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The normal need for fluids varies in low-birth-weight and full-term neonates through infancy to later childhood. This is the result of differences in metabolic rate, growth, the ratio of evaporative surface area to body weight, the degree of renal maturity and the amount of total body water at different ages. In most patients receiving intravenous fluids for short periods of time the normal fluid and electrolyte requirements can be satisfied easily. How-ever, the glucose content of the chosen fluid is usually sufficient only to prevent ketosis rather than to meet the child’s caloric requirements.

Daily water and electrolyte requirementsA daily intake of 1–2 mmol/kg of sodium and potassium is required by term infants and older children. For most children, a fluid containing 2.5 mmol of sodium, 2.5 mmol of potassium and 5 mmol of chloride per 100 ml of fluid is adequate. This equates to a solution of 4 or 5% dextrose and 0.18% saline with 20 mmol of KCl per litre. This is a hypotonic solution and if used to replace other losses or for prolonged periods, hyponatraemia may result, with severe consequences. In 2004, a recommendation to avoid use of this solution was made by the Royal College of Paediatrics and Child Health, preferring a solution containing 0.45% saline. A recent review of hyponatraemic deaths in children has prompted the National Patient Safety Agency to issue an alert on the use of hypotonic solutions, particularly in children having surgery. It will recommend the use of isotonic maintenance fluid during surgery and for the first 48 hours postoperatively. Because high levels of antidiuretic hormone are produced as a result of non-osmotic stim-uli such as subclinical volume depletion, pain, nausea, inhalational anaesthetics and opiods, large amounts of water can be retained if hypotonic fluids are used for maintenance requirements.

Maintenance fluid requirements can be extrapolated from estimates of metabolic rate or from the body surface area. Main-tenance fluid requirements are increased by:• pyrexia; by 12% per degree centigrade above 37.5°C• sweating; by 10–25%• hypermetabolic states (e.g. burns); by 25–75%• radiant heat or phototherapy; by 25%. Metabolic rate – in 1957, Holliday and Segar1 evaluated the caloric expenditure of hospitalized children of different weights and states of activity. They estimated that daily caloric expenditure is 100 kcal/kg up to 10 kg, 50 kcal/kg for each kg between 10 and 20 kg and 20 kcal/kg for each kg over 20 kg. This estimated caloric expenditure can be used to determine maintenance fluid requirements because 100 ml of water are normally lost for every 100 kcal expended. Thus, Holliday and Segar’s landmark paper described a simple formula for calculating children’s maintenance requirements for water. This formula was later simplified by Oh2 and has stood the test of time (Figure 1). Body surface area is determined from accurate measurements of height and weight and the use of nomograms; it is no longer commonly used for calculating maintenance fluid requirements.

Perioperative fluid managementPerioperative fluid management can be divided into replacing the preoperative deficit, continuing maintenance requirements and replacing intraoperative losses. Achieving this with the appropriate fluids maintains adequate circulating volume and cardiac output, while preventing electrolyte imbalance.

Preoperative deficit: the preoperative assessment must address any existing deficits in water and electrolytes. It should include a history of the duration of fasting, presence and duration of fever, vomiting or diarrhoea, and any particular disease state or surgical problem (e.g. bowel obstruction, peritonitis) that may affect fluid status. The main preoperative deficit in a healthy child undergoing elective surgery results from fasting. If the child is in fluid and electrolyte balance at the onset of fasting, the deficit consists of the child’s hourly requirement multiplied by the number of hours fasted. Current practice of allowing children to drink clear fluids up to 2 hours before surgery keeps fluid deprivation down to a minimum without increasing the risk of having a full stomach. It has been suggested that 50% of the fasting deficit is replaced during the first hour of surgery and 25% in each of the second and third hours.

Fluid and electrolyte balance in childrenHannah King

Mary Cunliffe

Hannah King has recently completed a post-CCST Clinical Research

Fellowship in Paediatric Anaesthesia at Alder Hey Children’s Hospital,

Liverpool, UK. She qualified from Leicester University and trained in

Leicester and Liverpool. She is currently on maternity leave in Sydney,

Australia, but plans to take up a consultant post in paediatric anaesthesia

on her return to the UK in 2006.

