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*Correspondence Email: karmen.kemp@uct.ac.za | *Correspondence Email: karmen.kemp@uct.ac.za | ||
== INTRODUCTION == | |||
Neonates present a challenge to the anaesthetist. They have unique physiology as they transition from intrauterine to extrauterine life, limited physiological reserve and immature drug handling. The goals of anaesthesia are to provide stable conditions for surgery, minimise physiological disturbance, reduce pain, and support the neonate during the postoperative period. This article will describe general considerations for anaesthesia in term and preterm neonates, and anaesthesia for some specific neonatal conditions. | Neonates present a challenge to the anaesthetist. They have unique physiology as they transition from intrauterine to extrauterine life, limited physiological reserve and immature drug handling. The goals of anaesthesia are to provide stable conditions for surgery, minimise physiological disturbance, reduce pain, and support the neonate during the postoperative period. This article will describe general considerations for anaesthesia in term and preterm neonates, and anaesthesia for some specific neonatal conditions. | ||
== REOPERATIVE ASSESSMENT OF THE NEONATE == | |||
As for any child undergoing anaesthesia, it is important to take a detailed history and examination, together with relevant investigations to assess the current physiological status and the impact of any associated congenital abnormalities, which may or may not be related to the surgical condition. This helps to plan when best to proceed with the surgery, and the level of postoperative support required. | As for any child undergoing anaesthesia, it is important to take a detailed history and examination, together with relevant investigations to assess the current physiological status and the impact of any associated congenital abnormalities, which may or may not be related to the surgical condition. This helps to plan when best to proceed with the surgery, and the level of postoperative support required. | ||
=== History === | |||
The history should include the gestational age, birth history, current age and weight, and significant peri-natal events such as low APGAR scores, respiratory distress requiring respiratory support, hypoglycaemic episodes, NICU admissions, evidence of sepsis or any antenatal concerns such as maternal illness. The anaesthetist should check whether intramuscular vitamin K has been given to prevent haemorrhagic disease of the newborn. The fasting status should be established if the child is receiving feeds - ideally 2 hours for clear fluids, 4 hours for breast milk, 6 hours for formula feed. | The history should include the gestational age, birth history, current age and weight, and significant peri-natal events such as low APGAR scores, respiratory distress requiring respiratory support, hypoglycaemic episodes, NICU admissions, evidence of sepsis or any antenatal concerns such as maternal illness. The anaesthetist should check whether intramuscular vitamin K has been given to prevent haemorrhagic disease of the newborn. The fasting status should be established if the child is receiving feeds - ideally 2 hours for clear fluids, 4 hours for breast milk, 6 hours for formula feed. | ||
DEFINITIONS | <blockquote>'''DEFINITIONS''' | ||
•Neonate is aged up to 28 days | •Neonate is aged up to 28 days | ||
•Term neonate is born between 37 to 40 weeks post conception | •Term neonate is born between 37 to 40 weeks post conception | ||
• Preterm neonate is born at <37 weeks post conception | • Preterm neonate is born at <37 weeks post conception | ||
•Extreme preterm neonate is born <28 weeks post conception | •Extreme preterm neonate is born <28 weeks post conception | ||
• Low birthweight <2.5kg | • Low birthweight <2.5kg | ||
• Very low birthweight <1.5kg</blockquote> | |||
Examination | === Examination === | ||
Examine the child carefully. In particular, it is important to look for signs of respiratory distress (respiratory rate, nasal flare, subcostal recession), and cardiovascular compromise (check heart rate, blood pressure, peripheral perfusion and capillary refill). Check the oxygen saturation – low oxygen saturation may be associated with respiratory disease, or in some cases with cyanotic congenital heart disease. | Examine the child carefully. In particular, it is important to look for signs of respiratory distress (respiratory rate, nasal flare, subcostal recession), and cardiovascular compromise (check heart rate, blood pressure, peripheral perfusion and capillary refill). Check the oxygen saturation – low oxygen saturation may be associated with respiratory disease, or in some cases with cyanotic congenital heart disease. | ||
Investigations | === Investigations === | ||
Relevant investigations will be guided by the clinical findings and the underlying condition, although resources may limit investigations that can be performed. They may include the following: | Relevant investigations will be guided by the clinical findings and the underlying condition, although resources may limit investigations that can be performed. They may include the following: | ||
Laboratory investigations: | ===== Laboratory investigations: ===== | ||
* Full blood count and haemtocrit | |||
* Blood glucose Urea and electrolytes | |||
* Coagulation studies | |||
* Liver function tests and bilirubin | |||
