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Chapter 16
| Question | Answer |
|---|---|
| What is the ultimate destination of gases | scavenging system |
| What is the pipeline pressure of O2 | 50 psi |
| Where are shutoff valves for O2 | OR, main and partial area |
| What size cylinder is nitrous oxide delivered to the hospital | Large H cylinders |
| What is the pipeline pressure of N2O | 50 psi |
| What safety system is put in place to prevent misconnections in piping delivery of O2 and N2O | Diameter index safety system |
| What safety mechanisms are present at the pipeline inlet | filter, check valve and pressure gauge are present |
| What does a check valve ensure | unidirectional flow so that a machine running on cylinder supplies, with the hoses disconnected at the wall outlet, does not leak |
| What does the filter do for protection | prevents damage to the anesthesia gas machine from particulate matter present in the pipeline gas supply |
| What agency adopted more stringent testing standards for pipeline supplies of gases | National fire protection association (NFPA) |
| If loss of O2 pressure is profound what alarm will sound off and what will happen | low pressure alarm sounds off and the fail safe valve halts the delivery of all other gases |
| What should happen with complete loss of O2 pipeline pressure | open the E cylinder completely, disconnect the pipeline, and consider the use of low fresh gas flows and manual ventilation |
| What happens if the E cylinder is not fully opened when using for loss of pipeline pressure | flow from it may end before the cylinder is empty |
| Why is the pipeline disconnected when pipeline pressure is lost | so that retrograde flow from within the machine to the pipeline is prevented |
| When will retrograde flow in the pipeline occur | when the pipeline inlet check valve fails simultaneously |
| What will happen if you open the E cylinder but do not disconnect from pipeline | the pipeline gas will cont to flow b/c the pressure distal to the cylinder is set to 45psi and pipeline is at 50 psi |
| Why is the cylinder pressure intentionally set lower than the pipeline pressure | in case the cylinder is inadvertently left open after the machine has been checked |
| What color is associated with air | yellow |
| What color is associated with O2 | green |
| What color is associated with N2O | blue |
| What is the psi for O2 cylinder | 1900 |
| What is the psi for N2O cylinder | 745 |
| What is the psi for air cylinder | 1900 |
| What is the cylinder capacity for O2 | 660 |
| What is the cylinder capacity for N2O | 1590 |
| What is the cylinder capacity for air | 625 |
| What is the pin position for a cylinder of O2 | 2-5 |
| What is the pin position for a cylinder of N2O | 3-5 |
| What is the pin position for a cylinder of air | 1-5 |
| How can the PISS system be defeated | when pins are missing, are removed or if more than one washer is used |
| What types of safety relief devices are used on cylinder valves | a frangible disk that bursts under pressure, a valve that opens at extreme pressure, or a fusible plug made of wood’s metal |
| Why are safety relief devices used on cylinders | if a fire causes the temperature and pressure within the cylinder to increase, safety relief devices release contents in a controlled fashion rather than explosively |
| What are the three functions of the hanger yolk | orientation of the cylinder, gas-tight seal and ensures unidirectional flow (also contains filter) |
| The cylinder pressure gauge is what type of gauge | Bourdon-type gauge |
| After the hanger yolk for each gas is what | regulator |
| What does the regulator do | converts the high cylinder pressure to a constant downstream pressure which is intentionally less than pipeline pressure (prevents depletion of cylinder contents) |
| If the cylinder is left open and the pipeline pressure drops below 45 psi gas will flow from cylinder. Why is this a problem | no alarm will sound to warn the user of this condition and the cylinder will be depleted, thus low O2 supply fail alarm will announce the END of emergency supply |
| Which agency issues regulations for the manufacture, handling, transport, storage and disposal of cylinders | U.S. department of transportation |
| If the O2 flow is 2L/min and the cylinder’s O2 gauge pressure is 500 psi how long will the cylinder last | 86 min |
| How is N2O stored | as a liquid |
| When the pressure guide on a N2O cylinder reads 745 psi, what is the contents of the cylinder | The N2O cylinder pressure gauge remains at 745 psi until the liquid is gone, the cylinder is more than ¾ empty. |
| Why does frost form on the valve with rapid removal of (>4L/min) of N2O from a cylinder | r/t loss of the latent heat of vaporization from the liquid nitrous oxide |
