What are the Parts of an Anesthesia Machine?

The most commonly used anesthesia apparatus is a continuous flow anesthesia machine. These machines regulate the mixture of medical gases, such as oxygen and nitrous oxide, with a precise dosage of anesthetic gas. Modern versions also have additional equipment for monitoring the vital signs of patients. Overall, the machines are a complex collection of parts, each designed to perform a very specific function.

Function

• The machine connects to outlets in the hospital wall which supply oxygen, air and nitrous oxide. Nitrous oxide makes an excellent carrier gas for stronger anesthetics. The gases enter the machine at a pressure of around 60 PSI. The ratio of nitrous oxide to oxygen put out by the anesthesia machine is usually 2-to-1.

  Devices called vaporizers convert the anesthetic agents to vapor and inject them into the outgoing air supply. This air supply is mechanically pumped to the patient using a device called a ventilator. The ventilator attaches to a face mask via hoses called breathing circuits. The face mask forms a seal around the patient's face to ensure that all of the gases get to the patient and do not escape into the air, where they may affect the medical staff.

Controls

• The anesthesiologist needs precise control over the mixture in order to ensure that a patient remains properly sedated and numbed during an operation. He can monitor vital signs and adjust the mixture in real time using regulators to independently adjust the flow of oxygen and nitrous oxide. Separate controls on the vaporizers allow the specialist to increase or decrease the amount of each anesthetic agent that makes it into the final mix.

Redundancy

• There are backup cylinders on the machine in case there is a malfunction with the hospital's supply lines. While the machine is in use the cylinders are turned on with the regulator set at around 45 PSI. Since the main lines are set at a higher pressure, the machine draws the gas from them as long as they are functioning properly. If the supply from the main lines is weakened or cut off entirely the reserve cylinders provide the gas without any interruption to the patient's supply.

Safety Features

• A patient waking up in the middle of an operation, or suddenly becoming sensitive to pain, can be disastrous. For this reason there are several safety mechanisms in place on modern anesthesia machines.

  Since high pressure gases can cause damage to the machine, or worse, the patient, all incoming gas lines contain pop-off valves. Pop-off valves are specialized valves that vent the gas if it reaches dangerous levels of pressure.

  Medical staff being exposed to anesthetic while performing surgery can spell disaster. Manufacturers are aware of this, so in addition to the seal formed by the face mask a scavenging system collects and disposes of expired gases so that they do not get into the operating room.

Other Types

• In addition to the continuous flow units used in hospitals, there are other anesthesia machines used for specialized purposes. One such machine is used on the battlefield where surgeons may have to perform emergency surgery. These portable machines are self contained, carrying their own oxygen and nitrous oxide tanks. Portable machines lack some of the sophistication of their bigger brothers. They have less backup systems in place and lack scavenging systems.