Acute Asthma Exacerbation in Pregnancy

Acute asthma exacerbation in pregnancy is a sudden or progressive worsening of wheeze, cough and breathlessness with falling peak flow. It is commonly triggered by viral infection or stopping preventer treatment. It matters because maternal hypoxia quickly causes fetal distress, and the normal pregnancy carbon dioxide level is low, so an apparently normal level signals exhaustion.

• Treat aggressively; oxygen and steroids protect the fetus.
• Severe attack: peak flow 33 to 50 percent of best, respiratory rate above 25 per minute, pulse above 110 per minute, unable to complete sentences.
• Life threatening: peak flow below 33 percent, silent chest, cyanosis, exhaustion, confusion, oxygen saturation below 92 percent.

Women are breathless, wheezy and anxious, using accessory muscles, and may be unable to speak in full sentences. Assess respiratory rate, pulse, oxygen saturation, peak flow and chest sounds, then check fetal movements and heart rate.

• Silent chest is an ominous sign.
• Fetal heart rate may be abnormal when the mother is hypoxic.
• Differential diagnosis: pulmonary embolism, pneumonia, pulmonary oedema, peripartum cardiomyopathy, anaphylaxis, pneumothorax, anxiety.
• Complications: respiratory failure, pneumothorax, fetal hypoxia, preterm labour, ventilation, maternal and fetal death.

The diagnosis is clinical and must not delay treatment.

• Peak flow compared with best or predicted; oxygen saturation by pulse oximeter.
• Arterial or venous blood gas for severe attacks: normal pregnancy carbon dioxide is 4.0 to 4.2 kPa (30 to 32 mmHg), so a value above 4.7 kPa (35 mmHg) is concerning.
• Chest X-ray with shielding for suspected pneumothorax or pneumonia; full blood count, urea and electrolytes (salbutamol lowers potassium).
• Cardiotocography after maternal stabilisation.

The principle is rapid bronchodilation, oxygen and steroids, with fetal monitoring after the mother is stable.

• Supportive: sit upright; oxygen 4 to 6 L/min by mask to keep saturation at 95 percent or above; IV access; continuous pulse oximetry; avoid sedatives; fetal heart monitoring once stable; sodium chloride 0.9 percent fluids if dehydrated.
• Pharmacological: salbutamol 5 mg nebulised, oxygen driven, every 20 minutes for 3 doses, then every 1 to 4 hours (or 10 puffs of 100 micrograms by spacer every 20 minutes); ipratropium bromide 500 micrograms nebulised every 20 minutes for 3 doses, then 6-hourly; prednisolone 40 to 50 mg oral daily for 5 to 7 days, or hydrocortisone 100 mg IV 6-hourly if unable to swallow; magnesium sulphate 2 g IV over 20 minutes once for a severe or life-threatening attack; amoxicillin 500 mg oral 8-hourly for 5 days only if there is bacterial infection; enoxaparin 40 mg subcutaneous daily during admission.
• Procedures: intubation and ventilation for exhaustion, confusion or rising carbon dioxide; caesarean section only for obstetric reasons or to ease ventilation in refractory cases.
• Special groups: if delivery is likely before 34 weeks give betamethasone 12 mg IM twice, 24 hours apart; avoid carboprost for postpartum haemorrhage and give oxytocin 10 IU IM.
• Red flags: silent chest, cyanosis, exhaustion, confusion, oxygen saturation below 92 percent, normal or rising carbon dioxide, peak flow below 33 percent.
• Follow-up: admit if there is no improvement within 1 hour or peak flow stays below 75 percent; discharge when peak flow is above 75 percent for 24 hours; review in 48 hours and again at 1 week; complete the steroid course; fetal growth scan at 2 weeks.