Neonatal Rauid Management Essay

Best Practice & Research Clinical Anaesthesiology 24 (2010) 365e374

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Best Practice & Research Clinical
Anaesthesiology
journal homepage: www.elsevier.com/locate/bean

6

Neonatal fluid management
Isabelle Murat, MD, PhD *, Alexis Humblot, MD, Laure Girault, MD,
Federica Piana, MD
Department of Anesthesia, Hôpital d’Enfants Armand Trousseau, 26 avenue du Dr Arnold Netter, 75571 Paris, Cedex 12, France

Keywords: blood transfusion colloid crystalloids fluid therapy hypoglycaemia hyperglycaemia neonate Perioperative fluid management in paediatrics has been the subject of many controversies in recent years, but fluid management in the neonatal period has not been considered in most
reviews and guidelines.1e3 The literature regarding neonatal fluid management mainly appears in the paediatric textbooks and few recent data are available, except for resuscitation and fluid loading during shock and major surgery.
In the context of anaesthesia, many neonates requiring surgery within the first month of life have organ malformation and/or dysfunction. This article aims at reviewing basic physiological considerations important for neonatal fluid management and mainly focusses on fluid maintenance and replacement during surgery.
Ó 2010 Elsevier Ltd. All rights reserved.

Physiological considerations: neonates are not just small adults
Major physiological changes occur within the first days and months of life. They mainly concern body composition, renal function and changes in the cardiovascular system.4
Body composition
Throughout foetal life and during the first 2 years of life the distribution of body fluid undergoes a gradual but significant change.5 Total body water (TBW) represents as much as 80% of body weight in premature infants, 78% in full-term newborns and 65% in infants of 12 months of age compared to 60% in adults (Table 1). These age-related changes in TBW mainly reflect changes in extracellular fluid (ECF) with growth. As the body cells proliferate and organ development progresses, the ECF
volume

* Corresponding author. Tel.: þ33 144736299; Fax: þ33 144736244.
E-mail address: [e-mail] (I. Murat).
1521-6896/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.bpa.2010.02.014 366

I. Murat et al. / Best Practice & Research Clinical Anaesthesiology 24 (2010) 365e374

Table 1
Body composition and morphometric data in children (ICF: intracellular fluid; ECF: extracellular fluid).
Premature
Body weight (BW kg)
Body surface area (BSA m2)
BSA/BW
Total body water (% BW)
ECF (% BW)
ICF (% BW)

Full-term

1 yr

3 yr

9 yr

Adult

1.5
0.15
0.1
80
50
30

3
0.2
0.07
78
45
33

10
0.5
0.05
65
25
40

15
0.6
0.04
60
20
40

30
1
0.03

70
1.7
0.02

decreases proportionally. It represents 50% of body weight in premature infants, 45% in full-term newborns and 25% in infants of 12 months of age compared to 20% in adults. The intracellular fluid compartment increases only moderately during the first year of life, representing 33% of body weight at birth and 40% of body weight by the end of the first year, and does not change substantially after that.
Renal maturation
Maturation of renal function is basically achieved by the end of the first month of life. Glomerular filtration increases rapidly from 34 weeks gestational age when kidneys have completed their nephronic structure.6e8 After birth, renal vascular resistances decrease abruptly while systemic vascular resistances and arterial pressure increase. As a consequence, renal blood flow increases dramatically.
This explains why glomerular filtration rate, still low during the first 24 h of life, rises very rapidly thereafter. During the first 6 weeks after birth, the area of cortical and juxtaglomerular nephrons, as well as the volume of glomerular capillaries and the size of glomerular membrane pores also increase.
Tubular function is less mature than glomerular function at birth. Renal threshold for glucose is low explaining the high incidence of glycosuria even after moderate hyperglycaemia. The tubular capacity to reabsorb sodium is low in premature infants.9 At term, the neonatal nephron begins to reabsorb sodium more actively in response to growth requirements. Sodium excretion in response to parenteral sodium load is also reduced. Careful control of sodium balance is essential in premature surgical neonates, as both hypernatraemia and hyponatraemia may have detrimental effects on the brain.
At birth, the newborn is unable to effectively concentrate urine. Clearance of free water is lower than that of adults thus explaining the impaired ability of newborn infants to cope with excessive water loading or water deprivation.
Finally, the renineangiotensinealdosterone system is functional in neonates10 but feedback mechanisms are immature, especially in premature infants.11
Developmental cardiovascular changes
Newborns and premature infants have limited cardiovascular reserves in response to increased preload or afterload.12e14 Any reduction in preload is also poorly tolerated owing to reduced compliance of the right ventricle and is rapidly followed by a reduction of systolic ejection volume. Cardiac output is high to compensate for the high oxygen affinity of foetal haemoglobin and to match the high oxygen consumption.15 Cardiac output is highly dependent on heart rate in the neonatal period.13
However, by the end of the first month of life, the capacity of the cardiovascular system to adapt is close to that of adults. In premature infants, excess of fluid will promote the persistence of patent ductus arteriosus.16,17
Maintenance requirements
Calorie requirement
The metabolic rate of a full-term newborn in a neutral environment is 32 kcal kgÀ1 per day during the first hours of life. Requirements increase rapidly during the first week of life, and then at a slower rate, increasing linearly with growth.18

