FRCA Notes

Respiratory disease in pregnancy

This page details the elements of respiratory disease management pertinent to pregnancy; see the asthma page from the ICM section for a more thorough overview of asthma in general.

There has not yet been a Final CRQ question dedicated to respiratory disease in pregnancy.

Curriculum

The "influence of concurrent medical diseases on pregnancy and the management of these patients" and "The anatomy, physiology and pharmacology related to pregnancy and labour" are relevant here.

Resources

  • Respiratory disease (including SARS-CoV-2) and thromboembolism are leading causes of maternal death in the UK and Ireland
  • Asthma is the most common respiratory disease, and the most common chronic medical condition, in pregnancy
  • Pregnancy increases the risk of developing respiratory failure and ARDS
  • Reference ranges for investigations differ from those of non-pregnant women


Parameter Change at term
Oxygen consumption ↑ 20% (BMR ↑ up to 15%)
Minute ventilation ↑ 40–50%; driven by VT (↑ 40%) with respiratory rate largely unchanged
FRC ↓ 20% due to diaphragmatic elevation
TLC ↓ 5%; clinically insignificant
Vital capacity Unchanged
FEV1, FEV1/FVC, PEFR Unchanged
Lung compliance and DLCO Unchanged; chest wall compliance ↓
PaCO2 3.7–4.2kPa
Bicarbonate 18–22mmol/L; compensated respiratory alkalosis

  • Progesterone sensitises the respiratory centre to CO2, shifting the CO2 ventilatory response curve to the left
  • Dead space/VT ratio is unchanged, so the rise in VT increases alveolar ventilation
  • The combination of ↑ O2 consumption and ↓ FRC causes rapid desaturation at induction of GA; this is accelerated further during labour
  • Spirometry should be normal in pregnancy; an abnormal result reflects disease rather than physiology

Physiological dyspnoea

  • 75% of women experience exertional dyspnoea by 30 weeks
  • A pregnant woman should still be able to climb a flight of stairs without stopping
  • Breathlessness that limits normal daily activity, is of sudden onset or occurs at night warrants further investigation

Differential diagnosis of breathlessness

Cause Key features
Asthma Known diagnosis; wheeze, nocturnal symptoms, variability; PEFR diurnal variation >10%
Pulmonary embolism Acute onset; pleuritic pain; tachycardia; hypoxia; signs of DVT; RV strain on echo
Pneumonia Fever, cough, purulent sputum, crackles; signs may be less obvious in pregnancy
Cardiac disease Progressive exertional dyspnoea, orthopnoea, PND; murmur; pulmonary oedema (e.g. pre-eclampsia, peripartum cardiomyopathy)
Anaemia Particularly postpartum if blood loss was underestimated
Physiological Gradual onset; does not limit activity; diagnosis of exclusion

Laboratory

  • WHO minimum Hb: 110g/L in the first half and 105g/L in the second half of pregnancy
  • Leucocytosis is normal: up to ~15 ×109/L in pregnancy and 25–30 ×109/L in labour; returns to normal within 21 days
  • CRP is mildly raised at baseline, so trends are more useful than single values
  • Procalcitonin is unaffected by pregnancy and is more specific for bacterial infection
  • D-dimer rises throughout pregnancy and is often above the 'rule out' threshold

Imaging

  • Imaging should never be withheld if needed to safeguard maternal life
  • The foetus is most sensitive to radiation during organogenesis (weeks 2–15)
  • Foetal dose from a CXR is negligible (<0.01mGy); CTPA and V/Q scans are well below the teratogenic threshold of ~50mGy
  • Non-contrast MRI is safe; gadolinium is generally avoided as it crosses the placenta
  • POCUS is invaluable for differentiating cardiac from pulmonary causes of hypoxia and for assessing pleural effusions, although body habitus and gestation may limit views

  • Multidisciplinary approach: obstetrics, obstetric anaesthesia, respiratory medicine, physiotherapy, midwifery and critical care as required
  • Optimisation should ideally begin before conception
  • Early referral to the obstetric anaesthetic clinic for complex or poorly controlled disease, to plan:
    • Mode and timing of delivery
    • Analgesia and anaesthetic technique
    • Need for invasive monitoring
    • Location of peripartum care (HDU/ICU)
  • Pregnancy should not become a barrier to appropriate treatment; management should mirror that of non-pregnant patients as closely as possible

