Neonatal anaesthesia: Difference between revisions

<blockquote>'''DEFINITIONS'''

 

=== Examination ===

=== Investigations ===

===== Laboratory investigations: =====

 

 

FIGURE 1

Standard monitoring must be applied prior to induction of anaesthesia. This includes oxygen saturation, ideally pre-ductal (right hand) and post-ductal (other limbs). A low post-ductal

oxygen saturation may be a sign of low pulmonary blood flow, for instance due to significant pulmonary hypertension in a septic neonate (see transitional circulation below).

 

 

 

=== Preparation of drugs ===

=== Induction of anaesthesia ===

Inhalational induction is ideally with sevoflurane although halothane can also be used. The MAC of volatile agents is lower in neonates than in older children, and the onset of anaesthesia is relatively fast due to the rapid respiratory rate and high cardiac output. However, the neonatal myocardium is extremely sensitive to the negative inotropic effects of volatile agents, so deep volatile anaesthesia must be avoided. Sevoflurane can cause apnoea at high concentrations and the induction concentration should not exceed 6%. The neonate might require assisted mask ventilation until an airway is secured as they may hypoventilate during induction; take care to turn the inspired concentration of volatile agent down if assisted ventilation is used, otherwise the child will become very deep, very quickly. Halothane is more likely to cause myocardial depression and the induction concentration should be kept less than 2%. Halothane can cause arrhythmias in high concentrations, especially if the CO2 is also high. Atropine (20mcg.kg

-1 IM or IV) should be considered prior to induction to reduce bradycardia, particularly if halothane is used. Alternatively, intravenous induction with ketamine (2mg.kg

-1) or thiopentone (2-4mg.kg-1) can be performed; induction of anaesthesia will be rapid (the anaesthetist must be confident they can manage the airway), and recovery may be delayed. Ketamine is particularly useful for the critically unwell neonate as cardiovascular depression is minimised. Use glycopyrrolate (10mcg.kg-1 IV) or atropine (20mcg.kg-1 IV or IM) to minimise the secretions caused by ketamine.

=== Maintenance of anaesthesia ===

Anaesthesia is maintained with volatile, oxygen and air or nitrous oxide. A ketamine infusion run at 2-4mg.kg.hr-1 is a useful alternative in unstable neonates. Attention must be paid when positioning the patient and pressure points must be protected. Whenever the child is moved, check the position of the tracheal tube as it is very easy to displace the tracheal tube in neonates, which could have potentially catastrophic consequences.

It is important to consider pain management in all neonates. Pain pathways are fully developed before birth, and neonates display the physiologic, hormonal, and metabolic markers of the stress response.1  Preterm infants have been shown to have an increased sensitivity to pain and even non-painful stimuli may be perceived as painful.2  Long-term effects on pain responses have been documented in neonatal boys who were circumcised without analgesia.3 However, immature metabolic pathways for drugs and immature respiratory control mean that neonates are more sensitive to the side effects of analgesics commonly used during surgery. Multimodal analgesia should be used for all neonates. Options include paracetamol (7.5mg.kg-1 IV, or 20mg.kg-1 PR), opioids such as fentanyl or morphine titrated to effect (fentanyl 1mcg.kg-1 IV, morphine 10-20mcg.kg-1 IV). Regional anaesthesia or infiltration of local anaesthetics should be used where possible. Non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided because of the immature renal system. Non nutritive sucking, sucrose and breast milk have also been shown to be safe and effective for reducing pain associated with procedures such as cannulation.4,5

=== Invasive monitoring ===

Invasive monitoring (intra-arterial and central venous pressure) may be indicated depending on the type of surgery and the physiological status of the patient. Invasive monitoring is mandatory in circumstances such as cardiac surgery where there is the potential for rapid changes in blood pressure, use of inotropes or potential for large volume blood loss. In other circumstances, for instance neonatal laparotomy, the risks/benefits should be considered. Invasive monitoring is time consuming to insert, associated with complications and may delay the start of surgery. If the surgery is sufficiently urgent it may be necessary to proceed without. 24G or 22G catheters may be inserted into radial or femoral arteries for arterial monitoring, but distal limb perfusion must be checked. 4Fr or 5Fr central lines may be inserted into the femoral or internal jugular vein, ideally with ultrasound guidance. Near infrared spectroscopy (NIRS) can be used, if available, as a non-invasive monitor of tissue perfusion.6

Unmonitored oxygen therapy leading to hyperoxia in neonates is associated with retinopathy of prematurity, bronchopulmonary dysplasia and damage to the developing brain. Neonatal exposure to 100% oxygen is rarely necessary, and should be avoided except prior to interventions such as intubation. Hypoxia is also harmful, so targeting oxygen saturation levels between 91% and 95% is probably the safest practice.7-9 In low income countries where it may not be possible to deliver a variety of inspired oxygen mixtures, an air/oxygen mix should be used if possible and oxygen saturations should be monitored before, during and after anaesthesia.

=== Postoperative apnoea ===

Apnoea can be defined as a pause in breathing of more than 20 seconds or cessation of respiration of any duration accompanied by bradycardia or oxygen desaturation. Preterm infants are particularly at risk apnoeas due to an immature respiratory control centre. This effect is potentiated by general anaesthetic agents, and all term neonates <44 weeks post-conceptual age (PCA) and pre-term neonates (<60 weeks PCA) are at risk of postoperative apnoea. Infants with multiple congenital abnormalities, a history of apnoea and bradycardia, chronic lung disease and anaemia (Hb <10g.dl-1) are at particular risk for postoperative apnoeas.10

orally) can be given to prevent post-operative apnoea in premature neonates.11 Intravenous aminophylline (5mg.kg-1) is an alternative although it has more side effects including tachycardia, jitteriness, irritability, feed intolerance, vomiting and hyperglycaemia.It is important to allow sufficient time for neonates to wake up at the end of the operation, and they should be closely monitored in recovery until the anaesthetist is happy that they have returned to their normal awake state. All neonates <44

=== Hypoglycaemia and hyperglycaemia ===