Acute Kidney Injury & IV Fluid Therapy

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<h1>AKI &amp; IV Fluid Therapy</h1>
<h2>Y4 MBChB Tutorial 2026-7 | Rob Hunter</h2>
<div class="intro-spacer"></div>
.callout-question[
**Two questions for you:**

- what % of hospital patients have AKI?

- what % of all doctors are nephrologists?  
]
</div>
</div>

???

---

# Why should we care?

### AKI:

- common: 10 - 20% of all hospital admissions  
- serious: 10 - 20% inpatient mortality

<br>

### IV Fluids:

- prescribing often delegated to junior staff  
- preventable harm in ~20% of patients on IV fluids

<br>

???

Prompt: Why do you think fluid prescribing is often poorly done, despite being so common?

(Junior doctors, time pressure, lack of formal teaching, assumption it's simple.)

---

.left-panel.navy[

#### Playbooks:

- AKI  
- IV fluids (assessment)  
- IV fluids (prescribing)
]

# Learning outcomes

#### Acute Kidney Injury
- Define AKI using KDIGO criteria
- Classify causes: **pre-renal, intrinsic, post-renal**  
- Structure an assessment and outline management principles

<br>

#### IV Fluid Therapy
- Apply the **5 Rs framework** to fluid prescribing decisions
- Choose an appropriate **fluid type, volume & rate**
- Recognise when fluids may be **harmful**

<br>

#### Cases
- Apply all of the above to **4 realistic clinical scenarios**, using real fluid charts

???
Ask students what they hope to get out of today before revealing objectives.

---
class: section, middle

# Part 1
## Acute Kidney Injury

---

# AKI definition

AKI is diagnosed if **any one** of the following is present (KDIGO/NICE):

- Serum creatinine rise of **≥26 μmol/L within 48 hours**
- Serum creatinine rise to **≥1.5× baseline** within 7 days
- Urine output **<0.5 mL/kg/hour for ≥6 hours**

.callout.callout-bottom[
**Key concept.** AKI is a **syndrome**, not a diagnosis. It describes a
*spectrum* of kidney injury — not just kidney failure — and always demands
a search for an underlying cause.
]

<br>

#### Staging

.compact-table[
| Stage | Creatinine | Urine output |
|:--|:--|:--|
| 1 | 1.5–1.9× baseline, or ≥26 μmol/L rise | <0.5 mL/kg/h for 6–12h |
| 2 | 2.0–2.9× baseline | <0.5 mL/kg/h for ≥12h |
| 3 | ≥3.0× baseline, or ≥354 μmol/L, or KRT started | <0.3 mL/kg/h ≥24h or anuria ≥12h |
]

???
Prompt: Why might urine output be a more sensitive early sign than creatinine?

Stage using **whichever criterion gives the higher (worse) stage**.

Higher AKI stage = higher mortality risk and higher likelihood of needing
renal replacement therapy. Even *minor* creatinine rises are associated with
increased mortality.

Baseline = lowest value in last 7 days, or lowest/mean value from 7 days–3 months if no recent value available.

---

# AKI causes

![:scale 60%](images/AKI_classification.png)

---

# AKI causes

![:scale 60%](images/AKI_classification_prerenal.png)

---

# AKI causes

.pull-left[
### Pre-renal (~80%)
Reduced *perfusion* — no structural damage (yet):
- Hypovolaemia (bleeding, D&V, poor intake)
- Sepsis / hypotension
- Heart failure, cirrhosis (reduced effective circulating volume)
- Drugs: NSAIDs, ACEi/ARB, diuretics
]

.pull-right[
### Intrinsic (~10–20%)
*Structural damage* to the kidney:
- Acute tubular injury (ATI: most common — often prolonged pre-renal insult)
- Glomerulonephritis / vasculitis
- Interstitial nephritis (drugs, infection)
- Rhabdomyolysis, myeloma

<br>

### Post-renal (~5–10%)
Urinary tract *obstruction*:
- Prostatic hyperplasia, stones, malignancy
]

???
Prompts:

- What determines whether pre-renal AKI progresses to ATN? (severity & duration)
- Can you have pre-renal AKI and be fluid overloaded at the same time?

<br>

Pre-renal AKI is a **functional, reversible** response to reduced perfusion —
**no structural damage has yet occurred**.

