Anaesthesia for fetal interventions

Key points.

• •Hydrops fetalis is a common endpoint of many fetal diseases that signals the need for fetal therapy.
• •Some interventions require a hysterotomy to access the fetus, and some may be performed with needles or fetoscopes inserted into the uterus.
• •Myelomeningocele is not life-threatening, but fetal treatment improves neurological outcomes.
• •Ex utero intrapartum therapy takes place immediately before birth to allow the fetus to make a successful transition to extrauterine life.
• •Uterine atony is important to provide good operative conditions and fetal perfusion.

Learning objectives.

By reading this article, you should be able to.

• •Describe which fetal diseases are amenable to intervention.
• •Explain the rationale for these interventions.
• •Discuss the broad classes of therapy and the basic surgical approach.
• •Formulate a plan for anaesthesia for fetal interventions in conjunction with the surgical team.

In the past few decades, the field of fetal surgery has rapidly evolved. It now includes a wide range of interventions, and anaesthesia for these procedures has evolved concurrently. This is an exciting, highly specialised and high-risk subspecialty of obstetric and paediatric anaesthesia, in which two high-risk patients are cared for simultaneously for the benefit of the developing fetuses.

Diseases and treatment concepts

A brief overview of the diseases commonly treated by fetal therapy will help the reader understand the rationale for treatment (Table 1). This is not an exhaustive list, as the field is constantly evolving. Most fetal interventions are performed to prevent intrauterine fetal demise, although some are performed to improve the quality of life after birth. Some interventions are performed to facilitate the transition from intrauterine to extrauterine life. In some cases, the health of the mother may be threatened by her sick fetus, and treating the fetus may save the life of the mother. This condition is known as maternal mirror syndrome.¹

Table 1.

Fetal conditions amenable to fetal interventions by gestational age

Fetal condition	Intervention
Mid-gestational fetal interventions
Twin reversed arterial perfusion	Ultrasound-guided radiofrequency ablation of umbilical cord
Twin–twin transfusion syndrome	Fetoscopic laser ablation of placental anastomosis
Cardiac anomalies	Catheter-based balloon aortic valvuloplasty or septoplasty
Congenital diaphragmatic hernia	Fetal endoscopic tracheal occlusion
Myelomeningocele	Open or fetoscopic repair of neural tube defect
Sacrococcygeal teratoma	Open resection of tumour
Urinary tract obstruction	Fetal cystoscopy; vesicoamniotic shunt
Term fetal interventions
Ex utero intrapartum treatment	Open airway management (i.e. tracheostomy, bronchoscopy, intubation and cystic hygroma resection)

Fetal anaemia

Fetal anaemia may arise from causes, such as alloimmunisation or parvovirus infection. Intrauterine transfusion (IUT) of red blood cells into the anaemic fetus does not treat the cause, but it temporarily reduces morbidity and mortality until the fetus can be delivered. Intrauterine transfusion may be repeated over the course of pregnancy to maintain the desired fetal haematocrit. Because of improved detection and timely referral, survival has improved dramatically.²

Complicated multiple gestations

Monozygotic twin pregnancies may develop complications, such as twin–twin transfusion syndrome (TTTS) or twin reversed arterial perfusion (TRAP) sequence. Twin–twin transfusion syndrome is associated with fetal preterm delivery, mortality, cardiac, neurological and developmental disorders. The pathophysiology involves unbalanced blood flow between the twins attributable to placental vascular anastomoses, which lead to relative hypovolaemia in one twin and hypervolaemia in the other.³ Cardiac complications typically occur in the recipient twin and are attributed to volume overload and fetal systemic hypertension. Neurological damage may result from prematurity, growth restriction and fetal haemodynamic instability.⁴ Preterm delivery and fetal mortality are closely tied to the increased complication rates of all monozygotic pregnancies. Ablation of the vascular anastomoses on the placenta will help balance the blood flow. Many consider laser ablation the best option for more advanced stages of TTTS.

