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 size H oxygen cylinder (factor 3.14 L/psi) reads 500 psi and runs at 4 L/min. Keeping a safe residual of 200 psi, how many minutes t will it last? Round down to a whole minute.
500 psif = 3.14 L/psi4 L/min200 psi
t = min
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A patient has Hb 120 g/L, SaO₂ 95%, PaO₂ 75 mmHg (10.0 kPa) and a cardiac output of 3.5 L/min. With CaO₂ = 1.34 × Hb (g/dL) × SaO₂ + 0.003 × PaO₂ (mmHg), find the oxygen delivery DO₂ = CaO₂ × CO × 10 in mL/min.
Practice values: Na⁺ 138 mmol/L, glucose 23.5 mmol/L and urea 10.5 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 138 mmol/Lglucose 23.5 mmol/Lurea 10.5 mmol/L
Osm = mOsm/kg
4.Arterial blood gas interpretationHard
A practice gas shows a metabolic acidosis: pH 7.29, PaCO₂ 26 mmHg (3.5 kPa), HCO₃⁻ 12 mmol/L. Compare the measured PaCO₂ with Winter’s formula. Click your interpretation.
pH 7.29PaCO₂ 26 mmHg (3.5 kPa)HCO₃⁻ 12 mmol/L
1appropriate compensation
2added respiratory acidosis
3added respiratory alkalosis
5.Clinical assessment scoresMedium
Practice exercise (made-up values, not clinical guidance). A practice chart records GCS 10, with E3 and V4. What motor score M was recorded, and which response does it describe? Give the number.
GCS 10E3V4
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 14/min, SpO₂ 90% on supplemental oxygen, blood pressure 118/70 mmHg, pulse 92/min, alert, temperature 38.4 °C. Which clinical risk group does the patient fall into? Click it.
RR 14SpO₂ 90%O₂SBP 118HR 92AT 38.4 °C
1low
2low–medium
3medium
4high
7.Med-surg: cardiovascular & respiratoryMedium
A patient with a mechanical heart valve asks to switch from warfarin to apixaban. What is the correct response?
AAspirin alone can replace warfarin once the valve has healed
BDirect oral anticoagulants are not used for mechanical valves
CMechanical valves do not need anticoagulation after the first month
DAny anticoagulant works equally well once the valve is in place
8.Med-surg: cardiovascular & respiratoryHard
A patient recovering from an MI is anxious about returning to normal life. Which intervention best supports recovery?
AAdvice to stop tablets once they feel well
BAdvice to rest in bed for three months
CReferral to cardiac rehabilitation
DAdvice to avoid all exercise permanently
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: t = 235 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
(500 − 200)·3.14 = 942 L
Duration
942/4 = 235.5 min → t = 235 min
Answer
t = 235 min
That is about 3 h 55 min.
2.Oxygen therapy & respiratory calculations
Answer: DO₂ = 542.5 mL/min
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.
Oxygen content
120 g/L = 12 g/dL
CaO₂ = 1.34·12·0.95 + 0.003·75 = 15.5 mL/dL
Oxygen delivery
DO₂ = 15.5·3.5·10 = 542.5 mL/min
Answer
DO₂ = 542.5 mL/min
A normal resting adult value is about 1000 mL/min.
3.Arterial blood gas interpretation
Answer: Osm = 310 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 = 2·138 + 23.5 + 10.5 = 310 ≈ 310 mOsm/kg
Answer
Osm = 310 mOsm/kg
4.Arterial blood gas interpretation
Answer: appropriate compensation
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 PaCO₂
1.5·12 + 8 = 26 → 24–28 mmHg
Compare
measured: 26 mmHg → appropriate compensation
Answer
appropriate compensation
5.Clinical assessment scores
Answer: M = 3
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 − 3 − 4 = 3
M3: abnormal flexion of the arms (decorticate posture)
Answer
M = 3
6.Clinical assessment scores
Answer: high
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 90% → 3
on oxygen → 2
SBP 118 mmHg → 0
HR 92/min → 1
alert (A) → 0
T 38.4 °C → 1
Total and red scores
NEWS2 = 0 + 3 + 2 + 0 + 1 + 0 + 1 = 7
At least one parameter scores 3.
Risk group
high
Answer
high
A total of 5 or more calls for an urgent clinical response.
7.Med-surg: cardiovascular & respiratory
Answer: B · Direct oral anticoagulants are not used for mechanical valves
Why this is the answer
Mechanical valves need lifelong anticoagulation with a vitamin K antagonist such as warfarin. Direct oral anticoagulants caused more clots and bleeding in mechanical valve patients and are contraindicated. Biological valves usually need only short-term anticoagulation.
Answer
B · Direct oral anticoagulants are not used for mechanical valves
8.Med-surg: cardiovascular & respiratory
Answer: C · Referral to cardiac rehabilitation
Why this is the answer
Cardiac rehabilitation combines supervised exercise, risk factor education, medication advice and psychological support. It improves quality of life and reduces cardiovascular mortality and readmissions. Patients are encouraged to return gradually to activity, including work, driving and sex, according to advice.