[level-membership-for-neonatal-and-perinatal-medicine-category]
CHAPTER 10 Fluids and nutrition
Renal function
In practical terms, renal function and fluid balance can be monitored using serial weight measurements, urine output and serum sodium as guides. Serum potassium is often falsely elevated in newborns because of the method of collection (heel-prick collection causes haemolysis and/or contamination with tissue fluids). Serum urea and creatinine may be confusing and probably do not add a great deal to what can be determined by using the measurements noted above.
Parenteral fluids
General
• The standard parenteral fluid used initially in infants is 10% dextrose. This gives some caloric intake for those babies not fed for some time. Alternatively, a variety of starting fluids that may contain maintenance saline or calcium can be used.
• If given through an umbilical arterial line, heparin at a concentration of 1 unit/mL is added (500 units per 500 mL bag).
• Standard starting infusion rate is 60 mL/kg/day. For very small, preterm babies, 80–100 mL/kg/day may be started. This can then be varied according to serial weight measurements or electrolyte concentrations. The initial infusion rate does not need to be routinely increased during the first three days of life, especially in infants with lung disease.
Electrolytes
• No standard electrolyte additives are normally necessary in the first few days. All preterm infants have an excess of extracellular fluid at birth and must undergo some electrolyte losses via urine when getting rid of this excess fluid.
• The most common fluid balance problem in the first 48 hours of life is excessive evaporative fluid loss in very small infants. This is reflected in excessive weight loss and rising serum concentrations of sodium and chloride ions, [Na+] and [Cl−]. Electrolytes may need to be measured every 8 to 12 hours in extremely low birth weight (ELBW) infants in the first 48 hours, and fluid intake adjusted accordingly. Fluids do not need to be increased until the serum [Na+] is in the high 140s (in mmol/L).
• When Na+ is added, the most convenient way to do so is to make a mixture in the burette of 80 mL 10% dextrose and 20 mL Nsaline (this is 8% dextrose/one-fifth Nsaline; Nsaline is Normal saline, 0.9%).
• The addition of potassium K+ should be undertaken with great caution. If required, it should be added to a burette, with the amount ordered in mmol and in mL to avoid confusion [e.g. 10% dextrose, 98 mL; KCl, 2 mL (= 2 mmol); run at 7 mL/hr]. It is safest for all burette additives to be ordered in mL of a stated concentration of the additive.
Other
• In most preterm infants the serum calcium concentration [Ca2+] will decrease in the first few days, and the total serum [Ca2+] will commonly be 1.5 mmol/L or less. There is good evidence that the ionised [Ca2+] remains normal down to a total [Ca2+] of 1.3 mmol/L.
• If hypocalcaemia is to be treated, the standard parenteral dose is 3 mL of 10% calcium gluconate/kg/day. Be very wary about giving this via a peripheral IV line, as nasty extravasation burns with necrosis occur if the line infiltrates. It is satisfactory to give this as an infusion into an umbilical artery, but boluses should be given very slowly and carefully.
Parenteral nutrition (PN)
• Parenteral nutrition usually consists of the infusion of a solution of amino acids (such as Vamin or Primene) and carbohydrate (dextrose), plus a solution of fat (Intralipid). Vitamins are also given, both water-soluble and fat-soluble.
• Some neonatal units make up individual prescriptions for PN with varying concentrations of dextrose and electrolytes on a base amino-acid solution. In practice this process is unwieldy and unnecessary. The baby is much smarter than you are at sorting out minor electrolyte problems.
A suggested procedure
• Use standard solutions with set concentrations of amino acids, dextrose, Na, K, Ca, Mg, Cl, P, Zn and Cu:
• Start with Solution 1, at the same rate as the baby’s maintenance fluids were being given, increasing by 20 mL/kg/day daily if fluid balance permits.
• Change the PN to Solution 2 after a couple of days (at the next line change). Total fluids are then usually increased (again if fluid balance permits) daily by 20 mL/kg/day up to 180 mL/kg/day. If the dextrose is not tolerated, insulin at 0.05–0.2 units/kg/hr can be infused
• Add water-soluble vitamins (e.g. Soluvit N) to the burette at the beginning of the first infusion after each line change (3 days per week — M,W,F), 2 mL/kg each time. The vitamins are thus given to the baby over the first few hours — minimising the vitamins’ exposure to light.
