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Cer.A.T.T. practice questions

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Question 1Anesthesia Equipment and Instrumentation

In the United States, which cylinder color identifies medical oxygen?

  1. Gray
  2. Yellow
  3. Green Correct answer.
  4. Black

Explanation

The US cylinder color code assigns green to oxygen, yellow to medical air, blue to nitrous oxide, and gray to carbon dioxide. Color is only a secondary check; the cylinder label and pin index must always be verified before use.

Question 2Anesthesia Equipment and Instrumentation

What is the normal operating pressure of the oxygen pipeline that supplies an anesthesia machine?

  1. 2200 psi
  2. 15 psi
  3. 50 psi Correct answer.
  4. 100 psi

Explanation

Hospital piped medical gas systems deliver oxygen at roughly 50 psi (about 345 kPa), which is the pressure the machine expects at its pipeline inlet. A full oxygen cylinder holds about 2200 psi and must pass through a regulator before reaching the machine.

Question 3Anesthesia Equipment and Instrumentation

In a variable-orifice flowmeter, gas flow is indicated by the:

  1. A spinning turbine inside the gas stream
  2. Thermal conduction of the gas
  3. A float suspended in a tapered tube Correct answer.
  4. A fixed-orifice pressure drop

Explanation

A Thorpe-tube flowmeter has a tapered bore in which a float rises until the annular area around it balances the gas flow. Because the tube is calibrated for a specific gas, viscosity and density differences make a tube inaccurate for other gases.

Question 4Anesthesia Equipment and Instrumentation

Which vaporizer design is agent-specific and maintains a relatively constant output concentration across its normal flow range?

  1. Variable-bypass Correct answer.
  2. Bubble-through
  3. Electrically heated
  4. Measured-flow

Explanation

A variable-bypass vaporizer splits fresh gas so that a small fraction passes through the vaporizing chamber while the rest bypasses it, and flow- and temperature-compensating elements keep output stable. Each such vaporizer is calibrated for one agent and must not be filled with a different agent.

Question 5Anesthesia Equipment and Instrumentation

What is the primary function of the carbon dioxide absorber in a circle breathing system?

  1. Adds moisture to inspired gas
  2. Measures exhaled tidal volume
  3. Cools the breathing gas
  4. Removes CO2 from exhaled gas Correct answer.

Explanation

The absorber canister contains soda lime or a similar hydroxide mixture that chemically binds carbon dioxide so exhaled gas can be rebreathed. This is what allows low fresh gas flows and reduces agent consumption in a circle system.

Question 6Anesthesia Equipment and Instrumentation

Which breathing system incorporates a carbon dioxide absorber and unidirectional valves?

  1. Circle system Correct answer.
  2. Mapleson A
  3. Bain circuit
  4. Jackson-Rees

Explanation

The circle system uses one-way valves to direct gas in a single path through the absorber, reservoir bag, and ventilator while preventing rebreathing of exhaled CO2 that has not been absorbed. Mapleson and Bain systems are semi-open circuits that rely on fresh gas flow rather than chemical absorption.

Question 7Anesthesia Equipment and Instrumentation

The Macintosh laryngoscope blade is characterized by:

  1. Curved blade seated in the vallecula Correct answer.
  2. Blade with an integrated camera
  3. Fiberoptic blade for awake intubation
  4. Straight blade that lifts the epiglottis

Explanation

The Macintosh blade is curved, and its tip is placed in the vallecula so that indirect lift exposes the glottis without directly loading the epiglottis. Straight blades such as the Miller are designed to pick up and lift the epiglottis directly.

Question 8Anesthesia Equipment and Instrumentation

A Yankauer suction tip is used primarily to:

  1. Clear secretions from the mouth Correct answer.
  2. Sample end-tidal gas
  3. Measure airway pressure
  4. Deliver oxygen to the trachea

Explanation

The Yankauer is a rigid, wide-bore suction tip designed for clearing blood, vomit, and secretions from the oral cavity and pharynx. It is not designed to be passed into the trachea and does not seal an airway.

Question 9Anesthesia Equipment and Instrumentation

The primary purpose of the anesthesia gas scavenging system is to:

  1. Prevent rebreathing of CO2
  2. Add humidity to the fresh gas
  3. Reduce circuit dead space
  4. Remove waste gas from the room Correct answer.

