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
What does a raised D-dimer result mean?
AThe anticoagulant dose is too low and must rise
BA pulmonary embolism or DVT has been confirmed
CFibrin breakdown is present, but it does not prove a clot
DA deep vein thrombosis has been safely excluded
2.Med-surg: cardiovascular & respiratoryHard
A nurse receives handover on four patients. Which patient should be seen first?
AA patient on day 1 after surgery who is newly restless, RR 30/min, SpO₂ 88% on 4 L/min
BA patient with pneumonia on IV antibiotics who now has a temperature of 38.2 °C
CA patient with asthma who wants a reliever inhaler before a walk
DA patient with COPD on 1 L/min whose SpO₂ has been 89% and stable throughout the night
3.Med-surg: neuro, endocrine & renalMedium
Why must potassium be monitored closely when IV insulin is given for DKA?
AInsulin moves potassium into cells, so the level can fall quickly
BInsulin makes the kidneys retain potassium, so the level will rise
CInsulin has no effect on potassium in DKA
DInsulin breaks down potassium in the bloodstream
4.Med-surg: neuro, endocrine & renalHard
A patient with acute glomerulonephritis has a BP of 190/115 mmHg, a severe headache and blurred vision. Which is the priority?
AGive extra oral fluids to correct the low urine output
BRecheck the BP at the next routine round
CEncourage a walk to relieve the headache
DUrgent escalation for BP control and close neuro checks
5.Med-surg: GI, perioperative & oncologyMedium
What is tumour lysis syndrome?
AA metabolic emergency from rapid breakdown of cancer cells
BAn allergic reaction to a chemotherapy infusion
CA skin reaction in an area recently treated with radiotherapy
DA slow-growing tumour that presses on the nerves
6.Med-surg: GI, perioperative & oncologyHard
A few hours after an ERCP, a patient has severe epigastric pain radiating to the back, with vomiting. Which complication is most likely?
APost-ERCP pancreatitis
BAcute appendicitis
CHepatitis B infection
DBiliary colic from a new stone
7.Clinical nursingMedium
Which type of painkiller should a patient with liver cirrhosis usually avoid?
AHot packs applied to a painful joint
BLocal anaesthetic creams
CParacetamol (acetaminophen), given in a carefully reduced and monitored dose
DNon-steroidal anti-inflammatory drugs such as ibuprofen
8.Clinical nursingHard
A patient's urine output has been very low for 12 hours and creatinine has risen sharply. Which drug on the chart is most likely to need review?
AParacetamol at usual doses
BA vitamin supplement
CAn emollient cream
DA non-steroidal anti-inflammatory drug such as ibuprofen
9.Lab values & electrolytesMedium
A patient's potassium is 7.0 mEq/L. Which ECG change would the nurse expect?
ADelta waves before the QRS
BTall, peaked T waves
CProminent U waves
DFlattened T waves
10.Lab values & electrolytesHard
The nurse teaches a patient with severe neutropenia after chemotherapy. Which statement shows a need for further teaching?
A"I'll check my temperature rectally to be accurate"
B"I'll wash my hands before eating and after the toilet"
C"I'll avoid people who have a cold or the flu"
D"I'll call the clinic if my temperature rises"
11.Arterial blood gas interpretationMedium
A practice gas shows a metabolic acidosis with HCO₃⁻ 18 mmol/L. Use Winter’s formula to find the expected PaCO₂ (the centre of the range) in mmHg.
HCO₃⁻ 18 mmol/L
PaCO₂ = mmHg
12.Arterial blood gas interpretationHard
Practice values: Na⁺ 136, Cl⁻ 103, HCO₃⁻ 22 mmol/L and albumin 24 g/L. Find the albumin-corrected anion gap AGc = AG + 0.25·(40 − albumin).
Measure the QT interval on this lead II strip, in seconds.
lead II, 25 mm/s, 10 mm/mV1 small box = 0.04 s, 1 large box = 0.20 sstrip length 6 s
QT = s
14.ECG rhythm strip interpretationHard
Interpret this lead II strip. Which interpretation can you defend from this single 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
1sinus bradycardia
2first-degree AV block
32:1 AV block (type undetermined)
4third-degree (complete) AV block
15.Prioritization & delegationMedium
Which postoperative patient should the nurse see first?