Twin reversed arterial perfusion occurs in monochorionic twin pregnancies, in which one twin with an absent or rudimentary heart is perfused by the other ‘pump’ twin via placental vascular anastomoses. The acardiac twin is non-viable and dependent on the pump twin for circulatory support. The pump twin is at risk for developing heart failure and other complications that may lead to preterm birth or demise without intervention. Treatment involves interrupting all blood flow to the acardiac twin with radiofrequency energy. In the North American Fetal Therapy Network Registry of radiofrequency ablation (RFA) procedure for TRAP, there were no maternal deaths, no women required blood transfusions and most women were hospitalised for ≤1 day after the procedure.⁵

Airway obstruction

Airway obstruction falls into two categories; it may be secondary to extrinsic causes, such as tumours, or from intrinsic causes, such as webs or atresia. Tumours causing airway obstruction will typically not interfere with fetal survival, but these tumours may cause life-threatening problems at birth. Ex utero intrapartum therapy (EXIT) utilises the placenta as the organ of respiration for the fetus to give the surgical team time to secure the fetal airway. A variety of means may be used, such as rigid bronchoscopy, tracheostomy or retrograde wire intubation. Laryngeal webs or atresia can cause complete obstruction of the fetal airway and will directly compromise fetal survival.⁶ The cause of demise is not a lack of fetal respiratory capacity. Complete airway obstruction impedes the egress of lung fluid, and the lungs can become so distended that the fetal heart is compressed. Cardiac compression will result in hydrops and fetal demise. This condition is called congenital high airway obstruction syndrome. Creating a small hole in the tracheal obstruction allows lung decompression and subsequent cardiac decompression.⁷ This decompression procedure is best done in the middle of gestation when evidence of hydrops develops, and subsequently, the fetus should continue growing and developing. At term, an EXIT procedure should be performed for delivery to secure an airway that is still at risk.

Lung pathology

Large intrathoracic tumours may cause fetal cardiac compression and lead to hydrops and fetal demise. These masses include congenital cystic adenomatoid malformations, bronchopulmonary sequestrations and lesions that are a hybrid of the two. If these tumours are cystic, serial aspiration or continuous catheter drainage (thoracoamniotic shunt) of the tumour is all that is needed. A solid tumour causing hydrops would likely require fetal pulmonary lobectomy. If the symptoms of hydrops occur in the middle of gestation with immature lungs, the therapies would occur in the middle of gestation, and the pregnancy should continue to term. If the hydrops occurs later in gestation with mature lungs or if the size of the tumour will present difficulty with neonatal resuscitation, then the fetus should be delivered via an EXIT procedure. In this case, the EXIT is done to facilitate resuscitation of the neonate.⁸

Congenital diaphragmatic hernia (CDH) is amenable to fetal therapy to improve neonatal survival. The antenatal treatment of CDH involves fetal endoscopic tracheal occlusion (FETO) with a balloon. As in the case of complete airway obstruction, fluid will accumulate and distend the lungs. The hope is that the distension of the hypoplastic lungs of fetuses with CDH will allow improved fetal lung maturation.⁹

Cardiac anomalies

Some anomalies, such as hypoplastic left heart syndrome (HLHS) with intact atrial septum or severe fetal aortic stenosis with evolving HLHS, may be amenable to fetal cardiac intervention. In the case of aortic stenosis with HLHS, a minimally invasive catheter-based fetal aortic valvuloplasty is performed to increase flow through the stenotic aortic valve to promote blood flow through the left ventricle.¹⁰ This flow may encourage the development of a two-ventricle circulation.¹¹ In the case of HLHS with intact atrial septum, a catheter-based atrial septoplasty is performed to pre-empt the need for an emergent atrial septoplasty at birth.