Explanation

Scavenging collects excess and exhaled anesthetic gas at the adjustable pressure limiting valve and ventilator exhaust and vents it outside the work area. This protects staff from chronic occupational exposure to trace anesthetic agents.

Question 10Anesthesia Equipment and Instrumentation

Which condition causes pulse oximetry to read falsely high?

  1. Carboxyhemoglobin Correct answer.
  2. Hypothermia
  3. Nail polish on the digit
  4. Poor peripheral perfusion

Explanation

Carboxyhemoglobin absorbs light at wavelengths similar to oxyhemoglobin, so the oximeter interprets the signal as saturated hemoglobin and overestimates SpO2. Co-oximetry is required to detect this.

Question 11Anesthesia Equipment and Instrumentation

In an intubated patient, a sudden fall in end-tidal CO2 to near zero most likely indicates:

  1. Alveolar hypoventilation
  2. Sodium bicarbonate bolus
  3. Tube disconnection Correct answer.
  4. Malignant hyperthermia

Explanation

End-tidal CO2 falls abruptly to near zero when there is no exhaled CO2 reaching the sensor, as in circuit disconnection, esophageal intubation, or complete obstruction. Malignant hyperthermia, bicarbonate, and hypoventilation all raise or sustain end-tidal CO2.

Question 12Anesthesia Equipment and Instrumentation

Which of the following is most likely to produce a falsely elevated noninvasive blood pressure reading?

  1. Undersized cuff Correct answer.
  2. Kinked inflation tubing
  3. Cuff above heart level
  4. Oversized cuff

Explanation

A cuff that is too small requires higher pressure to occlude the artery, systematically overestimating systolic and diastolic values. The cuff bladder should encircle about 80% of the arm circumference.

Question 13Anesthesia Equipment and Instrumentation

Which ECG lead is most sensitive for detecting intraoperative myocardial ischemia?

  1. Lead I
  2. Lead aVR
  3. Lead V5 Correct answer.
  4. Lead III

Explanation

Lead V5 overlies the left ventricular lateral wall, the region most often affected by ischemia, and detects ST-segment changes earlier than limb leads. Monitoring V5 together with lead II improves sensitivity.

Question 14Anesthesia Equipment and Instrumentation

What initial energy setting is typically used for biphasic defibrillation of adult ventricular fibrillation?

  1. 50 J
  2. 200 J Correct answer.
  3. 100 J
  4. 360 J

Explanation

Current guidelines recommend an initial biphasic shock in the range of about 120 to 200 J, with subsequent shocks at the same or higher energy. Monophasic devices use 360 J.

Question 15Anesthesia Equipment and Instrumentation

Free-flow protection on an infusion pump is designed to prevent:

  1. Occlusion alarm failure
  2. Battery depletion
  3. Gravity-driven overinfusion Correct answer.
  4. Air bubble entrainment

Explanation

If an infusion set is removed from a pump that lacks free-flow protection, fluid can run uncontrolled by gravity and cause a rapid overdose. Anti-free-flow mechanisms clamp the tubing whenever it is released from the pumping chamber.

Question 16Anesthesia Equipment and Instrumentation

A forced-air warming blanket should be avoided when:

  1. Skin over the area is ischemic Correct answer.
  2. Nitrous oxide is in use
  3. The patient is febrile
  4. The patient has a latex allergy

Explanation

Forced-air warming is contraindicated over skin with impaired perfusion, burns, or ischemic tissue because the already compromised skin cannot dissipate heat and may be injured further. Warming is otherwise a standard measure for preventing perioperative hypothermia.

Question 17Anesthesia Equipment and Instrumentation

A size 3 Macintosh blade is most appropriate for:

  1. Large adult needing a long blade
  2. Neonate
  3. Small child
  4. Adult with average anatomy Correct answer.

Explanation

Macintosh blades are sized 0 through 4; size 3 fits most average adults, while size 4 is used for larger adults and sizes 0 to 2 for infants and children. Blade choice should also be guided by direct visualization of the anatomy.

Question 18Anesthesia Equipment and Instrumentation

The laryngeal mask airway is designed to:

  1. Seal the nasopharynx
  2. Enter the trachea below the cords
  3. Seat over the laryngeal inlet Correct answer.
  4. Occlude the esophagus

Explanation

The LMA is a supraglottic device whose inflatable cuff forms a low-pressure seal over the laryngeal opening without entering the trachea. It does not protect against aspiration and is not a definitive airway.