- Kidneys try to preserve GFR via **RAAS activation** and **ADH release**
- Sodium and water are avidly retained > low urine sodium (<20 mmol/L)
- **Reversible** with prompt correction of perfusion — but prolonged or severe
  hypoperfusion leads to **acute tubular necrosis** (no longer reversible on
  restoring perfusion alone)

**Common pitfall.** Don't assume "pre-renal" always means "just give fluids."
In cardiac failure or cirrhosis, effective circulating volume is *low* despite
**total body fluid overload** — more fluid can cause harm.

---

# AKI: history

- **Fluid intake and losses**: vomiting, diarrhoea, bleeding, poor oral intake,
  fever, stoma output, polyuria
- **Comorbidities**: CKD, heart failure, liver disease, diabetes
- **Medications**:
  - NSAIDs, ACE inhibitors/ARBs, diuretics, aminoglycosides
  - SGLT2 inhibitors (?) — increasingly recognised as a "sick day" risk
  - metformin, opioids...
- **Urinary symptoms**: LUTS suggesting obstruction
- **Systemic features**: rash, joint pain, haemoptysis

???
Note the addition of SGLT2 inhibitors reflects recent MHRA safety updates
(2020 onwards) — flag this as an evolving area students should know for AKT.

---

# AKI: examination

.pull-left[
### Volume status
- Pulse, BP (including postural), JVP
- Capillary refill, mucous membranes, skin turgor
- Peripheral/pulmonary oedema
- Urine output (catheter if needed)
]

.pull-right[
### Look for a cause
- Peripheral pulses  
- Abdominal/pelvic mass, palpable bladder  
- Rash, joint swelling, red eyes, foot drop...  
- Signs of infection  
]

<br>

.callout[
**Tachycardia often precedes hypotension** as a sign of hypovolaemia —
compensatory vasoconstriction can maintain BP until significant volume loss
has occurred. Don't be falsely reassured by a normal BP.
]

.callout-warn[
Older/frail patients may not mount tachycardia (e.g., on beta-blockers)
— postural BP drop may be the only clue.
]

---

# AKI: investigations

#### Core set
- **U&Es** (creatinine trend, potassium, sodium, bicarbonate) — compare to baseline
- FBC, CRP, LFTs, calcium
- **Urinalysis**: blood + protein = intrinsic
- ECG if hyperkalaemia

<br>

#### Consider
- Renal tract ultrasound — **only if no clear cause**, or obstruction/pyonephrosis suspected
- Blood film, CK (rhabdomyolysis), serum/urine electrophoresis (myeloma, if >40y)
- Immunology (ANCA, ANA, complement) if intrinsic renal disease suspected

???
Reinforce that USS is not routine — NICE NG148 explicitly says do not offer it
routinely once a cause is identified. Only escalate if no clear cause, or
obstruction/pyonephrosis suspected (urgent, within 6h if pyonephrosis).

---

# AKI: management

1. Treat the **underlying cause** (e.g. infection, obstruction)
2. Optimise **fluid status** & monitor response  
3. Review **medications**
   - stop/withhold nephrotoxins and drugs impairing renal autoregulation
   - stor/dose-adjust renally cleared drugs
4. Treat **complications**: hyperkalaemia, acidosis, fluid overload, uraemia
5. **Refer** to renal if: suspected intrinsic cause or heading towards KRT

<br>

.callout-warn[
**"Sick day rules"**: during acute illness with poor intake/D&V, temporarily
stop ACEi/ARB, NSAIDs, diuretics, SGLT2 inhibitors, and metformin.
]

???
This is a heavily tested AKT concept. Ask students to try to name the "sick day"
drug list from memory before revealing it (Socratic questioning / think-pair-share
30 seconds).

---

.left-panel.amber[
# TL;DR

- pre-renal
- intrinsic
- post-renal
]

# Recap: AKI on one slide

- **Definition**: creatinine rise or oliguria  
<br>

- **Causes**: pre-renal (80%) > intrinsic > post-renal — often multifactorial  
<br>

- **Pre-renal AKI**: functional, reversible — but can progress to ATI if
  hypoperfusion persists  
<br>

- **Assessment**: volume status + look for a cause  
<br>

- **Management**: treat cause, optimise fluids, review drugs, treat complications,
  know when to refer

???

---
class: section, middle

# Part 2
## IV Fluid Therapy

---

![](images/latta.png)

???