Mary Cunliffe is Consultant Anaesthestist at Alder Hey Children’s

Hospital, Liverpool, UK. She qualified from the University of Newcastle

upon Tyne, and trained in anaesthetics in Newcastle and Manchester, and

spent a year abroad at Toronto Sick Children’s Hospital. She developed

and runs the Acute Pain Service at Alder Hey and is a member of the

external working group for the NPSA, looking at the use of hypotonic

fluids in children.

Determining requirements for water

Body weight Holliday and Segar1 Oh2

0–10 kg 4 ml/kg/hour 4 ml/kg/hour

10–20 kg 40 ml/hour + 2 ml/kg/

hour above 10 kg

20 + (2 x kg) ml/kg/hour

> 20 kg 60 ml/hour + 1 ml/kg/

hour above 20 kg

40 + (1 x kg) ml/kg/hour

Maximum volume of 2500 ml/day in males and 2000 ml/day in females

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Clinical assessment and correction of dehydration: an assess-ment of hydration is necessary in the child presenting for emer-gency surgery who may have a further deficit due to dehydration. This assessment is based largely on clinical signs (Figure 2). In children, the compensatory response to hypovolaemia is largely by way of increased heart rate and peripheral vasoconstriction. The ability to increase stroke volume as a means of increasing cardiac output develops with age. Hypotension is a late and ominous sign of hypovolaemia, suggesting imminent decompensation and requir-ing immediate treatment. Useful laboratory measurements include blood urea, serum and urinary creatinine, osmolality, electrolytes and haematocrit. These in combination with the clinical assess-ment aid in diagnosing the degree and type of dehydration.

Hyponatraemic dehydration (serum sodium < 130 mmol/litre) occurs when sodium loss is in excess of the accompanying water loss, but also when the gain of water is greater than the gain of sodium. It is usually associated with hypo-osmolality. Pure sodium deficiency is rare. Hyponatraemia may develop due to extrarenal causes, such as protracted vomiting and pyrexia or increased renal losses due to osmotic diuresis or hyperglycaemia. As well as symptoms due to volume depletion, non-specific symptoms include irritability, headache and weakness, and may progress to cerebral oedema with confusion, seizures and coma.

Hypernatraemic dehydration (serum sodium > 150 mmol/litre) is due to a relatively greater deficiency of water to salt but may also be caused by a greater gain of salt, relative to water. It does not reflect total body sodium, which may be normal, high or low. Hypernatraemia results in hyper-osmolality of the extracel-lular fluid (ECF), maintaining the volume of this compartment at

the expense of the intracellular fluid (ICF). As a result, though the water loss may be greater than in isotonic or hypotonic dehydration, the signs of dehydration may be less severe. The most common paediatric cause is viral gastroenteritis, but other causes include increased insensible losses or inadequate intake of water in an infant or child who cannot respond to the thirst mechanism. Neurological symptoms predominate over those due to fluid deficiency and include restlessness, lethargy, hyper-reflexia, seizures and coma.

Management of dehydration: regardless of the type of dehydra-tion, in moderate and severe cases with signs of hypovolaemia, correction should begin immediately with normal saline or Ringer’s lactate, at 20–30 ml/kg given over 1 hour or faster. A colloid solu-tion such as 4.5% albumin (10 ml/kg) may be needed if shock is present. Repeat as necessary until the patient’s vital signs improve and urine output is established. Figure 3 describes the continuing management and correction of hyponatraemic and hypernatraemic dehydration.

