Read the pH: below 7.35 is acidosis, above 7.45 alkalosis.
Find the value that explains it: PaCO₂ moving opposite to the pH is respiratory, HCO₃⁻ moving with the pH is metabolic.
Look at the other value: normal means uncompensated, abnormal in the compensating direction means partial compensation, and a normal pH with both abnormal means full compensation.
In a metabolic acidosis, compare PaCO₂ with Winter’s formula, 1.5·HCO₃⁻ + 8 ± 2, and calculate the anion gap Na⁺ − (Cl⁻ + HCO₃⁻).
Check a high anion gap with the delta ratio and, when albumin is low, with the corrected gap.
Nursing math & unit conversions
Metric steps
1 kg = 1000 g, 1 g = 1000 mg, 1 mg = 1000 mcg, 1 L = 1000 mL
Weight and length
1 kg = 2.2 lb, 1 lb = 16 oz, 1 in = 2.54 cm, 1 ft = 12 in
Household measures
1 tsp = 5 mL, 1 tbsp = 15 mL, 1 fl oz = 30 mL, 1 cup = 8 fl oz = 240 mL
Write the given quantity with its unit and the unit you want.
Pick the equivalent: 1000 between kg, g, mg and mcg or L and mL; 1 kg = 2.2 lb; 1 tsp = 5 mL, 1 tbsp = 15 mL, 1 fl oz = 30 mL, 1 cup = 240 mL.
Write it as a fraction so that the unwanted unit cancels; for a rate, use one fraction per unit that changes.
Check the direction: a smaller unit gives a bigger number.
Round only the final answer, to the precision the question names.
2Practice problems
1.Clinical assessment scoresMedium
Practice exercise (made-up values, not clinical guidance). Use the NEWS2 chart (SpO₂ scale 1) for these observations: respiration rate 20/min, SpO₂ 89% on supplemental oxygen, blood pressure 78/46 mmHg, pulse 70/min, alert, temperature 36.4 °C. What is the NEWS2 total score?
RR 20SpO₂ 89%O₂SBP 78HR 70AT 36.4 °C
NEWS2 =
2.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). An adult weighs 111 kg and is 187 cm tall. Calculate the BMI and click the WHO weight category.
111 kg187 cm
1underweight
2healthy weight
3overweight
4obesity class I
5obesity class II
6obesity class III
3.Arterial blood gas interpretationMedium
Practice values: Na⁺ 146 mmol/L, glucose 11.2 mmol/L and urea 7.4 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 146 mmol/Lglucose 11.2 mmol/Lurea 7.4 mmol/L
Osm = mOsm/kg
4.Arterial blood gas interpretationHard
A practice gas shows a respiratory acidosis: pH 7.24, PaCO₂ 80 mmHg (10.7 kPa), HCO₃⁻ 33 mmol/L. Use the rules ‘HCO₃⁻ rises 1 mmol/L per 10 mmHg (acute) or 3.5 mmol/L per 10 mmHg (chronic)’ to classify it. Click your answer.
pH 7.24PaCO₂ 80 mmHg (10.7 kPa)HCO₃⁻ 33 mmol/L
1acute
2chronic
3acute on chronic
5.Nursing fundamentalsMedium
Why is a slide sheet used to move a patient up the bed?
AIt warms the patient during the move
BIt lets one nurse lift the patient alone
CIt reduces friction and shear on the skin
DIt keeps the bed clean during the move
6.Nursing fundamentalsHard
A patient with COPD and a known risk of hypercapnia is acutely breathless with an SpO₂ of 82%. What is correct?
AWait for an arterial blood gas result before giving any oxygen at all
BWithhold oxygen completely, because oxygen is dangerous in COPD
CGive controlled oxygen, e.g. via a Venturi mask, aiming for 88–92%
DGive the highest oxygen flow possible and aim for 100%
7.Nursing math & unit conversionsMedium
Practice exercise (made-up values, not clinical guidance). A dose is charted at 22:10 (24-hour clock). Which entry is the same time on the 12-hour clock? Click it.
22:10
110:10 AM
212:10 PM
310:10 PM
49:10 PM
8.Nursing math & unit conversionsHard
Practice exercise (made-up values, not clinical guidance). A prescription reads 1½ tsp of an oral suspension twice a day for 7 days. Using 1 tsp = 5 mL, how many mL V are needed for the whole course?
