Selection Bias in Study Participants with Acute Hypercapnic Respiratory Failure/Reply

By excluding at least (i.e., Adler and collegaues' Figure 1 does not present the number of patients excluded for neuromuscular disease and iatrogenic respiratory failure) 46 (i.e., 26 patients with confusion or psychiatric comorbidities and 20 patients with life expectancy < 3 mo) out of the 197 (23.3%) patients assessed for eligibility, the remaining study population is heavily skewed toward other causes of AHRF, such as chronic obstructive pulmonary disease (COPD), obstructive sleep apnea, obesity hypoventilation syndrome (OHS), and congestive heart failure, which are the same comorbidities that the authors sought to investigate (1). [...]the investigators' conclusions that AHRF resulted primarily from COPD or obesity and is fraught with multimorbidity are riddled with bias and should be viewed with skepticism. [...]those with life expectancy less than 3 months are likely cachectic hospice patients without the comorbidities under investigation (e.g., COPD, OHS, obstructive sleep apnea, and congestive heart failure); these patients are also susceptible to AHRF from analgesics and sedatives, and by excluding them, the remaining study participants are more likely to be heavier and have multimorbidity (2, 3). [...]the exclusion of hypercapnic patients with confusion, major psychiatric disease, and neuromuscular disorders- potentially patients without the comorbidities of interest-adds additional bias to the already skewed study group (3, 4). Adler and colleagues sought to investigate the prevalence and impact of comorbidities in patients with AHRF treated with invasive or noninvasive mechanical ventilation in the intensive care unit but failed to devise a sample of patients with AHRF representative of the general...