A number of significant physiological changes occur within the maternal respiratory system throughout pregnancy, either as a result of hormonal or neonatal effects. Chapter 1 details these changes.
Asthma is a common condition characterized by intermittent reversible airways obstruction, chronic inflammation of the airways and bronchospasm. It affects approximately 5% of the population in the UK and is more common in women than men.
Asthma may be affected by pregnancy. Meta-analysis has shown approximately one-third of women will have improved symptoms, one-third will worsen and one-third will see no changes. Any worsening of symptoms will typically peak at six months gestation. There is often an improvement of symptoms during labour, perhaps due to endogenous corticosteroid production, with acute asthma being very rare at this stage.
Well-controlled asthma is unlikely to have any impact on the pregnancy. Uncontrolled asthma is associated with a variety of complications, including hyperemesis, hypertension, pre-eclampsia, vaginal haemorrhage, complicated labour, fetal growth restriction, preterm birth, increased perinatal mortality and neonatal hypoxia. Large cohort studies have shown an increased caesarean section rate in those with moderate and severe asthma.
Treatment should be optimized during pregnancy. A large case-controlled study showed no increased risk of congenital malformations in mothers being treated for asthma. There is good evidence that the older therapies have no teratogenic effects and no evidence to show the newer agents cause any harm. The risk of uncontrolled asthma is far greater than the theoretical risk of therapy.
Acute asthma should be managed in the standard way. Poor management is associated with poor outcomes for mother and fetus; there is no known risk to the fetus with standard treatment.
Asthma is not a contraindication to any form of labour analgesia. Should caesarean section be required, regional anaesthesia is suitable, as those with asthma are less likely to tolerate mechanical ventilation well.
Postpartum haemorrhage can safely be managed with syntometrine and prostaglandin E2. Prostaglandin F2α may cause bronchospasm.
Breastfeeding is not a contraindication to any of the treatments given for asthma, none of which are found in dangerous levels in the milk. Oral steroids may also be given safely to the breastfeeding mother.
Neurological disease in parturient prompts the anaesthetic and obstetric team to consider many aspects of care delivery. Pre-existing conditions may progress to cause significant compromise and the onset of new neurological symptoms may mimic more commonly encountered conditions, such as PET.
Even the presence of stable neurological conditions, of the spinal cord, neuro-axial skeleton or intracranium, may require careful consideration with respect to analgesia, anaesthesia and mode of delivery.
Quantification of anaesthetic risk is essential. A major anaesthetic concern relates to the safety of performing neuraxial blockade. The following questions arise:
• Is there risk of ‘coning?’ If a CSF leak results in a discrepancy in pressure within the cranium and infra foramen magnum (cranial: spinal CSF pressure gradient CSFCr:CSFSp), cerebellar tonsillar herniation can occur caudally with brain stem compression (coning).
• Is there risk of local trauma and neurological injury? Abnormal anatomy can result in spinal cord, cauda equina or spinal nerve trauma following needling of the perispinal region.
• Is there risk of spinal haemorrhage? Neuraxial vascular abnormalities can increase the risk of bleeding as a result of needling the spinal canal.
• Will the block work? Anatomical abnormalities can impede local anaesthetic spread.
General anaesthesia in parturients with neurosurgical pathologies is not without risks. Cardiovascular fluctuations during induction of anaesthesia can precipitate brain swelling or intracranial haemorrhage. Optimization of intracranial pressure (ICP), cerebral perfusion pressure (CPP) and cerebral blood flow (CBF) is essential. It is important, when evaluating known or perceived risk of complications of neuraxial blockade, to consider the risks of not performing the block or proceeding to general anaesthesia (see Chapter 11).
Neurosurgical issues relevant to pregnancy
See Chapter 17 for spinal abnormalities.
Intracranial mass lesions
Mass lesions can be caused by infection, tumour, vascular abnormalities, inflammation (e.g. MS), cystic lesions or haemorrhage. Presentation depends upon lesion size, rate of enlargement, aetiology and location, and includes:
• Asymptomatic; identified during investigation of other pathology
• Focal neurological deficit
• Global reduction in cerebral function
• Headache classically worse when supine
• Nausea and vomiting
Mass effect can cause disruption of neurological function by compression or destruction of brain tissue, causing oedema within the brain, causing hydrocephalus by obstructing CSF flow and by reducing cerebral compliance, thus increasing ICP and reducing CBF.
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