* Capillary blood gas | |||
===== Radiological investigations: ===== | |||
* CXR, AXR | |||
* Echocardiogram | |||
* Cranial/spinal/renal ultrasound | |||
Finally, the anaesthetic plan, including risks, should be discussed with the parent(s) or guardian(s), and consent taken for anaesthesia including regional anaesthesia and blood transfusion if indicated. | Finally, the anaesthetic plan, including risks, should be discussed with the parent(s) or guardian(s), and consent taken for anaesthesia including regional anaesthesia and blood transfusion if indicated. | ||
== GENERAL PRINCIPLES OF ANAESTHESIA IN NEONATES == | |||
It is important to prepare and check all equipment that may be | It is important to prepare and check all equipment that may be | ||
required, prior to the start of anaesthesia (see Figure 1). | required, prior to the start of anaesthesia (see Figure 1). | ||
FIGURE 1 | |||
=== Monitoring === | |||
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). | |||
be | |||
ECG and non-invasive blood pressure measurement should be used. The lower limit of mean arterial blood pressure can be estimated to be equivalent to the gestational age in weeks; by about 6 weeks of age, the normal mean arterial pressure is 50-60 mmHg. Basic intra-operative monitoring should ideally also include a precordial or oesophageal stethoscope and, if available, capnography must be used. | |||
=== Airway Equipment === | |||
Intubation and ventilation will be required unless it is an extremely short procedure. The size of the tracheal tube will depend on the weight of the neonate; most term babies require a size 3.5 tracheal tube (see Table 1). Make sure that strapping is available. Precut the tape to fix the tracheal tube firmly in place immediately after intubation. An appropriately sized oral airway (preterm 000 – 00 and term neonate 0) and face mask | |||
should be available. Dead space within the apparatus is kept to a minimum with the appropriate sized breathing circuit and filter. | |||
=== Warming === | |||
Neonates are extremely vulnerable to heat loss and hypothermia. Hypothermia (core temperature <36°C) is associated with postoperative apnoeas, coagulopathy and poor wound healing, and worsens outcomes. The theatre environment should be warmed (or air conditioning turned down) to at least 20-23°C and the baby kept covered as much as possible. A forced air warmer and a radiant heater should be used if available. Warmed packs should be considered if other sources of warming are not available; take care not to place warmed packs directly in contact with the skin. Fluids and blood products should be warmed. The temperature of the baby should be measured unless the procedure is very quick. | |||
=== Preparation of drugs === | |||
The first thing to be drawn up is a saline flush so that the IV | The first thing to be drawn up is a saline flush so that the IV | ||
line can be flushed immediately after a drug is given. Calculate | line can be flushed immediately after a drug is given. Calculate | ||
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Emergency drugs should be drawn up in the appropriate doses. These include atropine (20mcg.kg-1), suxamethonium (1-2mg.kg-1) and adrenaline (10mcg.kg-1 , i.e. 0.1ml.kg-1 1:10,000 adrenaline). | Emergency drugs should be drawn up in the appropriate doses. These include atropine (20mcg.kg-1), suxamethonium (1-2mg.kg-1) and adrenaline (10mcg.kg-1 , i.e. 0.1ml.kg-1 1:10,000 adrenaline). | ||
=== Induction of anaesthesia === | |||
Inhalational induction is ideally with sevoflurane although | 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 | ||
halothane can also be used. The MAC of volatile agents is | -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 | ||
lower in neonates than in older children, and the onset of | -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. | ||
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 | |||
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 | 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. | ||
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. | |||
used where possible. Non-steroidal anti-inflammatory drugs | === Pain management === | ||
(NSAIDs) should be avoided because of the immature renal | 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 | ||
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) | 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 | ||
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 | |||
=== Oxygen === | |||
Unmonitored oxygen therapy leading to hyperoxia in | 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. | ||
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 | 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 | ||
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 | |||
Prophylactic caffeine (10mg.kg | Prophylactic caffeine (10mg.kg | ||
-1 | -1 | ||
orally) can be given to prevent | 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 | ||
weeks post-conceptual age (PCA), ex-preterm infants up to 60 weeks PCA and any patients with whom there is any concern regarding the possibility of post-operative apnoeas should have post-operative apnoea and oxygen saturation monitoring for 24 hours. | |||
=== Hypoglycaemia and hyperglycaemia === | |||
Persistent, recurrent or severe hypoglycaemia (blood glucose | Persistent, recurrent or severe hypoglycaemia (blood glucose | ||
<2.5mmol.l | <2.5mmol.l |