3. Paediatrics Flashcards

1
Q

Classification of age group

A

> Premature – less than 37 weeks post-conception

> Neonate – first 28 days of life or
<44 weeks post-conception

> Infant – 1 month to 1 year

> Child – >1 year to 12 years

> Adolescent – 13 to 16 years

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2
Q

What are the major anaesthetic
considerations for the paediatric
patient?

Pre-operative visit:

Hx

A

> This is an important time to develop
trust and rapport with the child and parent.

A friendly, calm and reassuring
approach will help alleviate
parental and child anxiety.

> Take a medical and anaesthetic history.
This should cover the following:

  • Preterm/term baby
  • Developmental milestones
  • Medical conditions including congenital anomalies
  • Recent respiratory illness
  • Current medication
  • Recent immunisations
  • Allergies

• Any previous problems with
anaesthetics including family history

  • Loose teeth
  • Fasting times
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3
Q

Explain

A

> Explain the planned approach to
induction so both parent and child know
what to expect.

For a gas induction it is important
to inform parents of the ‘excitatory’ phase

of the induction and explain that their child may wriggle
and try and push the mask away
but that this phase is only transient and
the child will have no explicit recollection of the event.

> Gain consent for suppositories.

> Explain post-operative pain management.

> Obtain the weight of the child, as all drug doses and airway devices are based on weight.

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4
Q

Weights

Under 1 year

Formula for 1-10

A

Approximate estimates of weight under 1 year are:

> Neonates: 3–3.5 kg
> 3 months: 6 kg
> 6 months: 7–8 kg
> 9 months: 9 kg
> 12 months: 10 kg

For children aged between 1 year and 10 years, weight can be estimated using the formula:

Weight (kg) = (Age + 4) × 2

This is the standard formula that is universally used. However, newer formulas exist to adjust for the fact that children are now getting heavier.

Children 1–5 years: Weight = (Age × 2) + 8
Children 6–12 years: Weight = (Age × 3) + 7

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5
Q

> Consider pre-medication.

A

> Consider pre-medication.

• Oral sedative pre-medication (e.g. midazolam) is now infrequently used routinely.

It is useful in children who are very anxious or who are likely to be uncooperative.

To work effectively, it needs be given 30 minutes
in advance and therefore the list needs to be planned accordingly.

Buccal midazolam is gaining popularity as its onset time is quicker than the oral formulation (20 minutes).

  • Analgesic pre-medication is becoming more routinely used now (e.g. paracetamol and ibuprofen).
  • EMLA or amethocaine (Ametop) cream should be applied to identifiable veins if an intravenous induction is planned.
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6
Q

> Investigations

A

> Investigations are rarely required but on some occasions may be necessary:

  • Haemoglobin – if large blood loss expected, premature infants, systemic disease or congenital heart disease
  • Electrolytes – if renal or metabolic disease or dehydration
  • CXR – if significant active respiratory disease, scoliosis, congenital heart disease
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7
Q

Upper respiratory tract infections (URTIs

A

Upper respiratory tract infections (URTIs):

The decision to postpone or proceed 
with surgery in a child with an URTI is 
multifactorial and must take into 
consideration the child’s age, 
co-morbidities, presenting symptoms, 
urgency and type of surgery.

> Children under 1 year –
have a low threshold to cancel in this age
group as respiratory complications are higher.

> If the child appears well, with only clear nasal discharge and no other symptoms,
with surgery not involving the airway
and the child not
requiring intubation –
it would be reasonable to proceed with the case.

> If the child has purulent nasal discharge, productive cough and/ or fever, or there are clinical signs suggesting lower respiratory tract involvement such as desaturation or wheeze –
the case should be
postponed for at least 4 weeks.

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8
Q

Table 40.1 Paediatric fasting times

A

Fasting time Food type
6 hours Solids, cow’s milk and formal milk
4 hours Breast milk
2 hours Clear fluids

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9
Q

Anaesthetic preparation:

A

> Prepare your anaesthetic drugs and emergency drugs (e.g. atropine and suxamethonium).

