Newborn Physiology

Newborn Physiology

1. Fluids and Electrolytes
1. Fluid Requirements
• in a full-term infant, total body water accounts for 80% of total body weight
• neonates have increased insensible water losses (30 to 35 ml/kg/day) as compared to adults (15 ml/kg/day)
• urine output is a good indicator of fluid status in infants and should be at least 1 ml/kg/hr


1. Maintenance Fluids
• provided as D5.45 NS or D5.2 NS
• premature infants < 2 kg require 140 – 150 mL/kg/day
• fluid rates for term infants: 100 ml/kg up to 10 kg, add 50 ml/kg for 11 to 20 kg, and add 25 ml/kg for each additional kg
• fluid boluses may be given as 10 ml/kg of LR
• in a hypotensive infant or child, the bolus may be given as 20 ml/kg
• large fluid losses from a nasogastric tube, ostomy, or fistula should be measured and carefully replaced (0.5 cc per cc to 1.0 cc per cc)
• best indicators of adequate fluid intake are urine output and urine osmolality




2. Electrolyte Requirements
• sodium requirements are 2 to 4 mEq/kg/day and potassium requirements are 1 to 2 mEq/kg/day
• electrolyte content of fluid losses can be measured and replaced precisely


2. Blood Volume and Blood Replacement
• useful guide to the blood volume of an infant is 85 ml/kg
• transfusion volume is 10 ml/kg of PRBCs
• FFP is given in a dose of 20 ml/kg
• platelets are given as 10 ml/kg


3. Nutrition
1. Caloric Requirements
• neonate has a metabolic rate 2.5X that of an adult and requires 100 - 120 calories/kg/day for growth
• the ideal weight gain of an infant is 1% of body weight/day
• surgical stress, trauma, or fever will increase the daily caloric requirements
• breast milk should be used whenever possible
• most infant formulas, as well as breast milk, contain 20 cal/oz
• lactose-containing formulas (Enfamil, Similac) should be avoided after gastrointestinal surgery


2. Carbohydrates
• infants are susceptible to hypoglycemia because their liver and muscle masses (glycogen reservoirs) are disproportionately smaller than in adults
• minimum glucose infusion rate for infants is 4 – 6 mg/kg/min
• hyperglycemia must also be avoided because it can lead to hyperosmolarity and dehydration


3. Protein
• to support growth and development, infant protein requirements are as high as 3.5 gm/kg/day


4. Fat
• major source of nonprotein calories
• fat is also provided to prevent essential fatty acid deficiency


5. Hyperalimentation
• used when the gastrointestinal tract is not available
• requires placement of a central line
• infants require more protein, vitamins, and minerals than adults
• linoleic acid is an essential fatty acid
• histidine, tyrosine, and cystine are essential amino acids in infants (but not adults)
• calcium, phosphorus, zinc, copper, folate, and multivitamins are added


1. Complications
• electrolytes should be measured daily
• cholestatic jaundice can occur, especially in septic newborns
• cirrhosis has occurred as a late complication of TPN administered in the neonatal period


4. Thermoregulation
• neonates are extremely vulnerable to hypothermia (relatively large body surface area, lack of hair, lack of subcutaneous tissue, greater insensible losses)
• neonates are unable to shiver and respond to hypothermia by increasing their metabolic rate and mobilizing brown fat deposits
• in the OR, the infant is kept warm by the use of overhead heating lamps, a heating blanket, warming of inspired gases and irrigation fluids, tin foil caps, and coverage of the extremities with occlusive materials


5. Cardiovascular Physiology
• in the fetal circulation, arterial placental blood bypasses the lungs through the patent foramen ovale and ductus arteriosus
• at birth, the foramen ovale and ductus arteriosus closes, and pulmonary vascular resistance drops
• hypoxemia, acidosis, sepsis can contribute to persistent pulmonary hypertension
• prematurity is associated with a persistent patent ductus arteriosus
• NSAIDs (indomethacin) usually will induce closure of a patent PDA, but occasionally surgical ligation is required
• cardiac output is heart rate dependent
• capillary refill is a good indicator of adequate cardiac output



6. Pulmonary Physiology
• immature lungs produce less surfactant
• premature infants are at high risk of alveolar collapse, hyaline membrane formation, and barotrauma
• lecithin-to-sphingomyelin ratio is used to determine fetal lung maturity
• normal respiratory rate for a newborn is 40 – 60 breaths/min
• infants are obligate nasal breathers
• signs of respiratory distress include nasal flaring, grunting, intercostal and substernal retractions, and cyanosis
• exogenous surfactant administration has improved survival of premature infants
• nitric oxide is useful for treating persistent pulmonary hypertension


7. Immune System
• infants have lower levels of immunoglobulins and complement at birth, making them susceptible to sepsis
• iatrogenic sources of sepsis include central lines, arterial catheters, bladder catheters, endotracheal tubes


8. Pain Control
• managing pediatric pain is an important priority
• IV narcotics can be safely used in neonates and children