• Anaesthesia for patients with pacemakers:

 preoperatively:

– preoperative assessment is particularly directed towards the CVS.

– pacemaker type and indication are ascertained. Pacemakers are usually checked regularly (e.g. every 3 months).

– ECG:

– if pacing spikes occur before all or most beats, heart rate is pacemaker-dependent.

– although traditional advice was to convert older demand pacemakers to fixed rate by placing a magnet over the pulse generator, this is no longer recommended outside specialist cardiac pacing units since the effect on the device’s programming is unpredictable.

– CXR: pulse generator and lead position may be identified.

 perioperatively:

– potential electrical interference or pacemaker damage by diathermy is more likely if the latter is applied near the device. Sensing may be triggered, with resultant chamber inhibition, or arrhythmias induced. Diathermy may also reprogramme the pacemaker to a different mode.

– if avoidance of diathermy is not possible, risks are reduced by using bipolar diathermy, or placing the plate distant from the pacemaker if unipolar diathermy is used. Current should not be applied across the chest, and its strength and duration of use should be minimal.

– care should be taken with CVP/pulmonary artery catheters since they may dislodge the electrodes.

– temporary pacing facilities (or non-invasive transthoracic pacing) and an external defibrillator should be available.

– isoprenaline may be required if pacemaker failure occurs.

– alteration of pacemaker sensitivity by halothane has been described in older pacemaker models.

– avoidance of suxamethonium has been suggested in case fasciculations are sensed as arrhythmias.

– MRI may be hazardous since the pacemaker may be switched to asynchronous mode, may fail altogether or may move within the chest.

 postoperative pacemaker checking may be required.

 recognition of the infant or child at risk of cardiopulmonary arrest and the application of strategies for its prevention.

 identification of the cognitive and psychomotor skills necessary for resuscitating and stabilising the neonate, infant or child in respiratory failure, shock or cardiopulmonary arrest (e.g. drug dosages, airway and ventilation techniques, identification of normal and abnormal cardiac rhythms, defibrillation, vascular access).

• Thus in children compared with adults:

 RS:

– the tongue is large and the larynx situated more anteriorly and cephalad (C3–4). The epiglottis is large and U-shaped. A straight laryngoscope blade is thus often preferred for tracheal intubation, and the head should be in the neutral position (as opposed to the ‘sniffing position’ in adults).

– the cricoid cartilage is the narrowest part of the upper airway up to 8–10 years of age (cf. glottis in adults). A small decrease in diameter (e.g. caused by oedema or stricture formation following prolonged tracheal intubation) may lead to airway obstruction.

– the left and right main bronchi arise at equal angles from the trachea. At birth, the tracheobronchial tree is developed as far as the terminal bronchioles. Alveoli number 20 million, increasing to 300 million by 6–8 years.

– respiration is predominantly diaphragmatic, and sinusoidal and continuous instead of periodic. Neonates are obligatory nose breathers. Respiratory rate is increased. Tidal volume is about 7 ml/kg as in adults. The infant lung is more susceptible to atelectasis because the chest wall is more compliant and therefore pulled inwards by the lungs, decreasing FRC. Closing capacity may exceed FRC during normal respiration in neonates and infants. Surfactant may be deficient in premature babies.

– response to CO₂ is reduced at birth, and irregular breathing may also occur. Premature babies may suffer from apnoeic episodes; they are at risk of postoperative apnoea up to about 50 weeks postconceptual age. Gasp and Hering–Breuer reflexes are active.

– basal metabolic rate and O₂ consumption are high (the latter is 5–6 ml/kg/min, compared with about 3–4 ml/kg/min in adults). Hypoxaemia thus occurs more rapidly than in adults.

– the oxyhaemoglobin dissociation curve of fetal haemoglobin is shifted to the left (P₅₀ of 2.4 kPa [18 mmHg]). Haemoglobin concentration falls from 18 g/dl (1–2 weeks of age) to 11 g/dl (6 months–6 years).

 CVS:

– cardiac output is 30–50% higher than in adults, largely due to increased heart rate. Arterial BP is lower (Table 35).

– left and right ventricles are similar at birth, the former fibrous and non-compliant, making stroke volume relatively fixed.

– blood volume at birth is up to 90 ml/kg (or 50 + haematocrit). It falls to 80 ml/kg for children and 70 ml/kg by 14 years.

– veins are more difficult to cannulate.

– reversion to fetal circulation may occur in severe hypoxaemia.

 CNS:

– the spinal cord ends at L3 at birth, receding to L1–2 by adolescence.