> Drugs are calculated according to the child’s weight (see Table 40.2 for common paediatric drug doses).

You should calculate these in advance
and write them down (it is also worth documenting the volume of drug that this represents,
e.g. 15 μg fentanyl = 0.3 mL).

> When small volumes of drugs are to be administered, they should be drawn up undiluted in a 1 mL syringe.

> Prepare your airway equipment,
breathing circuit (e.g. T-piece) and
monitoring in advance and
ensure that you have a paediatric Ambu bag
with alternative oxygen supply immediately available.

> T-piece breathing circuit is used for patients below 20 kg
(Ayre’s original form was a Mapleson E system.
Jackson Rees modified this later by
including an open-ended reservoir bag and using a longer reservoir tube;
this is known as the Mapleson F system, or Ayre’s T-piece with Jackson Rees modification).

> If small volumes of intravenous fluids are to be administered, a burette should be used.

> Warm the theatre and prepare any warming devices.

> A parent and member of staff usually accompany the child into the anaesthetic room.
Some parents may be quite anxious and therefore a positive and empathetic approach can go a long way.

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10
Q

> Inhalational gas induction

A
• This is a good technique for 
neonates and infants 
(  small and easy to  hold), 
and also for children who fear needles
 or have difficult venous access.

• It is a two-person technique,
requiring one to perform the gas induction
and maintain the airway once the child is anaesthetised

and the other to gain intravenous access
(which must be done prior to siting an
airway due to the risk of laryngospasm).

• If the child is small, then often a gas induction can be performed with the child sitting on the parent’s lap (they will need to be strategically held/cuddled by the parent in order to prevent them from struggling
and pushing the mask away).

The best approach to anaesthetising
neonates and small/premature infants is with the child lying on the trolley once the parents have been escorted from the anaesthetic room/theatre.

• An oxygen–sevoflurane mix is used
(in the past halothane was used).

Sevoflurane has a pungent smell but is non-irritant.
It has a rapid onset and offset of action.

The concentration should ideally be increased
gradually in most cases in order to minimise the patients’ distress;

however, in certain situations
(e.g. uncooperative patients)

sevoflurane may be dialled up to 8% from the outset.

The use of nitrous oxide increases the speed of onset and depth of anaesthesia obtained.

MAC values are 3.3 in infants,
2.5 in children and 1.7 in adults.

Once anaesthesia is achieved
and IV access is secured, air–oxygen mixture
should be used as carrier gas.

• There is often an excitatory phase during the induction and this can worry some parents
unless they have been told about it beforehand.

• There is an ‘art’ to performing a good gas induction, which can only be gained with experience

(pay attention to subtle things, e.g. what
side of the parent and child to stand on, how to hold the mask so that it does not look like you are smothering the child, etc.).

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11
Q

Intravenous induction:

A
• This has a rapid and defined end point 
and may be considered an
easier technique by 
non-paediatric anaesthetists but
 the caveat to this is gaining intravenous access, 
which can be challenging, 
especially in toddlers with 
chubby little hands and feet. 

Patients may also desaturate more
quickly compared with a gas induction.

• The best sites for intravenous access are
back of the hand, inner wrist, l
ong saphenous vein and veins
on the dorsum of the foot.

  • Pre-oxygenation can be difficult in small children but should be undertaken if possible, especially if rapid sequence induction is planned.
  • Propofol, thiopentone or ketamine can all be used.
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12
Q

Airway devices:

A

Airway devices:

> Intubation

• All infants less than 5 kg
or under 44 weeks gestational age
should be intubated.

• Straight blades (Robertshaw or Miller):
use in neonates and infants.

• Curved blade: easier to use once the child is 6–10 kg.

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13
Q

ETT length Appropriate length can also be

calculated as follows:

A

• Ideally the ETT should be inserted such that its thick black marking is at the level of the vocal cords.