Question 19Anesthesia Equipment and Instrumentation

The pressure regulator attached to an oxygen cylinder serves to:

  1. Lower cylinder pressure Correct answer.
  2. Humidify the delivered gas
  3. Increase gas flow rate
  4. Measure remaining volume

Explanation

A regulator reduces the high, variable cylinder pressure to a stable working pressure suitable for the anesthesia machine. Without it, the machine's low-pressure components would be exposed to several thousand psi.

Question 20Anesthesia Equipment and Instrumentation

A high peak inspiratory pressure alarm during volume-controlled ventilation is most likely caused by:

  1. Cuff leak
  2. Circuit disconnection
  3. Kinked endotracheal tube Correct answer.
  4. Reduced tidal volume setting

Explanation

A kink, biting, mucus plug, or bronchospasm raises resistance and therefore the pressure needed to deliver the set tidal volume, triggering the high-pressure alarm. Disconnection and leaks produce low-pressure alarms instead.

Question 21Anesthesia Equipment and Instrumentation

The oxygen failure protection device (OFPD) on an anesthesia machine:

  1. Cuts nitrous oxide flow when oxygen pressure is lost Correct answer.
  2. Vents excess gas to the scavenging system
  3. Increases oxygen flow to compensate for a leak
  4. Sounds an alarm when the oxygen cylinder is nearly empty

Explanation

The OFPD is a pressure-sensing valve that proportionally reduces or shuts off nitrous oxide (and other gases) when oxygen supply pressure falls, preventing delivery of a hypoxic mixture. It is a safety device independent of the low-pressure alarm.

Question 22Anesthesia Equipment and Instrumentation

Which ventilation mode delivers a set tidal volume regardless of changes in airway resistance?

  1. Volume control ventilation Correct answer.
  2. Pressure control ventilation
  3. CPAP with PEEP
  4. Pressure support ventilation

Explanation

In volume control, the ventilator delivers a fixed tidal volume and peak pressure varies with compliance and resistance. Pressure control delivers a fixed pressure and lets tidal volume change, which is why volume monitoring is essential in that mode.

Question 23Anesthesia Equipment and Instrumentation

Which factor most limits the use of very low fresh gas flows in a circle system?

  1. Absorber overheating
  2. Nitrogen accumulation Correct answer.
  3. Increased dead space
  4. Loss of PEEP

Explanation

At low flows, nitrogen washed in from the patient and any air entrained accumulates in the circuit, and the inspired oxygen fraction can drift unless the analyzer is monitored. Trace gases and exhaled metabolites also accumulate, so gas analysis is required.

Question 24Anesthesia Equipment and Instrumentation

An E-cylinder of oxygen holds about 660 L when full at 2200 psi. Approximately how much oxygen remains when the gauge reads 1000 psi?

  1. 500 L
  2. 660 L
  3. 300 L Correct answer.
  4. 150 L

Explanation

For a gas that behaves nearly ideally, remaining volume is proportional to gauge pressure, so 1000/2200 times 660 L is about 300 L. This proportionality fails only when the cylinder is nearly empty and the pressure falls steeply.

Question 25Anesthesia Equipment and Instrumentation

In a Bain circuit, fresh gas travels to the patient through:

  1. An inner tube ending near the patient Correct answer.
  2. A one-way valve at the patient end
  3. The outer corrugated reservoir limb
  4. A CO2 absorber canister

Explanation

The Bain is a coaxial Mapleson D: fresh gas runs down a narrow inner tube and exits at the patient end, while exhaled gas returns through the outer limb to the reservoir bag and pressure-limiting valve. This coaxial design warms inspired gas but makes kinking or disconnection of the inner tube hard to detect.

Question 26Anesthesia Equipment and Instrumentation

In the United States, the color code used to identify an oxygen gas cylinder is:

  1. Yellow
  2. Gray
  3. Blue
  4. Green Correct answer.

Explanation

US cylinder color coding assigns green to oxygen, blue to nitrous oxide, gray to carbon dioxide, and yellow to medical air. Color coding is a secondary identifier only; the pin index and cylinder label remain the definitive checks.

