Anaesthetic Management

Anaesthetic Management

Regional techniques as the sole anesthetic are better avoided in those less than 15 years of age.

Pre-Operative Preparation of Patient

Check the medical state of the infant; look for congenital abnormalities, any other underlying medical disorders, the degree of dehydration, electrolyte imbalance etc. Check the time of the last feed. Prolonged starvation should be avoided. Babies may be breast-fed 4 hours before surgery but can be given clear fluids up to 2 hours pre-op. Infants and older children may be given food or milk up to 6 hours pre-operatively and clear fluids up to 2 hours before surgery. The fluids can be solutions containing glucose, as children are prone to hypoglycaemia. In emergency surgery it is important to note that the gastric emptying time can be delayed for the same reasons as it is in adults, e.g. peritoneal irritation, fear, head injuries etc. The patient is best considered to have a full stomach and the usual precautions of pre oxygenation, rapid sequence induction and cricoid pressure applied. Weigh the patient.

Psychological Preparation for Surgery

Seek to establish a rapport with the child, trying to allay any fears (e.g. the fear of venepuncture, anaesthesia, surgery). Discuss any fears expressed by the parents. Discuss the method of induction with the child if the child is old enough to understand. If there is no contraindication to either an inhalational or intravenous induction and there is no special benefit to be derived from using one technique over the other, then the child's wishes should be taken into account.

Premedication:

This is often omitted now but may be used:

• To dry secretions
• To block undesirable reflexes due to surgery
• To sedate the child before surgery
• To reduce the dose of anaesthetic drugs required

Drugs used for premedication:

Atropine 10 micrograms/kg IM as an antisialogogue

Midazolam 0.5mg/kg PO, trimeprazine 2-4mg/kg PO or

Chlor alhydrate 50mg/kg PO for sedation

Opioids are rarely used for premedication and painful IM injections should be avoided in pediatric anesthesia wherever possible. Opioids should be used with care in infants under the age of 6 months due to the difficulty of calculation of the correct dose, administration and the risks of respiratory depression.

Pre-Operative Preparation of Equipment

Check the machine, equipment and drugs as described in module 2. This must be done before the child is brought into theatre. Work out the following details and write them out on a sheet of paper before commencing the anaesthetic.

• The dose of each drug to be used, based on the child's weight.
• The size of the endotracheal tube to be used, based on the child's age.

(Always have a tube one size smaller and larger also available).

• The maintenance fluid that the child will need while in the operating theatre (based on the child's state of hydration and weight).
• The child's blood volume. This will depend on the child's age and weight. Knowing the blood volume will indicate the significance of any blood loss in theatre and the need to transfuse the patient.
• Draw up the drugs and label the syringes before commencing the anaesthetic. This is essential.

Intra-Operative Management

Monitoring

Always monitor the following:

Cardiovascular System

• Pulse.
• Heart rate. Use a precordial or oesophageal stethoscope.
• Blood pressure. Make sure the cuff is the right size.
• ECG if available.
• CVP if necessary.
• Blood Loss. Weigh the sponges. Blood on the drapes and gowns and also on the floor must be taken into account. If 10-15 % of the blood volume is lost consider replacement with blood.

Respiratory System

Observe the colour of the mucous membrane and the blood continuously. The respiratory rate and the tidal volume must be noted if possible. Use pulse oximetry and capnography if they are available. Remember the response of pediatrics to hypoxia is bradycardia.

Temperature

The usual sites of temperature monitoring are rectal, oesophageal or axillary. It has been mentioned previously that neonates and young children have poor control over body temperature, so every effort should be made to conserve heat. Here are some of these measures:

The temperature of the theatre environment should be between 75 and 80 degrees F (21-24oC).

Neonates and very young infants should be brought to the operating room in a humidicrib. A method of warming should be used for all patients weighing less than 5kg, or patients over 5kg who need prolonged surgery or large transfusions of cold blood. Minimise skin exposure by wrapping the patient in velband (cotton wool). Inspired gases should be humidified if possible.

Warm all blood and plasma solutions before they are infused. Large volumes of crystalloids if administered to the patient need to be warmed.

Induction

Particular care should be taken in the moribund patient and also in the patient who is at very great risk of regurgitating (e.g. very severe abdominal distension).

Inhalational induction is frequently used with children. Air or nitrous oxide/oxygen and halothane or ether/air/oxygen can be used. If the patient is very ill the oxygen concentration can be increased to 50-100%. An intravenous line is established as soon as possible if not established pre- induction. This will require a skilled assistant to maintain the airway. .

Intravenous induction is perhaps the kindest and quickest method in children who have accessible veins or an infusion running. The drugs available for intravenous induction have been discussed under pharmacology of anaesthetic agents. Thiopentone can be used in the fit patients. Ketamine IV may be used in the poor risk patients and atropine should be used to reduce secretions.