| How are air, O2 and N2O paths through the anesthesia machine similar | they all flow from the supply point to a flowmeter. |
| What gases pass through the fail-safe valve | all gases except O2 (and newer models air) |
| What helps keep the fail-safe valve open | It is held open by pressure in the O2 circuit within the anesthesia machine |
| Where do all the gases joined for the first time | common manifold |
| Where is O2 added to the common manifold | always downstream of other gases |
| The combined gases enter any vaporizer that is on and then pass through | common gas outlet |
| After gases are transported to the patient through the circuit where do they go | to the scavenger and then into the hospital ventilation or suction sytem |
| What are the five tasks of O2 | proceeds to fresh gas flowmeter; powers the O2 flush; activates fail-safe mechanisms; activates O2 low-pressure alarms; compresses the bellows of mechanical ventilators |
| How are the control knobs for the flowmeters coded for safety | color and touch coded |
| Flow increases when the knob is turned | counterclockwise |
| What is the name for the glass flowtube | Thorpe |
| How are flowtubes tapered | narrower at its bottom |
| Where do you read ball type indicator floats | center |
| Where do you read plumb bob type floats | top |
| What is the volume of gas delivered via the O2 flush valve | 35-75 L/min |
| What does the fail safe system ensure | if O2 pipeline pressure fails N2O flow is stopped by the fail safe system |
| How is the fail safe valve held open | through the pressure of O2 |
| How does O2 power the low pressure alarms | The machine will signal the operator when pressure is lost in the O2 circuitry |
| What is the hypoxic guard | an O2, N2O proportioning system that ensures that the final concentration of O2 is at least 23-25% |
| What is the permit-able ratio of N2O to O2 | 3 to one |
| What does an increase in temperature do to the rate of Vaporization | increases it |
| Why is copper a good material to use in vaporizers | since cooling limits the rate of vaporization, copper is chosen in vaporizers r/t its high thermal conductivity and high thermal capacity |
| The rate of vaporization of a volatile depends on what | temperature, vapor pressure of the liquid and partial pressure of the vapor above the evaporating liquid |
| What is the splitting ratio | gas entering the vaporizing chamber divided by total fresh gas flow |
| How is the splitting ratio determined | by the internal resistance to flow; the operator merely sets the control dial to desired conc |
| What volatiles use the variable-bypass vaporizer | sevo, iso |
| What volatiles us the Tech-6 Vaporizer | Des |
| Who may still use the measured flow (Vernitrol) vaporizer | the military |
| How does the Tech 6 differ from the variable-bypass vaporizer | In a tech 6 the fresh gas flow never flows over or comes in contact with the liquid agent; an appropriate amount of vapor is added to the fresh gas flowing through the vaporizer |
| At what degree of tipping does a vaporizer need to be serviced | 45 degrees |
| Why shouldn’t low flows be used during induction | induction at low flows would be extremely prolonged, creating the risk of awareness |
| How is CO2 eliminated from the breathing circuit | via washout with adequate fresh gas flow or by absorption in the CO2 granules |
| How can resistance to flow be lessened in breathing circuits | shortening the length, increasing the diameter, avoiding sharp bends, eliminating valves and maintaining laminar flow |
| How are rebreathing circuits on the anesthesia machine beneficial | cost reduction, increase in tracheal warmth and humidity, decrease in potential for expo of operating room personnel to trace and waste gases |
| How could a provider increase the amount of rebreathing | decreasing fresh gas flow |
| When are high fresh gas flows wanted | during induction and emergence |
| What does dead space do to CO2 levels | increase in dead space=increase in CO2 rebreathed |
| Where does mechanical dead space end | at the y-piece of the Circuit |
| How is Co2 washed out of a breathing circuit | with adequate fresh gas flow or absorption through CO2 granules |
| What is the classification of breathing circuits based on | whether a reservoir is present and on the degree to which rebreathing occurs |
| What are the common features of the nonrebreathing systems | no unidirectional valves, no soda lime CO2 absorption, amount of rebreathing is dependent on FGF, amount of resistance is low |
| What is the FGF necessary for a nonrebreathing system | 2-3 times minute ventilation (min 5L/min) |
| The Bain breathing system is referred to as the modified ______ | modified mapleson D circuit |
| How does the Bain system differ from the mapleson D | the fresh gas hose is directed coaxially within the corrugated limb and this configuration gives the inhaled gases greater heat and humidity |