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In 1957, Holliday and Segar19 estimated metabolic requirements for children at bed rest, and this estimation is still used in daily practice. The calculated calorie expenditure was 100 kcal kgÀ1 for infants weighing 3e10 kg, (1000 þ 50) kcal kgÀ1 for each kilogram more for children between 10 and 20 kg, and 1
(500 þ 20) kcal kgÀ1 for each kilogram over 20 kg. Half of those calories were thought to be required for basic metabolic needs and the remainder for growth. General anaesthesia essentially mimics calorie requirements at closer to basal metabolic rate.20 As the maintenance needs for water paralleled energy metabolism, the estimated caloric expenditure was used to determine the maintenance fluid therapy
(known as the 4e2e1 rule). Since the publication of this article, hypotonic solutions have had widespread use for decades until the danger of induced hyponatraemia was demonstrated in clinical practice.21e25
Water requirement
Under normal conditions, 1 ml of water is required to metabolise 1 kcal. This takes into account insensible water losses across the skin and respiratory tract, and urinary water loss. Therefore, in the awake child, calorie and water consumption are considered equal (Table 2). In anaesthetised children,
Lindahl20 calculated that 166 ml of water were required to metabolise 100 calories. Using indirect calorimetry, he calculated hourly maintenance fluid to be equal to the following expression
2.5Â kg þ 10 (ml hÀ1). In term neonates, water intake is progressively increased during the first days of life from 60 ml kgÀ1 per day the first day and subsequently increased by 20 ml kgÀ1 per day to achieve
150 ml kgÀ1 per day at the end of the first week of life. Insensible water loss increases with decreasing body weight in premature infants, especially when they are cared under radiant warmer.26 Several factors contribute to this large insensible water loss in premature infants: small size, an increased body-surface-area-to-body-weight ratio, increased thermal conductance, thinner more permeable and vascularised skin and a higher respiratory rate.
Electrolytes requirements
Daily sodium and potassium requirements were calculated by Holliday and Segar from the amount of electrolyte delivered by the same volume of human milk.19 The daily needs were 3 mmol kgÀ1 per day sodium and 1e2 mmol kgÀ1 per day potassium. The combination of maintenance-fluid and electrolyte requirements results in a hypotonic electrolyte solution (0.2% saline equivalent). In premature infants, sodium and potassium requirements are higher than later in life, 3e5 mmol kgÀ1 per day for sodium and 2e4 mmol kgÀ1 per day for potassium mainly because of the immaturity of renal tubular function. Calcium requirements range between 0.8 and 1 mmol kgÀ1 per day.
Preoperative assessment
The preoperative assessment of fluid volume and state of hydration varies from elective surgery patients with no or slowly developing fluid deficit such as those scheduled for hernia repair to the severely sick premature infant with necrotising enterocolitis who is undergoing a dynamic deficit in blood and interstitial volume and in whom it is more difficult to evaluate fluid balance.
Vascular volume
The ultimate goal of perioperative fluid therapy is to maintain a correct fluid and electrolyte balance and, as a consequence, normal cardiovascular stability.27 Indeed, dehydration and some medical conditions associated with third-space sequestration of fluids (e.g., intestinal occlusion) will in turn
Table 2
Fasting guidelines for elective surgery in neonates.
Ingested material

Minimum fasting period (h)

Clear liquids
Breast milk
Infant formula

2
4
4

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I. Murat et al. / Best Practice & Research Clinical Anaesthesiology 24 (2010) 365e374

affect vascular fluid volume. Restoration of an adequate vascular fluid volume is essential to maintain cardiovascular stability, organ perfusion and adequate tissue oxygenation. Isotonic transfer of fluid from the extracellular compartment to a non-functional interstitial space forms third-space volume.
Replacement of intravascular volume loss should be performed by administration of normotonic and normo-osmolar solution. Crystalloid solutions such as Ringer lactate or normal saline, or even a colloid solution such as albumin can be used (see below). The prognosis of some medical conditions such as septic shock depends on the quantity and the rapidity of vascular loading; the younger the child, the greater the quantity of fluid loading related to body weight.28e30 The fluid challenge is usually
10e20 ml kgÀ1 in children, but no clear recommendations can be found in the literature for the neonatal period even in the most recent published guidelines.31
Preoperative management of pyloric stenosis is much more codified. Pyloric stenosis is a medical emergency and not a surgical emergency. Preoperative correction of fluid and electrolyte deficits may require several hours or even days. The targets of preoperative fluid management is to correct dehydration and to obtain serum chloride !106 mmol lÀ1, serum Naþ !135 mmol lÀ1, serum bicarbonate
(HCOÀ) 26 mmol lÀ1, urine chloride (ClÀ) >20 mmol lÀ1 and urine output >1 ml kgÀ1 per hour. The
3
most severe cases usually require an initial fluid challenge of 20 ml kgÀ1 of crystalloids to restore vascular fluid volume.
Fasting guidelines
There is now a large body of evidence that free intake of clear fluids up to 2 h preoperatively does not affect the pH or volume of gastric contents at induction of anaesthesia in children. While there have been relatively few studies in infants, these suggest that infants may be allowed clear fluids up to 2 h and breast milk 4 h preoperatively.32,33 It was demonstrated >25 years ago that the gastric emptying of
110e200 ml of human milk was 82 Æ 11% after 2 h in neonates and infants of