- Pediatric patients have unique anatomic and physiologic features compared to adults that impact surgical care. These include differences in the airway, respiratory, cardiovascular, gastrointestinal, and other body systems. - Younger pediatric patients (neonates and infants) have particularly significant differences compared to older children and adults, such as an anatomically higher and smaller airway, immature organ systems, and distinct circulatory transitions at birth. - Understanding these developmental variations is essential for perioperative management of pediatric surgical patients to optimize outcomes and minimize risks related to their smaller sizes and developing physiology.

1. Peculiar anatomic and
physiologic features in
pediatric surgical patients

2. Outline
• Introduction
• Airway and Respiratory system
• Cardiovascular system
• Gastrointestinal system
• Genitourinary system
• Nervous system
• Musculoskeletal system
• Skin and Subcutaneous system
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3. Introduction
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Children are not little adults,
but they are little people.

4. Introduction
• The newborn infant is both physically and physiologically distinct from
the adult patient in several respects.
• These physiologic parameters are often the primary components that
dictate the preoperative and postoperative management.
• The smaller size, immature organ systems, and differing volume
capacities present unique challenges toward perioperative management.
• Treatment outcomes, both successful and unsuccessful, last a lifetime
and many may impact on future growth and development.
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5. Introduction
• Pediatric patients vary considerably and include the
following groups:
Neonates – a baby within 4 weeks of age from delivery
Infants – a child of up to 12 months of age
Child – 1 to 12 years
Adolescent – 13 to 16/18 years
• The physiology of the neonate, infant, child, and adolescent
differ significantly from each other and from the adult.
• Anatomic differences are more pronounced in younger
children (infant through preschool age); they begin to
disappear as the children age into school age and
adolescence.
• By the time they are 18, most of the changes are complete.
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6. Airway and Respiratory system
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7. INITIATION OF BREATHING
• Lung remains collapsed and filled with liquids in prenatal life.
• The first gasp of breath generates high negative inspiratory pressure
to initiate lung expansion
• The active pressure gradient thus developed shifts the lung fluids into
the interstitial tissue from where lymphatics and pulmonary
circulation gradually remove it.

8. REGULATION OF BREATHING
• Respiratory control is immature at birth and takes several weeks to months to
mature
• Response to hypoxia in preterm and neonates is biphasic:
# Initial hyperventilation
# Prolonged apnea
• Neonate’s ventilatory response to hypoxia and hypercarbia is impaired.
• Infants have an irregular and periodical breathing pattern.
• Prolonged apnoea may occur and is common in the first 12 hours
postoperatively (usually within 2 hours) especially in preterm infants.
• Prophylactic intravenous caffeine (10 mg/kg) or theophylline (8 mg/kg) can
be used intraoperatively to reduce the risk of postoperative prolonged apnoea.
• Afferent laryngeal stimulation during laryngoscopy or over inflation of lungs
(Herring–Breuer inflation reflex) also contributes to apnoea in neonates

9. ANATOMY OF THE UPPER AND LOWER
AIRWAY
• Children have large head and a big occiput compared to their body
size until around six years of age.
• Neonates have smaller oral cavity and a large tongue with a flat
dorsal surface and limited lateral mobility.
• Epiglottis is long omega-shaped horizontally positioned high in the
pharynx very near to the soft palate obscuring the glottis view on
direct laryngoscopy.
• Infants are obligate nasal breathers till age of 5 months
• The larynx is anterior and cephalad (C3-4 vs C6).
• The cricoid ring is functionally the narrowest part of the neonatal
airway.

10. 10

11. Unique respiratory anatomic differences
Upper airway features
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12. PHYSIOLOGY OF THE LUNG AND THORAX
• The alveoli are thick walled at birth.
• There is only 10% of the total number of alveoli found in adults.
• The alveoli clusters develop over the first 8 years of life.

13. THORAX cont’d
• The neonatal thorax has a rounder circumference and is very
compliant and susceptible to collapse during negative intrathoracic
pressure.
• The work of breathing is thus much greater in the child.
• intercostal muscles are poorly developed and less effective as the
accessory muscles of respiration.
• Ribs are horizontally aligned from the vertebral column and cannot
increase the cross-sectional area of the thorax during inspiration
• inspiration occurs almost entirely because of diaphragmatic descent
• However, the diaphragm has less type-1 muscle fibres and is prone to
early fatigue.
• Bulky abdominal organs or a stomach filled with gases from poor bag
mask ventilation can impinge on the contents of the chest and splint
the diaphragm, reducing the ability to ventilate adequately.

