Equipment & Monitoring
Anesthesia machine, capnography, evoked potentials, TEE, pulse oximetry, vaporizers, ventilator. ← Back to Q-Bank
Q1. Fail-safe valve threshold
The fail-safe valve on the anesthesia machine activates when oxygen pressure drops below:
A. 50 psi
B. 25 psi
C. 16 psi
D. 10 psi
E. 5 psi
Show answer
Answer: B. Fail-safe closes at <25 psi, cutting off N₂O flow. First-stage regulator brings cylinder/pipeline gas to 45 psi; second-stage to 16 psi. A separate oxygen analyzer is required to detect crossover (e.g., incorrect pipeline gas) — the fail-safe only senses pressure.
Q2. E-cylinder pressure and volume — oxygen
A full E-cylinder of oxygen contains approximately:
A. 350 L at 1900 psi
B. 660 L at 2200 psi
C. 1500 L at 2000 psi
D. 1900 L at 750 psi
E. 200 L at 1000 psi
Show answer
Answer: B. Oxygen E-cylinder: 660 L at 2200 psi (gas phase only — pressure drops linearly with volume). Estimate remaining minutes = (gauge psi / 2200) × 660 / flow rate. Nitrous oxide E-cylinder: 1590 L at 745 psi (liquid present until ~16% remaining).
Q3. Nitrous oxide cylinder pressure
A nitrous oxide E-cylinder shows 745 psi. The most accurate statement is:
A. The cylinder is full
B. The cylinder is half-full
C. The cylinder still contains liquid N₂O; the gauge will not begin to drop until ~16% (253 L) remains
D. The cylinder pressure is read incorrectly
E. The fail-safe should engage
Show answer
Answer: C. N₂O is stored as liquid at room temperature (boiling point −88°C). Gauge reads vapor pressure (745 psi at 20°C) as long as liquid is present — only drops once all liquid is gone (~16% remaining = 253 L). Weight the cylinder for accurate volume estimate.
Q4. Capnography waveform — obstruction
A capnograph waveform with a slow, blunted upstroke and absent plateau most likely represents:
A. Normal capnogram
B. Severe airway obstruction (asthma, bronchospasm, kinked ETT)
C. Esophageal intubation
D. Cardiac arrest
E. Hyperventilation
Show answer
Answer: B. Sloping (shark-fin) capnogram = airflow obstruction (asthma, COPD, kinked ETT, partial bronchial obstruction). Also seen with leaky circuit at low FGF. Compare with normal square wave.
Q5. Sudden EtCO₂ drop to zero
A sudden drop of EtCO₂ from 35 to 0 mmHg is most likely due to:
A. Sudden hyperventilation
B. Disconnection or accidental extubation
C. Massive PE
D. Cardiac arrest with ongoing CPR
E. Bronchospasm
Show answer
Answer: B. EtCO₂ to zero = no gas movement at sampling line: disconnection, esophageal intubation, accidental extubation, complete obstruction, sampling line failure. Sudden decrease (but not to zero) suggests PE, decreased CO, cardiac arrest, ventilator-perfusion mismatch.
Q6. Capnography — rebreathing
A capnograph shows a sustained baseline above zero between breaths. This indicates:
A. Hyperventilation
B. Incompetent expiratory valve OR exhausted CO₂ absorbent → rebreathing
C. Bronchospasm
D. Hypothermia
E. Tachypnea
Show answer
Answer: B. Rebreathing pattern: inspiratory baseline > 0. Causes: incompetent expiratory valve, exhausted soda lime, inadequate fresh gas flow in Mapleson circuit. Replace absorbent; check valves.
Q7. EtCO₂ during cardiac arrest
During CPR, an EtCO₂ <10 mmHg despite adequate ventilation suggests:
A. Hyperventilation
B. Poor cardiac output from compressions; consider quality of chest compressions or futile arrest
C. Esophageal intubation
D. Pneumothorax
E. Bronchospasm
Show answer
Answer: B. EtCO₂ during CPR reflects pulmonary blood flow → cardiac output from compressions. EtCO₂ <10 = poor perfusion (poor compressions, prolonged arrest with low chance of ROSC). Sudden rise in EtCO₂ during CPR = return of spontaneous circulation. AHA recommends EtCO₂ monitoring to guide compression quality.
