Gas Distribution - High pressure machine components
High-pressure system receives gases from cylinders at high, variable pressures & reduces those pressures to lower, more constant pressure suitable for use in the machine
- Hanger yoke (including filter and unidirectional valve)
- Yoke block
- Cylinder pressure gauge
- Cylinder presure regulators
Gas distribution - Intermediate Pressure components
The intermediate pressure system receives gases from the pipeline inlet or the pressure regulator (cylinder)
Intermediate pressure = 37-55 psi
This is pipeline pressure or the pressure after cylinder regulator
Pressure in intermediate pressure system will drop to zero when master switch is turned off
Pipeline inlets & pressure gauges
Gas power outlet
Master switch (pneumatic component)
Oxygen flush valve
Oxygen pressure failure device (fail-safe) & alarm
Oxygen & nitrous oxide second-stage pressure regulators
Flowmeter valves
How O2 flush valve works & possible hazards associated with its use
- receives oxygen from the pipeline inlet or cylinder pressure regulator & directs a high unmetered flow (between 35 & 75 L/min) directly to the common gas outlet
- Possible hazards include barotrauma & awareness during anesthesia (from agent dilution)
Oxygen fail-safe device/alarm
-Device that shuts off or proportionally decreases all gases except oxygen or alarms when oxygen pressure has fallen to a dangerous level (usually <30 psig)
- Depends on pressure, not flow
Oxygen fail-safe device/alarm: Datex Ohmeda
- machine stops the flow of nitrous oxide & air once oxygen pressure drops below 20 psi
- makes noise between 20-30 psi until it’s out of oxygen completely or reaches just over 30 psi
Oxygen fail-safe device/alarm: Drager
- decreases flow of nitrous oxide proportionally as oxygen pressure decreases to maintain FiO2 > 19%
- activated when O2 pressure <30 psig
Secondary pressure regulators: function, gases used, final pressures, and purpose
Function - Reduce intermediate pressure to low pressure (20 psi O2, 38 psi N2O), to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure
Low pressure machine components
Starts just after flow control valves
Hypoxic guard/proportioning systems (Link-25)
Flowmeter tubes
Vaporizers
Check valves (if present)
Common gas outlet
Hypoxic Guard System: Link-25 proprotioning system
- minimize the risk of delivering a hypoxic mixture to the patient by maintaining a minimum of oxygen concentration of 25% in the fresh gas supply
- There is a 14-tooth sprocket on the nitrous oxide flow control valve & a 29-tooth sprocket on the oxygen flow control valve.
- When the oxygen concentration reaches 25%, a pin on the oxygen sprocket engages a pin on the oxygen flow control knob. This causes the chain (“link”) to turn making the oxygen & nitrous oxide flow control valves turn together
If O2 supply pressure drops to 10 psi, in what order will the following things happen?
N2O flow stops
O2 fail safe alarm sounds
O2 fail-saffe device activates
- O2 fail-safe alarm sounds (30 psi)
- O2 fail-safe device activates (20 psi)
- N2O flow stops
Which of the following is not a mandatory safety feature of current anesthesia delivery systems?
A. Oxygen fail-safe device
B. Pulse Ox
C. Oxygen flowmeter at extreme right of flowmeter cluster
D. Vaporizer interlock device
E. All of the above are mandatory safety features
E. All of the above are mandatory safety features
If administering O2 and N2O on older Datex-Ohmeda machine, and lose pipeline O2 so switch to E cylinder without adjusting the flowmeters. What will happen to the floats in the flowmeter tubes?
A. both go to 0 and must be manually re-adjusted to their previous values
B. both floats go to 0 and rise back to their previous values
C. Both floats go to 0 and only the oxygen float rises back to its previous value, while N2O must be manually turned back on
B. both floats go to 0 and rise back to their previous values
Which of the following is not part of the low-pressure system of the anesthesia machine?
A. Vaporizer
B. Common gas outlet
C. Floats
D. Flowmeter tubes
E. O2 low pressure alarm
E. O2 low pressure alarm
