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  • Image not available.Liquid oxygen must be stored well below its critical temperature of –119°C because gases can be liquefied by pressure only if stored below their critical temperature.
  • Image not available.The only reliable way to determine residual volume of nitrous oxide is to weigh the cylinder.
  • Image not available.Because the critical temperature of air is –140.6°C, it exists as a gas in cylinders whose pressures fall in proportion to their content.
  • Image not available.A pin index safety system has been adopted by cylinder manufacturers to discourage incorrect cylinder attachments.
  • Image not available.Body contact with two conductive materials at different voltage potentials may complete a circuit and result in an electrical shock.
  • Image not available.The magnitude of a leakage current is normally imperceptible to touch (less than 1 mA and well below the fibrillation threshold of 100 mA). If the current bypasses the high resistance offered by skin, however, and is applied directly to the heart (microshock), a current as low as 100 μA (microamperes) may be fatal. The maximum leakage allowed in operating room equipment is 10 μA.
  • Image not available.Unlike the utility company’s pole-top transformer, the secondary wiring of an isolation transformer is not grounded and provides two live ungrounded voltage lines for operating room equipment.
  • Image not available.Malfunction of the return electrode may result from disconnection from the electrosurgical unit, inadequate patient contact, or insufficient conductive gel. In these situations, the current will find another place to exit (eg, electrocardiogram pads or metal parts of the operating table), which may result in a burn.
  • Image not available.Because pacemaker and electrocardiogram interference is possible, pulse or heart sounds should be closely monitored when any electrosurgical unit is used.


Anesthesiologists, who spend more time in operating rooms than any other group of physicians, are responsible for protecting unconscious patients from a multitude of possible dangers during surgery. Some of these threats are unique to the operating room. As a result, the anesthesiologist is primarily responsible for ensuring the proper functioning of the operating room’s medical gases, environmental factors (eg, temperature, humidity, ventilation, and noise), and electrical safety. This chapter describes the major features of operating rooms that are of special interest to anesthesiologists and the potential hazards associated with these systems. A case summary organizes some of this information into a protocol for testing a new operating room’s medical gas pipeline system.


The medical gases commonly used in operating rooms are oxygen, nitrous oxide, air, and nitrogen. Although technically not a gas, vacuum exhaust for waste anesthetic gas disposal (WAGD or scavenging) and surgical suction must also be provided and is considered an integral part of the medical gas system. Patients are endangered if medical gas systems, particularly oxygen, malfunction. The main features of such systems are the sources of the gases and the means of their delivery to the operating room. The anesthesiologist must understand both these elements to prevent and detect medical gas depletion or supply line misconnection. Estimates of a particular hospital’s peak demand determine the type of medical gas supply system required. Design and ...

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