Under the Spaulding classification, an item contacting intact mucous membranes is
Answer: C
Mucous membranes resist ordinary bacterial spores but are readily infected by other organisms, so high-level disinfection is accepted for items such as endoscopes and respiratory equipment. Sterilization is reserved for items that penetrate tissue.
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The D-value of a sterilization process is the
Answer: D
The D-value expresses killing as a rate: each D-value reduces the survivors tenfold, so inactivation is logarithmic rather than sudden. That is why sterility is specified as a probability of a survivor rather than as an absolute certainty.
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Saturated steam under pressure is normally used at
Answer: A
Raising the pressure about 15 pounds per square inch above atmospheric lets saturated steam reach 121 degrees, well above the 100 degrees available at open-air boiling. The holding time is at least 15 minutes, and longer for wrapped or dense loads, which is why 30 minutes is often specified.
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The four parameters of steam sterilization are
Answer: B
All four have to be right together: dry or superheated steam, inadequate pressure, a low temperature or too short a hold will each leave organisms alive. Monitoring only one of them, usually temperature, is why autoclave failures can go unnoticed.
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The other standard steam sterilization temperature, used in a prevacuum sterilizer, is
Answer: C
A prevacuum cycle removes air first so steam penetrates at once, allowing a higher temperature and a much shorter exposure. The trade is between time and temperature: the hotter the saturated steam, the less of it is needed.
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Moist heat kills microorganisms principally by
Answer: D
Saturated steam denatures enzymes and structural proteins beyond recovery, and the presence of water markedly lowers the temperature at which that coagulation occurs. Dry heat, lacking water, has to work by oxidation and therefore needs far higher temperatures.
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Dry heat in a hot air oven is typically used at
Answer: A
Without water to assist protein coagulation, dry heat must oxidise cell constituents, so both the temperature and the time are much greater than an autoclave needs. It suits glassware, powders and oils that steam would spoil or fail to penetrate.
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Dry heat is less efficient than moist heat at the same temperature because
Answer: B
Moisture is what makes protein coagulation happen at a modest temperature, so steam at 121 degrees achieves in minutes what dry air needs 160 degrees and hours to do. Steam also carries far more heat to the surface as it condenses.
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Incineration achieves sterilization by
Answer: C
Correct answer: reducing material to ash by burning
Incineration destroys the material along with everything living in it, converting it to ash and gases at several hundred degrees. It is therefore used for disposal rather than for anything that must be reused, and it is the method of choice for anatomical waste, sharps and highly infectious material where nothing is to be recovered.
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Boiling water at 100 degrees Celsius is unreliable for sterilization because it
Answer: D
Boiling kills vegetative bacteria, most fungi and many viruses within minutes, but endospores can survive it for hours. That single gap is why the autoclave, which exceeds 100 degrees by using pressure, replaced boiling for surgical instruments.
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