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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.
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