Anesthesia Machine.

Introduction on Anesthesia

Anaesthesia is the process of giving anaesthetics (in the form of drugs or gases) to the patient to induce sleep or make them unconscious throughout the process of surgery. The main aim of giving anaesthesia is to prevent painful sensation for the patient while undergoing the surgery. An anesthesiologist (a person specially trained for giving anaesthesia) carries out this process. 

There are three types of anaesthesia:

• General Anaesthesia -The surgeon advises for general anaesthesia when performing major surgeries, which are time-consuming such as Open-heart surgery, Organ transplantation, knee replacement etc. An anaesthetic drug is delivered to the whole body, driving the patient unconscious and they cannot even move their body.

• Regional Anaesthesia – This is used while performing surgeries in any parts of the body like endoscopy, surgery in the arm or leg and during pregnancy. The patient will experience numbness in the larger operating part. During this process, the patient may be either awake or in a drowsy state.

• Local Anaesthesia – Smaller surgeries like removing a mole, cataract operation or any other stitches involve local anaesthesia. This is often used in dentistry. Only the smaller area felt numb. In this process, the patient is conscious and he/she is aware of what was happening throughout the surgery.

How Anaesthesia is given to a patient?

At first, an anesthesiologist monitors the condition of the patient and depending upon the surgery he gives anaesthesia to the patient. It is given either in the form of gas or drug. An anaesthetic drug is delivered to the patient through the intravenous (IV line). 

Gaseous forms of anaesthetics are given by mask or through a breathing catheter. During anaesthesia, other vital signs of the patient’s body are also monitored by the doctor. The process of giving anaesthesia is achieved with the help of an anaesthesia machine.

ANAESTHESIA MACHINE:

An anaesthesia machine is a medical equipment which is used for delivering anaesthetic drugs or gases to the patient before performing the surgery. This prevents the patient from feeling any pain during the surgery.

This apparatus is combined with a ventilator (a breathing unit) and assists the patient in respiration. It also helps the surgeons to monitor the vital signs with the help of a monitoring system. 

HISTORY OF ANESTHESIA MACHINE

• In the year 1911, Dr. Frederick J.Cotton & Dr.Walter Boothby developed a basic anaesthesia apparatus in the Boston city hospital. In this apparatus, ether is used as an anaesthetic vapour combined with nitrous oxide and oxygen gases. The flow rate is determined by passing the gaseous mixture in a glass bottle of water, which causes bubbles. Therefore, it is called a bubble bottle.

• Dr.William Cavan Woolsley and Dr.James Tayloe Gwathmey, anaesthetists in the New York City, invented nitrous oxide-oxygen apparatus in the year1912. These gases are mixed with ether to form an anaesthetic drug. Their invention replaced the bubble bottle with a flow meter.

• Using Gwathmey’s basic design, Dr. Henry Edmund Gaskin Boyle, a British anaesthetist developed his new machine with much more advancement in the year 1919. He included ether as well as chloroform as anaesthetic agents. He developed the machine with a pressure gauge, flow meter, and a breathing circuit. Therefore, anaesthesia workstation is otherwise called as Boyle’s machine.

FUNCTIONS OF ANESTHESIA MACHINE

The major function of an anaesthesia machine is to deliver gaseous mixture like (oxygen O2 & Nitrous oxide N2O ) along with anaesthetic agents in a controlled pressure. The anaesthetic agents used in anaesthesia machine are isoflurane, desflurane and sevoflurane. These agents are available in the form of a vapouriser. 

The combined mixture of gas then passes through the breathing circuit. The pressure of gas flow is regulated depending on the patient’s ability to breathe. This is done with the help of a flowmeter. In the operation theatre, gas supply to the machine is provided by the centralised distribution system(i.e pipeline) or by using oxygen cylinders.

MECHANISM OF WORKING

The mechanism of the anaesthesia machine is to deliver a mixture of gases to the patient in controlled amounts. The machine’s working principle is divided into two categories: - High-pressure system and Low-pressure system. 

• Starting from the gas supply, pressure regulation and up to the flow meter it is involved in a high pressure system. 
• The low-pressure circuit consists of vapourisation technique, Breathing circuit, Co2 absorbing system and scavenging system.

High-pressure system:

• Gas supply – In the operation theatre, there will be a centralised gas supply system available in pipelines. The machine is directly connected to these pipelines for receiving Nitrous oxide, oxygen and air. In other ways, wall-mounted cylinders are present. They also use separate cylinders for these gases. A pressure gauge is available in order to indicate the available amount of gas inside the cylinder. 

• Pressure regulator –This is used for converting the high pressure in the machine to lower and constant pressure. Gas is delivered to the machine at a pressure of about 50psi. It is then regulated to 45psi. While performing an operation, it is must to maintain constant pressure in the anaesthesia machine. 

• Fail-safe valve – In case of any pressure drop in the oxygen level, the fail-safe valve is used to reduce the flow of nitrous oxide and also reduces its pressure. An oxygen safety alarm is present if the pressure of oxygen falls below the safety level.

• Flowmeter – Flow meter is used for controlling and measuring the rate of flow of gas in the machine. A flow control valve controls the flow of gas. The flow control valve is otherwise called a pin valve or needle valve. The control knob is present in the flow meter for each gas. It has separate colour coding. For oxygen, it is represented by white colour and for Nitrous oxide, it is represented by blue colour.