Question 27Anesthesia Equipment and Instrumentation

When the oxygen flush valve on an anesthesia machine is depressed, oxygen is delivered at a flow of approximately:

  1. 35 to 75 L/min Correct answer.
  2. 5 to 10 L/min
  3. 200 to 300 L/min
  4. 100 to 150 L/min

Explanation

The flush valve bypasses the flowmeters and vaporizers and delivers pipeline-pressure oxygen directly to the breathing system at roughly 35 to 75 L/min. Because it is a high-pressure, high-flow source, it can rapidly over-pressurize the lungs if used during a closed circuit.

Question 28Anesthesia Equipment and Instrumentation

The Miller laryngoscope blade differs from the Macintosh blade in that the Miller blade:

  1. contains a built-in oxygen insufflation channel
  2. is intended solely for adult patients
  3. is straight and directly lifts the epiglottis Correct answer.
  4. has a curved tip that rests in the vallecula

Explanation

A straight (Miller) blade is passed beneath the epiglottis and lifts it directly to expose the glottis. A curved (Macintosh) blade places its tip in the vallecula and lifts indirectly, and both are made in sizes for all age groups.

Question 29Anesthesia Equipment and Instrumentation

Pulse oximetry estimates arterial oxygen saturation by comparing light absorption at which pair of wavelengths?

  1. 805 nm and 880 nm
  2. 660 nm and 940 nm Correct answer.
  3. 540 nm and 570 nm
  4. 700 nm and 800 nm

Explanation

Oximeters use a red (about 660 nm) and an infrared (about 940 nm) light source; oxyhemoglobin and deoxyhemoglobin absorb these wavelengths differently. The ratio of pulsatile absorption at the two wavelengths yields the saturation estimate.

Question 30Anesthesia Equipment and Instrumentation

The pin index safety system on an E-cylinder yoke is designed to prevent:

  1. connection of a cylinder containing the wrong gas Correct answer.
  2. attachment of a cylinder that has not been grounded
  3. excessive gas flow through the pressure regulator
  4. overfilling of the cylinder at the filling plant

Explanation

Two pins on the yoke must line up with two holes in the cylinder valve, and the pin positions are different for each gas. A cylinder of the wrong gas therefore cannot be seated and connected.

Question 31Anesthesia Equipment and Instrumentation

During manual (bag) ventilation of an intubated patient, the adjustable pressure-limiting valve should be:

  1. closed or nearly closed to permit lung inflation Correct answer.
  2. removed to reduce circuit resistance
  3. fixed at 30 cm H2O throughout the case
  4. fully open so excess gas vents to the room

Explanation

Positive-pressure ventilation requires the APL valve to be closed or nearly closed so gas is directed to the lungs rather than vented. It must be reopened before spontaneous ventilation resumes to prevent excessive circuit pressure.

Question 32Anesthesia Equipment and Instrumentation

An endotracheal tube cuff inflated with air and exposed to nitrous oxide will most likely:

  1. rise in pressure as nitrous oxide diffuses into the cuff Correct answer.
  2. remain at a constant pressure indefinitely
  3. deflate as nitrous oxide leaves the cuff
  4. rupture within a few minutes of exposure

Explanation

Nitrous oxide is far more soluble in blood and tissue than nitrogen, so it diffuses into the cuff faster than nitrogen diffuses out. Intracuff pressure therefore rises during nitrous oxide anesthesia and should be checked and adjusted periodically.

Question 33Anesthesia Equipment and Instrumentation

Which monitoring technique places the carbon dioxide sensor directly in the patient's breathing circuit rather than aspirating gas to a remote analyzer?

  1. Aspiration capnography
  2. Microstream capnography
  3. Sidestream capnography
  4. Mainstream capnography Correct answer.

Explanation

Mainstream capnography mounts a heated cuvette containing the sensor in the breathing circuit at the airway. Sidestream and microstream systems aspirate gas through a sampling tube to a remote measuring chamber.

Question 34Anesthesia Equipment and Instrumentation

Which finding most strongly suggests that the carbon dioxide absorbent in a circle system is exhausted?

  1. The unidirectional valves begin to flutter
  2. The reservoir bag becomes overdistended
  3. The inspired CO2 concentration rises above zero Correct answer.
  4. The required fresh gas flow increases

Explanation

When the absorbent can no longer remove CO2, exhaled carbon dioxide passes through to the inspiratory limb. The capnogram or inspired gas analyzer then shows a CO2 concentration above zero during inspiration.