| Where might you still see mapleson systems used | in pediatrics (10-20 kg) |
| What is the most commonly used breathing circuit in the US | circle system |
| If the inspired CO2 is high what should a provider do | increase FGF, check the system |
| How do you find the time constant in breathing systems | capacity divided by flow |
| What is the significance of time constants in breathing systems | it measures how quickly a breathing system reaches equilibrium with a change in the inflow |
| Absolute contraindications for low flows in a breathing circuit are | pts with smoke inhalation injury, MH, or other conditions in which washout of potentially dangerous gases or a high O2 uptake is expected |
| What are relative contraindications for low flows in breathing circuits | face mask anesthesia, and during rigid bronchoscopy or with uncuffed ETT. |
| How is humidification and prevention of nosocomial infection addressed in breathing circuits | through the use of filters |
| What determines the amount of rebreathing in a circuit | gas flows |
| With low flows (03-0.5 L/min) the provider is reliant 100% on _____ to prevent rebreathing of CO2 | absorbent granules |
| Where does the CO2 absorption take place | on the surface of soda lime |
| Is CO2 absorption better with wet or dry soda lime | Moist granules ensure speed and efficiency of the reactions and dry granules become exhausted much more quickly |
| The absorption of 1 mole of CO2 produces how many kcal of energy | 13,000 kcal |
| Absorbents contain ethyl violet as an additive for what purpose | to serve as an indicatior of absorbent pH |
| What is the critical pH that changes ethyl violet changes from colorless to blue-purple | 10.3 |
| Does soda lime regenerate | NO |
| The main constituent in all absorbents is | Calcium hydroxide |
| What is the size of the absorbent granules | 4-8 mesh |
| What does soda lime degrade Sevo to | compound A |
| Compound A is lethal at how many ppm | 130-340 ppm |
| Absorbent efficacy is decreased by | channeling and the wall effect |
| When total rebreathing is occurring, the top canister of CO2 absorbent might be expected to last how long | 8-10 h |
| Each 100 g of granules can absorb as much as ___ of CO2 | 15L CO2 |
| Each canister of absorbent (aestiva) holds how much granules | 1-1.3 kg |
| What prevents the buildup of volume and pressure within the breathing circuit from the continual addition of fresh gas flow | ventilator relief valve (spill valve or overflow valve) |
| When does the spill valve remain open | during the expiratory phase |
| What does the fresh gas decoupling piston do | ensures that the TV set is the TV delivered and that the FGF does not augment the TV |
| What are the causes of critical incidences seen with anesthesia machines | disconnects from machine, failure to resume ventilation, barotrauma, fire and MH |
| What are the two types of gas scavenging systems | open and closed |
| Which gas scavenging system is passive—open or closed | closed |
| Failure of the scavenger interface relief valve can cause | barotraumas |
| Although equipment failures are rare, they are often the the result of | human error |
| What legal term describes the use of an anesthesia machine outside of the manufacturer’s instructions | Prima facie negligence |
| What are the four components of the anesthesia machine in the SPDD model | Supply, processing, delivery, and disposal |
| How many tasks to air and nitrous oxide have | Each has one task |
| Where is the ultimate destination of anesthetic gases | Scavenging system, not the patient |
| What is the normal pipeline pressure that supplies gases to the anesthesia machine | 50 psi (344 kPa) |
| What errors does the DISS (diameter index safety system) prevent | It prevents pipe misconnections (ex. oxygen to nitrous) |
| Are the cylinder pressure regulators and pressure gauges part of the low, intermediate, or high pressure system | High pressure system |
| Are the pipelines and check valves part of the low, intermediate, or high pressure system | Intermediate pressure system |
| Is the oxygen pressure-failure device part of the low, intermediate, or high pressure system | Intermediate pressure system |
| Is the flush valve part of the low, intermediate, or high pressure system | Intermediate pressure system |
| Are the flowmeters part of the low, intermediate, or high pressure system | Low pressure system |
| Are the vaporizers part of the low, intermediate, or high pressure system | Low pressure system |
| Is the common gas outlet part of the low, intermediate, or high pressure system | Low pressure system |
| If sensed inspired oxygen falls below a preset limit (18%) does a high, medium, or low priority alarm sound | High priority alarm |
