Induction and maintenance of anaesthesia in paediatric

Induction and maintenance of anaesthesia

The minimum acceptable monitoring of the paediatric patient in the anaesthetic room is a pulse oximeter; once the child is asleep, an electrocardiograph should be attached immediately. Depending on the age of the child, a blood pressure cuff is not always used; its use varies between anaesthetists. The AAGBI (2007) guidelines for patient monitoring allow for delayed attachment of monitoring equipment during the induction of children.

Alveolar concentrations of inhaled anaesthetics rise more rapidly in paediatric patients than in adults. This is because of the relatively greater blood flow and smaller functional residual capacity. Therefore, children have greater anaesthetic requirements. For example, neonates require 40% more halothane than adult patients for the same level of anaesthesia (Phillips 2007). Concentrations rise more rapidly in neonates, but inhaled anaesthetics are also metabolised more rapidly, so continuously higher levels are required to maintain the same depth of anaesthesia. In paediatric patients, anaesthetic agent is not held in reserve because there is little functional residual capacity.

Types of general anaesthesia

As with adults, the two main types of general anaesthesia induction are IV and inhalation. Both techniques are widely used for paediatric patients (Hardcastle 2007).

Intravenous: the IV method is rapid and studies have shown that there is less psychological trauma than when using the inhalation method (Phillips 2007). An IV induction using propofol is smooth and rapid (Hardcastle 2007), with a rapid recovery, and is usually associated with less post-operative nausea and vomiting than inhalation anaesthesia. Its main disadvantage is pain on injection, for which some anaesthetists add lidocaine. Contraindications to IV induction include a perceived difficult intubation and inhaled foreign body in the airways.

• Topical anaesthesia: topical anaesthetics help to prevent the psychological trauma of pain during cannulation (Hardcastle 2007). Distraction techniques can be useful when cannulating and during inductions (Hardcastle 2007); a common technique is to ask the parent to sit, holding the child on their lap, and wrap the child’s arm to be cannulated around their back, out of sight.
• Inhalation: inhalation induction may be preferable if the child is afraid of the cannulation process, and may be the only option if venous access cannot be obtained. However, some children become distressed during placement of a face mask. Other methods providing a less stressful induction include scented face masks.

Rapid induction using inhalation agents is possible but can cause breath holding and laryngospasm if the airway is stimulated while the patient is lightly anaesthetised (Hardcastle 2007). When venous access is not possible before induction, it is required as soon as deep anaesthesia is reached.

Complete time out activity 3

Consider what options may be available to you to comfort a distressed, crying child who arrives in the anaesthetic room and cannot be consoled.

Once completed your time out activity is saved and stored in "My Modules".

Volatile agents

Sevoflurane is the agent of choice for paediatric anaesthesia (Table 3). The indications for rapid sequence induction in the paediatric patient are the same as those in an adult (Allman and Wilson 2006).

Table 3

Airway

The purpose of an airway adjunct is to maintain a patent airway, provide ventilation that allows adequate gas exchange, and provide supplemental oxygen or anaesthetic agents to the patient when normal responses are compromised. The type of procedure to be conducted and the preferences of the surgeon and anaesthetist generally determine the type of airway to be used; the variety of airways is the same as for an adult. For intubation, an infant’s head should be elevated slightly but not hyper-extended. Adewale (2009) advocates the use of a neck or shoulder roll support to relieve the equally problematic hyper-flexion of the infant’s neck. If intubation takes longer than 30 seconds, the paediatric patient should be ventilated with 100% oxygen before any additional attempt to intubate.

Supraglottic airways

Supraglottic airway devices are commonly used in adults and paediatric patients. Allman and Wilson (2006) recommended using a bite block with a reinforced laryngeal mask airway to prevent occlusion if the child bites down on the tube of the laryngeal mask airway. They also advise that a size one laryngeal mask airway should be used only for short procedures. Assessment of the size and inflation of the airway can be made using the information on the packaging of the laryngeal mask airway, which gives a weight range and inflation level.

A study by Schunk et al (2013) suggested that the I-gel is more easily, more rapidly and more accurately placed than the laryngeal mask airway, and so it may be useful in an emergency situation when paediatric sizes are available.

