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.
falls 25, diagnosis 15, aid 15/30, IV 20, gait 10/20, mental status 15
NEWS2 risk
0–4 low; single 3 low–medium; 5–6 medium; ≥ 7 high
Mean arterial pressure
MAP = (SBP + 2·DBP)/3 = DBP + PP/3
Pulse pressure and shock index
PP = SBP − DBP, SI = HR/SBP
Body mass index
BMI = kg/m² = 703·lb/in²
Method
Find the score sheet that the question uses and its range (GCS 3–15, APGAR 0–10, Braden 6–23, Morse 0–125).
Score every item separately, matching the description to its level.
Add the item scores and check that the total lies inside the range.
Apply the cut-offs: for NEWS2 also look for any single parameter scoring 3.
For derived values use MAP = (SBP + 2·DBP)/3, PP = SBP − DBP, SI = HR/SBP and BMI = kg/m².
Med-surg: cardiovascular & respiratory
Method
Name the problem: pump failure, blocked artery, rhythm, clot, airway narrowing, infection or a device problem.
Check the danger signs first: hypoxia, hypotension, chest pain, new confusion, a cold pulseless limb.
Match the oxygen to the patient: 94–98% for most, 88–92% for those at risk of CO₂ retention.
Link each drug to its test and its risk: warfarin and INR, heparin and aPTT and platelets, diuretics and potassium.
Choose the safe first action, then escalate and reassess.
2Practice problems
1.Oxygen therapy & respiratory calculationsMedium
Practice exercise (made-up values, not clinical guidance). A ventilated patient who meets the other Berlin criteria for ARDS has PaO₂ 122 mmHg (16.3 kPa) on 50% oxygen with a PEEP of 8 cmH₂O. Calculate the P/F ratio and click the ARDS severity.
PaO₂ 122 mmHg (16.3 kPa)FiO₂ 50%PEEP 8 cmH₂O
1above 300: no ARDS grade
2mild
3moderate
4severe
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A transfer will take 20 minutes. The size D cylinder (factor 0.16 L/psi) reads 750 psi. Keeping a safe residual of 200 psi, what is the highest whole-number flow Q in L/min that lasts the whole transfer?
20 min750 psif = 0.16 L/psi200 psi
Q = L/min
3.Arterial blood gas interpretationMedium
Practice values: Na⁺ 136 mmol/L, glucose 21.2 mmol/L and urea 20.4 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 136 mmol/Lglucose 21.2 mmol/Lurea 20.4 mmol/L
Osm = mOsm/kg
4.Arterial blood gas interpretationHard
At sea level, a practice gas taken on 28% oxygen shows PaO₂ 52 mmHg (6.9 kPa) and PaCO₂ 33 mmHg (4.4 kPa). Use PAO₂ = FiO₂·(760 − 47) − PaCO₂/0.8 to find the A–a gradient.
Practice exercise (made-up values, not clinical guidance). A practice patient after a head injury opens the eyes only to pressure (a painful stimulus), makes only incomprehensible sounds such as moaning and shows as the best motor response: no movement at all. Work out the GCS and classify the head injury by it. Click your answer.
1mild
2moderate
3severe
6.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). A practice patient is assessed with the Braden scale: sensory perception: no impairment; moisture: very moist; activity: walks occasionally; mobility: very limited; nutrition: adequate; friction and shear: problem. Use the bands 19–23 not at risk, 15–18 mild, 13–14 moderate, 10–12 high and 9 or below very high. Click the risk level.
1not at risk
2mild risk
3moderate risk
4high risk
5very high risk
7.Med-surg: cardiovascular & respiratoryMedium
A patient with heart failure starts spironolactone in addition to an ACE inhibitor. Which blood result needs close monitoring?
APotassium, because both drugs can raise it
BHaemoglobin, because both drugs can cause bleeding
CCalcium, because both drugs can lower it
DGlucose, because both drugs can cause hypoglycaemia
8.Med-surg: cardiovascular & respiratoryHard
A healthcare assistant (unlicensed assistive personnel) reports four observations. Which one needs the nurse's attention first?
