Anesthesia Equipment and Delivery Flashcards

A nitrous oxide/oxygen flowmeter shows 4 L/min N₂O and 2 L/min O₂. The anesthesia assistant notices the patient is becoming progressively unresponsive. Beyond hypoxia, which equipment failure is MOST likely responsible if the oxygen analyzer reads 33%?

Answer: A crossed pipeline supply with N₂O inadvertently routed to the O₂ inlet

A crossed pipeline (N₂O plumbed to the O₂ inlet) is the most dangerous and underappreciated failure mode. In this scenario the analyzer reads ~33% because it is sampling what it believes is the O₂ source, which actually contains N₂O — the true delivered O₂ is far lower. The fail-safe valve and proportioning system would only prevent low O₂ line pressure situations and cannot protect against a correctly pressurized but mislabeled supply. This 'wrong gas in the right pipe' hazard bypasses virtually all machine safeguards.

During a lengthy oral surgery case under IV sedation with supplemental O₂ via nasal cannula at 4 L/min, the capnograph waveform suddenly loses its characteristic square shape and the ETCO₂ drops to 0 mmHg while SpO₂ remains 98%. Which is the MOST likely explanation?

Answer: The sample line has become kinked or disconnected from the nasal cannula port

A sudden drop to 0 mmHg ETCO₂ with maintained SpO₂ is a classic sign of a sampling line disconnect or kink rather than true apnea. True apnea would cause SpO₂ to fall within 1–2 minutes on supplemental O₂. Hyperventilation causes low ETCO₂ but does not zero it out completely with a normal waveform loss. Oral breathing dilutes the sample but does not eliminate the waveform entirely. A disconnected sample line produces no signal — zero ETCO₂ with a flat trace and preserved oxygenation.

A dental office is located at an elevation of 6,000 feet (1,829 m) above sea level. Compared with sea level, what adjustment must be made when using a Thorpe tube (variable-orifice) flowmeter calibrated at sea level?

Answer: The actual flow delivered will be HIGHER than indicated; set the dial lower than the desired flow

At altitude, ambient pressure is lower, so gas is less dense. A Thorpe tube calibrated at sea level uses float position as a surrogate for flow based on sea-level gas density. At altitude, the same float position corresponds to a higher volumetric flow because the gas is less dense — the machine under-reads. The actual delivered flow exceeds the indicated value. Therefore the clinician must set the flowmeter dial LOWER than the desired flow rate to avoid delivering more gas than intended, particularly relevant for N₂O percentage calculations.

An anesthesia machine equipped with a Diameter Index Safety System (DISS) is found to have a cracked O-ring on the oxygen DISS fitting. The MOST immediate clinical risk of continuing to use this machine without repair is:

Answer: Increased fire hazard from O₂ leaking into the ambient environment near electrosurgical equipment

A cracked O-ring on the O₂ DISS fitting causes oxygen to leak into the room atmosphere. In a dental surgical environment where electrosurgical units, lasers, or cautery may be in use, enriched ambient O₂ dramatically lowers the ignition threshold of drapes, gowns, and tissues — creating a serious fire and explosion risk. While reduced pressure could eventually trigger the fail-safe, a cracked O-ring typically produces a slow leak that does not immediately drop line pressure below the fail-safe threshold. Retrograde cross-contamination cannot occur through DISS because the check valves are one-directional.

When performing a pre-use leak check on a circle rebreathing system, the technician closes the APL valve, occludes the patient Y-piece, and pressurizes the circuit to 30 cmH₂O. After 10 seconds the pressure has dropped to 22 cmH₂O. Which component is LEAST likely to be the source of this leak?

Answer: A worn gasket on the vaporizer filler cap

The vaporizer filler cap gasket, when worn or missing, allows gas to escape from the vaporizer liquid agent compartment — however, during a standard circuit leak test with the vaporizer turned OFF, the filler cap is upstream of the vaporizer's internal flow path but external to the breathing circuit. A filler cap leak releases agent vapor to atmosphere rather than to the breathing circuit being tested, making it the least likely source of a circuit pressure drop on this test. Inspiratory valve discs, absorber connections, and tubing cracks are all directly within the tested circuit volume.

A patient receiving IV midazolam and fentanyl sedation develops a respiratory rate of 6 breaths/min, ETCO₂ of 68 mmHg, and SpO₂ of 84% despite a non-rebreather mask at 15 L/min O₂. After calling 911, the DAANCE-certified assistant prepares to assist ventilation with a bag-valve-mask. Which technique error would MOST dangerously worsen this patient's condition?

Answer: Ventilating with excessive tidal volume causing gastric insufflation and aspiration risk

Excessive tidal volume is the most dangerous BVM error in this context. Large breaths exceed lower esophageal sphincter pressure (approximately 20–25 cmH₂O), forcing air into the stomach — gastric insufflation leads to regurgitation and aspiration, which is rapidly fatal in a sedated patient who has lost protective airway reflexes. A one-handed seal reduces efficiency but does not directly worsen the patient. Correct rate and duration (10–12 breaths at 1 second each) are standard. Cricoid pressure (Sellick maneuver) is controversial and no longer universally recommended in current BLS guidelines — its omission is not the most dangerous error in this scenario.