Asthma


  • Affects 3–8% of parturients
  • Roughly a third improve, a third deteriorate and a third are unchanged; those with more severe disease are more likely to deteriorate

    • Factors aiding asthma Factors exacerbating asthma
    Progesterone-induced bronchial smooth muscle relaxation Reduced sensitivity to β-agonists
    Increased cortisol levels Increased prostaglandin levels causing bronchoconstriction
    Reduced cortisol sensitivity (as progesterone binds the receptor)
    Reluctance to take usual medications

  • Up to 10% of women will require hospital admission for an acute exacerbation during pregnancy
  • Poorly controlled asthma is associated with pre-eclampsia, pre-term delivery, low birth weight and congenital malformation

Ante-natal

  • Asthma review in early pregnancy and in the postpartum period
  • Continue all regular treatment; NICE advises SABAs, LABAs, inhaled steroids and oral theophyllines be used as normal
  • Leukotriene receptor antagonists and LAMAs should not be stopped if needed for control
  • Oral steroids should be offered for exacerbations; the benefits outweigh the risks
  • Regular home peak flow monitoring to detect deterioration early
  • Labetalol should be avoided for pre-eclampsia or hypertension; nifedipine or methyldopa are alternatives

Intra-partum

  • Acute asthma is rare in labour
  • Continue all regular medications, despite the possible uterine effects of β-agonists
  • Steroid cover for those on long-term oral steroids (e.g. prednisolone ≥5mg/day for >3 weeks):
    • Continue regular oral steroids and add IV or IM hydrocortisone once in established labour
    • At Caesarean section, give hydrocortisone at induction: 50mg if already given in labour, 100mg if not

  • Epidural analgesia is beneficial to avoid pain-associated hyperventilation, which can precipitate attacks
  • Caesarean section is reserved for usual obstetric indications
  • Regional anaesthesia is preferable to GA, as with virtually every parturient

Uterotonics and drugs to avoid

  • Carboprost (PGF2α) is contraindicated; it activates PGF2α receptors on bronchial smooth muscle, causing bronchospasm
  • Oxytocin, dinoprostone (PGE2) and misoprostol (PGE1) are safe; misoprostol is an option for PPH
  • Labetalol and other β-blockers
  • Histamine-releasing opioids should be used with caution

Acute attacks

  • Acute attacks may cause maternal hypoxia and hypocapnoea
  • This reduces foetal oxygen delivery via vasoconstriction of the umbilical artery and left-shift of the oxyHb-dissociation curve
  • Management is the same as for non-pregnant patients, with the addition of foetal monitoring and early involvement of the obstetric team
    • One difference is a patient should be deemed to be 'tiring' at a PaCO2 of 4.0kPa, rather than a normal PaCO2, owing to the lower levels during pregnancy

Postpartum

  • All asthma medications can be used as normal when breastfeeding

Other respiratory conditions


  • Improved survival means more patients now reach pregnancy
  • Viscous secretions affect the respiratory, gastrointestinal and reproductive tracts

  • Pregnancy increases the risk of chest infection, poor nutritional status and CF-related diabetes
  • MDT input including physiotherapy and dietetics; CFTR modulators, antibiotics and mucolytics are continued
  • Mode of delivery is determined by obstetric indications; timing balances maternal respiratory risk against prematurity
  • GA should be avoided where possible, especially if FEV1 ≤50% predicted or respiratory function is deteriorating

  • Uncommon, but becoming more frequent with rising maternal age
  • Conditions more common in women of childbearing age:
    • Sarcoidosis
    • Connective-tissue disease-related ILD
    • Lymphangioleiomyomatosis (LAM)

  • Oestrogen and progesterone accelerate LAM progression, increasing the risk of pneumothorax
  • An FVC <1L was historically considered a contraindication to pregnancy; more recent data show reductions in FVC are reasonably well tolerated
  • Risk is stratified by FVC and DLCO; echocardiography should screen for pulmonary hypertension
  • Pre-conception counselling allows teratogenic immunosuppressants to be switched
  • Vaccination against influenza, pertussis, SARS-CoV-2 and pneumococcus

