Neonatal anaesthesia: Difference between revisions

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.

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 the correct dose of analgesics, muscle relaxants and antibiotics  

and draw these up. Double check dose calculations – it is easy to make 10-fold errors in neonatal practice.

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).

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.

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.<ref>Anand KJ, Aynsley-Green A. Measuring the severity of surgical stress in newborn infants. J Pediatr Surg 1988; 23 297-305. 2.Anand KJ. Clinical importance of pain and stress in preterm neonates. Biol Neonate 1998; 73 1-9.</ref> Preterm infants have been shown to have an increased sensitivity to pain and even non-painful stimuli may be perceived as painful.<ref>Anand KJ. Clinical importance of pain and stress in preterm neonates. Biol Neonate 1998; 73 1-9.</ref> Long-term effects on pain responses have been documented in neonatal boys who were circumcised without analgesia.<ref>Taddio A, Katz J, Ilersich AL, Koren G. Effect of neonatal circumcision on pain response during subsequent routine vaccination. Lancet 1997; 349 599-603.</ref> 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.<ref>Stevens B, Yamada J, Lee GY, Ohlsson A. Sucrose for analgesia in newborn infants undergoing painful procedures. Cochrane Database Syst Rev 2013 1:CD001069.</ref>^,<ref>Shah PS, Herbozo C, Aliwalas LL, Shah VS. Breastfeeding or breast milk for procedural pain in neonates. Cochrane Database Syst Rev 2012 12:CD004950.</ref>

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.<ref>Cerbo RM, Maragliano R, Pozzi M, Strocchio L. Global perfusion assessment and tissue oxygen saturation in preterm infants: where are we? Early Hum Dev 2013; 89 (S1): S44-6.</ref>

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.<ref>Bancalari E, Claure N. Oxygenation targets and outcomes in premature infants. JAMA 2013; 117 2161-2.</ref><ref>Stenson B, Brocklehurst P, Tarnow-Mordi W. U.K. BOOST II trial; Australian BOOST II trial; New Zealand BOOST II trial. Increased 36-week survival with high oxygen saturation target in extremely preterm infants. N Engl J Med 2011; 364 1680- 82.</ref><ref>Schmidt B, Whyte RK, Asztalos EV et al. Canadian Oxygen Trial (COT) Group. Effects of targeting higher vs lower arterial oxygen saturations on death or disability in extremely preterm infants: a randomized clinical trial. JAMA 2013; 309 2111-20.</ref> 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.

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.<ref name=":0">Cote CJ Postoperative apnea in former preterm infants after inguinal herniorrhaphy: A combined analysis. Anesthesiology 1995; 82 809-22.</ref>

Prophylactic caffeine (10mg.kg^-1 orally) can be given to prevent post-operative apnoea in premature neonates.<ref>Henderson-Smart DJ, Steer P. Prophylactic caffeine to prevent postoperative apnea following general anesthesia in preterm infants. Cochrane Database Syst Rev 2001;4:CD000048.</ref> 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.

<2.5mmol.l^-1) may lead to irreversible neurological injury in neonates. Preterm infants and those with intrauterine growth retardation (IUGR) are at particular risk of hypoglycaemia. Fasting times should be minimized, blood glucose should be monitored and glucose containing maintenance fluids should be continued if they have been required prior to surgery. Treat hypoglycaemia with a bolus of 2ml.kg^-1 of 10% dextrose. Hyperglycaemia (blood glucose >10mmol.l^-1) is also detrimental and is associated with increased mortality and sepsis in extremely low birth weight infants, so do not use boluses of 50% glucose.<ref>Kao LS, Morris BH, Lally KP, Stewart CD, Huseby V, Kennedy KA. Hyperglycemia and morbidity and mortality in extremely low birth weight infants. J Perinatol 2006; 26 730-6.</ref>