Thomas Latta (1832)

---

# Types of fluid

![](images/infographic_fluids.png)

---

.left-panel.navy[

]

# Body fluid compartments

![](images/fluid-compartments_1.png)
---

.left-panel.navy.align-bottom[
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
For every 1L infused, intravascular volume will receive:  
- < 83 ml for 5% glucose  
- < 250 ml for 0.9% NaCl
]

# Body fluid compartments

![](images/fluid-compartments_2.png)

???

Only **~25% of infused isotonic crystalloid stays intravascular** — the rest
distributes into the interstitium. Large-volume crystalloid resuscitation can
cause interstitial oedema even while correctly expanding circulating volume.

---

# Before you prescribe: 4Qs & 5Rs

.callout[
1. **Does this patient need IV fluid at all?**
2. What **type** of fluid?
3. **How much?** & **how fast?**
4. How will I **monitor** the response — for both efficacy and safety?
]

<br>

???
IV fluid is a prescription — it carries the **same weight and risk** as any drug prescription.

5Rs are **not mutually exclusive**. A patient may need resuscitation,
*then* maintenance, *plus* ongoing replacement of stoma losses — three
separate prescribing decisions.

---

![](images/infographic_fluid-algorithm.png)

---

# Volume resuscitation

- Isotonic crystalloid, Na⁺ **130–154 mmol/L**
- **500 mL bolus over <15 minutes**
- **Reassess** (pulse, BP, cap refill, urine output, NEWS) after every bolus
- Repeat 250–500 mL boluses as needed

<br>

.callout-warn[
If **>2000 mL** given without haemodynamic improvement — **seek expert
help**. This is beyond independent FY1 management.
]

<br>

.callout[
Balanced crystalloids generally *preferred* over 0.9% saline for resuscitation. Evidence is conflicting (SMART/SALT-ED *vs* BASICS/PLUS).

Exceptions where 0.9% NaCl preferred: DKA; profuse vomiting; traumatic brain injury.
]

???
Emphasise the reassessment loop — this is not "give fluid and walk away."
Passive leg raise can be introduced here as a bedside test of fluid
responsiveness (rising BP = responsive; worsening breathlessness = overloaded).

Prompt: why is the 2L safety rule built in?

---

# Maintenance fluids

Daily requirements for a **haemodynamically stable, euvolaemic** patient unable to take fluids enterally:

<br>

.callout[
Standard UK regimen: **0.18% NaCl in 4% glucose**, with potassium as a
**pre-mixed** bag (20 or 40 mmol/L) — round to nearest available strength.
]

.callout-warn[
Prescribing **>2.5 L/day** of this hypotonic fluid increases the risk of
**hyponatraemia**, especially post-operatively (non-osmotic ADH release).
]

???
Work a quick worked example on the board: 70kg patient → ~1750–2100mL water,
~70mmol each electrolyte, 50-100g glucose. This maps directly onto Case 2.

---

# Replacement fluids

- **Add to or subtract from** the maintenance prescription based on measured
  or estimated ongoing losses

.compact-table[
| Loss Type | Na<sup>+</sup> | K<sup>+</sup> | Cl<sup>-</sup> | HCO<sub>3</sub><sup>-</sup> | Key Points |
| :--- | :---: | :---: | :---: | :---: | :--- |
| **Gastric / Vomit** | 20–60 | 10–20 | 140 | 0 | *chloride loss & H<sup>+</sup> > alkalosis* |
| **Bile** | 140 | 5 | 90–110 | 30 |  |
| **Pancreatic** | 130–140 | 5 | 50–110 | 90–115 | *alkali loss > acidosis* |
| **Small Bowel / Ileostomy** | 100–140 | 5 | 70–125 | 0-30 |  |
| **Diarrhoea** | 30–140 | 30–70 | - | 20–80 | *K-bicarbonate loss > hypoK acidosis* |
]

--
<br>

.callout-warn[
**IV potassium safety rules** (general ward):
- Maximum concentration **40 mmol/L**
- Maximum rate **10 mmol/hour**
- Never give as a bolus; obtain ECG first if K⁺ <2.5 or >5.5 mmol/L
]

???
This slide directly sets up Case 4 (ileostomy patient). Ask students what
electrolytes they'd expect to be lost in high stoma output (sodium, potassium,
bicarbonate).

