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Fluid and electrolyte balance

Daily requirements

For the „average‟ 70 Kg man

o Total body water is 42 L (~60% of body weight)o 28 L is in the intracellular and 14 L in the extracellular

compartments

o The plasma volume is 3 Lo The extravascular volume is 11 Lo Total body Na

+is 4200 mmol (50% in ECF)

o Total body K+

is 3500 mmol (only about 50-60 mmol in ECF)o Normal osmolality of ECF is 280 –295 mosmol/kg

Fluid replacement

When calculating fluid replacement for a patients need to consider:

Maintenance requirements

Daily maintenance fluid requirements vary between individuals.o 70 Kg male = 2.5 - 3.0L water, 120 – 140 mmol sodium and 70

mmol potassiumo 40 Kg woman = 2.0L water,70 – 90 mmol sodium and 40 mmol

potassium

Daily maintenance fluid requirements for children

o 0-10 kg is 100 ml/kgo 10-20 kg is 1000 ml + 50 ml/kg for each kg > 10o >20 kg is 1500 ml + 25 ml/kg for each kg > 20

Replacement of losses

Pre-operative or pre-admission

Ongoing losses

Nasogastric aspirate

Vomit, diarrhoea

Stoma, drains, fistula etc

Most „surgical „ ongoing losses are rich in sodium and should be replaced with0.9% saline

Insensible losses

Faeces approximately 100 ml/ day

Lungs approximately 400 ml/ day

Skin approximately 600 ml/ day

Composition of crystalloids

Hartmann’s

Solution NormalSaline

DextroseSaline

Sodium (mmol/l) 131 150 30



Chloride (mmol/l) 111 150 30

Potassium(mmol/l)

5 Nil Nil

Bicarbonate

(mmol/l) 29 Nil Nil

Calcium (mmol/l) 2 Nil Nil

3L of Dextrose saline is not equivalent to 2L 5% Dextrose and 1L Normalsaline

3L Dextrose Saline = 3L water and 90 mmol sodium

2L 5% Dextrose saline + 1L Normal saline = 3L water and 154 mmol sodium

Composition of colloids

Volumeeffect (%)

AverageMW (kDa)

Circulatoryhalf life

Gelatins(Haemaccel)

80 35 2-3 hours

4% Albumin 100 69 15 days

Dextran 70 120 41 2-12 hours

6% HydroxyethylStarch

100 70 17 days

Monodispersed = All molecules of similar molecular weight

Polydispersed = Molecules have spread of molecular weights

Albumin

Monodispersed

Expensive

Long half life

Accounts for 60-80% of normal plasma oncotic pressure

No adverse effect on coagulation

Dextrans

Polysaccharides Polydispersed with MW 10-90 kDa

Reduces plasma viscosity

Reduces platelet aggregation

1-5% develop anaphylaxis

Gelatins

Polypeptides

Polydispersed with MW ~35 kDa

Rapidly lost from vascular space

Hydroxyethyl starch

Synthetic polysaccharide polymers derived from amylopectin Polydispersed with MW 50-450 kDa



Large molecules engulfed by reticuloendothelial system

Associated with bleeding diathesis

Assessment of adequacy of resuscitation

Clinical history and observations – Pulse, blood pressure, skin turgor Urine output – oliguria < 0.5 ml/kg/hr

CVP or pulmonary capillary wedge pressure

Response of urine output or CVP to fluid challenge

A fluid challenge should be regarded as a 200-250 ml bolus of colloid

This should be administered as quickly as possible

A response in the CVP or urine output should be seen within minutes

The size and duration of the CVP response rather the actual values recordedis more important

GIFTASUP Recommendations (2008)

Recommendation 1

Because of the risk of inducing hyperchloraemic acidosis in routine practice,when crystalloid resuscitation or replacement is indicated, balanced saltsolutions (e.g. Ringer‟s lactate/acetate or Hartmann‟s solution) shouldreplace 0.9% saline, except in cases of hypochloraemia

