Respiratory Care and Oxygen Therapy: practice problems and exam questions

Oxygen delivery and the lungs for nursing and respiratory-care students: FiO₂ estimates, cylinder contents and duration, minute and alveolar ventilation, lung-protective tidal volumes, the P/F ratio and ARDS grades, oxygen content and delivery, blood gases and early-warning scores.

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Cram pack (PDF)Formula sheets, method steps and practice problems with full solutions, ready to print.

Topics in this course

  1. Oxygen therapy & respiratory calculationsFiO₂, cylinder contents and minute ventilation · cylinder duration, P/F ratio and oxygen content · oxygen delivery, ventilation targets and ARDS severitycalculations
  2. Arterial blood gas interpretationacid–base classification · compensation and expected values · mixed disorders and gas exchangecalculations
  3. Clinical assessment scoresGCS, APGAR, MAP and BMI · Braden, Morse, NEWS2 and shock index · risk categories and interpretationcalculations
  4. Med-surg: cardiovascular & respiratorykey terms and facts · applying the concepts · cases and analysismultiple choice

Exam tips for Respiratory Care and Oxygen Therapy

  • Use FiO₂ and SaO₂ as fractions in every formula.
  • Keep the safe residual in a cylinder and round its duration down.
  • Base tidal volumes on the predicted body weight from height and sex, not on the actual weight.

Worked examples

Oxygen therapy & respiratory calculationsEasy
0123456L/minFiO₂ ≈ ?21% + 4%·L/min

Practice exercise (made-up values, not clinical guidance). A patient receives oxygen by nasal cannula at 2 L/min. Using FiO₂ ≈ 21% + 4% per L/min, estimate the inspired oxygen FiO₂ in percent.

2 L/min

Find FiO₂ (%)

Show hints
  1. Room air already contains 21% oxygen.
  2. Each L/min adds about 4%.
  3. 4·2 = 8%.
Show the answer and the step-by-step solution

Estimating FiO₂: room air is 21% oxygen. A nasal cannula adds roughly 4% for every L/min, used from 1 to 6 L/min, so FiO₂ ≈ 21% + 4% × flow (about 25–45%). The real value depends on the breathing pattern. For calculations FiO₂ is used as a fraction: 40% = 0.40.

Estimate

FiO₂ ≈ 21 + 4·2 = 29 %
= 0.29 as a fraction

Answer

FiO₂ = 29 %
Arterial blood gas interpretationMedium

Practice values: Na⁺ 151 mmol/L, glucose 17.6 mmol/L and urea 22.7 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.

Na⁺ 151 mmol/Lglucose 17.6 mmol/Lurea 22.7 mmol/L

Find Osm (mOsm/kg)

Show hints
  1. Sodium and its anions make most of the osmolality: 2·Na⁺.
  2. Add glucose and urea as they are; all values are in mmol/L.
  3. 2·151 = 302.
Show the answer and the step-by-step solution

Derived values: calculated serum osmolality is 2·Na⁺ + glucose + urea with all values in mmol/L (2·Na⁺ + glucose/18 + BUN/2.8 with glucose and BUN in mg/dL); normal is about 275–295 mOsm/kg. The P/F ratio is PaO₂ divided by FiO₂ as a fraction. The alveolar oxygen pressure is PAO₂ = FiO₂·(760 − 47) − PaCO₂/0.8 mmHg at sea level, and the A–a gradient is PAO₂ − PaO₂.

Calculated osmolality

Osm = 2·151 + 17.6 + 22.7 = 342.3 ≈ 342 mOsm/kg

Answer

Osm = 342 mOsm/kg

How practising works

  • “Practise this course” mixes problems from all its topics, like a real exam.
  • Every problem has new values, so you learn the method instead of an answer.
  • Stuck? Open a small hint first, and the full explanation only when you need it.
  • Mock exams are timed and have no hints, and you get your score and a full review at the end.

Calculators for this course

Glasgow Coma Scale calculator (GCS and GCS-P)APGAR score calculatorBraden scale calculator (pressure injury risk)Morse fall scale calculator (fall risk)NEWS2 score calculator (National Early Warning Score 2)Oxygen cylinder duration calculator (tank factor)P/F ratio calculator with FiO2 estimate (nasal cannula)Anion gap calculator (albumin-corrected, delta ratio)

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Practise this course for freePractise this courseTake a mock exam5 free problems every day. No card needed.