Review Note

SS_OB 1.36 Discuss the pathophysiology and anaesthetic management of co-existing maternal conditions as described in the Perioperative medicine Clinical Fundamental, in particular:

• Cardiac Disease in Pregnancy
• Most common cause of mortality in pregnancy
• Cardiac disease has the potential to remain undiagnosed; it may present with CVS decompensation during pregnancy (usually after 20/40), at the time of delivery, or immediately postpartum.
• Causes of maternal death from cardiac disease (2003-2005) – see table
• Indirect deaths: Denote deaths from a cause worsened by pregnancy but not caused by pregnancy.
• Late deaths: Denote deaths within 1 year after delivery.

CVS Physiological Changes in Pregnancy
• Reduced SVR (from progesterone) with peripheral vasodilation.
• CO increases (up to 40-50% at 20-28/40) by increase in SV and HR.
  • Labour leads to further increases in CO (15% in first stage, 50% in second stage) from SNS stimulation and auto-transfusion of 300-500ml of blood with each uterine contraction.
  • Further increase in CO (up to 60-80%) immediately after delivery due to auto-transfusion of blood via uterine contraction and relief of aortocaval compression.
  • This increase in CO declines to pre-labour values within 1 hour.
Impact of CVS Physiological Changes to a Pregnant Woman with Cardiac Disease
The impact varies according to the type and severity of the disease:
• Women unable to increase CO are at risk of decompensation earlier in pregnancy and may present before 28/40.
• Those who tolerate the increased CO during pregnancy will be at further risk at the time of delivery and immediately postpartum of pulmonary oedema.
  
  
Management
• Main aims of management:
  • Early risk assessment.
  • Optimization.
  • Regular monitoring for deterioration.
  • Planning of delivery.
  • Surveillance for deterioration in immediate postpartum period.
    
    
Pre-Delivery
• Multidisciplinary team review of woman and obstetric planning – obstetrician, cardiologist, anaesthetists, midwives, neonatologists, intensivists.
• Referral to tertiary centre according to complexity of heart disease, risk assessment, and local available facilities and expertise.
• Optimization:
  • Beta-blockers.
  • Thromboprophylaxis.
  • Pulmonary arterial vasodilators.
  • Diuretics.
  • Digoxin.
  • Hydralazine.
• Fetal assessments to monitor for potential problems arising from pharmacological treatment of the mother.
  
  
Mode of Delivery
• Vaginal delivery:
  • Vaginal delivery with low-dose regional analgesia and careful fluid management is the preferred delivery mode in most cases.
    • RA during labour reduces further increases in CO and myocardial oxygen demand caused by pain and anxiety.
    • RA also facilitates instrumental delivery.
    • Best to aim for spontaneous onset of labour.
    • Induction of labour may be appropriate to optimize timing of delivery in relation to anticoagulation and availability of specific medical staff, or due to deteriorating maternal cardiac function.
  • Instrumental-assisted delivery is preferred to limit or avoid maternal effort in pushing.
  • LSCS (Caesarean Section)
    • Occurs if there are specific obstetric indications or a deterioration in cardiac performance necessitating early delivery.
    • LSCS rates are much higher for women with heart disease for this reason.
      
      
Anaesthetic Options
• General anaesthesia (GA), spinal, epidural, combined spinal-epidural (CSE).
• No good evidence to support any technique, but CVS stability is the goal.
  
  
Uterotonics
• Oxytocin:
  • Recommendation that oxytocin should only be administered by infusion with the omission of a bolus (due to its side effects of vasodilation, tachycardia, and fluid retention).
  • However, it has been argued that the CVS effects of a postpartum hemorrhage (PPH) in a patient with a fixed CO, and the potential risk of overzealous IV fluid replacement, are worse than the potential CVS effects of a slow infusion of oxytocin.
• Ergometrine: Should be avoided as it leads to vasoconstriction and hypertension, and increases the risk of myocardial infarction and pulmonary oedema.
• Carboprost: Not recommended in cardiac disease as it may exacerbate pulmonary oedema.
  