AAsking when the urinary catheter will be removed
BWants help with washing her hair before her visitors arrive this afternoon
CDressing soaked with bright red blood and a heart rate rising to 118/min
DPain of 4/10 one hour after an oral analgesic
16.Prioritization & delegationHard
A patient taking an SSRI is also given tramadol. A few hours later the patient is agitated, sweating and has a fever, jerking muscles and brisk reflexes. What is the most likely cause?
ANeuroleptic malignant syndrome
BOpioid withdrawal
CSerotonin syndrome
DAn anxiety attack
3Solutions
1.Med-surg: cardiovascular & respiratory
Answer: C · Fibrin breakdown is present, but it does not prove a clot
Why this is the answer
D-dimer is a breakdown product of fibrin. A normal result in a patient with a low clinical probability (for example a low Wells score) helps exclude DVT or PE. A raised result is common in many conditions, so imaging (duplex ultrasound or CT pulmonary angiography) is needed to confirm a clot.
Answer
C · Fibrin breakdown is present, but it does not prove a clot
2.Med-surg: cardiovascular & respiratory
Answer: A · A patient on day 1 after surgery who is newly restless, RR 30/min, SpO₂ 88% on 4 L/min
Why this is the answer
New restlessness, tachypnoea and hypoxaemia despite oxygen suggest acute deterioration such as a PE, pneumonia or bleeding, so this patient is seen first. SpO₂ 89% is within target for a stable COPD patient, a mild fever on antibiotics is expected, and the asthma patient is well.
Answer
A · A patient on day 1 after surgery who is newly restless, RR 30/min, SpO₂ 88% on 4 L/min
3.Med-surg: neuro, endocrine & renal
Answer: A · Insulin moves potassium into cells, so the level can fall quickly
Why this is the answer
Patients in DKA have a large total-body potassium deficit even if serum potassium is normal or high at first. Insulin shifts potassium into cells, which can cause dangerous hypokalaemia. Potassium is checked often and added to fluids as prescribed; if it is very low, insulin may be delayed until replacement has started.
Answer
A · Insulin moves potassium into cells, so the level can fall quickly
4.Med-surg: neuro, endocrine & renal
Answer: D · Urgent escalation for BP control and close neuro checks
Why this is the answer
Severe hypertension with headache and visual change suggests hypertensive encephalopathy. This needs urgent medical treatment and neurological monitoring. Seizures can occur.
Answer
D · Urgent escalation for BP control and close neuro checks
5.Med-surg: GI, perioperative & oncology
Answer: A · A metabolic emergency from rapid breakdown of cancer cells
Why this is the answer
Rapid tumour cell death, usually after starting treatment for fast-growing cancers such as acute leukaemia or high-grade lymphoma, releases potassium, phosphate and nucleic acids (converted to uric acid). This can cause AKI and arrhythmias.
Answer
A · A metabolic emergency from rapid breakdown of cancer cells
6.Med-surg: GI, perioperative & oncology
Answer: A · Post-ERCP pancreatitis
Why this is the answer
Pancreatitis is the most common serious complication of ERCP. Severe epigastric pain radiating to the back with raised amylase or lipase suggests it; management includes analgesia, IV fluids and close monitoring.
Answer
A · Post-ERCP pancreatitis
7.Clinical nursing
Answer: D · Non-steroidal anti-inflammatory drugs such as ibuprofen
Why this is the answer
NSAIDs increase the risk of GI bleeding and can trigger kidney failure and fluid retention in cirrhosis. Paracetamol is usually preferred at a lower, carefully chosen dose.
Answer
D · Non-steroidal anti-inflammatory drugs such as ibuprofen
8.Clinical nursing
Answer: D · A non-steroidal anti-inflammatory drug such as ibuprofen
Why this is the answer
In acute kidney injury, nephrotoxic drugs (such as NSAIDs and aminoglycosides) and drugs that reduce renal perfusion (such as ACE inhibitors and diuretics) are reviewed and often stopped.
