rob fleming specialty doctor – anaesthetics 22/07/2014 [email protected]
TRANSCRIPT
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withdrawn June 2013 by MHRA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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