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PRINCIPLES
Most of the general principles of anaesthesia can be applied
to children, but there are some significant anatomical and
physiological differences between children and adults that
can cause problems, especially in neonates and children weighing
less than about 15 kg.
Airway
Children have a large head in relation to body size and you
must therefore position them differently from an adult, sometimes
with a pillow under the
shoulders rather than the head, to clear the airway or to perform
laryngoscopy.
The larynx of a child also differs from that of an adult. In
the adult, the narrowest part of the air passage is at the
level of the vocal cords; in the child the narrowest part is
below this, at the level of the cricoid cartilage:
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The
airway is circular in cross–section, so a correct
fit can usually be obtained with a plain (not cuffed)
tracheal tube |
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A
small air leak should usually be present around the tube,
but if a completely airtight fit is required, pack the
pharynx with gauze
moistened with water or saline; never use liquid paraffin (mineral oil), as this
causes lung damage |
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It
is acceptable to use a cuffed tube of less than 6.0 mm,
but do not inflate the cuff.
Because the airway of a child is narrow, a small amount of oedema can produce severe
obstruction (Figure 14.3). |
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Oedema
can easily be caused by forcing in a tracheal tube that is
too tight, so if you suspect that your tube is too large,
change it immediately. Damage is most likely from a tube that
is both too large and left in the trachea too long.
As a rough guide for normally nourished children more than about 2 years old,
use the following formula to calculate the internal diameter of the tube likely
to be of the correct size.
Internal diameter of tube (mm) = (age in years + 4.5) ÷ 4
Other rough indicators of the correct size of tube are:
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Diameter
the same as the child’s little finger |
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Most
neonates will need a tube of 3 mm internal diameter |
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For
premature infants, a 2.5 mm tube may be necessary |
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To
estimate the length of tube needed, double the distance
from the corner of the child’s mouth to the ear
canal |
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To
check, look at the child’s head from the side while
holding the upper end of the tube level with the mouth
to give you an idea of how far into the chest the tube
will go. |
Always have one tube a size larger and one a size smaller ready in case you need
to change.
For infants, use a small straight laryngoscope blade. If one is not available,
use the tip of a Macintosh blade designed for adults as it is only slightly
curved. After intubation, always listen over both lungs to make sure that the tube
has not entered a bronchus.
Abdomen
A child’s abdomen is more protuberant than an adult’s and it contains
the greater part of the viscera. (Many of the viscera of an adult are situated
in the relatively larger pelvic cavity). The diaphragm is therefore less efficient
in a child. The rib cage is also less rigid than an adult’s. These factors
mean that abdominal distension can very easily give rise to respiratory difficulty.
Metabolic rate
The metabolic rate is higher in children than in adults, while the lungs are
less efficient and smaller in relation to oxygen requirements. For this reason,
children have higher respiratory rates than adults and their lungs must be
ventilated more rapidly. Obstruction or apnoea leads to a very rapid onset
of cyanosis.
Heart rate
The normal heart rate at birth is about 140 per minute, but it may swing widely
in response to stress.
A child’s heart rate is higher than that of an adult, but the resting
sympathetic tone is low, so reflex vagal stimulation can lead to severe bradycardia:
e.g during laryngoscopy or surgery. For this reason, atropine (0.015 mg/kg
of body weight) is almost always included in premedication for infants.
Hypothermia can occur very rapidly in an infant because of the high surfaceto-volume
ratio of the body; it may result in a severe metabolic disturbance.
Hypoglycaemia
Hypoglycaemia may be a problem in babies:
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Babies
do not need to be starved for more than three hours
preoperatively and should be fed as soon as possible after the operation |
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Use
glucose infusions during anaesthesia:
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To
help to maintain the blood sugar level |
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Infuse
glucose instead of physiological saline to avoid
a sodium
load that the baby’s kidneys are unable to excrete |
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For
most paediatric operations, other than minor ones,
give glucose
5% (or glucose 4% with saline 0.18%) at a rate of 5 ml/kg of body
weight per hour in addition to replacing the measured fluid losses. |
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Blood volume
The neonate has a proportionately higher blood volume (90 ml/kg of body weight)
than the adult (70 ml/kg) but, even so, what appears to be a small blood loss
may have serious effects:
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Measure
blood losses during the operation as accurately as
possible; if suction apparatus is in use, a simple method
is to use a measuring
cylinder in the suction line rather than the usual large container
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If
blood loss amounts to more than 5% of blood volume, an
intravenous infusion is necessary |
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If
blood loss exceeds 10–20% of blood volume, consider
blood transfusion. |
PAEDIATRIC ELECTIVE ANAESTHESIA
Most children weighing more than 15 kg can be anaesthetized by using the techniques
described in this book for adult patients, but with the dosage reduced in relation
to weight.
