Acute hypercapnic respiratory failure in adults (AHRF) results from an inability of the respiratory pump, in concert with the lungs, to provide sufficient alveolar ventilation
to maintain a normal arterial PCO2. Co-existent hypoxaemia is usually mild and easily corrected. Conventionally, a pH <7.35 and a PCO2
>6.5 kPa define acute respiratory acidosis and, when persisting
after initial medical therapy, have been used as threshold
values for considering the use of
non-invasive ventilation. More severe degrees of acidosis, such as
pH<7.25, have been used
as a threshold for considering
provision of IMV.
AHRF complicates around 20% of acute exacerbations of COPD. It signals advanced disease, a high risk of future hospitalisations and limited long-term prognosis. The median survival
following recovery from AHRF was 1 year in a large case series.
Around 12% of patients with hypercapnic COPD died during the index
admission and this increased to 33% if the respiratory
acidosis developed after
hospitalisation. In asthma, acute hypercapnia also signals an increased
risk of death and an increased
likelihood of future
life-threatening attacks.
The same risks apply to AHRF complicating CF and bronchiectasis,
although this has not been formally reported. In the neuromuscular
and CWDs, including morbid obesity,
respiratory pump failure is often insidious in its onset, but AHRF may
be acute and unexpected.
Acute on chronic ‘decompensated’
episodes of AHRF are more common and normally indicate the future need
for domiciliary NIV.
Full text:
No comments:
Post a Comment