– the immature blood–brain barrier results in increased sensitivity to centrally depressant drugs, particularly opioid analgesic drugs.

– vagal reflexes are particularly active in children. Bradycardia readily occurs in hypoxaemia.

– subependymal vessels are fragile in premature neonates, with risk of rupture if BP and ICP increase.

 temperature regulation is impaired. Ratio of body surface area to body weight is greater than in adults and there is less body fat. Thus heat loss is rapid, compounded by impaired shivering and increased metabolic rate. Brown fat is metabolised to maintain body temperature. Insensible water loss is increased in premature babies.

 prolonged fasting may cause hypoglycaemia in small children, and oral clear fluids are usually allowed up to 2 h preoperatively (4 h for milk). IV administration of dextrose may be required.

 fluid balance is delicate, since a greater proportion of body water is exchanged each day. Total body water is normally increased, with a higher ratio of ECF to intracellular fluid (ECF exceeds intracellular fluid in premature babies). The kidneys are less able to handle a water or solute load, or to conserve water or solutes. Thus dehydration readily occurs in illness.

Appropriate maintenance fluid requirements (using dextrose/saline) have traditionally been calculated thus:

  4 ml/kg/h for each of the first 10 kg, plus

  2 ml/kg/h for each of the next 10 kg, plus

  1 ml/kg/h for each kg thereafter.

  More recently, because of the risk of perioperative hyponatraemia (children being at particular risk from resultant encephalopathy), and because perioperative hypoglycaemia is less of a problem than traditionally thought, there has been a move away from hypotonic solutions such as dextrose/saline, with maintenance fluids given as 0.45–0.9% saline or Hartmann’s solution, and isotonic fluids avoided if plasma sodium concentration is under 140 mmol/l.

Blood is traditionally given above 10% of blood volume loss, but larger blood losses are increasingly allowed if starting haemoglobin concentration is high. In hypovolaemia, 10 ml/kg colloid is a suitable starting regimen.

 actions of drugs may be affected by the above factors, or by lower plasma albumin levels (up to 1 year of age), resulting in greater amounts of free drug. Renal and hepatic immaturity may contribute to reduced clearance. MAC of inhalational anaesthetic agents is increased in neonates, but may be reduced in premature babies. Neonates are more sensitive to non-depolarising neuromuscular blocking drugs, probably due to altered pharmacokinetics. They may be resistant to suxamethonium, requiring up to twice the adult dose.

• Practical conduct of anaesthesia:

 children are placed first on the operating list, to allow as short a fasting time as possible.

 most standard drugs are used, administered according to weight. As a rough guide the following scheme may be useful:

– 14 years: adult dose.

– 7 years: adult dose.

– 4 years: adult dose.

– 1 year: adult dose.

– newborn: adult dose.

– premature: adult dose.

 premedication is often given orally, to avoid injections, but standard im drugs are also given. Rectal administration has also been used. Atropine may be given to reduce excessive secretions and vagal reflexes.

 induction of anaesthesia:

– cyclopropane was popular but is no longer available in the UK. Halothane has been replaced by sevoflurane. Inhalational induction is rapid because of increased alveolar ventilation, a low FRC and a high cerebral blood flow.

– standard iv anaesthetic agents are suitable. Administration im (e.g. ketamine) is also used. EMLA or topical tetracaine (amethocaine) is routinely used before iv induction.

The presence of parents at induction is usually allowed, depending on the circumstances.

 appropriately sized laryngoscope handles and blades are employed. Uncuffed tracheal tubes are commonly used (usually until ~10 years), with a small air leak at 15–25 cmH₂O airway pressure, to avoid subglottic stenosis. The approximate size may be calculated thus:

– diameter = (age/4) + 4.5 mm.

   For neonates:

– under 750 g/26 weeks’ gestation: 2.0–2.5 mm.

– 750–2000 g/26–34 weeks: 2.5–3.0 mm.

– over 2000 g/34 weeks: 3.0–3.5 mm.

– length = (age/12) + 12 cm.

More recently, cuffed tubes have been used in term neonates and children, on the basis that a smaller tube with a low-pressure, high-volume cuff is better able to provide an adequate conduit for ventilation whilst minimising pressure on the cricoid cartilage (from the tube itself) and the trachea (from the cuff). A formula for cuffed tubes has been suggested: diameter = (age/4) + 3.0 mm.

 dead space and resistance should be minimal in anaesthetic breathing systems; adult forms are suitable if the child weighs over 20–25 kg but the Bain system is often avoided because of increased resistance to expiration. Ayre’s T-piece is suitable up to 25 kg. Spontaneous ventilation via a facemask or LMA is usually suitable for short procedures in children older than 3 months. Below this, tracheal intubation and IPPV are traditionally performed, although the LMA is preferred by some.

 for IPPV using a T-piece, the following fresh gas flows have been suggested, producing slight hypocapnia:

– 10–30 kg: 1000 ml + 100 ml/kg per min.