14. Fig 3: composition of intercostal muscles and diaphragm
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15. Cardiovascular system

16. The Fetal to Neonatal Circulatory Transition
The Fetal Circulation
• In the fetal circulation, the right and left ventricles exist in a parallel
circuit, as opposed to the series circuit of a newborn or adult .
• Because the lungs do not provide gas exchange, the pulmonary vessels
are vasoconstricted, diverting blood away from the pulmonary
circulation.
• Three cardiovascular structures unique to the fetus are important for
maintaining this parallel circulation:
-The ductus venosus,
-Foramen ovale,
-and Ductus arteriosus.
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17. Fetal circulation
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18. Transition during birth
• Several changes occur in the circulatory system at birth.
• Some of these changes are virtually instantaneous with the first breath,
whereas others develop over a period of hours or weeks.
• pulmonary vascular resistance is markedly decreased
# due to increased PaO2 and pulmonary vascular dilatation
# Is decreased to 50% than that of the systemic circulation at 3rd day
of life and to 15% by 3rd month of life
• closure of the ductus arteriosus- functional closure is usually complete
by 10-15 hr
• Closure of foramen ovale- usually functionally closed by the 3rd mo of
life
• Ductus venosus- closes in the first week
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19. Con’t
• Significant differences between the neonatal circulation and that of
older infants include:
(1) right-to-left or left-to-right shunting may persist across the patent
foramen ovale
(2) in the presence of cardiopulmonary disease, PDA may allow left-to-
right, right-to-left, or bidirectional shunting
(3) the neonatal pulmonary vasculature constricts more vigorously in
response to hypoxemia, hypercapnia, and acidosis
(4) the wall thickness and muscle mass of the neonatal left and right
ventricles are almost equal
(5) newborn infants at rest have relatively high oxygen consumption,
which is associated with relatively high cardiac output (~350
mL/kg/min).
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20. Cardiac physiology continued…..
• Cardiac stroke volume is relatively fixed by a noncompliant and
immature left ventricle in neonates and infants, thus, the Starling
response is limited
• The cardiac output is therefore very sensitive to changes in heart rate
• Especially in the first 3 months of life, the parasympathetic nervous
system influence on the heart is more mature than the sympathetic
system
• Bradycardia therefore is frequent in newborns and young infants in
response to several noxious and autonomic stimuli such as hypoxia
• The infant cardiovascular system displays a blunted response to
exogenous catecholamines because of High basal endogenous
catecholamines
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21. Summary of cardiovascular physiology
features in pediatric population
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22. Heart
• At birth the infant heart lies midway between the top of the head
and the buttocks.
• The long axis of the heart is directed horizontally in the 4th
intercostal space with its apex lateral to the MCL until 4 years of
age
• Heart gradually moves downward, due to the elongation of the
thorax comes to lie at the fifth intercostal space with its apex
inside MCL
• At birth the right ventricle has been working against systemic
pressure and the muscular bulk is therefore only 25% smaller than
the left.
• The left ventricle rapidly grows and its muscular bulk becomes
about twice of the right at 2 years of age.
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23. Gastrointestinal system
Oral cavity and esophagus
• The large tongue is short and broad, lying entirely within the oral
cavity.
• It begins to descend into the neck during the first year of life, the
posterior third forming part of the anterior wall of the pharynx by
age 4 years.
• During suckling the high position of the larynx is elevated further
so that the fluid passes directly into the pharynx.
• This enables the infant to feed and breathe at the same time.
• At birth the esophagus is approximately 8 - 10 cm long and
extends from the cricoid cartilage to the gastric cardia (C4 to T9)
and possesses the same constrictions as that of the adult.
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24. Abdominal wall and cavity
• The distance between the costal margin and iliac crest is
proportionately greater in the neonate.
• The anterior abdominal wall bulges forwards in the neonate to
accommodate the bladder, uterus and ovaries, which are pelvic in the
adult.
• Liver and spleen less protected by lower ribcage.
• In babies the abdomen is broader than it is long and open procedures
are generally made through transverse supraumbilical incisions.
• The peritoneal cavity is shallow antero-posteriorly because there is
no lumbar lordosis and the paravertebral gutters are poorly
developed.
• The inguinal canal in the newborn is short, the superficial inguinal
ring almost overlies the deep ring.
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25. Abdominal organs
• The stomach is very small at birth and lies under the liver. The
stomach distends fivefold in the first few days once swallowing
and feeds commence.
• Acid secretion begins during the first day of life. The stomach’s
anterior surface is nearly entirely covered by the left lobe of the
liver, only a small portion of the greater curvature being visible
below.
• Its size increases rapidly from 30 ml in a term baby to 100 ml by
the fourth week.
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26. Cont.…
• The small intestine has fewer and less marked circular folds than
are seen in adults
• The small intestine lies in a more transverse orientation than in
the adult due to the abdominal bladder.
• The mesentery contains very little fat.
• The large intestine is approximately 60 cm long and has a very
poorly developed muscularis.
• The ascending and descending colon are relatively short and the
transverse colon relatively longer.
• The haustra appear over the first 6 months.
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27. Cont.…
• The liver is relatively large in the neonate being 4% of body weight
compared to the adult where it constitutes only 2.5 - 3%.
• The right lobe extends below the costal margin anteriorly and lies
close to the iliac crest posteriorly.
• The left lobe can extend to the lateral wall of the abdomen,
overlying the stomach and the spleen.
• The gallbladder does not extend to the edge of the liver and has a
small peritoneal surface and the majority are embedded within
the liver until 2nd year of life.
• The pancreas has a relatively large head.
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28. 28

