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Craig Sims, Dana Weber and Chris Johnson (eds.) A Guide to Pediatric Anesthesiahttps://doi.org/10.1007/978-3-030-19246-4_5

5. Fluid Management in Children Undergoing Surgery and Anesthesia

Ric Bergesio¹ and Marlene Johnson¹

(1)

Department of Anaesthesia and Pain Management, Perth Children’s Hospital, Nedlands, WA, Australia

Ric Bergesio (Corresponding author)

Email: Riccardo.Bergesio@health.wa.gov.au

Marlene Johnson

Email: Marlene.Johnson@health.wa.gov.au

Keywords

Preoperative fastingBlood transfusion in childrenPediatric intravenous fluidsPediatric fluid managementMassive transfusion in childrenCritical bleeding in childrenTransfusion trigger in children

As with drug treatment, fluid treatment in children demands more precision than in adults. This chapter explains the management of fluids in infants and children in the peri-operative period. Topics include fluid resuscitation, maintenance fluids and the replacement of ongoing losses. Fasting guidelines and the management of electrolyte disturbances are also included.

5.1 Body Fluid Composition

Babies are ‘wet’ at birth—total body water (TBW) is about 70–75% of body weight in neonates, higher in preterm neonates. It falls by 5% in the first week, accounting for the weight drop of newborn babies, and falls to the adult level of about 60% by 1 year of age. The extracellular fluid volume is greater than the intracellular fluid volume (the opposite of adults), until 1 month of age when they become equal. ICF then becomes larger than ECF through to adulthood (Fig. 5.1). Adult values are achieved by 1 year of age. Blood volume is higher in neonates and falls with growth (Table 5.1).

../images/467929_2_En_5_Chapter/467929_2_En_5_Fig1_HTML.png — Fig. 5.1

Changes in body water composition with age. Modified from Jain, Pediatrics Rev 2015

Table 5.1

Blood volume at different ages

Age	Estimated blood volume (mL/kg)
Preterm	100
Term neonate	90
Infants and children	70–80
Adult	70

5.1.1 Hemoglobin

The hemoglobin concentration is high at birth because of the hypoxic environment in-utero. At birth, the hemoglobin level can be 160–200 g/L, depending on when the cord was clamped relative to uterine contraction. Most of the hemoglobin at birth is fetal hemoglobin (HbF). Although red blood cells containing adult hemoglobin (HbA) are produced from birth, production is low in response to the increased availability of oxygen and downregulation of erythropoietin. Eventually oxygen delivery is inadequate relative to metabolism, and erythropoietin production is stimulated again. These factors result in a falling hemoglobin, reaching a low point of 90–110 g/L at 2–3 months (called the ‘physiological anemia’ , Fig. 5.2). The hemoglobin level in very preterm infants can decline even lower (80 g/L) due in part to repeated phlebotomy, and the effects of transfusions on endogenous erythropoiesis. Nearly all of the hemoglobin at the time of physiological anemia is HbA, so tissue oxygen delivery is actually improved due to the lower oxygen affinity of HbA compared to HbF. Platelet numbers are at adult levels from birth.

../images/467929_2_En_5_Chapter/467929_2_En_5_Fig2_HTML.png — Fig. 5.2

The hemoglobin level dips in early infancy (‘physiological anemia of infancy’) as HbF production ceases and is replaced by HbA

5.1.2 Coagulation Changes

Coagulation factors are produced by the fetus and have low levels at birth, but this is balanced by lower levels of inhibitors than in adults, a stronger binding fibrinogen molecule and lower activity of the fibrinolytic system. Clotting tests can therefore be prolonged despite no bleeding tendency. The rotational thromboelastogram (ROTEM) of a neonate has clinically minor differences until about 4 months of age, when it becomes the same as that of an adult.

5.2 Preoperative Fasting

Minimizing fasting in children reduces anxiety and irritability as well as physiologic and metabolic derangements. Neonates in particular, have low glucose stores and are at risk of hypoglycemia—a 10% glucose in 0.22% saline infusion is started if the fasting time is longer than the usual time between the baby’s feeds.