Q8. Capnography in obstructed airway after intubation
A patient post-intubation has a capnogram that returns to baseline but rises again before the next inspiration with a "second peak." The most likely cause is:
A. Severe asthma
B. Single-lung transplant from a COPD donor: native diseased lung exhales separately from transplanted lung
C. Bronchospasm
D. Esophageal intubation
E. Ventilator malfunction
Show answer
Answer: B. Single-lung transplant: native diseased lung empties slowly → two peaks (one from each lung). Recognized pattern after single-lung transplant for COPD.
Q9. Pulse oximetry wavelengths
The pulse oximeter measures oxygen saturation by comparing absorbance at:
A. 500 and 700 nm
B. 660 nm (red) and 940 nm (infrared)
C. 800 and 900 nm
D. 400 and 600 nm
E. 1000 and 1500 nm
Show answer
Answer: B. Red 660 nm (deoxyhemoglobin absorbs more) and infrared 940 nm (oxyhemoglobin absorbs more). Beer-Lambert law applied to pulsatile component. Carboxyhemoglobin reads as 100% (looks like O₂Hb at 660 nm). Methemoglobin reads near 85% regardless of true saturation. Fluorescein, methylene blue, indigo carmine cause transient drop in SpO₂.
Q10. Pulse ox in methemoglobinemia
In severe methemoglobinemia, the pulse oximeter typically reads:
A. 100%
B. Trends toward 85% regardless of true SaO₂
C. <50%
D. Accurately reflects SaO₂
E. Reads zero
Show answer
Answer: B. MetHb absorbs at both 660 nm and 940 nm → ratio approaches 1 → SpO₂ ~85%. Carboxyhemoglobin reads falsely high (overlap with O₂Hb at 660 nm). Co-oximetry (4-wavelength) needed for accurate measurement.
Q11. CVP waveform a-wave abnormalities
Cannon a-waves on the CVP tracing indicate:
A. Tricuspid stenosis
B. Atrial fibrillation
C. AV dissociation (atrium contracting against closed tricuspid valve)
D. Tricuspid regurgitation
E. Right bundle branch block
Show answer
Answer: C. Cannon a-waves: complete heart block, junctional rhythm, ventricular pacing — atrium contracts against closed TV. Other CVP findings: absent a-waves = AFib; large a-waves = tricuspid stenosis, RV hypertrophy; large v-waves = tricuspid regurgitation; prominent x and y descents = pericardial constriction.
Q12. Arterial line transduction errors
An arterial line shows a damped waveform with a low pressure reading. The most common cause is:
A. Tubing too long
B. Air bubble in tubing, partial occlusion of catheter, or kinked tubing
C. Incorrect transducer height
D. Patient hypothermia
E. Excessive flush solution pressure
Show answer
Answer: B. Overdamping: air bubbles, kinks, partial clots, soft compliant tubing → underestimates systolic, overestimates diastolic, accurate MAP. Underdamping: too long tubing, excess catheter movement → overestimates systolic. Square wave (fast-flush) test for damping characteristics.
Q13. SSEP sensitivity to volatile anesthetics
Compared to MEPs, somatosensory evoked potentials (SSEPs) are:
A. More sensitive to volatile anesthetics
B. Less sensitive to volatile anesthetics than MEPs
C. Equal sensitivity
D. Not affected by volatiles
E. Enhanced by volatiles
Show answer
Answer: B. Volatile sensitivity (low to high): BAEPs < SSEPs < MEPs < VEPs. SSEPs tolerable at ~0.5–1 MAC + propofol. MEPs require TIVA (propofol-based) with no volatiles. Ketamine and etomidate increase amplitude.
Q14. SSEP significant change
A 50% drop in SSEP amplitude or 10% increase in latency is clinically significant during:
A. Lumbar spine surgery
B. Carotid endarterectomy
C. Scoliosis surgery and other spine cases
D. Coronary artery bypass
E. Neck dissection
Show answer
Answer: C. 50% amplitude drop or 10% latency increase = warning threshold for spinal cord injury during scoliosis, TAAA repair, or other spine surgery. MEPs preferred for anterior spinal artery monitoring (anterior cord motor function). Wake-up test as backup.