| Does the oxygen flush valve pass through vaporizers | No, it is required to bypass vaporizers |
| If oxygen pressure is lost to the machine what two safety mechanisms occur | Low pressure alarm sounds and fail safe valves halt delivery of other agents |
| What are the steps in the event of pipeline pressure failure or drop in fraction of inspired oxygen | Open back-up E-cylinder fully, disconnect pipeline, and ensure increase in FiO2. |
| What should be done if FiO2 does not increase after a pipeline failure or unexpected low FiO2 and switching to cylinder oxygen | Ventilate patient with ambu-bag on room air or with freestanding cylinder. |
| What is a complication of not opening the E-cylinder fully when using it as the oxygen source | Oxygen flow may stop before the cylinder is empty. |
| What occurs when there is excessive pipeline pressure | Hospital plant alarms are triggered, however there is no alarm on the anesthesia machine. |
| If the pipeline is not disconnected after opening an E-cylinder where will the oxygen come from in the event of cross connection (or a reason other than low pipeline pressure) | The gas will come from the pipeline since the pressure distal t o the cylinder regulator is 45 psi and pipeline pressure is 50 psi. Flow comes from the higher pressure source. |
| Why is the pressure from an E-cylinder after the pressure regulator lower (45 psi) than the pipeline pressure (50 psi) | So that flow proceeds from the higher pressure pipeline source if a cylinder is inadvertently left open after it was checked. |
| What is the most fragile portion of the cylinder | The cylinder valve. |
| What are the three types of cylinder valves | Frangible disk that bursts under pressure, a valve that opens at extreme pressure, or a fusible plug made of wood’s metal (melts at elevated temperatures). |
| What are the three functions of the hanger yoke | It orients the cylinder, provides an air-tight seal, and ensures unidirectional flow. |
| What is the risk of transfilling between two cylinders | Transfilling is a fire hazard since filling a cylinder generates heat. |
| What is the purpose of the regulator distal to the cylinders on the hanger yoke | To convert the high (nut variable) cylinder pressure to a constant lower downstream pressure (45 psi). |
| What type of gas cylinders are safe to use in MRI | Nonferrous (aluminum) cylinders. |
| What material are gas cylinders made of | Steel. |
| When installing a cylinder in the back of the anesthesia machine, what does the presence of an audible leak indicate | Malposition and the cylinder should be repositioned. |
| What the equation used to calculate how long an E-cylinder oxygen tank will last | Capacity L/Service pressure psi = Contents remaining L/Gauge pressure psi where contents remaining is x. Divide the final answer by the L/min of flow used on the patient (ie. 2L/min). |
| What is the full capacity and service pressure of an E-cylinder oxygen tank | 660 L and 2000 psi |
| How much nitrous oxide remains in the cylinder when the pressure gauge reads less than 745 psi | The pressure falls when the cylinder is more than ¾ empty and the liquid is gone. Once the pressure falls, the cylinder should be changed. |
| What are the three major constituents of air | Nitrogen (78%), oxygen (21%), and argon (1%). |
| What is the minimal battery life of an anesthesia machine | 30 minutes. |
| What types of devices should not be plugged into convenience receptacles on the back of anesthesia machine and why | Devices that convert electrical power into head (warming blankets, fluid warmers) because they draw a lot of amperage and can cause the circuit breaker to open. |
| Which vaporizes require wall-outlet electrical power and which do not | Desflurane Tec 6 and caporizers with electronic controls (Aladin cassettes in the ADU) require wall-outlet power. Variable bypass vaporizers do not require wall-outlet power. |
| What is the path of oxygen through the anesthesia machine | O2 goes from supply point to flow meter. Then enters common manifold downstream of other gases to prevent hypoxic mixture. o2 and other gases go through the open vaporizer, then common gas outlet before entering the delivery hose to the breathing circuit |
| What are the five tasks of oxygen in the anesthesia machine | 1: proceeds to the fresh gas flowmeter, 2: powers the oxygen flush, 3: activates fail-safe mechanisms, 4: activates oxygen low-pressure alarms, 5: compress bellows of mechanical ventilators. |
| If a flowmeter control knob is turned counter clock wise, does the gas flow increase or decrease | Increase. |
| Why are the flowtubes referred to as variable orifice flowmeters | The annular opening around the float is narrower at the bottom and larger at higher flows. |
| Where are oxygen flow tubes placed in relation to nitrous oxide and oxygen | Oxygen flow tubes are to the right of other gases in the US. |
