In the casualty at night, a man on home oxygen for COPD arrives by ambulance after receiving 15 L/min of oxygen through a reservoir mask for 40 minutes. He was talking on arrival but is now drowsy with a flapping tremor. SpO2 99%, RR 12/min, BP 150/90 mmHg. ABG: pH 7.21, PaCO2 92 mmHg, PaO2 210 mmHg, HCO3- 35 mmol/L. His old records show a usual PaCO2 of about 55 mmHg and a stable SpO2 of 89-90% at home. Besides arranging non-invasive ventilation, what should be done with his oxygen at once?

Titrate down to SpO2 88-92% via Venturi

Keep the reservoir mask at 15 L/min

Stop all oxygen at once until the PaCO2 falls

Switch to nasal prongs at 6 L/min

A family of four is found drowsy in the morning in a closed room in Shimla where a charcoal brazier was left burning overnight. One of them, a woman 26 weeks pregnant, lost consciousness briefly at home and now has a headache and confusion. The pulse oximeter reads SpO2 98%, carboxyhaemoglobin is 28% and the fetal heart rate is 168/min. She has been started on 100% oxygen through a tight-fitting reservoir mask. Her two children and husband have milder headaches and nausea. A hyperbaric chamber is available in the city, 1 hour away, and transfer by ambulance with oxygen can be arranged. What is the best next step?