Myasthenia gravis

Myotonic dystrophy

  • Respiratory muscle weakness, poor cough and hypoventilation; may worsen during pregnancy
  • Multisystem disease: cardiac conduction abnormalities and cardiomyopathy are important
  • Obstetric associations include polyhydramnios, placenta praevia, pre-term labour, prolonged first stage, uterine atony and higher rates of operative delivery
  • Requires continuous telemetry and pulse oximetry in labour and for at least 24 hours postpartum
  • Regional anaesthesia is preferred to GA

Scoliosis

  • Defined as a Cobb angle ≥10° with vertebral rotation; idiopathic scoliosis is the most common type
  • Restrictive physiology may worsen in pregnancy; severe cases may have pulmonary hypertension or RV hypertrophy
  • Assess early with spinal imaging, PFTs and echocardiography where appropriate
  • Higher rates of instrumental and Caesarean delivery due to cephalopelvic disproportion
  • Neuraxial techniques are associated with lower morbidity and mortality than GA, but are more technically challenging

Cerebral palsy

  • Recurrent chest infections and restrictive physiology from associated scoliosis are common
  • Contractures, spasticity and spinal deformity make neuraxial techniques difficult; most case reports describe elective Caesarean section under GA
  • Increased incidence of latex allergy, intra-operative hypotension and hypothermia

Osteogenesis imperfecta

  • Bone fragility, short stature, scoliosis, dental abnormalities and possible platelet dysfunction
  • Both neuraxial and general anaesthesia have been used successfully

Pulmonary embolism

  • Thromboembolism is the most common direct cause of maternal death, responsible for 16% of maternal deaths in the UK and Ireland
  • Presentation is similar to non-pregnant patients but may be confused with physiological dyspnoea

  • Start LMWH when PE is suspected unless contraindicated, dosed by booking weight
  • Investigations:
    • ECG
    • CXR ± CTPA (or V/Q if CXR is normal)
    • Compression duplex of the legs if DVT is suspected
    • In haemodynamic compromise: POCUS for RV strain; consider thrombolysis, catheter-directed therapy or surgical embolectomy

  • Anticoagulation continues for ≥6 weeks postpartum, with a minimum total of 3 months
  • Timing of LMWH must be carefully planned around delivery and neuraxial procedures

Amniotic fluid embolism

Venous air embolism

  • Most common at Caesarean section during uterine exteriorisation or manual removal of the placenta; usually between delivery and closure of the hysterotomy
  • Ranges from asymptomatic to cardiac arrest from air lock in the RV outflow tract
  • Detected by a sudden fall in ETCO2 under GA
  • Management: left lateral Trendelenburg position, 100% oxygen, flood the surgical field with saline, volume resuscitation and aspiration via a central line if present

Respiratory infection

  • Most upper respiratory tract infections are viral and self-limiting
  • Common causes of bacterial pneumonia: Strep. pneumoniae, H. influenzae, Mycoplasma and Legionella
  • Risk factors include anaemia, asthma, smoking and HIV
  • Remain vigilant for maternal sepsis; early microbiology and targeted antibiotics

ARDS

  • Pregnant women were at higher risk of severe disease during the SARS-CoV-2, H1N1 and MERS outbreaks, due to respiratory, cardiovascular and immune adaptations
  • Ventilatory strategies
    • If ventilated, oxygenation targets should be higher than in non-pregnant patients to protect foetal oxygenation; permissive hypercapnia should be limited due to foetal acidosis
    • PEEP must be balanced against reduced venous return and uteroplacental hypoperfusion
    • Prone positioning is effective and feasible, with care to offload the abdomen and allow foetal monitoring
    • iNO is usually reserved as rescue therapy or a bridge to ECMO; ECMO improves maternal survival
  • Corticosteroids are recommended in moderate to severe ARDS within 14 days of onset

