by Dr Minh Le Cong
Peer reviewed by Dr Penny Wilson
Pregnancy leads to significant anatomic and physiologic changes that must be understood by those who will provide emergency transport care.
Cardiac output increases along with heart rate. Functional systolic murmurs are common. There is a significant increase in plasma volume and a relative haemodilution. Hypertension is not a feature of normal pregnancy and its presence may indicate significant underlying pathology. The increased intravascular volume means that in maternal haemorrhage the signs of shock may present late.
The enlarging uterus becomes engorged with blood and its wall thins, placing it at risk of traumatic injury and catastrophic haemorrhage. The expanding uterine mass increasingly compresses ALL abdominal organs including the major vessels. Inferior vena caval compression particularly in the supine position will significantly reduce venous return and cardiac preload. This leads to a reduction in cardiac output and hypotension. Maternal physiologic compensation for these effects does occur, mainly through increased maternal intravascular volume and mild tachycardia. Any resuscitative efforts during pregnancy must begin with displacing the mass effect of the enlarged uterus from the inferior vena cava. Common practice is to use some form of wedge like a pillow or rolled blanket, placed under the right hip to position the mother in a tilted left lateral position.
There is an enormous increase in total body water during pregnancy and this can lead to pregnancy related oedema. This can affect multiple sites and can even lead to swollen airway tissues which may make airway management difficult if emergency intubation is required. This difficulty is compounded by the increased gastric stasis of pregnancy and the high risk for gastric regurgitation and aspiration. The first description of cricoid pressure by Dr Sellick was for this very patient group. Enlarged breasts can also sometimes limit the use of a laryngoscope.
Pregnancy induces an increase in minute ventilation to meet the body’s increased metabolic requirements. There is an increase in tidal volume and to a lesser extent respiratory rate, but total lung capacity is reduced in part by the mass effect of the uterus on the diaphragm. The Functional Residual Capacity ( FRC ) is decreased. Swollen breasts in the supine position can reduce tidal volume by weight effect upon the chest wall. Interestingly posture makes little difference to oxygenation in a normal pregnancy but transient desaturations will occur during normal contractions which increase oxygen consumption by around 60%. The reduced FRC and the high oxygen requirements mean that even short periods of apnoea can lead to rapid desaturation and hypoxia with both maternal and foetal implications.
Medications may need to be carefully selected as they can have dramatic deleterious effects upon the foetal condition. For example potent induction agents such as propofol and thiopentone in combination with opioids may lead to apnoea in the new born on emergency delivery. In the tertiary hospital setting there are often other options for emergency obstetric anaesthesia such as spinal or epidural regional blocks but in the retrieval setting this is often impractical or dangerous. There are also altered maternal responses to many drugs. As an example the elimination half life of thiopentone is more than doubled in pregnant women whilst many other drugs demonstrate increased renal excretion and therefore increased dose requirements.
Foetal physiology is of little consequence to the retrieval practitioner. Apart from choosing medications carefully there is little about the foetal condition that the retrieval clinician should or could alter without actually delivering the baby. The most important aspect of caring for the foetus is meticulous care of the mother as the two go hand in hand. Indeed evolution has placed the foetus at a greater survival advantage than the mother. Foetal haemoglobin extracts oxygen from the maternal circulation in preference to adult haemoglobin and so in the aeromedical setting the foetus maintains critical oxygenation better than the mother.
1. Flight team composition
Obstetric retrievals should be performed under the direction of an obstetrician or a doctor with experience in high risk pregnancy management and knowledge of aviation physiology. The decision to undertake the actual transport should be made by the whole retrieval team, using their collective experience and training.
The actual flight team should include as a minimum two practitioners with experience and training in emergency delivery, the management of preterm labour, the use of tocolytics, severe pre-eclampsia/eclampsia and acute post partum haemorrhage. It should also be a mandatory requirement to demonstrate competency in advanced neonatal resuscitation.
