The various anatomical & physiological differences affecting practice of pediatric anesthesia

1. APPLIED ANATOMY AND
PHYSIOLOGY FOR
PAEDIATRIC
ANAESTHESIA
Dr. Shailendra.V.L.
Specialist in Anesthesia
Al Bukeriya general hospital

2. Children are not MINI
adults

3. Children are different
• Children are different from adults in various
aspects
• Body weight
• Airway
• Drug behavior
• Fluid requirements
• Blood loss
• Thermo-regulation
• Respiratory system
• Cardio-vascular system
• Renal system etc.,

6. • Narrowest at
cricoid rather
than vocal cords
• Tube may be
small enough to
pass through
cords but not
cricoid
• Larynx is funnel
shaped, so
secretions
accumulate in
retropharangeal
space

7. RESPIRATORY SYSTEM
• The airway is funnel shaped & narrowest at level of
cricoid cartilage
– Epithelium loosely bound to underlying tissue
– Trauma to airway results in edema
– 1 mm of edema narrow baby’s airway by 60%
• Neonates – Obligatory nose breathers
– Narrow nasal passage  easily blocked by
secretions

8. RESPIRATORY SYSTEM
• A leak around endotracheal tube is preferred
• Prevents post extubation edema/stridor
• Neonates & infants have limited respiratory
reserve
• Ventilation mainly diaphragmatic
• Bulky abdominal organs limits movement

9. CARDIOVASCULAR
SYSTEM• In neonates:
–Myocardium less contractile
–Limits the size of stroke volume
–Cardiac output therefore rate dependent
–Ventricles less compliant
–Vagal sympathetic tone high = prone for
bradycardia
–Prophylactically atropine is given IV 0.01
mg/kg
–Diluted atropine ready

10. Infant kidneys : Immature at birth:
•↓ GFR/ Renal blood flow
– Till 2 years hence high renal vascular resistance
•↓ Concentrating capacity
– Urine output is 1-2mls/kg/hour
•↓ Na reabsorption
– Tubular function is immature till 8 months, so infants are
unable to excrete a large sodium load. Dextrose with ½ or ¼
Normal saline used
•↓HCO3/H exchange
RENAL SYSTEM

11. • Dehydration:
– Poorly tolerated
– Premature infants ↑insensible losses = large surface
area relative to weight
– Higher proportion of ECF in children (40% BW as
compared to 20% in adult)
• Conclusion:
– Newborn kidneys has limited capacity to compensate
for Volume EXCESS or Volume DEPLETION
RENAL SYSTEM

12. HEPATIC SYSTEM
• Immature liver function with decreased function of
hepatic enzymes
• Barbiturates & opioids have a longer duration of
action due to slower metabolism

13. GLUCOSE
METABOLISM
• Hypoglycaemia is common in stressed neonate
glucose level should be monitored regularly
• Glycogen stores are located in the liver &
myocardium

14. HAEMATOLOG
Y
• At birth 70-90% of haemoglobin = HbF
– < 3 months, levels ↓ 5% & HbA 95%
– Hb in newbown = 18-20g/dL , HCT ~ 0.6
– 3-6 months: 9-12 g/dl as the increase in circulating volume
increases more rapidly than bone marrow function
• Fetal Haemoglobin:
• less 2,3-DPG
• ODC shifted to right
• Tighter bond with Oxygen

15. HAEMATOLOG
Y
•Vit K dependant clotting factor (II, VII, IX, X) function are deficient in
first few months
•Transfusion recommended when 15% of the circulating volume has
been lost.

16. Temperature
control
• Newborns have a higher ratio of surface area to volume
than adults.
- newborns produce heat slowly and loose quickly
– Large surface area to weight ratio
– Minimal subcutaneous fat
– Poorly developed shivering/sweating/vasoconstriction
– Monitoring temperature is must
– Ambient temperature

17. Temperature
control
• Heat loss during anesthesia due to:
– Conduction/Convection/Evaporation
• Optimal ambient temp to prevent heat loss:
– Premature infant: 34⁰C
– Neonates: 32⁰C

18. • Effect of hypothermia:
– Causes respiratory depression
– Acidosis
– Decreased cardiac output
– Increases duration of action of drugs
– Decrease platelet function
– Increases risk of infection
Temperature
control

19. CENTRAL NERVOUS
SYSTEM
• Blood brain barrier(BBB) poorly formed
– Drugs (barbiturates, opioids, antibiotics, bilirubin cross
BBB = prolong & variable duration of action
• Cerebral vessels in preterm infant are thin walled &
fragile
– Prone to Intra-ventricular haemmorage
– Risk increased with hypoxia, hypercarbia, awake airway
manipulation, rapid bicarbonate administration

20. Practical application in pediatric anesthesia

21. TO SUMMARISE

22. What makes Pediatric Anesthesia
different?
Airway!! Airway!!! Airway!!!
• HYPOXIA is the most common cause of pediatric
perioperative cardiac arrest.
– Infants turn blue fast. upper airway obstruction
during anesthesia (particularly at induction and
emergence)
Laryngospasm is common
• Infants and young children are not small adults.
"one size fits all" does not apply.