---

# Monitoring patients on IV fluids

- **Daily**: clinical fluid status, U&Es (inc. TCO<sub>2</sub>), fluid balance chart review
- **Twice weekly**: body weight (1 kg change ≈ 1 L fluid)
- **Stop fluids** as soon as oral/enteral intake is adequate

<br>

.callout-question[
**Think–pair–share (2 min)**: why might a fluid balance chart *underestimate*
a patient's true fluid balance? Discuss with your neighbour, then feed back.
]

<br>

.callout-warn[
IV fluids can cause harm by causing:
- **overload** in cardiac failure, cirrhosis, renal failure...
- **hypoNa** with excessive hypotonic maintenance (esp. post-op)  
- **acidosis** with excessive 0.% NaCl
o]

???
Answer: insensible losses (breathing, sweating, ~0.5–1 mL/kg/hr) are not
usually charted. This is a nice subtle point for feedback.

---

.left-panel.amber[
# TL;DR

- resuscitation  
- maintenance  
- replacement  
]

# Recap: IV fluids on one slide

- Ask 4 questions before prescribing: need? type? volume/rate? monitoring?  
<br>

- Use the **5 Rs**: Resuscitation, Routine maintenance, Replacement,
  Redistribution, Reassessment  
<br>

- Prefer **balanced crystalloids** for resuscitation in most situations; know the exceptions  
<br>

- Maintenance requirements = 'all the 1s'  
<br>

- Fluid is a prescription like any other — review and stop it daily

.callout-question.callout-bottom[
After a short break, get your pens out ready to prescribe fluids for our four cases!
]

???
Hand out fluid charts now if not already distributed. Explain the case format:
each case has a "presentation" slide, then group discussion, then an
"investigations" slide, then further group discussion and debrief.

---
class: section, middle

# Part 3
## Cases

???

.callout-question.callout-bottom[
Work in groups. For each case, decide:
1) What extra information do you want?
2) What is your immediate management?
3) What fluid (if any) will you prescribe?
]

???
Read this slide aloud. Explain groups will have ~10-12 minutes per case:
~3 min after presentation slide, ~5 min after investigations slide, ~3-4 min
debrief. Circulate during group work.

---

1) what extra information would you like?  
2) if AKI then pre-renal, intrinsic or post?  
3) what fluid would you prescribe?  
4) other management?  
]
]

---
class: image-left

.left-panel.top[
![](images/case1_dehydration.png)
]

# 81 yo man with diarrhoea

- 3 days of **diarrhoea** and poor oral intake, fever, productive cough
- **PMH**: hypertension, T2DM, peripheral vascular disease
- **O/E**: BP 92/56, pulse 108, dry mucous membranes, right basal crackles

- **Ramipril** 10mg OD | **Bendroflumethiazide** 2.5mg OD | **Metformin** 1g BD
- Ibuprofen (over-the-counter)

<br>

.compact-table[
| Test | Result | Reference Range |
|:--|--:|:--|
| Urea | **18.2** | 2.5–7.8 mmol/L |
| Creatinine | **210** (baseline 120) | 60–110 μmol/L |
| Sodium | 138 | 133–145 mmol/L |
| Potassium | **5.7** | 3.6–5.5 mmol/L |
| TCO₂ (bicarbonate) | **17** | 22–30 mmol/L |
| Hb | 138 | 130–170 g/L |
| WBC | **14.2** | 4.0–11.0 ×10⁹/L |
]

???
Prompts:
- what extra information do you want? (baseline SCr, u/o, NEWS, lactate, CXR...)  
- pre-renal, intrinsic or post-renal?  
- how would you manage him? (cultures, meds, fluids...)

---
class: image-left

.left-panel.top[
![](images/case1_dehydration.png)
]

![:scale 100%](images/answer_case1.png)

---
class: image-left

.left-panel.top[
![](images/case2_stroke.png)
]

# 76 yo woman with stroke

- Large ischaemic stroke; **unsafe swallow** on SALT assessment
- Nil by mouth pending further review
- No prior regular medications; started on **aspirin and clopidogrel**
- **Haemodynamically stable and euvolaemic** on examination
- Estimated body weight **60 kg**

<br>

???
Prompts:
- what extra information do you want? (could she have NG feeding?)  
- what fluids will you prescribe?

---
class: image-left

.left-panel.top[
![](images/case2_stroke.png)
]

![:scale 100%](images/answer_case2.png)

---
class: image-left

.left-panel.top[
![](images/case3_hf.png)
]

# 84 yo man with breathlessness

- **1 week** of progressive breathlessness, **3 kg weight gain**
- **PMH**: HFrEF, CKD, atrial fibrillation
- **Medications**: candesartan, dapagliflozin, bisoprolol, bumetanide
- **O/E**: BP 158/88, raised JVP, bibasal crackles, pitting oedema to knees

<br>

- A&E have already started IV **resuscitation fluids** for AKI

<br>

???
Prompt:
- what extra information do you want? (recent diuretic compliance, weight trend, dapagliflozin as relevant sick-day drug)  
- what fluid would you prescribe?  
- how would you manage him?
- pre-renal, intrinsic or post-renal?  
- how can he have an AKI when he is overloaded?

