pediatric surgery seminar

1. Surgical physiology of
infants and children
By - Yoseph Mitiku (GSR - 2)
Moderator - Dr. Andinet Dessalegn (Consultant General and Pediatric
surgeon)
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2. Outline
 Introduction
 Fluid and electrolyte balance
 Acid-base balance
 Thermoregulation
 Nutritional support in the pediatric surgical patient
 Blood volume and blood replacment
 References
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3. Introduction
• Newborn infants who undergo
surgery are not just small adults.
• Neonates can be classified as
premature, term, or postmature
according to gestational age.
• Birth weight and gestational age are
strong indicators of mortality.
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4. Fluid and electrolyte balance
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5. Cont...
• Adequate systemic perfusion depends on adequate intravascular
volume, as well as many other factors.
• However infants and children can compensate for relatively large
losses in circulating volume.
• Signs and symptoms of shock may be difficult to detect if a child has
lost less than 25% of the circulating volume.
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6. Neonatal fluid balance
• Pulmonary fluid production decreases while existing fluid is
reabsorbed, and efflux through the trachea.
• During labor, arterial pressure increases and causes shifts in plasma
from the vascular compartment and a slight rise in hematocrit values.
• 5% to 10% of weight loss in the term neonate and 10% to 20% in the
premature newborn.
• By the fifth day postpartum, urinary excretion begins to reflect the
fluid status of the infant.
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7. Renal function
• The kidneys in neonates have small immature glomeruli and for this
reason the GFR is reduced (about 30 mL/min/1.73m2 at birth to 100
mL/min/1.73m2 at 9months).
Urine is concentrated in the loop of Henle using a countercurrent
system dependent on the osmolality of the medullary interstitium.
• Three phases of fluid and electrolyte homeostasis occur - prediuretic,
diuretic and postdiuretic phases
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8. Cont...
There is Inability to concentrate the urine in the proximal and distal
convoluted tubules of the kidney.
The serum osmolality is generally governed by ADH synthesis.
• Serum osmolality 275 mOsm - 280 mOsm
• The other major hormone involved in regulating sodium homeostasis
is ANP.
• The fractional excretion of sodium (FeNa) is a useful tool in
measuring sodium homeostasis and renal tubular function.
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9. Cont...
• Most potassium excretion is also regulated by the kidney.
• It is imperative that all the aforementioned features of the neonatal
kidney be kept in mind when resuscitating the neonate after operation.
•The immaturity of the neonatal kidney may complicates rehydration
strategies and may result in electrolyte abnormalities.
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10. Insensible water losses
• Evaporative losses from the respiratory epithelium and through the
skin, known as insensible losses.
• In the premature infant, the ratio of total body surface area to weight is
greater, thus greater percentage of insensible losses.
• It can take more than 4 weeks before a fully functional barrier is
attained in the preterm infant.
• Provide neutral ambient temperature and appropriate moisture in the
inspired air.
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11. Other surgical losses
• Stoma output and third-space losses
• Cc for cc replacement volume for stomas that produce greater than 40
cc per kg per day.
• A useful estimate for intraoperative deficit due to third spacing is 6 to
10 cc per kg per hour for intraabdominal procedures.
• Replacement is best accomplished with lactated Ringer's solution.
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12. Cont...
• It is difficult to estimate third-space losses in the postoperative period.
• Thus it is imperative to monitor urine output and overall perfusion
status frequently.
• Generally use D5 1/2 normal saline at one and a half times
maintenance for major abdomen operations.
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13. Fluid maintenance
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14. Acid-base balance
• Normal extracellular pH is maintained at 7.35 to 7.45.
• When the cause is respiratory—PaCO2 >45 mm Hg (acidosis) or <35
mm Hg (alkalosis)
• In case of metabolic causes— bicarbonate <21 mmol/L (acidosis) or
>26 mmol/L (alkalosis).
• Disorders are termed simple if there is only one primary disorder, or
mixed if two or more are involved.
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15. Cont...
• Treatment should be directed toward any underlying cause.