Myelomeningocele

Since publication of the Management of Myelomeningocele Study (MOMS), fetal surgery for myelomeningocele (MMC) has become a commonly offered option in many specialised centres. Management of Myelomeningocele Study was an RCT conducted between 2003 and 2010 at three institutions in the USA that evaluated the safety and efficacy of open in utero fetal surgery for the repair of MMC compared with postnatal repair.¹² Neurological and psychomotor outcomes were improved in the prenatal repair group. These benefits occurred despite a higher risk of preterm delivery and pulmonary complications amongst infants undergoing fetal surgery and of obstetrical complications, including placental abruption, dehiscence of the hysterotomy site and maternal transfusion at delivery.¹² The participants are being followed into childhood to evaluate the long-term effect of fetal intervention.¹³ Because fetal surgery is associated with risks of fetal and maternal complications, fetal surgery should only be offered at facilities with appropriate expertise and staffing.¹⁴

In April 2018, NHS England issued an urgent clinical commissioning policy statement for prenatal surgery for open spina bifida.¹⁵ The commissioning position of NHS England has concluded that there is sufficient evidence to support the routine commissioning of prenatal surgery for open spina bifida as long as meeting the clinical inclusion and exclusion criteria listed in Table 2. Both inclusion and exclusion criteria are per MOMS protocol.

Table 2.

Criteria for prenatal surgery for fetal congenital open spina bifida at T1–S1 with hindbrain herniation according to the MOMS protocol.¹¹

Inclusion criteria

Exclusion criteria

Gestational age of 19+0 to 25+6 weeks gestation Known maternal human immunodeficiency virus, hepatitis B virus and hepatitis C virus status for inclusion in the management plan No serious maternal medical complications Normal karyotype Ultrasound confirms congenital open spina bifida below T6 Fetal MRI confirms Arnold–Chiari malformation Amniocentesis (to provide a genetic diagnosis to rule out syndromic congenital abnormality, which would contraindicate surgery, e.g. trisomy 18) Fetal lateral ventricles below 20 mm (subject to clarification regarding level of benefit being reduced where there is ventriculomegaly >15 mm) No additional structural or functional fetal anomalies

Multiple pregnancy Other fetal anomaly not related to open spina bifida, which is likely to significantly impact on fetal surgery or the short- or long-term outcome Ultrasound confirms fetal spinal kyphosis of ≥30⁰ Current or planned cervical cerclage (a stitch placed around the cervix to keep it closed during pregnancy) or documented history of cervical insufficiency Obstetric complications, such as placenta previa or previous placental abruption Short cervical length <20 mm measured by transvaginal ultrasound Obesity as defined by BMI of ≥40 kg m−2 Previous spontaneous singleton delivery before 37 weeks as a contraindication to a safe near-term Rh isoimmunisation, Kell sensitisation or a history of neonatal alloimmune thrombocytopenia Uterine anomaly, such as large or multiple fibroids, or Müllerian duct abnormality Other maternal medical condition, which is a contraindication to surgery or general anaesthesia Previous hysterotomy in the active segment of the uterus (whether from a previous classical Caesarean section or a uterine anomaly, such as an arcuate or bicornuate uterus, major myomectomy resection or previous fetal surgery); a previous uncomplicated Caesarean section scar is acceptable Inability to comply with the travel and follow-up requirements needed by the open fetal surgery centre Maternal hypertension, which would increase the risk of preeclampsia or preterm delivery (including but not limited to uncontrolled hypertension, chronic hypertension with end-organ damage and new-onset hypertension in pregnancy)

Several centres are exploring a fetoscopic approach to prenatal repair of MMC.¹⁶ Whilst fetal and neonatal outcomes are still being evaluated, this approach will allow for vaginal delivery after repair.¹⁷

Sacrococcygeal teratoma

Sacrococcygeal teratoma (SCT) may cause high-output fetal heart failure. Arteriovenous shunting within the tumour can cause a steal phenomenon, in which the metabolic demand of the tumour is so high that the fetal heart cannot adequately supply both the tumour and the developing fetus. In utero interventions are temporising measures performed to reduce the size and metabolic demand of the SCT and thus allow the fetus to continue growing. Definitive surgical resection is required after birth. A systematic review of literature by Van Mieghem and colleagues showed that either minimally invasive or open fetal surgery in cases of high-risk SCT can improve survival.¹⁸ Selection criteria for fetal surgery include the presence of hydrops, rapid growth, indicators of cardiac failure and severe polyhydramnios.¹⁸