The duration of fasting of children before anesthesia has traditionally followed the 6-4-2 rule: 6 h for light food and milk, 4 h for breast and formula milk, and 2 h for clear fluids. Recently, this has changed to the 6-4-1 rule in many countries and is discussed below.

5.2.1 Clear Fluids

Clear fluids include drinks that contain no fats or solids, such as clear apple juice, cordial, lemonade and pulp-free orange juice.

Many centers are moving away from a 2 h clear fluid fasting time, instead encouraging children to consume clear fluids (up to 3 mL/kg) until 1 h before elective or minor emergency surgery (the 6-4-1 rule). This is safe and does not increase the incidence of aspiration. Some centers accept even shorter fasting times (using a 6-4-0 rule).

5.2.2 Milk

Milk is cleared from the stomach in a biphasic pattern—an initial phase of rapid clearance of liquid followed by a slower phase of clearance of solids.

Gastric emptying times vary between milk products and depend on protein (whey and casein) and fat content. Breast milk has a higher whey-to-casein ratio than other milks and empties faster from the stomach. Because of this, many centers accept shorter fasting intervals for breast milk than other types of milk. Cow’s milk is rich in casein and fat, and empties slowly. Formula milk is intermediate in composition and emptying time.

While there is consensus about fasting periods with clear fluids, this is not the case with milk, and there is variation across different regions. A fasting duration of 3 h for breast milk and 4 h for formula is commonly used for infants, with fasting increased to 6 h for all types of milk in children 1 year and older.

The Australian College currently suggests these shorter durations for breast and formula milk only until 6 months of age, rather than 12 months. In infants older than 6 months, it suggests 6 h fasting for both breast and formula. Some centers include cow’s milk with formula, and some in Europe allow cow’s milk and products such as yoghurt in all ages up until 4 h before anesthesia. An example of a commonly used set of fasting times is listed in Table 5.2.

Table 5.2

Fasting times for children

Substance	Fasting period
Clear fluids	1 h
Breast milk^a	3 h if <12 months age
Formula milk^a	4 h if <12 months age
Solids, cow’s milk	6 h

Note the different fasting periods in infants for different milks that have different amounts of fat and protein

^aThere is variation in fasting duration and age limits for milk—see text

Note

Different types of milk have different fat and protein contents, and the fasting duration after ingestion of each type is different.

5.2.3 Solids

Solids tend to have variable gastric clearance times. Emptying may be prolonged with increasing fat and calorie content and the size of the meal, and the 6 h duration generally applies only to a ‘light’ meal.

In children with traumatic injuries, the time to complete gastric emptying is unknown. However, not all of these children need to be treated as if they have a full stomach. Factors that affect gastric emptying include the severity of trauma, pain, anxiety, administration of opioids and the time interval between trauma occurring and last meal.

5.2.4 Unusual Foods

Food that becomes liquid in the stomach (jelly, icy poles, and lollipops) can be considered the same as liquids. Chewing bubble gum is also considered a clear liquid for fasting, but if it is swallowed, it is treated as a solid. Fluid thickeners do not alter gastric emptying and fasting times should be determined by the type of fluid they are used to thicken.

Note

Rare conditions affected by fasting:

Glycogen storage diseases, Fatty acid oxidation disorders, Urea cycle defects, Organic acidurias (including MMA), Homocystinuria.

5.3 Intravenous Fluid Requirements

There are three components to fluid management in children: replacement of existing deficits, maintenance requirements, and replacement of ongoing losses.

5.3.1 Replacement of Existing Deficits

Fluid deficit can cause dehydration or shock, and may be due to hemorrhage, gastrointestinal losses, insensible losses or sequestration from the intravascular space into tissues. These deficits can be estimated from weight loss, clinical signs and laboratory investigations.

Dehydration is difficult to assess, and individual clinical findings by themselves are unreliable. Symptoms and signs are more numerous and more severe with worsening dehydration (Table 5.3). The best measure of fluid loss is serial weight measurements, but this is often unavailable.