AA patient with heart failure who is newly confused, with SpO₂ 89%
BA patient after a PCI asking for a cup of tea
CA patient with a DVT whose leg is less swollen today
DA patient with COPD whose SpO₂ is 90% on 1 L/min, which is usual for him
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: mild
P/F ratio and ARDS (Berlin definition): P/F = PaO₂ (mmHg)/FiO₂ (as a fraction). With PEEP or CPAP of at least 5 cmH₂O, ARDS is graded mild for 200 < P/F ≤ 300, moderate for 100 < P/F ≤ 200 and severe for P/F ≤ 100 mmHg. The other Berlin criteria (onset within a week, bilateral opacities, not fully explained by heart failure) must also be met. PaO₂ in kPa × 7.5 gives mmHg. The ROX index (SpO₂/FiO₂)/respiratory rate is used to follow patients on high-flow nasal oxygen.
P/F ratio
P/F = 122/0.5 = 244 mmHg
Berlin severity
mild
Answer
mild
2.Oxygen therapy & respiratory calculations
Answer: Q = 4 L/min
Cylinder duration: usable litres = (gauge pressure − safe residual) × cylinder factor, with the safe residual usually 200 psi. Cylinder factors in L/psi: D 0.16, E 0.28, H (and K) 3.14. Duration (min) = usable litres/flow (L/min). Round a duration down, never up, so the cylinder is changed in time. In bar-based systems, the gas volume is the water capacity (L) × the pressure (bar).
Usable litres
(750 − 200)·0.16 = 88 L
Highest flow
88/20 = 4.4 L/min → Q = 4 L/min
Answer
Q = 4 L/min
3.Arterial blood gas interpretation
Answer: Osm = 314 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 + 21.2 + 20.4 = 313.6 ≈ 314 mOsm/kg
Answer
Osm = 314 mOsm/kg
4.Arterial blood gas interpretation
Answer: A–a gradient = 106.4 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.
Glasgow Coma Scale: add the best response in three areas. Eye opening E: 4 spontaneous, 3 to sound or speech, 2 to pressure, 1 none. Verbal V: 5 oriented, 4 confused, 3 inappropriate words, 2 incomprehensible sounds, 1 none. Motor M: 6 obeys commands, 5 localises, 4 normal flexion (withdraws), 3 abnormal flexion, 2 extension, 1 none. The total runs from 3 to 15. After a head injury, 13–15 is usually called mild, 9–12 moderate and 3–8 severe.
Score each area
E: opens the eyes only to pressure (a painful stimulus) → 2
V: makes only incomprehensible sounds such as moaning → 2
M: no movement at all → 1
Add
GCS = 2 + 2 + 1 = 5
Severity
GCS 5 → severe
Answer
severe
6.Clinical assessment scores
Answer: mild risk
Braden scale: six subscales for pressure-injury risk. Sensory perception, moisture, activity, mobility and nutrition score 1 to 4, from the worst level (1) to no problem (4); friction and shear scores 1 to 3. The total runs from 6 to 23, and a lower total means a higher risk. Common bands: 19–23 not at risk, 15–18 mild risk, 13–14 moderate risk, 10–12 high risk and 9 or below very high risk.
Score each subscale
sensory perception: no impairment → 4
moisture: very moist → 2
activity: walks occasionally → 3
mobility: very limited → 2
nutrition: adequate → 3
friction and shear: problem → 1
Add
Braden total = 4 + 2 + 3 + 2 + 3 + 1 = 15
Risk level
15 → mild risk
Answer
mild risk
7.Med-surg: cardiovascular & respiratory
Answer: A · Potassium, because both drugs can raise it
Why this is the answer
ACE inhibitors reduce aldosterone production and spironolactone blocks its receptor, so both reduce potassium excretion. Together they can cause dangerous hyperkalaemia, especially with impaired renal function. Potassium and renal function are monitored, and potassium supplements are usually avoided.
Answer
A · Potassium, because both drugs can raise it
8.Med-surg: cardiovascular & respiratory
Answer: A · A patient with heart failure who is newly confused, with SpO₂ 89%
Why this is the answer
New confusion with hypoxaemia suggests acute deterioration and needs immediate assessment. A COPD patient within their usual target range, a request for tea and an improving DVT are not urgent. Delegated observations must be reported and acted on promptly.
Answer
A · A patient with heart failure who is newly confused, with SpO₂ 89%