Question 35Anesthesia Equipment and Instrumentation

The desflurane vaporizer is unique among agent-specific vaporizers because it:

  1. uses a wick to increase the vaporizing surface area
  2. requires no temperature-compensating mechanism
  3. cannot be used at fresh gas flows below 1 L/min
  4. is heated and pressurized to keep output constant Correct answer.

Explanation

Desflurane has a vapor pressure near 669 mmHg at room temperature and boils readily, so its vaporizer is electrically heated to about 39°C and pressurized to deliver a controlled concentration. Output is regulated by injecting saturated vapor into the fresh gas stream.

Question 36Anesthesia Equipment and Instrumentation

A PEEP valve attached to the expiratory limb of a breathing circuit is used to:

  1. maintain a set positive pressure at end-expiration Correct answer.
  2. limit the peak inspiratory pressure during ventilation
  3. prevent negative pressure during the inspiratory phase
  4. measure the tidal volume being exhaled

Explanation

A PEEP valve provides a threshold resistance during exhalation so that airway pressure does not return to zero, keeping alveoli recruited. The applied PEEP is set on the valve or ventilator and is distinct from the peak inspiratory pressure limit.

Question 37Anesthesia Equipment and Instrumentation

An ascending (rising) bellows ventilator is preferred in anesthesia because it:

  1. is easier to sterilize between cases
  2. collapses and alarms if the circuit disconnects Correct answer.
  3. delivers tidal volume independent of compliance
  4. requires no driving gas to cycle

Explanation

Because the ascending bellows is filled by the driving gas and hangs from its own weight during exhalation, a circuit disconnection allows it to fall and remain down, triggering the alarm. A descending bellows may continue to cycle despite a disconnect.

Question 38Anesthesia Equipment and Instrumentation

During the pre-use leak test of the low-pressure circuit, the APL valve is closed and the Y-piece is occluded. Which result indicates that the circuit has passed the test?

  1. Pressure continues to rise until the bag ruptures
  2. The breathing bag doubles in size and stays inflated
  3. The ventilator bellows fills and empties repeatedly
  4. Pressure rises to about 25 cm H2O and holds steady Correct answer.

Explanation

With the valve closed and the Y-piece occluded, the circuit is pressurized to roughly 25 to 30 cm H2O and observed. A stable pressure indicates an intact circuit, whereas a steady decline signals a leak.

Question 39Anesthesia Equipment and Instrumentation

The vaporizer interlock system on an anesthesia machine is designed to:

  1. prevent the vaporizer from tipping over on the manifold
  2. prevent backflow of gas into the flowmeter block
  3. ensure that only one vaporizer can be turned on at a time Correct answer.
  4. limit agent concentration to 2 MAC

Explanation

The interlock mechanically prevents more than one vaporizer from being activated simultaneously, avoiding delivery of a mixture of potent agents at unpredictable concentrations. Turning on a second vaporizer requires turning the first off.

Question 40Anesthesia Equipment and Instrumentation

A nitrous oxide E-cylinder at room temperature that is about half emptied of its liquid contents will show a gauge pressure of approximately:

  1. 1900 psi
  2. 1100 psi
  3. 745 psi Correct answer.
  4. 2200 psi

Explanation

Nitrous oxide is stored as a liquid-vapor mixture, so the gauge reflects its vapor pressure (about 745 psi at 20°C) rather than the amount remaining. The pressure stays at this value until all the liquid has evaporated; only then does it begin to fall.

Question 41Patient Monitoring and Physiologic Data Interpretation

Pulse oximeters estimate arterial oxygen saturation by comparing light absorption at which pair of wavelengths?

  1. 540 nm and 570 nm
  2. 805 nm and 1300 nm
  3. 660 nm and 940 nm Correct answer.
  4. 450 nm and 495 nm

Explanation

Pulse oximetry compares the absorption of red light (about 660 nm) by deoxyhemoglobin with that of infrared light (about 940 nm) by oxyhemoglobin. Only the pulsatile portion of each signal is analyzed, which isolates the arterial component from venous blood and tissue.

Question 42Patient Monitoring and Physiologic Data Interpretation

The normal range for end-tidal CO2 in a healthy, spontaneously breathing adult is approximately:

  1. 50 to 60 mmHg
  2. 35 to 45 mmHg Correct answer.
  3. 10 to 20 mmHg
  4. 65 to 75 mmHg

Explanation

End-tidal CO2 approximates alveolar CO2, which equilibrates with arterial CO2 at roughly 40 mmHg in a healthy adult at rest. Values in the 35 to 45 mmHg range therefore reflect normal ventilation.