23. PRE-OPERATIVE
VISIT• Evaluate:
– Medical conditions of the child
– The needs of planned surgical procedure
– Physiological makeup of patient & family
• Weight -drugs calculated according to weight
• Investigations - Hb: Large expected blood loss, premature infant,
systemic disorder, congenital heart disease
– Electrolytes: Renal or metabolic disease, IV Fluid, dehydration
• Discuss regarding post op pain management:
– Suppository medications Explain to parents
– Nerve blocks for pain relief

24. Induction of anesthesia

25. PRE-OPERATIVE
VISITPRE-OPERATIVE FASTING
Solids 6 Hours
Formula milk 4-6 hours
Breast milk 3-4 hours
Clear fluids 2 hours
PREMEDICATIONS
Sedations Analgesics
Midazolam Paracetamol
Chloral hydrate Codeine
Ketamine Fentanyl

26. BASIC SET UP
TABLE
WARMER
ANESTHESIA
WORKSTATION
PEDIATRIC CIRCUIT
MONITORS
ROUTINE +
TEMPERATURE
AIRWAY ACCESS
EQUIPMENT
SUCTION
IV ACCESS DRUGS IN PROPER
DILUTION

30. Endotracheal tubes
Tube Size:
ID (mm) = Age (years) / 3 + 3.5 (Age < 6 years)
ID (mm) = Age (years) / 4 + 4.5 (Age > 6 years)
Length :
For oral = Age/2 + 12 cm
For nasal = Age/2 + 15 cm
The ideal position for the tip of the tube is mid-trachea
Auscultation on both sides to make sure both lungs are ventilated
Uncuffed tubes used till 8 years to prevent post extubation edema
Leak around the ET tube is deliberate
One size above &below is kept as standby

31. Endotracheal tubes
The rule of thumb is tube should be as large as the small finger of child
Age Weight in kgs Internal
diameter
External
diameter
Premature
infants
< than 2.5 2.5 12
Neonates 2.5 – 5 3 14
6 months 5 - 8 3.5 16
1 year 8 - 10 4 18
2-3 years 10 15 4.5 20
3-5 years 15 - 20 5 22

32. Laryngoscope
MILLER LARYNGOSCOPE MACINTOSH LARYNGOSCOPE

33. Breathing Circuits
• For children less than 20 kgs = Jackson Ree’s
modification of Ayre’s T piece is used
•Minimal dead space
•Minimal resistance
•Light weight
•Fresh gas flow = 3 times the
minute volume

34. Breathing circuit for older children (circle system)

35. Induction of anesthesia

36. Greater alveolar
to FRC ratio
High cardiac
output to vessels
rich organ (eg:
Brain)
Reduced tissue
blood
solubility
EFFECT OF FAST INDUCTION
INDUCTION:
1.IV Induction
2.Gas
induction

37. Ideal maneuvre is
combination of jaw thrust
& chin lift, keeping the
mouth open

43. FLUID MANAGMENT
• Administration: Volumetric chambers/Infusion Pump
• Warm fluid/blood/blood product
• Perioperative fluid management is divided into three phases
–Fluid Deficit
–Maintenance
–Replacement of losses (3rd
space loss)

44. FLUID DEFECIT MANAGMENT
• Calculated and replaced based on duration of fasting, presence
of associated conditions like
•Fever,
•Vomiting, diahorrea
•Surgical problem likely to affect fluid status (bowel
obstruction, peritonitis)

45. MAINTAINANCE FLUID
MANAGMENT

46. 3rd
SPACE FLUID MANAGMENT
Type of surgery ml/kg/hour
1 Intra-abdominal surgery 6-10 mls/kg/hr
2 Intra-thoracic surgery 4-7 mls/kg/hr
3 Neurosurgery 1-2 mls/kg/hr
4 Eye surgery --------
5 Superficial surgery --------

47. BLOOD MANAGMENT
ESTIMATED BLOOD VOLUME (EBV)
Premature Neonate 90-100mls/kg
Term neonate 80-90mls/kg
3mo – 1yr 75-80mls/kg
3-6 yrs 70-75mls/kg
>6 yrs 65-70 mls/kg
Allowable blood loss
ABL = WEIGHT x EBV X (H₀ - H₁)/Hₐ
H₀ = Starting Hematocrit
H₁ = Lowest acceptable hematocrit
H = average hematocritₐ

48. BLOOD MANAGMENT
• Intraoperative blood loss replacement is done with
Ringer’s lactate 3 ml per 1ml of blood loss
• 1 ml of colloid solution for each ml of blood loss
• 0.5 ml of red cell concentrates for each ml of blood loss
Allowable blood loss
ABL = WEIGHT x EBV X (H₀ - H₁)/Hₐ
H₀ = Starting Hematocrit
H₁ = Lowest acceptable hematocrit
H = average hematocritₐ

49. URTI & ANESTHESIA
• Children get URTI at least 7-9 infections per year
• Mostly viral infection (rota virus)
• Increased incidence of peri-operative airway complications
(within 4 weeks)
• Anesthesiologist will decide to postpone for 2-3 weeks or take
up the child for anesthesia
• Commonly referred to Pediatrician on call for help

50. URTI & ANESTHESIA
• Awareness of risk factors will guide the anesthetist in deciding
whether to proceed, and to tailor the anesthetic to optimize the
child’s condition.
• Minimize secretions
• Limit stimulation of airway
• LMA preferred over ETT
• Anti cholinergic to dry secretions
• Bronchodilators – Salbutomol
• Extubation under deeper planes of anesthesia
• Informed consent, good clinical judgment and experience are
crucial factors in the decision-making process

51. THANK YOU