In children below 15 kg, the anatomical and physiological differences described
above become more important and inhalational apparatus must be adapted, although
ketamine can be used without any modifications in technique. “Adult” breathing
systems give rise to problems in small children because the valves have too large
a dead space. In addition, vaporizers of the draw-over type do not work effectively
at the low minute/volumes and flows generated by an infant’s lungs. These
problems can be overcome in a number of ways:
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Replace
the adult-size breathing valve with an infant-size
valve that has a smaller internal volume and dead space |
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If
possible, replace the adult-size bag with a small one |
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You
must use intubation and controlled ventilation for infants
under 10 kg; the flow you generate into the bellows during
IPPV will be enough to allow the vaporizer to work reasonably
accurately. |
If
oxygen is available, you can convert a draw-over system to
a continuousflow mode.
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Connect
a flow of oxygen from a cylinder or concentrator (or
oxygen plus nitrous oxide) to the side arm of your
oxygen-enrichment T-piece and close off the open end
with a bung. |
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Set
the fresh gas flow to 300 ml/kg of body weight per minute
with a minimum of 3 litres/minute. |
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Intubate
and ventilate the patient or allow spontaneous breathing
using an Ayre’s T-piece system, as described below.
Use a T-piece system (Ayre’s T-piece) instead of
the Magill breathing system usually used for adults. The
valveless T-piece system requires a relatively high gas
flow, but is suitable
for both spontaneous and controlled ventilation. |
Spontaneous
breathing can be monitored by watching the slight movement of
the open-ended reservoir bag. To change to controlled ventilation:
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Hold
the bag in your hand with your thumb towards the patient. |
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Partly
occlude the outlet by curling your little finger round
it (this needs practice) and squeeze the bag in the palm
of your hand to inflate the lungs. |
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Then
release the bag to allow the expired gas to escape. |
Continuous monitoring of heart
rate and respiration is essential in small children. A precordial
or oesophageal stethoscope is invaluable for this.
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Use
an infant-sized cuff to measure the blood pressure |
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Palpate
the arterial pulses and check the colour and perfusion
of the extremities |
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Monitor
the urine flow if a urinary catheter is in place; a good
urine output (0.5 ml/hour per kg of body weight) is reassuring |
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At
the end of the operation, check the temperature to ensure
that the patient has not become hypothermic. |
PAEDIATRIC
EMERGENCY ANAESTHESIA
The techniques in emergency neonatal and paediatric anaesthesia are not
very different from those required in elective paediatric anaesthesia.
Few major paediatric surgical cases are performed at the district hospital
level. Here the common requirement is for ketamine or inhalation anaesthesia
with halothane for incision and drainage of abscess or removal of foreign
body.
Anaesthesia management for foreign body removal is given on pages 14–32 to
14–34. Other emergency airway problems in children include:
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Croup |
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Epiglottitis |
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Retropharyngeal
abscess |
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Laryngeal
polyps. |
Croup,
tracheobronchitis and epiglottitis
Croup is the name for laryngo-tracheitis and describes the characteristic
cough. Conservative treatment is usually possible: avoid over-stimulation
of the child and give:
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Humidified
oxygen |
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Nebulized
epinephrine |
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Antibiotics |
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Steroids:
dexamethasone 0.15 mg/kg intravenously daily. |
Epiglottitis (and severe croup that is not responding to treatment)
can make the epiglottis and larynx so swollen that the airway
is almost blocked. The child is very unwilling to lie down and
copious secretions run out of the mouth because swallowing is
painful. The child is also febrile, distressed, toxic and cyanosed
so careful handling is essential. Do not attempt to put up an
intravenous infusion while the child is awake as this will cause
deterioration. A lateral X-ray shows the “thumb print” sign
of the enlarged epiglottis.
Do not send a child in respiratory distress to the X-ray department.
Urgent management is needed.
