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 144 g/L, SaO₂ 86% and PaO₂ 52 mmHg (6.9 kPa). Find the arterial oxygen content CaO₂ = 1.34 × Hb (g/dL) × SaO₂ + 0.003 × PaO₂ (mmHg) in mL O₂/dL.
Hb 144 g/LSaO₂ 86%PaO₂ 52 mmHg (6.9 kPa)
CaO₂ = mL/dL
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A patient with acute hypoxaemia and bilateral opacities, not explained by heart failure, has PaO₂ 12.5 kPa on 70% oxygen by face mask, without PEEP or CPAP. Grade the ARDS severity with the Berlin definition. Click your answer.
PaO₂ 12.5 kPaFiO₂ 70%PEEP 0 cmH₂O
1above 300: no ARDS grade
2mild
3moderate
4severe
5not gradable: PEEP below 5
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⁻.
A practice gas shows a respiratory acidosis: pH 7.31, PaCO₂ 79 mmHg (10.5 kPa), HCO₃⁻ 38 mmol/L. Use the rules ‘HCO₃⁻ rises 1 mmol/L per 10 mmHg (acute) or 3.5 mmol/L per 10 mmHg (chronic)’ to classify it. Click your answer.
pH 7.31PaCO₂ 79 mmHg (10.5 kPa)HCO₃⁻ 38 mmol/L
1acute
2chronic
3acute on chronic
5.Clinical assessment scoresMedium
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: none, bed rest or nurse assists; IV therapy or saline lock: no; gait: normal, bed rest or wheelchair; 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). At 5 minutes after birth, a practice newborn has a pink body with blue hands and feet, a heart rate of 85/min, a grimace when stimulated, some flexion of the arms and legs and slow, irregular breathing with a weak cry. Score the APGAR and click how the score is interpreted.
1reassuring
2moderately abnormal
3low
7.Med-surg: cardiovascular & respiratoryMedium
Which patient is most typical of a primary spontaneous pneumothorax?
AA middle-aged woman with high blood pressure
BAn older woman with long-standing heart failure
CA child with a viral sore throat
DA tall, thin young man who smokes
8.Med-surg: cardiovascular & respiratoryHard
During tracheal suctioning, a patient's heart rate drops from 88/min to 48/min. What should the nurse do?
AContinue suctioning until the airway is completely clear
BStop suctioning, give oxygen and monitor the patient
CIncrease the suction pressure to finish faster
DGive a dose of atropine without a prescription
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: CaO₂ = 16.75 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
144 g/L = 14.4 g/dL
Bound oxygen
1.34·14.4·0.86 = 16.59 mL/dL
Dissolved oxygen
0.003·52 = 0.156 mL/dL
Oxygen content
CaO₂ = 16.59 + 0.156 = 16.75 mL/dL
Answer
CaO₂ = 16.75 mL/dL
2.Oxygen therapy & respiratory calculations
Answer: not gradable: PEEP below 5
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.
PEEP
PEEP 0 < 5 cmH₂O
PaO₂ in mmHg
12.5·7.5 = 93.75 mmHg
P/F ratio
P/F = 93.75/0.7 = 133.9 mmHg
Berlin severity
not gradable: PEEP below 5
Answer
not gradable: PEEP below 5
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: chronic
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 HCO₃⁻
acute: 24 + 1·3.9 = 27.9 mmol/L
chronic: 24 + 3.5·3.9 = 37.65 mmol/L
Compare
measured: 38 mmol/L → chronic
Answer
chronic
5.Clinical assessment scores
Answer: MFS = 15
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: none, bed rest or nurse assists → 0
IV therapy or saline lock: no → 0
gait: normal, bed rest or wheelchair → 0
mental status: knows own limits → 0
Add
Morse total = 0 + 15 + 0 + 0 + 0 + 0 = 15
Answer
MFS = 15
6.Clinical assessment scores
Answer: moderately abnormal
APGAR score: five signs, each scored 0, 1 or 2, checked at 1 and 5 minutes after birth. Appearance (colour): blue or pale 0, pink body with blue extremities 1, pink all over 2. Pulse: absent 0, below 100/min 1, 100/min or more 2. Grimace (reflex irritability): none 0, grimace 1, cry, cough or sneeze 2. Activity (tone): limp 0, some flexion 1, active movement 2. Respiration: absent 0, slow or irregular with a weak cry 1, good with a strong cry 2. A total of 7–10 is reassuring, 4–6 moderately abnormal and 0–3 low.
Score each sign
Appearance: a pink body with blue hands and feet → 1
Pulse: 85/min → 1
Grimace: a grimace when stimulated → 1
Activity: some flexion of the arms and legs → 1
Respiration: slow, irregular breathing with a weak cry → 1
Add
APGAR = 1 + 1 + 1 + 1 + 1 = 5
Interpretation
5 → moderately abnormal
Answer
moderately abnormal
Below 7 at 5 minutes, the score is usually repeated every 5 minutes up to 20 minutes.
7.Med-surg: cardiovascular & respiratory
Answer: D · A tall, thin young man who smokes
Why this is the answer
Primary spontaneous pneumothorax usually occurs in tall, thin young men, often smokers, when small apical blebs rupture. Secondary pneumothorax occurs in people with lung disease such as COPD and tends to be more serious.
Answer
D · A tall, thin young man who smokes
8.Med-surg: cardiovascular & respiratory
Answer: B · Stop suctioning, give oxygen and monitor the patient
Why this is the answer
Suctioning can cause hypoxaemia and vagal stimulation, leading to bradycardia and arrhythmias. The nurse stops, gives oxygen and observes. Each pass should be short (usually no more than about 10–15 seconds), with pre-oxygenation if needed.
Answer
B · Stop suctioning, give oxygen and monitor the patient