Fluids

Question 1

Why do fluids should be prescribed? (3) - general indications)

Answer 1

• resuscitation
• maintenance
• replacement

Question 2

General/ key considerations to remember before we prescribe fluids?

Answer 2

• aim of the fluid -> resuscitation, maintenance, or replacement
• weight and size of the patient
• co-morbidities -> e.g. heart failure or chronic kidney disease
• underlying reason for admission (e.g. sepsis or bowel obstruction will require aggressive fluid treatment)
• most recent electrolytes levels

Question 3

Fluid distribution around the body

(total body weight, intracellular, extracellular and transcellular)

Answer 3

• around 2/3^rd of total body weight is water -> around 2/3 of this distributes in to the intracellular fluid -> the remaining 1/3 will distribute in to the extracellular fluid
• Of that fluid in the extracelular space -> around 1/5th stays in the intravascular space -> 4/5th of this is found in the interstitium + a small proportion in the transcellular space

Question 4

What fluid compartments we want the fluid to stay in:

• general hydration purposes
• fluid resuscitation

Answer 4

• Maintenance of hydration -> all compartments
• Resuscitation -> we want to increase perfusion to the organs so we want most of the fluids in intravascular space

Question 5

What happens to the fluid in intravascular compartment in sepsis?

Answer 5

Sepsis -> thigh junctions between capillary endothelial cells break -> vascular permeability increases -> fluid leaves the vasculature and enters the tissues

Question 6

What’s required in terms of the fluids in sepsis?

Answer 6

As the fluid will escape intravascular compartment -> we need to give large amounts of IV fluids to maintain intravascular volume

• need to monitor fluid balance

Question 7

What population groups (2) and why should we take caution in while replacing the fluids?

Answer 7

Elderly and if HF -> due to risk of pulmonary oedema

Question 8

What are insensible fluid loses?

Answer 8

• insensible fluid loses -> loss of fluids in the patient that do not come from the urinary output (e.g. respiration, sweating and faeces)
• insensible fluid loses raise in unwell patient as they may be: febrile, tachypnoeic or have increased bowel output -> need to take it into account while planning fluid replacement

Question 9

Where does a fluid input come from?

Answer 9

• 3/5 of fluid input comes from an enteral route input
• the rest come from metabolic and food processes

*if pt NBM we need to replace or sources via parenteral route

Question 10

Why does a patient may excessively urinate in the post-op period?

Answer 10

As patient will be recovering, they vascular permeability may return to normal -> therefore if an excess of fluid (e.g. by fluid replacement) they may urinate more to correct the levels to their baseline

• allow it to happen but monitor their electrolytes

Question 11

Signs of the fluid depletion in a patient

Answer 11

In a fluid-depleted patient:

• dry mucous membrane
• reduced skin turgor
• orthostatic hypotension
• decreased urine output (<0.5 ml/kg/hr)

In worsening stages: tachycardia, hypotension, increased cap refill

Question 12

Signs of fluid overload in a patient

Answer 12

• peripheral and sacral oedema
• pulmonary oedema
• raised JVP

Question 13

What to monitor in case if a patient is fluid depleted/ overloaded?

Answer 13

• start daily fluid input/output balance chart
• daily weight measurement
• monitor urea and electrolytes (U&Es) -> to check for kidney hypoperfusion, dehydration, electrolyte abnormalities

Question 14

What are the components that need to be replaced in the fluids daily (apart from water) ? (4)

Answer 14

• water
• Na+
• K+
• glucose

Question 15

How much needs to be replaced in the fluid daily? (NICE guidelines)

• water
• Na+
• K+
• glucose

Answer 15

• water -> 25 ml/kg/day
• Na+ -> 1.0 mmol/kg/day
• K+ -> 1.0 mmol/kg/day
• glucose -> 50g / day

Question 16

• 2 main categories of fluids used (setting use and name of category)
• which one would give a faster fluid replacement effect

Answer 16

A. Crystalloids -> used widely in acute settings, theatres and as maintenance fluids

B. Colloids -> use in many hospital is decreasing (as significantly more expensive)

*there is no evidence that any of the categories is superior in terms of speed of fluid replacement

Question 17

Example of crystalloid fluid (just names)

Answer 17

• saline 0.9%
• dextrose 5%
• Dexterose saline
• Hartmann’s solution
• Dexterose 50%

Question 18

What’s the purpose of giving saline 0.9%?

Answer 18

It expands extravascular compartment (75% interstitial and 25% plasma)

*only 25% o plasma expansion so need a lot of crystalloid t expand plasma

Question 19

What’s the purpose of giving dextrose 5%?

Answer 19

Dexterose 5%

Aim: It is mostly to replace water deficit

• it contains 50g/L of glucose
• glucose will be readily metabolised by the liver -> water is left

Question 20

Hartmann’s solution

• what are the advantages
• what happens in excess administration

Answer 20

Hartmann’s solution

• Advantage: it is more physiologically similar -> as it contains Na+, K+, Cl-, Ca++ and lactate

*however once given it behaves like 0.9% saline -> expands extravascular volume

• Excess administration: may cause lactic acidosis

Question 21

What are the colloids?

What are they usually used for?

