applied aspects of anatomy : paediatric anesthesia

APPLIED ANATOMY : PAEDIATRIC ANAESTHESIA

Speaker : Dr. Tarun YadavModerator : Dr. S. Gosavi,

Dr. V. Chandak

We will be covering

• Classification of Pediatric Group• Applied Anatomy(related to Anesthesia)• Airway & Respiratory System• Cardiovascular System• Renal System• Hepatic System• Hematological System• Temperature Control• Central Nervous System• Neuraxial Blocks

• Spinal• Epidural• Caudal

Who are included in pediatric group ?

Neonates (< 30 days)

Infants (1-12 months)

Children (1-12 years)

Classification according to gestational age• Pre-term infant – born <37 weeks gestation• Moderately premature – 31-36 weeks gestation• Severely premature – 24-30 weeks gestation• Post term infant – born after 42 weeks gestation

Classification according to birth weight• Low birth weight (LBW) – Birth weight <2500 gms(regardless of duration of pregnancy).• Very low birth weight – Weight <1500 gms.

AIRWAY & Respiratory system

Larger head and tongue

Narrow nasal passages

Anterior and cephalad larynx (at a vertebral level of

C3-C4),

Long epiglottis (omega)

Short trachea and neck

• Obligate nasal breathers.• Subglottis : narrowest point of the airway.• Edema will have a proportionately greater

effect in children because of smaller tracheal diameters.

• Shorter length of trachea : – Endobronchial intubation– Accidental extubation

Successful Airway Managment

Equipment Selection :uncuffed tube, Miller Blade

Laryngoscopy technique

Optimal Position

Optimal head positioning

• Due to the large occiput, a small pillow placed under the occiput (similar to adults), will flex the head on neck instead of extending it for “sniffing position”.

• Thus it is preferable to place a pad under the neck and shoulders.

• With a large ring under the occiput to stabilize the head to aid in optimum head positioning for laryngoscopy.

Laryngoscopy technique

Cricoid pressure applied with little finger.

Insertion of Miller blade down the right side of the tongue. The blade is then turned and pressure is applied in the direction of the handle.

EQUIPMENTS

• � Horizontal ribs prevent the ‘bucket handle’ breathing

Limit an increase in tidal volume. Ventilation is primarily diaphragmatic.

Poor mask ventilation Air in stomach

Upward displacement of diaphragm

Inadequate ventilation

Apply gastric pressure

• The chest wall is significantly more compliant than that of an adult, FRC is relatively low.

• Minute ventilation is rate dependant as there is little means to increase tidal volume.

• The closing volume is larger than the FRC until 6-8 �years of age.

Increased tendency for airway closure & collapse specially during anaesthesia.

IPPV , Higher RR & PEEP

• Muscles of ventilation are easily subject to fatigue due to low percentage of Type I muscle fibres in the diaphragm.

• Alveoli are thick walled and less in number.• Respiratory neural control : immature

Post op apnea with desaturation / bradycardia

Optimal settings

• RR = 24 – age/2

• Spontaneous ventilation TV = 6-8 ml/kg�

• IPPV TV = 7-10ml/kg

Cardiovascular

• Vagal parasympathetic tone is the most dominant, which makes neonates and infants more prone to bradycardia.

• Bradycardia is associated with reduced cardiac output.

Less contractile myocardium

Ventricles less compliant

Fixed stroke volume

Cardiac output is therefore rate

dependent

Bradycardia with hypoxia (Neonate)HR(<60bpm)

Oxygen and ventilation HR still < 60 bpm

External cardiac compression HR still <60 bpm

Pharmacological treatment(Adr,Atropine)

Precordial stethoscope for Monitoring

Fetal Circulation

• The patent ductus contracts in the first few days of life and will fibrose within 2-4 weeks.

• Closure of the foramen ovale is pressure dependent and closes in the first day of life but it may reopen within the next 5 years.

• The neonatal pulmonary vasculature reacts to the rise in Pa02 and pH and the fall in PaCO2 at birth.

Avoid hypoxia and acidosis

RENAL system

• RBF and GFR are low in the first 2 years of life due to high renal vascular resistance.

• Tubular function is immature until 8 months, so infants are unable to excrete a large sodium load.

• Dehydration is poorly tolerated. • Premature infants have increased insensible losses as

that have a large surface .• There is a larger proportion of extra cellular fluid in

children (40% body weight as compared to 20% in the adult).

Hepatic System• Liver function is initially immature with

decreased function of hepatic enzymes. • The vitamin K dependent clotting factors (II,

VII, IX, X) and platelet function are deficient in the first few months. Vitamin K is given at birth to prevent haemorrhagic disease of the newborn.

