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''Originally from Update in Anaesthesia | www.wfsahq.org/resources/update-in-anaesthesia'' | ''Originally from Update in Anaesthesia | www.wfsahq.org/resources/update-in-anaesthesia'' | ||
Heidi Meyer | |||
Karmen Kemp | |||
Red Cross War Memorial Children’s Hospital Rondebosch | |||
Cape Town 7700 Western Cape | |||
Cape Town | |||
South Africa | |||
Heidi Meyer and Karmen Kemp* | |||
*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. | |||
preoperatiVe 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. | |||
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. | |||
DEFINITIONS | |||
•Neonate is aged up to 28 days | |||
•Term neonate is born between 37 to 40 weeks post conception | |||
• Preterm neonate is born at <37 weeks post conception | |||
•Extreme preterm neonate is born <28 weeks post conception | |||
• Low birthweight <2.5kg | |||
• Very low birthweight <1.5kg | |||
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. | |||
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: | |||
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. | |||
General principleS oF anaeStheSia in neonateS | |||
It is important to prepare and check all equipment that may be | |||
required, prior to the start of anaesthesia (see 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). | |||
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 | |||
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). | |||
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 CO | |||
2 | |||
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. | |||
pain management | |||
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 | |||
oxygen | |||
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 | |||
Prophylactic caffeine (10mg.kg | |||
-1 | |||
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 | |||
<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. | |||
12 | |||
perioperative fluids | |||
Assessment of the fluid status of the neonate will help to guide | |||
peri-operative fluid replacement. It is helpful to consider | |||
preoperative maintenance fluids, intraoperative fluids and | |||
postoperative maintenance. | |||
preoperative maintenance fluids | |||
A neonate may require preoperative maintenance fluids if | |||
they are unable to take fluids by mouth before surgery. In | |||
the first few days of life, the sodium requirement is not high, | |||
and typically 10% dextrose is recommended. After the post- | |||
natal diuresis has occurred at around day 3 of life, an isotonic | |||
fluid containing 5% dextrose and sodium should be used, and | |||
electrolytes and plasma glucose monitored (Table 2). | |||
intraoperative fluids | |||
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) (see Table 4). Suggested | |||
transfusion doses for blood and blood products are described | |||
in Table 5. | |||
transitional circulation | |||
In utero, the pulmonary vascular resistance is high and there | |||
is very little blood flow to the lungs as the placenta is the | |||
source of gas exchange. After birth as the neonate takes the | |||
first few breaths, a chain of events is set in place that results | |||
in the transition from the foetal circulation to the neonatal | |||
circulation with closure of the foetal shunts (foramen ovale, | |||
ductus venosus and ductus arteriosus). During the first few | |||
weeks of life the pulmonary vasculature is highly reactive; an | |||
increase in pulmonary vascular resistance can lead to reopening | |||
of the foetal shunts, in particular the arterial duct between the | |||
pulmonary artery and the aorta. As a result there is right-to- | |||
left shunting from the pulmonary artery (deoxygenated blood) | |||
to the aorta, causing profound hypoxia. The oxygen saturation | |||
measured in the right hand may be normal (‘pre-ductal’); the | |||
oxygen saturation in the other limbs (‘post-ductal’) will be low. | |||
During the perioperative period it is important to prevent | |||
factors that increase pulmonary vascular resistance such as | |||
sepsis, hypoxia, acidosis, hypercapnoea, pain and hypothermia. | |||
When post-ductal oxygen saturations drop in relation to | |||
preductal oxygen saturations it may indicate a return to a | |||
foetal circulation. | |||
neurodevelopmental effects of anaesthetics in | |||
neonates | |||
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. | |||
13 | |||
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. | |||
transfer of neonates | |||