During surgery, isotonic fluids such as Hartmann’s or Ringer’s lactate must be used for resuscitation, replacement and maintenance to maintain intravascular fluid volume, replace fluid deficits and avoid hyponatraemia. Blood glucose should be monitored. The decision whether to order or administer blood or blood products will depend on the cardiovascular status of the neonate, presence of haemorrhage, type of surgery, the most recent blood results and the normal expected values (Table 3). Once the decision to transfuse has been taken it may be worth transfusing to higher haemoglobin levels to avoid exposure to further donors. Ideally, the haematocrit should be measured during surgery using near-patient testing device such as a HemoCue® or a blood gas machine. The British Committee for Standards in Haematology (BCSH) has a suggested transfusion ‘trigger’ for neonatal top-up transfusion (Transfusion Guidelines for Neonates and Older Children [http://www.bcshguidelines.com (http://www.bcshguidelines.com]) (see Table 4). Suggested transfusion doses for blood and blood products are described in Table 5.

Inadequate anaesthesia and analgesia have been shown to be detrimental to neonates, and associated with increased mortality. However, many animal model studies have been published recently that have demonstrated accelerated neuronal cell death (‘apoptosis’) and long-term behavioural changes after animals are exposed to anaesthetic agents in the neonatal period. The situation in humans remains unclear.<ref>Olsen EA, Brambrink AM. Anesthetic neurotoxicity in the newborn and infant. Curr Opin Anaesthesiol 2013 August 29 (e-pub ahead of print).page 132</ref> The risks and benefits of surgery in neonates should be considered carefully, and non-essential elective surgery should be avoided in the neonatal period where possible.

Inguinal hernia is common in premature neonates. The timing of surgery depends on the risk of incarceration, bowel strangulation or testicular atrophy versus the risk of postoperative apnoea and the potential harm to neurodevelopment. The major anaesthetic risk is post- operative apnoea, which has been shown to vary from 4.7% to 49% of patients.<ref name=":0" /><ref>Malviya S, Swartz J, Lerman J. Are all preterm infants younger than 60 weeks postconceptional age a risk for post-anesthetic apnea? Anesthesiology 1993; 78 1076–81.</ref>14 Some units prefer spinal anaesthesia for inguinal hernia repair, others use a balanced anaesthetic technique using general anaesthesia with intubation, supplemented with a regional technique. There is currently not enough evidence to show whether the incidence of apnoea is lower using spinal anaesthesia, and the choice is usually determined by local preference of the surgeon and anaesthetist.<ref>Craven PD, Badawi N, Henderson-Smart DJ, O’Brien M. Regional (spinal, epidural, caudal) versus general anaesthesia in preterm infants undergoing inguinal herniorrhaphy in early infancy. Cochrane Database Syst Rev 2003;3:CD003669.</ref>

 

 

Caudal anaesthesia using 0.25% bupivacaine 0.75ml.kg^-1 provides excellent supplementary analgesia for inguinal hernia repair under general anaesthesia. Alternatively, an ilioinguinal block can be performed with 0.5-1.0ml.kg^-1 0.25% bupivacaine. These patients may require post-operative apnoea monitoring dependent on their PCA, as discussed earlier, and some premature infants will require post-operative ventilation or CPAP for treatment of apnoea. Paracetamol (7.5mg.kg^-1 IV or 20mg.kg^-1 rectal suppository) provides adequate post-operative analgesia

Anorectal malformations (ARM) occur in approximately 1:5000 live births. They represent a wide spectrum of disease, from a simple membrane involving the distal rectum and anus to more complex anomalies involving the genital and urinary tract. Spinal anomalies are frequently found in these patients. These include spinal dysraphism, low lying cord (LLC) and tethered cord.<ref>Teo AT, Gan BK, Tung JS, Low Y, Seow WT. Low-lying spinal cord and tethered cord syndrome in children with anorectal malformations. Singapore Med J 2012; 53 570-6.</ref> Plain spinal Xrays and spinal ultrasound are used to screen for these abnormalities although they may be normal in occult dysraphism. Caudal anaesthesia may be beneficial and can be used in ARM if there is certainty that anomalies of the spine and spinal cord have been excluded.<ref>Bozza P, Morini F, Conforti A, Sgrò S. Stress and ano-colorectal surgery in newborn/infant: role of anesthesia. Pediatr Surg Int 2012; 28 821-4.</ref>17 ARM may be associated with other anomalies including Vertebral, Anorectal, Cardiac, Tracheoesophageal, Renal and Limb abnormalities, collectively known as the VACTERL association.

