Australian research has shown that obstructive lung disease is the most common antecedent cause of hypercapnic respiratory failure (HRF), although neuromuscular disease and lower respiratory tract infections are associated with a higher risk of HRF death.
The findings, from a NSW study, suggest identifying potentially treatable causes of HRF may help improve outcomes for these critically ill patients.
The cross-sectional study comprised 873 patients with all-cause HRF presenting to the Liverpool Hospital with a PaCO2 >45 mmHg and pH ≤7.45 between 2013 and 2017.
The study found causes of HRF were obstructive lung disease (44%), lower respiratory tract infections (33%), congestive cardiac failure (32%), opioid use (6.5%), sleep disordered breathing (6.0%), benzodiazepine use (3%) and neuromuscular disease (1.7%).
Relatively few patients had ‘multifactorial’ HRF however a history of tobacco exposure, an indirect cause of HRF, was found in 50% of the cohort.
The study, published in Respirology [link here], found the overall in-hospital mortality rate was 12.8% with a substantial variation in the case fatality rate among the various causes.
The case fatality rate for HRF patients was highest when the condition was caused by neuromuscular disease (40%) followed by lower respiratory tract infections (18.2%) and congestive cardiac failure (13.0%).
The adjusted odds ratio for death related to antecedent neuromuscular disease was 8.02.
The investigators led by Dr Yewon Chung, from Liverpool Hospital, the University of NSW and the Ingham Institute for Applied Medical Research, said the aetiology of HRF had a significant impact on in-hospital death.
“To our knowledge, this is the first study to demonstrate that the presence of COPD and heart failure are associated with a lower risk of death, whereas respiratory tract infections and neuromuscular disease are associated with increased risk of death,” they said.
“Appreciating the impact of comorbidities among patients with HRF may allow for a greater degree of informed decision making particularly with respect to goals of care and avoiding potentially futile medical interventions.”
“Our results suggest that patients with HRF should not necessarily have treatment withheld for fear of worse outcomes based solely on the presence of COPD or heart failure.”
Drivers of respiratory failure
Dr Chung told the limbic that there hadn’t been a good understanding of the underlying causes of HRF at a population level.
“And if we know the big population drivers of respiratory failure, you can actually intervene. You can try and intervene at an early stage of illness. People with COPD and heart failure do respond to treatment, and they can actually get better and get out of hospital if they’re supported and treated appropriately.”
She said the study found a surprisingly low prevalence of sleep disordered breathing that could be contributing more to respiratory failure. She suspects this is due to underdiagnosis.
“We think it’s important and it’s common. And we know that there are a lot of barriers to access diagnostic tests and seeing specialists and … to developing optimal diagnostic and treatment pathways.”
“But it may be that if we find, for example, that sleep disordered breathing has a really big impact on severe respiratory failure then it’s actually worth looking for this much earlier on in the primary care setting. That’s the hypothesis that this sort of study raises for me at least,” she said.
She also noted the impact of opioid and benzodiazepine use on HRF.
“It supports a lot of the things that we see as clinicians on an individual basis, the fact that there are so many people using these drugs in the community. I think it should be a prompt for us to reflect on why these medications are being used. Are they being used appropriately? Certainly, these medications are effective for pain and certain other indications, but the liberal prescription of a lot of these agents that can have sedative effects on the respiratory system I think should be questioned.”