29. Genitourinary system
• The kidneys are lobulated at birth, have wide-calibre ureters and
lie under relatively large adrenal glands.
• The apex of the unfilled bladder lies midway between the pubis
and the umbilicus and, when filled, may reach the umbilicus.
• Only the posterior surface is covered with peritoneum and,
although considered intra-abdominal, about half lies within the
pelvic cavity.
• It does not truly become pelvic until about the sixth year of life.
• The top of the bladder is continuous with the urachal remnant
reaching the umbilicus.
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30. Cont..
• The ovaries are much larger than the testes at birth and weigh
approximately 0.3 g.
• They lie in the iliac fossae at birth and descend into their pelvic
position in early childhood.
• All the primary oocytes are present after the first trimester. Of the
1 million or so remaining at birth, only about 400 will actually
ovulate.
• The uterus is influenced by the maternal hormones during fetal
development and so usually decreases by about a third in size
after birth until puberty is reached.
• At birth it is approximately 2.5 - 5 cm long and 2 cm wide, the
uterine cervix accounting for two-thirds of this.
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31. Cont..
• The testes are situated at the deep ring by the sixth month of
gestation and 98% in term babies and 80% in preterm babies will
have descended into the scrotum by birth.
• The processus vaginalis is collapsed at birth, but not necessarily
obliterated.
• Eighty percent are obliterated 10 - 20 days after birth.
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32. 32

33. 33

34. Nervous system
• At term, the neonatal brain weighs between 300 and 400 g,
accounting for about 10% of body weight.
• Brain growth is especially rapid during the first year, when it
reaches 75% of its adult volume. ( 83 % by 2 years)
• The number of neurons is already established at birth and brain
growth is due to an increase in size of nerve cell bodies,
development of neuronal connections, proliferation of neuroglia
and blood vessels, and myelination of axons.
• Myelination is at its peak in the first six months of life but
continues until maturity.
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35. Cont…
• Children have immature blood-brain barriers and enhanced
central nervous system (CNS) receptivity.
• Thinner subarachnoid space.
• Brain demands greater amounts of oxygen and glucose.
• The termination of the spinal cord in the neonate may reach as
low as L3 whereas it is usually around the lower border of L1 in
the adult.
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36. Musculoskeletal system
 At birth the facial portion of the head is smaller than the cranium
having a face-to-cranium ratio of 1:8 (adult ratio of 1:2.5).
 The head of a full-term newborn infant accounts for about 25% of
its body length and 20% of its body surface area.
 The large head-small face pattern is noticeable in children even up
to ages 7 and 8.
 Vertical growth of the infant face occurs in spurts as related to
both respiratory needs and tooth eruption.
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37. Cont…
37

38. Cont…
• Infant head shape also differs significantly from that of the adult.
• At birth the circumference of the head is about 37 cm.
• It increases by 17% ( 2cm/mo )during the first 3 months of life,
and by 25% at 6 months of age.
• There is only a 1cm/yr increase in head circumference from the
end of the 4th year to the 20th year.
• The maxillary and ethmoid sinuses are present at birth but the
sphenoid sinus is poorly developed and the frontal sinuses are
absent.
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39. Cont…
• The vertebral column in the neonate has no fixed curvatures other
than a mild sacral curve.
• After birth, the thoracic curvature develops first and then, as the
infant learns to control its head, sit, stand and walk, curvatures in
the lumbar and cervical spine develop.
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40. Cont…
• These cervical vertebrae are mainly cartilaginous in the infant,
with complete replacement of this cartilage by bone occurring
slowly.
• Articular facets are shallow; neck ligaments, as elsewhere in the
body, are weaker than in adults.
• Neck muscle strength increases with age.
• The disproportionately large head, the weak cervical spine
musculature, and laxity contribute to a high incidence of injury to
the upper cervical spine as compared to the lower cervical spine
area.
40

41. Cont.…
• The lower limb muscles in the newborn are relatively
underdeveloped and the gluteal muscle mass is small.
• The thighs tend to be abducted and flexed, the knees flexed,
and the foot dorsiflexed and inverted.
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42. Psychology
•Infants less than 6 months of age are not usually
upset by separation from their parents
•Children up to 4 years of age are upset by the
separation from their parents
•School age children are more upset by the surgical
procedure, its mutilating effects and the possibility
of pain.
•Parental anxiety is readily perceived and reacted on
by the child.