Urinary tract obstruction

Congenital lower urinary tract obstruction results in pulmonary hypoplasia and renal dysfunction. Decompression of the fetal urinary tract is undertaken to attenuate these sequelae and may be achieved by placing a vesicoamniotic shunt or by performing fetal cystoscopy with fulguration of the obstruction.¹⁹

Classes of fetal interventions

Fetal interventions can be divided into three major subgroups according to the invasiveness of procedures and their anaesthetic requirements. First is minimally invasive and fetoscopic surgery that involves insertion of needles or fetoscopes through the abdominal and uterine walls to access the umbilical cord, placenta or fetus. No hysterotomy is performed for these procedures. Some fetoscopic procedures involve a maternal laparotomy to allow better access to the uterus and fetus. Whilst a maternal laparotomy is involved, the uterus remains intact, and the instruments are inserted into the closed uterus under direct vision. The second major category of fetal intervention is traditional open fetal surgery, which involves a maternal laparotomy and hysterotomy to gain direct access to the fetus. The fetus remains in the uterus, and the hysterotomy is closed at the end of the case with the goal of continuing the pregnancy to term. The third group is the EXIT procedure, which also involves a maternal laparotomy and hysterotomy. The EXIT procedures deserve distinction from open fetal surgery because the fetus is delivered at the end of the procedure. Multiple teams are involved, and communication and resource management are critical. Because the fetus will at least need further resuscitation if not more surgery immediately after birth, a team from the neonatal ICU should be present and a second operating theatre complete with nurses and anaesthetists prepared.

Minimally invasive and fetoscopic

Some procedures, such as IUT (Fig 1A), RFA for umbilical vessels, SCT or acardiac–acephalic twin (Fig 1B), and placement of thoracoamniotic and vesicoamniotic shunts are done with insertion of a needle into the uterus. It is guided to the area of interest with real-time ultrasound images. Cardiac interventions at experienced centres are also performed in a similar manner.

Fig 1.

(A) Intrauterine transfusion therapy for fetal anaemia. (B) RFA for SCT. (C) RFA of acardiac–acephalic twin.

Laser coagulation for TTTS and FETO for CDH involve percutaneous insertion of a small fetoscope to visualise the placenta or fetal trachea. Instruments, such as laser fibres or a catheter holding a tracheal balloon, can be introduced through the operating channel in the fetoscope whilst a second channel allows for irrigation and visualisation. For TTTS, the placental vessels are mapped, and anastomoses are coagulated with the laser (Fig 2). The fetoscope is removed, and amnioreduction is often performed. For CDH, the tracheal balloon is deployed and the fetoscopes are withdrawn. During these procedures, the fetal heart rate is monitored with ultrasound.

Fig 2.

Laser coagulation of previously mapped placental anastomosis for TTTS.

Some procedures, such as fetoscopic repair of MMC, may entail a maternal laparotomy. Less invasive approaches to fetal surgery are under active investigation because open fetal surgery can lead to reproductive and obstetric morbidity.²⁰ Fetoscopic surgeries allow for vaginal delivery and may reduce long-term maternal risks. These procedures involve insertion of two or three trocars into the uterus, either percutaneously or after laparotomy, to allow passage of multiple instruments to visualise a fetal defect and perform the necessary surgery (Fig 3).

Fig 3.

Fetoscopic repair of MMC involves insertion of several trocars into the uterus to allow passage of multiple instruments.

With the exception of RFA for TRAP, fetal bradycardia may necessitate stopping the procedure, administration of emergency medications (such as atropine 20 μg kg⁻¹ or adrenaline [epinephrine] 10 μg kg⁻¹) or even performing an emergency Caesarean section. These decisions will be informed by the condition and gestational age of the fetus. Steroids are given to the mother before the procedure to promote fetal lung maturity if the fetus is of viable gestational age.

