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.
ECG rhythm strip interpretation
Paper (25 mm/s, 10 mm/mV)
1 small box = 0.04 s, 1 large box = 0.20 s, 10 mm = 1 mV
Heart rate, regular rhythm
300 ÷ large boxes = 1500 ÷ small boxes = 60 ÷ RR (s)
Heart rate, irregular rhythm
QRS complexes in 6 s × 10
Normal PR interval
0.12–0.20 s
Normal QRS duration
< 0.12 s
QTc (Bazett)
QT/√RR
QTc (Fridericia)
QT/∛RR
QTc (Framingham)
QT + 154·(1 − RR)
Sinus rates
bradycardia < 60, normal 60–100, tachycardia > 100 /min
Escape rates
junctional 40–60, ventricular 20–40 /min
Fast rhythms
SVT 150–250 /min (narrow), VT > 100 /min (wide)
Method
Rate: for a regular rhythm divide 300 by the large boxes or 1500 by the small boxes between two R waves; for an irregular rhythm count the QRS complexes in 6 seconds and multiply by 10.
Rhythm: compare the R–R intervals. Equal is regular; a repeating pattern is regularly irregular; no pattern at all is irregularly irregular.
P waves: is there an upright P wave in lead II before every QRS, all alike? Look for fibrillatory or sawtooth waves, inverted P waves and P waves without a QRS.
PR interval: from the start of P to the start of the QRS, normally 0.12–0.20 s and constant. Watch whether it lengthens, stays fixed before a dropped beat, or varies at random.
QRS duration: below 0.12 s is narrow; 0.12 s or more is wide. Then name the rhythm, and for the QT use QTc = QT/√RR (Bazett) with times in seconds.
Prioritization & delegation
Method
Ask what will harm the patient soonest if nothing is done.
Apply ABC (C-A-B in cardiac arrest), then Maslow: physiological needs before safety, safety before psychological needs.
Compare the options: acute before chronic, unstable before stable, unexpected before expected, systemic before local, and check each finding against the patient’s baseline.
Assess before you act unless it is an emergency; then choose the step the others depend on.
For delegation, check the five rights: task, circumstance, person, directions and supervision. Assessment, teaching and evaluation stay with the RN.
2Practice problems
1.Med-surg: cardiovascular & respiratoryMedium
How does varenicline help people stop smoking?
AIt partly stimulates and partly blocks nicotine receptors
BIt makes cigarettes taste of metal so smoking feels unpleasant
CIt replaces nicotine through the skin, like a nicotine patch
DIt speeds the clearance of nicotine by the liver
2.Med-surg: cardiovascular & respiratoryHard
A nurse is planning care for four patients. Which patient should be assessed first?
AA patient with controlled hypertension asking about salt
BA patient with COPD whose SpO₂ fell from 90% to 83% with new drowsiness
CA patient with a venous ulcer due for a dressing change
DA patient with stable heart failure waiting for the daily weight
3.Med-surg: neuro, endocrine & renalMedium
Which symptoms are typical of hypokalaemia?
AExcess thirst and very high glucose
BHeat intolerance and weight loss
CTingling lips and facial twitching
DMuscle weakness, cramps and palpitations
4.Med-surg: neuro, endocrine & renalHard
The nurse has four urology patients. Which one needs to be seen first?
AA patient after TURP with light pink drainage and mild discomfort
BA patient with stress incontinence asking about pelvic floor exercises
CA patient with a nephrostomy who has rigors and a BP of 86/50 mmHg
DA patient with a suprapubic catheter due for a routine change
5.Med-surg: GI, perioperative & oncologyMedium
How large should the opening of a stoma appliance be cut?
AAny size, as long as the stoma is covered
BSlightly smaller than the stoma for a tight seal
CAbout 2–3 mm larger than the stoma all round
DAbout 2 cm larger than the stoma all round
6.Med-surg: GI, perioperative & oncologyHard
A patient who had a coronary stent placed two months ago, on aspirin and clopidogrel, presents with melaena and is now stable. What is the most appropriate approach to the antiplatelet drugs?