2. Who needs transfer
Generally mothers are transferred when local facilities are not able to meet either maternal or neonatal needs. Common causes are:
- Pre term labour
- Third trimester vaginal bleeding
- Pre – eclampsia or eclampsia
- Severe infection
In countries like Australia where the distance to definitive care can be vast and some transport times may be many hours, high risk mothers, and by inference high risk neonates, are often transferred electively at 36 weeks to a major Obstetric unit. The indications include:
- Minimal or nil availability of obstetric services
- Previous history of significant complications eg foetal death
- Severe comorbidity
- Extreme remote environment
3. What is the best way to transport a neonate?
There are two strategies to the management of the high risk neonate. Deliver locally and transfer to a tertiary centre or transfer antenatally in utero. Obstetric retrieval predominantly originated as a consequence of the recognition of the benefits of antenatal transportation.
The literature is conflicting but overall there would be general consensus that high risk neonatal transports are better done as in utero cases with ultimately better neonatal outcomes. Why is this so? Let us adopt an accepted resuscitation approach of Airway, Breathing and Circulation to exploring this issue.
In utero transfer obviates the need for neonatal airway considerations.
In utero transfers once again obviate the need for breathing considerations as the unborn baby does not breathe air. Oxygenation is derived by placental exchange of gases between maternal and foetal circulations. The nature of foetal haemoglobin allows for maximal oxygenation of the foetal circulation to the detriment of maternal circulation if need be, which means that the unborn baby has a physiologic capacity greater than its mother for tolerating the hypobaric hypoxic aeromedical environment. Whilst this advantage persists for several months after delivery due to persistence of foetal haemoglobin, the change to relying upon gas exchange via neonatal lungs can potentially lead to suboptimal oxygenation in the aeromedical setting as full lung function is not achieved until 18 months age.
The foetal circulation is closely interactive with maternal circulation. This provides major advantages for metabolic support and thermoregulation to the foetus. Foetal glucose requirements are drawn from the maternal circulation and in utero temperature is maintained at constant maternal body temperature. The fluid filled gravid uterus is a superior thermoregulatory environment for the foetus than any current air transport incubator. No evaporation can occur in it. The warmth it provides has no drying effect.
D: The aeromedical environment and the neonate
The aeromedical environment places significant physiologic stressors upon the neonate. Noise, vibration, hypoxia, cold, low humidity and acceleration/deceleration forces all serve to increase metabolic demands which increase the risk of neonatal hypoglycaemia during such transport. Whilst some of these factors can be ameliorated using a modern air transport incubator others such as noise, vibration and acceleration/deceleration forces cannot. These problems still exist with in utero transport but the risk of neonatal hypoglycaemia is generally not an issue as the foetal circulation is well supported from the mother. Health professionals can provide intravenous glucose infusion or even nasogastric tube feeds during aeromedical neonatal transport to manage this risk but managing an IV infusion or using a NGT in flight on a neonate inside an incubator while needing to do regular blood glucose monitoring is far more complicated than providing the neonate with its mother as the ultimate incubator. The need for invasive procedures also increases the risk to the neonate.
Another major risk to the neonate during transport in an incubator is that of unexpected turbulence. Most modern transport cots are large and heavy with sometimes poorly fitting restraints for the neonate. The incubators tend to have a high centre of gravity with the propensity to sway and possibly fall to one side. Subject to significant air turbulence possible dislodgement of lines and tubes could occur even with reasonable restraint. Maternal stretcher restraints are far superior and the unborn baby floats in a protective fluid filled cavity with an umbilical cord for life support that is unlikely to be disrupted by even the most violent air turbulence.
E: Special considerations
It should be borne in mind that there are circumstances that would require the baby to be delivered as soon as possible prior to transport either for the safety of the baby and/or the mother. These conditions present a significant threat from continued in utero status and the risk of delivery outweighs the problems associated with ex utero transport in a modern retrieval incubator.
The condition of most concern for obstetricians is of active obstetric haemorrhage usually of placental origin. In utero transport will place both mother and baby at grave risk if bleeding is not controlled prior to transport. Often this cannot be done at the referring facility/location due to lack of surgical services, equipment , adequate anaesthetic capability and blood products for transfusion. This makes for an extremely difficult transport of a patient with uncontrolled haemorrhage. The chances of survival for a baby in utero with active placental haemorrhage are grim if the process continues unimpeded. The mother may survive with appropriate resuscitation. The retrieval team should consider taking blood for transfusion before departing the home base.
