A. Fiziološke karakteristike i individualne razlike novorodenčeta

A. Fiziološke karakteristike i individualne razlike novorodenčeta

1. Metabolizam vode

Voda čini 70 do 80% telesne mase neonatusa i srazmerno prematurusa. Ukupna količina vode u telu (total body wather - TBW) varira u obrnutom odnosu sa sadržajem mastu, stim da je količina masti kod prematurusa manja. Ukupna količina vode u telu je raspoređena ekstracelularno i intracelularno. Ekstracelularna tečnost zauzima jednu trećinu ukupne količine tečnosti u telu sa natrijumom kao glavnim katjonom, a hlorom i bikarbonatima kao anjonima. Intracelularna tečnost zauzima dve trećine ukupne količine tečnosti u telu sa kalijumom kao glavnim katjonom. Metabolizam novorođenčeta je izražen i obezbeđuje velike potrebe energije koja je potrebna za održavanje temperature tela i za rast. A change in body water occurs upon entrance of the fetus to his new extrauterine existence. There is a gradual decrease in body water and the extracellular fluid compartment with a concomitant increase in the intracellular fluid compartment. This shift is interrupted with a premature birth. Površina tela novorođenčeta je mnogo veća nego kod odraslih i gubitak toplote preko nje je značajno. Neprimetni gubici vode ("insensible water loss") su preko pluća (1/3) i kože (2/3). Transepithelial (skin) water is the major component and decreases with increase in post-natal age. Insensible water loss is affected by gestational age, body temperature (radiant warmers), and phototherapy. Renalna funkcija novorođenčeta generalno je adekvatna potrebama normalnog odojčeta rođenog u punom terminu ali može biti ograničena tokom perioda stresa. Renalne karakteristike novorođenčeta su niska glomerularna filtracija i koncentraciona sposobnost (limited urea in medullary intersticium) što ga čini manje tolerantnim na dehidraciju. Kod novorođenčeta metabolizam je aktivniji i stvaranje rastvora za ekskreciju urinom je veća. Bubrezi novorođenčeta inicijalno mogu da koncentrišu samo oko 400 mOsm/L (500-600 mOsm/L - novorođenče u punom terminu, u poređenju sa 1200 mOsm/L kod odraslih), i shodno tome potrebno im je 2-4 ml/kg/h produkcije urina za čišćenje bubrežnog elektrolitnog opterećenja. Kod starije dece to je 1-2 ml/kg/h, a kod odraslih 0.5-1 ml/kg/h.

2. Tecnosti i elektroliti

Ćelijska energija posreduje u aktivnom transportu elektrolita kroz ćelijske membrane. To je jedan od najvažnijih mehanizama u uspostavljanju i očuvanju normalnog volumena i sastava ćelijske tečnosti. Odojče može da zadržava Na, ali ne može prekomeran Na da izbacuje iz ćelije. Potrebe u elektrolitima novorođenčeta rođenog u terminu su: Natrijum 2-3 mEq/kg/24h, Kalijum 1-2 mEq/kg/24h, Hloridi 3-5 mEq/kg/24h. Potrebe u tečnosti su 100 ml/kg/24h za prvih 10 kg telesne mase. Po pravilu, dnevne potrebe u tečnosti približno su:

- prematurus 120-150 ml/kg/24h

- neonatus (u terminu) 100 ml/kg/24h

- odojče 10-20kg telesne mase  1000 ml + 50 ml/kg/24h.

Special need of preterm babies fluid therapy are: conservative approach, consider body weight changes, sodium balance and ECF tonicity. They are susceptible to both sodium loss and sodium and volume overloading. High intravenous therapy can lead to patent PDA, bronchopulmonary dysplasia, enterocolitis and intraventricular hemorrhage. Impaired ability to excrete a sodium load that can be amplify with surgical stress (progressive renal retention of sodium). Estimations of daily fluid requirements should take into consideration:

(1) urinary water losses,

(2) gastrointestinalni gubici,

(3) insensible water losses, and

(4) hirurški gubici (drenovi).

Blood Volumes estimates of help during surgical blood loss are:

prematurus 85-100 ml/kg,

novorođenče 85 ml/kg,

odojče 70-80 ml/kg.

