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 14/min, SpO₂ 97% on supplemental oxygen, blood pressure 142/86 mmHg, pulse 70/min, alert, temperature 37.8 °C. What is the NEWS2 total score?
RR 14SpO₂ 97%O₂SBP 142HR 70AT 37.8 °C
NEWS2 =
2.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). The team aims for a mean arterial pressure of at least 60 mmHg. A patient’s systolic pressure is 80 mmHg. Using MAP = (SBP + 2·DBP)/3, what is the lowest diastolic pressure DBP that still gives a MAP of 60 mmHg?
MAP 60 mmHgSBP 80 mmHg
DBP = mmHg
3.Arterial blood gas interpretationMedium
Practice values: Na⁺ 136 mmol/L, glucose 16.2 mmol/L and urea 3.9 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 136 mmol/Lglucose 16.2 mmol/Lurea 3.9 mmol/L
Osm = mOsm/kg
4.Arterial blood gas interpretationHard
At sea level, a practice gas taken on 40% oxygen shows PaO₂ 61 mmHg (8.1 kPa) and PaCO₂ 54 mmHg (7.2 kPa). Use PAO₂ = FiO₂·(760 − 47) − PaCO₂/0.8 to find the A–a gradient.
ASecured upright in a holder or trolley, away from heat
BStacked on top of each other in a corridor
CIn a warm cupboard next to the radiator
DLying loose on the floor under the bed so they cannot fall over
6.Nursing fundamentalsHard
A urine culture reports a mixed growth of several organisms. What is the most likely explanation?
AThe patient has several serious infections at once
BThe sample was contaminated during collection
CThe laboratory used the wrong test
DThe patient is resistant to all antibiotics
7.Nursing math & unit conversionsMedium
Practice exercise (made-up values, not clinical guidance). A patient’s temperature is 37 °C. Convert it to degrees Fahrenheit T with °F = °C × 9/5 + 32. Round to one decimal place.
37 °C
T = °F
8.Nursing math & unit conversionsHard
Practice exercise (made-up values, not clinical guidance). An infusion delivers 2 mg/h. Express this dose rate D in mcg/min. Round to one decimal place.
2 mg/h1 mg = 1000 mcg1 h = 60 min
D = mcg/min
3Solutions
1.Clinical assessment scores
Answer: NEWS2 = 2
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 14/min → 0
SpO₂ 97% → 0
on oxygen → 2
SBP 142 mmHg → 0
HR 70/min → 0
alert (A) → 0
T 37.8 °C → 0
Add
NEWS2 = 0 + 0 + 2 + 0 + 0 + 0 + 0 = 2
Answer
NEWS2 = 2
2.Clinical assessment scores
Answer: DBP = 50 mmHg
Blood pressure values: pulse pressure PP = SBP − DBP. Mean arterial pressure MAP ≈ (SBP + 2·DBP)/3 = DBP + PP/3, an estimate based on the heart spending about two thirds of each beat in diastole at a normal heart rate (less accurate when the heart rate is fast); a MAP of at least about 65 mmHg is a common target for organ perfusion. The shock index SI = heart rate/SBP is normally about 0.5–0.7; a value above about 1 is a warning sign of shock.
Rearrange
DBP = (3·MAP − SBP)/2
Substitute
DBP = (3·60 − 80)/2 = 100/2 = 50 mmHg
Answer
DBP = 50 mmHg
3.Arterial blood gas interpretation
Answer: Osm = 292 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 = 2·136 + 16.2 + 3.9 = 292.1 ≈ 292 mOsm/kg
Answer
Osm = 292 mOsm/kg
4.Arterial blood gas interpretation
Answer: A–a gradient = 156.7 mmHg
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.
Answer: A · Secured upright in a holder or trolley, away from heat
Why this is the answer
Cylinders are heavy and contain gas under pressure. They are kept upright and secured, away from heat and flames, and are handled carefully.
Answer
A · Secured upright in a holder or trolley, away from heat
6.Nursing fundamentals
Answer: B · The sample was contaminated during collection
Why this is the answer
A mixed growth usually means skin or perineal bacteria contaminated the sample. A clean-catch midstream sample, or a sample from the catheter sampling port, gives a more reliable result.
Answer
B · The sample was contaminated during collection
7.Nursing math & unit conversions
Answer: T = 98.6 °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
37·9/5 = 66.6
Add 32
T = 66.6 + 32 = 98.6 °F
Answer
T = 98.6 °F
8.Nursing math & unit conversions
Answer: D = 33.3 mcg/min
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.