How it is examined
The CICM First Part written section is two papers, each with 10 short answer questions and 50 multiple choice questions, over 2.5 hours. Candidates who reach the Angoff standard in both the SAQs and the MCQs progress to cross-table vivas: 2 minutes of reading, then 10 minutes with the examiners on basic sciences applied to intensive care, including monitoring equipment. Up to five attempts are allowed. Check the CICM website and syllabus for current details.
SAQs often ask for the renal handling of a substance, the regulation of a variable such as plasma osmolality, or an explanation of an acid-base disturbance using strong ion difference.
Renal physiology
| Topic | Key points |
|---|---|
| GFR | Starling forces, autoregulation (myogenic and tubuloglomerular feedback), measurement |
| Proximal tubule | Reabsorbs about two-thirds of filtered sodium and water, bicarbonate reclamation |
| Loop of Henle | Countercurrent multiplication and medullary concentration gradient |
| Collecting duct | ADH and aquaporin-2; aldosterone and sodium/potassium exchange |
| Water balance | Osmoreceptors, ADH, thirst |
| Potassium | Distal secretion depends on flow, aldosterone and sodium delivery |
Acid-base: two approaches
The traditional approach uses pH, PaCO2, bicarbonate, base excess and the anion gap. The Stewart (physicochemical) approach says pH is determined by three independent variables: PaCO2, the strong ion difference (SID) and total weak acids (mainly albumin and phosphate).
| Change | Effect on pH |
|---|---|
| Fall in SID (e.g. hyperchloraemia, lactate) | Acidosis |
| Rise in SID (e.g. chloride loss from vomiting) | Alkalosis |
| Fall in albumin | Alkalosis |
| Rise in PaCO2 | Acidosis |
Large volumes of 0.9% saline lower SID because its sodium and chloride concentrations are equal, producing a hyperchloraemic metabolic acidosis.
Practice questions
SAQ-style practice
Explain how the kidney regulates plasma osmolality.
Show a model answer outline
- Hypothalamic osmoreceptors detect a rise in osmolality.
- ADH is released from the posterior pituitary.
- ADH inserts aquaporin-2 into collecting duct cells via V2 receptors.
- Water reabsorption depends on the medullary concentration gradient.
- Thirst increases intake; non-osmotic ADH release occurs with hypovolaemia.
Worked MCQ · Stewart
A patient receives 6 L of 0.9% saline. Which change explains the resulting acidosis by the Stewart approach?
- A A rise in PaCO2
- B A fall in strong ion difference
- C A rise in albumin
- D A rise in lactate production by the gut
- E A fall in phosphate
Show the reasoning
Answer B. Saline has a strong ion difference of zero, so large volumes dilute plasma SID toward zero, causing a hyperchloraemic metabolic acidosis.
Common mistakes
- Not stating the independent variables in Stewart analysis.
- Forgetting albumin when interpreting the anion gap.
- Confusing ADH and aldosterone effects.
- Vague descriptions of countercurrent multiplication.
- Ignoring time course of compensation.
Free sample renal and acid-base questions
Questions from our Intensive care (CICM) bank. Choose your answer, then open the explanation.
What proportion of filtered sodium is reabsorbed in the proximal tubule?
- AAbout 25%
- BAbout 65%
- CAbout 99%
- DNone
- EAbout 5%
Show answer and explanation
Answer B. The proximal tubule reabsorbs about 65% of filtered Na and water, nearly all glucose and amino acids, and most bicarbonate.
Learning point: PCT: 65% of Na and water, all glucose, most HCO3.
A patient has an anion gap of 26 and a bicarbonate of 18 (normal anion gap 12, bicarbonate 24). What does the delta ratio suggest?
- ANormal acid-base status
- BHigh anion gap acidosis plus alkalosis
- CRespiratory alkalosis only
- DPure raised anion gap metabolic acidosis
- EMixed raised and normal anion gap acidosis
Show answer and explanation
Answer B. Delta ratio = (26 - 12) / (24 - 18) = 2.3. A ratio above 2 suggests a concurrent metabolic alkalosis; below 1 suggests a coexisting normal anion gap acidosis.
Learning point: Delta ratio above 2 suggests coexisting metabolic alkalosis.
How is the anion gap calculated?
- ANa - (Cl + HCO3)
- BCl - HCO3
- C(Na + Cl) - HCO3
- DNa - HCO3 + albumin
- ENa + K - Cl only
Show answer and explanation
Answer A. AG = Na - (Cl + HCO3), normal about 8 to 12 (or with K, 12 to 16). Correct for albumin: add about 2.5 per 10 g/L fall below 40.
Learning point: AG = Na - (Cl + HCO3); correct for albumin.
Practise more renal and acid-base questions free
Every renal and acid-base subtopic in our bank
The bank holds 22 renal and acid-base questions across 20 subtopics. You can filter by any of them, build a custom block and track your accuracy subtopic by subtopic.
- ADH1
- Aldosterone actions1
- Anion gap1
- Delta ratio2
- Free water clearance1
- GFR1
- Loop of Henle1
- Metabolic alkalosis1
- Normal saline acidosis1
- Osmolar gap2
- Potassium handling1
- Proximal tubule1
- Raised anion gap acidosis1
- Renal autoregulation1
- Renal blood flow1
- Renal tubular acidosis1
- Respiratory acidosis compensation1
- RTA type 11
- Stewart approach1
- Winters formula1
Common questions
Do I need to know the Stewart approach for CICM?
It is widely taught in intensive care and useful for explaining fluid-related acidosis. Learn both approaches.
How should I correct the anion gap for albumin?
A common rule adds about 2.5 mmol/L to the anion gap for every 10 g/L fall in albumin below 40 g/L.
Is renal pharmacology also tested?
Diuretics and drug clearance in renal failure overlap with pharmacology topics.
How many renal and acid-base questions are in the Intensive care (CICM) bank?
There are 22 renal and acid-base questions across 20 subtopics, and the bank grows as new questions pass review.
Can I practise only renal and acid-base questions?
Yes. Filter by area or by any subtopic to build a custom block, in tutor mode with explanations after each question or in timed mode.
How are renal and acid-base questions explained?
Every question explains why the answer is right and why each other option is wrong, with a learning point and the Australian source behind it.
How much of the Intensive care (CICM) mock is renal and acid-base?
About 17 questions in each 100-question mock come from renal and acid-base, following our mock blueprint.
Which sources is this renal and acid-base page based on?
It summarises current Australian guidance, including CICM First Part Examination; CICM First Part Syllabus. Guidelines change, so always check the latest edition.
When was this renal and acid-base guide last updated?
It was last reviewed on 9 November 2026. We update topic pages when the exam or Australian guidance changes.
How do I unlock all Intensive care (CICM) questions?
Choose a Intensive care (CICM) plan: 3 or 6 months of access, from A$469.99, one payment with no auto-renew. It opens every area, not just renal and acid-base.
Sources
Clinical content is summarised from current Australian guidance at the date above. Guidelines change, so always check the latest edition.