Medical Gas Safety Systems Quiz

Study Notes

Shuts off flow of all other gases when oxygen pressure drops below a set limit (20-25 psi)
Activates if there is decreased flow of oxygen
Some machines have audible and visual alarms, even with low oxygen pressure
Does not prevent delivery of a hypoxic mixture
Datex-Ohmeda and Drager have proprietary versions

Provides oxygen at 35-55 L/min directly to the common gas outlet, bypassing flowmeters and vaporizers
Oxygen may reach a connected patient at a pressure of 45-50 psi
Potential for barotrauma
Used to rapidly refill or flush the breathing circuit
Must have a built-in rim to prevent inadvertent activation and a spring to prevent prolonged activation

Starts at the second stage regulator where all gas pressure is dropped from the intermediate pressure system to about 16 psi
Includes flowmeters, vaporizers, and the common gas outlet

Ensures that nitrous oxide can only be delivered in the presence of oxygen
Prevents delivery of low oxygen content nitrous oxide to the patient
Adds a minimum of 21-25% oxygen to the mixture when nitrous oxide is used
Oxygen is furthest on the right, so that in the event of a leak, the chances of a hypoxic mixture are lessened
To ensure oxygen is always delivered, there's a minimum setting of 50-150ml/min constant flow even with the oxygen flowmeter in the full-off position

Constant pressure, variable orifices with a low pressure of 16 psi
Tube is tapered, with the largest diameter on top
Hand calibrated, no two tubes are alike
Gas specific
The indicator floats freely at a point where the downward force (gravity) equals the upward force caused by gas molecules hitting the bottom of the float
Read the ball at the middle, and the arrow float at the top

Also known as the fresh gas outlet
Only one outlet on the anesthesia machine, compared to multiple gas inlets
Must have an anti-disconnect device to prevent accidental disconnection from the breathing circuit
Oxygen from the flush valve goes directly from the intermediate pressure system to this outlet, directly to the patient

Usually fully open during spontaneous ventilation, but must be partially closed during manual or assisted bag ventilation
If open too wide, too much volume escapes and not enough is delivered to the patient
If closed too tightly, not enough volume escapes, creating larger volumes and possibly high airway pressures
Requires very fine tuning

Maintain the flow of anesthetic gas in the intended direction
Maintains a minimum O2/N20 ratio of 1:3
O2/NO2 Proportioning Device automatically mixes O2 and NO2 to the setting selected on the dial

Constant-pressure variable-orifice flowmeters use an indicator ball or bobbin which displays the flow of gas through a Thorpe tube
Utilize a ball, bobbin or float as a marker
The tube is narrow at the bottom and low flow raises the marker; as the flows increase and the marker rises in the widened tube, greater flows pass around it and reach the common gas outlet
May be single or double tube design

Specifically designed and calibrated for each gas
The flow rate of a gas through a constriction depends on the gas’s viscosity at low laminar flows, and its density at high turbulent flow (Hagen-Poiseuille)
Floats should rotate freely; inside of tubes is coated to prevent static electricity
May malfunction due to dirt inside, misalignment, sticking markers
Leaks may occur and could cause hypoxic gas mixture to be delivered

Flow moves from left to right, exiting the common manifold to the right of the oxygen flowmeter
A leak in the first two flowmeters means oxygen continues uninterrupted out to the patient.
A leak in the oxygen flowmeter, or somewhere beyond it, can cause delivery of a hypoxic mixture.