Delivery in the critically ill parturient

  • An MDT decision based on the cause, maternal prognosis and gestation
  • If delivery is being considered purely for hypoxaemia, rescue oxygenation strategies should be tried first, especially if <32 weeks
  • It remains unclear whether delivery significantly improves maternal oxygenation
  • Antenatal patients on a general ICU require an emergency Caesarean section tray, delivery pack, neonatal resuscitaire and ongoing obstetric and midwifery input

Peripartum anaesthetic management of the parturient with respiratory disease


History and examination

  • Diagnosis, severity and trajectory during pregnancy: exacerbations, admissions, ICU, home oxygen or NIV
  • Functional capacity, orthopnoea, cough and ability to clear secretions
  • Medications, especially steroid use
  • Airway and spinal examination; previous spinal surgery

Investigations

  • Bloods: FBC, coagulation (e.g. platelet dysfunction in osteogenesis imperfecta), CRP
  • Consider ABG and interpret against pregnancy reference ranges
  • Spirometry/PFTs: FEV1, FVC and DLCO
  • Echocardiography: pulmonary hypertension, RV function, cor pulmonale
  • Spinal imaging in severe scoliosis or previous spinal surgery

Optimisation and planning

  • Treat infection and bronchospasm; chest physiotherapy
  • Plan peripartum steroid cover
  • Plan anticoagulation timing around anticipated delivery and neuraxial procedures
  • Early labour epidural or CSE where neuraxial access is anticipated to be difficult, as it can be extended for operative delivery
  • Counsel those with significant spinal deformity on the higher risk of block failure and complications; consider ultrasound guidance where the Cobb angle is ≥25°
  • Prepare for major obstetric haemorrhage in those with haematological abnormalities; haemorrhage worsens oxygen delivery in respiratory compromise
  • Arrange HDU or ICU bed

Monitoring and access

  • Arterial line for severe disease, cor pulmonale or mediastinal mass, allowing serial ABGs and cardiac output monitoring
  • Arterial line also avoids repeated cuff inflation in osteogenesis imperfecta

Neuraxial anaesthesia

  • Neuraxial anaesthesia is preferred in most moderate to severe respiratory disease

Advantages Disadvantages
Maintains spontaneous ventilation High block (mid-thoracic or above) may impair accessory muscle function in restrictive disease
Avoids airway instrumentation and bronchospasm Technically difficult with spinal deformity; higher failure rate
Avoids positive pressure ventilation and its effect on pulmonary hypertension Rapid onset spinal may be poorly tolerated in pulmonary hypertension
In labour: attenuates pain-driven hyperventilation and exertion Contraindicated by anticoagulation if timing not planned

  • Epidural or CSE techniques allow gradual titration and better control of block height

Risks of general anaesthesia

  • Rapid desaturation, hypercapnia and airway difficulty on top of the usual obstetric GA risks
  • Postoperative respiratory failure, particularly in neuromuscular and restrictive disease

General anaesthesia: condition-specific considerations

  • Asthma: consider ketamine for its bronchodilator properties; caution with histamine-releasing opioids

  • ILD: lung protective ventilation with lower VT, higher respiratory rate and pressure control

  • CF: lung protective ventilation to reduce the risk of bullae rupture and pneumothorax; tracheobronchial suction and recruitment manoeuvres

  • Myotonic dystrophy: avoid suxamethonium; have dantrolene and mexiletine available; ensure full reversal

  • Cerebral palsy and oseogenesis imperfecta: careful positioning and padding; thorough airway assessment due to risk of difficult intubation, mandibular fracture and dental trauma; antisialagogues for secretions

  • OI: TIVA may be used as a precaution given a possible predisposition to hyperthermia

  • Tranexamic acid is contraindicated in active thromboembolic disease

  • HDU or ICU for continuous monitoring and early recognition of respiratory or cardiovascular deterioration
  • Continuous pulse oximetry and telemetry for at least 24 hours in myotonic disorders
  • Opioid-sparing analgesia; caution with opioids in neuromuscular disease
  • Chest physiotherapy and early mobilisation
  • Thromboprophylaxis, or resumption of therapeutic anticoagulation, timed with neuraxial catheter removal
  • Continue steroid cover and regular respiratory medications