Open fetal surgery

Conditions amenable to open fetal therapy include but are not limited to MMC, fetal lung tumour, pericardial teratoma and anatomically favourable SCT. These procedures are generally performed between 24 and 26 weeks' gestation and involve open surgery for both the mother and the fetus. The maternal–fetal surgical team must have extensive experience and may include paediatric and obstetric anaesthetists, paediatric surgeons (general, cardiac and neurological), paediatric cardiologists, perinatologists and highly trained subspeciality nurses. The specific surgical approach to MMC has been described.¹² The general principles may be applied when performing open fetal surgery for other diseases. Briefly, the uterus is exposed and exteriorised. The placental edges are mapped by ultrasound and the fetus positioned within the uterus such that the area of interest is in the centre of the planned hysterotomy. In cases of an anterior placenta, a fundal or posterior hysterotomy is performed. In cases of a posterior placenta, hysterotomy is made anteriorly. A 6–8 cm hysterotomy is made to expose the fetus, and a uterine stapling device is used to maintain haemostasis and intact membranes. The fetal surgery is carried out, after which the uterus is closed. Warmed Ringer's lactate solution is infused into the uterus to keep the fetus warm and buoyant. If the fetus sinks too low, the umbilical cord may be compressed. After the fetal procedure is completed, the hysterotomy and laparotomy wounds are closed.

Risks of open fetal surgery include preterm birth, chorion–amnion separation, spontaneous membrane rupture, oligohydramnios, placental abruption, maternal pulmonary oedema and increased incidence of uterine thinning/dehiscence of the uterine scar at delivery. The mother will need to deliver via Caesarean section for all future pregnancies. Postoperative management after open fetal surgery centres around the prevention of these complications.

EXIT procedure

During an EXIT procedure, the goal is to maintain placental blood flow and gas exchange for the fetus whilst fetal intervention is performed before fully delivering the fetus and placenta. The conduct of the surgery is similar to that of open fetal surgery. The fetus is partially delivered through the hysterotomy whilst keeping the umbilical cord intact. At the beginning of the fetal procedure, the fetal trachea is intubated, but the lungs are not ventilated. This is to prepare for either the end of a successful procedure or to prepare for the emergent cutting of the umbilical cord and delivery to a second operating theatre for completion of the surgery. With good conditions, the surgical team has an hour or more to establish an airway or stabilise fetal pathology (Fig 4). At the completion of the fetal intervention, the umbilical cord is clamped and cut, and the neonate is taken by a team from the neonatal ICU for further resuscitation. In some situations, such as refractory fetal bradycardia or placental abruption, the fetus must be delivered emergently before the completion of the surgery. A second operating theatre must be ready with a full team of nurses and anaesthesiologists prepared to care for a neonate that is likely in extremis. After the neonate has been delivered, the maternal portion of the surgery proceeds similarly to a Caesarean section.

Fig 4.

EXIT procedure allows for the maintenance of placental blood flow and gas exchange for the fetus whilst fetal pathology (i.e. airway) is stabilised before fully delivering the fetus and placenta.

Lin and colleagues reported their 13 yrs experience with anaesthesia for 65 EXIT procedures at the Children's Hospital of Philadelphia (Philadelphia, PA, USA).²¹ In this series, most cases were performed for complex fetal airways, including tracheostomy, tumour resection, cyst drainage, neck dissection or retrograde intubation. Fewer EXIT procedures were performed for thoracotomies and resection of large lung lesions. A few cases included cannulation for extracorporeal membrane oxygenation, debulking of high-risk SCT or median sternotomy for resection of mediastinal teratoma.

Anaesthesia

Preoperative evaluation

Preoperative evaluation includes a comprehensive history and physical examination and other studies, as warranted by the mother's history and fetal disease process. Preoperative symptoms of supine hypotension should alert the anaesthetist to maintain extra vigilance during the procedure. Symptoms of back pain should prompt meticulous positioning of the patient. Physical examination should pay special attention to the mother's airway and spine. Investigations typically include a blood type and screening for antibodies, with further tests guided by the clinical history. A type and cross-match is often performed for open and EXIT procedures. The deep general anaesthesia required during open fetal surgery may slow conduction through the atrioventricular node and may cause previously hidden accessory conduction pathways to become evident. Fetal studies may include ultrasound, MRI and echocardiography, and genetic testing and fetal urine electrolytes in cases of urinary tract obstruction.

The mother undergoes psychosocial evaluation to ensure that she has adequate support systems, and the family undergoes extensive counselling by the maternal–fetal surgeons, neonatologist, anaesthetist and perinatologists.