Oral ETT length (in cm) = Age/2 + 12

Nasal ETT length (in cm) = Age/2 + 15

(or an easier one to remember is oral
ETT = ID × 3, for nasal ETT, add 2 cm)

• Appropriate ID size and length in neonates is
3–3.5 and 8–10 cm,
respectively,
and in infants 4–4.5 and 10–12 cm.

  • Once ETT is inserted, its correct placement should be confirmed with auscultation and ETCO2 monitoring.
  • Laryngospasm at extubation occurs less frequently if the child is fully awake at the time of extubation.
  • You may need to be with the child in recovery until fully awake if the recovery staff are inexperienced with children.
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14
Q

Estimating size of ETT

A

For children between the age

of 1 year and 10 years,

uncuffed endotracheal tube (ETT) 
internal diameter (ID) size can be estimated
using the formula:

ETT size = Age/4 + 4.5

(this is generally a better fit than: Age/4 + 4)

Uncuffed tubes:

typically used until 8–10 years of age to minimise

the risk of damage to the trachea.

A small leak should be present,
but if the leak is too large it will compromise ventilation.

Modern endotracheal tubes have low-pressure,
high-volume cuffs and there are centres that use cuffed tubes in very young children with no complications.

Opt for internal diameter 1/2 size smaller when using a
cuffed ETT.

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15
Q

> Laryngeal mask airway

A
> Laryngeal mask airway
• The size used is based on the weight of the child:
¡ 0–5 kg = size 1
¡ 5–10 kg = size 1.5
¡ 10–20 kg = size 2
¡ 20–30 kg = size 2.5
¡ >30 kg = size 3
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16
Q

Maintenance fluids:

A

Maintenance fluids:

> In 2007 the NPSA released an alert on the risk of hyponatraemia in children receiving intravenous fluids.

Since then hypotonic solutions
(e.g. 0.18% saline with 4% dextrose)
are not to be routinely used in children.

> NICE will release information on intravenous fluids for children in October 2015, which will provide recommendations on the types of fluids that
should be used for resuscitation and maintenance purposes.

> Currently, for peri-operative intravenous maintenance fluid, a balanced, isotonic solution should be used.

> Short operations (<1 hour) in healthy children do not usually require fluids if pre-operative fasting has not been excessive.

> Children undergoing intra-abdominal surgery or where there is anticipated blood loss should receive intravenous fluids.

> When calculating peri-operative fluid requirements, fluid lost during the pre-operative fasting period and intra-operative losses should be added
to the maintenance fluid requirements.

> Maintenance fluids are calculated as follows:

  • First 10 kg: 4 mL/kg/h (or 100 mL/kg/24 h)
  • Next 10 kg: 2 mL/kg/h (or 50 mL/kg/24 h)

• Subsequent kg: 1 mL/kg/h (or 20 mL/kg/24 h)
(so a 9 kg child would have a maintenance fluid requirement of 36 mL/h
and a 20 kg child would require 60 mL/h).

> Fluid boluses:
• Non-resuscitation: 10 mL/kg
• Resuscitation: 20 mL/kg

17
Q

Analgesia:

A

> Add regional analgesia where appropriate

(e. g. caudal for urological, inguinal hernia and lower limb procedures, axillary blocks for upper limb
surgery) .

> Pre-medicate where possible.

> Gain consent for suppositories.

> Do not give codeine to children under the age of 12 years.

> Use a multi-modal approach

18
Q

What are the main pharmacokinetic and

pharmacodynamic differences?

A

> Decreased lean body mass.

> Increased total body water (TBW is 85% at birth vs 60% in adult) – so higher initial dose required.

> Decreased total body fat and
therefore increased volume of distribution
(Vd) for water-soluble drugs.

Drugs terminated by redistribution will have
prolonged effects.

> Decreased plasma protein binding (PPB).

> Decreased drug metabolism and excretion.

> Increased drug uptake and distribution due to increased cardiac output, increased alveolar ventilation and increased TBW.