Recommendation 2

Solutions such as 4% / 0.18% dextrose/saline and 5% dextrose are importantsources of free water for maintenance, but should be used with caution asexcessive amounts may cause dangerous hyponatraemia, especially in

children and the elderly. These solutions are not appropriate for resuscitation or replacement therapy except in conditions of significant freewater deficit (e.g. diabetes insipidus)

Recommendation 3

To meet maintenance requirements, adult patients should receive sodium 50-100 mmol/day, potassium 40-80 mmol/day in 1.5-2.5 litres of water by theoral, enteral or parenteral route (or a combination of routes). Additionalamounts should only be given to correct deficit or continuing losses. Carefulmonitoring should be undertaken using clinical examination, fluid balancecharts, and regular weighing when possible

Preoperative fluid management

Recommendation 4

In patients without disorders of gastric emptying undergoing elective surgeryclear non-particulate oral fluids should not be withheld for more than twohours prior to the induction of anaesthesia

Recommendation 5

In the absence of disorders of gastric emptying or diabetes, preoperative

administration of carbohydrate rich beverages 2-3 h before induction of anaesthesia may improve patient well being and facilitate recovery from



surgery. It should be considered in the routine preoperative preparation for elective surgery

Recommendation 6

Routine use of preoperative mechanical bowel preparation is not beneficialand may complicate intra and postoperative management of fluid andelectrolyte balance. Its use should therefore be avoided whenever possible

Recommendation 7

Where mechanical bowel preparation is used, fluid and electrolytederangements commonly occur and should be corrected by simultaneousintravenous fluid therapy with Hartmann‟s or Ringer -Lactate/acetate typesolutions

Recommendation 8

Excessive losses from gastric aspiration or vomiting should be treatedpreoperatively with an appropriate crystalloid solution which includes anappropriate potassium supplement. Hypochloraemia is an indication for theuse of 0.9% saline, with sufficient additions of potassium and care not toproduce sodium overload. Losses from diarrhoea, ileostomy, small bowelfistula, ileus or obstruction should be replaced volume for volume withHartmann‟s or Ringer -Lactate/acetate type solutions. “Saline depletion,” for example due to excessive diuretic exposure, is best managed with abalanced electrolyte solution such as Hartmann's

Recommendation 9

In high risk surgical patients, preoperative treatment with intravenous fluid andinotropes should be aimed at achieving predetermined goals for cardiacoutput and oxygen delivery as this may improve survival

Recommendation 10

Although currently logistically difficult in many centres, preoperative or operative hypovolaemia should be diagnosed by flow-based measurementswherever possible. The clinical context should also be taken into account asthis will provide an important indication of whether hypovolaemia is possibleor likely. When direct flow measurements are not possible, hypovolaemiawill be diagnosed clinically on the basis of pulse, peripheral perfusion and

capillary refill, venous pressure and Glasgow Coma Scale together withacid-base and lactate measurements. A low urine output can be misleadingand needs to be interpreted in the context of the patient‟s cardiovascular parameters above

Recommendation 11

Hypovolaemia due predominantly to blood loss should be treated with either abalanced crystalloid solution or a suitable colloid until packed red cells areavailable. Hypovolaemia due to severe inflammation such as infection,peritonitis, pancreatitis or burns should be treated with either a suitablecolloid or a balanced crystalloid. In either clinical scenario, care must be

taken to administer sufficient balanced crystalloid and colloid to normalisehaemodynamic parameters and minimise overload. The ability of critically ill



patients to excrete excess sodium and water is compromised, placing themat risk of severe interstitial oedema. The administration of large volumes of colloid without sufficient free water (e.g. 5% dextrose) may precipitate ahyperoncotic state

Recommendation 12

When the diagnosis of hypovolaemia is in doubt and the central venouspressure is not raised, the response to a bolus infusion of 200 ml of asuitable colloid or crystalloid should be tested. The response should beassessed using the patient‟s cardiac output and stroke volume measured byflow-based technology if available. Alternatively, the clinical response maybe monitored by measurement/estimation of the pulse, capillary refill, CVPand blood pressure before and 15 minutes after receiving the infusion. Thisprocedure should be repeated until there is no further increase in strokevolume and improvement in the clinical parameters

Intraoperative fluid management

Recommendation 13

In patients undergoing some forms of orthopaedic and abdominal surgery,intraoperative treatment with intravenous fluid to achieve an optimal value of stroke volume should be used where possible as this may reducepostoperative complication rates and duration of hospital stay

Recommendation 14

Patients undergoing non-elective major abdominal or orthopaedic surgeryshould receive intravenous fluid to achieve an optimal value of stroke

volume during and for the first eight hours after surgery. This may besupplemented by a low dose dopexamine infusion

Postoperative fluid, and nutritional management.

