Discussion:
Negative Pressure Pulmonary Oedema (NPPE) is a known postoperative and anaesthetic complication and especially in cases of acute upper airway obstruction 4,5. It was described as early as 19275. Asphyxiation by choking /strangulation are also known causes of NPPE 5.
We hypothesize that, pulmonary haemorrhage in this case is due to accidental asphyxiation during breast feeding in a sling, generating forced inspiratory effort against an obstructed upper airway and led to NPPE and haemorrhage.
NPPE is triggered when forced inspiratory efforts are generated to overcome the obstructed upper airway which leads to highly negative intra thoracic pressure (ITP). The obstruction also leads to hypoxia and hypercarbia leading to a catecholamine surge. There is an increase in venous return by reducing right atrial pressure due to the transmission of negative ITP and the elevation of the mean systemic pressure due to catecholamine-induced venoconstriction. The right ventricular volume increases leading to shifting of the interventricular septum to the left. The catecholamine surge also causes elevation of the systemic vascular tone leading to an increase in the left ventricular transmural pressure, raising ventricular wall tension which leads to an increase in afterload which then reduces left ventricular ejection fraction. The consequence of these changes is a net shift of blood from systemic to the pulmonary circulation. Pulmonary capillary pressures increase as a result of the increased blood flow and the increased vascular tone while intra alveolar pressures drop, and alveolar-capillary membrane breaks. Fluid and blood move rapidly into interstitial and alveolar spaces leading to NPPE and pulmonary haemorrhage 4,5.
Approach to pulmonary haemorrhage should start with a careful history and examination to identify aetiology as listed before1-3.
Investigations should include full blood count and blood film to look for severity of haemorrhage and differentiate acute vs chronic anaemia1,2. Erythrocyte sedimentation rate (ESR) and C reactive protein (CRP) to look for evidence of inflammation or infection, renal function tests in the context of sepsis or systemic vasculitis1,2 .Coagulation studies to look for any coagulation related disorders1-3. Vasculitic screen to rule out systemic vasculitis1,2. Respiratory viral screens and cultures to look for any infectious pathology1-3.
Chest radiograph can show patchy or diffuse ground glass changes indicating haemorrhage and on occasions may point towards aetiologies such as focal infiltrates or consolidation suggestive of infective process, or unilateral hyperinflation suggestive of foreign body aspiration and other findings such as cavitation/nodules and hilar lymphadenopathy 1,2.
CT chest with contrast can help identify extent and sequelae of pulmonary haemorrhage and provide further etiological clues1,2. Echocardiogram to look for any cardiac disease1,2.
Bronchoscopy might be useful in identifying focal active bleeds and for therapeutic interventions 1,2. Broncho alveolar lavage can help find evidence of hemosiderin laden macrophages as an indication of previous pulmonary haemorrhage 1,2. Lung biopsy to be considered when diagnosis is not conclusive 1,2.
Investigations for specific aetiologies when suspected need to be carried out 1-3. Management should include treatment of acute presentation, respiratory failure and treatment targeted towards underlying cause and its complications when identified1-3.
Pulmonary haemorrhage though uncommon can be a life-threatening entity. Accidental asphyxiation by suffocation should be considered in the differential diagnosis of children especially infants presenting with pulmonary haemorrhage.