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 1900 psi and runs at 15 L/min. Keeping a safe residual of 200 psi, how many minutes t will it last? Round down to a whole minute.
1900 psif = 3.14 L/psi15 L/min200 psi
t = min
2.Oxygen therapy & respiratory calculationsHard
Practice exercise (made-up values, not clinical guidance). A transfer will take 30 minutes. The size E cylinder (factor 0.28 L/psi) reads 1600 psi. Keeping a safe residual of 200 psi, what is the highest whole-number flow Q in L/min that lasts the whole transfer?
30 min1600 psif = 0.28 L/psi200 psi
Q = L/min
3.Arterial blood gas interpretationMedium
A practice arterial blood gas shows pH 7.42, PaCO₂ 30 mmHg (4.0 kPa) and HCO₃⁻ 19 mmol/L. The primary disorder is respiratory alkalosis. How far is it compensated? Click your answer.
pH 7.42PaCO₂ 30 mmHg (4.0 kPa)HCO₃⁻ 19 mmol/L
1uncompensated
2partially compensated
3fully compensated
4.Arterial blood gas interpretationHard
A practice gas shows pH 7.31, PaCO₂ 35 mmHg (4.7 kPa) and HCO₃⁻ 17 mmol/L, with Na⁺ 141 and Cl⁻ 92 mmol/L. Use the anion gap and the delta ratio to click the best interpretation.
Practice exercise (made-up values, not clinical guidance). A patient has a pulse of 146/min and a blood pressure of 77/50 mmHg. Find the shock index SI = HR/SBP. Round to two decimal places.
HR 146/minBP 77/50 mmHg
SI =
6.Clinical assessment scoresHard
Practice exercise (made-up values, not clinical guidance). Use the NEWS2 chart (SpO₂ scale 1) for these observations: respiration rate 18/min, SpO₂ 88% on room air, blood pressure 136/82 mmHg, pulse 70/min, alert, temperature 35.2 °C. Which clinical risk group does the patient fall into? Click it.
RR 18SpO₂ 88%airSBP 136HR 70AT 35.2 °C
1low
2low–medium
3medium
4high
7.Med-surg: cardiovascular & respiratoryMedium
A patient stops ramipril because of a troublesome dry cough. Which drug class is a common alternative?
AA loop diuretic such as furosemide
BA nitrate such as isosorbide mononitrate
CA non-selective beta-blocker such as propranolol
DAn angiotensin II receptor blocker such as losartan
8.Med-surg: cardiovascular & respiratoryHard
A patient with COPD is going home on long-term oxygen. Which teaching point is most important for safety?
ATurn the flow up as high as needed when breathless
BUse petroleum jelly to soothe dry nostrils
CNever smoke or allow open flames near the oxygen
DStore spare cylinders next to the cooker
3Solutions
1.Oxygen therapy & respiratory calculations
Answer: t = 355 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
(1900 − 200)·3.14 = 5338 L
Duration
5338/15 = 355.9 min → t = 355 min
Answer
t = 355 min
That is about 5 h 55 min.
2.Oxygen therapy & respiratory calculations
Answer: Q = 13 L/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
(1600 − 200)·0.28 = 392 L
Highest flow
392/30 = 13.07 L/min → Q = 13 L/min
Answer
Q = 13 L/min
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 7.42: within 7.35–7.45
PaCO₂ 30 mmHg: low (35–45)
HCO₃⁻ 19 mmol/L: low (22–26)
Compensation
fully compensated
Answer
fully compensated
4.Arterial blood gas interpretation
Answer: added metabolic alkalosis
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 = 141 − (92 + 17) = 32
Delta ratio
(32 − 12)/(24 − 17) = 2.857
added metabolic alkalosis
Answer
added metabolic alkalosis
5.Clinical assessment scores
Answer: SI = 1.9
Blood pressure values: pulse pressure PP = SBP − DBP. Mean arterial pressure MAP ≈ (SBP + 2·DBP)/3 = DBP + PP/3, an estimate based on the heart spending about two thirds of each beat in diastole at a normal heart rate (less accurate when the heart rate is fast); a MAP of at least about 65 mmHg is a common target for organ perfusion. The shock index SI = heart rate/SBP is normally about 0.5–0.7; a value above about 1 is a warning sign of shock.
Shock index
SI = 146/77 = 1.896 ≈ 1.9
Answer
SI = 1.9
1 or more: a warning sign of shock in this practice case.
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 18/min → 0
SpO₂ 88% → 3
on air → 0
SBP 136 mmHg → 0
HR 70/min → 0
alert (A) → 0
T 35.2 °C → 1
Total and red scores
NEWS2 = 0 + 3 + 0 + 0 + 0 + 0 + 1 = 4
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: D · An angiotensin II receptor blocker such as losartan
Why this is the answer
Angiotensin receptor blockers (ending in -sartan) block the effects of angiotensin II without inhibiting ACE, so bradykinin does not build up and cough is much less common. They share other effects, such as raising potassium, and ACE inhibitors and ARBs are not normally combined.
Answer
D · An angiotensin II receptor blocker such as losartan
8.Med-surg: cardiovascular & respiratory
Answer: C · Never smoke or allow open flames near the oxygen
Why this is the answer
Smoking while using oxygen is a major cause of burns and fatal fires. Patients must keep oxygen away from flames and heat sources, use water-based (not oil-based) lubricants and follow the prescribed flow, because unsupervised increases can worsen CO₂ retention.
Answer
C · Never smoke or allow open flames near the oxygen