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 E oxygen cylinder (factor 0.28 L/psi) reads 500 psi and runs at 10 L/min. Keeping a safe residual of 200 psi, how many minutes t will it last? Round down to a whole minute.
500 psif = 0.28 L/psi10 L/min200 psi
t = min
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A patient has Hb 70 g/L, SaO₂ 98%, PaO₂ 107 mmHg (14.3 kPa) and a cardiac output of 4.6 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.
A practice arterial blood gas shows pH 7.65, PaCO₂ 37 mmHg (4.9 kPa) and HCO₃⁻ 39 mmol/L. The primary disorder is metabolic alkalosis. How far is it compensated? Click your answer.
pH 7.65PaCO₂ 37 mmHg (4.9 kPa)HCO₃⁻ 39 mmol/L
1uncompensated
2partially compensated
3fully compensated
4.Arterial blood gas interpretationHard
At sea level, a practice gas taken on 40% oxygen shows PaO₂ 66 mmHg (8.8 kPa) and PaCO₂ 36 mmHg (4.8 kPa). Use PAO₂ = FiO₂·(760 − 47) − PaCO₂/0.8 to find the A–a gradient.
Practice exercise (made-up values, not clinical guidance). Use the NEWS2 chart (SpO₂ scale 1) for these observations: respiration rate 18/min, SpO₂ 94% on supplemental oxygen, blood pressure 106/64 mmHg, pulse 92/min, alert, temperature 36.0 °C. What is the NEWS2 total score?
RR 18SpO₂ 94%O₂SBP 106HR 92AT 36.0 °C
NEWS2 =
6.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). Use the NEWS2 chart (SpO₂ scale 1) for these observations: respiration rate 21/min, SpO₂ 91% on supplemental oxygen, blood pressure 142/86 mmHg, pulse 40/min, alert, temperature 36.9 °C. Which clinical risk group does the patient fall into? Click it.
RR 21SpO₂ 91%O₂SBP 142HR 40AT 36.9 °C
1low
2low–medium
3medium
4high
7.Med-surg: cardiovascular & respiratoryMedium
A patient with COPD is prescribed long-term oxygen therapy. How many hours a day is it usually needed to improve survival?
AAt least 15 hours a day
BOnly during meals
COnly when walking outside
DAbout one hour each morning
8.Med-surg: cardiovascular & respiratoryHard
Two days after a coronary stent, a patient on aspirin and ticagrelor has black, tarry stools and feels faint on standing. What should the nurse do?
AReassure the patient that iron tablets cause black stools
BStop both antiplatelet drugs permanently on the nurse's own decision
CGive a laxative and repeat the observations tomorrow
DCheck vital signs, report urgently and anticipate a blood count
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: t = 8 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)·0.28 = 84 L
Duration
84/10 = 8.4 min → t = 8 min
Answer
t = 8 min
2.Oxygen therapy & respiratory calculations
Answer: DO₂ = 437.6 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
70 g/L = 7 g/dL
CaO₂ = 1.34·7·0.98 + 0.003·107 = 9.513 mL/dL
Oxygen delivery
DO₂ = 9.513·4.6·10 = 437.6 mL/min
Answer
DO₂ = 437.6 mL/min
A normal resting adult value is about 1000 mL/min.
3.Arterial blood gas interpretation
Answer: uncompensated
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 7.65: alkalaemia (above 7.45)
PaCO₂ 37 mmHg: normal (35–45)
HCO₃⁻ 39 mmol/L: high (22–26)
Compensation
Clinically, also check the expected compensation: for a metabolic alkalosis PaCO₂ ≈ 0.7·HCO₃⁻ + 21 = 46.3–50.3 mmHg, so the measured 37 mmHg points to an additional respiratory alkalosis (a mixed disorder). The answer above is the ROME exam classification.
uncompensated
Answer
uncompensated
4.Arterial blood gas interpretation
Answer: A–a gradient = 174.2 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.
Alveolar oxygen
PAO₂ = 0.4·713 − 36/0.8 = 285.2 − 45 = 240.2 mmHg
Gradient
A–a = 240.2 − 66 = 174.2 mmHg
Answer
A–a gradient = 174.2 mmHg
5.Clinical assessment scores
Answer: NEWS2 = 6
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 18/min → 0
SpO₂ 94% → 1
on oxygen → 2
SBP 106 mmHg → 1
HR 92/min → 1
alert (A) → 0
T 36.0 °C → 1
Add
NEWS2 = 0 + 1 + 2 + 1 + 1 + 0 + 1 = 6
Answer
NEWS2 = 6
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 21/min → 2
SpO₂ 91% → 3
on oxygen → 2
SBP 142 mmHg → 0
HR 40/min → 3
alert (A) → 0
T 36.9 °C → 0
Total and red scores
NEWS2 = 2 + 3 + 2 + 0 + 3 + 0 + 0 = 10
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: A · At least 15 hours a day
Why this is the answer
Long-term oxygen therapy improves survival in COPD with chronic hypoxaemia when used for at least 15 hours a day, including overnight. Patients must not smoke, because of the fire risk. Ambulatory oxygen for exercise is a separate assessment.
Answer
A · At least 15 hours a day
8.Med-surg: cardiovascular & respiratory
Answer: D · Check vital signs, report urgently and anticipate a blood count
Why this is the answer
Melaena with postural dizziness suggests upper gastrointestinal bleeding, a risk with dual antiplatelet therapy. The nurse assesses for shock, informs the team urgently and expects bloods, a group and save (type and screen) and possibly endoscopy. Stopping antiplatelets after a stent risks stent thrombosis, so the decision belongs to the medical and cardiology team.
Answer
D · Check vital signs, report urgently and anticipate a blood count