Continue reservoir-mask oxygen alone

Switch to a 28% Venturi as SpO2 is 98%

Monitoring, ventilation and oxygen therapy

40 NEET-PG practice questions on Monitoring, ventilation and oxygen therapy, part of Anaesthesia. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
During a craniotomy for a posterior fossa tumour in the sitting position, end-tidal CO2 suddenly falls from 34 to 18 mmHg. Within a minute, blood pressure drops to 80/50 mmHg and the SpO2 falls to 91%. A precordial Doppler, placed before positioning, has changed to a loud, mill-wheel sound. Ventilator settings and the circuit are unchanged. What is the most likely cause?
1. ATension pneumothorax
2. BMalignant hyperthermia
3. CVenous air embolism
4. DAccidental extubation
Show answerHide answer
Answer: C · Venous air embolism
In the sitting position the operative site is above the heart, so air can be sucked into open veins or dural sinuses. Air reaching the pulmonary circulation creates sudden dead space, so end-tidal CO2 falls abruptly, followed by hypotension and desaturation. The surgeon should flood the field with saline and lower the head, nitrous oxide should be stopped, and air aspirated through a right atrial catheter if one is in place. Key point: Sudden fall in end-tidal CO2 with hypotension in sitting craniotomy: venous air embolism.
- A: Tension pneumothorax raises airway pressures; the trigger here is the sitting craniotomy.
- B: Malignant hyperthermia raises end-tidal CO2.
- D: Extubation would make the capnogram disappear to zero.
Question 2 · Medium
SpO2 on the ward monitor has fallen from 97% to 90% over an hour in a man with lobar pneumonia breathing room air; his pH, PaCO2 and temperature are near normal. The house surgeon wonders how far his arterial oxygen tension has fallen, assuming a normal oxygen-haemoglobin dissociation curve with a P50 of about 27 mmHg. Which PaO2 most closely corresponds to an SpO2 of 90%?
1. AAbout 40 mmHg
2. BAbout 60 mmHg
3. CAbout 80 mmHg
4. DAbout 27 mmHg
Show answerHide answer
Answer: B · About 60 mmHg
On the normal dissociation curve, saturation of about 90% corresponds to a PaO2 of about 60 mmHg, the point where the curve turns from its flat upper part onto its steep part. Below this, small further falls in PaO2 cause large falls in saturation and oxygen content, so an SpO2 of 90% is a warning that oxygen is needed. A PaO2 of 40 mmHg gives about 75% saturation (mixed venous blood), and 27 mmHg is the P50, where saturation is 50%. Key point: SpO2 90% corresponds to PaO2 about 60 mmHg, the shoulder of the dissociation curve.
- A: A PaO2 of 40 mmHg corresponds to about 75% saturation.
- C: A PaO2 of 80 mmHg gives a saturation of about 95%.
- D: 27 mmHg is the P50, where haemoglobin is only 50% saturated.
Question 3 · Hard
In the casualty at night, a man on home oxygen for COPD arrives by ambulance after receiving 15 L/min of oxygen through a reservoir mask for 40 minutes. He was talking on arrival but is now drowsy with a flapping tremor. SpO2 99%, RR 12/min, BP 150/90 mmHg. ABG: pH 7.21, PaCO2 92 mmHg, PaO2 210 mmHg, HCO3- 35 mmol/L. His old records show a usual PaCO2 of about 55 mmHg and a stable SpO2 of 89-90% at home. Besides arranging non-invasive ventilation, what should be done with his oxygen at once?
1. AKeep the reservoir mask at 15 L/min
2. BTitrate down to SpO2 88-92% via Venturi
3. CStop all oxygen at once until the PaCO2 falls
4. DSwitch to nasal prongs at 6 L/min
Show answerHide answer
Answer: B · Titrate down to SpO2 88-92% via Venturi
Excess oxygen in COPD raises PaCO2 mainly by releasing hypoxic pulmonary vasoconstriction (worse V/Q matching), by the Haldane effect and, less, by reduced respiratory drive. The fix is controlled oxygen through a Venturi mask aiming at SpO2 88-92%, plus NIV for the acidosis. Stopping oxygen abruptly is dangerous: the high alveolar CO2 displaces oxygen and PaO2 crashes below baseline. Key point: Oxygen-induced hypercapnia in COPD: step down to controlled oxygen (target 88-92%), never stop it abruptly.
- A: Uncontrolled high-flow oxygen is causing the hypercapnia.
- C: Abrupt withdrawal causes rebound hypoxaemia because alveolar CO2 is so high.
- D: 6 L/min by cannula still gives an uncontrolled, high FiO2.
Question 4 · Hard
A family of four is found drowsy in the morning in a closed room in Shimla where a charcoal brazier was left burning overnight. One of them, a woman 26 weeks pregnant, lost consciousness briefly at home and now has a headache and confusion. The pulse oximeter reads SpO2 98%, carboxyhaemoglobin is 28% and the fetal heart rate is 168/min. She has been started on 100% oxygen through a tight-fitting reservoir mask. Her two children and husband have milder headaches and nausea. A hyperbaric chamber is available in the city, 1 hour away, and transfer by ambulance with oxygen can be arranged. What is the best next step?
1. AIV methylene blue 1 mg/kg
2. BContinue reservoir-mask oxygen alone
3. CSwitch to a 28% Venturi as SpO2 is 98%
4. DTransfer for hyperbaric oxygen
Show answerHide answer
Answer: D · Transfer for hyperbaric oxygen
Standard pulse oximeters read carboxyhaemoglobin as oxyhaemoglobin, so the SpO2 of 98% is falsely reassuring. Hyperbaric oxygen shortens the COHb half-life from about 75 minutes on 100% oxygen to about 20 minutes and is advised for loss of consciousness, neurological signs, COHb above 25% and pregnancy, since fetal haemoglobin binds CO tightly and clears it slowly. Normobaric 100% oxygen continues during transfer. Key point: Severe CO poisoning (coma, COHb above 25%, pregnancy): 100% oxygen at once, then hyperbaric oxygen where available.
- A: Methylene blue treats methaemoglobinaemia, not CO poisoning.
- B: Normobaric oxygen alone is less effective when there are hyperbaric indications.