Question 43Patient Monitoring and Physiologic Data Interpretation

A blood pressure cuff bladder is appropriately sized when its width is approximately what percentage of the limb circumference?

  1. 60% Correct answer.
  2. 80%
  3. 40%
  4. 20%

Explanation

A cuff that is too narrow transmits pressure inefficiently and falsely elevates the reading, while an oversized cuff falsely lowers it. A bladder width of about 40% of limb circumference, with a length of about 80%, provides the most accurate measurement.

Question 44Patient Monitoring and Physiologic Data Interpretation

Which ECG lead is most commonly used for continuous rhythm monitoring because it usually produces the largest P waves?

  1. Lead V5
  2. Lead II Correct answer.
  3. Lead aVR
  4. Lead I

Explanation

Lead II is oriented nearly parallel to the atrial depolarization vector, so P waves are usually upright and prominent. This makes it the standard choice for detecting arrhythmias and verifying atrioventricular relationships.

Question 45Patient Monitoring and Physiologic Data Interpretation

A normal central venous pressure in a spontaneously breathing adult is approximately:

  1. 22 to 26 mmHg
  2. 2 to 6 mmHg Correct answer.
  3. 10 to 15 mmHg
  4. 16 to 20 mmHg

Explanation

Central venous pressure reflects right atrial pressure, which is normally 2 to 6 mmHg when intrathoracic pressure is near atmospheric. Positive-pressure ventilation, PEEP, and right heart failure all raise this value.

Question 46Patient Monitoring and Physiologic Data Interpretation

A pulse oximeter probe and a cycling NIBP cuff are placed on the same arm. What is the most appropriate action?

  1. Set the NIBP to stat mode for faster readings.
  2. Wrap the probe in a light-blocking shield.
  3. Increase the NIBP cycle interval to 15 minutes.
  4. Move the probe to the opposite limb. Correct answer.

Explanation

Cuff inflation occludes the brachial artery and abolishes the pulsatile signal the oximeter needs, which can cause dropout or a false desaturation reading. Placing the probe on a limb without a cycling cuff preserves a reliable signal.

Question 47Patient Monitoring and Physiologic Data Interpretation

During general anesthesia, a BIS value in which range is most consistent with an adequate depth of hypnosis?

  1. 40 to 60 Correct answer.
  2. 70 to 90
  3. 0 to 20
  4. 20 to 40

Explanation

The BIS index is a processed EEG scale from 0 (electrical suppression) to 100 (awake). A value between 40 and 60 is the range generally targeted for general anesthesia.

Question 48Patient Monitoring and Physiologic Data Interpretation

Which value represents normal adult core body temperature?

  1. 37.0 °C Correct answer.
  2. 34.0 °C
  3. 36.0 °C
  4. 35.0 °C

Explanation

Normal core temperature in an adult is approximately 36.5 to 37.5 °C. Core temperatures below 36 °C define hypothermia, which has implications for drug metabolism, coagulation, and cardiac rhythm.

Question 49Patient Monitoring and Physiologic Data Interpretation

Immediately after intubation, the capnograph shows no CO2 waveform through several breaths despite chest rise with bag ventilation. This finding most strongly suggests:

  1. Normal CO2 washout after a long period of apnea
  2. Esophageal placement of the tube Correct answer.
  3. A mucus plug in the sampling line only
  4. Hyperventilation of the patient

Explanation

The esophagus contains no gas-exchanging surface, so an esophageal tube produces no sustained CO2 waveform. Because chest rise can be produced by esophageal ventilation, detection of CO2 over several breaths is the most reliable confirmation of tracheal placement.

Question 50Patient Monitoring and Physiologic Data Interpretation

A small cleft appears in the alveolar plateau of the capnogram of a paralyzed, mechanically ventilated patient. This most likely indicates:

  1. Calibration drift of the infrared CO2 sensor
  2. A leak around the endotracheal tube cuff during ventilation
  3. Complete obstruction of the gas sampling tubing
  4. Return of spontaneous breathing effort Correct answer.

Explanation

A cleft or notch in the plateau, sometimes called a curare cleft, is produced by a small spontaneous breath superimposed on mechanical ventilation. It signals partial return of neuromuscular function or an inadequate level of blockade.