Intramuscular induction may be carried out using ketamine IM in patients who have no accessible veins and in whom an inhalational induction is not possible, for instance anyone with facial burns.

Rectal induction- Thiopentone and methohexitone have been used in the past for this purpose. The technique is not recommended.

Intubation

Intubation can be performed as follows:

(Awake intubation is no longer recommended)

Intubation under deep general anaesthesia (inhalational)

Anaesthetise the patient with air/nitrous oxide/oxygen and halothane or ether/air and oxygen. Once the jaw is relaxed, insert a Guedel airway and give the patient a few more breaths of anaesthetic. Intubation is then performed. If there is any evidence that the patient is light when the laryngoscope is inserted, then the patient should be anaesthetised further and intubation deferred until the patient is in a deeper plane of anaesthesia. Swallowing, breath-holding, coughing etc. are signs that the patient is not ready for intubation and if it is attempted then laryngeal spasm may result.

This method (inhalational anaesthesia) for intubation may be appropriate in the following conditions:

• Very young infants.
• Children with airway problems. These patients may be difficult to ventilate with a mask and this makes the use of a relaxant hazardous.
• Lack of intubating experience on the part of the anaesthetist.

The problems of intubating a patient under deep inhalational anaesthesia are:

• The tongue may fall back and obstruct the airway during inhalational induction.
• Laryngeal spasm may occur if the intubation is performed too early.
• Bradycardia may resultfrom the use of halothane or during intubation.
• Circulatory collapse or cardiac arrest may occur if the patient is too deep.

Intubation Following the Use of a Relaxant

A relaxant makes intubation easier and is the preferred method in all children.Relaxants should be used before intubation only if the anaesthetist is able to ventilate the patient with a mask.

Suxamethonium can be used for intubation at a dose of2mg/kg IV in the neonatal period and 1.5mg/kg IV thereafter.

Suxamethonium is useful in the following cases:

• A patient with a full stomach.
• Patients likely to have intubation problems and who need good intubating
• Very ill patients who need quick intubation and for whom oxygenation is mandatory. A modified rapid sequence induction may be used (ventilation with 100% oxygen with the application of cricoid pressure) as it is difficult to pre-oxygenate an anxious, upset child.
• Patients who may be difficult to ventilate by mask but who need rapid intubation e.g. treatment of laryngeal spasm.

The choice of the non-depolarising relaxant will depend on the relaxant available.

Maintenance

The anaesthetic is maintained with air or nitrous oxide/oxygen, halothane, relaxant (e.g. pancuronium) or ether/air/oxygen and pancuronium. Analgesia is titrated IV as required. A peri-operative combination of simple analgesics (paracetamol, NSAIDs), local anaesthesia +/- opioid or ketamine analgesia should be used whenever possible. Position the patient with care.

Peri-Operative Fluids

Fluids may be classified as replacement fluids (including fluid for resuscitation) or maintenance fluids. Children are vulnerable to cerebral oedema from hyponatraemia (low plasma sodium) and so hypotonic fluids, (especially 4% dextrose/0.18% saline), should be avoided in the peri-operative period.

Pre-Operative Fluids

Prolonged starvation should be avoided and free clear fluids can be given orally up to 2 hours before elective surgery.

Fluid resuscitation may be required if the child is unwell. Diagnosis of hypovolaemia or dehydration is made on clinical grounds. Important clinical signs include delayed capillary refill time greater than 2 seconds (a child who is well hydrated and warm should have an instantaneous capillary refill time), cool peripheries, altered mental status, either lethargic or agitated and rising heart rate. Hypotension, cold white peripheries and a child who is unresponsive are late and extremely ominous signs. In case of difficult venous access, intraosseous access should be considered (20G butterfly needle inserted directly e.g. proximal tibia).

The immediate treatment is 100% oxygen by facemask and a rapid fluid bolus of 0.9% saline 20 ml/kg. The child should be re-assessed and the fluid bolus repeated if necessary. A common problem in management of severe hypovolaemic shock is failure to administer enough fluid. Blood or colloid should be considered if there is no improvement after 40ml/kg of fluid.

Intra-Operative Fluids

Replacement fluid with isotonic solution (Ringers or 0.9% saline), colloid or blood should be administered as required. Fluid may be required to counter the effects of anaesthesia or replace intra-operative fluid losses. Intra-operative fluid losses depend on the type of surgery and should be guided by clinical monitoring (heart rate, capillary refill, blood pressure). Most children do not require dextrose containing solutions during surgery.

• Minor surgical procedures 10ml/kg bolus (only).
• Major surgical procedures up to 20ml/kg/hour with additional bolus 20ml/kg as required.

If 10-15% of the blood volume is lost then blood transfusion should be considered. As a rough guide, 4ml/kg of packed cells (or 8ml/kg whole blood) will raise the haemoglobin by 1g/dL. Once the decision is made to transfuse the child, use as much of a single donor unit as possible to limit exposure to other donors.