- C: The SpO2 is falsely normal in CO poisoning; reducing oxygen would be harmful.
Question 5 · Medium
A man whose son had a malignant hyperthermia reaction is listed for a laparoscopic hernia repair under general anaesthesia. The anaesthetist reviews which drugs are safe for him: 1. Propofol 2. Desflurane 3. Rocuronium 4. Nitrous oxide. Which of these can be used safely?
1. A1, 2, 3 and 4
2. B1 and 2 only
3. C3 and 4 only
4. D1, 3 and 4 only
Show answerHide answer
Answer: D · 1, 3 and 4 only
All volatile agents (halothane, isoflurane, sevoflurane, desflurane) and succinylcholine trigger malignant hyperthermia. Propofol, thiopentone, ketamine, opioids, benzodiazepines, non-depolarising relaxants, nitrous oxide and local anaesthetics are safe, so a total intravenous or regional technique with a vapour-free machine is used. Key point: MH triggers are volatile agents and succinylcholine only; propofol, nitrous oxide, non-depolarising relaxants and local anaesthetics are safe.
- A: Desflurane is a trigger, so not all four are safe.
- B: Desflurane, like every volatile agent, is a trigger, and rocuronium and nitrous oxide are safe.
- C: Propofol is also safe; it is the basis of a trigger-free anaesthetic.
Question 6 · Medium
As the relaxant wears off during a long abdominal operation, a notch appears in the plateau of each capnogram waveform while the patient is on volume-controlled ventilation. What does this cleft mean?
1. ASpontaneous breathing effort against the ventilator
2. BBronchospasm from light anaesthesia
3. CLeak around the tracheal tube cuff
4. DCardiac oscillations from a slow heart
Answer and explanation in LearnFree account
Question 7 · Hard
In the casualty at night, a man who collapsed after drinking several bottles of a fizzy cola mixed with alcohol is intubated by the duty medical officer because of a falling GCS. The bag is attached and the capnograph shows CO2 waveforms of about 30 mmHg for the first four breaths, which then become smaller with each breath and disappear by the seventh breath. The SpO2 is drifting down from 94% to 86%, the epigastrium is getting fuller with each squeeze, and he still has a pulse of 110/min with BP 106/70 mmHg. What is the most appropriate next step?
1. AStart chest compressions for cardiac arrest
2. BRemove the tube, mask-ventilate and re-intubate
3. CPush the tube 3 cm deeper and recheck
4. DKeep ventilating; the trace will stabilise
Answer and explanation in LearnFree account
Question 8 · Medium
Half an hour into a general anaesthetic with a circle system, the capnogram baseline no longer returns to zero; inspired CO2 reads 7 mmHg and end-tidal CO2 is slowly rising. Fresh gas flow is 1 L/min with oxygen, air and sevoflurane, the heart rate and temperature are normal, and the absorbent canister has not been changed for two days. What is the most likely cause?
1. AOesophageal intubation
2. BPartial airway obstruction from secretions
3. CExhausted carbon dioxide absorbent
4. DExcessive minute ventilation
Answer and explanation in LearnFree account
Question 9 · Hard
Two minutes after IV succinylcholine for a rapid sequence induction to reduce a fractured forearm, a boy who walks with a waddling gait and has enlarged calves develops peaked T waves followed by pulseless ventricular tachycardia. End-tidal CO2 had been 35 mmHg and temperature is 36.9 °C. CPR is started and a defibrillator is being charged. Which drug is the most important specific treatment?
1. AIV lignocaine
2. BIV dantrolene
3. CIV calcium chloride
4. DIV amiodarone
Answer and explanation in LearnFree account
Question 10 · Medium
During a monitoring tutorial in the recovery room, the interns list possible errors of pulse oximetry: 1. Dark blue or black nail polish can give a falsely low reading. 2. Moderate anaemia with Hb 8 g/dL makes SpO2 read falsely low. 3. Venous pulsation, as in severe tricuspid regurgitation, can lower the reading. 4. A finger probe shows a sudden fall in arterial saturation later than an ear probe. Which statements are correct?
1. A2, 3 and 4 only
2. B1, 2, 3 and 4
3. C1 and 3 only
4. D1, 3 and 4 only
Answer and explanation in LearnFree account
Question 11 · Medium
ABG on a 28% Venturi mask: pH 7.28, PaCO2 68 mmHg, PaO2 60 mmHg, HCO3- 31 mmol/L. The patient is a retired handloom weaver with COPD admitted with an exacerbation; he is alert and cooperative, RR 30/min, BP 136/80 mmHg, not vomiting and coughing out sputum. Nebulised bronchodilators and steroids have been given an hour ago. What is the best next form of respiratory support?
1. ACPAP alone at 10 cmH2O
2. BHigh-flow nasal oxygen at FiO2 0.6
3. CIntubation and invasive ventilation
4. DBilevel non-invasive ventilation
Answer and explanation in LearnFree account
Question 12 · Medium
Immediately after IV propofol and succinylcholine for elective squint surgery, a child's mouth cannot be opened for laryngoscopy because of jaw rigidity, though the limbs are flaccid. Bag-mask ventilation is easy, end-tidal CO2 is 38 mmHg, heart rate 110/min and temperature 36.8 °C. What is the most appropriate management?
1. ARepeat succinylcholine and proceed
2. BContinue as planned with sevoflurane
3. CPostpone; monitor for MH and rhabdomyolysis
4. DGive dantrolene, then proceed with sevoflurane
Answer and explanation in LearnFree account
Question 13 · Medium
SpO2 drops to 75% for about two minutes in a patient with normal ABG values, just after the urologist injects a dye intravenously to look for leakage during a procedure. Breath sounds, airway pressures, blood pressure and end-tidal CO2 are unchanged, and the patient remains pink. The reading returns to 99% within five minutes without any intervention. Which dye was most likely given?
1. AGadolinium
2. BIndocyanine green in a small dose
3. CMethylene blue
4. DFluorescein