19
Q

What effect do these pharmacokinetic and pharmacodynamic changes have on the commonly used drugs in anaesthesia?

Inhalational agents:

A

Inhalational agents:

> Gas inductions are faster due to increased alveolar ventilation
compared with FRC,
high cardiac output, l
ower blood/gas solubility and lower
tissue/blood solubility of volatile agents.

> MAC is age related. MAC values for an infant are:
• sevoflurane = 3.3%
• isoflurane = 1.9%
• desflurane = 9.4%.

20
Q

Barbiturates

Propofol

A

Barbiturates:
> Increased sensitivity to thiopentone and a more prolonged recovery (due
to reduced Vd and redistribution).

Propofol:
> Licensed for induction in infants over 1 month and for infusion in children aged 3 years and above.

> Painful on injection (it is acceptable to add a small amount of 1% lignocaine to the propofol).

21
Q

Opioids:

A

Opioids:

> Increased sensitivity due to reduced PPB,
reduced hepatic metabolism
and immature blood–brain barrier.

> Beware of using narcotics and sedative agents in preterm babies and neonates due to the increased risk of apnoea.

22
Q

Muscle relaxants:

Local anaesthetics:

A

Muscle relaxants:

> Depolarising –

decreased sensitivity to suxamethonium due to

increased Vd and
immature neuromuscular junction;
therefore, higher dose used (2 mg/kg).

> Non-depolarising –

atracurium has increased Vd
but also increased clearance
and so very little change in overall pharmacokinetics.

Local anaesthetics:
> Decreased protein binding and reduced metabolism increase risk of toxicity.

23
Q

Intraosseous route (IO):

A
Intraosseous route (IO):
> In emergency setting, when intravenous access cannot be gained,
intraosseous access can be life saving.

> In the long bones, the medullary cavity consists of a network of venous sinusoids that drain into large medullary venous channels. These in
turn drain into nutrient or emissary vessels. These vessels exit the bone via the nutrient foramina and empty directly into the systemic venous circulation.

> All resuscitation fluids, drugs and blood products can be administered through the IO route.

> Anatomical landmarks (note that there are other sites that can be used, e.g. sternum):

• Tibia: medial side, 2–3 cm below the tibial tuberosity

• Femur – 3 cm above the lateral condyle
(these sites avoid epiphyseal growth plates and joint spaces)

> Commercially prepared, single-use needles should ideally be used
(many now come as powered drill devices).

> Can be left in for up to 72 hours (although the risk of infection increases with time).

> Complications: Infection, extravasation, dislodgement of needle,
embolism, compartment syndrome due to extravasation, fracture,
pain.

> Contraindications: fracture of target bone, recent IO access (in last 24–
48 hours), signs of infection at insertion site, osteogenesis imperfecta.

24
Q

Table 40.2 Paediatric drug doses

A

Table 40.2 Paediatric drug doses

Atropine 10–20 mcg/kg

Adrenaline (cardiac arrest) – 1:10 000 10 mcg/kg or 0.1 ml/kg

Suxamethonium 2 mg/kg

Propofol 2–5 mg/kg

Fentanyl 1–3 mcg/kg

Morphine IV: 50-100 mcg/kg

PO: 100–200 mcg/kg

Atracurium 0.5 mg/kg
Reversal Neostigmine: 50 mcg/kg / Glycopyrrolate
10 mcg/kg (easy way to remember is 0.1 ml of
premixed ampoule for every 5 kg)

Ondansetron 0.1 mg/kg
Dexamethasone 0.1 mg/kg
Cyclizine 1 mg/kg

Paracetamol IV: 15 mg/kg if >10 kg (max 90 mg/kg/day)
IV: 10 mg/kg in neonates and infants <10 kg
(max 60 mg/kg/day)
PO: loading dose: 20 mg/kg; subsequent doses:
15 mg/kg
Diclofenac 1 mg/kg
Ibuprofen (give only for >6 months and
>7 kg)
5 mg/kg (max 30 mg/kg/day)