Page 19 - 59peadiatric-surgery-speciality8-14_opt

58 Anaesthesia and Perioperative Care
Laryngeal Mask Airways Laryngoscopy and Intubation
LMAs (Figure 10.6) are useful airway management tools. They are less The airway should be ventilated in all but the shortest of procedures
traumatic than endotracheal tubes and do not require laryngoscopy to because the paediatric airway is very prone to obstruction during anaes-
insert. They do not, however, protect against regurgitation and aspira- thesia. For neonates and infants, a slight external pressure on the larynx
tion. Sizes 1, 1½, 2, 2½, and 3 can be used in children from 2 months helps to bring the glottis into view. A small leak should be allowed around
to 12 years of age, according to the weight of the child. the tube to prevent oedema formation and postoperative airway obstruc-
3
Endotracheal Tubes tion, which may follow prolonged intubation. If the patient is at risk of
Endotracheal tubes used for children younger than 6 years of age are aspiration, a pharyngeal gauze pack should be placed around the tube.
usually uncuffed. Table 10.1 provides a guide for choosing an appropri- A gaseous induction using 100% oxygen with halothane is the
ate endotracheal tube. technique of choice in small children and those with difficult airways.
The aim is to attain a plane of anaesthesia that is deep enough
Mask Ventilation to allow laryngoscopy. Once the pupils become constricted and
Due to the neonate’s relatively large head, a small roll should be posi- central, laryngoscopy and orotracheal intubation can be performed.
tioned under the shoulders to prevent hyperflexion of the head and align Suxamethonium at a dose of 2 mg/kg can be used to facilitate
the axis of the mouth, pharynx, and larynx to allow for easy flow of air. intubation. Atropine (0.02 mg/kg) or glycopyrrolate (0.01 mg/kg)
For the older child, no pillow or roll is needed. An appropriately sized should be given to prevent bradycardia and to dry secretions. Both
oropharyngeal airway can improve mask ventilation. lungs should be auscultated for bilateral air entry after intubation, and
the endotracheal tube should be secured firmly in position.
Signs of respiratory obstruction include an increase in respiratory
rate (>50 per minute in an infant and 30 per minute in a child); a
“see-saw” pattern of chest and abdominal breathing movements;
flaring of the alar nasi; and the use of accessory muscles of respiration
(sternomastoids, scalene muscles) resulting in suprasternal, intercostal,
and subcostal retraction.
In acute airway obstruction, for which one cannot intubate or
Figure 10.4: Miller’s blades and handle. ventilate, cricothyrotomy may be the only option. Cricothyrotomy
is difficult in a small child and carries many risks. Where difficult
tracheal intubation is anticipated, experienced help should be sought
beforehand. There are fibre-optic laryngoscopes suitable for use in
children, but this requires expertise and experience and is not an option
in emergency airway obstruction.
Muscle Relaxants
Muscle relaxants are used to facilitate tracheal intubation and provide
muscle relaxation during surgery, thus permitting lighter planes of
anaesthesia and reducing the risk of cardiovascular depression. They
Figure 10.5: Macintosh blade and handle. are used in intraperitoneal, intrathoracic, and intracranial procedures.
Muscle relaxants are classified into depolarising and nondepolarising
groups. Succinylcholine is the only depolarising neuromuscular blocker
in use today, and it remains the agent with the quickest onset and
shortest duration of action. Unfortunately, succinylcholine is associated
with some life-threatening side effects (hyperkalaemia, malignant
hyperthermia), and its use has reduced somewhat in recent years.
Nondepolarising muscle relaxants are classified based on structure
and mode of elimination. The benzoquinolones are atracurium, cis-
atracurium, and mivacurium, which may be available in some African
urban centres. The first two are eliminated by Hoffmann degradation
and ester hydrolysis by nonspecific plasma esterases. Mivacurium is
Figure 10.6 Laryngeal mask airways. metabolised by plasma cholinesterase.
The aminosteroids (pancuronium, vecuronium, and rocuronium) are
metabolised in the liver, and their inactive end products are eliminated
Table 10.1: Endotracheal tube sizes for children.
by the kidney.
Age Size of endotracheal tube (mm)
Monitoring
Premature 2–2.5
The purpose of monitoring is to measure physiological variables and to
Full-term newborn 3.0 indicate trends of change, thus enabling corrective action to be taken.
The anaesthetist remains the most important monitor and must remain
6–12 months 3.5
in close contact with the patient during all aspects of the anaesthetic.
The precordial (or oesophageal) stethoscope is an invaluable monitor
1–2 years 4–4.5
for many paediatric anaesthetists. It provides a direct way to continuously
>2 years 4.5 + [age (in years) ÷ 4] monitor heart rate and rhythm as well as breath sounds; it allows early
detection of changes in the rate and character of these sounds.
The electrocardiogram (ECG) is useful for diagnosing rate-related
arrhythmias, especially bradycardia and supraventricular tachycardia
(SVT). The ECG is an index of electrical activity. A normal waveform