures and maintain the performance of machine as per requirement at the time of surgeries; sometimes there occur faults due to carelessness. To overcome that Automation of Heart-Lung machine is a need.

During surgery, Pressure in the arterial line is monitored continuously to instantly detect any increased resistance to arterial inflow into the

patient.

Computerized CPB SystemThe computerized CPB system consists of an

80286 microcomputer. a reservoir blood level sensor, a collapse sensor, and temperature sensor.

Safety mechanismsThe computer regularly verifies all samples with

their prior values and detects not only artifacts but also hardware failures.

On detecting the improper sensor output, the computer maintains both the flow rates constant and displays a warning message with estimated locations of the trouble.

The pump rotation speeds are also monitored and matched with the computer's command.

In case the computer breaks down, a perfusionist can take over the pump control by turning an automatic/manual switch to the manual mode.