Answer and explanation in LearnFree account
Question 14 · Medium
PaO2/FiO2 ratio of 96 mmHg on FiO2 0.8 and PEEP 14 cmH2O is recorded in a man with ARDS from leptospirosis in a Kottayam medical college ICU. He is already ventilated at 6 mL/kg predicted body weight with a plateau pressure of 27 cmH2O, is deeply sedated and haemodynamically stable. Which additional measure has been shown to reduce mortality in this situation?
1. ARoutine high-dose methylprednisolone
2. BHigh-frequency oscillatory ventilation
3. CInhaled nitric oxide
4. DProne positioning, 16 hours a day
Answer and explanation in LearnFree account
Question 15 · Easy
Which two wavelengths of light does a standard pulse oximeter use?
1. A540 nm and 760 nm
2. B450 nm and 660 nm
3. C660 nm and 940 nm
4. D805 nm and 1300 nm
Answer and explanation in LearnFree account
Question 16 · Medium
In the ICU, a woman intubated for life-threatening asthma becomes hypotensive (BP 72/40 mmHg) 15 minutes after being placed on volume control at a rate of 24/min, tidal volume 500 mL and I:E ratio 1:2. The expiratory flow curve does not return to zero before each new breath. Breath sounds are equal on both sides and the trachea is central. What is the best immediate step?
1. ADisconnect the ventilator briefly
2. BIncrease set PEEP to 15 cmH2O
3. CRaise the rate to 32 breaths/min
4. DInsert bilateral chest drains
Answer and explanation in LearnFree account
Question 17 · Medium
SpO2 falls from 99% to 93% during a long neurosurgical operation in a patient ventilated with FiO2 1.0 and no PEEP since preoxygenation 4 hours earlier. Airway pressures are normal, the tube is correctly placed and an intra-operative chest X-ray shows plate-like opacities at both bases. What is the main mechanism of this oxygenation problem?
1. AReduced production of surfactant
2. BLoss of hypoxic pulmonary vasoconstriction
3. CFree-radical injury to the alveolar lining
4. DAbsorption atelectasis after nitrogen washout
Answer and explanation in LearnFree account
Question 18 · Medium
As the ICU registrar, you review a farmer ventilated for 5 days for severe pneumonia. He is now awake and obeys commands, needs FiO2 0.35 with PEEP 5 cmH2O, is off vasopressors with BP 124/76 mmHg, has a strong cough and little secretion. His rapid shallow breathing index on a brief check is 62. What is the best next step towards extubation?
1. AExtubate without any further test
2. BSwitch to SIMV and lower the rate over 3 days
3. CElective tracheostomy before weaning
4. DA spontaneous breathing trial for 30-120 minutes
Answer and explanation in LearnFree account
Question 19 · Easy
Capnography in a ventilated asthmatic shows a waveform with a slowly rising upstroke and no flat alveolar plateau, like a shark fin. What does this pattern indicate?
1. AObstruction to expiratory airflow
2. BCircuit disconnection
3. COesophageal intubation
4. DRebreathing of expired gas
Answer and explanation in LearnFree account
Question 20 · Hard
ABG results from a ventilated man in the ICU, taken while the monitor shows end-tidal CO2: pH 7.31, PaCO2 50 mmHg, PaO2 88 mmHg on FiO2 0.5; end-tidal CO2 at the same time is 29 mmHg. He had a massive upper GI bleed, is on noradrenaline, and his blood pressure is 84/52 mmHg. He has received four units of blood so far, and the chest X-ray shows no pneumothorax. Minute ventilation and tube position are unchanged from an hour earlier, when the arterial to end-tidal CO2 gradient was 4 mmHg. What does the present gradient most likely indicate?
1. AIncreased shunt from collapsed alveoli
2. BIncreased alveolar dead space from low pulmonary perfusion
3. CA leak around the endotracheal tube cuff
4. DIncreased CO2 production from sepsis
Answer and explanation in LearnFree account
Question 21 · Medium
On the post-operative ward, a man receiving a morphine infusion is on 6 L/min oxygen by face mask. SpO2 is 98%, but he is very drowsy, with a respiratory rate of 7/min. ABG shows PaCO2 72 mmHg and pH 7.18. Why did pulse oximetry fail to warn of his deterioration?
1. AMorphine shifts the dissociation curve to the left
2. BSupplemental oxygen keeps SpO2 normal despite hypoventilation
3. CAcidosis makes the probe miss the pulse signal
4. DPulse oximeters read falsely high when CO2 is high
Answer and explanation in LearnFree account
Question 22 · Hard
Ventilator settings are being chosen for a woman with ARDS after falciparum malaria. She is 160 cm tall and weighs 82 kg. Predicted body weight for women = 45.5 + 0.91 x (height in cm - 152.4). She was admitted from a tribal area of Odisha with cerebral malaria and is now sedated and paralysed, and her PaO2/FiO2 ratio is 120 mmHg on PEEP 12 cmH2O. Chest X-ray shows bilateral infiltrates and echo shows normal heart function. Her plateau pressure will be checked after each change. Using lung-protective ventilation at 6 mL/kg, which tidal volume is closest to the target?
1. AAbout 655 mL
2. BAbout 315 mL
3. CAbout 490 mL
4. DAbout 420 mL
Answer and explanation in LearnFree account
Question 23 · Easy
Which oxygen delivery device gives a fixed, predictable FiO2 that does not change with the patient's breathing pattern?
1. AVenturi mask
2. BNon-rebreathing reservoir mask
3. CNasal cannula
4. DSimple face mask
Answer and explanation in LearnFree account
Question 24 · Medium
A simple face mask is running at 2 L/min of oxygen on a post-operative patient. What is the main hazard of this low flow?
1. ARebreathing of exhaled carbon dioxide
2. BOxygen toxicity to the lungs
3. CDrying of the nasal mucosa
4. DAbsorption atelectasis
Answer and explanation in LearnFree account
Question 25 · Easy
On the yoke of an anaesthesia machine, the pin-index holes for an oxygen cylinder are at which positions?
1. A3 and 5
2. B2 and 5
3. C1 and 5
4. D7 only
Answer and explanation in LearnFree account