AReport the bleed; the team decides with cardiology input, balancing bleeding against stent thrombosis
BDouble both doses, because bleeding means the stent is at greater risk of clotting
CStop both drugs permanently, because any bleeding means they are no longer safe
DContinue both drugs unchanged and do not mention the bleeding to the team
7.Clinical nursingMedium
What should a patient starting oral iron tablets be told?
ATheir urine will turn bright green
BTheir stools may turn dark or black
CThey must take the tablets with strong tea
DThe tablets will cause weight loss
8.Clinical nursingHard
A nurse is unsure whether a prescribed dose of a high-risk drug is correct. What is the safest action?
AWithhold it and check with the prescriber or pharmacist first
BGive half the dose as a compromise until the doctor is available
CGive the dose because the doctor has signed the prescription
DAsk the patient whether the dose looks the same as usual and give it
9.Lab values & electrolytesMedium
A stable adult who is not bleeding receives one unit of packed red cells. By about how much is the hemoglobin expected to rise?
AAbout 0.1 g/dL (1 g/L)
BAbout 5 g/dL (50 g/L)
CAbout 3 g/dL (30 g/L)
DAbout 1 g/dL (10 g/L)
10.Lab values & electrolytesHard
A patient with acute kidney injury after severe dehydration has a rising creatinine. Which urine findings support a prerenal cause rather than acute tubular necrosis (ATN)?
AWhite cell casts with positive nitrites on the dipstick
BHigh urine sodium and dilute urine with muddy brown granular casts
CRed cell casts with heavy protein loss in the urine
DLow urine sodium and concentrated urine with a high specific gravity
11.Arterial blood gas interpretationMedium
Practice values: Na⁺ 150 mmol/L, glucose 27.5 mmol/L and urea 12.2 mmol/L. Calculate the serum osmolality Osm = 2·Na⁺ + glucose + urea to the nearest whole number.
Na⁺ 150 mmol/Lglucose 27.5 mmol/Lurea 12.2 mmol/L
Osm = mOsm/kg
12.Arterial blood gas interpretationHard
A practice gas shows a metabolic alkalosis with HCO₃⁻ 37 mmol/L. Use expected PaCO₂ = 0.7·HCO₃⁻ + 21 to find the expected PaCO₂.
HCO₃⁻ 37 mmol/L
PaCO₂ = mmHg
13.ECG rhythm strip interpretationMedium
Interpret this lead II rhythm strip. Which rhythm is it? Click your answer.
lead II, 25 mm/s, 10 mm/mV1 small box = 0.04 s, 1 large box = 0.20 sstrip length 6 s
1atrial fibrillation
2normal sinus rhythm
3sinus bradycardia
4junctional rhythm
14.ECG rhythm strip interpretationHard
Identify the rhythm on this lead II strip. Click your answer.
lead II, 25 mm/s, 10 mm/mV1 small box = 0.04 s, 1 large box = 0.20 sstrip length 6 s
1atrial flutter, 2:1 conduction
2supraventricular tachycardia (SVT)
3idioventricular rhythm
4torsades de pointes
15.Prioritization & delegationMedium
Which finding is unexpected and needs prompt follow-up?
AA patient on a heparin infusion has a new black, tarry stool
BA patient with long-standing COPD has a barrel-shaped chest
CA patient with known cirrhosis has yellow skin that has not changed
DA patient one day after laparoscopic gallbladder surgery has right shoulder pain
16.Prioritization & delegationHard
A patient is bleeding internally after a fall. Which finding is usually an early sign of hypovolemic shock?
AA very low blood pressure with fixed, dilated pupils
BRestlessness and a rising heart rate while the blood pressure is still normal
CA slow heart rate with warm, dry, flushed skin and a normal blood pressure throughout
DLoss of consciousness with gasping breaths
3Solutions
1.Med-surg: cardiovascular & respiratory
Answer: A · It partly stimulates and partly blocks nicotine receptors
Why this is the answer
Varenicline is a partial agonist at nicotinic acetylcholine receptors. It reduces cravings and withdrawal and makes smoking less rewarding. Nausea is common, and patients are asked to report mood changes.
