Pulmonary edema can be broadly classified as cardiogenic or non-cardiogenic. Cardiac output increases very early on and is the highest in the post-partum period. Plasma volume expands due to sodium and water retention, thereby increasing preload, but afterload reduces due to vasodilation systemically [5]. The most common causes of non-cardiogenic acute pulmonary edema in pregnancy are the use of tocolytic agents, fluid overload, preeclampsia, sepsis, trauma or following aspiration of gastric contents [6, 7].

Pre–eclampsia associated pulmonary edema – Pulmonary edema is a frequently encountered complication in patients with pre-eclampsia with most cases occurring after delivery. Initial management involves lowering the blood pressure urgently especially in patients who have severe elevations of blood pressure that persists longer than 15 min. Once pulmonary edema occurs, parenteral therapy is more effective, and nitroglycerine is the agent of choice as recommended by The European Society of Cardiology [8]. Diuretics should be instituted to promote pre load reduction recognizing that the preeclamptic patient may have complex fluid balance needs due to low oncotic pressure. When necessary, noninvasive ventilation is recommended, in patients with increased work of breathing or hypoxemia as it is known to improve these parameters and can decrease the need for invasive mechanical ventilation by [9].

Tocolytic induced pulmonary edema is relatively uncommon [10]. Tocolytics such as ritodrine and terbutaline are beta agonists that increase heart rate and stroke volume but cause peripheral vasodilation and decrease blood pressure. Management involves firstly stopping the tocolytic therapy and treating pulmonary edema with diuretics. These patients tend to recover well and reported mortality is low [11].

Peripartum cardiomyopathy – These patients usually have no known prior heart disease and present with congestive heart failure typically in the last month of pregnancy and up to 5 months post-partum. Unfortunately, the mortality can be as high as 20–50 % [12, 13].

Ovarian hyperstimulation syndrome (OHSS) is another uncommon cause of pulmonary edema with a prevalence of 1–10 %. Mechanisms are not entirely clear but involve increased vascular permeability. Treatment is supportive care [14].

Aspiration – Certain factors such as an incompetent lower esophageal sphincter coupled with a decrease in stomach motility can increase the risk for aspiration. One must have a high index of suspicion as not all events are witnessed. Treatment is usually supportive [15].

Asthma is seen very frequently with prevalence in pregnancy ranging from 1 to 8 % [16]. Certain factors easily obtained by a good history can help you understand who is at increased risk of complications from asthma, these being history of exacerbations, intubations, and recent steroid use. Most exacerbations are characterized by cough, wheezing, and dyspnea. The National Asthma Education and Prevention (NAEP) group recommends obtaining a baseline peak expiratory flow in order to guide further management. If the patient is approaching less than half of what their baseline is, then treatment with supplemental oxygen to correct hypoxemia and bronchodilators such as a beta-agonist and anticholinergic agents are to be given. A target oxygen saturation above 90 % with consideration for invasive mechanical ventilation in those who are in impending respiratory failure. A partial pressure of carbon dioxide within the normal range of 36–40 on an arterial blood gas can be a early sign of imment respiratory failure in the gravid patient. Intravenous steroids also have to be instituted. Care should be taken during mechanical ventilation to avoid a short expiratory time that can cause auto peep [16]. Intravenous magnesium sulfate may be beneficial in acute severe asthma in addition to bronchodilators especially in patients with coexistent hypertension or preterm uterine contractions [16, 17].

Large airway obstruction mostly arises due to a difficult intubation and the incidence is anywhere between 0.4 and 5.5 %. Intubation may be difficult during pregnancy and the peripartum period due to upper airway edema, pharyngeal mucosal friability and diminished airway caliber, especially late in pregnancy. The gravid patient especially third trimester, should be considered a difficult airway patient with high risk of aspiration and decreased oxygen reserve. Other causes of airway obstruction such as tumors, hematoma and laryngeal edema are rarely encountered [18, 19].

Increased upper airway resistance may occur in pregnancy as a result of pharyngeal edema and increased pharyngeal tone could potentially worsen OSA in pregnant women. Incidence of OSA is estimated to be between 8.4 % in the first trimester and 19.7 % in the third trimester [20]. Maternal risks include increased morbidity from conditions that have been associated with OSA and underlying obesity such as preeclampsia, eclampsia, gestational hypertension, cardiomyopathy and gestational diabetes [21]. These patients are at higher risk for hypoxemia during labor, and continuous monitoring is necessary. CPAP therapy remains the first line of therapy and women are instructed to bring in their device when they come during labor.

Varicella and influenza are the most common pathogens associated with viral pneumonia in pregnancy [22].

Estimated mortality rate amongst the H1N1 pandemic ranged from 12.5 to 42.1 % [23]. The risk of hospitalization is highest in the third trimester. Mortality related to influenza is mostly due to secondary bacterial pneumonia, although the 2009 H1N1 pandemic differed in this aspect with more patients dying primarily from the effects of H1N1 virus. The most commonly implicated pathogens are S. pneumonia and Staphylococcus aureus followed by H. influenza and it is reasonable to start empiric antibacterial agents at the time of presentation [24].

Streptococcus pneumonia followed by Hemophilus Influenza are the most commonly encountered agents [22]. Some of the risk factors for pneumonia in pregnancy include anemia, asthma, antepartum corticosteroids given to enhance fetal lung maturity, and the use of tocolytic agents to induce labor [25].

Oxygen supplementation is necessary with a goal of keeping the partial pressure of oxygen above 70 mmHg. The penicillins, cephalosporins, and macrolides are considered safe to use in pregnancy [22]. A history of contact with farm animals should raise suspicion for Q fever and therapy with macrolides is preferred [26].