– > 30 kg: 2000 ml + 50 ml/kg per min.

Set minute volume should equal twice fresh gas flow.

 routine monitoring, including temperature measurement.

 anaesthetic rooms and operating theatres should be warmed. Warming blankets and reflective coverings should also be used, with humidification of inspired gases.

 tracheal extubation may be performed with the child awake or anaesthetised, depending on the clinical context.

 regional techniques are effective for peri- and postoperative analgesia, e.g. caudal analgesia, inguinal field block, penile block. Local wound infiltration is also effective. Spinal and epidural anaesthesia have also been used.

 paracetamol and codeine are often used for postoperative analgesia, with morphine for severe pain. Antiemetic drugs are given as required; ondansetron and cyclizine are commonly used.

• Other problems are related to the procedure performed, e.g.:

 repair of congenital defects, e.g. tracheo-oesophageal fistula, pyloric stenosis, gastroschisis, diaphragmatic hernia, congenital heart disease.

 related to trauma.

 ENT, dental and ophthalmic surgery.

• Main clinical problems encountered include:

 acute respiratory failure:

– upper airway obstruction:

– neonates: choanal atresia, congenital facial deformities, laryngeal/tracheal abnormalities.

– infants/children: inhaled foreign body, tonsillar/adenoidal hypertrophy, croup, epiglottitis and angioedema.

– lung disorders:

– neonates: meconium aspiration, respiratory distress syndrome, diaphragmatic hernia, pneumothorax, chest infection.

– infants/children: pneumonia, asthma, bronchiolitis, cystic fibrosis, congenital heart disease, trauma, near-drowning, burns.

– in neonates, respiratory impairment may result in the development of a persistent fetal circulation.

 neurological disease:

– neonates: birth asphyxia, central apnoea, convulsions.

– infants/children: meningitis, encephalitis, status epilepticus, Guillain–Barré syndrome.

 trauma: the leading cause of death in children under a year old and the third leading cause in older children (after sudden infant death syndrome and congenital abnormalities). Non-accidental injury must always be considered.

– head injury occurs in 50% of cases of blunt trauma. A modified Glasgow coma scale is used for assessment; otherwise, management is along similar lines to that of adults.

– spinal cord injury and thoracic/abdominal trauma is usually caused by road traffic accidents.

 poisoning and overdoses.

• Specific attention must be paid to:

 smaller equipment, drug doses and fluid volumes; specialised equipment.

 nutrition and electrolyte/fluid balance.

 temperature regulation.

 sedation and analgesia.

 educational and psychological needs.

 the risk of retinopathy of prematurity in neonates.

• Methods used depend on the setting and whether the pain is acute or chronic:

 experimental methods (e.g. assessing analgesic effects of new drugs):

– animals: tail-flick response to heat; pedal withdrawal response to pinching the foot; head-shaking response to ear pinching.

– humans: degree of tolerated digital pressure; tolerated duration of immersion of the forearm into icy water.

 acute pain, e.g. postoperative: linear analogue scale; using numbers or words to rate the degree of pain (patient and observer assessment may be used); demand for analgesia. Babies have been studied by recording and analysing their cries.

 chronic pain: the pain is characterised by noting its type, duration, location, quality, intensity, modifying factors (e.g. food, exercise), time relations, and associated symptoms and mental changes. Clinical examination and investigations are performed as appropriate. Linear analogue and rating scales may be used as above. More complicated psychological questionnaires for analysis of personality and pain (e.g. Minnesota multiphasic personality inventory, McGill questionnaire) have been used.

• Chronic pain management may involve the following, after pain evaluation:

 simple measures, e.g. rest, exercise, heat and cold treatment, vibration.

 systemic drug therapy:

– analgesic drugs: different drugs, dosage regimens and routes of administration may be chosen, depending on the severity and temporal pattern of the pain, and efficacy and side effects of the drugs. Drugs used range from mild NSAIDs to opioid analgesic drugs. The latter are usually reserved for severe pain of short duration, or pain associated with malignancy; they may require concurrent antiemetic and aperient therapy. Implantable devices may be used for intermittent iv, epidural or subarachnoid injection or continuous infusion of opioids.

– other drugs used include: