Aortocaval Compression

Beyond 20 weeks’ gestation (or in a noticeably pregnant patient) all resuscitation efforts must be performed with left lateral tilt of the pelvis greater than 15° to minimise aortocaval compression (see Figure 2.1). If the vena cava is partly occluded due to the pregnant uterus, cardiac output can be reduced by up to 40% [4]. This can promote maternal collapse. During resuscitation, aortocaval compression further reduces cardiac output during chest compression [5].

Figure 2.1 Patient in left lateral tilt position with Cardiff wedge.

Changes in Lung Function and Risk of Hypoxia

Pregnant women develop hypoxia much more rapidly because of a 20% reduction in functional residual capacity of the lungs [6]. Oxygen demand is increased in pregnancy due to the markedly increased oxygen consumption of the fetoplacental unit and makes adequate oxygen delivery challenging during resuscitation. This is further complicated by the increased weight of abdominal contents and breasts in late pregnancy, which can make effective rescue breaths difficult to perform.

Difficult Intubation and Risk of Aspiration

The risk of aspiration during resuscitation is increased due to a more relaxed lower oesophageal sphincter muscle and elevated gastric acid volume production [7]. Airway protection and effective ventilation via an endotracheal tube should be established as soon as possible. However, weight gain and laryngeal oedema can make intubation significantly more difficult and may require experienced staff.

Circulation

Pregnancy leads to an increase in circulation blood volume and cardiac output. Therefore, blood loss is tolerated if there is no pre-existing anaemia or underlying maternal morbidity. The fetomaternal unit receives 10% of the cardiac output at term; hence a large volume of blood can be lost rapidly in obstetric haemorrhage [8].

Perimortem Caesarean Section

The uteroplacental unit sequesters blood and hinders effective cardiopulmonary resuscitation (CPR). Evidence supports the positive effect of evacuating the uterus on maternal outcome during CPR in later stages of pregnancy (beyond 20 weeks) [9]. Survival is inversely proportional to the time between maternal cardiac arrest and delivery. Current recommendations promote emergency caesarean delivery within 4 minutes of maternal collapse if there is no response to resuscitation efforts, and to be completed within 5 minutes [10].

Haemorrhage

Worldwide, haemorrhage is still the leading cause of maternal mortality and it is the leading cause of maternal collapse on the delivery unit. The estimated incidence is 3.7 per 1000 maternities [12]. Predisposing factors are multiple pregnancy, high parity, placenta praevia, uterine fibroids and multiple previous caesarean sections, prolonged labour, maternal clotting disorders and preeclampsia. A high index of suspicion can be lifesaving. It is helpful to memorise the risk factors because haemorrhage can be concealed and pregnant women may lose a significant amount of blood without any haemodynamic disturbance. Cases of major haemorrhage due to arterial rupture (splenic artery, hepatic artery) have been described. It is important to note that blood loss is frequently underestimated and if haemodynamic changes become apparent, the mother has usually already lost a third of her circulating blood volume.

Thromboembolism

A careful risk assessment for thrombotic complications should be performed in all pregnant women during the ante- and postnatal periods. Multiple risk factors can make thromboprophylactic treatment necessary in pregnancy and postpartum for up to 6 weeks depending on risk assessment [13]. Remember that deep vein thrombosis (DVT) of the pelvic venous system is often asymptomatic until pulmonary embolism develops.

Amniotic Fluid Embolism

The incidence of amniotic fluid embolism (AFE) is estimated at 1.25–12.5 in 100,000 maternities. While this is an unpreventable event, the speed of diagnosis determines the outcome. Survival rates have improved to 80%; however neurological morbidity is recognised [14]. There is no diagnostic test to determine AFE; therefore, the clinical picture should lead to a high index of suspicion. Clinical features include respiratory distress, followed by cardiovascular collapse with cardiogenic shock, frequently in combination with haemorrhage due to coagulopathy within 30 minutes of delivery. AFE can also occur antepartum during labour and become manifest as fetal collapse of unknown origin that precedes maternal collapse. In all cases there is absence of any other significant medical condition or other explanation for the rapid deterioration.

Maternal Cardiac Disease

Due to changes in lifestyle (later age of conception) and overall maternal health (obesity, diabetes and smoking, preexisting congenital heart disease), cardiac disease in pregnancy is increasingly common. In cases of known maternal cardiac disease a multidisciplinary approach is essential to predict complications and define antenatal and peripartum care. However, the majority of deaths secondary to cardiac disease occur with no previous cardiac history [15]. The risk of myocardial infarction is increased three- to four-fold in pregnancy (compared with a non-pregnant population) and is significantly greater in women beyond 36 years of age and/or of black ethnicity. Percutaneous angioplasty can be safely performed in pregnancy and should be offered where available. In addition, there is a greater risk of coronary artery or aortic dissection in pregnancy, as well as cardiomyopathy. It is important to remember that pregnant women with cardiac disease frequently present with atypical symptoms that can mimic physiological changes in pregnancy such as palpitations, shortness of breath or tachycardia.

Sepsis

Morbidity and mortality from pregnancy-related sepsis is common and has not significantly declined in recent years. Sepsis must be treated promptly as a medical emergency and appropriately managed with a ‘one-hour bundle’ to improve outcomes [16]. Obstetric risk factors include prolonged rupture of membranes, cervical cerclage, retained placenta and operative trauma. Patient-related risk factors include obesity, anaemia, diabetes mellitus, sickle cell disease and group B streptococcus infection. Adequate antibiotic prophylaxis for patients at risk is crucial.

Common clinical signs are temperature, tachycardia and altered mental state, ranging from anxiety to confusion. Special attention should be paid to changes in the respiratory rate as an early diagnostic sign of the physiological reaction to a developing metabolic acidosis due to sepsis.

Complications of Labour Analgesia

Even in a correctly sited epidural catheter, a regular top-up with local anaesthetic drugs can cause maternal collapse due to hypotension; therefore regular blood pressure observations are required after each administration of local anaesthetic. More serious complications of epidural labour analgesia are high block (inadvertent spinal injection of an epidural top-up dose) and unintended intravascular injection of a large dose of local anaesthetic, which are both due to catheter misplacement. Clinical signs can be sudden loss of consciousness, with or without convulsions, and cardiovascular collapse or ventricular arrhythmias [17]. These are rare but serious complications that require advanced life support and involvement of an experienced senior obstetric anaesthetist.

Drug Toxicity

Drug overdose should be considered as a potential diagnosis in out-of-hospital cardiac arrest. In women with preeclampsia and renal failure on magnesium infusion, careful monitoring should focus on signs of magnesium overdose, which are muscle weakness, loss of tendon reflexes, respiratory depression, bradycardia and cardiac arrest.

Eclampsia, Epilepsy and Intracranial Haemorrhage

Warning signs preceding an eclamptic fit can be severe headache, flashing lights, hyperreflexia and confusion. The differential diagnosis of epilepsy must be considered. Uncontrolled hypertension can lead to intracranial haemorrhage. Typical clinical signs are severe, ‘never-experienced’ headache preceding maternal collapse. Similar symptoms occur if the intracranial haemorrhage is due to arteriovenous malformations or ruptured intracranial aneurysms; therefore urgent imaging is indicated.