Severe pre-existing disease in pregnancy

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Chapter 57 Severe pre-existing disease in pregnancy

The two main sources of information about the spectrum of pre-existing conditions that result in severe morbidity in pregnancy are national or local registries/databases and published case series of admissions to intensive care, high-dependency units or obstetric units. Information about mortality comes from registries of maternal death such as the Confidential Enquiries into Maternal and Child Health (CEMACH; formerly Reports on Confidential Enquiries into Maternal Deaths) in the UK, or from individual case series. Taken together, the most important pre-existing conditions likely to lead to intensive care unit (ICU) admission and/or death overall are cardiac disease, respiratory disease, neurological disease, psychaiatric disease (including drug addiction) and haematological, connective tissue and metabolic disease.

With increasingly successful medical care during childhood and early adulthood, the number of women with severe disease who survive to child-bearing age has increased. Part of such women’s wishes to live a normal life includes the desire to have children, and this places increasing demands on obstetric, anaesthetic and ICU services, as well as on women’s physiological reserves.

It is important that women with severe disease are appropriately counselled before pregnancy since the risks to both them and their fetuses may be considerable. This early counselling should ideally include anaesthetic input.

CARDIAC DISEASE

There are more maternal deaths in the UK from cardiac disease than from pre-eclampsia and haemorrhage combined.¹ Over the last 20–40 years, there has been a shift away from acquired cardiac disease (mainly rheumatic heart disease) towards congenital heart disease as modern techniques of cardiac surgery in early life enable female babies with previously fatal conditions to reach maturity. More recently, there has been an increase in prevalence of ischaemic heart disease resulting from increased obesity, maternal age and smoking. Mortality varies from less than 1% in uncomplicated conditions to over 40% in Eisenmenger’s syndrome, even with modern methods of medical management.²

PHYSIOLOGY AND PATHOPHYSIOLOGY

The physiological changes of pregnancy are discussed in Chapter 56. The changes most relevant to cardiac disease are:

• susceptibility to aortocaval compression

• reduction in systemic vascular resistance

• increases in blood volume and cardiac output by up to 40–50% by the 20th week of gestation, with a potential further increase in cardiac output (up to 50%) during labour

In patients whose cardiac function is already impaired, such as those with cardiomyopathy or valvular stenoses, inability to meet these challenges may result in cardiac failure. If there is a right-to-left shunt, the fall in systemic vascular resistance encourages blood to bypass the lungs; this, together with the increasing demands of the fetus and the reduced maternal pulmonary reserve, may lead to severe exacerbation of hypoxaemia.

GENERAL ANTEPARTUM AND PERIPARTUM MANAGEMENT

Antepartum management consists mainly of regular assessments and measures to reduce cardiac workload, for example, by reducing activity and treating arrhythmias/cardiac failure.

Electrocardiography, chest X-ray and echocardiography are the most useful investigations. Flow gradients across stenosed valves can be expected to increase in pregnancy because of the increase in cardiac output that occurs, and echocardiographic measurement of valve areas provides a more consistent and useful measure of severity in such cases. Pulse oximetry is a simple, non-invasive tool for monitoring the degree of right-to-left shunt and can easily be repeated during pregnancy.

An obstetric and anaesthetic plan should be prepared and the intensivists informed of the anticipated delivery date. Antithromboembolic prophylaxis should be considered since cardiac patients are more at risk, even without prolonged bedrest. Low-molecular-weight heparins are now standard for prophylaxis, although both heparin and warfarin have been used for patients with prosthetic heart valves, the main decision being between the better safety profile of heparin for the fetus but with greater risk of thrombosis in the mother, and the more effective anticoagulation achieved with warfarin but with greater risk of fetal complications.³ The requirements for heparin increase in pregnancy, so greater doses than normal are usually required.

The principles of peripartum management have moved over the last few years towards vaginal delivery unless caesarean section is indicated for obstetric indications. Elective caesarean section has been advocated in the past as a matter of course, traditionally under general anaesthesia, but the stresses and complications of surgery are now generally felt to exceed those of a well-controlled vaginal delivery. Low-dose epidural regimens using weak solutions of local anaesthetic (e.g. 0.1% bupivacaine or less) with opioids such as fentanyl have been found to be effective and cardiostable.⁴ Combined spinal epidural analgesia using similar low concentrations are also suitable, and continuous spinal analgesia has also been described. In patients with marked exercise intolerance, outlet forceps or ventouse delivery is usually recommended to limit pushing and the duration of the second stage. If caesarean section is required, both regional and general anaesthesia have their advocates,^5,⁶ but either is acceptable so long as due care is taken.

Peripartum complications such as bleeding, pulmonary oedema, arrhythmias and sudden increases in pulmonary vascular resistance or drops in systemic vascular resistance may be tolerated badly by patients with limited reserves.

Oxytocin analogue (Syntocinon) has marked cardiovascular effects ^7,⁸ that, although tolerable in normal patients, may cause a calamitous drop in systemic vascular resistance with hypotension, tachycardia and worsening of shunt in susceptible patients. If Syntocinon is required it should be diluted and given very slowly (e.g. 5 units infused over 10–20 minutes). Withholding of oxytocics altogether may be a problem as such patients may be especially sensitive to acute blood loss. In patients with fixed cardiac outputs and no pulmonary hypertension, ergometrine may be preferable. At caesarean section, mechanical compression of the uterus with a ‘brace’ suture may be used to reduce or avoid the need for oxytocics.⁹ Exacerbation of right-to-left shunt is manifested by worsening hypoxaemia, which may be improved by vasoconstrictors such as phenylephrine – the chronotropic and inotropic effects of ephedrine are often undesirable in patients with cardiac disease.

Monitoring ranges from simple non-invasive methods to peripheral arterial, central venous and pulmonary arterial cannulation, depending on the severity of the underlying disease.¹⁰ Arterial cannulation is usually straightforward but central venous cannulation is often difficult because of the increased maternal body weight and fluid retention, and the inability to lie flat, let alone head-down. The antecubital fossa should be considered as a route for cannulation first. Scrupulous attention must be paid to avoiding intravascular air in patients with right-to-left shunts, because of the risk of systemic embolism.

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