Answer 21

Colloid - a substance that is unable to pass through the semi-permeable membrane -> it remains in extracellular compartment (they have greater osmolarity than plasma)

Use: extracellular volume replacement (e.g. haemorrhage or hypotension)

*not used as a general fluid replacement as stay only in extracellular compartment

Question 22

Examples (3) of colloids

Answer 22

• gelatin derivatives (e.g. Haemaccel, Gelofusin) - made from animal gelatine; anaphylactic reactions possible
• Human albumin solution (HAS)- only used at consultant’s/ expert’s request
• Starch (e.g. Hetastarch, Pentastarch)

Question 23

How to manage initially a reduced urine output (in terms of fluid)

Answer 23

Reduced urine output (<0.5 ml/kg/hr)

• commence fluid challenge
• then, re-check clinical parameters and urine output
• check that no urinary retention; no obstructed catheter

Question 24

How to do a fluid challenge?

Answer 24

250 ml or 500 ml over 15-30 mins

Question 25

How much fluid should be given (fluid challenge) may differ from: A. 30 y old 120 kg lady B. Frail, 80y old lady with renal disease and IHD

Answer 25

A. May need to give \>500ml of fluid to make any difference B. 250 ml of fluid may be enough

Question 26

What's the normal range of serum potassium?

Answer 26

**K+ range:** 3.5 - 5.5 mmol/L

Question 27

Routes of potassium replacement in case of hypokalaemia

Answer 27

- oral is preferred - IV - if unable to tolerate oral or if potassium is really low - K+ \<2.5 mmol/L may require ITU admission and administration via a central line

Question 28

What are **'third space loses**'?

Answer 28

Loss of fluid ( other than urine, faeces, respiration and sweat) into the non-visible spaces e.g. through bowel lumen (intestinal obstruction) or retroperitoneum (in pancreatitis)

Question 29

Common electrolyte pattern in dehydration

Answer 29

_Dehydration_ **high urea****:creatinine****ratio and high ­PCV** \*PCV - packed cell volume; proportion of blood that is made up of cells

Question 30

Common electrolyte pattern in **vomiting**

Answer 30

Vomiting: **low K⁺, low Cl^–,** and **alkalosis**

Question 31

Common electrolytes pattern in **diarrhoea**

Answer 31

Diarrhoea: **low K+** and **acidosis**

Question 32

Main use of: - crystalloids - colloids

Answer 32

**Crystalloids** -\> general fluid replacement **Colloids** -\> hypovoluemia (haemorrhage or hypotension)

Question 33

Initial assessment of a **post-op** patient with a **low urine output**

Answer 33

_Post-up low urine output =\> Check/ ensure that there is no:_ ## Footnote - **ABC** assessment - ***acute urinary retention*** -\> feel for palpate bladder and positive fluid balance on the fluid chart (should be urinating) - ensure that a catheter is not blocked - ***hypovolemic shock*** -\> check BP, HR, actively bleeding wounds and drains

Question 34

Case: a patient is post op and low urinary output; no signs of hypovolemia or acute urinary retention - possible cause? - what to do? - reassessment and possible further causes

Answer 34

_Possible cause:_ dehydration _Management:_ increase IV infusion + reassess If still low urinary output and positive response to fluid challenge-\> *AKI* may be suspected

Question 35

Investigations to be done in a **dehydrated** patient (4)

Answer 35

* U&Es * FBC * ABG * urinealysis

Question 36

Severity % scale of dehydration (3)

Answer 36

* 15% → mild * 30% → moderate * 40% → severe

Question 37

Why in dehydration there may be mental state changes?

Answer 37

Due to the brain not being perfused

Question 38

What to give first: crystalloid or colloid?

Answer 38

Crystalloid first then colloid (better in terms of the fluid movement across compartments)

Question 39

What fluids are commonly used for a fluid replacement?

Answer 39

**Plasmalyte** or **Hartmann's** (they contain substances similar to a normal physiological state e.g. K+, Na+, Cl-)

Question 40

***Hyponatraemia*** * causes * presentation

Answer 40

**Hyponatraemia** ## Footnote **Causes:** excess water, TURP syndrome (due to over-irrigation through an intratracheal catheter) **Presentation**: impaired consciousness, confusion, clammy

Question 41

Management of **hyponatraemia** - calculation - what to use

Answer 41

**Slow correction**!!! (if done too fast → possible *pontine demyelination syndrome*) _Calculation:_ **weight (kg) x (pre-post Na) x 0.6** \*pre - normal Na level/ level pre TURP \* post - current hyponatraemic level **GIve 1/2 in the first 8 hrs, 1/4 in next 8 hrs, 1/4 in next 8 hrs** **Use:** NaCL 1.% (infusion pump)

Question 42

***Hypokalaemia*** * cause * presentation * management

Answer 42

**Cause**: low intake or excess loss **Presentation:** ectopic beats, arrhythmia **Management:** * Slow correction with **20mmol of KCl/hr** * ECG monitoring

Question 44

What can an excess of 0.9% NaCl cause?

Answer 44

hyperchloraemic acidosis

Question 45

What are the requirements for maintenance fluid? - water - Na, Cl, K - glucose

Answer 45

* **25-30 ml**/kg/day of **water** * approximately **1 mmol/kg/day of potassium, sodium and chloride** * approximately **50-100 g/day** of **glucose** to limit starvation ketosis

Question 47

What is meant by 3rd space fluid loses?

Answer 47

**Space Losses = ↓ ECF** • **Bowel obstruction** → ↓ fluid reabsorption → 3rd space loss • **Sudden diuresis on day 2-3 post-op** = recovery of ileus • **Peritonitis** → ascites → 3rd space loss

Question 48

What's Parkland's Formula? What fluid to use for that?

Answer 48

**Parkland’s formula:** 4 x wt x %burn = mL in 1st 24hrs Use ***Hartmann's***