---
class: image-left

.left-panel.top[
![](images/case4_stoma.png)
]

# 58 yo woman, weak & dizzy

- Recovering from emergency operation for diverticular perforation  
- New ileostomy  
- In pain, poor oral intake  
- **O/E**: BP 96/60, HR 104, dry mucous membranes
- Pre-op weight 66 kg; weight now 62 kg

<br>

]

???
Prompts:

- what extra information do you want? (stoma output volume over 24h, colour/consistency, full U&Es...)
- what fluid would you prescribe?  
- what other management? (anti-motility agents e.g. loperamide)

---
class: image-left

.left-panel.top[
![](images/case4_stoma.png)
]

![:scale 60%](images/replacement.png)

---

# Part 4
## Close

---

# Reflection

.pull-left[
### Reflect
- The **most important thing** I learned today was...
- One thing I am **still unclear on** is...
]

.pull-right[
### Commit
- One concrete thing I will **do differently** next time I'm involved in a
  patient's fluid management (as a student or FY1)
]

???

---

.left-panel.amber[
# TL;DR

- pre-renal
- intrinsic
- post-renal
]

# Take-home points

1. AKI is a **syndrome**: always ask *why* and think pre-renal / intrinsic
   / post-
2. Pre-renal AKI is reversible — but can progress to **ATI** if hypoperfusion
   persists
3. Not all patients with AKI need more fluid  
4. Prescribe IV fluid for **resuscitation**, **maintenance** or **replacement**
5. **Balanced crystalloids** are generally preferred for resusication (with exceptions)

.callout-ref.callout-bottom[
See playbooks on:

- AKI  
- IV fluids (assessment)
- IV fluids (prescribing)
]

---

![](images/QR_questionairre.svg)

---

# Part 5
## Supplemental slides

---

# Crystalloids

| Fluid | Na⁺ | K⁺ | Cl⁻ | Notes |
|:--|--:|--:|--:|:--|
| 0.9% NaCl | 154 | 0 | 154 | High chloride → risk of hyperchloraemic acidosis with large volumes |
| Hartmann's | 131 | 5 | 111 | "Balanced" — lactate buffers to bicarbonate |
| Plasma-Lyte 148 | 140 | 5 | 98 | "Balanced" — acetate/gluconate buffers |
| 5% glucose | 0 | 0 | 0 | Distributes as free water — **not** for resuscitation |
| 0.18% NaCl/4% glucose | 31 | 0 | 31 | Standard UK maintenance fluid (+ KCl) |

<br>

.callout[
Balanced crystalloids generally *preferred* over 0.9% saline for resuscitation. Evidence is conflicting (SMART/SALT-ED *vs* BASICS/PLUS). 
]

.callout-warn[
Exceptions where 0.9% NaCl preferred: DKA; profuse vomiting; traumatic brain injury.
]

???
Use this as a chance for critical appraisal discussion — guidelines (NICE
CG174) have not yet fully caught up with BaSICS/PLUS. Flag this evidence-
practice lag explicitly, as noted in the recent-updates summary — good AKT
exam awareness point without over-simplifying "balanced is always better."

**Never** add potassium chloride concentrate directly to a fluid bag at the
bedside — this is a **Never Event** and can cause fatal cardiac arrest. Use
pre-mixed bags only.

---

# Colloids — mostly avoid

.pull-left[
### Use
- **Red blood cells**: fluid of choice for active haemorrhage
- Human albumin 4–5%: specific specialist indications only (e.g. SBP in
  cirrhosis)
]

.pull-right[
### Avoid
- **Hydroxyethyl starch (HES)**: nephrotoxic — increases AKI and mortality.
  MHRA/EMA advise against use in **all** hospital inpatients
- **Gelatins**: no proven benefit over crystalloid; anaphylaxis risk
]

.callout-warn[
For FY1-level practice: use crystalloids for resuscitation and maintenance.
Do not prescribe HES or gelatin. Albumin is a specialist decision.
]

???
This is a strong, easily testable "never do this" rule — good for AKT.