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 breathes 14 times a minute with a tidal volume of 470 mL. The anatomical dead space is 140 mL. Find the alveolar ventilation V̇A in L/min.
VT 470 mL14/minVD 140 mL
V̇A = L/min
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A ventilated man is 187 cm tall and weighs 94 kg. Lung-protective ventilation is set at 5 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.
187 cm94 kg5 mL/kg
VT = mL
3.Arterial blood gas interpretationMedium
A practice arterial blood gas shows pH 7.43, PaCO₂ 25 mmHg (3.3 kPa) and HCO₃⁻ 16 mmol/L. The primary disorder is respiratory alkalosis. How far is it compensated? Click your answer.
pH 7.43PaCO₂ 25 mmHg (3.3 kPa)HCO₃⁻ 16 mmol/L
1uncompensated
2partially compensated
3fully compensated
4.Arterial blood gas interpretationHard
Practice values: Na⁺ 140, Cl⁻ 99, HCO₃⁻ 21 mmol/L and albumin 27 g/L. Find the albumin-corrected anion gap AGc = AG + 0.25·(40 − albumin).
Practice exercise (made-up values, not clinical guidance). A practice patient is assessed with the Braden scale: sensory perception: completely limited; moisture: rarely moist; activity: chairfast; mobility: no limitation; nutrition: very poor; 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 14/min, SpO₂ 97% on room air, blood pressure 90/54 mmHg, pulse 58/min, alert, temperature 37.1 °C. Which clinical risk group does the patient fall into? Click it.
RR 14SpO₂ 97%airSBP 90HR 58AT 37.1 °C
1low
2low–medium
3medium
4high
7.Med-surg: cardiovascular & respiratoryMedium
Why is pyridoxine (vitamin B6) often given with isoniazid?
ATo prevent orange discolouration of urine
BTo prevent peripheral neuropathy
CTo prevent gout attacks
DTo prevent loss of colour vision
8.Med-surg: cardiovascular & respiratoryHard
A patient with pneumonia has a heart rate of 118/min, BP 86/50 mmHg, RR 28/min and a high lactate. Sepsis is recognised. Which action should not be delayed?
AGive oral antibiotics and reassess the next day
BDelay fluids until a chest X-ray has been reported
CTake blood cultures and give IV antibiotics within the first hour
DWait for the sputum culture result before choosing an antibiotic
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: V̇A = 4.62 L/min
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).
Alveolar part of a breath
470 − 140 = 330 mL
Alveolar ventilation
V̇A = 330·14 = 4620 mL/min = 4.62 L/min
Answer
V̇A = 4.62 L/min
2.Oxygen therapy & respiratory calculations
Answer: VT = 407 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·(187 − 152.4) = 81.49 kg
Tidal volume
VT = 5·81.49 = 407.4 ≈ 407 mL
Answer
VT = 407 mL
3.Arterial blood gas interpretation
Answer: fully compensated
Reading a blood gas (ROME): first the pH: below 7.35 is acidaemia, above 7.45 alkalaemia. Then find the value that explains it. PaCO₂ (normal 35–45 mmHg, 4.7–6.0 kPa) is the respiratory part and moves Opposite to the pH in a respiratory disorder; HCO₃⁻ (normal 22–26 mmol/L) is the metabolic part and moves in the same direction as the pH (Respiratory Opposite, Metabolic Equal). The other value shows the compensation: normal means uncompensated; abnormal in the direction that pulls the pH back while the pH is still abnormal means partially compensated; a normal pH with both values abnormal means fully compensated. Ranges differ slightly between laboratories; these are practice values.
ROME, value by value
pH 7.43: within 7.35–7.45
PaCO₂ 25 mmHg: low (35–45)
HCO₃⁻ 16 mmol/L: low (22–26)
Compensation
fully compensated
Answer
fully compensated
4.Arterial blood gas interpretation
Answer: AGc = 23.25 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.
Anion gap
AG = 140 − (99 + 21) = 20
Correction for albumin
20 + 0.25·(40 − 27) = 23.25 mmol/L
Answer
AGc = 23.25 mmol/L
Above about 12 after correction: a high anion gap.
5.Clinical assessment scores
Answer: B = 15
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: completely limited → 1
moisture: rarely moist → 4
activity: chairfast → 2
mobility: no limitation → 4
nutrition: very poor → 1
friction and shear: no apparent problem → 3
Add
Braden total = 1 + 4 + 2 + 4 + 1 + 3 = 15
Answer
B = 15
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 14/min → 0
SpO₂ 97% → 0
on air → 0
SBP 90 mmHg → 3
HR 58/min → 0
alert (A) → 0
T 37.1 °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: B · To prevent peripheral neuropathy
Why this is the answer
Isoniazid increases pyridoxine loss, which can cause peripheral neuropathy, especially in people with diabetes, alcohol dependence, malnutrition or HIV. Pyridoxine prevents this. Isoniazid can also cause hepatitis. Ethambutol affects vision; pyrazinamide can cause gout.
Answer
B · To prevent peripheral neuropathy
8.Med-surg: cardiovascular & respiratory
Answer: C · Take blood cultures and give IV antibiotics within the first hour
Why this is the answer
In sepsis with shock, blood cultures, IV antibiotics within the first hour, IV fluids, lactate measurement, oxygen if hypoxic and urine output monitoring are started together. Cultures should not delay antibiotics. Persistent hypotension may need vasopressors in critical care.
Answer
C · Take blood cultures and give IV antibiotics within the first hour