• The slow infusion of buffers should be used as therapeutic adjuncts.
• The amount of sodium bicarbonate required can be calculated using
the following equation:
 NaHCO3 (mmol) = 1/4base excess x body weight (kg)
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16. Cont...
• Acid-base balance is maintained by a complex system achieved by
intracellular and extracellular buffer systems, respiration, and renal
function.
• Respiratory compensation occurs through the carbonic anhydrase
system.
• Renal compensation is the most important mechanism available to the
neonate for acid-base balance.
Proximal tubules reabsorp 85% to 90% of filtered bicarbonate but
function less efficiently in the premature neonate.
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17. Cont...
Metabolic acidosis
 Non-anion gap acidosis
• Profuse diarrhea
• High-output fistulae or stomas
• Diversion of the urinary stream
• Renal tubular acidosis
 Anion-gap acidosis
• ketoacids
• Lactic acidosis
• Ingestion of toxic materials
Metabolic alkalosis
• Persistent emesis
• Diuretics
• Adrenal adenomas or hyperplasia
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18. Cont...
Respiratory acidosis
• Pneumonia
• Airway obstruction
• Bronchiolitis
• Cystic fibrosis
• Narcotic overdose
• Overfeeding
Respiratory alkalosis
• Anxiety
• Fever
• Sepsis
• Primary CNS abnormalities, and
• Mechanical ventilation
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19. Thermoregulation
• After delivery, there is increase heat loss from the newborn.
• Neonates are homeotherms.
 They have a small mass and relatively large surface area.
 They possess relatively little insulating tissue such as fat and hair.
They are unable to make significant behavioral alterations.
 They have limited energy reserves.
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20. Cont...
• The thermoneutral zone is of critical importance to infants.
• The generation of heat is accomplished with nonshivering
thermogenesis.
• The organ system responsible for carrying out nonshivering
thermogenesis is the brown fat or brown adipose tissue.
• In general, adipose tissue is generated during the last 8 weeks of
gestation, and consists of white fat and brown fat.
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21. Cont...
• During periods of cold stress, there is a redistribution of blood flow to
the brown fat.
• The control center for this process is located in the hypothalamus and
is mediated by the sympathetic nervous system.
• Thyroid hormone also plays an important role in the initiation of
thermogenesis.
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22. Cont...
• Respiratory drive may also be influenced by thermogenesis and
thermoregulation.
• Once brown adipose stores are depleted or completely replaced by
white fat, the infant transitions to shivering thermogenesis for the
regulation of body temperature.
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23. Nutritional support in the pediatric surgical patient
• Growth and development affect the goals and objectives of nutritional
support.
• The preterm infant’s growth pattern is quite distinct from term infants.
• An important question is how long the gastrointestinal tract will be
dysfunctional after major surgery.
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24. Nutritional assessment
• Can be divided into subjective and objective components.
• Two basic tools are available: the Mini Nutrition Assessment and the
Subjective Global Assessment (SGA).
• Biochemical measurment of nutritional status - Serum albumin,
prealbumin binding protein, and retinol-binding protein
• Use of indirect calorimetry
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25. Nutritional requirements
• Well-balanced diet is as follows: protein
- 15%; fat - 35%; and carbohydrate -
50%
• The daily consumption of fluid by
healthy infants - 10% to 15% of their
body weight.
• Newborn infants have relatively limited
glycogen reserves (34 g), most of which
reside in the liver - risk of
hypoglycemia
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26. Enteral nutrition
Indications
• Premature infants less than 32 to
34 weeks
• Resolution of the postoperative
ileus
• Once oral feeds are clinically
possible
Delivery modalities
• Nasogastric and nasojejunal
feedings
• Gastrostomy tube
• Jejunal tubes
Complications
• Lactose intolerance
• Suboptimal feeding
• Aspiration
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27. Cont...
•For term infants, intermittent enteral feeding can be initiated at 2 to 5
mL/kg every 3 to 4 hours and advanced in increments of 2 to 5 mL/kg.