43. Skin and subcutaneous tissue
• Body fat is laid down in the fetus from about 34 weeks of gestation
and, with appropriate intrauterine nutrition, increases until term.
• Brown fat is a modified form of adipose tissue concentrated at the
back of the neck, in the interscapular region, and in pararenal
areas.
• At birth, breast tissue is similarly developed in girls and boys.
• It may appear prominent due to the influence of maternal
hormones.
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44. Cont.…
• Children have a proportionately larger body surface area (BSA)
than adults do.
• Children are at greater risk of excessive loss of heat and fluids.
• Neonatal skin is relatively thin but the ability to see peripheral
veins is very dependent on the thickness of the subcutaneous
tissues.
• Their epidermis is thinner and under-keratinized, compared with
adults.
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45. THERMOREGULATION
• Newborns have difficulty maintaining body temperature due to their
relatively large surface area, poor thermal regulation, and small mass
to act as a heat sink.
• Heat loss may occur as a result of:
(1) evaporation (wet newborn);
(2) conduction (skin contact with cool surface);
(3) convection (air currents blowing over newborn)&
(4) radiation (non-contact loss of heat to cooler surface, which is the most
difficult factor to control).

46. • Low body temperature causes respiratory depression, acidosis,
decreased cardiac output, increases the duration of action of drugs,
decreases platelet function and increases the risk of infection.
• In the operating room, special care must be exercised to maintain the
neonate’s body temperature in the normal range
• Brown adipose tissue (BAT) metabolism is required for non-
shivering thermogenesis.

47. summary
Respiratory system
• Anatomical variations
1. Small number of alveoli
2. Cartilaginous rib cage
3. Weak intercostal and diaphragmatic muscular
4. Horizontally placed ribs
5. Large head and tongue
6. Narrow airway passages
7. Anterior and cephalad larynx
8. Long epiglottis
9. Short neck and trachea
10. Prominent adenoids and tonsils
11. Narrow cricoid cartilage

48. Respiratory system
• Physiological variations
1. Decreased lung compliance
2. Increased chest wall compliance
3. Higher closing capacity than FRC
4. Less efficient ventilation
5. Increased work of breathing
6. Increased respiratory rate
7. Underdeveloped hypoxic hypercapnia ventilator drive
8. Obligate nasal breathing until about 5 months of age
9. Decreased 02 reserve and higher rate of O2 consumption so
predispose to hypoxia and atelectasis

49. Cardiovascular system
• Anatomical variations
1. Non compliant poorly developed left ventricle
2. Immature sympathetic nervous system and baroreceptor reflexes
3. Low catecholamine stores
4. Residual fetal circulation
5. Cardiac ca stores are reduced because of immaturity of
sarcoplasmic reticulum

50. Cardiovascular system
• Physiological variations
1. Almost fixed stroke volume, CO is very much dependent on HR
2. Blunted response to exogenous catecholamines
3. Limited ability to cope with hemodynamic stress
4. More sensitive to ca channel blocking properties of volatile
anaesthetics and opioid induced bradycardia
5. Hallmark of intraventricular fluid depletion is hypotensive and
without tachycardia

51. Renal and GI functions
• Anatomical and Physiological variations
1. GFR is markedly diminished in neonates and preterm infants
2. Near complete maturation of GF and tubular function occurs 20
weeks after birth
3. Complete maturation of renal functions occurs by about 2 years of
age
4. Premature neonates possesses multiple renal defect e.g
decreased CrCL

52. Renal and GI functions
• Anatomical and Physiological variations…
1. Impaired hepatic drug metabolizing activity due to immature
enzyme systems
2. Minimal hepatic glycogen storage in neonates esp premature, SGA
and born to diabetic mothers
3. Lower plasm level of albumin and other proteins necessary for
binding drugs
4. No proper coordination of swallowing and respiration until 4 to 5
months of age so high chances of GERD

53. Metabolism and temperature regulation
• Anatomical and Physiological variations
1. Increased surface area /weight ratio
2. Thin skin, low fat content, higher surface area allow greater heat
loss
3. Major mechanism for heat production in neonates are non
shivering thermogenesis by metabolism of brown fat
4. Metabolism of brown fat is severely limited in premature infants
and sick neonates.

54. Central nervous system
• Anatomical variations
1. Incomplete myelination of neurons
2. BBB is not fully developed
3. Lower termination of spinal cord
4. Increased volume of CSF
5. Open cranial sutures
6. Poor myelination of nerves
7. Deficient baroreceptors

55. References
• Coran textbook of Pediatrics Surgery, 7th edition
• Barash Clinical Anesthesiology, 6th edition
• Ashcraft’s Pediatric Surgery 2010
• International Journal of Scientific Research and Management
(IJSRM)

56. Thank you