Acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a condition of widespread inflammation in the lungs, characterized by bilateral infiltrates on chest radiography and impaired gas exchange, not as­sociated with left heart failure.

Management of ARDS is supportive and not different to the non­pregnant patient. Endotracheal intubation in the pregnant patient is associated with an increased risk of failure compared with the non­pregnant patient, and should preferably be performed by someone with experience in obstetric anaesthesia. Mechanical ventilatory sup­port should target tidal volumes of 6 mL/kg (predicted body weight) and plateau pressures less than 30 cmH2O. The reduced chest wall compliance in pregnancy may require slightly higher airway pres­sures than in the non-pregnant patient. Non-conventional modes of ventilation have been used successfully in pregnancy as a rescue intervention, including extracorporeal membrane oxygenation (30). Delivery is sometimes, but not always, beneficial to the mother and should be considered on an individualized basis by the multidiscip­linary team (31).

Amniotic fluid embolism

Although small amounts of amniotic fluid are likely to enter the circulation during uncomplicated pregnancy, occasionally the cata­strophic syndrome of amniotic fluid embolism results.

Gastric acid aspiration

Contributing factors for gastric acid aspiration include the effect of progesterone lowering the tone of the oesophageal sphincter, the in­creased intra-abdominal pressure due to the enlarged uterus, and use of the supine position for delivery. The majority of cases of aspir­ation occur in the delivery suite, and all pregnant women should be considered to have a full stomach. Limited data suggest that a com­bination of antacids and H2 antagonist are optimal for increasing gastric pH in this situation (35) Acidic gastric contents produce a chemical pneumonitis and permeability oedema in the lung, that is, ARDS. Bacterial pneumonia may follow in some cases.

Transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) may complicate blood component therapy, and is not uncommon in pregnancy (36). The clinical presentation is of a sudden onset of dyspnoea occurring during or within 6 hours of transfusion of plasma-containing blood products.

Other causes

Influenza pneumonitis is an important cause of severe ARDS in the pregnant woman, highlighted during the 2009 influenza A (H1N1) epidemic (Figure 25.2) (11). Preeclampsia may be complicated by pulmonary oedema, which may be a combination of a hydrostatic mechanism (related to increased afterload) and increased perme­ability (ARDS). Sepsis, either obstetric or non-obstetric, may be complicated by ARDS. Several series have demonstrated an associ­ation between pyelonephritis in pregnancy and ARDS (37). This is likely due to the fact that pyelonephritis is the most common cause of severe sepsis during pregnancy.

cause of respiratory insufficiency, significant hypercapnia or hyp­oxia, and pulmonary hypertension and cor pulmonale are associated with less favourable pregnancy outcomes.

Polycythaemia gives an indirect assessment of the degree of hyp­oxia and in itself is associated with an increased risk of thrombosis due to hyperviscosity. Women are often delivered preterm due to deterioration in respiratory function in the third trimester, and by caesarean section because of associated abnormalities of the bony pelvis and of abnormal presentations of the fetus.

Management should start with prepregnancy counselling. Multidisciplinary care and delivery planning is essential. Women with nocturnal hypoxia/hypercapnia may require supplemental oxygen and non-invasive ventilation. Liaison with obstetric an­aesthetists is important. Regional analgesia/anaesthesia where the block is high may be dangerous in a woman with limited respira­tory reserve. In addition, some women have had Harrington rods inserted that may preclude regional anaesthesia. Elective caesarean section may occasionally be indicated for anaesthetic reasons in women in whom regional techniques are not possible and emer­gency general anaesthesia is deemed too risky because of airway concerns.