26. ANAESTHESIA FOR INFANTS AND CHILDREN

The anaesthetist must access the child and prepare for anaesthesia and must also gain the trust of the child and the parents. The anaesthetist should explain to the child where appropriate, and the parents what will happen, especially preoperative fasting, the method of induction of anaesthesia and what to expect after the operation.

Preoperative Assessment

The preoperative assessment is the same for children as for adults. It is very important to assess the severity of any upper respiratory tract infection, which is very common in preschool children. Elective surgery should be cancelled if the child is unwell with a high fever and has signs and symptoms of a respiratory tract infection. These children are at risk of laryngospasm, bronchospasm and hypoxia. If the upper respiratory tract infection is mild, then the anaesthetist should decide if the surgery should be delayed. The anaesthetist must consider the size and type of surgery.

The child must be weighed. Drugs need to be given accurately based on weight.

As with adults, the child needs assessment of their heart and lungs. The airway should be assessed. Children often have loose teeth. The anaesthetist should ask about previous anaesthetics and about a family history of anaesthetic problems.

Premedication

Premedication may be useful to produce preoperative sedation. Injections should be avoided and medications should be given orally if possible. Sedative drugs include benzodiazepines (e.g. diazepam, midazolam), chloral hydrate and antihistamines (e.g. trimeprazine, promethazine). Choral hydrate (40 mg/kg) has been used safely and effectively for many years but has a bitter taste. Midazolam may be given orally (0.5 mg/kg up to a maximum of 20 mg) or intranasal (0.3 mg/kg) and produces sedation within 30 minutes. Midazolam can rarely cause respiratory depression. Occasionally it may make the child hyperactive. For oral administration it should be mixed with a small amount of clear sweet liquid (e.g. apple juice). Though injections are best avoided, midazolam may also be given intravenously (0.1 to 0.2 mg/kg or intramuscularly 0.5 mg/kg).

Paracetamol is very effective in providing analgesia and can be given orally or rectally. It should be given at least 30 minutes before the operation. The initial maximum dose is 30 mg/kg. Further doses should be 15 mg/kg every 4 hours. The rectal dose is 30 mg/kg initially then 20 mg/kg every 6 hours. The maximum daily dose during the first two days is 90 mg/kg. After two days the maximum daily dose should not exceed 60 mg/kg.

Ibuprofen is a non-steroidal anti-inflammatory drug, which may be given orally (5 to 10 mg/kg every 4 to 8 hours).

Ketamine may also be used as premedication orally (5 mg/kg). The intramuscular dose is 2 to 4 mg/kg.

Opioids are best avoided as premedication unless the child is in severe pain.

Fasting

Small children and babies are more likely to become distressed with fasting. Clear fluids up to two hours preoperatively reduces anxiety and may decrease gastric volume. Neonates and infants may have breast milk up to four hours preoperatively. Fasting time for cow’s milk, solids and formula should be six hours. It is important not to fast children and babies for too long, as they have a smaller glycogen store which puts them at risk of hypoglycaemia. Premature infants cannot maintain adequate blood sugar for any period of fasting. Severe hypoglycaemia can result in apnoea, convulsions and brain damage. Premature infants should have intravenous dextrose whilst they are fasting.

Parents in the Induction Room

Parents in the induction room may be of benefit as they may reduce the level of anxiety in the child. Children, especially between 10 months and 6 years may have separation anxiety. Some parents, however, are very anxious and may make the child more anxious. Some parents are not happy to be present at induction of anaesthesia. Parents who are anxious or fearful will make their children anxious and fearful. Careful explanation to the parents during the preoperative assessment can reduce fear. The anaesthetist giving the anaesthetic must decide if they are happy to have a parent present. If a parent is accompanying their child, they must be told of what to expect and they must leave when told to. Someone must be available to take the parent out of the induction room.

Inhalational Induction

Inhalational induction is easily achieved with halothane or sevoflurane with oxygen. Nitrous oxide can be added. The child is encouraged to breathe 70% nitrous oxide (if available) and oxygen for a few breaths before adding the volatile anaesthetic agent. If the child is unhappy with a mask, the gas can be given with a cupped hand held away from the face. The hand is gradually placed on the face and finally replaced with a mask. The child can be encouraged to “blow up the balloon“ (inflate the reservoir bag) or told to blow hard to blow the smell away. The volatile agent is gradually introduced 0.5% every few breaths. Wiping the inside of the mask with a food flavouring like chocolate essence can hide the smell of the volatile anaesthetic agent. Once anaesthesia is obtained an intravenous cannula is inserted.