Management of minimally invasive and fetoscopic procedures

This is the most heterogeneous group of interventions, and the management of anaesthesia will vary with the procedure and the needs of the mother and the fetus. In very minimally invasive cases, after prophylaxis against pulmonary aspiration and positioning with a left uterine displacement, infiltration of local anaesthesia may be is all that is needed. With increased size of needles or trocars or particularly anxious mothers, small doses of opioids, benzodiazepines, propofol and dexmedetomidine may be used. In some cases, the surgeons may prefer that fetuses be still. This procedure may be accomplished by giving medications to the mother and counting on transplacental passage. The results of this strategy vary greatly between patients. If the surgeons need a completely still fetus, an i.m. injection of medications to the fetus can be used, including opioids, non-depolarising neuromuscular blocking agents and atropine. The level of maternal sedation for these cases should be quite minimal to avoid the risk of aspiration. In addition, mild airway obstruction can occur if the mother becomes too sedated, and paradoxical motion of her chest and abdomen can create poor operative conditions. The location of the placenta affects the trajectory of the needle, and in some cases, left uterine displacement cannot be performed. In these cases, the surgical and anaesthesia teams must cooperate to find reasonable and safe positioning solutions. Some centres have reported use of neuraxial anaesthetic techniques for some procedures if the instruments are too large to be managed with local anaesthetic infiltration or when the placenta has implanted onto the anterior surface of the uterus. In other cases, as for fetoscopic repair of MMC, general anaesthesia with tracheal intubation is used. The management of anaesthesia for five percutaneous fetoscopic MMC repairs has recently been described in detail.²²

Management of open fetal surgery

Whilst specific details of management will certainly vary between institutions, what follows is a fairly standard practice. A low thoracic epidural catheter is placed for postoperative analgesia before general anaesthesia is induced. Whilst blood loss is usually low for these cases, the risk for sudden catastrophic blood loss is real, and so two large-bore peripheral venous catheters are inserted. Drugs for aspiration prophylaxis are given, and the mother is placed supine with left uterine displacement. After rapid sequence intubation, the mother's trachea is intubated. Optimal uterine perfusion pressure is maintained using vasopressors, such as phenylephrine or ephedrine. Careful arterial blood pressure monitoring is important for titration of vasopressors, and invasive blood pressure monitoring is commonly performed.

Crystalloid fluids are often used in restricted volumes (500–1000 ml), as mothers undergoing fetal surgery are at an increased risk for pulmonary oedema.²³ Anaesthesia has traditionally been maintained with high concentrations of a volatile anaesthetic agent (1.5–2 minimum alveolar concentration [MAC]). Many centres use desflurane as the chosen agent for its rapid titratability. In 2010, Boat and colleagues reported the use of supplemental i.v. anaesthesia (SIVA) with propofol and remifentanil combined with lower concentrations of desflurane.²⁴ The team was able to reduce the dose of volatile anaesthetic whilst providing adequate maternal depth of anaesthesia and uterine relaxation. Suitable conditions were achieved with about 1.5 MAC of desflurane in the SIVA group compared with about 2.5 MAC in the desflurane-only group. Fetuses in the SIVA group had a lower incidence of left ventricular systolic dysfunction and need for fetal resuscitation.²⁴ Many centres are working to reduce the dose of volatile anaesthetic agents given to the mother, either by using SIVA, modifications of SIVA or other means (such as nitroglycerine infusions).

During closure of the hysterotomy, a bolus of magnesium sulphate 6 g is given, followed by an infusion of 2–4 g h⁻¹ to prevent preterm labour. In some institutions, magnesium is given at maternal skin incision to reduce the total anaesthetic exposure to the fetus compared with dosing at uterine closure.²⁵

After the hysterotomy is closed, the volatile anaesthetic agent is weaned, and the epidural catheter is dosed with local anaesthetic. When the patient is fully awake, her trachea is extubated.