Table 5.3

Signs and symptoms of dehydration and shock in children

Signs and symptoms
Dehydration	Shock
Looks unwell or deteriorating ^a
Altered consciousness: lethargy, restless ^a	Reduced consciousness
Decreased skin turgor ^a
Sunken eyes ^a
Tachycardia ^a	Tachycardia, then bradycardia
Increased respiratory rate ^a	Increased or decreased respiratory rate
Normal skin color	Mottled skin, pale
Warm extremities	Cold extremities
Dry mucous membranes
Normal blood pressure	Hypotensive
Capillary refill <2 s	Capillary refill >3 s
Normal peripheral pulses	Reduced peripheral pulses
Reduced urine output

^aThese signs of dehydration, if present, are suggested as ‘red flags’ warning of progression to shock or collapse. (Based on National Institute Clinical Excellence guideline CG84)

Dehydration may be detectable when a child is 2.5–5% dehydrated. Severe dehydration causes circulatory shock, and the child may become acidotic and hypotensive. Hypotension is a late, premorbid sign because young children are able to mount a strong sympathetic response and maintain blood pressure until severe hypovolemia develops. Clinical signs, serum electrolytes and glucose can guide replacement.

Keypoint

If a child is 5% dehydrated, this means they have lost 5 mL per 100 g of body weight, or 50 mL/kg.

Clinical dehydration is detectable when a child is 2.5–5% dehydrated.

If a child presents with symptoms and signs of dehydration in the absence of shock, they are approximately 5% dehydrated.

If shock is present, there is at least 10% dehydration.

Practice Point

The capillary refill time—Pressure on the skin for 5 s then observe the time for blanching to disappear. Normal refill time is 2 s or less. 2–3 s is borderline abnormal. The finger is the best site, the sternum is an alternative. Refill times are longer in the foot. Refill time doesn’t correlate with blood pressure, reflecting the child’s ability to maintain BP until late.

Skin turgor—Gently pinch a fold of skin for a few seconds and let go. Normally, the skin will recoil to its original position instantly. A delay in return to normal suggests dehydration. In a child, the best place to test skin turgor is on the abdomen.

Keypoints

Shock

If the child has signs of shock or is at increased risk of developing shock (presence of red flags), 10–20 mL/kg of an isotonic crystalloid solution should be given immediately. A further 10–20 mL/kg bolus may be given if signs of shock persist. Judicious fluid boluses of 5–10 mL/kg should be used in cardiac disease and severe trauma.

After resolution of signs of shock, rehydration should occur with an isotonic crystalloid +/− glucose. 100 mL/kg (ie. 10% dehydration) should be given over 24–48 h in addition to maintenance fluid requirements.

Dehydration

For children presenting with dehydration in the absence of shock, 50 mL/kg (ie. 5% dehydration) of an isotonic crystalloid +/− glucose should be given over 24–48 h in addition to maintenance fluids.

5.3.2 Maintenance Fluids

Maintenance fluids replace fluid and solute losses from the kidney, gut, respiratory tract and skin. Approximately 50% of the losses are from the renal system and 50% from the lungs and skin. Maintenance fluid requirements are a function of metabolic rate and caloric requirements, and so are higher in neonates than in children and adults. They are also higher in the presence of fever, burns, or sepsis.

In the 1950s, Holliday and Segar linked water requirements and caloric expenditure to body weight, and then linked electrolyte requirements to the composition of milk. Their work resulted in the formula for maintenance fluid requirements. This formula calculates a full day’s fluid requirements: 100 mL/kg per day for the first 10 kg of body weight, then 50 mL/kg per day for the next 10 kg of body weight, and 20 mL/kg per day for the rest of the weight. The formula has been adapted to give a more practical, hourly calculation- the ‘4-2-1 rule’ (Table 5.4). This formula is widely used, but there are concerns it overestimates the fluid requirements in the postoperative period or in sick, hospitalized children.

Table 5.4

The 4-2-1 formula for calculating hourly maintenance fluid requirements of children

Weight	Fluid rate (mL/kg/h)
First 10 kg	4
Next 10–20 kg	2
Part of weight over 20 kg	1

For example, a 24 kg child would need 40 mL/h for the first 10 kg, 20 mL/h for the next 10 kg, and 4 mL/h for the rest of the weight, giving an hourly maintenance rate of 64 mL/h

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Tags: A Guide to Pediatric Anesthesia

Nov 27, 2021 | Posted by admin in ANESTHESIA | Comments Off

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