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 131 mmHg (17.5 kPa) on 40% oxygen with a PEEP of 12 cmH₂O. Calculate the P/F ratio and click the ARDS severity.
PaO₂ 131 mmHg (17.5 kPa)FiO₂ 40%PEEP 12 cmH₂O
1above 300: no ARDS grade
2mild
3moderate
4severe
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A ventilated woman is 177 cm tall and weighs 78 kg. Lung-protective ventilation is set at 4 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.
177 cm78 kg4 mL/kg
VT = mL
3.Arterial blood gas interpretationMedium
A practice gas shows PaCO₂ 20 mmHg (2.7 kPa). Use the rule that in acute respiratory alkalosis HCO₃⁻ falls by 2 mmol/L for every 10 mmHg that PaCO₂ is below 40, starting from HCO₃⁻ 24 mmol/L, to find the expected HCO₃⁻.
At sea level, a practice gas taken on 40% oxygen shows PaO₂ 75 mmHg (10.0 kPa) and PaCO₂ 41 mmHg (5.5 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 is assessed with the Morse fall scale: history of falling in the last 3 months: no; secondary diagnosis: yes; ambulatory aid: holds on to furniture; IV therapy or saline lock: no; gait: weak; mental status: knows own limits. Find the Morse total MFS.
0–125
MFS =
6.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). A practice patient is assessed with the Braden scale: sensory perception: very limited; moisture: very moist; activity: bedfast; mobility: completely immobile; nutrition: very poor; 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 on warfarin has started eating large spinach and kale salads every day. What is the main concern?
AThe extra vitamin K may lower the INR
BThere is no interaction between food and warfarin
CGreen vegetables damage the liver on warfarin
DThe extra vitamin K may raise the INR
8.Med-surg: cardiovascular & respiratoryHard
A patient with a confirmed type A aortic dissection is hypertensive and tachycardic while awaiting surgery. Which drug class is usually given first to lower the heart rate and blood pressure?
AAn intravenous beta-blocker
BAn intravenous thrombolytic
CAn intravenous fluid bolus
DOral aspirin
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: above 300: no ARDS grade
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 = 131/0.4 = 327.5 mmHg
Berlin severity
above 300: no ARDS grade
Answer
above 300: no ARDS grade
2.Oxygen therapy & respiratory calculations
Answer: VT = 272 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·(177 − 152.4) = 67.89 kg
Tidal volume
VT = 4·67.89 = 271.5 ≈ 272 mL
Answer
VT = 272 mL
3.Arterial blood gas interpretation
Answer: HCO₃⁻ = 20 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
|20 − 40| = 20 mmHg → 2 × 10 mmHg
Expected HCO₃⁻
HCO₃⁻ = 24 − 2·2 = 20 mmol/L
Answer
HCO₃⁻ = 20 mmol/L
4.Arterial blood gas interpretation
Answer: A–a gradient = 158.9 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.
Morse fall scale: six items. History of falling: no 0, yes 25. Secondary diagnosis: no 0, yes 15. Ambulatory aid: none, bed rest or nurse assistance 0; crutches, cane or walker 15; holding on to furniture 30. IV therapy or saline lock: no 0, yes 20. Gait: normal, bed rest or wheelchair 0; weak 10; impaired 20. Mental status: knows own limits 0; overestimates or forgets limits 15. The total runs from 0 to 125. Risk cut-offs differ between hospitals; a common set is 0–24 low, 25–44 moderate and 45 or more high.
Score each item
history of falling in the last 3 months: no → 0
secondary diagnosis: yes → 15
ambulatory aid: holds on to furniture → 30
IV therapy or saline lock: no → 0
gait: weak → 10
mental status: knows own limits → 0
Add
Morse total = 0 + 15 + 30 + 0 + 10 + 0 = 55
Answer
MFS = 55
6.Clinical assessment scores
Answer: very high 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: very limited → 2
moisture: very moist → 2
activity: bedfast → 1
mobility: completely immobile → 1
nutrition: very poor → 1
friction and shear: problem → 1
Add
Braden total = 2 + 2 + 1 + 1 + 1 + 1 = 8
Risk level
8 → very high risk
Answer
very high risk
7.Med-surg: cardiovascular & respiratory
Answer: A · The extra vitamin K may lower the INR
Why this is the answer
A sudden increase in vitamin K intake can reduce the INR and increase clot risk. Patients do not have to avoid these foods but should keep their intake consistent and tell the anticoagulation service about big dietary changes.
Answer
A · The extra vitamin K may lower the INR
8.Med-surg: cardiovascular & respiratory
Answer: A · An intravenous beta-blocker
Why this is the answer
In acute dissection, IV beta-blockers are usually given first to reduce heart rate and the rate of rise of pressure, limiting extension of the tear. Vasodilators may follow once the heart rate is controlled. Antiplatelets, anticoagulants and thrombolytics are avoided. Type A dissection needs urgent surgery.