Neonatal surgery should ideally be undertaken in an | |||
environment where the facilities and expertise are available for | |||
definitive treatment and on-going care. In certain situations, | |||
if the baby is unstable and not suitable for transfer to theatre, | |||
it may be necessary to undertake surgery on the NICU itself. | |||
In certain situations the baby may need to be transferred to a | |||
specialist centre. In low-income countries this may not be an | |||
option and treatment may not always be possible. | |||
Prior to transfer the appropriate personnel, equipment, drugs | |||
and fluids should be prepared and checked using a transfer | |||
checklist (Table 6). The neonate should be carefully assessed | |||
for stability for transfer or if necessary transfer may need to be | |||
delayed for further resuscitation and optimisation. Check that | |||
the monitoring is functional and the patient is adequately fluid | |||
resuscitated. Take time to ensure that the neonate is stable | |||
prior to transfer on the current drug infusions and mode of | |||
ventilation. | |||
Careful monitoring during transfer is extremely important and | |||
will highlight clinical trends. A detailed handover is essential | |||
for good continuity of care. | |||
SpeciFic neonatal patholoGieS | |||
inguinal hernia repair | |||
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. | |||
10,14 | |||
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. | |||
15 | |||
Editors’ note: As this edition of Update goes to press, the editors are | |||
aware that the GAS study is reporting its preliminary findings on | |||
apnoea comparing GA and spinal in >700 neonates, publication of | |||
full results is expected late 2018. | |||
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 | |||
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. | |||
16 | |||
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. | |||
17 | |||
ARM may be associated with other anomalies including | |||
Vertebral, Anorectal, Cardiac, Tracheoesophageal, Renal and | |||
Limb abnormalities, collectively known as the VACTERL | |||
association. | |||
Primary surgical repair can be undertaken in the neonatal | |||
period although more commonly a colostomy is performed | |||
and a definitive repair is carried out at a later date. | |||
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. | |||
The patient may be positioned supine or prone depending | |||
on the surgical technique. Prone positioning is associated | |||
with increased risk to pressure areas, abdominal compression | |||
resulting in difficulty with ventilation, endobronchial | |||
intubation or tracheal tube displacement. Long-term outcome | |||
is variable depending on the complexity of the anorectal | |||
malformation. These patients usually require serial anal | |||
dilatations following repair. | |||
intestinal malrotation | |||
Malrotation occurs in approximately 1:500 live births. Normal | |||
intestinal rotation around the superior mesenteric artery | |||
(SMA) and fixation during foetal development is interrupted. | |||
It may also be associated with congenital diaphragmatic hernia, | |||
exomphalos and gastroschisis. | |||
Nearly 50% of cases will present in the first week of life most | |||
commonly with bilious vomiting secondary to duodenal | |||
obstruction. | |||
18 | |||
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. | |||
These patients require adequate volume resuscitation and | |||
electrolyte replacement for ongoing fluid losses and should be | |||
taken to theatre as soon as is feasible. A nasogastric tube is | |||
inserted to suction the stomach. Prophylactic antibiotics such as | |||
co-amoxiclav or benzylpenicllin, gentamicin and metronidazole | |||
are required. Ideally invasive monitoring is inserted although it | |||
should not delay surgery in the sick neonate. If the gut has been | |||
compromised, inotropes may be needed and any coagulopathy | |||
will require correction. A central venous line may be required | |||
for ongoing total parenteral nutrition in the septic neonate. | |||
An opioid based technique can be used although a caudal may | |||
be considered if the patient is haemodynamically stable, there | |||
are no other contra-indications and extubation is anticipated. | |||
Post-operative NICU care and ventilation is often necessary. | |||
Long-term outcomes depend on the extent of the necrotic | |||
bowel. Some patients will develop short bowel syndrome and | |||
if there is extensive bowel necrosis the mortality is 100%. | |||