If caudal anaesthesia is contraindicated an opioid-based technique is used (fentanyl 1-2mcg.kg^-1 or morphine 20-50mcg.kg^-1 [0.02-0.05mg.kg^-1], with infiltration with local anaesthetic. Rectal suppositories cannot be used but intravenous paracetamol is a useful adjunct if available. Standard monitoring is usually all that is required. Opioids should be carefully titrated as the usual aim is to extubate at the end of surgery.

Nearly 50% of cases will present in the first week of life most commonly with bilious vomiting secondary to duodenal obstruction.<ref>Millar AJ, Rode H, Cywes S. Malrotation and volvulus in infancy and childhood. Semin Pediatr Surg 2003; 12 229-36.</ref> This may be due to a midgut volvulus, or physical compression secondary to peritoneal tissue bands or abnormal locations of the duodenum and its surrounding structures. If the condition is diagnosed early the neonate  

may be relatively well with only subtle abdominal signs. The neonate may present late with frank sepsis and peritonitis secondary to perforated or necrotic bowel. The gold standard radiological investigation is an upper GI contrast series. Plain X-rays are useful if there is concern of another diagnosis or to exclude visceral perforation.

Necrotising enterocolitis occurs in approximately 0.5 – 5:1000 live births. More than 90% of infants diagnosed with NEC are preterm.<ref>Llanos AR, Moss ME, Pinzòn MC, Dye T. Epidemiology of neonatal necrotizing enterocolitis: a population-based study. Paediatr Perinat Epidemiol 2002; 16 342-9.</ref> Morbidity and mortality are inversely proportional to the infant’s post-conceptual age (PCA) and birth weight.  

NEC may present with subtle gastrointestinal signs including abdominal distension, intolerance of feeds, abdominal tenderness, blood in the stool and bilious vomiting or may present with perforation and peritonitis with systemic signs including shock, temperature instability, acidosis and disseminated intravascular coagulopathy. Supine and decubitus plain X-rays may show the presence of hepatic venous gas, free intraperitoneal air, dilated bowel loops, ascites and asymmetric bowel gas patterns along with pneumatosis intestinalis.  

These patients are often already intubated and ventilated. A high dose fentanyl technique (10-20mcg.kg^-1) may be used to promote cardiovascular stability and reduce the systemic stress response.<ref>Anand KJ, Sippell WG, Aynsley-Green A. Randomised trial of fentanyl anaesthesia in preterm babies undergoing surgery: effects on the stress response. Lancet 1987; 1 62–6 [published correction appears in Lancet 1987; 1 234].</ref> Nitrous oxide should be avoided because of the risk of bowel distension. Low cardiac output state, organ hypoperfusion and acidosis secondary to large fluid shifts is common, and large volumes of intravenous fluids are frequently required. Invasive monitoring is useful to guide fluid management and allow frequent arterial blood gas sampling although this must be balanced against the risk of limb ischaemia in the preterm neonate. Insertion of an arterial or a central line should not delay the start of surgery in the sick infant. There is a significant risk of coagulopathy and significant blood loss, and inotropes are often required. Packed red cells should be available and fresh frozen plasma and platelets are often indicated based on laboratory results or clinical evidence of bleeding. Hypothermia and glucose instability are common and should be managed appropriately.  

Neonates with TOF classically present within a few hours of birth with frothy sputum as they are unable to swallow oral secretions; delayed diagnosis is associated with episodes of coughing and choking associated with cyanosis, particularly if feeding is attempted. There may be copious oral secretions and abdominal distension due to gastric insufflation via the fistula. Left untreated the neonate will develop aspiration pneumonia. The diagnosis of oesophageal atresia is confirmed if it is not possible to pass a nasogastric tube and the chest X-ray will show the nasogastric tube coiled in the proximal blind-ending oesophagus (Figure 3). There may be an absent gastric bubble in isolated oesophageal atresia without a tracheoesophageal fistula.