Barbiturates and opioids have a longer duration of action

Haematology

• At birth, 70-90% of the haemoglobin molecules are HbF. • Within 3 months the levels of HbF drop to around 5%

and HbA predominates.• A haemoglobin level in a newborn will be around 18-20

g/dl which is a haematocrit of about 0.6. • The haemoglobin levels drop over 3-6 months to 9-12

g/dl as the increase in circulating volume increases more rapidly than bone marrow function.

• The 02/Hb dissociation curve shifts to the right as levels of HbA and 2,3-DPG rise.

• Transfusion is generally recommended when 15% of the circulating blood volume has been lost.

Temperature Control

• Babies and infants have a large surface area to weight ratio with minimal subcutaneous fat & Less brown fat

• They have poorly developed shivering, sweating and vasoconstriction mechanisms.

Avoid hypothermia

CNS

• Neonates can appreciate pain and this is associated with increased heart rate, blood pressure.

• Narcotics depress the ventilation response to a rise in PaC02.

• The blood brain barrier is poorly formed. • Drugs such as barbiturates, opioids, antibiotics

cross the BBB : prolonged and variable duration of action.

• The cerebral vessels in the preterm infant are thin walled, fragile.

• They are prone to intraventricular haemorrhages.• The risk is increased with hypoxia, hypercarbia,

hypernatraemia, low haematocrit, awake airway manipulations, rapid bicarbonate administration and fluctuations in blood pressure and cerebral blood flow.

• Cerebral autoregulation is present and functional from birth.

Neuraxial Blocks

• During the early stages of development the spinal cord occupies the spinal canal entirely, but later on the growth of vertebrae exceeds that of the cord, and the last spinal nerves, the cord, and its envelopes are “attracted” within the spinal canal.

• At birth the dura mater ends at the level of the third or fourth sacral vertebra and the cord (conus medullaris) at the L3 or L4 level.

• A, Eight weeks; B, 24 weeks; C, newborn; D, 8-year-old child and adult.

Avoid spinal/epidural approaches

above L3

Lower projection of dural sac (S3-4)

Increased risk of inadvertent penetration of the dura mater.

Cartilaginous structure of bones and vertebrae

Danger of direct trauma and bacterial contamination of ossification nuclei.

Use short and short beveled needles

Delayed myelinization of nerve fibers

Easier intraneural penetration

of local anesthetics

Onset time shortened

Diluted local anesthetic as effective as

more concentrated

anesthetic

Delayed development of curvatures of the spine.

Same orientation of epidural needles at all level before 6

months of age

Delayed ossification and growth of iliac crests

Tuffier’s line passes over L5-S1 interspace .

Lack of fusion of sacral vertebrae

Persistence of sacral intervertebral spaces.

Caudal Block

Changing axis of coccyx and absence of growth of sacral hiatus

1. Difficult Identification of sacral hiatus difficult above 6-8 years .2. Increased failure rate of caudal anesthesia.

Increased fluidity of epidural fat.

Increased diffusion of local anesthetic up to 6-7 years of age with excellent caudal blockade.

Loose attachment of sheaths and aponeuroses to underlying structures.

1. Larger volume of LA for epidural blocks due to leakage along spinal nerve roots.

2. Increased spread along nerve paths with danger of penetrating remote anatomic spaces and blocking distant nerves.

Sympathetic immaturity, diminished autonomic adaptability of the heart, smaller vascular bed in lower extremities.

• Hemodynamic stability during neuraxial blocks• Fluid preloading and use of vasoactive agents

unnecessary

Sacral Hiatus

• V-shaped aperture formed d/t lack of dorsal fusion of the 5th and 6th sacral vertebral arches• Limited laterally by sacral cornua.• Covered by sacrococcygeal membrane.• Mean distance from skin to anterior sacral wall: 21

mm (2 mo to 7 yr)• Less suitable after 6-7yrs as• Change in axis of sacrum• Difficulty to identify sacral hiatus• Densely packed epidural fat

Caudal block

Technique of caudal anaesthesia

Positioning the patienta. Sim’s positionb. Semipronec. Prone- esp. in non anaesthetized (frog position)

Palpate for sacral cornua along the spinal processes at the level of sacrococcygeal joint

The sacral hiatus along with both PSIS forms an equilateral ∆Introduce needle in midline at 45⁰ or lessResistance felt on piercing the sacrococcygeal ligamentAcute the angle of needle by 10-15 degree.Inject the LA with frequent aspirationsFinger should palpate the skin cephalad t the injection to ensure drug is not

s/c

References• APPLIED ASPECTS OF ANATOMY AND PHYSIOLOGY OF RELEVANCE TO

PAEDIATRIC ANAESTHESIA, Swamy, Sept 2004 IJA.• PAEDIATRIC ANATOMY AND PHYSIOLOGY AND THE BASICS OF

PAEDIATRIC ANAESTHESIA, Macfarlane, 2010,12 An Tutorial of Week. • Clinical Anesthesia Barash• Millers Anesthesia• Royal College of Anesthesia Resource 2014

(www.frca.co.uk)

Thanks ;-)