Maintenance requirementsThe 4:2:1 rule (Figure 1) should be used to calculate the child’s hourly maintenance fluid requirements. The choice of intraopera-tive fluid depends on glucose content and electrolyte composition. For maintenance requirements use of an isotonic solution of either normal saline or Ringer’s lactate solution is recommended. Pre- and postoperatively this is combined with 5% dextrose to prevent ketosis. During surgery, the stress response maintains the blood glucose concentration in most children and if a solution contain-ing 5% dextrose is used, hyperglycaemia results. This causes an osmotic diuresis and increases urinary losses. Outcome after an

Assessment of dehydration

Signs and symptoms

Mild Moderate Severe

Weight loss (%) 5% 10% 15%

Deficit (ml/kg) 50 100 150

Appearance Thirsty,

restless

Thirsty, restless

or lethargic but

rousable, pale

Drowsy to

comatose, limp,

cold, sweaty,

grey, cyanosed

Skin turgor Normal Decreased Markedly

decreased

Anterior fontanelle Normal Sunken Markedly sunken

Capillary refill time Normal Slow (>2 sec) Very slow

Pulse Normal Weak Feeble

Blood pressure Normal Normal/low Reduced

Respiration Normal Deep Deep and rapid

Mucous

membranes

Moist Dry Very dry

Urine output

(ml/kg/hour)

< 2 < 1 < 0.5

2

Continuing management of hyponatraemic and hypernatraemic dehydration

Hyponatraemic dehydration ([Na+] < 130 mmol/litre)• Need to replace extracellular fluid volume + [Na+] deficit

• Replace fluid deficit with normal saline + appropriate

maintenance fluids

• Aim to correct fluid and [Na+] deficit over 24 hours

• If serum [Na+] < 120mmol/litre give 12 ml/kg of 3% saline

solution over 1 hour

Hypernatraemic dehydration ([Na+] > 150 mmol/litre)• Calculate fluid deficit based on body weight (Figure 2)

• Add together fluid deficit, 48 hours maintenance fluid and

estimated continuing losses to determine total volume of fluid

to be administered at a constant rate over 48 hours

• Use 0.45% saline + 5% dextrose with 20 mmol/litre KCl

• Closely monitor plasma [Na+] and do not allow to fall faster

than 1 mmol/litre/hour

• If fall is greater than this the rate of administration should be

reduced by 30–50%

• The rate of administration should be increased by 30–50% if

the rate of fall of [Na+] is less than 0.25 mmol/kg/hour

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Electrolyte free water in parenteral fluids1

Intravenous fluid Sodium (mEq/litre)

Osmolality (mOsm/kg/H2O)

Percentage electrolyte free water2

5% dextrose 0 252 100

0.2% NaCl/5%

dextrose

34 321 78

0.45% NaCl/5%

dextrose

75 406 50

Ringer’s lactate 130 273 16

5% dextrose/

Ringer’s lactate

130 525 16

5% dextrose/

0.9% NaCl

154 560 0

2.5% dextrose/

0.45% NaCl

75 293 50

1Source: Moritz M L, Ayus J C. Prevention of hospital-aquired hyponatraemia: a case for using isotonic saline. Pediatrics 2003; 111: 227–30.2Based on a sodium plus potassium concentration in the aqueous phase of plasma of 154 mEq/litre assuming that plasma is 93% water with a serum sodium of 140 mEq/litre and a potassium concentration of 4 mEq/litre.Normal plamsa osmolarity is 290–310 mOsm/litre.

4

Management of electrolyte abnormalities

Hypokalaemia[K+] < 3.5 mmol/litre

Hyperkalaemia[K+] > 5.5 mmol/litre

HypocalcaemiaCorrected total [Ca2+] < 2.0 mmol/litre

Symptoms Asymptomatic until < 3 mmol/litre

Weakness, cramps, arrhythmias,

decreased cardiac contractility,

paralytic ileus

ECG changes when [K+] > 7 mmol/litre

Prolonged PR interval, tented T waves,

shortening of QT interval, widened QRS

Skeletal muscle weakness

Irritability, anxiety, jitteriness, twitching,

seizures

Perioral/finger/toe paraesthesia

Masseter spasm (Chvostek’s sign)

Carpopedal spasm (Trousseau’s sign)

Prolonged QT interval, decreased cardiac

contractility

Laryngospasm, bronchospasm

Management Mild to moderateIncrease [K+] in diet or oral KCl

supplements 3–5 mmol/kg/day

Severe Intravenous supplementation, no

faster than 0.25 mmol/kg/hour

(maximum peripheral concentration

40 mmol/litre KCl)

