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.