Take the child to the operating room and prepare every available
aid to intubation:
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Smaller
size tracheal tubes with pre-inserted, lubricated stylets |
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Spare
laryngoscopes with different blades |
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Emergency
cricothyroid puncture kit or intravenous cannula, if available. |
Without
any delay, with suction ready:
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Hold
the child firmly in the sitting position and give inhalation
induction with halothane and oxygen until asleep. |
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Continue
for as long as possible (usually the airway will become
obstructed at some stage) then transfer to the supine
position and intubate as quickly as you can:
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Be
prepared for distorted anatomy |
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A
small tracheal tube with introducer is essential |
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Make
sure the surgeon is prepared for an emergency cricothyroid
puncture if you cannot intubate and cardiorespiratory
arrest is about to occur. |
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Keep
the child intubated for at least 24 hours in an intensive
care location with constant nursing, suction, oxygen
and high dose antibiotics. |
Ensure
that the nurses understand the need to prevent the tube becoming blocked
with dried secretions.
Retropharyngeal abscess
Retropharyngeal abscess is quite common in younger babies. In
areas of high HIV prevalence, it can occur in any age group.
The cry is characteristic of obstruction just above the larynx.
Feel the swollen neck and examine the oropharynx with a wooden
spatula or your finger and the presence of a fluctuant retropharyngeal
abscess should be very obvious. A wide bore needle aspiration
confirms the diagnosis.
There are two ways to manage the case.
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Inhalation
induction with oxygen and halothane, tracheal intubation
and incision and drainage with a rigid sucker to completely
evacuate the cavity, |
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Or |
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In
very young babies before dentition, avoid any anaesthesia,
puncture the abscess with a pair of forceps while the
patient is awake, then immediately turn the baby face-down
so the pus runs out. |
The first method allows better access for suction and complete
evacuation of the retropharyngeal space.
Laryngeal polyps or papillomata
Laryngeal polyps are a problem in children of all ages. Acute
airway obstruction can occur, so patients sometimes present
as emergencies:
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Induce
deep inhalational anaesthesia |
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Gently
remove as many papillomata as you can with Magill’s
forceps, avoiding damage to the cords from where the papillomata
are arising |
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Have
good suction ready and wear a pair of goggles |
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Have
a small endotracheal tube with introducer ready at all
times. |
The polyps can recur for years and semi-permanent tracheostomy
is sometimes required.
Other paediatric emergencies
Typical major emergency cases presenting at a referral hospital
might be laparotomy (for colostomy in cases of imperforate
anus, Hirschsprung’s
disease or other intestinal obstruction), peritonitis or surgery
for major trauma.
PREPARATIONS BEFORE INDUCTION
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Intravenous
infusion:
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Always
use a paediatric burette and avoid, if at all possible,
connecting a neonate or infant to a 1 litre bag
via a normal adult giving set (see page 13–17) |
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Add
10 ml 50% dextrose to 100 ml in the burette |
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Endotracheal
tube sizes: have available all the sizes from 3.0 to
6.5 mm |
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Empty
a full stomach:
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Just
before starting anaesthesia, pass a wide bore orogastric
tube
into the stomach to empty it |
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Apply
gentle suction while moving the tube around then
remove
it. |
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Temperature
Most patients undergoing emergency surgery and anaesthesia
will become hypothermic during the procedure, particularly
during a long operation. This is especially true of babies
and neonates. There are various measures that will minimize
hypothermia:
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Warm
the operating room |
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Use
an electric heating blanket, but check the control and
beware of overheating, burns and electric shock |
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Wrap
the baby in warm, dry towels |
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Reduce
the time that skin is uncovered during induction and preparation
of the skin |
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Warm
blood and IV fluids: see The Clinical Use of Blood (WHO,
2001, pages 120–121) |
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Use
heated IV fluid bags near the patient; again, beware
burns |
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Transfer
the patient from the incubator to the operating table
at the latest possible moment |
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Use
an overhead radiant heater during induction and postoperatively in
ICU. |
Hypothermia
down to 33–34°C causes:
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Respiratory
depression |
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Shivering |
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General
circulatory collapse with vasoconstriction. |
Hypothermia does not itself cause any harm and the patient
may be allowed to warm up with the assistance of an overhead
heater, if available, provided that:
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Ventilation
is supported for a few hours postoperatively |
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Oxygenation
is maintained |
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Cardiovascular
indices are maintained, such as urine output and blood pressure. |
As the temperature rises, vasodilatation will cause a fall
in blood pressure which must be corrected with volume replacement.
Atropine is well known to exacerbate hyperthermia and tachycardia
and may even precipitate febrile convulsions. It should be avoided
in a febrile child.
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