Recommendation 15

Details of fluids administered must be clearly recorded and easily accessible

Recommendation 16

When patients leave theatre for the ward, HDU or ICU their volume statusshould be assessed. The volume and type of fluids given perioperativelyshould be reviewed and compared with fluid losses in theatre including urineand insensible losses

Recommendation 17

In patients who are euvolaemic and haemodynamically stable a return to oralfluid administration should be achieved as soon as possible

Recommendation 18

In patients requiring continuing i.v. maintenance fluids, these should besodium poor and of low enough volume until the patient has returned their



sodium and fluid balance over the perioperative period to zero. When thishas been achieved the i.v. fluid volume and content should be thoserequired for daily maintenance and replacement of any on-going additionallosses

Recommendation 19

The haemodynamic and fluid status of those patients who fail to excrete their perioperative sodium load, and especially whose urine sodiumconcentration is <20mmol/L, should be reviewed

Recommendation 20

In high risk patients undergoing major abdominal surgery, postoperativetreatment with intravenous fluid and low dose dopexamine should beconsidered, in order to achieve a predetermined value for systemic oxygendelivery, as this may reduce postoperative complication rates and durationof hospital stay

Recommendation 21

In patients who are oedematous, hypovolaemia if present must be treated,followed by a gradual persistent negative sodium and water balance basedon urine sodium concentration or excretion. Plasma potassiumconcentration should be monitored and where necessary potassium intakeadjusted

Recommendation 22

Nutritionally depleted patients need cautious refeeding orally, enterally or parenterally, with feeds supplemented in potassium, phosphate andthiamine. Generally, and particularly if oedema is present, these feedsshould be reduced in water and sodium. Though refeeding syndrome is arisk, improved nutrition will help to restore normal partitioning of sodium,potassium and water between intra and extra-cellular spaces

Recommendation 23

Surgical patients should be nutritionally screened, and NICE guidelines for perioperative nutritional support adhered to. Care should be taken tomitigate risks of the refeeding syndrome

Fluid management in acute kidney injury

Recommendation 24

Based on current evidence, higher molecular weight hydroxyethyl starchshould be avoided in patients with severe sepsis due to an increased risk of

AKI

Recommendation 25

Higher molecular weight hydroxyethyl starch should be avoided in brain-deadkidney donors due to reports of osmotic-nephrosis-like lesions



Recommendation 26

Balanced electrolyte solutions containing potassium can be used cautiously inpatients with AKI closely monitored on HDU or ICU in preference to 0.9%saline. If free water is required 5% dextrose or dextrose saline should be

used. Patients developing hyperkalaemia or progressive AKI should beswitched to non potassium containing crystalloid solutions such as 0.45%saline or 4%/0.18 dextrose/saline Ringer‟s lactate versus 0.9% saline for patients with AKI

Recommendation 27

In patients with AKI fluid balance must be closely observed and fluid overloadavoided. In patients who show signs of refractory fluid overload, renalreplacement therapy should be considered early to mobilize interstitialoedema and correct extracellular electrolyte and acid base abnormalities

Recommendation 28

Patients at risk of developing AKI secondary to rhabdomyolysis must receiveaggressive fluid resuscitation with an isotonic crystalloid solution to correcthypovolaemia. There is insufficient evidence to recommend the specificcomposition of the crystalloid.

Bibliography

Choi P T-L, Yip G, Quinonez L G, Cook D J. Crystalloids vs. colloids in fluidresuscitation: a systematic review. Crit Care Med 1999; 27: 200-210.

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