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 patient has Hb 171 g/L, SaO₂ 94% and PaO₂ 73 mmHg (9.7 kPa). Find the arterial oxygen content CaO₂ = 1.34 × Hb (g/dL) × SaO₂ + 0.003 × PaO₂ (mmHg) in mL O₂/dL.
Hb 171 g/LSaO₂ 94%PaO₂ 73 mmHg (9.7 kPa)
CaO₂ = mL/dL
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A ventilated woman is 163 cm tall and weighs 72 kg. Lung-protective ventilation is set at 5 mL per kg of predicted body weight. Using PBW = 45.5 + 0.91 × (height cm − 152.4) kg, find the tidal volume VT to the nearest mL.
163 cm72 kg5 mL/kg
VT = mL
3.Arterial blood gas interpretationMedium
A practice gas shows PaCO₂ 80 mmHg (10.7 kPa). Use the rule that in acute respiratory acidosis HCO₃⁻ rises by 1 mmol/L for every 10 mmHg that PaCO₂ is above 40, starting from HCO₃⁻ 24 mmol/L, to find the expected HCO₃⁻.
Practice values: Na⁺ 136, Cl⁻ 110 and HCO₃⁻ 11 mmol/L. Calculate the delta ratio (AG − 12)/(24 − HCO₃⁻), using AG = Na⁺ − (Cl⁻ + HCO₃⁻). Give two decimals.
Na⁺ 136 mmol/LCl⁻ 110 mmol/LHCO₃⁻ 11 mmol/L
delta ratio =
5.Clinical assessment scoresMedium
Practice exercise (made-up values, not clinical guidance). A practice chart records GCS 10, with E2 and V4. What motor score M was recorded, and which response does it describe? Give the number.
GCS 10E2V4
M =
6.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). Use the NEWS2 chart (SpO₂ scale 1) for these observations: respiration rate 16/min, SpO₂ 98% on room air, blood pressure 222/134 mmHg, pulse 82/min, alert, temperature 37.0 °C. Which clinical risk group does the patient fall into? Click it.
RR 16SpO₂ 98%airSBP 222HR 82AT 37.0 °C
1low
2low–medium
3medium
4high
7.Med-surg: cardiovascular & respiratoryMedium
Before the first treatment dose of a low-molecular-weight heparin for a PE, what does the nurse need to make sure of?
AAn accurate, recent body weight is recorded
BA chest drain is in place
CThe patient's blood glucose is above 10 mmol/L (180 mg/dL)
DThe patient has fasted for 12 hours
8.Med-surg: cardiovascular & respiratoryHard
The monitor of a patient with a permanent pacemaker shows pacing spikes, but none of them is followed by a QRS complex. What does this mean?
AFailure to sense
BFailure to capture
CNormal pacemaker function
DAtrial fibrillation
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: CaO₂ = 21.76 mL/dL
Oxygen content and delivery: CaO₂ = 1.34 × Hb (g/dL) × SaO₂ + 0.003 × PaO₂ (mmHg), in mL O₂ per dL of blood, with SaO₂ as a fraction. Almost all oxygen is bound to haemoglobin; the dissolved part is small. Delivery DO₂ = CaO₂ × cardiac output (L/min) × 10 (mL/min), because 1 L = 10 dL; a normal resting adult value is about 1000 mL/min.
Hb in g/dL
171 g/L = 17.1 g/dL
Bound oxygen
1.34·17.1·0.94 = 21.54 mL/dL
Dissolved oxygen
0.003·73 = 0.219 mL/dL
Oxygen content
CaO₂ = 21.54 + 0.219 = 21.76 mL/dL
Answer
CaO₂ = 21.76 mL/dL
2.Oxygen therapy & respiratory calculations
Answer: VT = 276 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 = 45.5 + 0.91·(163 − 152.4) = 55.15 kg
Tidal volume
VT = 5·55.15 = 275.7 ≈ 276 mL
Answer
VT = 276 mL
3.Arterial blood gas interpretation
Answer: HCO₃⁻ = 28 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
|80 − 40| = 40 mmHg → 4 × 10 mmHg
Expected HCO₃⁻
HCO₃⁻ = 24 + 1·4 = 28 mmol/L
Answer
HCO₃⁻ = 28 mmol/L
4.Arterial blood gas interpretation
Answer: delta ratio = 0.2308
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 = 136 − (110 + 11) = 15
Delta ratio
(15 − 12)/(24 − 11) = 3/13 = 0.2308
Answer
delta ratio = 0.2308
Below 1: an added normal anion gap acidosis.
5.Clinical assessment scores
Answer: M = 4
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.
Motor score
M = 10 − 2 − 4 = 4
M4: withdraws the limb from pressure (normal flexion)
Answer
M = 4
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 16/min → 0
SpO₂ 98% → 0
on air → 0
SBP 222 mmHg → 3
HR 82/min → 0
alert (A) → 0
T 37.0 °C → 0
Total and red scores
NEWS2 = 0 + 0 + 0 + 3 + 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: A · An accurate, recent body weight is recorded
Why this is the answer
Treatment doses of LMWH are based on body weight, so an accurate measured weight is essential. Renal function and platelet count are also checked before starting. Guessing the weight can lead to under- or overdosing.
Answer
A · An accurate, recent body weight is recorded
8.Med-surg: cardiovascular & respiratory
Answer: B · Failure to capture
Why this is the answer
Failure to capture means the pacing stimulus does not depolarise the myocardium, so no QRS follows the spike. Causes include lead displacement, a raised threshold or battery problems. It can cause bradycardia or asystole, so the patient is assessed and the team informed urgently.