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28. Parenteral nutrition
• Indications
 Gastrointestinal disorders
 Congenital anomalies
 Radiation, chemotherapy and ARDS in premature infants
 Very-low-birth-weight
 Periods of starvation
• Peripheral VS central venous access
• Addatives of parentral nutrition - heparine, h2 blockers, regular
insulin, iron dextran
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29. Monitoring of laboratory values
• Dextrose solution initiated at 10% to
12.5%, and slowly increased on a daily
basis to between 20% and 25%.
• PN should be initiated as a continuous
infusion spanning 24 hours.
• For patients receiving long-term PN,
delivery may be given spanning a
shortened period of time (e.g., 16
hours).
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30. Complications of parenteral nutrition
 Metabolic Complications
• Hyperglycemia
• Hypoglycemia
• Hypertriglyceridemia
• Metabolic Acidosis
• Electrolyte Disturbances
• Metabolic Bone Disease
 Hepatobiliary Complications
• cholestasis, steatosis, and
cholelithiasis.
Infectious Complications
Complications from Overfeeding
Technical Complications
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31. Blood volume and blood replacment
• Blood volume can be estimated as 106 mL/kg in preterm infants, 90
mL/kg in neonates, 80 mL/kg in infants and children and about 65
mL/kg in adults.
• The decision to transfuse RBCs should be based on several factors.
• Fresh whole blood (less than 48 hours in storage)
• 10 to 15 mL/kg is transfused over 1 to 2 hours.
• Massive transfusions that involve replacing an amount of blood equal
to the patient’s blood volume in 24 hours.
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32. Choice of red blood cell products
• Fresh whole blood - massive transfusion and exchange transfusion
• Packed RBCs - moderate acute blood loss or chronic anemia
• Washed RBCs - nonhemolytic transfusion reactions
• Frozen deglycerolized RBCs - chronic transfusions
• Leukocyte-reduced RBCs - less likely to transmit CMV and other
viruses
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33. Transfusion reactions, toxicity, and other
complications
 Citrate toxicity
 Reactions - febrile and nonhemolytic, urticarial and hemolytic
 Transfusing infectious agents - HIV, Hepatitis B and C, CMV, EBV
 Graft-versus-host disease
 ALI
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34. Platelet Transfusion
• Platelet counts less than 10,000/mL is risk for hemorrhage.
• Platelet counts less than 50,000/mL carry a risk for bleeding during
surgical intervention.
• Transfusion of one random donor unit per 10 kg is predicted to
increase the platelet count by 40,000 to 50,000 per uL.
• Single-donor collections are useful for transfusion in patients who
have become alloimmunized to random donor concentrates.
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35. Cont...
• Efficacy of transfusion can be documented by determining platelet
counts just before, 1 hour after, and 24 hours after infusion of platelets.
• The half-life of transfused platelets is 4 days.
• Risks - febrile reaction, allergic transfusion reactions, transmission of
viral infection, bacterial contamination
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36. Transfusion of plasma and plasma derivatives
• The patient with laboratory abnormalities but no serious bleeding or
thrombosis should be treated supportively while rapid correction of the
underlying illness is attempted.
• If the disease is severe
Platelet count of 50,000 with platelet transfusions and
Transfuse with fresh frozen plasma to fibrinogen level at 100 mg per
dL or greater
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37. Cont...
• Cryoprecipitate, which has a higher concentration of fibrinogen, may
also be used.
• Vitamin K-deficiency states can result in low levels of factors II, VII,
IX, and X, as well as of proteins C and S.
• Synthetic vasopressin analogue - hemophilia and VWD
• Factor replacement is reserved for the patient who is actively bleeding
or who is reasonably expected to do so.
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38. Cont...
• Fresh frozen plasma at 10 to 20 mL per kg is generally used for
replacement of factors II, V, X, XI, and low levels of fibrinogen.
• Cryoprecipitate is used for replacement of factor XIII, severe von
Willebrand disease, hypofibrinogenemia, and dysfibrinogenemia.
• Reasonably safe, pure replacement products are available for factors
VII, VIII, and IX.
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39. References
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40. Thank You!!!
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