Anesthesia Machines

History of Anesthesia Machines

Early History (Mid-19th Century)

The development of anesthesia machines is deeply intertwined with the history of anesthesia itself, which started in the mid-1800s. The discovery of substances like ether, chloroform, and nitrous oxide that could produce reversible unconsciousness or analgesia marked the beginning of modern anesthesia practice. These early anesthetics were delivered in simple, rudimentary forms, often without adequate control or precision. Ether and chloroform were administered using soaked sponges or simple inhalers, with little to no control over the concentration or dose delivered to the patient.

Early Devices (Late 19th and Early 20th Century)

The development of more sophisticated anesthesia machines came about as the medical field began recognizing the need for precise delivery of anesthetic gases. One of the first major innovations was the invention of the Boyle’s Machine by British anesthetist Henry Boyle in 1917. The original Boyle machine consisted of flowmeters for gases, a vaporizer to deliver a volatile anesthetic, and a breathing circuit. Boyle’s design established the basic framework for modern anesthesia machines.

Mid-20th Century: Advancements in Gas Delivery and Safety

During the 1940s and 1950s, anesthesia machines became more sophisticated, with added features to improve patient safety. By this time, machines included devices for measuring and controlling gas flow and concentration, oxygen delivery, and mechanical ventilation. Key developments included:

• Endotracheal intubation techniques, which allowed anesthetists to protect the airway and deliver more precise concentrations of anesthetic gases.
• Mechanical Ventilators were incorporated into anesthesia machines to assist or control breathing during surgery.
• Absorber Systems to remove carbon dioxide from exhaled air, enabling rebreathing circuits that reduced the consumption of anesthetic gases.

Late 20th Century: Introduction of Electronics and Monitoring

In the 1970s and 1980s, anesthesia machines saw the introduction of electronic components, significantly improving the precision of gas delivery. Machines were now equipped with built-in monitors to display vital signs such as blood pressure, oxygen saturation, and exhaled carbon dioxide (capnography), allowing for better intraoperative monitoring and patient safety. The inclusion of alarms for low oxygen concentration or disconnections in the breathing circuit marked another leap in patient safety.

Modern Era: Computerized and Integrated Systems

In the 21st century, modern anesthesia machines have evolved into complex, computer-controlled systems. They are equipped with advanced ventilation modes, integrated monitoring, and automated safety checks. Modern machines can deliver precise combinations of gases, monitor patient physiology in real-time, and assist with or fully take over ventilation for the patient. They have also become highly modular, allowing anesthetists to customize the machine based on the specific needs of the surgery or patient.

How Anesthesia Machines Work

An anesthesia machine delivers a carefully controlled mixture of gases, including oxygen, anesthetic agents (either volatile liquids or gases), and sometimes nitrous oxide. This mixture maintains a patient in a state of unconsciousness or analgesia while ensuring that the patient’s vital functions (breathing, circulation) are supported.

Basic Principles

1. Gas Supply: The machine is connected to a central gas supply (oxygen, nitrous oxide, air) or uses gas cylinders.
2. Vaporizers: Liquid anesthetics are converted into a vapor to be mixed with the gases.
3. Breathing Circuit: The mixture is delivered to the patient through a breathing circuit, which allows controlled ventilation.
4. Carbon Dioxide Removal: Expired gases are scrubbed of CO2 and can be either rebreathed or expelled.
5. Ventilator: When patients are unable to breathe adequately, the machine can assist or control breathing via a mechanical ventilator.
6. Monitors and Alarms: Systems continuously monitor gas concentrations, airway pressures, and patient vitals to ensure safety.

Components of an Anesthesia Machine

1. Gas Supply:

• Oxygen: Delivered from a central supply in the hospital or from a cylinder.
• Nitrous Oxide: A commonly used anesthetic gas.
• Air: Used to dilute oxygen and nitrous oxide or as a carrier gas.

1. Flowmeters: These control the flow of each gas. Each gas has its own dedicated flowmeter, calibrated to ensure accurate delivery to the patient.
2. Vaporizers: These are critical components where liquid anesthetic agents (such as isoflurane, sevoflurane, or desflurane) are converted into vapor. Vaporizers are calibrated to deliver precise concentrations of the anesthetic agent into the gas mixture.
3. Breathing Circuit:

• Patient Breathing Circuit: Connects the machine to the patient. This includes the mask, endotracheal tube, and hoses.
• Rebreathing System: Recirculates gases through the use of an absorbent that removes CO2 (soda lime or similar compounds).
• Non-Rebreathing System: In this system, expired gases are not recirculated but are vented out.

1. Mechanical Ventilator:

• Bag-Valve Mask (BVM): For manual ventilation.
• Automatic Ventilator: Provides positive-pressure ventilation to the patient, with settings for rate, tidal volume, and inspiratory/expiratory ratios.

1. Oxygen Flush Valve: Delivers a high flow of 100% oxygen directly to the patient, bypassing the vaporizers. This is used in emergency situations to quickly oxygenate the patient.
2. Pressure Gauges and Regulators:

• Oxygen Pressure Gauge: Ensures that adequate oxygen pressure is being delivered.
• Cylinder Pressure Gauge: Shows the remaining gas in attached cylinders.