Answer
A · It partly stimulates and partly blocks nicotine receptors
2.Med-surg: cardiovascular & respiratory
Answer: B · A patient with COPD whose SpO₂ fell from 90% to 83% with new drowsiness
Why this is the answer
A falling saturation with new drowsiness suggests acute respiratory failure, possibly with hypercapnia, and needs immediate assessment. The other patients are stable and their needs can wait briefly.
Answer
B · A patient with COPD whose SpO₂ fell from 90% to 83% with new drowsiness
3.Med-surg: neuro, endocrine & renal
Answer: D · Muscle weakness, cramps and palpitations
Why this is the answer
Low potassium causes muscle weakness, cramps, constipation and arrhythmias. ECG changes include flattened T waves and U waves. Tingling and twitching suggest low calcium.
Answer
D · Muscle weakness, cramps and palpitations
4.Med-surg: neuro, endocrine & renal
Answer: C · A patient with a nephrostomy who has rigors and a BP of 86/50 mmHg
Why this is the answer
Rigors and hypotension in a patient with a nephrostomy suggest urosepsis, which needs immediate assessment and treatment. Light pink drainage after TURP is expected. The other patients are stable.
Answer
C · A patient with a nephrostomy who has rigors and a BP of 86/50 mmHg
5.Med-surg: GI, perioperative & oncology
Answer: C · About 2–3 mm larger than the stoma all round
Why this is the answer
The aperture is cut to fit closely around the stoma, leaving a small margin of about 2–3 mm (about 1/8 inch). Too large exposes skin to output; too small can cut into the stoma. Stomas shrink during the first weeks, so measurement is repeated.
Answer
C · About 2–3 mm larger than the stoma all round
6.Med-surg: GI, perioperative & oncology
Answer: A · Report the bleed; the team decides with cardiology input, balancing bleeding against stent thrombosis
Why this is the answer
Early after coronary stenting, stopping dual antiplatelet therapy carries a high risk of stent thrombosis and MI, while continuing increases bleeding. Decisions are made by the medical team, ideally with cardiology and gastroenterology input; often aspirin is continued and the second agent paused briefly or continued depending on bleeding severity and endoscopic findings.
Answer
A · Report the bleed; the team decides with cardiology input, balancing bleeding against stent thrombosis
7.Clinical nursing
Answer: B · Their stools may turn dark or black
Why this is the answer
Oral iron commonly darkens the stool and can cause constipation or stomach upset. Tea and antacids reduce absorption, while vitamin C may increase it.
Answer
B · Their stools may turn dark or black
8.Clinical nursing
Answer: A · Withhold it and check with the prescriber or pharmacist first
Why this is the answer
Nurses must understand any drug they administer. If a dose seems wrong, they should check with the prescriber or pharmacist and document the action.
Answer
A · Withhold it and check with the prescriber or pharmacist first
9.Lab values & electrolytes
Answer: D · About 1 g/dL (10 g/L)
Why this is the answer
In an average-sized adult without ongoing bleeding or hemolysis, one unit of red cells raises the hemoglobin by about 1 g/dL (and the hematocrit by about 3%). A smaller rise suggests ongoing blood loss or red cell destruction.Checked against:Blood Transfusion · StatPearls (NCBI Bookshelf) (2026)
Answer
D · About 1 g/dL (10 g/L)
10.Lab values & electrolytes
Answer: D · Low urine sodium and concentrated urine with a high specific gravity
Why this is the answer
In prerenal AKI the tubules are intact, so they keep sodium and water, giving a low urine sodium and concentrated urine. In ATN the damaged tubules cannot do this, so urine sodium is high, the urine is dilute and muddy brown casts appear.Checked against:Urine specific gravity test · MedlinePlus (NIH) (2025)
Answer
D · Low urine sodium and concentrated urine with a high specific gravity
11.Arterial blood gas interpretation
Answer: Osm = 340 mOsm/kg
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.