Post-Operative Fluids

Intravenous fluids should only be given if the child is unable to tolerate oral fluids. Replacement with isotonic fluids may be required to replace ongoing losses such as blood loss, vomiting, nasogastric fluid loss or wound drain losses.

Maintenance fluids should be given to provide the requirements for water, sodium and potassium (potassium not required on the first post-operative day, 1-2 mmol/kg/day thereafter). These may be given as 0.45% or 0.9% saline with 5% dextrose, calculated at the rate of either 10ml/kg/hour for the first hour and 5 ml/kg/hour thereafter or 4ml/kg/hour for the first 10kg + 2ml/kg/hour for the next 10kg + 1ml/kg/hour for any additional kgs.

An easily remembered formula based on the weight of the child is as follows:

Example:

Fluid balance should be measured carefully to avoid fluid overload

Reversal

At the close of the operation the relaxant is reversed. Atropine 20 micrograms/kg or glycopyrrolate 8 micrograms/kg is given intravenously, followed by neostigmine 50 micrograms/kg. It is easier to draw up the atropine and neostigmine in separate syringes as the doses are much smaller than adult doses. The same precautions must be taken before extubation as have been described for adults. Before extubation the patient must breathe deeply and regularly and must be given at least 10 breaths of 100% oxygen. The pharynx must be suctioned before and after extubation. Administer oxygen by mask after extubation and ensure that the patient is still breathing adequately.

The patient should be nursed on his side during the recovery period.

Never leave patients unattended (even for a minute!) until they are awake and fully conscious.

Other Anaesthetic Techniques Available

Spontaneous respiration using air or nitrous oxide/oxygen/volatile. This is similar to the technique described for adults . A mask and an airway of appropriate size or a LMA can be used.

Ketamine, given either intravenously or intramuscularly in combination with diazepam. It is believed but not confirmed that the incidence of hallucinations after ketamine is less frequent in children.

These techniques are used in fit infants who are due to have brief, minor, superficial surgery e.g. removal of foreign bodies from the ear, cystoscopies, reduction of fractures, removal of lesions from the limbs. Ketamine infusions are used widely in older children when muscle relaxation is not necessary.

Post-Operative Care

The patient is observed in the recovery ward until fully awake, with careful monitoring of analgesia, fluids and oxygen therapy. Post-operative complications as outlined in the relevant chapters must be watched for and treated vigorously.

Pain Relief: A combination of analgesic techniques should be used whenever possible - simple analgesics such as paracetamol and NSAIDs, local anaesthetics, either infiltrated or regional blocks such as a caudal block and/or ketamine or opioid analgesia.

Early Postoperative Complications

Laryngeal Oedema

This may occur in young children following extubation and is caused by the endotracheal tube in the larynx. Laryngeal oedema is associated with:

• Large endotracheal tubes.
• Endotracheal tubes made of irritant material, e.g. red rubber or irritant chemicals used in sterilising tubes.
• Any infection in the upper respiratory tract or a history of croup.
• Trauma to the upper airway, e.g. difficult, clumsy or repeated laryngoscopies or bronchoscopies. These will predispose to oedema of the mucosa of the larynx.

The small diameter of the child's respiratory tract makes it especially susceptible to obstructioneven with a small degree of oedema of the mucous membrane.

Stridor, which is a harsh noise during inspiration, is one of the cardinal signs of laryngeal oedema but if the anaesthetist is conscious of this complication arising in young children and watches out for it after extubation, the condition can be treated in the early stages. Late and worrying signs are restlessness, sweating and cyanosis. The pulse and respiratory rate rise initially and then fall indicating impending respiratory arrest. Treatment needs to start at the earliest indication of the problem.

Treatment:

• Humidified oxygen.
• Careful observation. If there is no relief, then try:
• Adrenaline nebules 0.5mg/kg (1:1,000 solution containing 1mg/ml) up to a maximum of 5mg. Can be repeated after 2-3hours.
• Steroids: -dexamethasone 0.25mg/kg IV to a maximum of 8mg. -hydrocortisone 1-2mg/kg IV.
• If the condition is still not relieved, it may be necessary to consider re-intubation or even tracheostomy.

Laryngospasm

Another frequent acute complication of anaesthesia in children is laryngospasm. This can be caused by:

• Secretions or vomit
• Inhalational anaesthetic agents
• Attempts at intubation
• Light anaesthesia
• Surgical stimulus
• Extubation

Treatment:

• 100% oxygen/a tight fitting face mask/ CPAP
• Jaw thrust
• Airway suction
• Deepen anaesthetic if possible
• Stop surgical stimulus

If This Fails

• Give suxamethonium 0.25- 0.5mg/kg
• Ventilate with face mask if possible
• Consider re-intubation