  
Tocolytic Agents
• GTN infusion post-delivery may improve pulmonary oedema, but it may increase risk of PPH due to uterine relaxation.
  
  
Post-Partum
• High level maternal surveillance is required until the main haemodynamic changes after delivery have resolved.
  • This may be required in hospital for up to 2 weeks in patients with unstable cardiac conditions.
• Occurrence of chest infection or development of PPCM in some cases leads to worse compromise post-delivery.
  
  
Specific High-Risk Conditions
1. Myocardial Infarction
   • Leading cause of cardiac death in 2003-2005.
   • All women had identifiable risk factors: obesity, older age, high parity, smoking, diabetes, hypertension, family history.
   • Low threshold for diagnosis is recommended.
   • Management should not be withheld in the pregnancy or puerperal woman: coronary angiography, emergency coronary intervention, thrombolysis.
     • Thrombolysis at time of delivery carries a significant risk of haemorrhage and management needs to be on an individual basis.
     • First choice of ACS treatment in pregnant women is percutaneous coronary intervention (PCI).
     • The need for anti-platelet meds (e.g., clopidogrel) would at present preclude the use of regional anaesthesia.
   • Delivery:
     • Spontaneous delivery with or without epidural, LSCS under CSE, or LSCS under GA.
2. Aortic Dissection
   • Highest risk near full term or the immediate postpartum period, in the presence of systolic hypertension.
   • Associated with Marfan's syndrome.
   • Pre-pregnancy counseling should occur.
   • If aortic root diameter >4cm, risk of aortic dissection is greatly increased, so aortic root replacement should be offered before pregnancy.
   • Beta-blockers should be continued or started in pregnant patients with Marfan's who have hypertension or aortic dilation, as they have been found to reduce the rate of aortic dilatation.
   • Monitoring in pregnancy: Regular TTE (every 4 weeks) to assess aortic root diameter.
3. Valvular Heart Disease
   • Mitral Stenosis (MS):
     • MS has the highest risk in pregnancy and should be managed in tertiary centres with expertise in this condition.
     • Greatest risk is pulmonary oedema at time of delivery due to increased CO.
     • This risk increases considerably if pre-eclampsia (PET) develops (with increased pulmonary capillary permeability).
     • Management:
       • MR & AR: Beta-blockers and heparin to prevent AF.
       • Early admission.
       • If vaginal delivery is planned, IAL early in labour, slow and careful titration of epidural, cautious IVF administration.
       • If LSCS is planned, low dose CSE, continuous spinal anaesthesia, and GA have all been described in patients.
   • Aortic Stenosis (AS):
     • Avoid sudden decreases in SVR either via careful RA or GA, depending on situation and preferences of those involved.
     • Balloon dilation should only be considered in high-risk cases as it carries a lower success rate and higher risk.
4. Pulmonary Hypertension
   • Very high risk during pregnancy (30-50% mortality).
   • This needs to be discussed pre-conception.
   • It is appropriate in most cases for the question of termination of pregnancy (TOP) to be raised and discussed with the mother.
   • If the decision is to continue with the pregnancy, efforts should be made to optimize her condition (i.e., with sildenafil).
   • Plans should be made for the rest of pregnancy and delivery.
Delivery and Anaesthesia for Pulmonary Hypertension
• Most units tend to opt for elective LSCS under a ‘cardiac’ GA as it allows control over ventilation, permits more invasive monitoring (e.g., TOE), and may lead to greater CVS stability.
• Success has been described using regional anaesthesia for LSCS.
Cardiac Surgery
• Should only be considered in cases refractory to medical treatment or when there is no catheter-based intervention alternative.
• Hypothermic CPB carries a risk of 30% to the fetus.
  • If hypothermia is avoided and perfusion pressures maintained at a relatively high level, fetal mortality is reduced to 10%.