Q15. BAEP resistance
Brainstem auditory evoked potentials (BAEPs) are useful for posterior fossa surgery because:
A. They are easily abolished by volatiles
B. They are most resistant to volatile anesthetics of evoked potentials
C. They require N2O for amplification
D. They are independent of CN VIII
E. They only monitor frontal cortex
Show answer
Answer: B. BAEPs are most resistant to volatile effects. Useful in CN VIII surgery (acoustic neuroma resection), posterior fossa surgery — monitors integrity of auditory pathway brainstem → cortex.
Q16. NIM (recurrent laryngeal) monitoring
During thyroidectomy, recurrent laryngeal nerve monitoring requires:
A. Specialized NIM ETT with electrodes contacting vocal cords; avoid NMB or use partial reversal
B. Standard ETT
C. Sugammadex-only reversal
D. Awake intubation
E. Avoidance of all opioids
Show answer
Answer: A. NIM tube has electrodes that contact the vocal cords. Avoid NMB after intubation (or use partial reversal) to allow EMG signal. Notify surgeon if paralytic given.
Q17. Cerebral oximetry NIRS
Near-infrared spectroscopy (cerebral oximetry) measures:
A. Cerebral blood flow
B. Regional cerebral tissue oxygen saturation (rSO₂), primarily venous-weighted
C. ICP
D. CMRO₂
E. Hemoglobin concentration only
Show answer
Answer: B. NIRS uses ~700–900 nm light to measure rSO₂ (25% arterial : 75% venous mixed). Normal 60–75%. Trending used during CEA, beach-chair shoulder cases, CPB. >20% drop from baseline or absolute <50% suggests cerebral ischemia.
Q18. TEE absolute contraindications
Absolute contraindications to transesophageal echocardiography include:
A. Esophageal stricture, perforation, scleroderma, recent upper GI surgery
B. Hiatal hernia
C. Mild dysphagia
D. Anticoagulation
E. Recent CABG
Show answer
Answer: A. Absolute: perforated viscus, esophageal stricture/trauma/tumor, scleroderma, Mallory-Weiss tear, Zenker diverticulum, active UGI bleed, recent UGI surgery, esophagectomy. Relative: severe cervical arthritis, prior chest radiation, symptomatic hiatal hernia, coagulopathy.
Q19. TEE LV function — sphericity index
The sphericity index (LV long-axis / short-axis) is normally:
A. <1.0
B. 1.0
C. >1.5
D. >3.0
E. Negative
Show answer
Answer: C. Normal sphericity index >1.5. Dilated cardiomyopathy → globular LV → index decreases. Important predictor of LV remodeling and outcome.
Q20. E/A ratio interpretation
A mitral inflow E/A ratio >2 indicates:
A. Normal diastolic function
B. Impaired relaxation
C. Pseudonormal
D. Restrictive filling — severe diastolic dysfunction
E. Atrial fibrillation
Show answer
Answer: D. Diastolic function grading: normal E > A; grade 1 (impaired relaxation) E < A; grade 2 (pseudonormal) E ≈ A (unmasked by Valsalva); grade 3 (restrictive) E >> A (E/A >2). Tissue Doppler e' < 8 cm/s confirms diastolic dysfunction independent of preload.
Q21. Train-of-four
For appropriate extubation from neuromuscular blockade, TOF ratio should be:
A. ≥0.5
B. ≥0.7
C. ≥0.9
D. 4 visible twitches
E. Any return of T4
Show answer
Answer: C. TOF ratio ≥0.9 indicates adequate recovery (clinical signs: sustained head lift 5 sec, hand grip, eye opening — all unreliable). Quantitative monitor recommended. Sugammadex achieves TOF >0.9 more reliably than neostigmine.