• Give lipid as a 20% solution of Intralipid at a dose of 2 g/kg/day (10 mL/kg/day). Fat-soluble vitamins can be added as Vitalipid N — 4 mL/kg/day to a maximum of 10 mL/day. Other neonatal units will start at 1 g/kg/day and increase over a few days up to as high as 3 g/kg/day, with monitoring of triglyceride levels. Some stop lipid infusion if the baby has septicaemia; we don’t.
General
• Parenteral nutrition given via peripheral lines must be very carefully managed as extravasation burns occur at sites of infiltration, and evidence from randomised controlled trials demonstrates that where peripheral IV lines are used the babies get much less nutrition because of the time spent without IV access.
Enteral feeding
Preterm babies have four main difficulties with respect to feeding:
Feeding therefore presents the need for:
If a baby is not being enterally fed, always ask yourself why not?
Babies who might not be started on enteral feeds from soon after birth include:
• babies who were growth-restricted in utero and who had absent/reverse diastolic flow in the umbilical artery
• those whose mothers wish to exclusively breast feed but have not produced any expressed breast milk (EBM) yet.
Feeding regimes
• In a well baby, who is able to tolerate full enteral feeds from day 1, feeds can be started at 60 mL/kg/day and increased to 180 mL/kg/day by day 7.
• A baby that is not fed and who is only getting a dextrose/saline solution (i.e. no feeds or PN) doesn’t need more than 120–140 mL/kg/day of total fluids.
• Start all feeds as bolus feeds given every 3 hours, usually at around 2–3 mL/kg.
— For babies weighing <1500 g, the aim is to change to feeds every 2 hours once tolerance of reasonable volumes 3-hourly has been established.
Supplementation of breast milk
• For phosphate, either:
[/level-membership-for-neonatal-and-perinatal-medicine-category][not-level-membership-for-neonatal-and-perinatal-medicine-category]
CHAPTER 10 Fluids and nutrition
Renal function
In practical terms, renal function and fluid balance can be monitored using serial weight measurements, urine output and serum sodium as guides. Serum potassium is often falsely elevated in newborns because of the method of collection (heel-prick collection causes haemolysis and/or contamination with tissue fluids). Serum urea and creatinine may be confusing and probably do not add a great deal to what can be determined by using the measurements noted above.
Parenteral fluids
General
• The standard parenteral fluid used initially in infants is 10% dextrose. This gives some caloric intake for those babies not fed for some time. Alternatively, a variety of starting fluids that may contain maintenance saline or calcium can be used.
• If given through an umbilical arterial line, heparin at a concentration of 1 unit/mL is added (500 units per 500 mL bag).
• Standard starting infusion rate is 60 mL/kg/day. For very small, preterm babies, 80–100 mL/kg/day may be started. This can then be varied according to serial weight measurements or electrolyte concentrations. The initial infusion rate does not need to be routinely increased during the first three days of life, especially in infants with lung disease.
Electrolytes
• No standard electrolyte additives are normally necessary in the first few days. All preterm infants have an excess of extracellular fluid at birth and must undergo some electrolyte losses via urine when getting rid of this excess fluid.
• The most common fluid balance problem in the first 48 hours of life is excessive evaporative fluid loss in very small infants. This is reflected in excessive weight loss and rising serum concentrations of sodium and chloride ions, [Na+] and [Cl−]. Electrolytes may need to be measured every 8 to 12 hours in extremely low birth weight (ELBW) infants in the first 48 hours, and fluid intake adjusted accordingly. Fluids do not need to be increased until the serum [Na+] is in the high 140s (in mmol/L).
• When Na+ is added, the most convenient way to do so is to make a mixture in the burette of 80 mL 10% dextrose and 20 mL Nsaline (this is 8% dextrose/one-fifth Nsaline; Nsaline is Normal saline, 0.9%).
• The addition of potassium K+ should be undertaken with great caution. If required, it should be added to a burette, with the amount ordered in mmol and in mL to avoid confusion [e.g. 10% dextrose, 98 mL; KCl, 2 mL (= 2 mmol); run at 7 mL/hr]. It is safest for all burette additives to be ordered in mL of a stated concentration of the additive.
