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 9/min, SpO₂ 91% on room air, blood pressure 118/70 mmHg, pulse 82/min, alert, temperature 37.7 °C. What is the NEWS2 total score?
RR 9SpO₂ 91%airSBP 118HR 82AT 37.7 °C
NEWS2 =
2.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). Use the NEWS2 chart (SpO₂ scale 1) for these observations: respiration rate 7/min, SpO₂ 97% on room air, blood pressure 150/90 mmHg, pulse 58/min, alert, temperature 36.7 °C. Which clinical risk group does the patient fall into? Click it.
RR 7SpO₂ 97%airSBP 150HR 58AT 36.7 °C
1low
2low–medium
3medium
4high
3.Arterial blood gas interpretationMedium
A practice gas shows PaCO₂ 68 mmHg (9.1 kPa). Use the rule that in chronic respiratory acidosis HCO₃⁻ rises by 3.5 mmol/L for every 10 mmHg that PaCO₂ is above 40, starting from HCO₃⁻ 24 mmol/L, to find the expected HCO₃⁻.
A practice gas shows a respiratory acidosis: pH 7.29, PaCO₂ 65 mmHg (8.7 kPa), HCO₃⁻ 30 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 7.29PaCO₂ 65 mmHg (8.7 kPa)HCO₃⁻ 30 mmol/L
1acute
2chronic
3acute on chronic
5.Nursing fundamentalsMedium
When is a sputum sample for culture best collected?
AAt any time, using saliva from the mouth
BIn the evening, after the patient has eaten and drunk
CAfter the first few doses of antibiotics
DIn the morning, from a deep cough, before antibiotics start
6.Nursing fundamentalsHard
Lying and standing blood pressure are measured. Which result meets the usual definition of orthostatic hypotension?
AA rise in systolic pressure of 20 mmHg on standing
BA fall in systolic pressure of 20 mmHg or more within 3 minutes of standing
CA fall in systolic pressure of 5 mmHg or more after 10 minutes of standing still
DA rise in heart rate of 5 beats per minute on standing
7.Nursing math & unit conversionsMedium
Practice exercise (made-up values, not clinical guidance). A patient’s temperature is 38.6 °C. Convert it to degrees Fahrenheit T with °F = °C × 9/5 + 32. Round to one decimal place.
38.6 °C
T = °F
8.Nursing math & unit conversionsHard
Practice exercise (made-up values, not clinical guidance). An infusion starts at 23:40 and finishes at 00:50 the next morning (24-hour clock). How many minutes t did it run?
23:4000:50
t = min
3Solutions
1.Clinical assessment scores
Answer: NEWS2 = 4
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 9/min → 1
SpO₂ 91% → 3
on air → 0
SBP 118 mmHg → 0
HR 82/min → 0
alert (A) → 0
T 37.7 °C → 0
Add
NEWS2 = 1 + 3 + 0 + 0 + 0 + 0 + 0 = 4
Answer
NEWS2 = 4
2.Clinical assessment scores
Answer: low–medium
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 7/min → 3
SpO₂ 97% → 0
on air → 0
SBP 150 mmHg → 0
HR 58/min → 0
alert (A) → 0
T 36.7 °C → 0
Total and red scores
NEWS2 = 3 + 0 + 0 + 0 + 0 + 0 + 0 = 3
At least one parameter scores 3.
Risk group
low–medium
Answer
low–medium
A single score of 3 needs an urgent review even when the total is low.
3.Arterial blood gas interpretation
Answer: HCO₃⁻ = 33.8 mmol/L
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.
Change in PaCO₂
|68 − 40| = 28 mmHg → 2.8 × 10 mmHg
Expected HCO₃⁻
HCO₃⁻ = 24 + 3.5·2.8 = 33.8 mmol/L
Answer
HCO₃⁻ = 33.8 mmol/L
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 + 1·2.5 = 26.5 mmol/L
chronic: 24 + 3.5·2.5 = 32.75 mmol/L
Compare
measured: 30 mmol/L → acute on chronic
Answer
acute on chronic
5.Nursing fundamentals
Answer: D · In the morning, from a deep cough, before antibiotics start
Why this is the answer
An early-morning sample from deep in the chest gives the best yield. Saliva is not sputum, and antibiotics can stop organisms growing in the lab.
Answer
D · In the morning, from a deep cough, before antibiotics start
6.Nursing fundamentals
Answer: B · A fall in systolic pressure of 20 mmHg or more within 3 minutes of standing
Why this is the answer
Orthostatic hypotension is usually defined as a fall of at least 20 mmHg systolic or 10 mmHg diastolic within 3 minutes of standing. It is an important finding in falls assessment.
Answer
B · A fall in systolic pressure of 20 mmHg or more within 3 minutes of standing
7.Nursing math & unit conversions
Answer: T = 101.5 °F
Temperature: °C = (°F − 32) × 5/9 and °F = °C × 9/5 + 32. Subtract 32 before you multiply when going from °F, and add 32 after you multiply when going from °C. A quick check: 37 °C is 98.6 °F, and every 1 °C is 1.8 °F.
Multiply by 9/5
38.6·9/5 = 69.48
Add 32
T = 69.48 + 32 = 101.5 °F
Answer
T = 101.5 °F
8.Nursing math & unit conversions
Answer: t = 70 min
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.