15 more Monitoring, ventilation and oxygen therapy questions

Answer them one by one, keep your score and see your weak topics in Learn. Signed-out visitors try 25 per exam; sign in with Google to see them all.

Study Anaesthesia

Monitoring, ventilation and oxygen therapy

A man whose son had a malignant hyperthermia reaction is listed for a laparoscopic hernia repair under general anaesthesia. The anaesthetist reviews which drugs are safe for him: 1. Propofol 2. Desflurane 3. Rocuronium 4. Nitrous oxide. Which of these can be used safely?

As the relaxant wears off during a long abdominal operation, a notch appears in the plateau of each capnogram waveform while the patient is on volume-controlled ventilation. What does this cleft mean?

Which two wavelengths of light does a standard pulse oximeter use?

Capnography in a ventilated asthmatic shows a waveform with a slowly rising upstroke and no flat alveolar plateau, like a shark fin. What does this pattern indicate?

On the post-operative ward, a man receiving a morphine infusion is on 6 L/min oxygen by face mask. SpO2 is 98%, but he is very drowsy, with a respiratory rate of 7/min. ABG shows PaCO2 72 mmHg and pH 7.18. Why did pulse oximetry fail to warn of his deterioration?

Which oxygen delivery device gives a fixed, predictable FiO2 that does not change with the patient's breathing pattern?

A simple face mask is running at 2 L/min of oxygen on a post-operative patient. What is the main hazard of this low flow?

On the yoke of an anaesthesia machine, the pin-index holes for an oxygen cylinder are at which positions?