| Where should ball-type indicators in flowemeters be read | In the center of the ball. |
| Where should plump bob-type floats in flowmeters be read | At the top of the float. |
| Where does the auxiliary oxygen flow meter receive its oxygen source form | The pipeline. |
| The oxygen flush valve delivers oxygen at _____ L/min | 35-75 |
| The flush valve should be avoided during inspiration or expiration | Inspiration, to avoid barotrauma. |
| The oxygen flush valve delivers oxygen directly from the gas supply source to the common gas outlet. Why is this important for anesthesia providers to know | The oxygen will bypass vaporizers and nitrous oxide, delivering 100% oxygen to the breathing circuit. If partial pressures of nitrous oxide or VAA has been established, they will be diluted. |
| In which gas line are fail-safe devices placed | In the nitrous oxide pipeline. |
| What is the purpose of the fail-safe system | In the event of loss of oxygen pipeline pressure, nitrous oxide is discontinued to prevent a hypoxic mixture. |
| What are the two types of fail-safe systems | 1: Flow of nitrous oxide is shut off with low oxygen pressure (Avance, Fabious GS) or 2: Flow of nitrous oxide is proportionately decreased with low oxygen pressure (Aestiva, ADU). |
| What is the oxygen low-pressure alarm | When pressure is low in the oxygen circuitry, an alarm is sounded to alert the anesthetist. The cylinder should be used in this case. |
| How are bellows compressed in piston ventilators | Electric motors. |
| What is the highest acceptable ratio of nitrous oxide: oxygen | 3:1 |
| What are the two types of hypoxic guard systems | 1: Pneumatic-mechanical proportioning system/Link-25 (Aestiva). N2o and o2 are linked by a chain and o2 is increased as nitrous oxide increases. 2: Electronic hypoxic guard (Apollo, Fabius, 6000) limits nitrous oxide flow based on oxygen flow. |
| What are four circumstances under which hypoxic guards will not prevent a hypoxic mixture | 1: wrong supply gas in oxygen pipeline or cylinder, 2: defective pneumatics or mechanics, 3: leaks downstream of flow control valves, 4: inter gas administration (3rd gas such as helium). |
| What are the only two gases that the hpoxic guard system links | Oxygen and nitrous oxide. |
| What is the definition of a vapor | Molecules in the gaseous phase of a substance that is liquid at room temperature and 1 atmosphere of pressure. |
| What three factors does vaporization depends on | Vapor pressure of the liquid, partial pressure of the vapor above the liquid, and temperature. |
| Does evaporation increase or decrease with elevated temperature | Evaporation is increased. |
| As vaporization proceeds, does the anesthetic vaporizer heat up or cool and how does this affect future vaporization | It cools because the heat energy is carried away from the liquid with the energetic, mobile, evaporating molecules. Vaporization is slowed as the remaining liquid is cooled. |
| Why is copper used in current vaporizers | To prevent cooling of remaining liquid as vaporization of the anesthetic occurs. |
| What two characteristics does copper have that prevents anesthetic cooling | High thermal conductivity (transferring environmental heat easily to liquid anesthetic) and high thermal capacity (acts as a thermal reservoir to help stabilize the liquid temperature). |
| When the vaporizer dial is set to a higher percentage, what occurs to the amount of flow sent through the vaporizer chamber | The flow is increased. |
| What is the splitting ratio | The total fresh gas flow is split into the bypass flow and carrier gas/chamber flow and is automatically determined in variable bypass vaporizers. |
| Does the splitting ratio occur in variable bypass vaporizers, Tec 6 vaporizers, or both | Variable bypass vaporizers only. |
| Does fresh gas flow come into contact with the liquid agent in the Tec 6 vaporizers | No. |
| What is the temperature the Tec 6 is heated to and what vapor pressure does this temperature produce | 39C and a vapor pressure of 1500 mmHg. |
| If Desflurane were placed in a variable bypass vaporizer what would occur and why | The output would be nearly 100% and a hypoxic mixture would occur because Desflurane is near boiling point at room temperature. |
| Which vaporizer requires electric power and a 10 minute warm up period | Tec 6 vaporizer (for Desflurane). |
| What machine test is used to detect leaks from the vaporizer | A negative pressure test. |
| What are three advantages to a rebreathing system | Cost reduction, increase in tracheal warmth and humidity, and decreased potential for exposure of operating room personnel to waste gases. |
| How does total fresh gas flow affect the degree of rebreathing | Increased fresh gas flows decrease rebreathing. |
