Pregnant patients constitute less than 1% of intensive care unit admissions, and fewer than 1% of obstetric patients become critically ill. Critical illness may result from pregnancy-specific diseases, diseases that pregnancy predisposes to, or are co-incidental to pregnancy. The presence of a second patient—the foetus—may necessitate adjustments to therapeutic and supportive strategies. However, the foetus is generally robust despite maternal illness. The physiological changes of pregnancy are significant, but may delay the diagnosis of critical illness, requiring modifications to standard management approaches. These include increases in minute ventilation, resulting in a ‘low normal’ PaCO2, a reduction in mean arterial pressure, but increased heart rate, low serum creatinine, relative hypoglycaemia, relative leukocytosis, and reduced lower oesophageal sphincter tone. Pre-eclampsia is a disease of the uteroplacental unit that results in abnormal maternal physiology. Pregnant women are at risk for acute respiratory distress syndrome, due to gastropulmonary aspiration and increased risk of community-acquired pneumonia, sepsis, principally of the genito-urinary system, and thromboembolic disease.