Answer
D · A non-steroidal anti-inflammatory drug such as ibuprofen
9.Lab values & electrolytes
Answer: B · Tall, peaked T waves
Why this is the answer
Hyperkalemia first causes tall, peaked T waves, then a prolonged PR interval, loss of P waves and a wide QRS, which can lead to ventricular fibrillation or asystole. U waves and flat T waves are signs of hypokalemia.Checked against:High potassium level · MedlinePlus (NIH) (2025); Potassium test · MedlinePlus (NIH) (2025)
Answer
B · Tall, peaked T waves
10.Lab values & electrolytes
Answer: A · "I'll check my temperature rectally to be accurate"
Why this is the answer
Rectal temperatures, suppositories and enemas are avoided in neutropenia, because injury to the rectal mucosa can let bacteria into the blood. Prompt reporting of fever, hand hygiene and avoiding sick contacts are correct.
Answer
A · "I'll check my temperature rectally to be accurate"
11.Arterial blood gas interpretation
Answer: PaCO₂ = 35 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.
Winter’s formula
PaCO₂ = 1.5·18 + 8 = 35 mmHg
range: 33–37 mmHg
Answer
PaCO₂ = 35 mmHg
12.Arterial blood gas interpretation
Answer: AGc = 15 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.
Anion gap
AG = 136 − (103 + 22) = 11
Correction for albumin
11 + 0.25·(40 − 24) = 15 mmol/L
Answer
AGc = 15 mmol/L
Above about 12 after correction: a high anion gap.
13.ECG rhythm strip interpretation
Answer: QT = 0.42 s
QT and QTc: the QT interval runs from the start of the QRS complex to the end of the T wave. It shortens as the heart rate rises, so it is corrected for rate with the R–R interval in seconds: Bazett QTc = QT/√RR and Fridericia QTc = QT/∛RR. Bazett is the formula most textbooks use; it over-corrects at fast rates, where Fridericia is preferred. Limits differ between references: a QTc above about 0.45 s in men or 0.46 s in women is usually called prolonged, and above 0.50 s markedly prolonged.
Measure
10.5 small boxes from the start of the QRS to the end of the T wave
Convert
QT = 10.5 × 0.04 s = 0.42 s
Answer
QT = 0.42 s
A rough rule: at normal rates the QT should be less than half the R–R interval (here R–R = 0.84 s).
14.ECG rhythm strip interpretation
Answer: 2:1 AV block (type undetermined)
2:1 AV block: with two P waves for every QRS, no two conducted P waves follow each other, so you cannot see whether the PR would lengthen (type I) or stay constant (type II) before a non-conducted P wave. From one strip it is called a 2:1 AV block; a longer strip or a change in the conduction ratio decides the type. A narrow QRS makes type I more likely and a wide QRS type II, but neither proves it.
Five steps
1. Rate: R–R = 42 small boxes, 1500 ÷ 42 ≈ 36 per minute.
2. Rhythm: regular, every R–R is 1.68 s.
3. P waves: upright and regular (P–P 0.84 s, 71 per minute), two for every QRS.
4. PR interval: constant at 0.16 s in the conducted beats.
5. QRS: 0.12 s, wide (0.12 s or more).
Why the type stays open
Every second P wave is not conducted, so no two conducted beats follow each other and a lengthening PR could never show.
2:1 AV block (type undetermined)
Answer
2:1 AV block (type undetermined)
A narrow QRS makes type I more likely and a wide QRS type II, but only a longer strip or a change in the conduction ratio decides.
15.Prioritization & delegation
Answer: C · Dressing soaked with bright red blood and a heart rate rising to 118/min
Why this is the answer
Heavy fresh bleeding with a rising heart rate suggests hemorrhage and early shock. The other patients have routine needs that can wait.
Answer
C · Dressing soaked with bright red blood and a heart rate rising to 118/min
16.Prioritization & delegation
Answer: C · Serotonin syndrome
Why this is the answer
SSRIs and tramadol both raise serotonin. Agitation, fever, clonus and hyperreflexia that start quickly suggest serotonin syndrome; neuroleptic malignant syndrome follows antipsychotics and causes rigid muscles with slow reflexes.