| Match: open, semi-open, semi-closed, closed Circle at high FGF (> than minute ventilation) / non breathing circuit Circle at extremely low FGF, with APL valve closed Open drop, insufflation, nasal cannula Circle at low FGF (< than minute ventilation) | Open: Open drop, insufflation, nasal cannula Semi-open: Circle at high FGF (> than minute ventilation) / non breathing circuit Semi-closed: Circle at low FGF (< than minute ventilation) Closed: Circle at extremely low FGF, with APL valve closed |
| Why do nonrebreathing systems involve high heat loss and high VAA use | Due to the requirement of high fresh gas flows. |
| What gas does the circle system prevent the patient from rebreathing | Carbon dioxide. |
| How does gas exit the circle system (via which valves) | During manual or spontaneous ventilation gas exits via the APL valve and via the ventilator relief valve during mechanical ventilation. |
| What are the two common reasons that inspired carbon dioxide increases | Absorbent granules are exhausted or unidirectional valves are faulty. |
| What should be done if inspired carbon dioxide is greater than 1-3 mmHg | Fresh gas flows should be increased to 5-8L/min to convert to a semi-open system. If this does not lower inspired carbon dioxide, unidirectional valve incompetency should be considered. |
| What are two patient conditions that are absolute contraindications for low fresh gas flows (<1L/min) | Smoke inhalational injury and maliganant hyperthermia (or other conditions in which washout of potentially dangerous gases or high oxygen uptake is expected). |
| What are relative contraindications for low fresh gas flows (<1L/min) | older equipment that is less leak proof, face mask, rigid bronchoscopy, or with uncuffed ETTs. |
| What is the purpose of adding NaOH and KOH to absorbent granules | NaOH and KOH are activators and increase the speed of reaction. |
| How much heat energy is produced with the absorption of 1 mole of CO2 | 13,000 kcal |
| What is the mechanism in which CO2 absorbent turns purple | Fresh CO2 absorbent has a caustic alkaline pH due to the sodium hydroxide (NaOH). As reactions proceed, the pH becomes alkaline. The granules turn purple once the pH is less than 10.3. |
| What does degradation of VAAs by soda lime produce | Sevoflurane degradation produces compound A and degrdation of ethyl methyl ethers produces carbon monoxide. |
| Which VAA most produces carbon monoxide when in contact with absorbent granules | Desflurane. |
| What is the main constituent in CO2 absorbent | Calcium hydroxide. |
| When do ascending (standing) bellows ascend – during inspiration or expiration | Expiration. |
| When do descending (hanging) bellows descend – during inspiration or expiration | Expiration. |
| Which type of bellows (ascending or descending) bellows will not fill in the event of circuit disconnect | Ascending (standing) bellows. |
| What are indications for pressure control ventilation | When high inspiratory pressure is particularly dangerous (LMA, emphysema, neonates/infants). |
| In older ventilators, increased fresh gas flows increase the tidal volume. What is the actual tidal volume in a patient with the ventilator set as follows: fresh gas flow 4L/min, respiratory rate 10, I:E of 1:2, tidal volume 700ml | During each minute the patient spends 1/3 of each minute in inspiratory time. 1/3 of 4000 ml/min = 1320 ml. 1320 ml/10 breaths per minute = 132 ml per breath. Total tidal volume = 832 ml/breath. |
| What was the concern with add-on PEEP adaptors | If they were accidently placed on the inspiratory limb there would be complete flow obstruction. |
| What are the two most important actions to prevent circuit fires | Turn off gas flows and vaporizers in between cases and at end of the day and ensuring that CO2 absorbent is changed regularly. |
| What is the maximum exposure to waste gases published by OSHA | 2 ppm of halogenated agents (0.5 ppm if using nitrous oxide) and 25 ppm of nitrous oxide. |
| Which disposal interface uses valves – open or closed | Closed. Closed interfaces communicates with the atmosphere only by valves. |
| When are closed interfaces useful for disposal systems | When passive scavenging is used (no dedicated suction line for the scavaneger). |
| Which interface requires a pressure relief valve – open or closed | Closed interfaces have a pressure relief valve in case of suction failure to prevent pressure buildup in the circuit and lungs. |
| What is an indicator that a closed interface is leaking gas into the operating room | A soft intermittent hissing sound is heard. |
| What does a continuous hissing sound indicate in an open interface | Properly functioning scavenging. |
| What is the most effective test for leaks in the low-pressure system | The negative pressure test. |
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