Calculated osmolality
Osm = 2·150 + 27.5 + 12.2 = 339.7 ≈ 340 mOsm/kg
Answer
Osm = 340 mOsm/kg
12.Arterial blood gas interpretation
Answer: PaCO₂ = 46.9 mmHg
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 PaCO₂
0.7·37 + 21 = 46.9 mmHg
Answer
PaCO₂ = 46.9 mmHg
The rise has a limit: PaCO₂ rarely goes above about 55 mmHg from compensation alone.
13.ECG rhythm strip interpretation
Answer: junctional rhythm
Rhythm criteria (lead II): sinus rhythm has an upright P wave before every QRS, a constant PR of 0.12–0.20 s and a narrow QRS: normal sinus rhythm at 60–100/min, sinus bradycardia below 60, sinus tachycardia above 100. Atrial fibrillation: no P waves, a fibrillatory baseline and an irregularly irregular R–R. Atrial flutter: sawtooth flutter waves at about 250–350/min with a fixed conduction ratio such as 2:1 or 4:1. First-degree AV block: sinus rhythm with a constant PR above 0.20 s. Junctional rhythm: narrow QRS at 40–60/min with absent or inverted P waves (PR below 0.12 s, or P after the QRS). A PVC is an early, wide (0.12 s or more), bizarre QRS without a P wave, with the T wave in the opposite direction and usually a full compensatory pause; in bigeminy every second beat is a PVC.
Five steps
1. Rate: R–R = 26 small boxes, 1500 ÷ 26 ≈ 58 per minute.
2. Rhythm: regular, every R–R is 1.04 s.
3. P waves: inverted, just after each QRS.
4. PR interval: not measurable.
5. QRS: 0.10 s, narrow (below 0.12 s).
Interpretation
junctional rhythm
Answer
junctional rhythm
14.ECG rhythm strip interpretation
Answer: torsades de pointes
More ventricular rhythms: torsades de pointes is a polymorphic ventricular tachycardia, usually 150–250/min, in which the wide complexes change in height and twist around the baseline, pointing up for a few beats and then down. Textbooks link it to a prolonged QT interval, and magnesium sulfate is the drug resuscitation guidelines name for it. An idioventricular rhythm is a ventricular escape rhythm: regular, wide QRS (0.12 s or more), no P waves, at 20–40/min (an accelerated idioventricular rhythm runs at 40–100/min). Monomorphic VT has identical wide complexes at more than 100/min. VF is chaotic, without any repeating complex.
Five steps
1. Rate: very fast, the complexes are about 6 small boxes apart (about 250 per minute).
2. Rhythm: fast and roughly regular, but the height and direction of the complexes change in a repeating spindle pattern.
3. P waves: none identifiable.
4. PR interval: not measurable.
5. QRS: wide and polymorphic; the complexes twist around the baseline, pointing up for a few beats and then down.
Interpretation
torsades de pointes
Answer
torsades de pointes
Torsades de pointes is a polymorphic VT linked to a prolonged QT interval. This is identification practice only.
15.Prioritization & delegation
Answer: A · A patient on a heparin infusion has a new black, tarry stool
Why this is the answer
Black, tarry stool (melena) suggests bleeding from the upper gut, a dangerous complication of anticoagulation. Shoulder pain after laparoscopy from the gas used is common, and a barrel chest in COPD and stable jaundice in cirrhosis are expected.
Answer
A · A patient on a heparin infusion has a new black, tarry stool
16.Prioritization & delegation
Answer: B · Restlessness and a rising heart rate while the blood pressure is still normal
Why this is the answer
In early shock, the body keeps the blood pressure up by raising the heart rate and narrowing vessels, so restlessness and tachycardia appear first. A falling blood pressure is a later sign.
Answer
B · Restlessness and a rising heart rate while the blood pressure is still normal