Anesthetic Equipment and Safety Flashcards

A circle breathing system is being used with a fresh gas flow of 1 L/min (O₂:air 1:1). The soda lime canister is noted to have a violet discolouration that partially reverses after 30 minutes of non-use. What is the most accurate interpretation?

Answer: Regeneration phenomenon is occurring; the soda lime still has residual capacity but its CO₂ absorption is unreliable

Colour-reversal ('regeneration') of exhausted soda lime is a well-recognised phenomenon caused by redistribution of the pH-sensitive dye when CO₂ partial pressure falls during non-use. The canister appears falsely fresh but its absorptive capacity is critically reduced and unpredictable. Amsorb Plus (calcium hydroxide lime) does NOT regenerate its colour — permanent colour change is a safety feature distinguishing it from soda lime, making option 4 incorrect. The canister must be replaced, but the key clinical point is not simply that it is exhausted, but that regeneration makes its state deceptive and unsafe.

During low-flow anaesthesia at 0.5 L/min total fresh gas flow, compound A accumulates in the breathing circuit. Which property of compound A makes it of greatest clinical concern at low flows compared to high flows?

Answer: Its production increases as desiccated absorbent temperature rises, and its accumulation is proportional to the ratio of circuit volume to fresh gas flow

Compound A (fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether) is produced from sevoflurane reacting with CO₂ absorbents, particularly when desiccated and at elevated temperature. At low flows, the ratio of rebreathed gas volume to fresh gas washout is high, causing Compound A to accumulate in the circuit rather than being diluted. Inorganic fluoride nephrotoxicity (option B) is the mechanism proposed for older agents like methoxyflurane and is not the primary concern with Compound A. Option D describes an incorrect metabolic pathway. Compound A's clinical nephrotoxicity in humans remains debated, but the mechanism of accumulation is the circuit dilution ratio.

An anaesthesia workstation with a Dräger-style ascending bellows ventilator shows the bellows failing to fully ascend during the expiratory phase at a PEEP of 5 cmH₂O. The most likely cause is:

Answer: A leak in the patient breathing circuit exceeding the fresh gas flow rate

Ascending (standing) bellows are a crucial safety feature because they will NOT fully ascend during expiration if there is a significant leak — gravity prevents them from rising without adequate gas return from the patient circuit. This is the principal safety advantage over descending bellows, which can complete their excursion even in the presence of a large leak (giving a false sense of security). A partially open APL valve in ventilator mode is typically isolated from the circuit. Excessive driving gas pressure would prevent bellows descent (inspiration), not ascent. Auto-PEEP would cause air trapping and actually aid bellows ascent. A circuit leak greater than fresh gas inflow will prevent complete bellows ascension.

A fibreoptic bronchoscope is used through an 8.0 mm ID endotracheal tube with the patient receiving 100% O₂ at 8 L/min via the anaesthetic circuit. The bronchoscope occupies approximately 60% of the tube's cross-sectional area. Which immediate ventilatory consequence is MOST likely if peak airway pressure alarms are deliberately disabled?

Answer: Dynamic hyperinflation and barotrauma due to creation of a ball-valve obstruction during expiration

When a bronchoscope partially occludes an ETT, the annular gap between bronchoscope and tube acts asymmetrically: during inspiration, positive pressure forces gas past the obstruction into the lungs, but during expiration, when airway pressure is lower, the soft tissues can collapse around the bronchoscope creating a ball-valve effect. This traps gas, causing progressive dynamic hyperinflation (auto-PEEP) and ultimately barotrauma (pneumothorax, pneumomediastinum). This is the key mechanism underlying bronchoscopy-related barotrauma, particularly relevant with high FGF and in ventilated patients. Hypercapnia and hypoxia can occur but are not the most immediately dangerous mechanical consequence of partial obstruction in a ventilated patient with disabled pressure alarms.

The ISO 80601-2-13 standard requires that an anaesthetic workstation be capable of delivering oxygen even during complete electrical failure. Which of the following design mechanisms PRIMARILY fulfils this requirement in a modern workstation?

Answer: A mechanical O₂ flush valve and a pneumatically-operated bag-valve-mask bypass that function without electrical power

ISO 80601-2-13 mandates that the minimum safety function — ability to oxygenate and ventilate a patient manually — must be achievable without electrical power. This is fulfilled by purely pneumatic/mechanical components: the O₂ flush valve (which operates via direct pipeline/cylinder pressure) and the ability to ventilate manually with a self-inflating bag attached to the common gas outlet or mask. Electronic O₂ flow controllers (option A) depend on power. Option C describes an uncontrolled dump to atmosphere, which is not a recognised design. Option D describes an automatic cylinder changeover (though these exist, they are not the primary mechanism fulfilling this standard, and they may themselves require power). The key principle is that manual oxygenation must remain possible via entirely pneumatic pathways.

A paramagnetic O₂ analyser in the inspiratory limb of a circle system reads 32% during maintenance of anaesthesia with sevoflurane in an O₂/air mixture (set FiO₂ 0.40). The agent analyser simultaneously reads sevoflurane 2.1%. The MOST likely explanation for the discrepancy in the O₂ reading is:

Answer: Paramagnetic interference from the diamagnetic properties of sevoflurane vapour at elevated concentrations

Paramagnetic O₂ analysers measure oxygen by exploiting its unique paramagnetic susceptibility (O₂ is attracted into a magnetic field). However, most volatile anaesthetic agents — including sevoflurane, isoflurane, and desflurane — are diamagnetic (weakly repelled from a magnetic field) and at clinically significant concentrations can interfere with the paramagnetic cell, causing artificially low O₂ readings. At 2.1% sevoflurane, this interference is measurable and clinically relevant. This is a known limitation of paramagnetic analysers not fully compensated by older instruments. A 10-percentage-point drop for a set FiO₂ of 0.40 would be extreme for a simple cell leak (option A). Nitrous oxide (option B) is not in the circuit. Option D would require metabolic O₂ consumption to exceed delivery, which would show on other monitors first.