Paediatric anaesthesia practical tips

Dr . S. Parthasarathy

MD. DA. DNB., Dip.diab. MD(acu) , DCA, Dip. Software-statistics.

PhD (physio)

Mahatma Gandhi medical college and research institute ,

puducherry – India

Practical paediatric anaesthesia

Children are not mini adults

Definitions

Neonates – a baby within 44 weeks of age from the date of conception

Infants – a child of up to 12 months of age

Child – 1 to 12 years

Adolescent – 13 to 16 years

Physiology, Pharmacologyand practical considerations

• oxygen consumption in infants may

exceed 6ml/kg/min, twice that of adults

• physiological adaptations in paediatric cardiac

and respiratory systems to meet this increased

demand.

physiology

• The cardiac index

• (defined as the cardiac output related to the body surface area)

• is increased by 30-60 percent in neonates and infants to help meet the increased oxygen consumption.

• Neonates have a higher haemoglobinconcentration (17 g/dl) and blood volume

Cardiovascular system

• Neonatal myocardium is stiff and increase in cardiac output is rate dependent

• Stroke volume ?? So tachycardia is important

• BUT

• The sympathetic nervous system is not well developed predisposing the neonatal heart to bradycardia.

• Sinus arrhythmia is common in children and all other irregular rhythms are abnormal

Some differences

neonate Infant Above 1 Around 5 Adult

O2 consumtion

6 5 5 4 3

Systolic BP 65 90 95 95 120

Heart rate 130 120 120 90 75

Blood volume

85 80 80 75 70

Hb gm% 17 11 12 13 14

Respiratory- airway

• The head is relatively large with a prominent occiput

• The neck is short.

• The tongue is large.

• The airway is prone to obstruction because of these differences

Infant airway

Large head

Prom.occiput

Small neck

Infant airway

• Infants and neonates breathe mainly through their nasal airway, although their nostrils are small and easily obstructed.

• The larynx is higher in the neck (more cephalad), being at the level of C3 in a premature infant and C4 in a child compared to C5-6 in the adult.

Infant airway

• The epiglottis is large, floppy and U shaped. The trachea is short (approximately 4-9cm) directed downward and posterior and the right main bronchus is less angled than the left.

• Right main stem intubations are therefore more likely.

Infant airway

• The glottic opening (laryngeal opening) is more anterior and the narrowest part of the airway is at the cricoid ring. (In the adult airway the narrowest point is the vocal cords).

• At cricoid level, epithelium is loosely bound to the underlying areolar tissue. Trauma to the airway easily results in oedema.

narrowest

Epiglottis large floppy

ET tube

Airway model

Respiratory system

• Ribs and cartilages are more pliable

• Chest wall collapse more with increased negative intrathoracic pressure

• Control of respiration poor

• Prolonged apnoea common after anaesthesia• (caffeine 10 mg/kg)

• Hypoxia inhibits rather than stimulates breathing

Resp. system

• Respiration is mainly diaphragmatic (type 1 fibres

20%) Minute ventilation is more rate dependent

• The closing volume is larger than the FRC until 6-8

years of age

• RR = 24 – age/2

Spontaneous ventilation

• TV = 6-8 ml/kg; IPPV TV = 7-10ml/kg

Length and type

• length (Age / 2) + 12

• 1-2-3-----7,8,9 formula

• Size of the ETT

• (Age /3) + 3.5 or (Age /4) + 4.5

• Below 8 years – uncuffed – allow leak at 30 cm water pressure

LMA sizes

• 1 LMA up to 5 kg;

• 1.5 LMA 5-10 kg;

• 2 LMA 10-20 kg;

• LMA 2.5 20 – 30 kg;

• LMA 3 for over 30 kg

Renal System

• Renal blood flow and glomerular filtration are low in the first 2 years of life due to high renal vascular resistance..

• GFR 45 ml/min to adult values of 125 ml/min

• Tubular function is immature until 8months,

• so infants are unable to excrete a large sodium load.

