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 48 mmHg (6.4 kPa) on 70% oxygen with a PEEP of 5 cmH₂O. Calculate the P/F ratio and click the ARDS severity.
PaO₂ 48 mmHg (6.4 kPa)FiO₂ 70%PEEP 5 cmH₂O
1above 300: no ARDS grade
2mild
3moderate
4severe
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A ventilated man is 182 cm tall and weighs 131 kg. Lung-protective ventilation is set at 4 mL per kg of predicted body weight. Using PBW = 50 + 0.91 × (height cm − 152.4) kg, find the tidal volume VT to the nearest mL.
182 cm131 kg4 mL/kg
VT = mL
3.Arterial blood gas interpretationMedium
Practice values: Na⁺ 144 mmol/L, glucose 19.4 mmol/L and urea 5.1 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 144 mmol/Lglucose 19.4 mmol/Lurea 5.1 mmol/L
Osm = mOsm/kg
4.Arterial blood gas interpretationHard
Practice values: Na⁺ 139, Cl⁻ 88 and HCO₃⁻ 17 mmol/L. Calculate the delta ratio (AG − 12)/(24 − HCO₃⁻), using AG = Na⁺ − (Cl⁻ + HCO₃⁻). Give two decimals.
Na⁺ 139 mmol/LCl⁻ 88 mmol/LHCO₃⁻ 17 mmol/L
delta ratio =
5.Clinical assessment scoresMedium
Practice exercise (made-up values, not clinical guidance). A practice patient is assessed with the Braden scale: sensory perception: very limited; moisture: rarely moist; activity: walks occasionally; mobility: slightly limited; nutrition: probably inadequate; friction and shear: no apparent problem. Find the Braden total B.
6–23
B =
6.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 96% on room air, blood pressure 112/68 mmHg, pulse 58/min, alert, temperature 36.9 °C. Which clinical risk group does the patient fall into? Click it.
RR 7SpO₂ 96%airSBP 112HR 58AT 36.9 °C
1low
2low–medium
3medium
4high
7.Med-surg: cardiovascular & respiratoryMedium
What is the purpose of cardiac resynchronisation therapy (a biventricular pacemaker)?
ATo deliver a shock whenever the heart rate exceeds 100/min
BTo make both ventricles contract together and more efficiently
CTo replace a damaged heart valve
DTo slow the atrial rate in patients with atrial fibrillation
8.Med-surg: cardiovascular & respiratoryHard
A patient taking dabigatran has a serious gastrointestinal bleed. Which specific reversal agent may be used?
APhytomenadione (vitamin K)
BIdarucizumab
CProtamine sulfate
DTranexamic acid alone
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: severe
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 = 48/0.7 = 68.57 mmHg
Berlin severity
severe
Answer
severe
2.Oxygen therapy & respiratory calculations
Answer: VT = 308 mL
Ventilation: minute ventilation V̇E = tidal volume × respiratory rate (normal adult about 5–8 L/min). Alveolar ventilation V̇A = (tidal volume − dead space) × rate, because the air in the airways (about 150 mL in an adult) takes no part in gas exchange. Lung-protective ventilation uses about 6 mL per kg of predicted body weight (PBW): men 50 + 0.91 × (height in cm − 152.4) kg, women 45.5 + 0.91 × (height in cm − 152.4) kg (with inches: 2.3 per inch above 60 in).
Predicted body weight
PBW = 50 + 0.91·(182 − 152.4) = 76.94 kg
Tidal volume
VT = 4·76.94 = 307.7 ≈ 308 mL
Answer
VT = 308 mL
3.Arterial blood gas interpretation
Answer: Osm = 313 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 = 2·144 + 19.4 + 5.1 = 312.5 ≈ 313 mOsm/kg
Answer
Osm = 313 mOsm/kg
4.Arterial blood gas interpretation
Answer: delta ratio = 3.143
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.
Anion gap
AG = 139 − (88 + 17) = 34
Delta ratio
(34 − 12)/(24 − 17) = 22/7 = 3.143
Answer
delta ratio = 3.143
Above 2: an added metabolic alkalosis.
5.Clinical assessment scores
Answer: B = 17
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: very limited → 2
moisture: rarely moist → 4
activity: walks occasionally → 3
mobility: slightly limited → 3
nutrition: probably inadequate → 2
friction and shear: no apparent problem → 3
Add
Braden total = 2 + 4 + 3 + 3 + 2 + 3 = 17
Answer
B = 17
6.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 96% → 0
on air → 0
SBP 112 mmHg → 0
HR 58/min → 0
alert (A) → 0
T 36.9 °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.
7.Med-surg: cardiovascular & respiratory
Answer: B · To make both ventricles contract together and more efficiently
Why this is the answer
In heart failure with a wide QRS (often left bundle branch block), the ventricles contract out of step. Pacing both ventricles restores coordinated contraction, improving symptoms and survival. Many devices also include a defibrillator.
Answer
B · To make both ventricles contract together and more efficiently
8.Med-surg: cardiovascular & respiratory
Answer: B · Idarucizumab
Why this is the answer
Idarucizumab binds dabigatran and reverses its effect within minutes. Andexanet alfa (or prothrombin complex concentrate where it is not available) is used for factor Xa inhibitors. Protamine reverses heparin and vitamin K reverses warfarin. Tranexamic acid may support haemostasis but is not a reversal agent.