Stepen dehidracije može se odrediti klčiničkim parametrima kao što su: telesna masa, turgor tkiva-kože, stanje periferne cirkulacije, ugnutost fontanele, suvoća usana i diureza. Intravenska ishrana je jedan od glavnih napredaka u neonatalnoj hirurgiji i neophodna je kad period gladovanja traje duže od pet dana. Peroralna ishrana je najbolji način, a grudi su najbolji izvor hrane za ishranu novorođenčeta. Potrebe novorođenčeta su 100-200 cal/kg/24h za normalan rast i razvoj. Ove potrebe se povećavaju u toku stresa, rashlađivanja, infekcije, operacije i traume. Minimalne dnevne potrebe su 2-3 gr/kg proteina, 10-15 gr/kg ugljenih hidrata i mala količina esecijalnih masnih kiselina.

3. Metabolizam i imunitet 

Handling of the breakdown products of hemoglobin is also a difficult task for the premature infant. The ability of the immature liver to conjugate bilirubin is reduced, the life span of the red blood cell is short, and the bilirubin load presented to the circulation via the enterohepatic route is increased. "Physiologic" jaundice is, therefore, higher in the preterm infant and persists for a longer period. Unfortunately, the immature brain has an increased susceptibility to the neurotoxic effects of high levels of unconjugated bilirubin, and kernicterus can develop in the preterm baby at a relatively low level of bilirubin. Other problems affecting the baby include the rapid development of hypoglycemia (35 mg%), hypocalcemia and hypothermia. Newborns have a poorly developed gluconeogenesis system, and depends on glycolysis from liver glycogen stores (depleted 2-3 hrs after birth) and enteral nutrition. Immature infants can develop hyperglycemia from reduced insulin response to glucose causing intraventricular hemorrhage and glycosuria. The preterm and surgical neonate is more prone to hypocalcemia due to reduced stores, renal immaturity, and relative hypoparathyroidism (high fetal calcium levels). Symptoms are jitteriness and seizures with increase muscle tone. Calcium maintenance is 50 mg/kg/day. Human beings are homeothermic organisms because of thermoregulation. This equilibrium is maintained by a delicate balance between heat produced and heal lost. Heat production mechanisms are: voluntary muscle activity increasing metabolic demands, involuntary muscle activity (shivering) and non-shivering (metabolizing brown fat). Heat loss occurs from heat flow from center of the body to the surface and from the surface to the environment by evaporation, conduction, convection and radiation. There is an association between hypothermia and mortality in the NICU's. The surgical neonate is prone to hypothermia. Infant produce heat by increasing metabolic activity and using brown fat. Below the 35°C the newborn experiences lassitude, depressed respiration, bradycardia, metabolic acidosis, hypoglycemia, hyperkalemia, elevated BUN and oliguria (neonatal cold injury syndrome). Factors that precipitate further these problems are: prematurity, prolonged surgery, and eviscerated bowel (gastroschisis). Practical considerations to maintain temperature control are the use of humidified and heated inhalant gases during anesthesia, and during all NICU procedures use radiant heater with skin thermistor-activated servo-control mechanism. The newborn's host defenses against infection are generally sufficient to meet the challenge of most moderate bacterial insults, but may not be able to meet a major insult. Total complement activity is 50% of adults levels. C3,C4,C5 complex, factor B, and properdin concentration are also low in comparison to the adult. IgM, since it does not pass the placenta, is absent.

4. Tipovi novorođenčadi

a) Novorođenče rođeno u terminu (the full-term, full-size infant) sa gestacionom starošću od 38 nedelja i telesnom masom iznad 2500 grama (TAGA) - koje je imalo odgovarajuću intrauterinu ishranu, prošlo kroz celokupan fetalni razvoj i čije se fiziološke funkcije mogu predvideti.

b) Novorođenče rođeno pre termina (the preterm infant) sa gestacionom starošću ispod  38 nedelja a telesnom masom odgovarajućom za starost (PreTAGA);

c) Novorođenče malo za gestacionu starost (the small-for-gestational-age infant) (SGA) sa gestacionom starošću iznad 38 nedelja i telesnom masom ispod 2500 grama - i čiji je intrauterini razvoj rettardiran.

d) Kombinacija (b) i (c), novorođenče rođeno pre termina koje je takođe malo za gestacionu starost.

The characteristic that most significantly affects the survival of the preterm infant is the immature state of the respiratory system. Between 27 and 28 weeks of gestation (900-1000 grams), anatomic lung development has progressed to the extent that extrauterine survival is possible. It is only after 30 to 32 weeks of gestation that true alveoli are present. Once there is adequate lung tissue, the critical factor that decides extrauterine adaptation and survival of the preterm infant is his capabilities to produce the phospholipid-rich material, surfactant that lines the respiratory epithelium.

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