Complete time out activity 4

Calculate the size of endotracheal tube required for children aged three, six and ten, and make a list of which tubes you would prepare.

Once completed your time out activity is saved and stored in "My Modules".

Endotracheal tube

Allman and Wilson (2006) suggested that uncuffed endotracheal tubes should be used in paediatric patients aged under eight years. However, there is debate over this. The theory is that using an uncuffed endotracheal tube avoids causing trauma to the narrow and delicate airways, preventing later airway obstruction as a result of oedema. On the other hand, an uncuffed tube does not protect against emptying of stomach contents (Subhash 2004).

Where the fasting state of a patient is unknown, an endotracheal tube is always used in preference to a supraglottic airway; this is also true for intra-abdominal, intra-thoracic and neurological procedures. Uncuffed endotracheal tubes allow for a slight space around their exterior circumference and a wider internal diameter than a cuffed tube (Wright 2007).

A correctly sized tube allows adequate ventilation, but with an audible leak during positive pressure ventilation at 20cm H2O. The commonly used calculation for a paediatric endotracheal tube is provided in Box 1, although there are slight variations. A range of tube sizes around the original calculation should be available for use; half a size above and below your calculation. Laryngeal mask airways are also required in case of emergency.

Box 1. Calculation of endotracheal tube size for the paediatric patient

Tube size (internal diameter in mm) = (Age ÷ 4) + 4

Length of oral tube (cm) = (Age ÷ 2) + 12

Length of nasal tube (cm) = (Age ÷ 2) + 15

Extubation and emergence from anaesthesia

Airway issues are the most common concern on emergence from anaesthesia and in the immediate post-operative period (Hatfield and Tronson 2009). Suction equipment should be available and some suctioning is usually performed before extubation.

Extubation is usually preceded by administration of oxygen and followed by high-flow oxygen administration. There is a greater risk of laryngospasm if extubation is not timed so that the patient is either deeply or lightly anaesthetised; if the patient is somewhere in between, they are unable to safely maintain their own airway. If they are still deeply anaesthetised, the extubation is unlikely to trigger laryngospasm; if lightly anaesthetised, then their own reflexes are sufficient to protect them from laryngospasm.

When emerging from anaesthesia, younger patients may develop muscle rigidity and experience violent shaking. This uses energy and therefore high-flow oxygen is required (Hatfield and Tronson 2009). Oxygen masks should be kept on and the patient should be kept warm. Many patients aged from early teens through to young adulthood appear resistant to analgesia and sedative medications and can be restless on waking. In stress, a young person’s body diverts most of its blood supply to muscles, meaning that when drugs are given intravenously, they are less likely to reach the brain (Hatfield and Tronson 2009).

It is important to secure a cannula properly, usually by wrapping it in flexible bandage, to prevent harm and to enable immediate access to the IV route in case of emergency.

Complete time out activity 5

Does your place of work have a paediatric airway trolley? Do you know where to find it and what equipment it should have?

Once completed your time out activity is saved and stored in "My Modules".

Learning points

1. The minimum acceptable monitoring of the paediatric patient in the anaesthetic room is a pulse oximeter. Alveolar concentrations of inhaled anaesthetics rise more rapidly in paediatric patients than in adults because of the relatively greater blood flow and smaller functional residual capacity. Therefore, children have greater anaesthetic requirements.
2. Volatile agents used in paediatric anaesthesia are sevoflurane, halothane, isoflurane and nitrous oxide. Among these sevoflurane is the agent of choice for paediatric anaesthesia.
3. If intubation takes longer than 30 seconds, the paediatric patient should be ventilated with 100% oxygen before any additional attempt to intubate. Using a bite block with a reinforced laryngeal mask airway is recommended to prevent occlusion if the child bites down on the tube of the laryngeal mask airway.
4. The calculations used to determine the correct internal diameter of a paediatric endotracheal tube is (age ÷ 4) + 4; length of oral tube is (age ÷ 2) + 12 and length of nasal tube is (age ÷ 2) + 15.