Management of EXIT procedures

Initial anaesthetic management of an EXIT procedure is similar to an open fetal procedure. However, there is no longer a need for magnesium administration or fluid restriction. After delivery and umbilical cord clamping, desflurane concentration is titrated down whilst oxytocin is started to establish uterine tone with methylergonovine and prostaglandins as adjuncts.²¹

The unique challenges of managing EXIT procedures come from resource utilisation. These procedures have a 32% chance of occurring before the planned date, which is usually 37 weeks' gestation. Lin and colleagues also reported an 18% chance of these procedures happening as emergencies during night-time or other times when staffing levels are lower.²¹ The participants in these cases are usually a specially trained subset of the nurses and doctors, so ad hoc on-call teams and phone call trees may need to be established. In the course of a case, the fetal or maternal conditions may change rapidly, and all teams, including surgical, neonatal, anaesthesia and nursing, must be ready to change course. Less experienced centres would be well served by planning a series of team meetings and simulations to establish expectations and roles, and to develop a shared mental model of the course of the operation. The usually simple logistics of ordering medications and blood must be carefully planned when sharing these resources between three different teams (i.e. maternal–fetal operating theatre, neonatal intensive care and backup neonatal operating theatre).

Specific fetal considerations

During open fetal and EXIT procedures, volatile agents given to the mother afford the fetus some degree of anaesthesia to help blunt the stress response to surgery. In addition, the fetus receives an i.m. injection of fentanyl 20 μg kg⁻¹, vecuronium 0.2 mg kg⁻¹ and atropine 20 μg kg⁻¹. These medications are usually mixed in a single syringe. During minimally invasive cases, the i.m. Injection to the fetus will vary depending on the needs of the procedure.

Fetal monitoring can range from intermittent ultrasound checks of the heart rate to pulse oximetry to continuous echocardiography.²⁶ The type of monitoring will be guided by the nature of the procedure and the access to the fetus.

Cardiovascular compromise is more common during open fetal surgery and EXIT than minimally invasive surgery. Myocardial depression can occur from effects of inhalational anaesthesia independent of maternal haemodynamics. Placental insufficiency or mechanical cord compression can lead to alterations in the cardiovascular status.

In cases of fetal bradycardia or hypoxaemia, communication is vital. The anaesthetist must first ensure that the mother is safe and her haemodynamics are optimal for the fetus. Then, measures can be taken to assess and help the fetus. Umbilical cord compression is common and easily fixed. For fetal cardiac catheter-based interventions and open fetal and EXIT procedures in particular, several doses of emergency medications for the fetus should be prepared. Such medications include atropine 20 μg kg⁻¹ and adrenaline 10 μg kg⁻¹ and calcium gluconate 50 mg kg⁻¹. For open fetal procedures and EXITs, O negative blood that has been cross matched against the mother's sample should also be available for the fetus. If the team has access to the fetus, chest compressions can be done in the sterile field, whilst the anaesthesia team can give medications and fluids. A fetal peripheral venous catheter or loop of umbilical cord close to the fetal abdominal cord insertion site may be used.

Conclusions

As the field of fetal surgery continues to grow, the field of maternal–fetal anaesthesia for these complex procedures will also continue to evolve.^27,28 In addition to understanding the diseases and procedures, important elements are open communication, clear understanding and careful preparation for all scenarios. The formation of specialised centres equipped with all the necessary resources that can be available at a moment's notice is key in ensuring success.

Declaration of interests

The authors declare that they have no conflicts of interest.

Biographies

Chang Amber Liu MD MSc FAAP is a paediatric and obstetric anaesthesiologist at Massachusetts General Hospital. She is the director of paediatric regional anaesthesia and of maternal fetal anaesthesia. She is an assistant professor at Harvard Medical School.

Sarah Low MD is a fellow in paediatric anaesthesia. She is the associate director of the Massachusetts General Hospital Multimedia, Arts and Design Laboratory. She is an instructor at Harvard Medical School.

Kha Tran MD is a paediatric anaesthesiologist at the Children's Hospital of Philadelphia. He is the clinical director of the fetal anaesthesia team. He is an assistant professor of anaesthesiology at the Perelman School of Medicine at the University of Pennsylvania.

Matrix codes: 1H02; 2A07; 3B00

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.