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Evolution of the modern anesthetic machine

The evolution of the modern anesthetic machine has been driven by safety standards. Anesthetists can quickly learn to use these different machines because of such standardization. The current diversity in standards among various countries has prevented the international distribution of a single anesthesia workstation. Even as computer-controlled systems have become more common, anesthetists should be familiar with the basic concepts that underlie the subsystems of the modern anesthetic machine. Here are the basic standard features of an anesthesia unit.

Anesthesia workstation
Devices that continuously or intermittently administer a mixture of gases (e.g., O,2, N2O, vapor of a volatile liquid halogenated hydrocarbon); also designed to facilitate spontaneous, controlled, or assisted ventilation.

An anesthesia unit
Typically comprise of four basic subunits – a gas supply and control circuit, breathing and ventilation circuit, scavenging system for exhaled gases, and set of function and breathing circuit monitors.

Technical characteristics
Flow management – should be compact, ergonomic and easy to use. Multicolor TFT display with virtual meters for O2, N2O, or air. Dual flow sensing capability at inhalation and exhalation ports. Should have backup O2 control, which provides an independent fresh gas source and flow-meter control in case of electronic failure. Flow-control valves shall be of modular design/graphic display. Pipeline connections should have diameter-indexed safety systems (DISSs) or some other means of preventing connection of dangerous gases. The system should permit connection of at least two yokes, one dedicated to O2 cylinder to meet clinical needs during failure of pipeline supply. All cylinder yokes (regardless of the gas for which they are intended) should include pin-index safety systems to prevent connection of dangerous gases. Hypoxic guard to ensure minimum 25 percent O2 across all O2–N2O mixtures and oxygen-failure warning.

Breathing system
Latex-free fully autoclavable/disposable with minimal flow of 250 mL of O2. Sensor should not require daily maintenance. The bag to vent switch shall be stable and automatically begins mechanical ventilation in the ventilator position. Adjustable pressure-limiting valve shall be flow- and pressure-compensated.

Provision to mount following selectable vaporizers, such as desflurane, halothane, isoflurane, and sevoflurane with interlocking facility to allow use of only one vaporizer at a time.

The workstation should have integrated anesthesia ventilator system with following ventilation modes – manual/spontaneous, VCV, PCV, SIMV or pressure support, advanced modes.

Anesthesia monitoring specifications
Monitoring of vitals – ECG, NIBP, SPO2, and invasive BP. Twin temperature measurement with skin and core temperature probes. Automatic identification and measurement of anesthetic agents EtCO2, O2, N2O, MAC value, and FiO2. Facility to store snapshots during critical events of waveform for review at a later stage. Audio-visual and graded alarming system.

Standards and safety
Sterilization not required.

Should provide two sets (hard copy and soft copy) of user, technical, and maintenance manuals in English/Hindi/regional language, along with machine diagrams; list of equipment and procedures required for local calibration and routine maintenance; service support contact details of manufacturer, supplier, and local service agent to be provided.

It is vital that any clinician checking and using an anesthetic machine is familiar with the type of machine and possesses detailed knowledge of how it operates.

Pre-use checklists, regular inspections, and maintenance can help reduce hazard.

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