Second active infection of the uterus (chorioamnionitis) in pregnancy presents manifestly grave danger to the baby and mother particularly if it is at an advanced stage. In utero transport would be prolonging this hazardous state and delivery pre transport would be warranted if at all possible to remove the baby from a septic milieu at the earliest opportunity.
Third in the case of a term gestation with severe maternal pre-eclampsia there should be strong consideration for delivery of the baby as soon as is practicable even if this means pre-transport delivery as this is an essential part of the definitive treatment for this condition. It is generally much safer for the baby to have to tolerate an ex utero transport than being kept in a hypoperfused circulatory state due to placental dysfunction secondary to the pre-eclampsia.
Active labour would also generally be considered a contraindication to immediate transfer. During aeromedical retrieval inflight delivery is generally considered high risk to both mother and baby even on dedicated air ambulances with obstetric trained transport attendants. All Royal Flying Doctor Service Flight Nurses in Australia are qualified midwives Our guidelines for transporting obstetric patients describe the risks of inflight delivery as being that of the difficulties of active resuscitation of possibly two patients at the same time in a limited noisy , dry and cold space. Obviously this scenario is not ideal for best outcomes and there is even additional risk to the aircraft itself! If amniotic fluid and/or blood leaks under the floor panels and reaches the air frame it can cause corrosive damage to operating lines, wires and structure and there has been at least one King Air B200 RFDS aircraft grounded for 5 days due to this occurring.
In summary in utero transport of the neonate is preferable on many levels compared with transport in a modern retrieval incubator. The issues of Airway, Breathing and Circulatory support of the neonate are elegantly simplified with in utero status during aeromedical retrieval. The maxim that good care of the mother will ensure good care of the baby is a worthy one to remember. However some conditions would make in utero transport dangerous for both parties and in the setting of severe placental bleeding, chorionamnionitis and pre-eclampsia due consideration should be paid to the merits of a judicious pre-transport delivery strategy at the earliest opportunity.
4. Is it safe to fly pregnant women? Won’t they deliver inflight?
This statement belies the reality that many pregnant women at varying stages of their pregnancy travel via commercial airlines each year with no apparent harm to either themselves or their unborn babies. Most commercial airlines will allow pregnant women to travel up to 36 weeks gestation. However this is not to say that there are not specific risks presented to the pregnant air traveller.
Indeed probably the most concerning risk that may cause harm to mother and/or baby is that of unplanned/unexpected delivery inflight. Concerns about increased risk of spontaneous miscarriage have also been raised for early pregnancy air travellers. Concomitantly fears of excessive radiation exposure to the unborn baby for pregnant flight crew have appeared in the aerospace literature. On a more basic level there have also been practical concerns about the use of seat belts inflight for pregnant women. Finally risk of deep vein thrombosis is increased by prolonged air travel and pregnancy respectively and when combined theoretically provides additive risk.
What is the evidence for these concerns and fears for the pregnant woman either working in the air travel industry or being a commercial air passenger?
There is a paucity of research into the risk of preterm labour and delivery inflight for air travellers. Expert opinion such as the American College of Obstetricians and Gynaecologists have published statements of advice to pregnant women on air travel, advising the safest period is the second trimester and certainly not supporting air travel after 36 weeks. This expert statement has some support in the aerospace medical literature.
There is conflicting data on the question of the effects of air travel on the rate of miscarriage. Many studies have shown no correlation between flying and adverse outcomes. Conversely there are a few studies that have suggested harm. Overall flight is generally accepted to be safe and the most one can extrapolate from the literature is the possibility of a slight increase in spontaneous abortion if exposed to flight in early pregnancy and a slight increase in risk of preterm delivery in primips only. Further well constructed and larger studies are required to provide better evidence in regards to risk at any gestational age. All the published evidence to date has been of a retrospective nature and some did not utilize a control group with the additional problems of self reporting bias and poor response rates. It remains that the best interpretation of the current evidence base is reflected in expert statements such as from the American College of Obstetricians.
Radiation exposure appears to be negligible and not a significant issue.
Generally despite the theoretical increased risk there is no good data that demonstrates that DVT is more common in pregnant women.
The studies examining the risk of inflight delivery suggest that it is low. One American air ambulance review indicated no inflight deliveries in 357 helicopter transports and only one in 88 fixed wing transfers. In another American study looking at 80 fixed wing transports of obstetric patients there was not one inflight delivery.