necrotising enterocolitis (nec) | |||
Necrotising enterocolitis occurs in approximately 0.5 – 5:1000 | |||
live births. More than 90% of infants diagnosed with NEC are | |||
preterm. | |||
19 | |||
Morbidity and mortality are inversely proportional | |||
to the infant’s post-conceptual age (PCA) and birth weight. | |||
The aetiology of NEC is multifactorial. Risk factors | |||
include vascular compromise of the gastrointestinal tract, | |||
commencement of enteral feeding, immature gastrointestinal | |||
immunity and sepsis. Hypoxia or ischaemia combined with | |||
reduced splanchnic blood flow can occur with patent ductus | |||
arteriosus (PDA), cyanotic heart disease, respiratory distress | |||
syndrome, shock, asphyxia and with the use of umbilical | |||
catheters. | |||
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 Xrays may show the presence of hepatic venous gas, free | |||
intraperitoneal air, dilated bowel loops, ascites and asymmetric | |||
bowel gas patterns along with pneumatosis intestinalis. | |||
Initial management includes discontinuation of enteral feeds, | |||
insertion of a nasogastric tube and commencement of broad- | |||
spectrum antibiotics such as benzylpenicillin, gentamicin and | |||
metronidazole. Ongoing fluid and electrolyte management | |||
with parenteral nutrition will be required. Frequent clinical | |||
monitoring of systemic and abdominal signs together with | |||
radiographic examination, monitoring of laboratory values | |||
and acid-base status guides further management. The only | |||
absolute indication for surgery is bowel perforation although | |||
the decision to proceed to surgery may be made if there is a | |||
clinical deterioration. | |||
The preoperative assessment should evaluate and optimise any | |||
cardiovascular instability, metabolic acidosis, coagulopathy | |||
and respiratory compromise. If the patient is too unstable it | |||
may be necessary to carry out surgery on the NICU. | |||
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. | |||
20 | |||
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. | |||
Mortality remains significant and long term complications | |||
include short bowel syndrome and neurodevelopmental delay. | |||
oesophageal atresia and tracheoesophageal fistula | |||
Congenital tracheoesophageal fistula (TOF) occurs in | |||
approximately 1:3,000 live births. It arises during foetal | |||
development as a result of incomplete separation of the | |||
oesophagus from the laryngotracheal tube. It is classified based | |||
on the site and presence of the fistula and whether there is | |||
oesophageal atresia (Figure 2). There may be other associated | |||
VACTERL anomalies. | |||
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 Xray 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. | |||
The goals of pre-operative management are to stabilise the | |||
child, minimise respiratory embarrassment and assess for | |||
timing of surgery. A nasogastric tube is inserted into the | |||
upper oesophageal pouch to drain secretions. The patient | |||
must be nursed head up or on the side to minimise the risk | |||
of aspiration. Intravenous fluids and prophylactic antibiotics | |||
should be commenced. This allows time for investigations such | |||
as an echocardiogram to exclude other associated congenital | |||
abnormalities. | |||
Our preferred technique is to induce anaesthesia after pre- | |||
oxygenation and to maintain spontaneous ventilation initially | |||
with volatile or intravenous anaesthesia. Prior to repair the | |||
surgeons may perform flexible or rigid bronchoscopy to assess | |||
the level of the fistula and to see if there is a second or proximal | |||
fistula. Take note of the distance measured from the cords | |||
to the fistula to guide tracheal tube placement; the fistula is | |||
mid-tracheal in two thirds of cases, and located at level of the | |||
carina in one third of cases. Muscle relaxants and gentle mask | |||
ventilation may be given prior to intubation. If possible the | |||
tracheal tube is placed distal to the fistula, with the bevel of the | |||
tracheal tube facing anteriorly. | |||
A right thoracotomy is performed with the patient on the | |||
side with a roll under the chest. The tube position must be | |||
checked and effective ventilation confirmed after the change | |||
of position. The lung is then retracted which often results in | |||
difficulty with ventilation, hypercapnoea and acidosis. Periods | |||
of manual ventilation may be required. If gastric distension | |||