• Dehydration poorly tolerated

• Urine output 1-2 ml/kg/hr

Renal

• a faster turnover of extracellular fluid

• Renal function – almost normal in adult levels -- age of 2 years

• 4-2-1 formula of IV fluids acceptable

• Options

• RL

• 1/2 NS

• 1/5th NS

Hepatic System

• Liver function is initially immature

• Cytochrome P450 enzymes (phase I reactions)

are fully developed, whereas others are

approximately 50% of adult values.

• Phase II reactions, usually impaired in neonates

• Barbiturates, opioids – prolonged action

• Age of 1 year - ok

Temperature regulation

• Neonates and infants have a large surface area to volume ratio and therefore a greater area for heat loss, especially from the head

• increased metabolic rate but insufficient body fat for insulation and heat is lost more rapidly

• They don’t shiver

• Take all precautions to maintain temperature

Central Nervous System

• Neonates can appreciate pain

• The blood brain barrier is poorly formed

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

• Cerebral autoregulation is present

Psychology

• Less than 6 months – separation ok

• Children up to 4 years of age are upset by the separation

• Parental anxiety

• fear narcosis and pain

Pharmacologic principles

• Excess body water

• Suxa . Antibiotics

• Fat and muscle content ↓ ↓

• Fat soluble drugs – Vd less- thio more

dose

• a drug that redistributes into muscle

may have a longer clinical effect (e.g.,

fentanyl,)

Pharmacologic principles

• immature hepatic and renal function,

• altered drug excretion caused by lower protein binding.

Anaesthetic agents

• smaller lung functional residual capacity per unit body weight and a greater tissue blood flow, especially to the vessel rich group (brain, heart, liver and kidney)

• Induction and recovery faster

• MAC of inhalational agents are greatest in the young and decrease with age

Nitrous oxide

• Odourless

• Ideal to supplement with agents

• Rapid turnover

• No change in paediatrics

Halothane ok

• Halothane has undoubtedly been wrongly

incriminated in many patients for hepatic

injury when a more detailed investigation

would have cleared the anaesthetic from any

blame.

Other agents

• Enflurane – pungent smell not much use

Epileptiform activity

• Isoflurane – pungent smell but maintenance ok

• Desflurane - pungent smell- excellent rapid recovery

Sevoflurane

• Smooth and Rapid induction and recovery

• Non pungent

• Turn the vaporizer to 8%

• No coughing , spasm

• No use of adding N2O

• Ideal in patients with airway obstruction

Intravenous agents – more doses

• Thio 5-6 mg/kg

• Propofol induction and maintanance – Ok

• Pain on injection

• Anticholinergic + benzodiazipines + ketamineacceptable but hallucinations may occur in the recovery period

Muscle relaxants

• Neonates and infants require more

suxamethonium for skeletal muscle paralysis,

• 2 mg/kg for infants

• Neonates and infants are more sensitive than

adults to non-depolarising muscle relaxants.

• Initial doses are similar in both age groups

• because the increased extracellular fluid volume

and volume of distribution in younger patients

Opioids ,Bz,neostigmine

• Opioids morphine – safety ??

• Remifentanyl ideal

• Diazepam:

• 0.1-0.3 mg/kg orally

• T1/2 80 hours contraindicated < 6 months

• Clonidine , midazolam – ok

• 0.1-0.15 mg/kg IM

• 0.5-0.75 mg/kg orally

• Midazolam – effect ??

• The dose of neostigmine per kg required for

antagonism of non-depolarising muscle relaxants is

similar in children to adults

Regional anaesthesia

• Spinal cord ends at L2 L3

• Lower projection of dural sac

• Delayed myelinization of nerve fibers

• Cartilaginous structure of bones and vertebrae

• Delayed development of curvatures of the spine

• Tuffier's line, L 5 and lower

• Increased fluidity of epidural fat and Loose attachment of sheaths

Remember in paediatrics

• Oxygenation

• IV fluids

• Temperature

Thank you all