1½ tsptwice a day7 days1 tsp = 5 mL
V = mL
3Solutions
1.Clinical assessment scores
Answer: NEWS2 = 8
NEWS2 (National Early Warning Score 2, Royal College of Physicians 2017): score each of the seven parameters with the chart (respiration rate, SpO₂ on scale 1, air or supplemental oxygen, systolic blood pressure, pulse, consciousness on the ACVPU scale and temperature) and add the scores. Clinical risk: 0–4 low; a score of 3 in any single parameter low–medium; 5–6 medium; 7 or more high. A total of 5 or more needs an urgent response.
Score each parameter
RR 20/min → 0
SpO₂ 89% → 3
on oxygen → 2
SBP 78 mmHg → 3
HR 70/min → 0
alert (A) → 0
T 36.4 °C → 0
Add
NEWS2 = 0 + 3 + 2 + 3 + 0 + 0 + 0 = 8
Answer
NEWS2 = 8
2.Clinical assessment scores
Answer: obesity class I
Body mass index: BMI = weight (kg)/height (m)², with the height converted to metres first. With pounds and inches, BMI = 703 × weight (lb)/height (in)². WHO adult categories: below 18.5 underweight, 18.5–24.9 healthy weight, 25.0–29.9 overweight, 30.0–34.9 obesity class I, 35.0–39.9 obesity class II and 40 or more obesity class III.
BMI
BMI = 111/1.87² = 31.74
Category
obesity class I
Answer
obesity class I
3.Arterial blood gas interpretation
Answer: Osm = 311 mOsm/kg
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 = 2·146 + 11.2 + 7.4 = 310.6 ≈ 311 mOsm/kg
Answer
Osm = 311 mOsm/kg
4.Arterial blood gas interpretation
Answer: acute on chronic
Expected compensation: in metabolic acidosis Winter’s formula predicts PaCO₂ = 1.5·HCO₃⁻ + 8 ± 2 mmHg; a measured value above that range points to an additional respiratory acidosis, below it to an additional respiratory alkalosis. The anion gap AG = Na⁺ − (Cl⁻ + HCO₃⁻), normally about 8–12 mmol/L, separates high-gap from normal-gap metabolic acidosis; low albumin hides a high gap (add 2.5 per g/dL that albumin is below 4.0). The delta ratio (AG − 12)/(24 − HCO₃⁻) between about 0.8 and 2 fits a pure high-gap acidosis (some texts use 1 instead of 0.8), below that an added normal-gap acidosis, and above 2 an added metabolic alkalosis.
Expected HCO₃⁻
acute: 24 + 1·4 = 28 mmol/L
chronic: 24 + 3.5·4 = 38 mmol/L
Compare
measured: 33 mmol/L → acute on chronic
Answer
acute on chronic
5.Nursing fundamentals
Answer: C · It reduces friction and shear on the skin
Why this is the answer
Slide sheets let the patient glide rather than be dragged, protecting the skin from friction and shear and reducing strain on staff.
Answer
C · It reduces friction and shear on the skin
6.Nursing fundamentals
Answer: C · Give controlled oxygen, e.g. via a Venturi mask, aiming for 88–92%
Why this is the answer
Oxygen must not be withheld from a hypoxic patient. In those at risk of hypercapnia it is given in a controlled way to a target of 88–92%, with blood gases checked.
Answer
C · Give controlled oxygen, e.g. via a Venturi mask, aiming for 88–92%
7.Nursing math & unit conversions
Answer: 10:10 PM
24-hour clock: from 1 PM onwards add 12 to the hour (3:45 PM = 15:45). Midnight to 12:59 AM is 00:00–00:59, and 12:00–12:59 PM stays 12:00–12:59. Going back, subtract 12 from hours 13–23 and add PM; hours 00 become 12 AM. Count time across midnight in two parts: up to 24:00 (00:00), then from 00:00 on.
Convert the hour
22 − 12 = 10 → PM
Answer
10:10 PM
Answer
10:10 PM
8.Nursing math & unit conversions
Answer: V = 105 mL
Dimensional analysis: write the given quantity, then multiply by conversion factors written as fractions (for example 60 min/1 h or 1 mg/1000 mcg) so that each unwanted unit appears once on top and once underneath and cancels. When only the wanted unit is left, calculate. Use the equivalents the question gives and round only the final answer.