occurs prior to ligation of the fistula, the tracheal tube should | |||
be disconnected intermittently to decompress the stomach via | |||
the airway. An arterial line is useful to facilitate arterial blood | |||
gas measurement as end tidal CO | |||
2 | |||
measurement is unreliable. | |||
Alternatively, transcutaneous CO | |||
2 | |||
monitoring can be used. | |||
Hypercapnoea and acidosis is of particular importance in | |||
the presence of certain cardiac anomalies as the increased | |||
pulmonary vascular resistance can lead to right-to-left shunting | |||
and severe hypoxia. Other pitfalls include ligation of the | |||
wrong structure, intubation of the fistula and endobronchial | |||
intubation. | |||
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 | |||
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 Xray | |||
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. | |||
21 | |||
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. | |||
22 | |||
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. | |||
23 | |||
These include permissive hypercapnoea (PaCO | |||
2 | |||
<70mmHg), limiting inflation pressures (avoid PIP>25cm | |||
H | |||
2 | |||
O and PEEP > 5 cm H | |||
2 | |||
O) and accepting relative hypoxaemia | |||
(aim for pre-ductal SpO | |||
2 | |||
90-95%). Surgery may need to be | |||
performed whilst the neonate is on high-frequency oscillation | |||
ventilation or extra-corporeal membrane oxygenation. | |||
24 | |||
Preoperative assessment must pay particular attention to the | |||
presence of significant pulmonary hypertension, ventilation | |||
requirements, and associated cardiac anomalies. If the infant | |||
is not already intubated, anaesthesia is induced with care to | |||
avoid gastric insufflation with bag valve mask ventilation and | |||
further lung compression. A nasogastric tube is inserted to | |||
decompress the stomach. Invasive monitoring is required to | |||
allow serial blood gas measurement. There is a risk of blood loss | |||
and a unit of packed red cells should be available. In patients | |||
with significant pulmonary hypertension, having nitric oxide | |||
available in theatre may be critical for treatment of pulmonary | |||
hypertensive crises. | |||
A subcostal or transverse abdominal incision is made and | |||
the herniated viscera are reduced into the abdomen. The | |||
diaphragmatic defect is then either closed primarily or with | |||
a prosthetic patch if the defect is large. Thoracoscopic repair | |||
is being undertaken in some centres. Following abdominal | |||
closure, raised intra-abdominal pressures may lead to | |||
difficulty with ventilation and a risk of developing abdominal | |||
compartment syndrome, and delayed closure may be necessary. | |||
Lung compliance decreases post-operatively and post-operative | |||
ventilation is usually necessary. These patients often suffer from | |||
chronic respiratory disease, gastro-oesophageal reflux disease | |||
and neurodevelopmental delay. | |||
Gastroschisis and exomphalos (omphalocele) | |||
Gastroschisis and exomphalos are both ventral wall defects | |||
resulting in herniation of abdominal viscera. Diagnosis is | |||
ideally made on antenatal ultrasound scan. | |||
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. | |||
25 | |||
Exomphalos occurs in approximately 1:5000 live births. Failure | |||
of normal embryological development results in the bowel | |||
remaining within the umbilical cord and not returning to the | |||
abdomen. The herniated viscera is covered by a sac. There is a | |||
high incidence of associated congenital abnormalities including | |||
cardiac anomalies. Specific chromosomal associations include | |||
trisomies 13, 15, 18 and 21 and it can be associated with | |||
Beckwith-Wiedemann syndrome. | |||
To avoid bowel injury the baby is delivered by caesarean | |||
section. The operating theatre should be warmed, the baby | |||
dried, any exposed bowel covered with plastic and a nasogastric | |||
tube is inserted to decompress the stomach. Fluid resuscitation | |||
is commenced, a urinary catheter inserted and broad spectrum | |||
antibiotics started. Co-existing congenital abnormalities, | |||
especially cardiac, should be assessed. A renal or cranial | |||
ultrasound may also be indicated. | |||
Surgery is more urgent in gastroschisis due to the ongoing fluid | |||
losses and electrolyte and metabolic derangement. If primary | |||
closure is not possible then a ‘silo’ is placed over the exposed | |||
bowel, which may require a general anaesthetic if the defect | |||
