FEATURES INTENDED TO PREVENT HUMAN ERROR

FEATURES INTENDED TO PREVENT HUMAN ERROR

·        The medical gas pin index and diameter index safety systems ensure that medical gas connections are made correctly.

·        Therefore, one cannot hang a nitrous oxide cylinder in an oxygen hanger yoke or connect a nitrous oxide hose to the oxygen pipeline inlet of the machine.

·        The “fail-safe” valve is a pressure-sensitive device that interrupts flow of all hypoxic gases on the machine to their flow control valves if the supply pressure of oxygen in the intermediate-pressure system (i.e., components downstream of the first stage oxygen regulator that reduces the high pressure in the tank to 45 pounds per square inch gauge [psig] and upstream of the oxygen flow control needle valve) falls below a threshold (˜20 psig in GE machines; 12 psig in Dräger machines).

·        When the pressure of oxygen in the intermediate-pressure system falls below 30 psig, an oxygen supply pressure failure alarm is annunciated.

·        The oxygen flow control knob is “touch coded”; that is, it is fluted and larger in diameter than the other gas flow control knobs and is normally located on the right of all other gas flow control valves.

·        In the Dräger Fabius GS workstation, the gas flow controls are arranged vertically, with the oxygen flow control knob as the lowest.

·        Key-fill systems for anesthesia vaporizers are safety features that also decrease the likelihood of atmospheric contamination during vaporizer filling.

·        The most important of such systems is the Safe-T-Fill system used on desflurane bottles and desflurane vaporizers because filling a vaporizer specific for another agent with desflurane could result in a lethal overdose of desflurane.

·        A pressure relief valve built into the machine common gas outlet, breathing system, or ventilator provides some protection against positive pressure barotrauma.

FEATURES TO CORRECT FOR USE ERROR

·        Gas flow proportioning systems ensure a minimum oxygen concentration of 25% when nitrous oxide and oxygen are being used.

·        Therefore, if the anesthesiologist were to accidentally attempt to increase the flow of nitrous oxide, either the oxygen flow would be increased automatically or the flow of nitrous oxide would be limited according to the flow of oxygen that was set.

·        On older machines, during use of the anesthesia ventilator, changes in fresh gas flow, inspiratory-expiratory (I:E) ratio, or respiratory rate cause changes in delivered tidal volume that might result in overventilation, underventilation, or even barotrauma.

·        On modern systems (e.g., GE workstations that incorporate a ventilator with the Smart Vent feature, Dräger Fabius GS, and Apollo workstations), once the ventilation parameters have been set, they are maintained because the ventilator or circuit automatically compensates for changes in gas flow settings.

·        In the GE workstations with Smart Vent, tidal volume is monitored continually by a computer.

·        If measured tidal volume changes from that set to be delivered, the computer adjusts the volume delivered by the ventilator bellows.

·        Dräger and Datascope Anestar workstations use fresh gas decoupling to maintain a constant tidal volume.

·        In this system, during the inspiratory phase, a decoupling valve closes so that fresh gas entering the breathing system is directed into the reservoir bag and only gas from the ventilator is delivered to the patient.

·        During exhalation, the ventilator chamber refills from the fresh gas flow and the fresh gas that was collected in the reservoir bag during the previous inspiration.

·        A vaporizer interlock system prevents the unintentional simultaneous use of more than one vaporizer.

MONITORING SYSTEMS

·        A monitor of oxygen in the gas delivered to the patient is mandatorily enabled, and the low oxygen concentration alarm is

activated whenever the anesthesia workstation is capable of delivering an anesthetic gas mixture from the common gas

outlet.

Other monitors in the anesthesia workstation include pressure, volume, flow, and gas composition. Some also incorporate

airway gas flow monitoring. The breathing system lowpressure monitor alarm is automatically enabled when the ventilator

is turned on.

ALARM SYSTEMS

Contemporary workstations incorporate an integrated prioritized alarm system with visible and audible alerts when set

parameter limits are exceeded.

An important safety feature of all modern machines/workstations is the preuse checkout. In 1993, the U.S. Food and Drug

Administration (FDA) published anesthesia apparatus checkout recommendations. The machine should be checked by

an educated user. Item no. 1 on the FDA checklist is that an alternative means to ventilate the patient's lungs should be

present and functioning. Therefore, if a problem arises with the machine, the patient's lungs can be ventilated using a selfinflating

resuscitation bag (e.g., Ambu bag). If a machine problem arises and the cause/remedy is not immediately obvious, one should instinctively reach for the resuscitation bag and call for help. A recent analysis of the American

Society of Anesthesiologists Closed Claims Project data found that 35% of adverse outcomes were likely preventable if a

proper preuse checkout had been performed.

Recognizing that not all of the FDA 1993 checkout recommendations can be applied to many of the contemporary

workstations, in 2008, the American Society of Anesthesiologists published guidelines applicable to all anesthesia

delivery systems so that individual departments can develop their own workstation-specific preuse checkout that can be

performed consistently and expeditiously. The 2008 guidelines are intended to provide a template for developing checkout

procedures that are appropriate for each individual anesthesia machine design and practice setting. They discuss which

systems and components should be checked, the checkout interval (e.g., before first case vs. before every case), and who

may be responsible for performing each checkout procedure—the anesthesiologist or technician (Table 59.1). Examples

of user-developed workstation-specific checkouts are available on the American Society of Anesthesiologists'