Anesthesia Equipment and Delivery Flashcards

During a nitrous oxide/oxygen sedation procedure, the flowmeter indicates 4 L/min N₂O and 2 L/min O₂. Which immediate action is required?

Answer: Increase oxygen flow to restore a minimum 30% oxygen concentration

At 4 L/min N₂O and 2 L/min O₂, the oxygen concentration is only 33% of a 6 L/min total flow — but more critically, the N₂O percentage (67%) exceeds the safe maximum of 70%, and the absolute O₂ delivery must never fall below 30% of the total flow per DAANCE standards. The immediate correction is to increase O₂ flow so that O₂ constitutes at least 30% of the total gas mixture. Simply decreasing N₂O slightly does not address the underlying O₂ deficit fast enough, and full discontinuation is not warranted before first correcting the ratio.

A fail-safe device on a nitrous oxide delivery unit is designed to accomplish which of the following?

Answer: Prevent the nitrous oxide from flowing if oxygen supply pressure drops below a threshold

The fail-safe (or 'oxygen-failure protection') device is a pressure-sensitive mechanism that interrupts or shuts off nitrous oxide flow whenever the oxygen supply pressure falls below a set minimum (typically around 20–30 psi). This prevents delivery of a hypoxic gas mixture if the oxygen source fails. It does NOT cap the N₂O concentration at 50% (that is the operator's responsibility), nor does it perform an automatic oxygen flush or sound an alarm about cylinder level — those are separate safety features.

Which component of the nitrous oxide/oxygen delivery system is responsible for converting high-pressure gas from the cylinder to a working pressure usable by the flowmeters?

Answer: Pressure-reducing valve (regulator)

The pressure-reducing valve (regulator) steps down the high cylinder pressure (e.g., ~750 psi for N₂O, ~2,200 psi for O₂) to a consistent, safe working pressure (typically 50 psi) that the flowmeters and delivery circuit can handle. The reservoir bag stores a volume of gas for the patient to draw from during deep inhalation. The scavenging interface removes exhaled gases from the operatory. A demand valve opens only when the patient creates negative pressure by inhaling, and is not standard in typical dental sedation units.

When using a nasal hood with a built-in scavenging system, trace gas levels in the operatory are BEST minimized by which technique?

Answer: Ensuring the nasal hood fits snugly and adjusting scavenging flow to 45–55 L/min

Effective scavenging requires both a well-sealed nasal hood to capture exhaled gas at the source and a scavenging flow rate high enough (typically 45–55 L/min on most systems) to remove exhaled gas without creating excessive negative pressure that would collapse the reservoir bag. Mouth breathing defeats nasal hood capture entirely. Reducing total fresh gas flow does not reduce the volume of exhaled N₂O that needs scavenging. Turning off scavenging during recovery is contraindicated — this is when residual N₂O is being exhaled in the highest concentrations.

An anesthesia machine's vaporizer is classified as a 'variable bypass' type. What is the primary function of the bypass channel in this design?

Answer: It carries the fraction of fresh gas flow that does NOT pass through the anesthetic agent, diluting the output to the desired concentration

In a variable bypass vaporizer (e.g., the Tec series), the total fresh gas flow is split: one portion enters the vaporizing chamber and becomes saturated with vapor, while the remainder travels through the bypass channel, bypassing the chamber entirely. These two streams are then recombined downstream. The ratio of bypass flow to vaporizing-chamber flow — controlled by the concentration dial — determines the final output concentration. The bypass does not handle exhaled gases, does not switch agents, and has no direct effect on oxygen percentage.

A patient is receiving IV sedation with a propofol infusion via a syringe pump. The pump alarms with 'occlusion downstream.' Which assessment finding is MOST consistent with this alarm?

Answer: The IV catheter has infiltrated or the line distal to the pump is kinked or clamped

A 'downstream occlusion' alarm indicates that the pump is detecting increased resistance beyond the pump head — meaning the pathway from the pump outlet to the patient is obstructed. The most common clinical causes are IV infiltration (catheter no longer in the vein, causing extravasation), a kinked line, or a closed stopcock distal to the pump. An empty syringe triggers a 'syringe empty' or 'end of infusion' alarm, not an occlusion alarm. Air in the line is an 'upstream' or air-in-line concern. Sensor failure is rare and would typically generate a machine fault code rather than an occlusion alarm.