5. Specific disorders
A. Vaginal bleeding
In retrieval medicine vaginal bleeding and known pregnancy should be regarded as an obstetric emergency till proven otherwise regardless of gestational age. The further progressed in pregnancy the more likely that vaginal bleeding may signify catastrophic bleeding. The life threatening conditions of pregnancy related bleeding are placenta previa, placental abruption and post partum haemorrhage.
In the retrieval setting access to operative management is not feasible for all but retained placenta and even that procedure in a remote retrieval setting without proper operating theatre facilities and blood bank may be overly risky for all but the most experienced obstetric trained retrievalist.
Placenta previa presents classically with painless vaginal bleeding and is due to the placenta covering the cervical canal. Catastrophic bleeding may be precipitated if manual vaginal examination is performed and digital cervical assessment undertaken. This should be only performed in a fully prepared operating room with adequate blood products immediately available. For the retrieval team nowadays portable ultrasound assessment of placental position can help diagnose this condition early.
Placental abruption presents classically with acute severe uterine pain and vaginal bleeding. However atypical painless abruptions do occur as do ones without any vaginal bleeding, so called concealed abruptions. Abruption is due to a tear in the placenta and may progress to catastrophic bleeding , disseminated intravascular coagulopathy and amniotic fluid embolism. The latter occurs when amniotic fluid enters the maternal circulation and causes pulmonary vascular obstruction thereby presenting like a classic pulmonary embolism as well as triggering widespread consumptive coagulopathy. It carries a mortality of over 70%.
In the retrieval setting there is usually no recourse other than judicious IV fluid resuscitation with colloid/crystalloid/blood products that are available at the time and a rapid transport to definitive surgical care.
Causes of post partum haemorrhage can be summarised under the 4 Ts:
For post partum bleeding emergency measures to address common aetiologies such as uterine atony and birth tract trauma may and should be instituted early within the capabilities of the retrieval team. External uterine massage, IV oxytocin, IMI ergometrine or rectal misoprostol may all reduce bleeding due to atony. Careful examination of the vagina and cervix may identify aggressive bleeding from tears that will need direct pressure and probable suturing for effective haemostasis prior to transport.
A retained placenta is a challenge to a retrieval team in the presence of active post partum bleeding. This is one of the very reasons why avoiding delivery and transporting the baby in utero is considered superior to delivering in a remote area and then effecting transport of two patients. It is left to the individual retrievalist to determine the level of risk of undertaking a manual removal of retained placenta considering the local resources, personal skill/confidence and worst case scenario backup plans that are feasible at the time. It is not of small risk but can be life saving. Important questions to consider include how will anaesthesia be provided in a remote setting for such a procedure, can it be done under sedation alone and are there other options. Improvised balloon tamponade can be effective utilising standard Foley bladder indwelling catheters of 30 ml volume inflated to 60 ml. Usually 2-3 are needed to be inserted up into the uterine cavity, inflated and then gentle traction applied to occlude the cervical canal and allow tamponade.
B. Preterm labour & Premature rupture of membranes
This is the most common cause for undertaking an acute obstetric transport. Assessment and risk prediction are fraught with inaccuracy. The definition of labour is regular painful abdominal contractions leading to progressive shortening and dilatation of the cervix but staff at referral sites may be either unwilling or inexperienced in assessing cervical changes. This can leave the retrieval team with the dilemma of being totally unprepared for a case of advanced labour at the time of arrival at the referring hospital or clinic. Of particular risk is the obstetric patient who has had none or inadequate antenatal care and where little is known of her history.
If at all possible preference is to maintain the pregnancy in utero for the purposes of transport as has been previously discussed. This depends upon the stage of labour and a commonly accepted reference point utilised to decide on the merits of rapid transport versus a stay and deliver approach is a cervical dilatation of at least 7 cm or more in the presence of regular contractions. In most settings this scenario would dictate a stay and deliver approach as inflight delivery is considered suboptimal care. However a short transport time, the degree of prematurity of the baby and the gravidity of the mother may influence that commonly accepted dictum. For example a transport time of only 20 minutes with a 28 week old baby in a first time mother would favour aggressive measures to cease contractions to allow transport to occur as delivery in a centre with neonatal intensive care resources and adequate time to administer effective antenatal steroid therapy all will contribute to significant survival advantage to the baby.