1 Reduce [K+] load• Decrease dietary K+

• Decrease K+ containing drugs

• Eliminate acidosis/sodium restriction

2 Antagonize membrane effects• Calcium gluconate 100–200 µg/kg per

dose (0.5–1.0 ml/kg of 10% solution

3 Increase intracellular shift• NaHCO3 1–2 mmol/kg-1 per dose

• Glucose 0.3–0.5 g/kg as 10% glucose

(3–5 ml/kg) solution with insulin 1U for

every 5 g of glucose

• Nebulized salbutamol (2.5–5.0 mg)

4 Removal of [K+] from body• Calcium resonium 1g/kg per dose

(rectal or oral)

• Furosemide, 1 mg/kg, per dose

• Dialysis or haemofiltration

Calcium gluconate 10% (0.22 mmol/ml)

0.5ml/kg, maximum 20 ml over 10 min

or

Calcium chloride 10% (0.7 mmol/ml)

0.2 ml/kg, maximum 10 ml over 10 min

5

ischaemic event may also be adversely affected, with an increase in cell damage. A fluid containing 1–2.5% dextrose maintains normoglycaemia and prevents lipid metabolism and ketosis. If this type of solution is not available it is better to use Ringer’s lactate or normal saline to replace both maintenance requirement and other losses. Patients given large volumes of normal saline develop a hyperchloraemic metabolic acidosis because of the high chloride load. Large volumes of Ringer’s lactate solution cause a metabolic alkalosis from the metabolism of lactate. If the solution does not contain dextrose, blood sugar must be monitored.

Replacement of fluid lossesDuring many surgical procedures large amounts of ECF may be redistributed into the interstitial fluid volume as a result of surgi-cal manipulation. This is known as ‘third-space loss’ and if not replaced results in depletion of the plasma volume. Although impossible to measure, the volume of transudated fluid varies according to the degree of surgical trauma. Third-space loss is low in neurosurgery and peripheral surgery (1–2 ml/kg/hour), moder-ate in thoracic surgery (4–7 ml/kg/hour) and high in abdominal surgery (6-10 ml/kg/hour). The lost fluid has a composition similar to plasma and must be replaced using an isotonic solution such as normal saline or Ringer’s lactate. In addition, blood loss should always be replaced in children undergoing major surgery, initially

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with a crystalloid in a ratio of 3:1 or with a colloid in a ratio of 1:1. The decision to transfuse with blood should be based on the concept of an allowable blood loss.

Postoperative fluid managementIn the postoperative period, hourly maintenance fluids should be continued. The recommended maintenance fluid is 0.9% saline in 5% dextrose with the addition of 20 mmol of KCl per litre. This avoids giving a significant amount of free water (Figure 4) at a time when high levels of antidiuretic hormone may cause reten-tion of this water, leading to hyponatraemia. Additional losses resulting from nasogastric tube drainage, gut fistulae, peritoneal drainage and continuing blood loss also have to be replaced with the appropriate fluid. Figure 5 shows the diagnosis and manage-ment of other electrolyte abnormalities.

KEY REFERENCES1 Holliday M A, Segar W E. The maintenance needs for water in parenteral

fluid therapy. Pediatrics 1957; 19: 823–32.

2 Oh T H. Formulas for calculating fluid maintenance requirements.

Anesthesiology 1980; 53: 351.

FURTHER READINGNPSA alert. Reducing the risk of harm when administering intravenous

fluids to childern. Anticipated release date, June, 2006.

Planten R, Shorten G. Renal function, acid-base and electrolyte

homeostasis. In: Bissonnette B, Dalens B, eds. Pediatric anesthesia,

principles and practice. New York: McGraw Hill, 2001.

Siker D. Pediatric fluids, electrolytes and nutrition. In: Gregory G A, ed.

Pediatric anesthesia. 4th ed. New York: Churchill Livingstone, 2001.