1. Clinical Chemistry and the Pediatric Patient

2. DEVELOPMENTAL CHANGES FROM NEONATE TO ADULT
When an infant is born, adaptation from intrauterine life to extrauterine life is essential.
Homeostasis in intrauterine life is maintained by maternal and placental means.
Self-maintenance is needed to adapt to extrauterine life.
Adaptation is complicated by prematurity or intrauterine growth retardation.

3. DEVELOPMENTAL CHANGES FROM NEONATE TO ADULT Respiration and Circulation
At birth, the normal infant rapidly adapts by initiating active respiration.
The stimuli for this process include clamping of the umbilicus, cutting off maternal delivery of oxygen, and the baby’s first breath.
Initiation of breathing requires the normal expression of surfactant in the lungs.
Surfactant is necessary for the normal expansion and contraction of alveoli and allows gaseous exchange to take place.

4. DEVELOPMENTAL CHANGES FROM NEONATE TO ADULT Growth
A normal baby delivered at term weighs about 3.2 Kg.
A baby weighing less than 2.5 Kg at term is regarded as small for gestational age, which is usually a result of intrauterine growth retardation.
Premature babies have low birth weight and born before term.
As feeding is initiated, weight gain is 6 g/Kg/d, an infant’s body weight will double in 4-6 months.
Premature babies grow at a slower rate.

5. DEVELOPMENTAL CHANGES FROM NEONATE TO ADULT Organ Development
Most organs are not fully developed at birth.
Glomerular filtration rate (GFR) of the kidney and renal tubular function mature during the first year of life.
Liver function can take 2-3 months to fully mature.
Motor function and visual acuity develop during the first year of life.
A switch from fetal hemoglobin to adult Hb takes place.
This coincides with significant hyperbilirubinemia as fetal hemoglobin is broken down, coincident with immature hepatic pathways of bilirubin metabolism.

6. DEVELOPMENTAL CHANGES FROM NEONATE TO ADULT Organ Development
Bone growth is rapid in the first few years of life and at puberty.
Sexual maturation results in significant endocrine changes, particularly of the hypothalamic-pituitary- gonadal hormone pathway which leads to adult secondary sexual characteristics and eventually to the adult.

7. Problems of Prematurity and Immaturity
Intrauterine development is programmed for a normal week gestation.
Many organs are not fully ready to deal with extrauterine life before this time.
This organ immaturity results in many of the clinical problems that are associated with prematurity, which include:
respiratory distress (lung immaturity),
electrolyte and water imbalance (kidney immaturity), and
excessive jaundice (liver immaturity).

8. PHLEBOTOMY AND CHOICE OF INSTRUMENTATION FOR PEDIATRIC SAMPLES
The small blood volume of small patients dictates both the number of tests that can safely be performed on the patient and the number of times that blood can safely be drawn for repeat analysis.

9. PHLEBOTOMY AND CHOICE OF INSTRUMENTATION FOR PEDIATRIC SAMPLES

10. PHLEBOTOMY AND CHOICE OF INSTRUMENTATION FOR PEDIATRIC SAMPLES
Capillary samples are often collected when suitable veins are not available.
usually contaminated, at least to some extent, by interstitial fluid and tissue debris.
The concentration of protein (and protein-bound constituents) is approximately three times lower in interstitial fluid than in plasma.
Excessive squeezing or milking of the lancet site can result in both hemolysis and factitious hyperkalemia from tissue fluid leakage.

12. REGULATION OF BLOOD GASES AND pH IN NEONATES AND INFANTS
Lungs and kidneys must be mature for maintenance of blood gas and pH homeostasis (regulation of acid and base metabolism).
At about 24 weeks of gestation, the lungs express two distinct types of cells; type 1 and type 2 pneumocytes.
Type 2 pneumocytes are responsible for the secretion of surfactant, which contains the phospholipids lecithin and sphingomyelin.
Type I alveolar cells are squamous (giving more surface area to each cell) and cover approximately 90–95% of the alveolar surface. Type I cells are involved in the process of gas exchange between the alveoli and blood.

13. REGULATION OF BLOOD GASES AND pH IN NEONATES AND INFANTS
Surfactant is required for the lungs to expand and the transfer of blood gases following delivery.
Oxygen crosses into the circulation and carbon dioxide is removed and expired.
Immaturity of the surfactant system as a result of prematurity or IGR results in respiratory distress syndrome (RDS).
In RDS, there is failure to excrete carbon dioxide then acidosis develops, as oxygen levels are low, additional oxygen is required for the baby

14. REGULATION OF BLOOD GASES AND pH IN NEONATES AND INFANTS
The relative amounts of lecithin and sphingomyelin are critical for normal surfactant function.
The measurement of amniotic fluid L/S ratio has been used for many years to predict fetal lung maturity.
A ratio less than 1.5 is considered indicative of surfactant deficiency.
The fetal fibronectin test is designed to determine the likelihood of premature delivery and risk of fetal maturity, this protein is found in maternal cervical fluid toward term
Testing will produce a negative or a positive result. When the fFN test is positive, the result is an excellent predictor of preterm labor risk.
Fetal fibronectin "leaks" into the vagina if a preterm delivery is likely to occur and can be measured in a screening test.[2]
Testing will produce a negative or a positive result. When the fFN test is positive, the result is an excellent predictor of preterm labor risk. A negative result means that there is little possibility of preterm labour within the next 7 to 10 days, and the test can be repeated weekly for women who remain at high risk.

15. REGULATION OF ELECTROLYTES AND WATER: RENAL FUNCTION
From the 35th week of gestation, the fetal kidneys develop rapidly in preparation for extrauterine life.
The kidneys, critical organs for the maintenance of electrolyte and water homeostasis, control the rate of salt and water loss and retention.
At term, neither the glomerular nor the renal tubules function at the normal rate.
The GFR is about 25% of the rate seen in older children and does not reach full potential until age 2 years
Tubular function also develops at a similar rate.

16. REGULATION OF ELECTROLYTES AND WATER: RENAL FUNCTION

17. REGULATION OF ELECTROLYTES AND WATER: RENAL FUNCTION
The maximal concentrating power of the kidney is only about 78% of that of the adult kidney at this time, the tubular response to antidiuretic hormone appears to be normal.
The kidneys maintain water loss and retention.
However, in the newborn period, insensible water loss through the skin is also an important cause of water and electrolyte imbalance.
Increased water loss also occurs via respiration in children with RDS.
Up to one third of insensible water loss may occur through this route.
The ratio of body surface area to volume is about three times greater for an infant than for an adult

18. Disorders Affecting Electrolytes and Water Balance
Both hypernatremia (Na>145mmol/L) and hyponatremia (Na<130mmol/L) can have dire outcomes, with high risk of seizures.
This is a result of the shift of water out of or into brain cells, with concurrent shrinkage or expansion of these cells.

19. Hormone production is extremely low in this form of the disorder
Hormone production is extremely low in this form of the disorder. Affected individuals lose large amounts of sodium in their urine
Salt lost through sweat in CF causes an imbalance in sodium levels in the blood and tissues.

20. Disorders Affecting Electrolytes and Water Balance
Clinical evaluation and measurement of other components, including hematocrit, serum albumin, creatinine and blood urea nitrogen can be used to confirm diagnosis.
Treatment of electrolyte and water loss is directed at replacing the loss to regain normal Physiologic levels.
Care must be taken to avoid too rapid replacement, particularly with hypertonic dehydration.
Quick replacement may result in rapid expansion of neuronal cell volume ending in seizures.