- 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.
- The only reliable way to determine residual volume
of nitrous oxide is to weigh the cylinder.
- 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.
- A pin index safety system has been adopted by cylinder
manufacturers to discourage incorrect cylinder attachments.
- Body contact with two conductive materials at different
voltage potentials may complete a circuit and result in an electrical
- 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
- 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.
- 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.
- Because pacemaker and electrocardiogram interference
is possible, pulse or heart
sounds should be closely monitored when any electrosurgical unit
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 ...