A balanced anaesthetic should be given, with bolus fentanyl analgesia as required (1-2mcg.kg^-1). Blood loss should be minimal and Ringer’s lactate 10-20ml.kg^-1 is usually all that is required. The wound should be infiltrated with local anaesthetic at the end of surgery. Some term infants born in good condition and with normal preoperative pulmonary function may be extubated at the end of surgery; most are likely to require post-operative ventilation and they should be transferred to a facility able to provide this level of care for their surgery. Many patients will require serial dilatation of the oesophagus during infancy.

Congenital diaphragmatic hernia (CDH) occurs in approximately 1:3000 live births. In most cases the aetiology remains unknown. A defect in the diaphragm, usually on the left side, results in herniation of midgut structures into the thoracic cavity. Pulmonary vascular structure and reactivity are abnormal and there is a varying degree of lung hypoplasia. Diagnosis is made on antenatal ultrasound or on plain X-ray postnatally when the abnormal bowel loops can be seen within the thoracic cavity.  

Morbidity and mortality is related to the degree of pulmonary hypertension, right ventricular dysfunction and lung hypoplasia.<ref>Wynn J, Krishnan U, Aspelund G, Zhang Y et al. Outcomes of congenital diaphragmatic hernia in the modern era of management. J Pediatr 2013; 163 114-9 e1.</ref> A pre-operative echo is performed as a significant proportion of CDH have associated cardiac anomalies. Mortality still remains high in patients with significant co-existing congenital cardiac disease.<ref>Graziano JN. Cardiac anomalies in patients with congenital diaphragmatic hernia and their prognosis: a report from the Congenital Diaphragmatic Hernia Study Group. J Pediatr Surg 2005; 40 1045-9</ref> It is generally accepted that delaying surgery, usually for 24-48 hours, allows a period of stabilisation. The reduction in pulmonary artery pressures and improvement in right ventricular dysfunction may improve outcome.  

There has been a significant improvement in survival over the past 20 years due to the introduction of ‘gentle ventilation’ strategies.<ref>Guidry CA, Hranjec T, Rodgers BM, Kane B. Permissive hypercapnia in the management of congenital diaphragmatic hernia: our institutional experience. J Am Coll Surg 2012; 214 640-645.</ref> These include permissive hypercapnoea (PaCO2 <70mmHg), limiting inflation pressures (avoid PIP>25cm H2O and PEEP > 5 cm H2O) and accepting relative hypoxaemia

(aim for pre-ductal SpO2 90-95%). Surgery may need to be performed whilst the neonate is on high-frequency oscillation ventilation or extra-corporeal membrane oxygenation.<ref>Fallon SC, Cass DL, Olutoye OO, Zamora IJ et al. Repair of congenital diaphragmatic hernias on Extracorporeal Membrane Oxygenation (ECMO): Does early repair improve patient survival? J Pediatr Surg 2013; 48 1172-6.</ref>

Gastroschisis occurs in approximately 1:3000 live births. The herniated viscera are not covered by a sac. It is thought to occur secondary to an ischaemic insult during abdominal wall development or due to early rupture of the hernia of the umbilical cord. A relatively small percentage (10-20%) are associated with other congenital abnormalities and these predominantly involve the gastrointestinal tract.<ref>Molik KA, Gingalewski CA, West KW et al. Gastroschisis: a plea for risk categorization. J Pediatr Surg 2001; 36 51–5.</ref>

The neonate will require intubation and ventilation for surgery. Expect significant ongoing fluid and heat losses due to the exposed viscera. Peripheral intravenous access may be all that is required, but central venous pressure monitoring and an arterial line are useful to help guide fluid administration. Avoid the femoral vessels as there is a risk of decreased perfusion with the increased abdominal pressures. Placing the post-ductal oxygen saturation probe on either lower limb helps to give an indication if there is poor perfusion. Muscle relaxants will assist the surgeons in reducing the abdominal contents. Reduction of the bowel may cause abdominal compartment syndrome, diaphragmatic splinting and high ventilation pressures. If the intra gastric pressures are >20mmHg or the peak inspiratory pressures exceed 30cm H2O then a staged repair is indicated.<ref>Yaster M, Scherer TL, Stone MM et al. Prediction of successful primary closure of congenital abdominal wall defects using intraoperative measurements. J Pediatr Surg 1989; 24 1217–20.</ref>