Q22. Hagen-Poiseuille and gas flow
In laminar flow, gas flow rate is most affected by:
A. Length of tubing
B. Pressure gradient
C. Viscosity of gas
D. Fourth power of the radius
E. Density
Show answer
Answer: D. Hagen-Poiseuille: Q = πr⁴ΔP / 8μL. Doubling radius → 16× flow. Critical in pediatric airway (small ETT). Turbulent flow (Reynolds >4000) depends on density (Graham's law) → heliox useful in upper airway obstruction.
Q23. Mapleson circuits
Which Mapleson circuit is most efficient for spontaneous ventilation?
A. Mapleson A
B. Mapleson B
C. Mapleson C
D. Mapleson D
E. Mapleson E
Show answer
Answer: A. Spontaneous: A > D > C > B ("All Dogs Can Bite"). Controlled: D > B > C > A ("Dead Bodies Can't Argue"). To prevent rebreathing during spontaneous ventilation, FGF = MV; during controlled, FGF = 2 × MV.
Q24. Vaporizer altitude
A desflurane vaporizer set at 6% delivers what concentration at altitude (atmospheric pressure 380 mmHg, half of sea level)?
A. 3% concentration
B. 6% concentration (because it's a heated electronic vaporizer that delivers fixed %)
C. 12% concentration
D. Cannot be calculated
E. 6% partial pressure equivalent
Show answer
Answer: B. Desflurane uses a heated electronic vaporizer (39°C, 2 atm internal pressure) that delivers a fixed concentration (%). At altitude, 6% delivered = 6% concentration, but partial pressure is halved → less anesthetic effect. Variable-bypass vaporizers (sevo, iso) deliver fixed partial pressure → at altitude % is higher but effect unchanged.
Q25. PIP vs Plateau pressure interpretation
A ventilated patient develops elevated peak inspiratory pressure but unchanged plateau pressure. The most likely cause is:
A. Decreased lung compliance (pneumonia, atelectasis)
B. Increased airway resistance (bronchospasm, kinked ETT, mucus plug)
C. Pneumothorax
D. Volume overload
E. Auto-PEEP
Show answer
Answer: B. ↑PIP with normal plateau → increased airway resistance (bronchospasm, kinked tube, secretions). ↑PIP with ↑plateau → decreased compliance (atelectasis, pneumonia, pulmonary edema, pneumothorax, intubation of mainstem bronchus). Plateau >30 cm H₂O = risk of ventilator-induced lung injury.
Q26. Core temperature monitoring sites
The gold standard for core temperature is:
A. Tympanic
B. Esophageal
C. Pulmonary artery catheter
D. Nasopharyngeal
E. Rectal
Show answer
Answer: C. Pulmonary artery temperature is the gold standard. Good alternatives: tympanic, nasopharyngeal, esophageal, oropharynx. Bladder (only accurate at high UOP), axillary, rectal (affected by stool, enteric organisms) are less reliable. Main cause of perioperative heat loss is radiation.
Q27. Bispectral index range
The target BIS (Bispectral Index) range for general anesthesia is:
A. 0–20
B. 40–60
C. 60–80
D. 80–100
E. >90
Show answer
Answer: B. BIS 40–60 = adequate depth of GA. BIS 0 = isoelectric EEG; 100 = awake. Reduces awareness when titrated to range (especially in high-risk: TIVA, NMB, paralyzed trauma). Affected by hypothermia, hypoglycemia, electrocautery, NMBDs (give a falsely high reading if patient is paralyzed under light anesthesia). Don't reliably trend with ketamine, dexmedetomidine, or nitrous.
Q28. Stroke volume variation
Stroke volume variation (SVV) is a reliable predictor of fluid responsiveness in patients who are:
A. Spontaneously breathing
B. Closed chest, regular sinus rhythm, mechanically ventilated with TV ≥8 mL/kg, no high PEEP
C. In atrial fibrillation
D. On VV-ECMO
E. With open chest
Show answer
Answer: B. SVV/PPV reliability requires closed-chest mechanical ventilation, regular rhythm, TV ≥8 mL/kg, no excessive PEEP, no RV failure. SVV >13% or PPV >12% predicts fluid responsiveness. Passive leg raise alternative for spontaneously breathing or arrhythmic patients.