needs extending to fit the device. The silo is suspended above | |||
the patient postoperatively, and the bowel is gradually reduced | |||
into the abdominal cavity under gravity over the ensuing few | |||
days in the NICU. When the patient is stable and spontaneous | |||
reduction of the bowel has reached a plateau, then surgery | |||
for reduction and closure of hernia is performed. Surgery for | |||
exomphalos is less urgent, unless the sac has ruptured. If the | |||
patient is stable and the defect is small a primary repair can | |||
usually be done. In large defects, if the sac has not ruptured, | |||
it may be treated with topical silver sulfadizine to allow | |||
epithelisation with definitive surgery at a later stage. | |||
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 H | |||
2 | |||
O then a staged repair is indicated. | |||
26 | |||
Unless there is a very small defect the infant will require post- | |||
operative ventilation and a generous opioid-based anaesthetic | |||
technique can be used (fentanyl 10-20mcg.kg | |||
-1 | |||
). These patients | |||
often require parenteral nutrition and a significant proportion | |||
present for further abdominal surgery. | |||
conclUSion | |||
Improving outcomes in neonatal anaesthesia is dependent | |||
on a thorough understanding of the unique anaesthetic | |||
requirements of the neonate and a detailed knowledge of | |||
the different pathologies that present during this period. | |||
Unnecessary surgery should be avoided during the neonatal | |||
period as anaesthesia and surgical stress may have detrimental | |||
effects on the very immature child. | |||
reFerenceS | |||
1. | |||
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. | |||
3. | |||
Taddio A, Katz J, Ilersich AL, Koren G. Effect of neonatal | |||
circumcision on pain response during subsequent routine | |||
vaccination. | |||
Lancet | |||
1997; | |||
349 | |||
: 599-603. | |||
4. | |||
Stevens B, Yamada J, Lee GY, Ohlsson A. Sucrose for analgesia | |||
in newborn infants undergoing painful procedures. Cochrane | |||
Database Syst Rev 2013 1:CD001069. | |||
5. | |||
Shah PS, Herbozo C, Aliwalas LL, Shah VS. Breastfeeding or | |||
breast milk for procedural pain in neonates. Cochrane Database | |||
Syst Rev 2012 12:CD004950. | |||
6. | |||
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. | |||
7. | |||
Bancalari E, Claure N. Oxygenation targets and outcomes in | |||
premature infants. | |||
JAMA | |||
2013; | |||
117 | |||
: 2161-2. | |||
8. | |||
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. | |||
9. | |||
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. | |||
10. | |||
Cote CJ Postoperative apnea in former preterm infants after | |||
inguinal herniorrhaphy: A combined analysis. | |||
Anesthesiology | |||
1995; | |||
82 | |||
: 809-22. | |||
11. | |||
Henderson-Smart DJ, Steer P. Prophylactic caffeine to prevent | |||
postoperative apnea following general anesthesia in preterm | |||
infants. Cochrane Database Syst Rev 2001;4:CD000048. | |||
12. | |||
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. | |||
13. | |||
Olsen EA, Brambrink AM. Anesthetic neurotoxicity in the | |||
newborn and infant. | |||
Curr Opin Anaesthesiol | |||
2013 August 29 | |||
(e-pub ahead of print). | |||
page 132 | |||
14. | |||
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. | |||
15. | |||
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. | |||
16. | |||
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. | |||
17. | |||
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. | |||
18. | |||
Millar AJ, Rode H, Cywes S. Malrotation and volvulus in infancy | |||
and childhood. | |||
Semin Pediatr Surg | |||
2003; | |||
12 | |||
: 229-36. | |||
19. | |||
Llanos AR, Moss ME, Pinzòn MC, Dye T. Epidemiology of | |||
neonatal necrotizing enterocolitis: a population-based study. | |||
Paediatr Perinat Epidemiol | |||
2002; | |||
16 | |||
: 342-9. | |||
20. | |||
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]. | |||
21. | |||
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. | |||
22. | |||
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 | |||
23. | |||
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. | |||
24. | |||
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. | |||
25. | |||
Molik KA, Gingalewski CA, West KW et al. Gastroschisis: a plea | |||
for risk categorization. | |||
J Pediatr Surg | |||
2001; | |||
36 | |||
: 51–5. | |||
26. | |||
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. |