Low-pressure system:

• Vapouriser – The anaesthetic agents are present in liquid form. The vapouriser coverts them into a vapourised form for delivering them in controlled amounts to the patient. There are two forms of anaesthetic drugs used. 
• Ether – Isoflurane, Sevoflurane
• Non-ether – Halothane, Chloroform (these are not in use in recent times, because they are very toxic.)
• Most commonly, ether forms of drugs are used in the anesthesia machine. Xenon is sometimes used, but this is costly. Through the common gas outlet, The gases and vapours are delivered to the breathing system of the patient.

• Breathing circuit –This circuit consists of a Co2 absorber, Adjustable Pressure Limiting (APL) valve, ventilation. The APL valve is used to control the pressure in the breathing system. This valve prevents the backflow of gases back into the vapouriser.

• Ventilator consists of a breathing bag or artificial lung. This does the exact operation of the lungs. The bag contracts and produces the gases to the patient through the breathing tube. Positive pressure from the breathing circuit passes back to the machine during controlled ventilation. This backflow of pressure is controlled by a unidirectional check valve. Rebreathing circuit is present in order to prevent positive or negative pressure in the machine.

• CO2 absorber – A canister is present in the carbon dioxide absorption system. It is the transparent glass cylinder consists of soda lime. The exhaled gases are collected in the absorber and is then passes through the gas outlet which is connected to the scavenging system.

• Scavenging system –The scavenging system absorbs the exhaust gases from the machine to prevent them from causing pollution. These gases are exhausted outside or absorbed by the absorbent materials like activated charcoal. The main aim of having a scavenging system is to reduce the exposure to waste gases. Because this may harm others in the operating room.

DISPLAY

A monitor is used in the display system. Vital signs of the patient are monitored using a patient monitoring system.

• Respiration rate
• Heart rate
• Blood pressure
• A pulse oximeter (oxygen saturation in the blood)
• Temperature
• EtCo2 (amount of Co2 exhaled)

SAFETY FEATURES IN ANESTHESIA MACHINE

• Colour coding of the cylinders
• Pressure gauges or pressure reducing valve
• Safety in the flow meter – Color coding, touch coding
• Vapouriser lock preventing leakage 
• Oxygen flush valve
• Soda-lime in Co2 absorber
• Enclosed tubings in the machine

EQUIPMENT MAINTENANCE

• Regular service should be done by the service engineers or trained personnel.
• Must follow the instructions provided by the manufacturer
• Flow transducers must be cleaned to avoid moisturiser
• O2 sensors should be cleaned
• Batteries must be replaced if needed
• Replace exhausted Co2 absorber, because exhausted soda lime does not absorb Co2 from the patient.
• Check whether the machine is power off after use.

TROUBLESHOOTING

• Check for leakages in any part of the machine-like flowmeter, vapourises, tubings and valve.
• Check the Co2 absorber if it is exhausted or not
• Check pressure gauges from the pipeline/cylinder
• Check whether oxygen supply is on.
• Inspect functioning of the ventilator
• Check whether all connections are made

CALIBRATIONS

• Clean the O2 sensor and pressure valves
• Clean and calibrate the vaporisers
• Check other safety devices like a fail-safe valve, Oxygen failure alarm.

👉 Please Watch Our Anesthesia Machine Videos from Our YouTube Channel Below:-

REFERENCE

• Anesthesia https://www.mayoclinic.org/tests-procedures/anesthesia/about/pac-20384568
• https://www.webmd.com/a-to-z-guides/what-is-general-anesthesia#1
• Types of Anesthesia https://www.medicalnewstoday.com/articles/265592#types
• Delivering anaesthesia to patient https://www.nigms.nih.gov/education/pages/factsheet_anesthesia.aspx
• https://www.shutterstock.com/video/clip-11151038-hand-patient-under-anesthesia-during-surgery
• Anaesthesia machine https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3821260/
• https://www.indiamart.com/proddetail/advanced-anesthesia-workstation-machine-9829976233.html
• History of Anesthesia machine https://www.woodlibrarymuseum.org/museum/item/76/cotton-boothby-apparatus
• https://www.woodlibrarymuseum.org/museum/item/78/gwathmey-&-woolsey-apparatus
• https://anaesthesianews.wordpress.com/2018/02/09/anaesthesia-machine-history-and-evolution/
• https://twitter.com/storiamedicina/status/1054369475863158784
• Anaesthesia machine functions https://www.slideshare.net/meckelbt/vets-238-anesthetic-equipment-final
• https://moodle.digital-campus.org/mod/page/view.php?id=34913.
• Working of anaesthesia machine https://www.researchgate.net/publication/258703083_The_Modern_Integrated_Anaesthesia_Workstation
• Pressure systems https://www.slideshare.net/imran80/anaesthesia-machine
• Circuit diagram https://www.apsf.org/article/the-low-pressure-alarm-condition-safety-considerations-and-the-anesthesiologists-response/
• Components and their working https://slideplayer.com/slide/10525204/
• Flowmeter https://www.slideshare.net/swadheenrout/low-pressure-system-in-anaesthesia-machine
• Display system https://zonemedical.com.au/patient-monitoring/patient-monitors/northern-anesthesia-patient-monitor-virgo/
• Maintenance and calibration https://aneskey.com/anesthesia-machine-operation-maintenance-and-troubleshooting/

Article Written By:-

👉Sumitha Ramadass