Pins and Needles: Fluids

Rob FlemingSpecialty Doctor – Anaesthetics22/07/2014

Robert.Fleming@doctors.org.uk

Introduction

Why is it important?

Basic science Body fluid compartments Barriers to fluid movement Commonly used fluids

Assessing fluid status Prescribing: the 5 Rs

Summary

Why is it important?

Fluid management not (very) complicated, but is often done badly

Inappropriate fluid management can lead to: Hypoperfusion, renal failure, shock (too little) LVF, pulmonary oedema (too much) Electrolyte abnormalities ( / Na+, K+, Cl-),

peripheral oedema (wrong fluid)

Good fluid management reduces both morbidity and mortality

Body fluid compartments

Water is a large fraction of total body weight: Adult men: 60% Adult women 55% Neonates: 75 - 80%

Total body water:40L in a 70kg male Extracellular (ECF) 1/3 – 15L Intracellular (ICF) 2/3 – 25L

Extracellular fluid (ECF)

Interstitial 80% – 12L Plasma 20% – 3L “Transcellular” /

special extracellular fluids: CSF, lymph etc. – <1L

Barriers

Water and electrolytes enter the body via the plasma: absorption from the gut IV administration

To enter most body cells, water and electrolytes must pass:

Plasma -> Interstitium -> Cell cytoplasm

The water will always follow the solutes

Barriers: Plasma -> Interstitium

Capillary wall: allows passage of water, electrolytes prevents passage of plasma proteins (in

health)

Barriers: Interstitium -> Cell

Cell membrane: Permeable to water Selectively permeable to electrolytes

Composition of fluid compartments

(mmol/L) Plasma Interstitium Intracellular

Na+ 135 - 145 135 - 145 12

K+ 3.5 – 5.3 3.5 – 5.3 150

Mg2+ 0.75 - 1.05 0.75 - 1.05 40

Ca2+ (total) 2.2 – 2.5 2.2 – 2.5 1.0 – 2.0

Cl- 95 - 105 95 - 105 4

HCO3- 22 - 25 22 - 25 12

Protein (g/dL) 6 - 8 - 2.5

Medical Fluids

Crystalloids

Colloids

Crystalloids

Electrolyte / small molecule solutions 0.9% NaCl (“normal” saline) 5% glucose 4% glucose, 0.18% saline (“dextrose”

saline) Compound sodium lactate (Hartmann’s)

Hypertonic saline Glucose 10% / 20% / 50% 5% glucose, 0.45% saline

Crystalloids

(mmol/L)

Plasma 0.9% NaCl

0.18% NaCl4% Glucose

5% Glucose

CSL (Hartmann’s)

Na+ 135 - 145

154 31 - 131

K+ 3.5 – 5.3

- - - 5

Mg2+ 0.75 - 1.05

- - - -

Ca2+ (total)

2.2 – 2.5

- - - 2

Cl- 95 - 105 154 31 - 111

Glucose 3.5 - 6 - 222 278 -

HCO3- 22 - 25 - - - -

Lactate 0.5 – 2.2

- - - 29

Colloids

Large chain protein / starch molecules in an electrolyte solution Starches – Voluven, Hemohes, Volulyte,

...withdrawn June 2013 by MHRA

Gelatins – Gelofusine / Geloplasma, ...lack of good quality evidence

Blood products / Human Albumin Solution

Assessing fluid status

History: Thirst Abnormal losses: Sweating, Vomiting /

diarrhoea, Haemorrhage, Sepsis / SIRS / post-operatively

Comorbidities, medications

Examination: Pulse, blood pressure, capillary refill and jugular

venous pressure (JVP) – current / trends Pulmonary or peripheral oedema Postural hypotension Dry mucous membranes, loss of skin turgor

Assessing fluid status

Monitoring (current / trends): National Early Warning Scoring (NEWS) Fluid balance charts Weight

Investigations: Urea, creatinine and electrolytes (U&Es) Full blood count (FBC)

NICE guidelines: the 5 Rs

Resuscitation

Routine maintenance

Replacement & Redistribution

Reassessment

Fluid Resuscitation

Cardiac output is partially dependent on venous return: Frank – Starling law of the heart

Fluid Resuscitation

Is the patient hypovolaemic?: systolic blood pressure is less than 100 mmHg heart rate > 90 beats / min capillary refill > 2 seconds or cold peripheries respiratory rate > 20 breaths / min National Early Warning Score (NEWS) ≥ 5

ABCDE approach, call for help Identify cause and treat it

Fluid bolus (challenge) of 500ml 0.9% NaCL or CSL Reassess and repeat as needed

Routine Maintenance Fluids Fluid and electrolytes are lost daily in:

Faeces (100ml/day) Urine (1500ml/day) “Insensible” evaporative losses (500 –

1000ml/day)

Routine maintenance fluids alone are indicated only where there is: No abnormal fluid loss No abnormal redistribution

Routine Maintenance Fluids To maintain homeostasis water and electrolytes

must be replaced at a minimum rate of....

Water 25 – 30 ml/kg/day (2 - 2.5 L in a 70kg male)

Na+ 1 (– 1.5) mmol/kg/day (70 – 100 mmol) K+ (0.7 –) 1 mmol/kg/day (50 – 70 mmol) Cl- 1 (– 2) mmol/kg/day (100 – 140mmol) 50 – 100 g/day glucose

....IN HEALTH!

Routine Maintenance Fluids This equates roughly to:

either 1L 0.9% NaCl and 1 - 2L 5% glucose

or 2 – 3L of 0.18% NaCl in 4% Glucose ...with 60 mmol kCl added to either of

the above

Remember, this is the minimum requirements of an otherwise well 70kg man

In the majority of cases, fluid prescribing is also replacing fluid loss / redistribution

Replacement and Redistribution

Abnormal losses:

Gut: Vomiting Diarrhoea Stomas/ fistulae/

drains Sweating / pyrexia

Polyuria ( e.g. DI) Hyperventilation Haemorrhage

Replacement and Redistribution Redistribution

Stress response: Activation of renin-angiotensin-aldosterone system -> Sodium and water retention Increased secretion of cortisol and catecholamines Reduced secretion of insulin -> Hyperglycaemia

Increased capillary permeability leads to increased interstitial volume (SIRS / sepsis / post-operatively)

Replacement and Redistribution Fluid prescribing should attempt to meet losses

in both volume and electrolyte composition

Seek expert help if patients have complex fluid / electrolyte requirements: gross oedema severe sepsis severe hyponatraemia or hypernatraemia renal, liver and/or cardiac impairment post-operative fluid retention and redistribution malnutrition / refeeding

Reassessment

All patients continuing to receive IV fluids need regular monitoring: Fluid balance and U&Es daily Weight measurement twice weekly

Patients receiving IV fluids for replacement or redistribution problems may need more frequent monitoring

Patients on longer-term IV fluid therapy whose condition is stable may be monitored less frequently

Always reassess!

Reassessment

Urinary sodium measurement may be helpful in patients with high-volume GI losses Urinary sodium < 30 mmol/l indicates total body

sodium depletion Urinary sodium may also indicate the cause of

hyponatraemia, and guide a negative sodium balance in patients with oedema

If patients have received IV fluids containing high chloride concentrations, monitor serum chloride concentration daily to prevent hyperchloraemic acidosis

Summary and hints

Fluid management is not (very) complicated Estimate fluid status based on history,

examination and investigations Is this maintenance? What are you replacing?? Does the patient need resuscitation???

Always reassess! Any patient receiving IV fluids should have

their U&Es checked daily Stop IV fluids as soon as possible

Questions

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