Common tocolytics utilised in Australia are oral nifedipine and IV beta agonists such as salbutamol. Nifedipine is simple to administer and avoids many of the complications of IV salbutamol such as excessive maternofoetal tachycardia, diaphoresis and hypokalaemia. It also has been shown to be as effective in suppressing labour and may have better outcomes compared with salbutamol or terbutaline.
The essential element in planning the aerial evacuation of an woman in preterm labour is careful preparation for possible inflight emergent delivery. This is why it is vital to ensure a two person minimum flight team. One must be prepared to not only safely deliver the baby but potentially have to resuscitate the mother and baby simultaneously. As in most emergencies if one has a choice , preparation and planning are preferable to unexpected chaos. Therefore setting out and checking two sets of resuscitation kit, drawing up delivery drugs such as oxytocin, hanging bags of IV fluids prepared with giving sets, laying out a specified neonatal resuscitation area and warming the aircraft cabin environment are all sensible actions to undertake pre-flight.
Premature rupture of membranes is not normally a major transport problem. It is worthy of note due to the risk of going into active labour over the next 24 hrs. Its management for transport is little different from that of preterm labour apart from administration of IV and oral antibiotics until delivery is effected. Clearly a significant leak of amniotic fluid may present a risk to the aircraft if it continues during the transport and consideration and preparation for this problem will need to be made. Large trauma sheets or plastic garbage bin liners have been used in the past to prevent amniotic fluid spilling onto the aircraft cabin floor. The risk of corrosive damage is the problem as previously mentioned.
Pre-eclampsia is essentially a vasculopathy triggered by pregnancy and predominates from the 20th week onwards. It is typified by high blood pressure and proteinuria and ranges in clinical presentation from simple hypertension to life threatening multiorgan dysfunction with severe coagulopathy, renal and hepatic failure.
An advanced complication is eclampsia which is generally defined as seizure activity and/or coma in a woman with signs and symptoms of pre-eclampsia. This carries a high risk of mortality for both mother and baby.
The only definitive treatment for both conditions is delivery of the baby/cessation of pregnancy. Having said that there is a well recognised sub set of women who develop eclampsia in the post partum period.
Retrieval teams must be confident to diagnose and stabilise a pregnant women with pre-eclampsia. Clinical assessment begins with vital signs as usual and the BP levels that should trigger suspicion of at least mild pre-eclampsia are >140/90 mmHg. Urine dipstick protein >2+ is also suspicious. Associated symptoms would include headache, right upper quadrant pain and blurred vision. Associated physical signs would include ankle clonus, hyper-reflexia, right upper quadrant tenderness and significant peripheral/facial oedema..
Acute stabilisation for transport would be to reduce BP aiming for a target of around 140/90 mmHg. This can be achieved simply and safely with oral nifedipine. IV hydralazine is a traditional emergency antihypertensive agent for severe pre-eclampsia. IV nitrates can be utilised but carry a risk of methaemoglobinaemia.
Magnesium sulphate loading and infusion is accepted standard management for the prevention of primary seizures in pre-eclampsia. It has been shown to reduce the incidence of eclampsia and mortality. It has at best modest antihypertensive effects in this condition so its benefit is more likely due to a reduction in the incidence of acute vasospasm particularly in the cerebral circulation.
Acute eclamptic seizure should be managed with urgent cessation using preferably an IV magnesium sulphate bolus and subsequent infusion to minimise rhe risk of recurrence. Other agents such as benzodiazepines or phenytoin are probably not as useful to reduce mortality but should be used if magnesium is not available. It is likely that for aeromedical transport it would be safer to control the airway definitively by intubating and ventilating an eclamptic woman. In this setting it is better to use whatever intubation technique and drugs you are most comfortable with to rapidly secure the airway and control the situation rather than worry too much about what drugs may or may not affect the baby.
Care needs to be taken to avoid over aggressive fluid resuscitation which can lead to pulmonary oedema which carries a high maternal mortality. If available central venous pressure may help guide therapy. Remember that a brief period of oliguria is not unusual following delivery. Antenatal steroid therapy should be administered prior to 34 weeks to help accelerate foetal lung maturity.