1. Absorber System (for CO2): These systems contain canisters of soda lime or barium hydroxide lime that absorb carbon dioxide from exhaled gases, allowing for rebreathing of anesthetic gases.
2. Scavenging System: Prevents anesthetic gases from escaping into the operating room environment. It collects excess gases and vents them outside or into a vacuum system.
3. Alarms and Monitoring:
   • Oxygen and Gas Concentration Monitors: Measure the concentration of oxygen, nitrous oxide, and anesthetic gases delivered.
   • Pressure Alarms: Indicate high or low pressures in the system.
   • Capnography: Monitors CO2 levels in the patient’s exhaled breath.
   • Pulse Oximetry and ECG: Non-invasive monitoring of patient oxygen levels and heart function.

Variations of Anesthesia Machines

1. Basic Machines: These machines are used for minor surgeries or settings with limited resources. They often have simpler, manual controls and fewer monitoring features.
2. Intermediate-Level Machines: These are used in most surgical settings. They feature electronic flowmeters, built-in vaporizers, and basic monitoring equipment.
3. High-End, Computerized Machines: Modern high-end machines are fully computerized, allowing for precise control of ventilation and gas delivery. They are often integrated with monitoring systems that provide real-time data on the patient’s physiological state.
4. Portable Anesthesia Machines: These are smaller, lightweight machines designed for transport, use in emergency settings, or field operations.
5. Specialty Anesthesia Machines:

• Pediatric Anesthesia Machines: Designed specifically for use in infants and children, with lower tidal volumes and more precise control of gas delivery.
• MRI-Compatible Machines: These are specially designed to function in the MRI environment without interference from or to the magnetic fields.

Clinical Use of Anesthesia Machines

Anesthesia machines are critical for ensuring safe and controlled sedation or unconsciousness during surgical procedures. Clinically, they are used to:

1. Induce and Maintain Anesthesia: Administering anesthetic gases or vapors, along with oxygen, to maintain the desired depth of anesthesia.
2. Provide Ventilatory Support: Assisting or completely controlling the patient’s breathing when they are under deep sedation or anesthesia.
3. Monitor Patient Vital Signs: Continuously monitoring vital parameters like oxygen saturation, CO2 levels, and airway pressures to ensure the patient remains stable throughout surgery.
4. Emergencies: Providing rapid oxygenation through oxygen flush valves or adjusting ventilation parameters when a patient’s respiratory function deteriorates.

Daily User Checks for Anesthesia Machines

1. Pre-use Check:

• Gas Supply Check: Ensure adequate supply of gases (O2, air, N2O) from either central lines or cylinders.
• Flowmeter Test: Ensure flowmeters are functioning and that gases are flowing appropriately.
• Vaporizer Test: Check that vaporizers are properly filled with anesthetic agents and are calibrated correctly.
• Breathing Circuit Check: Inspect the breathing circuit for leaks or damage, ensuring all connections are secure.
• Pressure and Leak Test: Perform a system leak test to ensure the integrity of the breathing circuit and machine components.

1. Alarm Systems: Verify that all alarms (O2, pressure, CO2) are functional and properly set.
2. Ventilator Function Check: Test the ventilator’s settings (rate, tidal volume, inspiratory/expiratory ratio) to ensure they meet the clinical needs of the patient.
3. Absorber Check: Confirm the CO2 absorbent is fresh and capable of removing CO2 from exhaled gases.

Preventative Maintenance Requirements

1. Regular Calibration: Ensure that all flowmeters, vaporizers, and ventilators are regularly calibrated by trained biomedical engineers.
2. Routine Cleaning: Disinfect and sterilize components of the breathing circuit and patient interfaces (masks, tubing) to prevent cross-contamination.
3. Absorber Canister Replacement: Replace the CO2 absorber granules when they are spent, typically indicated by a color change.
4. Oxygen Sensor Replacement: Periodically replace the O2 sensor to ensure accurate monitoring of oxygen levels.
5. Software Updates: For computerized systems, regularly update software to ensure optimal functionality and integration with monitoring systems.

Common Troubleshooting Steps

1. No Gas Flow:

• Check for disconnected or obstructed hoses.
• Verify gas cylinder contents and proper valve operation.

1. Low or Inconsistent Anesthetic Delivery:

• Ensure vaporizers are filled and correctly calibrated.
• Inspect the breathing circuit for leaks or blockages.

1. High Pressure Alarms:

• Check for kinks or obstructions in the breathing circuit.
• Ensure that the patient’s airway is not blocked.

1. Oxygen Supply Failure:

• Switch to a backup oxygen cylinder or use the oxygen flush valve if necessary.
• Check that oxygen pressure from the central supply is within the normal range.

1. Ventilator Malfunction:

• Manually ventilate the patient using the bag-valve mask (BVM) while troubleshooting or replacing the ventilator.

Manufacturers of Anesthesia Machines

• GE Healthcare: Offers the Aisys and Carestation lines, known for their advanced ventilator modes and integrated monitoring.
• Dräger: Provides the Primus and Zeus series, featuring high-end anesthesia systems with advanced safety features and ventilation modes.
• Mindray: Supplies the A-series anesthesia workstations with a focus on affordability and ease of use.
• Penlon: A manufacturer known for producing both high-end and portable anesthesia machines, especially the Prima series.
• Datex-Ohmeda: A subsidiary of GE Healthcare, well-known for its anesthesia machines with integrated monitoring and safety systems.

Typical Cost and Lifespan

• Cost: Basic anesthesia machines start at around $20,000, while high-end, computerized machines can cost $100,000 or more, depending on the features and integrated monitoring.
• Lifespan: Anesthesia machines have a typical lifespan of 7-15 years, depending on the frequency of use and maintenance. Proper preventative maintenance can extend the lifespan of these devices significantly.