Intravenous Induction

Intravenous induction has become easier with the introduction of topical local anaesthetic agents (e.g. EMLA). This local anaesthetic cream is put on the skin over a vein and covered with an occlusive dressing 30 minutes before surgery.

Thiopentone (3 to 5 mg/kg), propofol (1 to 3 mg/kg) and ketamine (1 to 2 mg/kg) are all suitable for intravenous induction of paediatric anaesthesia. Ketamine may also be given intramuscularly (5 to 10 mg/kg). Thiopentone and propofol will cause hypotension and respiratory depression and apnoea. If these drugs are used the anaesthetist must be skilled at paediatric airway management. Ketamine will maintain the blood pressure and spontaneous respiration though this does not guarantee that the airway will not obstruct. The anaesthetist still needs experience with airway management. Ketamine will provide analgesia. It may be given for maintenance of anaesthesia (2 mg/kg/h).

Muscle Relaxants

Neonates and infants require a greater dose suxamethonium (2 mg/kg) than adults (1 mg/kg). Children less than 6 months should be given atropine before the suxamethonium to avoid bradycardia. Atropine should be given before any second dose of suxamethonium for all children.

Non-depolarising muscle relaxants should be reversed at the end of surgery. Add 2.5 mg of neostigmine to 1 mg of atropine in the same syringe. Dilute this to 5 ml and give 1 ml/10 kg (or give neostigmine 0.05 to 0.07 mg/kg with atropine 20 micrograms/kg).

Inhalational Agents

All the volatile inhalational agents and nitrous oxide can be used in paediatric anaesthesia. Halothane and sevoflurane are both suitable for inhalation induction of anaesthesia. Infants and children are very sensitive to the cardiac depression produced by halothane. The anaesthetist must take care not to give an overdose.

Analgesia

Children need intra-operative and postoperative analgesia. Propofol, thiopentone and the inhalation agents are not analgesics. Morphine (and pethidine) can be given orally, rectally, intravenously, intramuscularly or subcutaneously. All may cause respiratory depression, nausea and vomiting. It is best to give a smaller dose and check the sedation score and pain score. Further small doses can be given if needed.

Intravenous administration is the most effective and rapid route. It is also the route with the greatest potential for overdose and acute respiratory depression.

The anaesthetist must check the child’s weight and age. Morphine and pethidine both need dilution before intravenous administration. There is always a risk of incorrect calculation. The anaesthetist must check the dilution and the dose/weight.

[Morphine 10 mg/ml and pethidine 100 mg/ml can be diluted in 100 ml of normal saline giving a final concentration of morphine 100 microgram/ml and pethidine 1mg/ml. The usual intravenous bolus dose with this dilution would be 0.2 to 0.5 ml/kg. Ideally this bolus dose volume should be placed in a burette and given over 5 minutes.]

Before giving an intravenous bolus the anaesthetist should check the patient’s pain score and sedation score. The child should be monitored every 5 minutes for 20 minutes (blood pressure, pulse rate, respiratory rate, sedation score and pain score).

Oxygen, resuscitation equipment and naloxone should be available.

The morphine dose (age over 6 months) is

0.02 to 0.05 mg/kg intravenously

0.5 mg/kg orally every 4 hours

to 0.2 mg/kg intramuscularly every 4 hours

to 0.2 mg/kg subcutaneously every 4 hours.

The dose of opioids can be reduced by also using paracetamol, non-steroidal anti-inflammatory drugs and regional anaesthesia.

The efficacy of paracetamol and non-steroidal anti-inflammatory drugs are often underestimated. When given at the correct dosage and regularly these drugs can provide excellent analgesia.

Postoperative pain is best anticipated and pretreated. Paracetamol (20 to 30 mg/kg orally) should be given 30 minutes before surgery or with induction (20 to 30 mg/kg rectally). Postoperatively paracetamol may be given at dosages of 15mg/kg every 4 to 6 hours strictly up to a maximum of 90 mg/kg/day for the first two days and then as required.